Program Summary
1. Introduction
2. Science Review
    2.1. Precipitation Process Studies
    2.2. Electrification Studies
    2.3. Hydrometeor Identification Studies
    2.4. Complementary Studies
           2.4.1 Early Cumulus Congestus Clouds
           2.4.2 Transient Luminous Events
           2.4.3 MCS Stratiform Region Lightning
3. Field Observing Systems
4. Field Operations Plan
5. Program Management Structure
6. Data Management Plan
7. References
    Appendices:
      A. Participants
      B. Proposals
      C. Supplemental Material
      D. Daily Severe Weather Probability - NWSO Goodland KS
      E. Weekly Severe Storm Reports with Positive Cloud-to-ground Lightning
      F. Dryline Positions near Goodland for 1998 and 1999

Program Summary:
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The broad goal of the Severe Thunderstorm Electrification and Precipitation Study (STEPS) is to achieve a better understanding of the interactions between kinematics, precipitation production, and electrification in severe thunderstorms on the High Plains. Several fundamental processes are still not well understood, but can now be investigated due to technological advances in the proposed instrumentation. There appear to be systematic differences in these processes in different types of storms, and STEPS will focus on understanding these differences. STEPS combines two separately conceived projects: the Cloud Electrification Studies using Aircraft and Radars ( CESAR) and the Low Precipitation Storms Experiment ( LPEX).

The specific scientific objectives of STEPS are:

1. To understand the apparent major differences in storm processes that have led supercells to be considered as either low, medium (also referred to as classic) or heavy precipitation (LP, MP, and HP) producers.

2. To understand how observed differences in the distribution of precipitation and cloud particles in different types of severe storms cause systematic differences in the way these storms electrify and in the types and rates of intracloud and cloud-to-ground lightning that are produced.

3. To understand the initiation and development of individual lightning flashes as a function of storm evolution and storm electrification, particularly for severe storms.

4. To understand the formation of precipitation and its influence on electrical development, especially in those storms producing large hail.

5. To verify and/or to improve inferences of precipitation type from polarimetric radar measurements.

6. To improve microphysical and electrical parameterizations in numerical models of deep convection through intercomparisons of dual-polarimetric radar measurements and comparisons of these with aircraft and ground-based observations of precipitation types and electrical properties.

The objectives of three separate ancillary studies that are complementary to STEPS are:

1. To understand how preciptiation forms in early, growing cumulus clouds and how these clouds might become electrified.

2. To understand how lightning with certain characteristics triggers transient luminous events above the tops of storms.

3. To understand the origin of lightning discharges in mesoscale convective systems.

The proposed study will also offer valuable insight into quantitative precipitation forecasting (QPF) efforts associated with the USWRP by addressing issues relevant to estimating precipitation efficiency as well as the strength of the convectively produced surface cold pool which impacts storm regeneration, longevity, and severe weather potential.

The field phase of the program will be based along the Colorado-Kansas border area somewhere near the climatological position of the dry line, and is currently being planned for a 12-week period 15 May - 10 August 2000, with two subperiods: 15 May - 1 July (when isolated, supercell-type storms are more likely) and 20 July - 10 August (when, additionally, mesoscale convective systems become likely).

Convective Storm Season for the Northeast Colorado Area
Precipitation Probability and Average Thunderstorm Days

Advances in instrumentation and observing techniques make this a good time to further advance the understandings achieved in earlier major field programs. The primary instrumentation includes two S-band polarimetric radars, S-Pol from the National Center for Atmospheric Research (NCAR) and CSU-CHILL from Colorado State University (CSU), along with the National Weather Service (NWS) WSR-88D Doppler radar at Goodland, KS for determining the internal flow and precipitation structure of storms, the South Dakota School of Mines and Technology (SDSMT) armored T-28 aircraft for storm penetrations, the University of North Dakota (UND) Citation aircraft for flanking cell and anvil penetrations, two mobile sounding systems (GLASS or a substitute) to characterize the storm environment on both sides of the dry line, four mobile mesonet stations from the Joint Mobile Research Facility (JMRF) of the University of Oklahoma (OU) and the National Severe Storms Laboratory (NSSL) to observe the meteorological conditions and precipitation types beneath the storms, the deployable lightning mapping system from New Mexico Institute of Mining and Technology (NMIMT) to map the three-dimensional distribution of lightning, mobile sounding systems from the JMRF and NMIMT for balloon-borne measurements of electric fields inside storms, the Yucca Ridge Field Station (YRFS) for low light optical recording of storm top phenomena at night, data from the National Lightning Detection Network (NLDN) for mapping characteristics of cloud-to-ground lightning, and data from the CSU flat plate antenna network for quantifying intra-cloud discharges.

1. Introduction
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Severe storms, which by definition produce strong winds, tornadoes, large hail, or flooding and which often produce heavy precipitation or frequent lightning, are a primary concern to weather forecasters and to the public. The spectrum of severe storms exhibits a wide range of electrical activity and precipitation type and amount. In fact, precipitation amount and location relative to airflow have been widely used, with some controversy, to classify supercell storms as Low-Precipitation (LP), Classic or Medium-Precipitation (MP), and Heavy-Precipitation (HP) supercell types (e.g., Doswell and Burgess 1993). The cause of this variation is poorly understood, particularly toward the LP end of the spectrum. Better understanding of the variations in precipitation formation is key to better understanding of much of the behavior of supercell storms, including mechanisms that influence storm precipitation efficiency, feedback effects between precipitation formation and storm dynamics, and storm conditions responsible for the unusual lightning observed in many supercell storms. Such knowledge has considerable potential to improve forecasts of weather hazards.

LP storms as a class are especially significant for study for three reasons: (1) Their precipitation formation appears to represent an extremum among supercell storms. (2) They often produce cloud-to-ground flashes that lower positive charge (+CG flashes), instead of the usual negative charge (-CG flashes), to ground. (3) They are not documented very well. We hypothesize that the unusual lightning characteristics of these storms are in some way physically related to their unusual dynamical organization and to their unusual microphysical characteristics.
Investigating these storms promises to enhance our understanding of the relation between storm kinematics and microphysics and also of the link between microphysics and electrification.

An important component of the analysis of this powerful data set is to be direct description and interpretation of phenomena about which little is now known. However, the precipitation processes, cloud microphysics, kinematics, and electrification of supercell storms cannot be measured with enough spatial and temporal resolution to determine all relevant parameters for the phenomena being studied. Thus, an equally important component of the analysis is to use numerical modeling to provide more detail about storm dynamics and microphysics which, in conjunction with radar and in situ measurements, should allow a better and more quantitative assessment of the relation and interactions among precipitation formation, electrification, lightning, and storm kinematics. Observations from the field program are crucial for the numerical modeling, both to provide model verification and to provide information to help design microphysical and electrical parameterizations for the dynamical cloud models. However, calculations using the model fields also will be crucial for interpreting observations. For example, growth trajectory calculations using the model fields will be used to examine why LP storms produce so little rain while sometimes producing large hail.

