Events (Upcoming & Past)

Past MMM Events

MMM Seminar - Thursday, August 8, 2019 - 3:30pm

Speaker: Joshua J. Alland

Affiliation: Advanced Study Program, NCAR

To better understand how midlevel moisture and vertical wind shear (VWS) synergistically modulate tropical cyclone (TC) development via ventilation, a three-dimensional modeling framework is utilized to conduct a suite of experiments. Each experiment has a different combination of initial midlevel moisture and VWS environments. A strong, positive, linear relationship exists between the low-level vertical mass flux in the inner core and TC intensity. The linear increase in vertical mass flux with intensity is not due to an increased strength of upward motions, but instead, is due to an increased area of strong upward motions (w>0.5 m s-1). This relationship suggests that physical processes influencing the vertical mass flux, such as downdraft and radial ventilation, directly influence the intensity of a TC.

The three-dimensional structure of downdraft ventilation has different orientations and strengths, which are controlled by the vertical tilt of the vortex. The modulating effect of downdraft ventilation on TC development is the transport of low-equivalent potential temperature air left-of-shear and into the upshear semicircle from downdraft ventilation regions, which aids in reducing the area of strong upward motions, reducing the vertical mass flux in the inner core, and stunting TC development.

The three-dimensional structure of radial ventilation shows two pathways: the first pathway is associated with rainband activity at low- and mid-levels, and is co-located with downdraft ventilation; while the second pathway at mid- and upper-levels is associated with the vertical tilt of the vortex and, in stronger-sheared environments, storm-relative flow induced by VWS. The modulating effect of radial ventilation on TC development is the inward transport of low-equivalent potential temperature air left-of-shear and in the upshear semicircle at low- and mid-levels, and low-RH air upshear and right-of-shear at mid- and upper-levels, which aids in reducing the area of strong upward motions, reducing the vertical mass flux in the inner core, and stunting TC development.

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: 
Thursday, August 1, 2019 to Thursday, August 8, 2019
Calendar Timing: 
Thursday, August 8, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
4978946

MMM Seminar - Thursday, July 25, 2019 - 3:30pm

Speaker: Hing Ong

Affiliation: University at Albany, State University of New York

The nontraditional Coriolis terms (NCTs) are omitted in most of the current global atmospheric models. However, NCTs are significant in tropical large-scale dynamics in the following four aspects. (1) NCTs coupled with diabatic forcing yield considerable Ertel potential vorticity (EPV) flux, using reanalysis data. At the zonal annual mean heating maximum in the tropics, NCT-diabatic and mean-advective EPV flux can yield about 2 m s–1 month–1 of westward and 5 m s–1 month–1 of eastward acceleration; the former is considerable using the latter as a reference. (2) Omitting NCTs causes considerable westerly bias in the response to prescribed diabatic forcing mimicking the intertropical convergence zone (ITCZ), using linearized forced-dissipative models. The westerly bias lies in the heating region. In terms of the ratio of the maximum westerly bias to the maximum westerly wind, a normalized zonal wind bias increases with a narrower ITCZ or an ITCZ closer to the equator; for example, the normal wind bias is 0.120 ± 0.007 given the width of 1000 km and the location of 600 km. (3) omitting the NCT in the hypsometric equation biases geopotential height estimation using rawinsonde data. It causes geopotential height error of ~ 1 m, which is considerable with respect to geopotential height variability of ~ 10 m associated with the Madden–Julian oscillation (MJO) or convectively coupled equatorial waves (CCEWs). (4) NCTs transmit meridional vorticity disturbances eastward given the vertically decreasing density, i.e., the compressional beta-effect, using linearized unforced models. With a statically neutral profile and initial large-scale disturbances given a half vertical wavelength spanning the troposphere on Earth, compressional Rossby waves are expected to propagate eastward at a phase speed of 0.24 m s–1. Aspect (1), (2), and (3) encourage restoring NCTs into global atmospheric models for more-accurate simulations of MJO, CCEWs, and ITCZ-forced flow. Aspect (4) can serve as a benchmark for development of deep atmospheric dynamical cores for Earth system models.

 

Building:
Room Number: 
Large Auditorium, Room 1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Monday, July 22, 2019 to Thursday, July 25, 2019
Calendar Timing: 
Thursday, July 25, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
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*MMM Seminar - Thursday, July 18, 2019 - 3:30pm

*PLEASE NOTE SPECIAL LOCATION: FL2-1001 Small Auditorium

Speaker:  Dale Barker

Affiliation: United Kingdom Meteorological Office

Global NWP capabilities at the Met Office are currently based on a 10/20km deterministic/ensemble configuration based on the Unified Model (UM), providing forecasts out to 7 days. Deterministic initial conditions are provided by a ‘hybrid 4DVar’ technique, with ensemble initial perturbations updated via an Ensemble Transform Kalman Fillter (ETKF). A major project in recent years has been to replace the ETKF with an ‘ensemble of 4DEnVar data assimilations’ (En4DEnVar), to be implemented together with a major upgrade to global model physics (GA7) in winter 2019/20. Latest results indicate a very significant (4-5%) improvement in ensemble (CRPS) performance. A review of this, and other recent upgrades, will be presented. 

