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.
** 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
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