The proposed location for the field program is eastern Colorado and western Kansas, a region well known climatologically for producing severe hailstorms (Changnon 1977) as well as storms with frequent +CG lightning.

Severe Storm Days Compared to Predominately
Positive CG Lightning (PPCG) Severe Storm Days

Though not being submitted to the USWRP program, STEPS addresses USWRP's goal to improve the specificity, accuracy, and reliability of weather forecasts for disruptive, high impact weather, particularly for heavy precipitation, hail, and tornadoes. STEPS plans to directly address one USWRP theme, quantitative precipitation forecasting, by investigating polarimetric radar estimation of precipitation, the microphysics of precipitation formation in supercell storms, the representation of microphysics in numerical cloud models, and effects of precipitation on storm kinematics and on the forcing, initiation, and dissipation of convection. Furthermore, the field program will provide more comprehensive data sets and better measurements than are now available for supercell storms, particularly LP supercell storms. These data sets will be used by projects within and outside STEPS to investigate the mix of data (including radar, satellite, and lightning data) that is most useful for warning of weather hazards and for assimilation into forecast models.

2. Science Review
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The science review is divided into three main or core program sections: (1) Precipitation Process Studies, (2) Electrification Studies, and (3) Hydrometeor Identification Studies. Although these could be interpreted as separate components to the field efforts, they are strongly interrelated, both in their scientific goals and field observation requirements, and should be interpreted as such. As of the writing of this science review, a few other studies which will be complementary to the STEPS core program have been identified and are included in the Complementary Studies section.

2.1. Precipitation Process Studies
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The field measurements and analysis for STEPS are designed to explore the mechanism of precipitation formation in supercell storms. It has long been realized that supercell updrafts are often too strong to allow much precipitation growth in a single upward pass. The existence of weak echo regions has been explained in this way for many years, and the explanation is surely, in general, correct. From this standpoint one expects a priori that recycling processes bringing roughly millimeter-sized hydrometeors into the updraft are likely to be a major factor in precipitation formation in supercells.

More recently, the characterization of supercells as LP, MP or HP (Doswell and Burgess 1993; Rasmussen and Straka 1998) suggests that there is a spectrum of ways in which supercells can be organized so as to encourage or discourage such recycling. For instance, Marwitz (1972a, 1972b) suggested that precipitation formation might be especially inefficient in highly sheared storms with a single strong updraft. Similarly, Rasmussen and Straka (1998) contrasted the environments of LP with those of HP and MP supercells, and found that the only discriminating factor for LP storms was the storm-relative wind at anvil levels (9-10 km), which was stronger for the LP storms. They hypothesized that strong upper-level flow inhibits recycling of precipitation from these high levels back into the updraft, thereby accounting for the weak precipitation. Storm size could be a very important factor here as well. Small, isolated storms may have less capability to recycle hydrometeors, and therefore could be precipitation inefficient. The aim is to analyze several isolated storms within the range from LP to HP to clarify the general features of these recycling processes.

The particles that get recycled could be any one of the following: ice crystals, drizzle drops, graupel, or small raindrops. Miller et al. (1988, 1990) found that recycled particles must be as large as 100 micron to 1 mm in diameter upon entering the main updraft to be effective embryos for further growth to hail. Questions still remain regarding how and where potential embryos are produced and which actually grow to hail. Polarimetric radar measurements should help identify where in the storm the various particle types are located, and particle growth trajectories will help determine the most likely embryo source regions.

LP storms (e.g., Donaldson et al. 1965; Davies-Jones et al. 1976; Burgess and Davies-Jones 1979; Bluestein and Parks 1993) as a class are especially significant for study because they are not well documented and they very likely represent an extreme type of supercell in terms of precipitation formation. LP storms are unusual, but not rare, being encountered by storm chasers on the High Plains several times every season, especially near the dry line. They appear to have strong, rotating updrafts and to produce some hail, even large hail, but little rain. The visible cloud is a skeleton compared with other supercell storms, consisting of a bell shaped cloud around the updraft (often showing striations indicative of rotation) that merges with anvil cloud at middle levels, but has no visible rain shaft.

Schematic of Supercell and LP storms

The analysis for this portion of STEPS will rely heavily upon numerical models. Dynamical models of supercells with very simple, parameterized microphysics have been successful in duplicating the main characteristics of supercell organization and in relating their formation to the environmental wind shear and CAPE (e.g., Weisman and Klemp 1982, 1984, 1986). Weisman and Bluestein (1985) produced a model storm looking very much like an LP supercell simply by turning off the precipitation process (setting fall velocities equal to zero) in an ordinary supercell simulation (NO RAIN, right panel). No storm outflow was produced and all the hydrometeors advected downwind within the anvil. Though this obviously is an unphysical approach to the microphysics of LP storms, the fact that the lack of precipitation affected the kinematics of the storm is important.

Model Results for Rain (Squall Line) and No Rain (LP storm)

For STEPS, the idea is to analyze the observed storms by combining model results and observations. Observations from radar, the T-28, and soundings will be used to "teach" the model to come as close as possible (or practical) to the real storms. The Doppler-derived winds and the soundings will provide the model's initial conditions and boundary conditions, which have a strong influence on subsequent convection. Microphysical information from the polarimetric radar data and the T-28 will be used to help devise microphysics parameterizations tailored to these storms. All of the data act as a check on how well the model succeeds in simulating the actual storm.

The model then will be used as the basis for a detailed analysis of precipitation formation. Three-dimensional wind fields and liquid water contents derived from the full model simulations will be used as input to simple precipitation growth trajectory calculations (Knight 1990). Knight intends to use this simple approach to examine various options for particle initiation, such as ice nucleation and multiplication schemes, and shedding from hailstones either melting or in wet growth. The object is to find a reasonable microphysics and growth trajectory scenario that matches in considerable detail the actual observations. This is the critical step to go beyond a particular microphysics parameterization to get the model to behave about like the actual storm. This procedure itself also directly addresses the research objective: to construct a physical understanding of the important processes of supercell precipitation.

For this part of the program numerical modeling efforts will be conducted using the COMMAS model, with supportative collaboration from Bill Skamarock (NCAR/MMM) and Lou Wicker (NSSL). The COMMAS model is fully non-hydrostatic, has an adaptive grid capability for fine-resolution (100-500 m) simulations, and is well established for use in studying a large variety of convective phenomena, from midlatitude mesoscale convective systems (e.g., Skamarock et. al 1994) to tornadic supercell storms (e.g., Wicker and Wilhelmson 1995; Gilmore and Wicker 1998). COMMAS currently has two alternate ice microphysical schemes incorporated into the code (Tao and Simpson 1993; Ferrier 1994) that can be tested against the in situ aircraft and polarimetric radar data, and it is planned to incorporate additional schemes over the next 6-12 months (e.g., Straka 1998).

