Events (Upcoming & Past)

Past MMM Events

*MMM Seminar - Wednesday, January 8, 2020 - 3:30pm

*Please note special day - Wednesday

Speaker: Zhiquan (Jake) Liu

Affiliation: National Center for Atmospheric Research (NCAR)

Different from numerical weather prediction that is mainly an initial condition problem, the accuracy of air quality forecast relies on not only the initial state of a chemical model, but also the surface emissions of chemical constituents. The latter is to a large extent related to the human activities such as those from industrial, residential, and agricultural sectors and is subject to large uncertainties. In this talk, I will demonstrate both the usefulness and the limitations of data assimilation for chemical initial condition analysis and source emission estimation when using different data assimilation techniques and various combinations of different observations from satellite (e.g., aerosol optical depth) and ground observing networks (e.g., surface particulate matters and chemical gases). While it is demonstrated that data assimilation is overall very useful for improving the accuracy of chemical weather prediction, its limitations will also be shown, e.g., short-lasting impact and the lack of sufficient observations of chemical speciation to constrain the large number of model prognostic variables and emission parameters. A recent study on using data assimilation as a tool to separate the effects of weather condition change and emission control in recent trend of winter time air quality in China will also be presented before closing with future perspectives.

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?: 
Announcement Timing: 
Friday, December 20, 2019 to Wednesday, January 8, 2020
Calendar Timing: 
Wednesday, January 8, 2020 - 3:30pm to 4:30pm
Nancy
Kerner
8946

*Special RAL/MMM Joint Seminar - Thursday, December 5, 2019 - 3:00pm

*Please note special time - 3:00pm

Speaker: Dr. David L. Darmofal

Affiliation: Department of Aeronautics & Astronautics, Massachusetts Institute of Technology

For phenomenon that exhibit a wide range of scales, adaptive methods can enable efficient yet accurate discretizations.  In this talk, we consider the use of space-time adaptive methods to solve time-dependent, multi-scale phenomenon in which the space-time domain is discretized using simplices (i.e. pentatopes for 3D+time) that are not required to have face aligned with the temporal direction.  The adaptive method utilizes an goal-oriented approach in which an adjoint solution and dual-weighted residual is employed to estimate the local contribution to the discretization error of a desired output.  The dependence of the error estimate on the mesh is then synthesized into a model using the Metric Optimization through Error Sampling and Synthesis (MOESS) algorithm, and the resulting error model is then optimized to produce adapted meshes with minimal error at a fixed computational cost. We demonstrate this approach for higher-order finite element discretizations applied to convection-dominated flows and porous media.  Also, similar to parallel-in-time strategies, we show that parallel solution of space-time adapted meshes are more scalable than time-marching approaches.  We conclude with a discussion of remaining challenges and opportunities for space-time adaptive methods.

Refreshments: 2:45pm

Building:
Room Number: 
FL2-1022 - Large Auditorium
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Tuesday, December 3, 2019 to Thursday, December 5, 2019
Calendar Timing: 
Thursday, December 5, 2019 - 3:00pm to 4:00pm
Nancy Sue
Kerner
8946

*MMM Seminar - Distinguished Speaker Series  - Tuesday, 3 December 2019 - 3:30pm *Please note special day - TUESDAY

Speaker: Chun-Chieh Wu

Affiliation: Department of Atmospheric Sciences, National Taiwan University

     This study examines the roles of surface heat fluxes, particularly in relation to the wind-induced surface heat exchange (WISHE) mechanism, in the (i) secondary eyewall formation (SEF) and (ii) rapid intensification (RI) of tropical cyclones.

     (i) To examine the sensitivity of SEF to the WISHE mechanism, the surface wind used for the calculation of surface heat fluxes is capped at several designated values and at different radial intervals.  When the heat fluxes are moderately suppressed around and outside the SEF region observed in the control experiment, sensitivity experiments show that the formation of the outer eyewall is delayed, and the intensity of both eyewalls is weaker.  When the heat fluxes are strongly suppressed in the same region, SEF does not occur.  In contrast, suppressing the surface heat fluxes in the storm’s inner-core region has limited effect on the evolution of the outer eyewall.  This study provides important physical insight into SEF, indicating that the WISHE mechanism plays a crucial role in SEF.

     (ii) Sensitivity experiments with capped surface fluxes and reduced WISHE exhibit delayed RI and weaker peak intensity, while WISHE could affect the evolutions of TC both before and after the onset of RI.  Before RI, more WISHE leads to faster increase of  in the lower levels, resulting in the eruption and the axisymmetrization of the convection (especially in the lower levels).  In addition, TCs in experiments with more WISHE reach a certain strength earlier, before the onset of RI.  During the RI period, more surface heat fluxes cause more efficient intensification in a TC, leading to a stronger peak intensity, more significant and deeper warm core in TC center, and the axisymmetrization of convection in the higher levels.  In both stages, different levels of WISHE alter the thermodynamic environment and convective-scale processes.  With WISHE, a consequent development in the convective activity is identified, resulting in a stronger secondary circulation and increased diabatic heating.  Within the inner-core region, deeper inflow increases the transport of angular momentum from the outer radii, leading to faster spin-up of the tangential circulation.  In all, the important role of the WISHE feedback in RI, both during the pre-RI stage and during the RI period, is highlighted.

