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.
** Special MMM Seminar **
Simulation of ice particle shape effects using NTU multi-moment microphysics scheme
Jen-Ping ChenNational 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 timeRefreshments 9:45 AM
** 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 LehnerAffiliation: 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
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 Day, Time, and LocationSpeaker: Brenda PhilipsAffiliation: University of Massachusetts, Amherst
When people receive a hazard warning and decide to take protective action, such as sheltering in place, avoiding flooded roads, or protecting property, that decision is not made all at once. Theoretical and empirical research has demonstrated that individuals go through a process that involves receiving the warning, understanding the warning, personalizing the risk, and then taking protective action. Personalizing the risk, the expectation of personal impacts to self, family, property and daily activities, is a critical component of the protective action decision-making process. While hazards research focuses on the cognitive and emotional dimensions of personalization, there is also an important spatial and temporal component. Home, work, and areas of daily activity are physical locations that can be mapped over time to create individual mobility patterns, or footprints. Research in mobility patterns shows that people are creatures of habit and their mobility patterns are largely predictable. If we can predict people’s location and activities at different times of the day, why not use that information for weather alerts and warnings?
This talk will present exploratory research on the potential benefits of incorporating individual footprints into the severe weather warning systems for tornados, flash floods and severe thunderstorms. Our exploratory research examines the potential of warning people based on their individual perceptions and contexts, and how the complexity of human perception and response can be incorporated operationally into warning system technology. Advances in high resolution weather sensing, the Internet of Things (IoT), mobility-enabled Information and Communications Technology (ICT), and high levels of mobile phone usage makes these individualized warnings possible.
This research uses an innovative, multidisciplinary living lab infrastructure located in the Dallas Fort Worth Metroplex in north Texas to explore individualized warning. The CASA Dallas Fort Worth Living Lab for Severe Weather is a sensors-to-human warning system infrastructure where research can be conducted during live severe weather events with stakeholders and the general public. As part of this research platform, we have created a mobile phone app called CASA Alerts that delivers real-time, user-driven weather alerts to the public. The app also functions as a tool for conducting cross-sectional and longitudinal research on human behavior, perception and response.
Refreshments: 1:45 PM
Special Day, Time, and Location
Speaker: Brenda Philips
Affiliation: University of Massachusetts, Amherst
When people receive a hazard warning and decide to take protective action, such as sheltering in place, avoiding flooded roads, or protecting property, that decision is not made all at once. Theoretical and empirical research has demonstrated that individuals go through a process that involves receiving the warning, understanding the warning, personalizing the risk, and then taking protective action. Personalizing the risk, the expectation of personal impacts to self, family, property and daily activities, is a critical component of the protective action decision-making process. While hazards research focuses on the cognitive and emotional dimensions of personalization, there is also an important spatial and temporal component. Home, work, and areas of daily activity are physical locations that can be mapped over time to create individual mobility patterns, or footprints. Research in mobility patterns shows that people are creatures of habit and their mobility patterns are largely predictable. If we can predict people’s location and activities at different times of the day, why not use that information for weather alerts and warnings?
This talk will present exploratory research on the potential benefits of incorporating individual footprints into the severe weather warning systems for tornados, flash floods and severe thunderstorms. Our exploratory research examines the potential of warning people based on their individual perceptions and contexts, and how the complexity of human perception and response can be incorporated operationally into warning system technology. Advances in high resolution weather sensing, the Internet of Things (IoT), mobility-enabled Information and Communications Technology (ICT), and high levels of mobile phone usage makes these individualized warnings possible.
This research uses an innovative, multidisciplinary living lab infrastructure located in the Dallas Fort Worth Metroplex in north Texas to explore individualized warning. The CASA Dallas Fort Worth Living Lab for Severe Weather is a sensors-to-human warning system infrastructure where research can be conducted during live severe weather events with stakeholders and the general public. As part of this research platform, we have created a mobile phone app called CASA Alerts that delivers real-time, user-driven weather alerts to the public. The app also functions as a tool for conducting cross-sectional and longitudinal research on human behavior, perception and response.