2.2. Electrification Studies
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STEPS has two broad goals for electrification studies: (1) to improve understanding of the electrification of severe storms, particularly understanding of how the charge generation and charge distribution depend on the microphysics and kinematics of severe storms, and (2) to better document and understand the apparently systematic variations in the types and rates of lightning relative to severe storm type and evolution. Of particular interest are ground flashes that lower positive charge to ground (+CG flashes) instead of the usual negative charge (-CG flashes), because only in the last decade has it been discovered that they occur preferentially in a few severe storm situations and are important to the production of sprites. Though several hypotheses have been offered to explain why severe storms produce electrical discharges with unusual characteristics, few of the comprehensive data sets needed to test these hypotheses have been obtained, so far. However, all of the hypotheses involve either unusual microphysics or particular distributions of precipitation relative to storm winds. (More details than can be presented in this summary are available on the project web site at http://silver.sdsmt.edu/~detwiler.)

Based on a considerable body of laboratory experiments, storm observations, and numerical modeling studies amassed over the last 25 years, most scientists now believe that noninductive interactions occurring during collisions between cloud ice and riming graupel/hail are what cause most instances of storm electrification strong enough to produce lightning (e.g., chapters 3, 7, and 9 of MacGorman and Rust 1998). It is reasonable, therefore, to expect that variations in the microphysics and kinematics of storms should have a strong effect both on the amount and configuration of charge generated by a storm. The amount and configuration of charge would be expected, in turn, to affect the frequency and type of lightning.

Specific ways in which variations in microphysics and kinematics affect charge distributions, flash rates, and flash type are mostly a matter of informed conjecture, but a few relationships are fairly well established. For example, several investigators have observed that a storm's intracloud (IC) flash rate increases dramatically with the onset of large updraft speeds and/or an increase in the horizontal extent of precipitation in the mixed phase region (e.g., Lhermitte and Krehbiel 1979; Dye et al. 1999; MacGorman et al. 1989). Also, Stolzenburg et al. (1998) found that charge regions tend to be elevated farther above ground in regions of greater updraft speed.

While many other systematic variations in flash type and characteristics have been documented, data about them are inadequate to test the hypotheses offered to explain them. The scarcity of data sets suitable for testing hypotheses is particularly acute for severe storms, though some of the most intriguing lightning behaviors have been observed in severe storms. For example, decades of observations have established that supercell tornadic storms often produce extraordinarily large flash rates (e.g., Vonnegut and Moore 1958; Taylor 1973). These large rates probably were associated with large updraft speeds, as found by MacGorman et al. (1989) and Williams et al. (1998), but simultaneous wind and lightning data are available for too few cases to test causality.

Only in recent years has it been possible to observe one of the most intriguing behaviors, an apparently systematic tendency for most cloud-to-ground lightning to be +CG flashes, instead of the usual -CG flashes, for extended periods in some types of severe storms. Relatively large +CG flash rates seem to occur preferentially toward the LP and MP end of the supercell spectrum (e.g., Branick and Doswell 1992). They often seem to be associated with the production of large hail in such storms, but probably are not caused by the hail itself (e.g., Carey and Rutledge 1998). Also, the dominant polarity of ground flashes sometimes switches from positive to negative, and this often is associated with a change in the morphology of the storm, such as a change from LP to MP characteristics (e.g., MacGorman and Burgess 1994). If the dominant polarity switches shortly after large +CG flash rates, the switch often appears to be associated with the genesis of the most violent tornado produced by the storm. Data sets needed to explain these observed behaviors will be gathered in STEPS and do not currently exist.

STEPS proposes to collect several comprehensive microphysical and electrical data sets to improve understanding of electrification and lightning in severe storms of the High Plains. Advances in instrumentation make the time ripe for such a project. Besides having improved capabilities for observing precipitation microphysics, as mentioned previously, advances have also improved capabilities for observing electrical phenomena. For example, in situ airborne and balloon-borne measurements of the electric field now have greater dynamic range and lower noise (from both internal circuits and the aircraft). NASA/MSFC recently developed a more versatile technique for the difficult problem of calibrating aircraft distortion of electric field measurements. Furthermore, NMIMT is designing a new telemetry system for ballooning in STEPS that will allow sensors to measure the electric field simultaneously at more locations. Closely spaced simultaneous balloon measurements will enable us to estimate the vertical profile of total space charge much more accurately than we now can from single-instrument soundings of the electric field. The T-28 will also be equipped with a HVPS capable of detecting particle charge.

Comparable advances have been made in lightning mapping technology, used to investigate relationships of both intracloud (IC) and cloud-to-ground (CG) lightning to storm structure and evolution. The National Lightning Detection Network (NLDN) detects both +CG flashes and -CG flashes, locates where each CG flash strikes ground, and estimates its peak current. In 1994, an overhaul of the NLDN improved typical errors in the mapped strike locations from 2-5 km to less than 500 m. Also, NMIMT has developed a deployable system for mapping all flashes, so that lightning can now be mapped in regions where such systems have been unavailable in the past. The NMIMT lightning mapper operated for the first time in 1998 and gave spectacular views of lightning channels within the Oklahoma storms studied in MEaPRS. Not only does this system allow us to "look" within the storm to study the initiation and development of lightning flashes, it also allows us to determine total and IC flash rates for storms and individual cells much more accurately than has been possible previously.

Lightning Activity in a Supercell Storm

During the proposed field operations, we expect to collect data from a variety of storm types, ranging from small airmass thunderstorms to supercell storms. Because we know so little about the electrical characteristics of many types of severe storms, particularly LP storms, documenting and contrasting the electrical characteristics of the various types of storms will be one objective. However, the collected data should be adequate also to examine basic unanswered questions about several of the topics discussed above, such as the genesis and development of lightning flashes relative to the charge distributions of various types of severe storms. A particular goal will be to examine whether the reported association of +CG flashes with hail production and large IC flash rates with updraft intensification are supported by the new data sets, in part because these relationships should be useful to forecasters who warn of hazardous weather.

As in the STEPS precipitation studies, numerical cloud modeling will be an important component of electrification and lightning studies. Much can be learned from observations alone, but none of the observational data sets can be obtained with enough temporal and spatial resolution to address all of the relevant issues involved in evaluating and refining some hypotheses. To address such topics, STEPS will use modeling studies, which provide idealized, but complete, physically consistent data fields with which to examine hypotheses. (We recognize that models are not a panacea for incomplete sets of observations, but must be used with care and checked where possible against observed behavior.) Modeling studies will use the numerical cloud models from the SDSMT (Helsdon et al. 1992) and from the University of Oklahoma/NSSL (MacGorman et al. 1998). Both are sophisticated cloud models that include various parameterizations for microphysical processes, several charge generation mechanisms, and lightning. Both models have been used successfully to study the onset of lightning in selected kinds of storms.

