Events (Upcoming & Past)

Upcoming MMM Events

Joseph Olson
Global Systems Division
NOAA--Earth System Research Laboratory 

The Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) are NOAA real-time operational hourly updating forecast systems run at 13- and 3-km grid spacing, respectively. Both systems use the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) as the model component of the forecast system. During the second installment of the Wind Forecast Improvement Project (WFIP 2), the RAP/HRRR have been targeted for the improvement of low-level wind forecasts in the complex terrain within the Columbia River Basin (CRB), which requires much finer grid spacing to resolve important topographic features in/near the CRB. Therefore, this project provides a unique opportunity to test and develop the RAP/HRRR physics suite within a very high-resolution nest (∆x = 750 m) over the northwestern US. Special effort is made to incorporate scale-adaptive flexibility into the RAP/HRRR physics suite, with emphasis on the representation of subgrid-scale boundary layer and orographic drag processes.

Many wind profiling and scanning instruments have been deployed in the CRB in support the WFIP 2 field project, which spanned 01 October 2015 to 31 March 2017. During the project, several forecast error modes were identified, such as: (1) too-shallow cold pools during the cool season, which can mix-out more frequently than observed and (2) the low wind speed bias in thermal trough-induced gap flows during the warm season. Development has been focused on improving these common forecast failure modes with the criteria of achieving at least neutral impacts in all other operational forecast objectives. This presentation will highlight the testing and development of various model components, showing the improvements over original RAP/HRRR physics. Examples of case studies and retrospective periods will be presented to illustrate the improvements.  Ongoing and future challenges in RAP/HRRR physics development will be touched upon.

Refreshments: 3:15 pm

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, November 30, 2017 - 3:30pm to 4:30pm

William Skamarock
NCAR/MMM 

One of the unsolved questions in atmospheric dynamics concerns the energetics responsible for the horizontal wavenumber k^(-5/3) scaling observed in the mesoscale portion of the atmospheric kinetic energy (KE) spectrum.  Model spectra qualitatively reproduce the observations-based spectrum in both the synoptic-scale k^(-3) and mesoscale k^(-5/3) regions, and given the limitations of the observations, modeling-based studies have become the primary approach for examining the mesoscale dynamics of the spectrum.  We are computing atmospheric spectra for global NWP forecasts using the atmospheric component of the Model for Prediction Across Scales (MPAS) to study these dynamics.  As in past studies, we find a mesoscale region in the model spectrum when resolution is sufficiently fine.  The first part of the present study examines the accuracy of model solutions, where we find that typical model configurations produce solutions that are significantly under-resolved vertically as revealed in convergence test results for KE spectra and examination of inertia gravity wave structure.  The second part of this study examines KE dissipation and its associated dynamics.  The mesoscale region is thought to be characterized as possessing a net downscale energy cascade, and the dynamics in the regions of energy dissipation should play a role in the downscale cascade.   Understanding these dynamics should help test existing theories for the mesoscale KE spectrum.  We will present results illustrating these points,  and we will discuss the implications of these results for current theories for the mesoscale KE spectrum.  We will also discuss the implications for atmospheric modeling applications in weather and climate given that current operational weather and climate model configurations do not resolve well the mesoscale KE, particularly in the upper troposphere and lower stratosphere.

Refreshments: 3:15 pm

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, December 7, 2017 - 3:30pm to 4:30pm

Past MMM Events

Raymond A. Shaw
Atmospheric Sciences Program
Michigan Technological University 

Aerosol particles, such as sea salt, dust and anthropogenic pollution, influence the optical properties of clouds and the tendency of a cloud to form precipitation through droplet collisions. We have investigated cloud droplet growth in a turbulent environment under varying levels of aerosol concentration. The results reveal a surprising role of turbulence in cloud droplet growth that leads to two regimes: a polluted cloud regime in which thermodynamic conditions are rather uniform and cloud droplet sizes are similar, and a clean cloud regime in which thermodynamic conditions are highly variable and cloud droplet sizes are very diverse. The narrowing of droplet size range under polluted conditions introduces a new stabilizing factor by which increased aerosol concentration can suppress precipitation and enhance cloud brightness. 

Cloud droplet growth in a turbulent environment is studied by creating turbulent moist Rayleigh-Benard convection in a laboratory chamber (the Pi Chamber). Cloud formation is achieved by injecting aerosols into the water-supersaturated environment created by the isobaric mixing of saturated air at different temperatures. In steady state, the injection and activation of aerosol particles to form cloud droplets is balanced by cloud droplet growth through vapor condensation and loss by gravitational settling. A range of steady-state cloud droplet number concentrations is achieved by supplying aerosols at different rates. As steady-state droplet number concentration is decreased the mean droplet size increases as expected, but also the width of the size distribution increases. This increase in the width is associated with larger supersaturation fluctuations due to the slow droplet microphysical response (sink of the water vapor) compared to the fast turbulent mixing (source of the water vapor). The boundary between the two regimes can be identified with a cloud Damkoehler number of order unity.

