Events (Upcoming & Past)

Past MMM Events

Kristen L. Rasmussen and Robert A. Houze, Jr.1. Department of Atmospheric Sciences, University of Washington, Seattle, WA**Only Kristen will be presenting*2. National Center for Atmospheric Research, Boulder, CO

Extreme convection tends to form in the vicinity of mountain ranges, and the Andes in subtropical South America help spawn some of the most intense convection in the world. An investigation of the most intense storms for 11 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data shows a tendency for squall lines to initiate and develop in this region with the canonical leading convective line/trailing stratiform structure. The synoptic environment and structures of the extreme convection and MCSs in subtropical South America are similar to those found in other regions of the world, especially the United States. In subtropical South America, however, the topographical influence on the convection initiation and maintenance of the MCSs is unique. A capping inversion in the lee of the Andes is important in preventing premature triggering. The Andes and other mountainous terrain of Argentina focus deep convection initiation in the foothills of western Argentina. Subsequent to initiation, the convection often evolves into propagating mesoscale convective systems similar to those seen over the U.S. Great Plains and produces damaging tornadoes, hail, and floods across a wide agricultural region.

Numerical simulations conducted with the NCAR Weather Research and Forecasting (WRF) Model extend the observational analysis and provide an objective evaluation of storm initiation, terrain effects, and development mechanisms. The simulated mesoscale systems closely resemble the storm structures seen by the TRMM Precipitation Radar as well as the overall shape and character of the storms shown in GOES satellite data. A sensitivity experiment with different configurations of topography, including both decreasing and increasing the height of the Andes Mountains, provides insight into the significant influence of orography in focusing convection initiation in this region. Lee cyclogenesis and a strong low-level jet are modulated by the height of the Andes Mountains and directly affect the character, intensity, and spatial distribution of the convective systems. A conceptual model for convection initiation in subtropical South America that integrates the results of the topographic sensitivity experiments will be presented. Additional research on these storms including lightning, climatological rain contribution, and severe storm impacts will also be presented.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 23 April 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Kristen L. Rasmussen
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, April 23, 2015 - 3:30pm to 5:00pm

Chris DavisThe National Center for Atmospheric ResearchBoulder, Colorado

The upscale aggregation of convection is used to understand the emergence of rotating, coherent mid-tropospheric structures and the subsequent process of tropical cyclone formation. The CM1 model is integrated on an f-plane with uniform SST and prescribed uniform background flow. Moist cyclonic vortices form, merge, and eventually result in a single dominant vortex that subsequently forms a tropical cyclone. Consistent with previous studies, the approach to saturation within the mid-tropospheric vortex accelerates the genesis process. A novel result is that, while updrafts do not intensify prior to genesis, downdrafts do. Stronger downdrafts produce cold pools that maximize their negative buoyancy about one day prior to genesis. Shear-cold-pool dynamics promote organization of lower-tropospheric updrafts that spin up the surface vortex. It is inferred that the observed inconsistency between convective intensity and thermodynamic stabilization prior to genesis results from sampling limitations of the observations wherein the important cold pool gradients are unresolved.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 9 April 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Chris Davis
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, April 9, 2015 - 3:30pm to 5:00pm

James DoneThe National Center for Atmospheric ResearchBoulder, Colorado

An approach to assessing the damage potential of tropical cyclones is developed using a combination of physical reasoning and empirical assessment. Using readily available and key damaging cyclone parameters of intensity, size, and translational speed a Cyclone Damage Potential index is developed that represents offshore damage and onshore wind and coastal surge damage. The index is applicable to individual tropical cyclones, and to seasonal and global summaries. Actual damage assessment or prediction requires the additional step of incorporating historical damage data and regional peculiarities.

The index is then modified to use large-scale climate data available from global climate models, thereby sidestepping the need for information on individual cyclones. Relative sea surface temperature and steering flow are used as proxies for cyclone intensity, size, and translational speed. Application to climate model simulations under representative concentration pathways (RCPs) 4.5, 6.0, and 8.5 shows a future reduction in damage potential, driven by a cooling relative SST. However, the spread in damage potential reduction among the RCPs is less than the spread due to internal variability over the 21st century, as assessed using a climate model initial condition large ensemble. Improving understanding of spatial SST change may therefore be key to understanding future change in TC damage potential.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 2 April 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
James Done
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, April 2, 2015 - 3:30pm to 5:00pm

Tom AulignéNCAR, Boulder

Hybrid variational/ensemble data assimilation (aka hybrid DA) is widely used in research and operational systems, and it is considered as the current state-of-the-art for the initialization of numerical weather prediction models. However hybrid DA requires a separate ensemble DA to estimate the uncertainty in the deterministic variational DA, which can be suboptimal both technically and scientifically. A new NCAR-developed algorithm called the Ensemble-Variational Integrated Localized (EVIL) data assimilation addresses this deficiency by updating both the deterministic and ensemble analyses within a single variational system. Idealized cases with a simplified model have shown the potential of EVIL to outperform existing DA systems. Recently, the algorithm has been implemented within the GSI framework for regional and global models. Particular attention was devoted to the affordability of the algorithm in preparation for operational applications. In this seminar, we will explain the theory of EVIL, describe various implementation strategies and show early results with the WRF model.