The overall goal of model studies in STEPS will be to simulate much of the spectrum of unusual electrical characteristics observed in severe storms by the field program. These characteristics are expected to include +CG flashes and unusually large IC flash rates. One approach will be to examine the contribution of specific electrification mechanisms to the charge in various regions of storms, with emphasis on trying to simulate and explain any charge distribution that appears to be distinctively associated with a specific type of lightning. For example, recent soundings through the anvils of two severe storms in which most CG flashes were +CG suggest that the main interior charge in each anvil was negative, instead of positive as usual (D. MacGorman, private communication), a finding which, if verified, will provide a challenge for modeling.

2.3. Hydrometeor Identification Studies
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Intensive research over the last quarter century with meteorological radars having a polarimetric capability has led to an emerging capability for identifying hydrometeor types remotely. Such work began with efforts to discriminate between hail and rain (e.g. Barge 1974), and the early work is summarized in Jameson and Johnson (1990). As the research polarimetric radars have become more sophisticated, the number of measurable variables and thus the number of potential discriminants has increased. For example, the differential reflectivity (the ratio of equivalent reflectivity factors measured respectively with horizontal and vertical linear polarizations, known as ZDR) is an indicator of the (reflectivity-weighted mean) shapes of the particles in the radar contributing volume. The linear depolarization ratio (the ratio of the cross-polar to copolar backscatter measured with linear, usually horizontal, transmitted polarization; known as LDR) helps to identify the presence of wet non-spherical particles. Combinations of these variables with others can be employed in schemes to classify the dominant particle types within the contributing volume.

The distinctions between the observable variables for different classes of hydrometeors are not clear-cut, and therefore the "compartment" boundaries are actually not sharply delineated. Recognizing this, Vivekanandan et al. (1999) applied the recent technique known as "fuzzy logic" (Kosko, 1994) to the problem and developed a "fuzzy classifier" that takes better account of the actual diffuse character of the boundaries. This classifier is sufficiently fast that it can run in real time on the NCAR S-Pol radar.

Hydrometeor Classification in a Severe Storm

Like all remote sensing techniques, the polarimetric hydrometeor classifier needs in situ verification to establish and improve the scope of its validity. The use of two comparable radars offers significant advantages in the resolution of polarimetric ambiguities that can occur. For example, recently it has been reported that the radar transmittted wave suffers more attenuation in heavy precipitation than what is predicted by models. This has been attributed to an excess of large drops in drop size distribution spectra. Other sources of anomalous radar returns are three-body scattering due to the presence of large hail, reflectivity gradients, beam sidelobes, and possible beam blockage which depends on radar location. Some of these problems are even more prominent in large hailstorms due to their broad distributions of hydrometeor types and high reflectivity factors. Having polarimetric radar views of the same storm regions from two different azimuth angles will allow us to investigate these problems. Further, the use of two polarimetric radars will help determine if there is any aspect angle dependence in hydrometeor scattering, which is usually neglected in scattering models.

Single precipitation growth trajectories can be an effective diagnostic tool to help reveal what are reasonable trajectories, given the Doppler-derived wind fields and polarimetric measurements along the growth trajectory. Many such single-particle growth trajectories will be used to characterize the various particle (hail) growth regimes within the observed storms for direct comparison with microphysical inferences from the polarimetric data.

Single Hail Growth Trajectory

Hail Growth Trajectories as a Diagnostic Tool

The CSU Regional Atmospheric Modeling System (RAMS) (Walko et al. 1995; Meyers et al. 1997) will be used primarily to investigate the microphysical processes and storm kinematics important in hail production and to aid in verifying the microphysical inferences. The RAMS model will also be used in the study of MP and HP storm types. This model, initially developed by Cotton (1972a, 1972b), predicts the mixing ratios and number concentrations for rain, pristine ice crystals, snow, aggregates, graupel and hail. The general gamma distribution is the basis function used for hydrometeor size in each category. New features include: use of stochastic collection for number concentration tendency, breakup of rain droplets, diagnosis of ice crystal habit dependent on temperature and saturation, evaporation and melting of each species, shedding formulations, two moment microphysical parameterization and mixed phase hydrometeor categories. Recently, a T-matrix based scattering program has been interfaced to the RAMS output so that time evolution of radar parameters can be predicted. The microphysical processes of the RAMS model will be adjusted so that a storm similar to a radar observed storm is produced. The modeled storm dynamics, the various microphysical processes and the hydrometeor size distributions can be used in conjunction with radar data and in situ verification for storm analysis.

The basic objectives for the Hydrometeor Identification Studies may be summarized as follows:

1. Intercompare the S-Pol and CSU-CHILL radar data for: a) general radar cross calibration, b) attenuation studies, c) investigation of three-body scattering effects, and d) correction of polarimetric fields biased due to reflectivity gradients/radar beam pattern sidelobes.

2. Improve polarimetric-based interpretive algorithms and hydrometeor classification methods by comparing linearly-polarized radar data with in situ hydrometeor images from the HVPS probe on the T-28.

3. Use particle growth trajectories and detailed numerical modeling to develop consistencies between these results and the observations from penetrating aircraft and polarimetric radar.

2.4. Complementary Studies
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STEPS contains three ancillary studies. These are highly complementary to the core program, and each will contribute in significant ways.

2.4.1 Study of Early Cumulus Congestus Clouds
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As a complement to STEPS, the UND Citation aircraft will be used to study precipitation formation and electrification in early, growing cumulus clouds. Knight et al. (1974), Dye et al. (1974, 1983), and Miller et al. (1983) found that in northeastern Colorado precipitation formed through the Bergeron ice process: nucleation and diffusional growth of ice followed by riming and/or aggregation. In their cloud studies in New Mexico, Blyth and Latham (1993) and Blyth et al. (1997) found that, although large supercooled drops were not observed in clouds with cooler bases, drizzle-sized drops were present in clouds with warmer bases. It is therefore important that we investigate the somewhat warmer-based clouds in the general area of Colorado, Kansas, and Nebraska with new instruments such as the CPI and polarimetric radar to determine if the conclusions from NHRE are true, or if coalaescence rather than the Bergeron ice process is the dominant process in forming precipitation.

The main goals of the Cumulus Congestus Studies will be:

1. to understand how precipitation forms in early, growing cumulus clous of this region, how these clouds become electrified, and the microphysical conditions where the first few lightning flashes are initiated and spread,

2. to evaluate particle identification schemes based on polarimetric radar measurements in early clouds since most polarimetric studies have been done for mature storms, and

3. to investigate the early stages of cloud electrification. This would be a first in combining radar and aircraft measurements with detailed lightning mapping to examine where and when lightning initiates and spreads relative to the electrical, kinematic and microphysical structure of growing cumulus clouds.

The UND Citation will also penetrate flanking turrets and anvils of mature storms to make microphysical and electrical measurements. For example, one hypothesis as to why some storms have low precipitation outputs is that most of the ice mass simply goes into the anvil. Microphysical measurements in the anvil outflow will help determine if there are real differences in particle types, sizes, concentrations, and masses between LP and other more prolific precipitation-producing storms. The electrical measurements also could be a key to improved understanding of the differences in structure of storms which produce predominantly positive CG discharges compared to the more usual negative CGs.