High-resolution (km-scale) UK NWP utilizes hourly-cycling 4DVar feeding 1.5/2.2km deterministic/ensemble forecasts out to 5 days. Data assimilation research is currently focussed on the extension to ‘hybrid’ 4DVar and the direct assimilation of radar reflectivity in 4DVar. Model physics activities are focussed on the development of a single regional atmosphere (RA) configuration suitable for both mid-latitude and tropical application. An overview of an expanding range of research applications beyond the UK (e.g. US HWT ensemble, tropical SE Asia) will be given.

Weather Science is completely overhauling its NWP post-processing capabilities, creating a new ensemble-based system that will provide consistent gridded and site-specific calibrated, blended products for the web, app, etc. In recent months, the ‘IMPROVER’ team have explored the use of machine learning techniques to further improve the quality of post-processed weather forecast. Promising early results will be presented.

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: 
Tuesday, July 9, 2019 to Thursday, July 18, 2019
Calendar Timing: 
Thursday, July 18, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
8946

MMM Seminar - Distinguished Speaker Series  - Thursday, July 11, 2019 - 3:30pm

Speaker: Christoph Schär

Affiliation: ETH Zurich, Switzerland

Currently major efforts are underway towards refining the horizontal grid spacings of climate models to about 1 km, either by increasing the resolution of current GCMs, or by extending the computational domain of high-resolution RCMs. There is well-founded hope that this increase in resolution represents a quantum jump, as it enables replacing the parameterizations of moist convection and gravity-wave drag by explicit treatments. It is expected that this advance will improve the simulation of the water cycle and extreme events, and reduce uncertainties in climate projections. However, the development of such modeling strategies requires a concerted effort.

In exploring high-resolution climate models, we utilize an RCM that allows decade-long continental-scale simulations at 2 km resolution. The model employed is a version of the COSMO model that runs entirely on graphics processing units (GPUs). It is demonstrated that horizontal resolutions around 1 km enable the credible simulation of many mesoscale phenomena. Although cloud structures are not yet fully resolved, analyses suggest that there is convergence at grid resolutions around 2 km in a bulk sense.

On a technical level, it is argued that the output avalanche of high-resolution simulations will make it impractical or impossible to store the data. Rather, repeating the simulation and conducting online analyses may become more efficient. A prototype system of this type will be presented. An assessment will be provided of the potential of these novel approaches.

The presentation is largely based on a paper that is currently in review: Schär, C., O. Fuhrer, A. Arteaga, N. Ban, C. Charpilloz, S. Di Girolamo, L. Hentgen, T. Hoefler, X. Lapillonne, D. Leutwyler, K. Osterried, D. Panosetti, S. Ruedisuehli, L. Schlemmer, T. Schulthess, M. Sprenger, S. Ubbiali, H. Wernli, 2019: Kilometer-scale climate models: Prospects and challenges. Bull. American Meteorol. Soc., in review.

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?: 
Announcement Timing: 
Monday, July 8, 2019 to Thursday, July 11, 2019
Calendar Timing: 
Thursday, July 11, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
8946

*Special MMM/RAL Joint Seminar - Monday, July 15, 2019 - 11:00am

*PLEASE NOTE SPECIAL DAY/TIME & LOCATION

Speaker: Jon Petch

Affiliation: United Kingdom Meteorological Office

I will present an overview of current and planned efforts to evaluate and develop the kilometre gird-scale regional modelling system in the Met Office. This will include current and longer term research and developments as well as specific results from recent evaluation activities.  I will also highlight the importance of science partnerships in the Met Office in underpinning this activity.

