***Special MMM Seminar - Tuesday, November 12, 2019 - 11:00am**

***Please note special day/time and location!**

**Speaker: ****Jon Reisner**

**Affiliation: ****Los Alamos National Laboratory**

Nuclear winter is based upon the premise that nuclear weapons will produce numerous firestorms and large quantities of soot that can be lofted into the stratosphere causing significant surface cooling. Hence one of the key aspects to addressing the possibility of crop defeating global cooling is understanding the source. Unfortunately, high uncertainty is associated with the ability of buildings, especially those made of cement, to burn sufficiently to induce a firestorm. At DOE and DOD labs, a variety of efforts are underway to address this uncertainty and make scientific based judgements regarding soot production. For example, at Sandia a solar furnace and tower have been recently used to examine how various materials ignite and possibly combust under thermal fluences comparable to those found after a detonation. Likewise, experiments are being planned at the Large Blast Thermal Simulator (LBTS) at White Sands to begin examining shock-fire interactions---another crucial piece in this complex puzzle. Given this new experimental data, simulations are being run using combustion codes at both Sandia and Los Alamos to begin addressing how small scales fires initiated by a thermal fluence could possibly upscale into a firestorm. Next, results from these detailed source calculations can be used in various climate models, e.g., CESM or GEOS-5, to examine their impact on climate. And finally, given a scientifically defensible source it is expected that global cooling impacts (see Reisner et al., JGR-Atmos., 2018 for preliminary study) will be significantly less than suggested by nuclear winter advocates.

**Refreshments: 10:45 AM**

Building:

Room Number:

*FL2-1001 Small Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 - https://www.ucar.edu/live?room=fl21001

Announcement Timing:

Tuesday, November 5, 2019 to Tuesday, November 12, 2019

Calendar Timing:

Tuesday, November 12, 2019 - 11:00am to 12:00pm

Nancy Sue

Kerner

8946

***MMM Seminar - Thursday, November 7, 2019 - 3:30pm **

***Please note special location - FL2-1001/****Small Auditorium**

**Speaker: ****Alexandra N. Ramos-Valle**

**Affiliation: ****Rutgers University**

Atmospheric forcing is the primary driver of storm surge, and as such the magnitude of the storm surge impacts depends on various tropical cyclone (TC) characteristics including the size, intensity and impact angle. Although the factors contributing to storm surge are known, uncertainties remain regarding the level of sensitivity to these TC characteristics. From a modeling standpoint, the wind models used as atmospheric forcing to the hydrodynamic models influence the ability of these to accurately forecast storm surge. Improvement of storm surge modeling systems relies on the understanding and advancement of this model coupling. Moreover, understanding the relation between storm surge and TC physical parameters is a key step in increasing forecasting accuracy. The work presented thus seeks to determine the impact of atmospheric forcing in storm surge modeling, and to assess the sensitivity of storm surge to TC physical parameters, specifically focusing on the impact of cyclone landfall angle. To address these two goals, we performed simulations of TCs and their associated storm surge with a coupled WRF-ADCIRC model. First, we explored the use of a parametric vortex wind model versus a full-physics atmospheric model as meteorological forcing. Results highlighted the advantages of using full-physics atmospheric models for this purpose. Secondly, we performed simulations of synthetic TCs to determine the sensitivity of storm surge to cyclone landfall angle. We employed the use of the Hybrid WRF Cyclone Model, a newly developed modeling capability derived from WRF. Results highlighted the sensitivity of storm surge off-shore extent and inundation to the TC impact angle. Moreover, results also point to the importance of coastal and geographic features.