More detailed CuCg material contributed by J. Dye can be found at STEPS: additional material.

2.4.2 Study of Transient Luminous Events (TLEs)
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A complementary study is planned to investigate the recently discovered transient luminous events (TLEs, e.g., sprites, elves and blue jets) in the stratosphere and mesosphere above thunderstorms, taking advantage of the unique data sets and infrastructure provided by STEPS. Many processes for producing TLEs have been hypothesized (e.g., EMP, quasi-electrostatic breakdown, and runaway electrons), but there has not yet been collected a comprehensive data set on the parent lightning discharges needed to evaluate the theoretical models. A primary interest will be correlation of TLEs with that of +CGs [often with very large peak currents (LPCs) and vast horizontal dendritic components] as monitored by the NMIMT Lighting Mapping System (LMS), the NLDN, ELF signatures, and optical sensors. The STEPS study region, at 200-400 km range from Yucca Ridge near Fort Collins, is optimal for low-light video detection. TLEs occur most commonly with LPC+CGs (Lyons et al. 1998) above the stratiform region of MCSs and dissipating supercells, though all evening storms traversing the study area will be monitored. In addition to the LMS, one or both of the multiparameter radars could be manned after dark when conditions are favorable to TLEs. As opportunities allow, balloon-borne measurements of electric fields, electric field changes, and X-rays may also be acquired after dark during STEP.

Specific goals include:

1. Categorize storm systems which generate TLEs, and specifically the favorable regions within these storms and periods during their life cycle,

2. Characterize the differences between +CGs which do and do not produce sprites and elves, obtaining data suitable for improving parameterizations of lightning used in theoretical TLE models, and

3. Quantify ELF Schumann resonance transient signatures (Huang et al. 1999) as a global sprite detection and geolocation system.

A detailed description can be found at STEPS: additional material.

2.4.3 Study of MCS Stratiform Region Lightning
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Previous studies have shown that positive cloud-to-ground lightning is also associated with the trailing stratiform regions of Mesoscale Convective Systems. The bulk of the negative cloud-to-ground lightning occurs within the convective portion of these systems, thus defining a "bipolar" lightning pattern. Two mechanisms have been developed to explain the presence of positive cloud-to-ground lightning in the stratiform regions: advection of primarily positive charge from the convective line into the stratiform region, followed by discharge to ground; and development of an inverted dipole charge structure in the stratiform region (positive charge underlying negative charge; thus the positive charge layer is nearest to ground). This inverted charge structure is thought to be associated with in-situ microphysical processes driven by the mesoscale updraft. Previous observational studies have been hampered by the fact that 3-D mapping of lightning discharges in MCSs has been unavailable. Hence these hypotheses have been developed from indirect observations or other reasoning. With the lightning mapping capabilities planned for STEPS, in the context of Doppler air motion, in-situ aircraft and balloon soundings, we have our best opportunity for confirming or refuting the above hypotheses. This ancillary objective will not only be highly complementary to the core objective to better understand the causative agents for positive cloud-to-ground lightning, but will also be very complementary to ancillary objective 2.4.2, since positive CGs in regions of stratiform precipitation associated with MCSs have been linked to TLEs.

3. Field Observing Systems
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We propose to deploy field observing systems to monitor environmental wind and thermodynamic vertical profiles, storm windfields, hydrometeor contents, electric fields, particle charge, lightning, and other electrical activity.

Fixed Ground-based Observing Systems

Operations Center: An Operations Center will be established at one of the research radar sites. There will be displays of these radar data with electronically overlaid aircraft tracks. The location and time of balloon launches and other surface-based activities will be manually noted when possible. The Center will have real-time access over the Internet for display of weather information from the UCAR/COMET and NCAR/RAP weather websites. Pre-operations weather briefings and meetings will likely be conducted at a facility at Goodland Kansas, perhaps at the NWS field office.

Communications: VHF radios will be used for communications between the Operations Center, aircraft, radars, and ground-based mobile units. Communications with the aircraft will come only from the Operations Center, though other sites can monitor the aircraft frequencies. Communications between the Operations Center, radars, and ground-based units will be done on a different frequency from the one used for aircraft to avoid confusion. The large distances involved may require a VHF repeater for ground-based units. If it becomes possible, cellular phones will be used in place of VHF radio for communication between the Operations Center and ground-based mobile units.

Radars: To obtain radial velocity measurements for determining the evolving 3D winds, a triple-Doppler radar network will consist of the CSU-CHILL and NCAR S-Pol polarimetric Doppler radars along with the WSR-88D at Goodland Kansas. The three radars will be located at the vertices of a roughly equilateral triangle with 60 km sides surrounding the lightning mapping system. With this configuration, three dual-Doppler areas exist outside the triangle, along with one triple-Doppler area inside the triangle.

The research radars can complete volume scans in about 5 min or less, with radar range-azimuth-elevation sampling intervals to resolve scale sizes (for example, width of an updraft) of about 3 km or better. In addition to their Doppler radial velocity measurements, CSU-CHILL and S-Pol will provide dual-polarization measurements. Meteorologists with access to a CSU-CHILL or S-Pol display will coordinate operations of the triple-Doppler system, providing scan information about selected storm(s) to the other research radar to ensure that all radars are scanning the same region at the same time. This mode of operation will also ensure that dual-polarimetric data are properly taken in conjunction with the Doppler measurements.

The NWS WSR88D will normally be doing full 360-deg surveillance scans in one of the precipitation Volume Coverage Patterns (VCPs): either VCP21 (9 elevation angles, 6-min updates) or VCP11 (14 elevation angles, 5-min updates). The range gates are spaced 1-km for reflectivity factor and 250m for radial velocity while beams are typically about 1-deg apart in azimuth. Though these scan modes and spatial resolutions are not ideal for research purposes, they are deemed sufficient to remove the baseline ambiguities that are present when only two Doppler radars are used. The WSR88D will also provide broad-scale coverage at all times.

Given the relative rarity of LP supercells, these storms will have the highest priority for focused observations, if they develop. The second highest priority will be storms in which most ground flashes are +CG flashes, because such storms also are relatively infrequent, though less infrequent than LP supercells. All research instruments will be focused on the target storm, where the radars will do sector scans at a sequence of constant elevation angles (PPIs). Occasionally, low-level surveillance scans will be done to identify new storm areas and to provide environmental information. RHIs will rarely be done by the Operations Center radar during aircraft operations. RHIs may be used when storms are near the research radar baseline for detailed intercomparisons of polarimetric measurements. For storms occurring at times and/or in places where aircraft operations are not conducted, the priority will be dual-Doppler volumes from storm regions containing lightning and/or TLE activity.