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: 
Monday, July 1, 2019 to Monday, July 15, 2019
Calendar Timing: 
Monday, July 15, 2019 - 11:00am to 12:00pm
Nancy
Kerner
8946

Special MMM/RAL Joint Seminar - Thursday, June 27, 2019 - 3:30pm

Speaker: Bert Holtslag

Affiliation: Wageningen University, the Netherlands

Urbanization affects human thermal comfort and health, especially for vulnerable groups such as the elderly and people with established health issues. To mitigate heat stress and accompanying excess mortality there is an urgent need of urban weather observations as well as updated tools for fine scale weather forecasting on short to medium-range time scales. In this presentation first an overview will be given of weather observations made within Dutch cities of variable size. Subsequently, experiences with the setup and use of a high-resolution forecasting system for urban areas will be discussed. The forecasting system is based on the Weather Research & Forecasting (WRF) model, which is used to make forecasts for the city of Amsterdam on a very high spatial resolution of 100 meter and which is driven by extensive and very detailed land surface information. The forecasting system has been used to make 48-hourly daily forecasts for the urban and surrounding areas for the summer period of 2015. The forecasts are validated with observations that were taken at 25 automated weather stations at different locations within the city of Amsterdam. Validation is done for parameters that are important for the well-being of citizens in cities such as the temperature, the evening temperature, the humidity and Wet Bulb Globe Temperatures (WGBT). The potential of future use and improvements of the forecasting system will be discussed.

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?: 
Announcement Timing: 
Wednesday, June 12, 2019 to Thursday, June 27, 2019
Calendar Timing: 
Thursday, June 27, 2019 - 3:30pm to 4:30pm
Nancy
Kerner
8946

*Special MMM/CGD Joint Seminar *Please note Special Day and Time

Title: Mesoscale Eddy Momentum Flux in a 7km Mesh Global Atmosphere Model

Presenter: Brian Mapes, University of Miami

Abstract:  A two-year global nonhydrostatic atmosphere simulation on a 7km mesh (G5NR from NASA’s GEOS-5 model) is queried for one of its most unique strengths: What is the vertical momentum flux (u’w’ and v’w') by explicit air motions in the mesoscale (7-444 km) scale range? After motivating this classic question, especially in light of the hypothesis that organized convection can act as an upscale energy transfer (via upgradient flux, a “negative viscosity”), we address it comprehensively with the data. A global climatology indicates that these mesoscale motions overall act as positive viscosity (damping the shear kinetic energy SKE), except perhaps for some grid points with steep topography. However, cases of positive SKE tendency are also seen. We drill down into full-resolution data for selected situations to expose the nature of the calculation and the phenomena involved. Cyclones in shear are especially prodigious in producing convection-momentum interactions, of both signs, through preferential sampling of non-average low-level momentum. 

*Special Day and Time: Friday, August 17, 2018, 11:30am Refreshments 11:15am FL2-1022 Large Auditorium, Live webcast http://ucarconnect.ucar.edu/live

Thursday, August 9, 2018 to Friday, August 17, 2018

Building:
Room Number: 
Main Auditorium, Room 1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Thursday, August 9, 2018 to Friday, August 17, 2018
Calendar Timing: 
Friday, August 17, 2018 - 11:30am to 12:30pm

Speaker: Jordi Vilà-Guerau de Arellano

Affiliation:  Wageningen University, The Netherlands

In regional and global models uncertainties arise due to our incomplete understanding of the coupling between biochemical and physical processes. Representing their impact depends on our ability to calculate these processes using physically sound parameterizations, since they are unresolved at scales smaller than the grid size. More specifically over land, the coupling between evapotranspiration, turbulent transport of heat and moisture, and clouds lacks a combined representation to take these sub-grid scales interactions into account. Our approach is based on understanding how radiation, surface exchange, turbulent transport and moist convection are interacting from the leaf-to the cloud scale. We therefore place special emphasis on plant stomatal aperture as the main regulator of CO2-assimilation and water transpiration, a key source of moisture source to the atmosphere.

Plant functionality is critically modulated by interactions with atmospheric conditions occurring at very short spatiotemporal scales such as cloud radiation perturbations or water vapour turbulent fluctuations. By explicitly resolving these processes, the LES (large-eddy simulation) technique is enabling us to characterize and better understand the interactions between canopies and the local atmosphere. This includes the adaption time of vegetation to rapid changes in atmospheric conditions driven by turbulence or the presence of cumulus clouds. Our LES experiments are based on explicitly coupling the diurnal atmospheric dynamics to a plant physiology model. Our general hypothesis is that different partitioning of direct and diffuse radiation leads to different responses of the vegetation. As a result there are changes in the water use efficiencies and shifts in the partitioning of sensible and latent heat fluxes under the presence of clouds.

Our presentation is as follows. First, we discuss the ability of LES to reproduce the surface energy balance including photosynthesis and CO2 soil respiration coupled to the dynamics of a convective boundary layer. Second, we perform systematic numerical experiments under a wide range of background wind conditions and stomatal aperture response time. Our analysis unravel how thin clouds, characterized by lower values of the cloud optical depth, have a different impact on evapotranspiration compared to thick clouds due to differences in the partitioning between direct and diffuse radiation at canopy level. Related to this detailed simulation, we discuss how new instrumental techniques, e.g. scintillometery, might enable us to obtain new observational insight of the coupling between clouds and vegetation. We will close the presentation with open questions regarding the need to include parameterizations for these interactions at short spatiotemporal scales in regional or climate models.