This seminar will be webcast live at: http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here: https://www.mmm.ucar.edu/events/seminars

Thursday, 26 March 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Tom Auligné
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, March 26, 2015 - 3:30pm

Peter WestonThe Met OfficeUnited Kingdom

In the last 3 years advances in satellite data assimilation have resulted in significant improvements to the accuracy of operational Met Office forecasts both at global and regional scales. This talk will summarise these changes which include assimilating data from new instruments, improvements to the assumed observation errors, optimised thinning procedures, more accurate observation operators and improved pre-processing of the data. Headline verification results show that each of these incremental changes results in a small benefit to forecast accuracy but when they are put together as a package the improvements are significant.

One such change which had a reasonably large impact was the introduction of the treatment of correlated observation errors for IASI. The observation errors are diagnosed using a posteriori methods, the diagnosed matrix is then adjusted to make it suitable for use and then passed to the assimilation scheme. The use of correlated errors allows the data to be given adaptive weights depending on the inter-channel structure of the first guess departures. Generally more weight is given to the observations which means the data is being used more effectively. Results from assimilation trials which show that this change leads to improved forecast accuracy will be shown.

Another recent change is the introduction of the assimilation of IASI data into the UKV, the operational convective scale model which is run at the Met Office to provide high resolution short-range forecasts over the UK and surrounding area. The assimilation of this data results in small but consistent improvements to short-range surface temperature and precipitation forecasts.

Future work will include the implementation of a variational bias correction scheme, use of reconstructed radiances derived from principal components, use of data from the Chinese FY-3 series of satellites, and better use of radiances over different surface types and in cloudy conditions. As a first step in researching the use of IR radiances in cloudy conditions a simple Ensemble Kalman Filter cloud analysis scheme has been developed and initial results from this system will be shown.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 19 March 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Peter Weston
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, March 19, 2015 - 3:30pm to 5:00pm

Mesoscale and Microscale Meteorology/Cloud Physics Across Scales Seminar

Wojciech W. GrabowskiNational Center for Atmospheric ResearchBoulder, Colorado

Formation and growth of cloud and precipitation particles (“cloud microphysics”) affect cloud dynamics and such macroscopic cloud field properties as the mean surface rainfall, cloud cover, and liquid/ice water paths. Traditional approaches to investigate the impacts rely on parallel simulations with different microphysical schemes or with the same scheme with different parameters. Such methodologies are not reliable because of the natural variability of the cloud field that is affected by the feedback between cloud microphysics and dynamics. We developed a novel modeling methodology to assess the impact of cloud microphysics on cloud dynamics and on simulated macroscopic cloud field characteristics. The main idea is to use two sets of thermodynamic variables driven by two microphysical schemes (or by the same scheme with different parameters), with one set coupled to the dynamics and driving the simulation, and the other set piggybacking the simulation, that is, responding to the simulated flow but not affecting it. We will discuss application of this methodology to cloud field simulations of shallow and deep convection. We will show that the methodology allows assessing the impact of cloud microphysics on cloud field properties with unprecedented accuracy. By switching the sets (i.e., the set driving the simulation becomes the piggybacking one, and vice versa), the impact on cloud dynamics can be isolated from purely microphysical effects. We will show that the new methodology documents a rather insignificant impact of the assumed cloud droplet concentration on convective dynamics for the case of scattered unorganized deep convection. These results cast doubt on the dynamic basis of the deep-convection invigoration in polluted environments.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 5 March 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Wojciech W. Grabowski
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, March 5, 2015 - 3:30pm to 5:00pm