Aircraft: The essential aircraft for STEPS is the SDSMT armored T-28, which will provide in situ observations of hydrometeors, winds, and electric fields in the lower to middle altitude range within updrafts and hail shafts. The T-28 is equipped to measure the complete spectrum of water and ice particles in clouds, ranging from cloud droplets a few micrometers in diameter to about 5-cm diameter hail. It typically spends roughly one hour on-station and can reach altitudes just over 20 kft MSL. One of its three precipitation particle imaging probes (the HVPS) has the capability to determine particle charge as the particle is imaged. In addition, it will be equipped with a 6-instrument electric field mill system that will be used to map the total vector electric field inside and outside clouds.

The UND Citation II twin-engined jet aircraft will complement the core program by providing in situ observations in the upper regions of cumulus congestus clouds, new convective cells in the flanking line, and anvil regions downshear from the deep convection. The Citation will carry its normal complement of instruments for making thermodynamic, microphysical and wind measurements, as well as the SPEC Cloud Particle Imager (CPI) and six electric field mills to measure the 3-D electric field. The electric field mills are low noise, high sensitivity mills recently designed and built by NASA Marshall. Its ceiling is 13 km with an endurance of 3+ hours with typical IFR reserves. The aircraft is certified for flight into known icing conditions and can penetrate storm regions with radar reflectivities less than 45 dBZ.

Environmental Sounding Units: The vertical profile of environmental winds and thermodynamic parameters will be monitored with two mobile MGLASS sounding units. Based on the daily weather briefing, these units will be deployed one to either side of the dry line in situations when isolated supercell storms are expected, or to more general locations to monitor the evolving environment. Additional wind information will come from the NCEP operational analyses and the NWS wind profilers.

Mobile Mesonets: Four mobile mesonet vehicles from the NSSL-OU Joint Mobile Research Facility, under the direction of Erik Rasmussen, will be available to take observations of wind, temperature, and moisture under and near targeted storms. These mobile units will also provide reports on whether targeted storms "appear" to be LP, MP, or HP. Photographic and video documentation will also be done as well as qualitative assessment of precipitation amounts and types, especially hail and its size. This information will be used to help verify microphysical inferences from the polarimetric measurements.

Lightning Mapping System: The deployable 3D lightning mapping system developed by New Mexico Tech was successfully operated in central Oklahoma during June of 1998 as part of the MEaPRS program. This system detects lightning of all types, not just cloud-to-ground lightning, out to a range of roughly 200 km. It determines the time and location at which a lightning channel segment radiates electromagnetic noise, typically as the segment forms initially or as it subsequently conducts a large, fast electric current surge. Thus, the system maps the initiation and development of a lightning flash inside the storm. Absolute location errors are less than 100 m over the network and increase with range outside the network. For STEPS the system will be deployed over an area comparable to that of the radar system. To improve coverage in the external Doppler lobes, three additional stations will likely be operated at substantially greater distances outside the Doppler array.

National Lightning Detection Network (NLDN): CG lightning activity will be monitored in real-time using the NLDN. This is a nationwide network for monitoring the location, polarity, and other characteristics of CG lightning events. The mapped location is the point where the flash strikes ground. The NLDN provides no information about the extent or initiation of the flash inside the cloud, but its ability to identify CG flashes is critical to STEPS goals, and its real-time display provides key information to help guide data collection. The NLDN typically detects 70-90% of CG flashes, with location errors of less than 500 m. A display of NLDN CG strike locations will be available at the Operations Center. The lightning information will be used to help characterize and track storms during operations, particularly to identify storms that produce +CG flashes and to help guide mobile teams to such storms.

Both the NLDN and Lightning Mapping System will be supplemented by the CSU three-station flat plate antenna network. This network measures total lightning flash rates within 30 km of each station.

Storm Soundings: Investigators from NSSL, OU, and NMIMT will make balloon soundings into storms to measure internal temperature, pressure, humidity, wind, and electric field. Balloons will be launched from a mobile laboratory of the JMRF which will carry at least two balloon receiving and tracking systems (MGLASS or MCLASS), to allow simultaneous balloon flights. These systems were used for MEaPRS in 1998, and similar systems have been used for many years. Also, NMIMT plans to develop a new measurement and telemetry system in time for STEPS, to allow even more simultaneous flights. The plan is for the new telemetry to use the NMIMT lightning mapping system to track the balloon and receive data from its sensors. Vertical profiles of the electric field are valuable data in themselves, but can also be used to infer space charge. Soundings of the electric field by two or more closely spaced sensors will allow a more reliable estimate of space charge than can be obtained from a sounding by a single sensor. Weather guidance and coordination with other platforms will come from the Operations Center, but the decision to launch will be made by the crew chief of the mobile laboratory, to optimize targeting and maintain crew safety in a storm environment.

Yucca Ridge Field Station: The YRFS vantage point on a high plateau 20 km northeast of Ft. Collins CO provides a panoramic view of the entire Front Range and High Plains. Line-of-sight measurements of CG channels have been obtained from this station to as far as 200 km, IC events to 400 km, and sprites to 1000 km. The observation deck can accommodate sensing systems from as many as half-a-dozen research teams. FMA Research will provide 24-hour command and control for the sprite-related aspects of STEPS. FMA can also generate forecasts of sprite potential for storm systems, and then, using LLTV monitoring, vector other investigators to sprite-active regions of thunderstorms.

4. Field Operations Plan
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Preliminary site selection and logistical arrangements in the study area will begin in the fall of 1999. Sites for the two research radars and the lightning mapping system will be established early enough that field installations can be completed by the end of April 2000. One prospective research radar site is located about 50 miles west of Goodland near Stratton, CO on I-70. The other prospective radar site will be near Wray, CO, about 50 miles north of the midway point between Goodland and Stratton. There should be ample lodging along the I-70 corridor for the 12-18 people needed for the Operations Center and radars. Crews for several other STEPS facilities, including the lightning mapping system, ballooning team and sounding units, will also be based near Goodland. The T-28 and Citation aircraft, along with the ballooning crew, will deploy to Goodland by 15 May. The Operations Center and radars will be set up and operating by about 10 May.

Weather forecasting will be based at the field site, with input from NCAR and YRFS. MGLASS radiosondes will be launched when and where needed, before and during operations, in order to monitor the evolution of the thermal stratification, humidity profile, and vertical shear of the horizontal wind in the target region.

Three individuals selected from the STEPS investigators will rotate in one-week shifts through the position of daily Operations Director (OD). The OD will be located at the Operations Center and will be assisted by a rotating deputy OD, selected from the same group. The OD will be responsible for directing the deployment of the observing facilities to obtain an optimum data set for meeting the STEPS objectives, given the day's storm activity. The Deputy Director will handle most routine communications during operations. Observing Systems Coordinators (OSCs) will assist the OD and communicate directly with outlying crews and remotely located Radar Scientists. The OSCs will get feedback from outlying crews about local weather conditions, including radar echo descriptions, and help direct them to the target storm(s) selected by the OD. These OSCs also pass information along to others not located in the Operations Center. Radar and aircraft operations will be coordinated from the Operations Center by these OSCs, under the overall direction of the OD.