Thursday, 16 November 2017, 3:30 PM
Refreshments:  3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, November 16, 2017 - 3:30pm to 4:30pm

Richard Rotunno
NCAR/MMM 

From the point of view of the shallow-water equations (SWE), the hydraulic jump is a discontinuity in fluid-layer depth and velocity at which kinetic energy is dissipated. To provide an understanding of the origin and internal dynamics of the hydraulic jump, three-dimensional numerical solutions of the Navier-Stokes Equations (NSE) are carried out alongside SWE solutions for nearly identical physical initial-value problems. Analysis of the solutions to the initial-value problem shows that the tendency to form either the lee-side height/velocity discontinuity in the SWE, or the overturning density interface in the NSE, is a feature of inviscid, nonturbulent fluid dynamics. Dissipative turbulent processes associated with the lee-side hydraulic jump are a consequence of the inviscid fluid dynamics that initiate and maintain the locally unstable conditions. Implications for the modeling of atmospheric mountain waves and lee vortices are discussed.

Refreshments:  3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, November 9, 2017 - 3:30pm to 4:30pm

Piotr Smolarkiewicz
European Center for Medium Range Weather Forecasts (ECMWF)
United Kingdom 

The talk highlights the development of the Finite-Volume Module (FVM) of the Integrated Forecasting System (IFS) at ECMWF. FVM represents an alternative dynamical core that enhances the spectral dynamical core of the IFS with new capabilities, such as a compact-stencil finite-volume discretisation, flexible meshes, conservative non-oscillatory PDATA transport, and all-scale nonhydrostatic governing equations. As a default, FVM solves the compressible Euler equations in a geospherical framework, using a centred two-time-level time-stepping scheme with 3D implicit treatment of acoustic, buoyant and rotational modes. A hybrid computational mesh, fully unstructured in the horizontal and structured in the vertical, enables efficient global atmospheric modelling. Theoretical considerations are illustrated with results of benchmark simulations of intermediate complexity, and comparison to the operational spectral dynamical core of the IFS.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, October 26, 2017 - 3:30pm to 4:30pm

Paul Field
UK Met Office
Exeter, United Kingdom

We use convection permitting global aquaplanet simulations to explore the interaction between aerosol and mid-latitude cyclones. Based on model simulations we propose a hypothesis about how midlatitude cyclones will respond to increases in aerosol loading.  In this talk, I will introduce the model results and describe how we tested it with a decade of satellite observations and a more focused period coinciding with the Icelandic volcanic eruption in 2014.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, September 28, 2017 - 3:30pm to 4:30pm

Xiaolei Zou
Earth System Science Interdisciplinary Center (ESSIC)
University of Maryland

Abstract: The Advanced Technology Microwave Sounder (ATMS) onboard Suomi National Polar orbiter Partnership (S-NPP) satellite combines Advanced Microwave Sounding Unit-A (AMSU-A) and Microwave Humidity Sounder (MHS) onboard NOAA and Meteorological Operational Satellite Program of Europe (MetOP) satellites to simultaneously provide collocated radiance measurements of the atmospheric temperature and moisture profiles under almost all weather conditions except for heavy precipitation. The two lowest frequency ATMS window channels 1-2 (23.8GHz and 31.4 GHz) are the same as AMSU-A channels 1-2 and the other two high-frequency ATMS window channels 17-18 (88.2GHz and 165.5GHz) are similar to MHS window channels 1-2. These four ATMS window channels can be used together for identifying both liquid and ice cloudy radiances. This important feature of ATMS proved to be important for improving the forecast skill of severe weathers populated with clouds (e.g., hurricanes) through satellite microwave radiance assimilation (Zou et al., 2013). Assimilation of microwave radiance data in numerical weather prediction (NWP) models has traditionally been carried out with AMSU-A and MHS data in two separate data streams since the launch of NOAA-15 in 1998. Inspired by the ATMS data assimilation success, a new approach was proposed to combine AMSU-A and MHS radiances into one data stream for their assimilation. It was shown that the spatial collocation between AMSU-A and MHS field of views (FOVs) allows for an improved quality control of MHS data, especially over the conditions where the liquid-phase clouds are dominate. It was found that the quantitative precipitation forecast (QPF) skill associated with landfall hurricanes was significantly improved by the one data stream approach, resulting from a closer fit of analyses to AMSU-A and MHS observations is obtained, especially for AMSU-A surface-sensitive channels (Zou et al., 2017). A shortcoming was also found for S-NPP ATMS whose radiance observations displayed a clear across-track striping noise, which was not found in AMSU-A radiances. Three algorithms were subsequently developed for mitigating the ATMS striping noise for the upper-level sounding channels (Qin et al., 2013), for an operational implementation (Ma and Zou, 2015) and for surface sensitive channels (Zou et al., 2017). Impacts of striping noise mitigation on observation error variances were also quantified for assimilation of destriped ATMS radiance observations.