Refreshments: 1:45 PM
Rescheduled Date from June 14, 2018 Speaker: Michael Ek Affiliation: NCAR/RAL/JNT
Local land-atmosphere coupling involves the interactions between the land-surface and the atmospheric boundary layer (ABL), and in turn with the free atmosphere above. Initiation of fair-weather cumulus requires an increase in relative humidity at the ABL top, and depends on a number of processes, some opposing each other. Those processes include the evolution of surface fluxes, sub-surface heat and moisture transport, surface-layer turbulence, boundary-layer development, and warm- and dry-air entrainment into the ABL from the free atmosphere above. Following an analytical development, we use modeling and observational data sets to examine this question.
Refreshments: 3:15 PM
Speaker: Prof. Christopher RufAffiliation: University of Michigan
The CYGNSS constellation of eight satellites was successfully launched on 15 December 2016 into a low inclination (tropical) Earth orbit. Each satellite carries a four-channel bistatic radar receiver which measures GPS signals scattered by the ocean, from which ocean surface roughness, near surface wind speed and air-sea latent heat flux, and land surface soil moisture and flood inundation are estimated. The measurements are unique in several respects, most notably in their ability to penetrate through all levels of precipitation, made possible by the low frequency at which GPS operates, and in the frequent sampling of extreme weather events and complete sampling of the diurnal cycle, made possible by the large number of satellites. Engineering commissioning of the constellation was successfully completed in March 2017 and the mission is currently in its science operations phase.
Level 2 science data products have been developed for near surface (10 m referenced) ocean wind speed, ocean surface roughness (mean square slope) and latent heat flux. Level 3 gridded versions of the L2 products have also been developed. A set of Level 4 products have also been developed specifically for direct tropical cyclone overpasses. These include the storm intensity (peak sustained winds) and size (radius of maximum winds), its extent (34, 50 and 64 knot wind radii), and its integrated kinetic energy. Assimilation of CYGNSS L2 wind speed data into the HWRF hurricane weather prediction model has also been developed. Measurements over land demonstrate sensitivity to near-surface soil moisture and the ability to image flood inundation.
An overview and the current status of the mission will be presented, together with highlights of on-orbit performance and recent scientific results.
Refreshments: 3:15 PM
Speaker: Prof. Christopher Ruf
Affiliation: University of Michigan
The CYGNSS constellation of eight satellites was successfully launched on 15 December 2016 into a low inclination (tropical) Earth orbit. Each satellite carries a four-channel bistatic radar receiver which measures GPS signals scattered by the ocean, from which ocean surface roughness, near surface wind speed and air-sea latent heat flux, and land surface soil moisture and flood inundation are estimated. The measurements are unique in several respects, most notably in their ability to penetrate through all levels of precipitation, made possible by the low frequency at which GPS operates, and in the frequent sampling of extreme weather events and complete sampling of the diurnal cycle, made possible by the large number of satellites. Engineering commissioning of the constellation was successfully completed in March 2017 and the mission is currently in its science operations phase.
Level 2 science data products have been developed for near surface (10 m referenced) ocean wind speed, ocean surface roughness (mean square slope) and latent heat flux. Level 3 gridded versions of the L2 products have also been developed. A set of Level 4 products have also been developed specifically for direct tropical cyclone overpasses. These include the storm intensity (peak sustained winds) and size (radius of maximum winds), its extent (34, 50 and 64 knot wind radii), and its integrated kinetic energy. Assimilation of CYGNSS L2 wind speed data into the HWRF hurricane weather prediction model has also been developed. Measurements over land demonstrate sensitivity to near-surface soil moisture and the ability to image flood inundation.
An overview and the current status of the mission will be presented, together with highlights of on-orbit performance and recent scientific results.
Refreshments: 3:15 PM
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