On days when storms are developing or are forecast to develop within the region with prime radar and lightning mapping system coverage, a suitable storm or region will be chosen by the OD. This selection will be based on radar observations, weather observations available on-site, and input from other facility operators. Storms likely to be relatively isolated and severe will have high priority, with LP supercell storms having the highest priority and storms producing many +CG flashes having the second highest priority.

The T-28 will usually operate between 15 and 20 kft MSL and perform reciprocal cloud penetrations along the wind shear vector at fixed altitudes through the main updraft and precipitation-containing regions of storms during their active phase. The usual experience with the T-28 has been that penetration-altitude changes consume so much time that significant fractions of a cloud's evolution are lost while the aircraft is out of cloud coming to a new altitude. Therefore in STEPS, ever effort will be made to make all T-28 penetrations at one altitude that is as high as possible, to try to get into regions colder than freezing, preferably with mixed phase microphysics.

The Citation will operate above 20 kft to make penetrations of anvil regions, or in the upper portions of flanking convective turrets to make penetrations through as much of a cell life cycle as possible. The Citation will be able to penetrate at altitudes above the -10 deg C level, but will not penetrate where reflectivities exceed 45dBZ in High Plains storms. It can change altitudes more readily than the T-28 and can be expected to remain aloft for a little over three hours, extending storm surveillance into the later stages of evolution. During periods of complementary cumulus congestus studies, the Citation will be devoted to penetrations of cumulus clouds, such as those expected to form early on or near the dryline.

The balloon crew will try to obtain electrical soundings near mature storms being studied with the aircraft and radars. Mobile mesonet crews will also be vectored to storms to take surface observations of wind, temperature, moisture, and precipitation amounts, types, and hailstone sizes within and around the targeted storm. The location of roads, the distance to storms, and other logistical considerations will enter into the choice of storm for operations. However, if an otherwise high-priority storm occurs in the operations area in a region mobile ground crews cannot reach in time, the OD may still choose that storm for aircraft and radar operations. In that case, the OD will also evaluate whether ground crews can intercept the targeted storm later or can intercept an alternative storm in an accessible region with lightning mapping and radar support. Besides communicating with the Operations Center, as discussed above, mobile ground crews will also have vehicle-to-vehicle radios for field communication.

5. Program Management Structure
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Pre-Field-Phase Preparations: A Scientific Steering Committee consisting of V. Bringi (CSU), Paul Krehbiel (NMIMT), Don MacGorman (NSSL), Charlie Knight (NCAR/MMM), Andy Detwiler (SDSMT), John Helsdon (SDSMT), Walt Lyons (FMA), Earle Williams (MIT), and Steve Rutledge (CSU) was selected during the combined CESAR/LPEX meeting held on 9 April 1999 at CSU. This committee is responsible for pre-field operations planning, including overseeing the preparation of this Scientific Overview Document and ensuring that Facilities Requests are submitted to the OFAP in a timely fashion. They are also responsible for defining usage of the requested facilities in order to reach the Broad Goal and Specific Scientific Objectives as set forth in this Overview. This committee will convene a meeting to establish a detailed Operations Plan soon after funding is established.

Field Phase: During the field phase, the Scientific Steering Committee or their representatives will establish the scientific priorities for each day's operations. This will be done after a critique of the previous day's operations, the current weather briefing, and equipment status reports. These reviews and briefings will be open to all participants, subject to available space, and will be held at a facility in Goodland, Kansas.

The position of Operations Director will rotate among three participants, each of whom will serve at least a week at a time. The main responsibilities of the OD will be to implement the scientific priorities established by the Steering Committee and to manage the daily operations. The OD will select the storm(s) of interest and will be assisted by Observing Systems Coordinators (OSCs) who will be in direct communication with outlying crews and who will get feedback from them on local conditions and help direct them to the targeted storm. These coordinators will also pass information along to others not located in the Operations Center. Several scientists will be selected to help in directing detailed operations at the remote research radar site, with general guidance from the Radar Coordinator located at the Operations Center.

6. Data Management Plan
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A central data base, consisting of quick-look products and data catalogs of potential cases for analysis, will be provided via the Internet. Besides this central data base, each group that is directly responsible for a specific Observing System will maintain a data base for that system. These specialized databases will include basic measurements (Level I data, such as voltages and radar processor counts) that have been converted to meteorological units (Level II data, such as radar reflectivity and radial velocity data). These specialized data bases will describe the calibration and processing used to produce the Level II data. Products that require considerable effort to produce, such as vertical profiles of the electric field or three-dimensional flow fields from Doppler radar measurements, are Level III data and will be produced for selected cases, not on a routine basis.

7. References
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Appendix A. Participants
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The participants along with their email addresses, affiliations, and broad area of scientific interest are listed here.

NAME    (email)	AFFILIATION	AREA OF INTEREST
Beasley, William    (wbeasley@ou.edu)	U. Oklahoma	Lightning and TLEs
Blyth, Alan    (blyth@kestrel.nmt.edu)	NMT	Early cumulus congestus
Bringi,Viswanathan    (bringi@engr.colostate.edu)	CSU	Hydrometeor identification and storm processes
Carey, Larry    (carey@olympic.atmos.colostate.edu)	CSU	Storm electrification
Chandra    (chandra@engr.colostate.edu)	CSU	Hydrometeor identification and storm processes
Detwiler, Andy    (andy@ias.sdsmt.edu)	SDSMT	Storm electrification
Dye, Jim    (dye@ucar.edu)	NCAR/MMM	Early cumulus congestus
Helsdon, John    (jhelsdon@taz.sdsmt.edu)	SDSMT	Storm electrification
Hodanish, Steve    (Steve.Hodanish@noaa.gov)	NWS/Pueblo	Forecast applications of lightning data
Hager, Bill    (hager@math.ufl.edu)	U. Florida	Lightning discharge processes
Hubbert,John    (hubbert@engr.colostate.edu)	CSU	Hydrometeor identification and storm processes
Kennedy, Pat    (pat@lab.chill.colostate.edu)	CSU	?????
Knight, Charles    (knightc@ucar.edu)	NCAR/MMM	Dynamical/microphysical processes in LP-MP-HP storms
Krehbiel, Paul    (krehbiel@ibis.nmt.edu)	NMIMT	Storm electrification and TLEs
Lyons, Walt    (walyons@frii.com)	FMA	Storm electrification and TLEs
MacGorman, Don    (don.macgorman@nssl.noaa.gov)	NSSL	Storm electrification
Miller, L. Jay    (ljmill@ucar.edu)	NCAR/MMM	Hydrometeor identification and storm processes
Peterson, Walt    (walt@olympic.atmos.colostate.edu)	CSU	Storm electrification
Poellot, Mike    (poellot@aero.und.edu)	UND	Early cumulus congestus
Rasmussen, Erik    (rasm@ucar.edu)	NSSL/Boulder	Dynamical/microphysical processes in LP-MP-HP storms
Rutledge, Steve    (rutledge@olympic.atmos.colostate.edu)	CSU	Storm electrification
Ryan, Jesse    (jesser@atmos.colostate.edu)	CSU	Storm electrification
Smith, Paul    (psmith@ias.sdsmt.edu)	SDSMT	Hydrometeor classification
Stith, Jeff    (stith@aero.und.edu)	U. North Dakota	Anvil dynamics and hydrometeor classification
Straka, Jerry    (jstraka@pig.cgn.ou.edu)	OU	Dynamical/microphysical processes in LP-MP-HP storms
Weisman, Morris    (weisman@ucar.edu)	NCAR/MMM	Dynamical/microphysical processes in LP-MP-HP storms
Weckwerth, Tammy    (tammy@ucar.edu)	NCAR/ATD	ATD/RSF field program manager
Williams, Earle    (earlew@ll.mit.edu)	MIT	Storm electrification
Winn, Bill    (winn@loon.nmt.edu)	NMIMT	Storm electrification
Zajac, Brad    (zajac@cira.colostate.edu)	CSU-CIRA	Lightning and satellite nowcasting applications