Judith BernerNational Center for Atmospheric ResearchBoulder, Colorado Four model-error schemes for probabilistic forecasts over the contiguous United States with the WRF-ARW mesoscale ensemble system are evaluated in regard to performance. Including a model-error representation leads to significant increases in forecast skill near the surface as measured by the Brier score. Combining multiple model-error schemes results in the best-performing ensemble systems, indicating that current model error is still too complex to be represented by a single scheme alone.To understand the reasons for the improved performance, it is examined whether model-error representations increase skill merely by increasing the reliability and reducing the bias—which could also be achieved by postprocessing—or if they have additional benefits. Removing the bias results overall in the largest skill improvement. Forecasts with model-error schemes continue to have better skill than without, indicating that their benefit goes beyond bias reduction.Decomposing the Brier score into its components reveals that in addition to the spread-sensitive reliability, the resolution component is significantly improved. This indicates that the benefits of including a model-error representation go beyond increasing reliability. This is further substantiated when all forecasts are calibrated to have similar spread. The calibrated ensembles with model-error schemes consistently out- perform the calibrated control ensemble.Including a model-error representation remains beneficial even if the ensemble systems are calibrated and/ or debiased. This suggests that the merits of model-error representations go beyond increasing spread and removing the mean error and can account for certain aspects of structural model uncertainty.This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 26 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Judith Berner
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, February 26, 2015 - 3:30pm to 5:00pm

Weather predictions have improved significantly in recent decades. Yet as recent events such asSuperstorm Sandy illustrate, meteorologists still face major challenges in effectively conveying weatherforecasts and warning information. Advances in information and communication technology are alsorapidly changing how people access, interact with, and share weather-related information. Thispresentation will discuss results from recent research studies to understand communication, interpretation,and use of weather forecast and warning information, with an emphasis on improving communication ofweather risk and forecast uncertainty. It will focus on interdisciplinary physical-social science research tobuild empirical understanding of how people conceptualize weather-related risks, how they perceive andinterpret different types of forecast and warning information, and how they use information in protectivedecisions. First, results will be presented from a nationwide survey examining people's perceptions,interpretations, and uses of weather forecast uncertainty. Results will then be presented from studies ofpeople’s forecast and warning decisions when extreme weather events (such as hurricanes or flash floods)threaten, including their responses to different warning messages. Next, an ongoing project will bedescribed that investigates how interactions among actors and information influence risk interpretationsand behavioral responses as a hurricane approaches and arrives, using computational modeling, analysisof social media data, and other methods. Potential implications of the findings for communication ofweather and climate information will also be discussed, as well as priority areas for future research.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 19 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Rebecca E. Morss
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, February 19, 2015 - 3:30pm to 5:00pm

John J. Finnigan (presenter) in collaboration with Edward G. Patton and Roger H. Shaw1. CSIRO Oceans and Atmosphere, Canberra, Australia2. National Center for Atmospheric Research, Boulder, Colorado3. University of California, Davis

The origin of the coherent eddy structures in and above tall plant canopies in neutrally stratified flow has for some years been known to result from the hydrodynamic instability of the inflected mean velocity profile that develops at the canopy top. A cascade of secondary instabilities yields canopy eddies of characteristic form and these are responsible for most of the turbulent kinetic energy and transport in the canopy’s vicinity.

Above the surface layer, in neutral and weakly unstable flows, large-scale roll-like structures dominate transport throughout much of the larger atmospheric boundary layer (ABL). When buoyancy forces become dominant, these rolls transition into Rayleigh-Benard-like cells spanning the depth of the convectively driven ABL. At the canopy level, these ABL-scale structures modulate the near-surface wind and temperature fields so that canopy regions are alternately subjected to enhanced or reduced wind shear and diabatic stability at horizontal scales ranging from 100-1000 canopy heights.

Beneath these ABL-scale structures in regions of strong shear, the canopy eddy structure corresponds to the inflection point instability described above. However in regions of low shear, diabatic effects dominate and convective plumes develop, extending vertically to several canopy heights and with horizontal widths of order canopy height. These canopy plumes are a mode of buoyant instability with Rayleigh-Benard type eigenmodes, whose horizontal scale is related to the vertical profile of canopy air temperature.

The horizontally-averaged heat and momentum transfer between the canopy layers and the ABL above therefore results from two distinct coherent eddy structure types, according to whether the canopy is below ascending or descending regions of the larger ABL-scale structures. Because the structure of the large ABL-scale rolls or cells above the canopy depends upon the area-averaged heat and momentum transfer from the surface through the parameter zi/LMO (the ABL depth divided by the Obukhov length), these three modes of instability, two at canopy scale and one at ABL scale, are intimately coupled.

We have studied this situation using canopy-resolving large eddy simulation (LES) of the full ABL. In addition, we complement those full LES simulations with idealized studies of the canopy plume instability.

In this talk we will discuss the implications of this fully coupled picture of canopy-ABL turbulent exchange for Monin-Obukhov scaling in the surface and canopy-roughness sublayers, and for observational strategies for tower measurements of turbulent fluxes. We will also comment on the usefulness of linear and non-linear stability analysis in revealing attractors for dominant turbulence structures even in fully turbulent flows.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

**PLEASE NOTE THE SPECIAL DAY OF THIS SEMINAR**Tuesday, 17 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
John J. Finnigan
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Tuesday, February 17, 2015 - 3:30pm to 5:00pm

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