**Refreshments: 3:15 PM**

Building:

Room Number:

*FL2-1001 Small Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 - https://www.ucar.edu/live?room=fl21001

Announcement Timing:

Friday, November 1, 2019 to Thursday, November 7, 2019

Calendar Timing:

Thursday, November 7, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

**Special MMM/CGD Joint Seminar - Thursday, October 31, 2019 - 3:30pm**

**Speaker: ****Falko Judt**

**Affiliation: ****Mesoscale and Microscale Meteorology Laboratory, NCAR**

Since the inception of numerical weather and climate prediction, our models have struggled to accurately simulate the tropical atmosphere. In this talk, I will demonstrate that global storm resolving models (global models with 5 km grid spacing or less) eliminate some issues that previous models had, mostly by foregoing the need to parametrize deep convection. In particular, I will show how global storm-resolving models improve the representation of tropical cyclones and equatorial waves. This presentation will also explain why, in theory, the weather has longer predictability in the tropics than in the middle latitudes. Notwithstanding their overall positive impact, global storm-resolving models still suffer from substantial biases. A model intercomparison reveals that all participating models over-predict tropical cyclone intensity, whereas each model struggles in its own way to predict the number of cyclones in a given ocean basin.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Wednesday, October 23, 2019 to Thursday, October 31, 2019

Calendar Timing:

Thursday, October 31, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

**MMM Seminar - Thursday, October 24, 2019 - 3:30pm**

**Speaker: ****Tom Hamill**

**Affiliation: ****NOAA Earth System Research Lab, Physical Sciences Division, Boulder, Colorado**

Ensemble methodologies are now commonly used in the prediction of weather and climate forecast probabilities. To produce sets of forecasts with realistic estimates of forecast uncertainty, ensemble weather predictions require a set of initial conditions that are statistically consistent with the analysis uncertainty, and they require a treatment of the forecast uncertainty due to model imperfections. In this seminar, a time series of analyses and sets of initial conditions are considered from the European Centre for Medium-Range Weather Forecasts (ECMWF). The talk focuses on understanding the source of deficiencies in the initialization of the ensemble. Leveraging the development of an independent and highly accurate reference analysis procedure for estimating the surface temperatures over the US, it is possible to evaluate the statistical character of the ECMWF's surface temperature initial conditions. In particular, it is suggested that the differences of the ECMWF mean analyses from the reference can be decomposed into a systematic component that varies slowly over time plus a residual component. This systematic component is large enough to suggest that there are significant remaining model errors in the ECMWF system that degrade their surface initialization. These would be fixed through improving the underlying forecast model, a time-intensive procedure. After accounting for covariances between systematic error and the residual error, we find that the estimated random component of the error is somewhat larger than the typical size of ensemble surface-temperature perturbation, indicating that ECMWF surface-temperature perturbations should be enlarged to provide higher-quality ensemble forecasts.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Monday, October 21, 2019 to Thursday, October 24, 2019

Calendar Timing:

Thursday, October 24, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

**MMM Seminar - Thursday, October 17, 2019 - 3:30pm**

**Speaker: ****Piotr Smolarkiewicz**

**Affiliation: ****Mesoscale and Microscale Meteorology Laboratory, NCAR**

This talk outlines a novel numerical approach for accurate and computationally efficient integrations of PDEs governing all-scale atmospheric dynamics. Such PDEs are not easy to handle, due to a huge disparity of spatial and temporal scales as well as a wide range of propagation speeds of natural phenomena captured by the equations. The novel Finite-Volume Module of the Integrated Forecasting System (IFS) at ECMWF (IFS-FVM) solves perturbation forms of the fully compressible Euler/Navier-Stokes equations under gravity and rotation using non-oscillatory forward-in-time semi-implicit time stepping and finite-volume spatial discretisation. The IFS-FVM complements the established semi-implicit semi-Lagrangian pseudo-spectral IFS (IFS-ST) with the all-scale deep-atmosphere formulation cast in a generalised height-based vertical coordinate, fully conservative and monotone advection, flexible horizontal meshing and a predominantly local communication footprint. Yet, both dynamical cores can share the same quasi-uniform horizontal grid with co-located arrangement of variables, geospherical longitude-latitude coordinates and physics parametrisations, thus facilitating their synergetic relation. The focus of the talk is on the mathematical/numerical formulation of the IFS-FVM with the emphasis on the design of semi-implicit integrators and the associated elliptic Helmholtz problem. Relevant benchmark results and comparisons with corresponding IFS-ST results attest that IFS-FVM offers highly competitive solution quality and computational performance.