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?: 
Announcement Timing: 
Monday, December 2, 2019 to Tuesday, December 3, 2019
Calendar Timing: 
Tuesday, December 3, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
8946

*Special RAL/MMM Joint Seminar - Wednesday, November 20, 2019 - 3:30pm

*Please note special day - Wednesday

Speaker: Prasanth Prabhakaran

Affiliation: Michigan Technological University

The formation of ice in mixed-phase clouds greatly impacts Earth’s hydrologic cycle. The intensity, distribution, and frequency of precipitation as well as radiative properties of clouds in the mid-latitudes are strongly influenced by the number concentration of ice particles. A long-standing riddle in cold clouds is the frequent observation of measured ice particle concentrations several orders of magnitude higher than measured ice-nucleating particle concentrations. Here, we report laboratory observations of copious cloud droplets and ice crystals formed in the wake of a warm, falling water drop. Aerosols were activated in the transient regions of very high supersaturation due to evaporative mixing in the wake. We extend these results to typical mixed-phase atmospheric conditions, and our calculations show that the induced evaporative supersaturation may significantly enhance the activated ice nuclei concentration in the particle’s wake. 

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?: 
Announcement Timing: 
Monday, November 11, 2019 to Wednesday, November 20, 2019
Calendar Timing: 
Wednesday, November 20, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
8946

*Special MMM/GTP Joint Seminar - Thursday, November 14, 2019 - 3:30pm

*Please note special location - FL2/1001 Small Auditorium

Speaker: Shaun Lovejoy

Affiliation: McGill University, MontréalQuébec

     A hundred years ago, Lewis Fry Richardson made the first numerical weather forecast, founding the field of numerical weather prediction (NWP).  Based on deterministic continuum mechanics, today it is not only ubiquitous in daily weather forecasts, but has been extended to seasonal predictions through to multidecadal climate projections. 

    But Richardson also pioneered the development of high level turbulent laws.  In 1926 he proposed the “Richardson 4/3 law” of turbulent diffusion, a law that wasn’t vindicated until 2013.   Whereas NWP attempts to account for every whirl, cloud, eddy, structure, the 4/3 law exploits the idea of scaling to statistically account for the collective outcome of billions upon billions of structures jointly acting from millimetres up to the size of the planet. 

    The idea that high-level statistical laws could explain the actions of myriads of vortices, cells and structures was shared by successive generations of turbulence scientists.  Unfortunately, they faced monumental mathematical difficulties largely connected to turbulent intermittency: the fact that most of the activity (e.g. energy flux) is inside tiny, violently active regions, themselves buried in a hierarchy of structures within structures.  The application of turbulence theory to the atmosphere, encounters an additional obstacle: stratification that depends on scale. 

    The 1980’s marked a turning point when Richardson’s deterministic and statistical strands parted company, the unity of the atmospheric sciences was broken.  On the one hand, computers revolutionized NWP, on the other hand, the nonlinear revolution promised to tame chaos itself, including turbulent chaos with its fractal structures within structures. 

    In this talk, I summarize four decades of work attempting to understand atmospheric variability that occurs over an astonishing range of scales: from millimetres to the size of the planet, from milliseconds to billions of years.   The variability is so large that standard ways of dealing with it are utterly inadequate: in 2015, it was found that classical approaches had underestimated the variability by the astronomical factor of a quadrillion.  The new understanding allows us to finally reunite Richardson’s strands. 

    For example, I show that the deterministic weather models respect the stochastic scaling laws very well.  I explain “macroweather” and how it sits in between the weather and climate, finally settling the question: “What is Climate”?  I answer the question “how big is a cloud?” and show that Mars is our statistical twin and why this shouldn’t surprise us.  I explain how the multifractal butterfly effect gives rise to events that are so extreme that they have been called “black swans”. 

    By using data from the real world – not model – climate, and with the help of the Fractional Energy Balance Equation (FEBE), I explain how the emergent scaling laws can make accurate monthly to decadal (macroweather) forecasts by exploiting an unsuspected but huge memory in the atmosphere-ocean system itself.  I show how the FEBE can help to significantly reduce the large uncertainties in our current climate projections to 2050 and 2100.

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?: 
Announcement Timing: 
Friday, November 8, 2019 to Thursday, November 14, 2019
Calendar Timing: 
Thursday, November 14, 2019 - 3:30pm to 4:30pm
Nancy Sue
Kerner
8946

*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?: 
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?: 
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?: 
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?: 
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

Pages