*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
Speaker: Sean Healy
Affiliation: ECMWF
*Please note Special Location- FL2-1001 Small Seminar Room
ECMWF has assimilated GPS radio occultation (GPS-RO) measurements operationally since December 2006, and they are now considered to be a key component of the global observing system. Importantly, these measurements complement the information provided by satellite radiances, because they have good vertical resolution and they can be assimilated without bias correction to the background model. This talk will review how the assimilation of the GPS-RO data at ECMWF has evolved since 2006, and summarise the current impact of this data in the numerical weather prediction system. Current efforts to improve the forward modelling of the GPS-RO data will be described, and areas which require further improvement, such as improved observation error statistics, will be highlighted. Recent wave optics simulation results estimating the size of both the instrument errors and forward model/retrieval errors in the troposphere will be presented.
The importance of GPS-RO measurements for climate reanalyses will be demonstrated. It will be shown that the consistency of ERA5, JRA55 and MERRA-2 temperature estimates in the lower/middle stratosphere has improved since the active assimilation of COSMIC data in 2006.
Refreshments: 3:15pm
The Capacity Center for Climate and Weather Extremes (C3WE/MMM) is hosting a Climate and Weather Extremes Tutorial designed for students, researchers, and professionals who are interested in climate and weather extremes. The Tutorial will cover approaches to analyzing and modeling extremes, as well as methods to understand and characterize uncertainty. The Tutorial will also feature a clinic focused on workflows for accelerated science discoveries and overcoming barriers to understanding and predicting weather and climate extremes.
The Tutorial consists of both lectures and hands-on laboratory exercises, which will be taught by a team of NCAR climate scientists and members of the NSF Earthcube ASSET (Accelerating Scientific WorkflowS using Earthcube Technologies) project.
The Climate and Weather Extremes Tutorial will be offered over a 3-day period from Wednesday August 1– Friday August 3, 2018 at the NCAR Foothills Laboratory, Boulder, Colorado.
Topics include:
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.
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
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
2018 NORTH AMERICAN WORKSHOP ON HAIL & HAILSTORMSAUGUST 14 - 16, 2018, BOULDER, COLORADONCAR CENTER GREEN CAMPUS
Across North America, hailstorms are responsible for over $10 billion dollars in annual property damage. The increase in the impact of hailstorms has outpaced advances in detection, forecasting, and mitigation. The National Science Foundation, the National Center for Atmospheric Research and the Insurance Institute for Business & Home Safety are organizing the first North American Workshop on hail, and hailstorms. The workshop will bring together public and private stakeholders to discuss the current state of the science regarding all facets of this peril and provide a look to the future. The workshop will be held at the NCAR Center Green 1 (CG1) campus, 3080 Center Green Drive, Boulder, Colorado.
Call For Abstracts: The deadline for abstract submissions is May 1, 2018.
For information: https://www.mmm.ucar.edu/north-american-hail-workshop
What gives supercells a leg-up over ordinary convection in resisting entrainment?
John Peters
Naval Postgraduate School
Using high-resolution numerical simulations, it is shown that supercells’ low-level inflow substantially increases with time as they begin to propagate strongly to the right of the mean advective flow. Mass continuity necessitates a compensatory increase in vertical mass flux as a response to the increase in horizontal low-level inflow, which in many cases results in a widening updraft rather than in increase in updraft vertical velocity. At the same time, substantial updraft vertical vorticity in supercells results in centrifugally stable flow within the supercell’s lower updraft, which inhibits the buoyant generation of toroidal vorticity along the updraft’s flanks. These two factors – increasing diameter and centrifugal stability with time – are shown to inhibit the breakdown of the supercell updraft into discrete thermals, and to promote a plume-like updraft structure. As a result of the wide diameter and plume-like nature of supercell updrafts, their cores become less-susceptible to entrainment-driven dilution than ordinary convection. Evidence is shown for the transport of nearly pure boundary layer air into the lower stratosphere in supercell updrafts, whereas nearly pure air is only present in the lowest few kilometers of the troposphere in ordinary convection.