**Refreshments: 3:15 PM**

**This seminar will be webcast live at: ****https://www.ucar.edu/live?room=fl21022**** **

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Announcement Timing:

Wednesday, October 9, 2019 to Thursday, October 17, 2019

Calendar Timing:

Thursday, October 17, 2019 - 3:30pm

Nancy

Kerner

8946

**MMM Seminar - Thursday, October 3, 2019 - 3:30pm**

**Speaker: Susan Joslyn**

**Affiliation: ****Department of Psychology, ****University of Washington**

How do everyday users understand weather forecast information? What is the best way to provide them with information that is relevant to critical decisions but not confusing? This talk will describe a psychological research program that investigates each of these questions using a cognitive-experimental approach. We show, in a series of experimental studies that including numeric uncertainty estimates (30% chance) in weather forecasts leads to better decisions and increases trust in the forecast when compared to deterministic forecasts. Surprisingly comprehending probabilistic expressions does not depend on the user's level of education. However, understanding depends critically on how uncertainty is expressed. Communication formats that take into account users' decision goals are much better understood than those that ignore the user's perspective. In addition some typical misunderstandings will be discussed, particularly those that occur when visualizations are used. Finally we will describe the evidence suggesting that forecast consistency may not be as important as was once thought. In sum, this line of research suggests that people can attain a “working understanding” of fairly complex and updating information as long as it is communicated in a way that is compatible with how people think about the issues.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Monday, September 23, 2019 to Thursday, October 3, 2019

Calendar Timing:

Thursday, October 3, 2019 - 3:30pm to 4:30pm

Nancy Sue

Kerner

8946

**MMM Seminar - Thursday, October 10, 2019 - 3:30pm**

**Speaker: Wojciech W. Grabowski**

**Affiliation: Mesoscale and Microscale Meteorology Laboratory, NCAR**

Representation of cloud microphysics is a key aspect of simulating clouds. From the early days of cloud modeling, numerical models have relied on an Eulerian approach for all cloud and thermodynamic and microphysics variables. Over time the sophistication of microphysics schemes has steadily increased, from simple single-moment bulk warm-rain schemes, through double- and triple-moment bulk warm-rain and ice schemes, to complex bin (spectral) schemes that predict the evolution of cloud and precipitation particle size distributions. As computational resources grow, there is a clear trend toward wider use of bin schemes, including their use as benchmarks to develop and test simplified bulk schemes. We argue that continuing on this path brings fundamental challenges due to the complexity of processes involved (especially for ice), the multiscale nature of atmospheric flows that Eulerian approaches are not able to cope with, conceptual issues with the Smoluchowski equation that is solved by bin schemes to predict evolution of the particle size distributions, and numerical problems when applying bin schemes in multidimensional cloud simulations. The Lagrangian particle-based probabilistic approach is a practical alternative in which the myriad of cloud and precipitation particles present in a natural cloud is represented by a judiciously selected ensemble of point particles called super-droplets or super-particles. Advantages of the Lagrangian particle-based approach when compared to the Eulerian bin methodology will be explained and illustrated with computational examples. Prospects of applying the method to more comprehensive simulations involving clouds, for instance targeting deep convection or frontal cloud systems, will be discussed.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Tuesday, September 24, 2019 to Thursday, October 10, 2019

Calendar Timing:

Thursday, October 10, 2019 - 3:30pm to 4:30pm

Nancy Sue

Kerner

8946

**RAL/MMM Joint Seminar - Distinguished Speaker Series - Thursday, August 29, 2019 - 3:30pm**

**Speaker: Professor Kerry Emanuel**

**Affiliation: Massachusetts Institute of Technology, Cambridge, Massachusetts**

I will present a linear model of the equatorial waveguide based on the assumptions of hydrostatic balance and a temperature profile that remains moist adiabatic at all times. As has been shown before, these assumptions reduce the primitive equations to the mathematical form of shallow water equations of the kind first explored by Matsuno. Some of the classical Matsuno modes are destabilized in this model by cloud-radiation and/or wind-surface-heat-flux feedbacks (WISHE); no instability arises purely from the interaction of convection with circulation.