Refreshments:  10:45 AM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Wednesday, August 23, 2017 - 11:00am to 12:00pm

Sisi Chen
Department of Atmospheric and Oceanic Sciences, McGill University
Montreal, Quebec, Canada

Shallow convective clouds are ubiquitous, and warm rain largely contributes to the total annual rainfall, particularly in the tropics. Therefore, understanding the microphysical processes inside these cloud systems becomes important. Classical parcel models often produce narrow droplet size distributions (DSDs) which disagree with observations in cumulus clouds. Since the last century, turbulence have been postulated to explain the effective DSD broadening in early cloud stage.

This work studies the very fundamental process involving droplet condensational and collisional growth to explore the fast warm-rain initiation using the direct numerical simulation (DNS). DNS model can accurately resolve small-scale turbulence and simulates the turbulence impacts on droplets that are tracked in the Lagrangian framework, which is infeasible in other models.

This is the first modeling study that incorporates both droplet condensational process and collisional process into the DNS model and investigates the full droplet growth history in the turbulent environment. 

Model results show that condensational growth by itself produces narrow DSD under small-scale turbulence, which is similar to the parcel model results. Results from the simulations that consider pure collision-coalescence process show that small-scale turbulence significantly increases the collision rate between small droplets and thus accelerates the formation of large droplets. In particular, the enhancement is the strongest between similar-sized droplets, which indicates that turbulence effectively broadens the narrow DSD formed by condensational growth. On the other hand, condensational growth considerably brings tiny droplets to 5-10 microns, dynamically shifting the collision rates of those droplets in turbulence. To study how collisional process and condensational process interact under the effect of turbulence, simulation results that consider both condensational and collisional processes will be compared to pure collision-coalescence case. It is shown that the inclusion of condensation significantly changes the behavior of droplet collisions in the turbulence and thus has strong feedback on the DSD broadening. Detailed results and comparison will be presented in the talk.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, August 17, 2017 - 3:30pm to 4:30pm

Dale Barker
UK Met Office

The Met Office global and regional NWP applications are centered around the use of the Unified Model (UM) to provide short-range forecasts out to 5-7 days of global and local significant weather. This talk will describe some of the major upgrades implemented or planned during the timeframe of the new Cray XC40 supercomputer (2015 - 2020) beginning with a brief description of the basic NWP configurations and a summary or recent major upgrades e.g. variational bias correction, additional satellite data, etc.

In July 2017, the resolution of the global NWP system at the Met Office was increased to ~10km, with an associated increase to 20km for the global (MOGREPS-G) ensemble. A more significant change is the introduction of hourly-cycling four dimensional variational (4DVar) data assimilation for the km-scale UK model. The relative contributions to forecast skill improvements of hourly-cycling, the use of the 4DVar technique, and improved driving global model will be assessed in this talk.

Looking forward, additional major upgrades are planned in the next 1-2 years including weakly coupled ocean-atmosphere data assimilation, extension of the km-scale MOGREPS-UK ensemble to T+5 days (plus resolution increase from 2.2km to 1.5km), replacement of the current ETKF ensemble system with an ‘Ensemble of 4D Ensemble Vars’. Details of these promising scientific developments will be provided. Finally, a brief summary of plans for the post-UM ‘Exascale Era’ beginning in ~2023 will be outlined.

Note special date and time. 

Refreshments: 10:45 AM 

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Tuesday, August 8, 2017 - 11:00am to 12:00pm

Nedjelika Žagar
University of Ljubljana
Ljubljana, Slovenia

Many studies of the forecast error growth focused on the extra-tropical quasi-geostrophic dynamics and often considered the error-free large-scale initial state.  In contrast, the operational global numerical weather prediction and ensemble prediction systems are characterized by uncertainties in the initial state at all scales, especially in the tropics.  In this seminar the evidence will be discussed about the dominant role of the large-scale error growth early in the forecasts in comparison with the errors cascades from the smaller scales.   A new parametric model for the representation of the error growth will be derived.  In contrast to the commonly used models, the new model does not involve computation of the time derivatives of the empirical data. The asymptotic error is not a fitting parameter, but it is computed from the model constants. 