Refreshments 3:15 PM

 

Building:
Room Number: 
Main Auditorium, Room 1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Announcement Timing: 
Thursday, August 16, 2018
Calendar Timing: 
Thursday, August 16, 2018 - 3:30pm to 4:30pm

Speaker:  Jean-Pierre Chaboureau

Affiliation: Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, Toulouse, France

Convection-permitting simulations (CPSs) and large-eddy simulations (LESs) have been long used for process-oriented case studies because of their ability in resolving the details of complex atmospheric circulation. This allows one to focus on convective objects, i.e. mesoscale convective systems (MCSs), convective updrafts and overshoots. Such gain in resolving fine-scale processes was also found when running convection-permitting models over longer time periods. The added value of such simulations was demonstrated using usual metrics such as the diurnal cycle of precipitation or the occurrence of extreme events, for example. This opens up new possibilities in exploring convective objects over a much larger sampling. Examples will be given from current on-going studies over the Tropics. In a Giga-LES (more than 1 billion grid points with 100 m spacing) of the Australian thunderstorm Hector the convector, the 10-km wide updrafts that overshoot into the stratosphere are characterized by a weak dilution. The km-scale eddies at the top of the overshoots produce the irreversible mixing with the stratospheric air and finally the hydration. In a CPS over northern Africa, the tracking of the MCSs shows a remarkable realism of terms of precipitation and deep convective activity when considering the radiative effect of dust. Too numerous MCSs are however predicted with a lack of organization for the longest-lived MCSs. Challenges in the CPM and LES approaches will be discussed.

Refreshments: 3:15 PM

Building:
Room Number: 
Main Auditorium, Room 1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Thursday, August 9, 2018 - 3:30pm to 4:30pm

Thursday, 2 August 2018, 3:30PM 

Speaker: Xiquan Dong

Affiliation: University of Arizona  

MCSs have regions of both convective and stratiform precipitation where significant different microphysical and thermodynamical features are observed. In a recent study, a classification method has been developed to objectively identify components of MCS as convective rain (CR, heavy rain), stratiform rain (SR, moderate-light rain), and anvil clouds (AC, no rain) using ground-based NEXRAD radar reflectivity, which provides a thorough means for studying the lifecycle of MCSs’ components, as well as their associated cloud and precipitation properties. We also developed a tracking algorithm using GOES IR temperature and tracked and analyzed a total of 4221 MCSs during two warm seasons from 2010 to 2011 over the central US and found that the CR precipitation intensity is an order higher than the SR one, but the SR coverage is much larger than the CR one.   

The DOE Atmospheric Radiation Measurement (ARM) conducted a field campaign, the Midlatitude Continental Convective Clouds Experiment (MC3E), at the ARM Southern Great Plains site from April to June 2011. During the MC3E field campaign, the University of North Dakota (UND) Citation II research aircraft carried out the major in situ measurements of cloud microphysical properties. This study investigates microphysical properties at ice-phase layer using the measurements collected by UND Citation II aircraft and the focus is on the correction of cloud ice water content (IWC) and the reconstruction of particle size distribution (PSD) based on multiple sensors measurements.   
 
To investigate the NSSL WRF simulated the warm season (April-September) precipitation over the Great Plains (GP), we use long-term (NCEP) Stage IV data over the Great Plains (GP).  Specifically, two subdomains, namely the Southern Great Plains (SGP, 99.985o W to 94.985o W, 34.66o N to 38.66o N) and Northern Great Plains (NGP, 100.75o W to 95.75o W, 45o N to 49o N) are selected. By using Self-Organizing-Map (SOM) method, a total of 808 convective systems during the period 2007-2014 are objectively classified into 6 classes according to the integrative analysis of synoptic characteristics over each sub-domain respectively.  Despite the difference in regional climatology, both regions demonstrate prominent seasonal contrast in dominant synoptic patterns.  The early summer convective systems are more impacted by the extratropical cyclone, while the late summer/early fall events are strongly associated with subtropical ridge.  Based on the SOM results, the real-time weather forecast product generated by the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory (NSSL) is evaluated using NCEP Stage IV data for each individual SOM class over each region.
 
Refreshments 3:15PM

 

Building:
Room Number: 
Main Auditorium, Room 1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Thursday, August 2, 2018 - 3:30pm to 4:30pm

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