Based on this and previous published work, I will argue that convectively coupled Kelvin waves are amplified WISHE while eastward propagating disturbances of nearly constant, low frequency are driven mostly by cloud-radiation feedback but driven eastward by WISHE. In addition, mixed-Rossby-gravity waves and equatorial Rossby waves can be destabilized and propagated by WISHE and/or cloud-radiation feedback. These feedbacks can be strong enough to drive the modes substantially far away from the Matsuno dispersion curves, calling for alternative descriptions of their physics.

**Refreshments: 3:15 PM**

Building:

Room Number:

Large Auditorium, Room 1022

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Monday, August 26, 2019 to Thursday, August 29, 2019

Calendar Timing:

Thursday, August 29, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

**MMM Seminar - Thursday, August 22, 2019 - 3:30pm**

**Speaker: Lian-Ping Wang**

**Affiliation: University of Delaware and Southern University of Science and Technology, China**

Gas kinetic schemes (GKS’s) are a class of CFD methods based on the kinetic theory and have gained much success in flow simulations ranging from continuum compressible flows to rarefied non-equilibrium flows. As a mesoscopic CFD method, GKS’s can handle rich dynamics beyond the classical CFD methods based on the Euler and Navier-Stokes-Fourier equations. This lecture gives an introduction of the GKS methods, including the original GKS for continuum flows and its recent variants for multiscale flows. I will discuss how the details of GKS’s can be inversely designed to address different complex flow problems, as well as open research problems. Several examples of using gas kinetic schemes to solve complex flows will be provided, including an incompressible particle-laden flow, an immiscible two-phase flow and a compressible thermal flow. Indeed, this class of schemes have a lot to offer and could serve as a unified framework to simulate many different complex flows.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Wednesday, August 21, 2019 to Thursday, August 22, 2019

Calendar Timing:

Thursday, August 22, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

**MMM Seminar - Thursday, August 15, 2019 - 3:30pm**

**Speaker: ****McKenna Stanford**

**Affiliation: ****University of Utah**

Models run within the convective “grey” zone (i.e. 1-3 km horizontal grid spacing) are unable to resolve the spectrum of updraft sizes produced by large eddy simulations (LESs). This deficiency results in updrafts in km-scale models being too wide, and since lateral mixing is inversely proportional to updraft width, leads to reduced dilution. Addressing this issue is becoming increasingly important as global models approach convection-permitting resolution but global LES remains intractable. Since shortcomings associated with the model’s effective resolution are inevitable, more sophisticated parameterizations are necessary to overcome the mixing problem. In this work, we allow for enhanced but variable mixing in time and space by applying a stochastic framework within a Smagorinsky-type first order turbulence closure. Specifically, a stochastic multiplicative factor is applied to the closure’s horizontal eddy diffusion coefficient, which controls lateral mixing. Conceptually, this framework allows some updrafts to mix vigorously with mid-level environmental air while also allowing other updrafts to remain relatively undilute.

The stochastic scheme is used to simulate a quasi-idealized squall line using a sounding from the pre-convective environment of an observed mesoscale convective system (MCS) that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E). Comparisons are made between stochastic simulations at 1-3 km grid spacing, baseline simulations using the standard Smagorinsky-type (non-stochastic) closure at the same grid spacing, and a LES run at 125 m grid spacing. These comparisons show that the stochastic scheme alters vertical profiles of mass flux and vertical velocity as well as other key squall line features such as cold pool strength and condensate mass spatial structure. Moreover, the stochastic scheme alters these features and structures in a manner not capable by simply diagnostically applying constant multiplicative factors to the diffusion coefficient. Finally, scale adaptability is discussed along with potential expansion of the scheme to non-idealized frameworks.

**Refreshments: 3:15 PM**

Building:

Room Number:

FL2-1022 - Large Auditorium

Type of event:

Will this event be webcast to the public by NCAR|UCAR?:

Yes - FL2-1001 with chat - http://www.fin.ucar.edu/it/mms/v2/fl-1001-chat.html

Announcement Timing:

Friday, August 9, 2019 to Thursday, August 15, 2019

Calendar Timing:

Thursday, August 15, 2019 - 3:30pm to 4:30pm

Nancy

Kerner

8946

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