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Judith BernerNational Center for Atmospheric ResearchBoulder, Colorado Four model-error schemes for probabilistic forecasts over the contiguous United States with the WRF-ARW mesoscale ensemble system are evaluated in regard to performance. Including a model-error representation leads to significant increases in forecast skill near the surface as measured by the Brier score. Combining multiple model-error schemes results in the best-performing ensemble systems, indicating that current model error is still too complex to be represented by a single scheme alone.To understand the reasons for the improved performance, it is examined whether model-error representations increase skill merely by increasing the reliability and reducing the bias—which could also be achieved by postprocessing—or if they have additional benefits. Removing the bias results overall in the largest skill improvement. Forecasts with model-error schemes continue to have better skill than without, indicating that their benefit goes beyond bias reduction.Decomposing the Brier score into its components reveals that in addition to the spread-sensitive reliability, the resolution component is significantly improved. This indicates that the benefits of including a model-error representation go beyond increasing reliability. This is further substantiated when all forecasts are calibrated to have similar spread. The calibrated ensembles with model-error schemes consistently out- perform the calibrated control ensemble.Including a model-error representation remains beneficial even if the ensemble systems are calibrated and/ or debiased. This suggests that the merits of model-error representations go beyond increasing spread and removing the mean error and can account for certain aspects of structural model uncertainty.This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 26 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory 3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Judith Berner
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, February 26, 2015 - 3:30pm to 5:00pm

Weather predictions have improved significantly in recent decades. Yet as recent events such asSuperstorm Sandy illustrate, meteorologists still face major challenges in effectively conveying weatherforecasts and warning information. Advances in information and communication technology are alsorapidly changing how people access, interact with, and share weather-related information. Thispresentation will discuss results from recent research studies to understand communication, interpretation,and use of weather forecast and warning information, with an emphasis on improving communication ofweather risk and forecast uncertainty. It will focus on interdisciplinary physical-social science research tobuild empirical understanding of how people conceptualize weather-related risks, how they perceive andinterpret different types of forecast and warning information, and how they use information in protectivedecisions. First, results will be presented from a nationwide survey examining people's perceptions,interpretations, and uses of weather forecast uncertainty. Results will then be presented from studies ofpeople’s forecast and warning decisions when extreme weather events (such as hurricanes or flash floods)threaten, including their responses to different warning messages. Next, an ongoing project will bedescribed that investigates how interactions among actors and information influence risk interpretationsand behavioral responses as a hurricane approaches and arrives, using computational modeling, analysisof social media data, and other methods. Potential implications of the findings for communication ofweather and climate information will also be discussed, as well as priority areas for future research.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

Thursday, 19 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
Rebecca E. Morss
Organization(s):
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, February 19, 2015 - 3:30pm to 5:00pm

John J. Finnigan (presenter) in collaboration with Edward G. Patton and Roger H. Shaw1. CSIRO Oceans and Atmosphere, Canberra, Australia2. National Center for Atmospheric Research, Boulder, Colorado3. University of California, Davis

The origin of the coherent eddy structures in and above tall plant canopies in neutrally stratified flow has for some years been known to result from the hydrodynamic instability of the inflected mean velocity profile that develops at the canopy top. A cascade of secondary instabilities yields canopy eddies of characteristic form and these are responsible for most of the turbulent kinetic energy and transport in the canopy’s vicinity.

Above the surface layer, in neutral and weakly unstable flows, large-scale roll-like structures dominate transport throughout much of the larger atmospheric boundary layer (ABL). When buoyancy forces become dominant, these rolls transition into Rayleigh-Benard-like cells spanning the depth of the convectively driven ABL. At the canopy level, these ABL-scale structures modulate the near-surface wind and temperature fields so that canopy regions are alternately subjected to enhanced or reduced wind shear and diabatic stability at horizontal scales ranging from 100-1000 canopy heights.

Beneath these ABL-scale structures in regions of strong shear, the canopy eddy structure corresponds to the inflection point instability described above. However in regions of low shear, diabatic effects dominate and convective plumes develop, extending vertically to several canopy heights and with horizontal widths of order canopy height. These canopy plumes are a mode of buoyant instability with Rayleigh-Benard type eigenmodes, whose horizontal scale is related to the vertical profile of canopy air temperature.

The horizontally-averaged heat and momentum transfer between the canopy layers and the ABL above therefore results from two distinct coherent eddy structure types, according to whether the canopy is below ascending or descending regions of the larger ABL-scale structures. Because the structure of the large ABL-scale rolls or cells above the canopy depends upon the area-averaged heat and momentum transfer from the surface through the parameter zi/LMO (the ABL depth divided by the Obukhov length), these three modes of instability, two at canopy scale and one at ABL scale, are intimately coupled.

We have studied this situation using canopy-resolving large eddy simulation (LES) of the full ABL. In addition, we complement those full LES simulations with idealized studies of the canopy plume instability.

In this talk we will discuss the implications of this fully coupled picture of canopy-ABL turbulent exchange for Monin-Obukhov scaling in the surface and canopy-roughness sublayers, and for observational strategies for tower measurements of turbulent fluxes. We will also comment on the usefulness of linear and non-linear stability analysis in revealing attractors for dominant turbulence structures even in fully turbulent flows.

This seminar will be webcast live at:http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:https://www.mmm.ucar.edu/events/seminars

**PLEASE NOTE THE SPECIAL DAY OF THIS SEMINAR**Tuesday, 17 February 2015, 3:30 PMRefreshments 3:15 PMNCAR-Foothills Laboratory3450 Mitchell LaneBldg 2 Main Auditorium, Room 1022

First Name: 
Michelle
Last Name: 
Menard
Phone Extension (4 digits): 
8189
Email: 
menard@ucar.edu
Presenter(s): 
John J. Finnigan
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Tuesday, February 17, 2015 - 3:30pm to 5:00pm

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