** Special MMM Seminar **
Simulation of ice particle shape effects using NTU multi-moment microphysics scheme
Jen-Ping Chen
National Taiwan University
Ice crystal shape effect (ICSE) on cloud microphysical processes remains an unresolved issue in cloud modeling. This study incorporated a newly developed three-moment modal parameterization with shape representation for pristine ice crystal and snow aggregates into the WRF model to investigate ICSE. This NTU-v2 scheme allows gradual adaptation of ice crystal habits under varying environmental conditions and thus keeps previous memory of shape. Furthermore, density variations are considered for pristine cloud ice, snow aggregate, and rimed ice (graupel). Shape and density variations are taken into account in calculating the particle fall speed and radar reflectivity. This talk presents a C3VP case to demonstrate the sensitivity of ICSE, as well as a mid-latitude cold front case during the DIAMET campaign for further comparison with aircraft observations. Both cases showed strong influence of ICSE on cloud structure and precipitation. In addition, the effect of particle shape on radar reflectivity calculation is also demonstrated.
*Please note special day and time
Refreshments 9:45 AM
Speaker: Flavio Lehner
Affiliation: NCAR/RAL/CGD
The Southwestern US experiences substantial natural variability in precipitation and temperature, on timescales ranging from daily to decadal. This variability makes the environment for prediction and management of water resources – critical tasks to ensure the well-being of society in this water-scarce region – challenging. Strong trends from the 1980s to the 2010s from cool and wet to warm and dry conditions, have led to intermittent drought conditions and reduced streamflow predictability. These impacts have led to discussion about the role of anthropogenic climate change, and have also led to other initiatives such as policy-driven drought mitigation and new drought adaptation plans issued by federal agencies.
Here I will address three questions that the trends toward drying and warming have prompted: (1) How unusual are these trends? (2) Can we attribute these trends to anthropogenic climate change? (3) How can we use the answers to question (1) and (2) to increase the resilience of society to such trends in the future? Using tree-ring based reconstructions of hydroclimate, I document the influence of precipitation and temperature on streamflow during the several hundred years before instrumental records became available, providing a baseline for the role of internal versus externally forced climate variability. I then use a constructed circulation analog technique and a set of climate model simulations to dissect and attribute the recent trends. Finally, I will illustrate how we can use this information to improve operational seasonal streamflow forecasts in the Southwest, in an attempt to close the notoriously open circle of research-to-operations.
Refreshments: 3:15 PM
*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
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
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
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.
Thursday, 26 July 2018, 3:30PM (*Please note Special Location: FL2-1001 Small Seminar Room) Speaker: Paul Stoy Affiliation: Montana State University
The northern North American Great Plains (NNAGP) have seen massive land use changes over the past half-century. Increases in agricultural intensity are consistent with observed cooling and increases in precipitation during the vegetative growing season. Have land managers responded to these climate changes in a way that further cools growing season climate, creating a positive feedback? Here, I review decadal changes in land management, hydrology, and climate in the NNAGP and demonstrate that it has experienced globally unique hydroclimate trends. Increases in evapotranspiration at the expense of sensible heat flux (a decrease in the Bowen ratio) have increased convective precipitation likelihood. The surface-atmosphere coupling framework used to quantify these changes also indicate that convective precipitation was anomalously unlikely weeks before the onset of the 2017 “flash” drought. Surface-atmosphere feedbacks in the NNAGP appear to be tipping toward a more closely coupled state, with both advantageous and deleterious effects on human livelihoods. From these results, I will argue that understanding the mechanisms underlying human-climate feedbacks in the NNAGP provides a framework for quantifying regional climate services across the globe.
Refreshments: 3:15 PM
The Capacity Center for Climate and Weather Extremes (C3WE/MMM) is hosting a Climate and Weather Extremes Tutorial designed for students, researchers, and professionals who are interested in climate and weather extremes. The Tutorial will cover approaches to analyzing and modeling extremes, as well as methods to understand and characterize uncertainty. The Tutorial will also feature a clinic focused on workflows for accelerated science discoveries and overcoming barriers to understanding and predicting weather and climate extremes.
The Tutorial consists of both lectures and hands-on laboratory exercises, which will be taught by a team of NCAR climate scientists and members of the NSF Earthcube ASSET (Accelerating Scientific WorkflowS using Earthcube Technologies) project.