Simulated forecast errors by the operational ensemble prediction system of the European Centre for Medium-Range Weather Forecasts are decomposed into scales and the new model is applied independently to every zonal wavenumber.  A combination of hyperbolic tangent functions in the parametrization of the error growth proves robust to reliably model complex growth dynamics across many scales.  The range of useful prediction skill, estimated as a scale where forecast errors exceeds 60% of their asymptotic values is around 7 days on large scales and 2-3 days at 1000 km scale.  The new model is easily transformed to the widely used model of Dalcher and Kalnay (1987) to discuss the scale-dependent growth as a sum of two terms, the so-called a and b terms.  Their comparison shows that at planetary scales their contributions to the growth in the first 2 days are similar whereas at small scales the b term describes most of a rapid exponential growth of errors towards saturation. 

Refreshments: 3:15pm


First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Calendar Timing: 
Thursday, August 10, 2017 - 3:30pm to 4:30pm

James Done 
NCAR/MMM

As populations increase in hazard-prone regions, the human, cultural and economic costs rise, and will continue to rise in the future. The likely scenario of the weather and climate hazards themselves changing in the future will compound the problem. A transformation of how weather and climate risk is assessed and integrated with risk management practice is needed for society to confront this new era of weather and climate risk. Bringing physics to bear on risk assessment has the potential to transform our understanding of weather and climate risk. Furthermore, physically based risk assessments that are informed by risk management practice are a potentially powerful component of climate resilience. Three recent examples will be presented to illustrate the flow between physically based weather and climate risk assessments and community action.

The first example is the development of a terrain-aware tropical cyclone wind probability assessment at the global scale. In collaboration with a reinsurance broker, an approach to modeling tropical cyclone wind footprints is developed by fitting a parametric wind field model to historical and synthetic cyclone track data, and bringing the winds down to the surface using a 3-dimensional numerical boundary model, accounting for terrain and surface roughness effects. The new wind probability assessments are being used to understand inland wind risk in regions of complex topography, and assess public and private risk management strategies in regions of sparse historical data. The second example explores how the relationship between residential losses and hurricane winds is modified through building codes. Adherence to the Florida building code drives down losses by up to 70%, and the code is cost-effective with a return on investment after 12 years under current climate. The final example explores the role of decadal climate predictions in water resource and flood risk management. The multi-disciplinary UDECIDE (Understanding Decision-Climate Interactions on Decadal Scales) project combines statistical and physical assessments of climate prediction skill with data from interviews with managers to identify intersections at the decadal scale in support of effective management.

Refreshments:  3:15pm

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Note Location)
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, August 3, 2017 - 3:30pm to 4:30pm

Lotte Bierdel
Ludwig Maximilians University
Munich, Germany 

The current literature discussing predictability of atmospheric flow and the nature of the underlying scale interactions considers the problem from two main perspectives. One approach is based on statistical closure models in a homogeneous and isotropic turbulent flow, where the predictability time is determined solely by the background kinetic energy spectrum and not by the underlying dynamical model. An alternative approach is based on results from numerical weather prediction models that suggest that latent heat release associated with deep moist convection is a primary mechanism for small-scale error growth. From this point of view error growth in the atmosphere is an initially localized, highly intermittent phenomenon that expands upscale, leading to a complete loss of predictability on scales below 100 km within a few hours. The error growth process then depends on the underlying dynamics of the respective scale range and the errors in particular have to transition from geostrophically unbalanced to balanced motion while propagating through the mesoscale. In this talk a study will be presented that examines the geostrophic adjustment process as possibly underlying this transition. To that end, an analytical framework for the geostrophic adjustment of an initial pointlike pulse of heat (modeling a convective cloud or an error within the prediction of a cloud) is developed. Spatial and temporal scales of the geostrophic adjustment mechanism are deduced and three characteristics of the solution are shown to be potentially useful for identifying the geostrophic adjustment process in numerical simulations. These three predictions are then tested in the framework of error growth experiments in idealized numerical simulations of a convective cloud field. Three different rotation rates are employed in order to identify the geostrophic adjustment mechanism and allow a quantitative comparison with the predictions of the analytical model. As will be shown, the numerical simulations agree well with the predictions developed from the analytical model. Based on these findings it is suggested that the geostrophic adjustment process governs upscale error growth through the atmospheric mesoscales.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Note Location)
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, July 20, 2017 - 3:30pm to 4:30pm

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