Appendix B. Proposals
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Listed here are known proposals: the principal investigators, the title of the proposal, the status of the proposal, and the funding agency to which the proposal was (will be) submitted.

PRINCIPAL INVESTIGATOR(S)	TITLE of PROPOSAL	STATUS	FUNDING AGENCY
John Helsdon (SDSMT) Andy Detwiler (SDSMT)	Airborne Observations and Storm Modeling in Support of the Severe Thunderstorm Electrification and Precipitation Study (STEPS)	Under review	NSF
Paul Smith (SDSMT) J. Vivekanandan (NCAR)	In-situ Verification of Hydrometeor Algorithms for Polarimetric Radar	Under review	NSF
V. Bringi (CSU) John Hubbert (CSU) Jay Miller (NCAR)	Advanced Hydrometeor Classification Applied to Microphysics and Kinematics of Severe Storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS)	Under review	NSF
Paul Krehbiel (NMIMT) William Rison (NMIMT) Ron Thomas (NMIMT)	Lightning and Thunderstorm Studies	Being drafted	NSF
Earle Williams (MIT) Walt Lyons (FMA)	Meteorological Applications of Schumann Resonances	To be submitted	NSF
Walt Lyons (FMA) Earle Williams (MIT)	Characterization of Lightning Which Produces Mesopheric Transient Luminous Events (Sprites and Elves)	To be submitted late July or early August	NSF
V. Chandrasekar (CSU)	Study of Polarimetric Radar Signatures in Winter and Spring Time Storms Using the CSU-CHILL Radar	Continuation of existing grant	NSF
Kathy Whaler (?) Martin Fuellekrug    (U. Frankfurt)	The Global Distribution of Sprites	Submitted	UK NESC
Steven Rutledge (CSU) Larry Carey (CSU) Walt Petersen (CSU)	Dynamics, Microphysics and Electrification in Convective Cloud Systems	Submitted	NSF
Mike Poellet (UND) Alan Blyth (NMT) Jim Dye (NCAR)	Microphysical and Electrical Evolution of CuCg and Mature Storm Anvils in STEPS	Submitted	NSF
Bill Winn (NMIMT)	Balloon-borne electric field measurements in thunderstorms using a novel method of telemetry	Submitted	NSF
Don MacGorman (NSSL-OU) Dave Rust (NSSL-OU)	Measurement and Analysis of Vertical Profiles of the Electric Fields in Severe Storms During STEPS	Submitted	NSF
Jerry Straka (OU) Erik Rasmussen (NSSL) Conrad Ziegler (NSSL)	Numerical Modeling Studies of Electrification, Microphysics, and Lightning in Severe, High Plains Thunderstorms	To be submitted	NSF

Appendix C. Supplemental Material
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There is additional material supporting and supplementing the STEPS Overview document that has been posted at SDSMT. This material includes more detailed information on some of the studies proposed for STEPS as well as important messages concerning preparations for the field program.

Appendix D. Daily Severe Weather Probability - NWSO Goodland KS
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Severe weather reports (NWS definition) and daily severe weather probabilities for the four counties (Yuma CO, Kit Carson CO, Cheyenne KS, and Sherman KS) near the triple-Doppler radar triangle for both 5- (1995-1999) and 10-year (1990-1999) periods. If severe weather was reported in any one of the above counties on a day during May 1 - August 31, that day was considered a "severe weather day." For each day of the two counting periods, the total number of severe weather reports was divided by the number of possible days (5 or 10) in the period and subjected to either 5- or 10-day running centered-averages to obtain the daily severe weather probabilities. These graphs were provided by Llyle Barker, Science and Operations Officer at the NWSO Goodland KS.

Appendix E. Weekly Severe Storm Reports with Positive Cloud-to-ground lightning
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Weekly severe storm reports dominated by positive cloud-to-ground lightning for the 1989-1998 warm seasons within the STEPS study region defined by a box from -103.5 to -101 longitude and 38.5 to 40.5 latitude and shown in Fig. 1. These figures were provided by Dr. Larry Carey, Research Associate, Department of Atmospheric Science, Colorado State University.

The mean frequency of severe storm reports and reports dominated by +CG lightning is given in Fig. 2. Both severe weather in general and +CG dominated severe weather in particular is most frequent during the later part of May and early part of June. The trend towards more severe weather reports during late July is not accompanied by a corresponding increase in severe weather dominated by +CG lightning.

Figure 3 is a frequency histogram broken down by week for each year 1989-1998 for the occurrence of severe storm reports accompanied by 50% +CG lightning. There is considerable year-to-year variability with some years having a noteable mid-end May peak (1991, 1994, and 1998), while other years have significant maxima in mid-late July (1992, 1993, and 1996). Several years have no dominate peak and are spread throughout the summer. In any given year there can be at least one week with zero probability of severe weather.

Not shown is a similar analysis of predominately positive severe weather events having high flash densities (greater than 0.01 per sq km per hr). It would take several more years to show any trends since these are very rare events and the year-to-year variability is large. However, it does appear that July is a more favorable month for these monster +CG severe events, for example, 4 of the 10 years had their overall frequency maximum in July.

It is not clear from these analyses whether dominate +CG production is uniquely associated with supercells. That is to say the common-knowledge climatology or impressions of supercells does not seem to be reflected in reality--there is much more variability year-to-year.

Appendix F. Dryline Positions near Goodland for 1998 and 1999
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Dryline positions near Goodland Kansas for the month of June, 1998 and 1999. These graphs were provided by Llyle Barker, Science and Operations Officer at the NWSO in Goodland.

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