The Climate and Weather Extremes Tutorial will be offered over a 3-day period from Wednesday August 1– Friday August 3, 2018 at the NCAR Foothills Laboratory, Boulder, Colorado.
Topics include:
30- 31 July 2018
NCAR Foothills Lab, Boulder, CO
OVERVIEWThe Mesoscale and Microscale Meteorology (MMM) Laboratory of the National Center for Atmospheric Research (NCAR) will be hosting a Tutorial on the Model for Prediction Across Scales – Atmosphere (MPAS-A). The tutorial will be held 30 – 31 July 2018 at NCAR’s Foothills Laboratory at 3450 Mitchell Lane in Boulder, Colorado. The tutorial will cover the basics of how to set-up, run, and post-process stand-alone MPAS-A simulations, and topics that will be covered will include:
The primary audience for this tutorial is new or beginning users of MPAS-Atmosphere. Basic knowledge of atmospheric science and numerical modeling, as well as experience working within a Unix computing environment, is required for the tutorial.
The Weather Research and Forecasting (WRF) model Tutorial will be held at the NCAR Foothills Laboratory (FL2) located at 3450 Mitchell Lane, Boulder, Colorado from July 23-27, 2018.
The Basic tutorial will consist of lectures on various components of the WRF modeling system along with hands-on practice sessions. The topics include:
Basic knowledge of atmospheric science and numerical modeling, as well as experience working with a Unix computer environment, is required for the class. WRF Tutorial participants are strongly encouraged to work through the WRF-ARW online tutorial, especially if you have not used the model before. Reviewing the online tutorial will provide an overview of the system, which can help enhance your learning experience once you are here (even if you cannot compile and run the code physically).
Speaker: Professor Lian-Ping Wang
Affiliation: Department of Mechanics and Aerospace Engineering, SUSTech
Since the 1980s, direct numerical simulations have served as a vital research tool to probe flow structures and nonlinear dynamics in complex flows such as multiphase flows and turbulent flows. Most of these simulations were performed based on the continuum (conventional or macroscopic) Navier-Stokes equation. In recent years, mesoscopic methods based on the Boltzmann equation, such as the lattice Boltzmann method and gas kinetic schemes, have been developed and applied to these complex flows. In this talk, I will discuss some recent advances in applying mesoscopic methods for rigorous simulations of such complex flows. Three specific examples will be considered: (a) turbulent channel flow laden with finite-size moving particles, (b) hydrodynamic interactions of cloud droplets, and (c) compressible turbulent flow. A few implementation issues in these simulations will be discussed. The purpose is to expose the capabilities of these mesoscopic methods, open research issues, and their potentials for various complex flow problems.
What gives supercells a leg-up over ordinary convection in resisting entrainment?
John Peters Naval Postgraduate School
Supercell thunderstorms are dynamically distinct from ordinary nonrotating convection. Supercells are often capable of maintaining a distinct plume-like updraft for several hours, whereas ordinary convection is characterized by series of episodic thermals with typical lifespans of < 30 minutes. This research presents new insights into why supercells are able to sustain updrafts for lengthy intervals.Using high-resolution numerical simulations, it is shown that supercells’ low-level inflow substantially increases with time as they begin to propagate strongly to the right of the mean advective flow. Mass continuity necessitates a compensatory increase in vertical mass flux as a response to the increase in horizontal low-level inflow, which in many cases results in a widening updraft rather than in increase in updraft vertical velocity. At the same time, substantial updraft vertical vorticity in supercells results in centrifugally stable flow within the supercell’s lower updraft, which inhibits the buoyant generation of toroidal vorticity along the updraft’s flanks. These two factors – increasing diameter and centrifugal stability with time – are shown to inhibit the breakdown of the supercell updraft into discrete thermals, and to promote a plume-like updraft structure. As a result of the wide diameter and plume-like nature of supercell updrafts, their cores become less-susceptible to entrainment-driven dilution than ordinary convection. Evidence is shown for the transport of nearly pure boundary layer air into the lower stratosphere in supercell updrafts, whereas nearly pure air is only present in the lowest few kilometers of the troposphere in ordinary convection.
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