The Influence of Assimilated Upstream, Pre-Convective Dropsonde Observations on Ensemble Forecasts of Convection Initiation During the Mesoscale Predictability Experiment

The Influence of Assimilated Upstream, Pre-Convective Dropsonde Observations on Ensemble... AbstractThis study tests the hypothesis that assimilating middle- to upper-tropospheric, meso-α- to synoptic-scale observations collected in upstream, pre-convective environments is insufficient to improve short-range ensemble convection initiation (CI) forecast skill over the set of cases considered by the 2013 Mesoscale Predictability Experiment (MPEX) due to a limited influence upon the lower tropospheric phenomena that modulate CI occurrence, timing, and location. The ensemble Kalman filter implementation within the Data Assimilation Research Testbed as coupled to the Advanced Research Weather Research and Forecasting model is used to initialize two nearly identical thirty-member ensembles of short-range forecasts for each case: one initial condition set that incorporates MPEX dropsonde observations and one that excludes these observations. All forecasts for a given mission begin at 1500 UTC and are integrated for 15 h on a convection-permitting grid encompassing much of the conterminous United States. Forecast verification is conducted probabilistically using fractions skill score and deterministically using a 2 x 2 contingency table approach at multiple neighborhood sizes and spatiotemporal event matching thresholds to assess forecast skill and support hypothesis testing. The probabilistic verification represents the first of its kind for numerical CI forecasts. Forecasts without MPEX observations have high fractions skill score and probabilities of detection on the meso-α-scale but exhibit a considerable high bias for forecast CI event count. Assimilating MPEX observations has a negligible impact upon forecast skill for the cases considered, independent of verification metric, as the MPEX observations result in only subtle differences primarily manifest in the position and intensity of atmospheric features responsible for focusing and/or triggering deep, moist convection. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Monthly Weather Review American Meteorological Society

The Influence of Assimilated Upstream, Pre-Convective Dropsonde Observations on Ensemble Forecasts of Convection Initiation During the Mesoscale Predictability Experiment

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0493
D.O.I.
10.1175/MWR-D-17-0159.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThis study tests the hypothesis that assimilating middle- to upper-tropospheric, meso-α- to synoptic-scale observations collected in upstream, pre-convective environments is insufficient to improve short-range ensemble convection initiation (CI) forecast skill over the set of cases considered by the 2013 Mesoscale Predictability Experiment (MPEX) due to a limited influence upon the lower tropospheric phenomena that modulate CI occurrence, timing, and location. The ensemble Kalman filter implementation within the Data Assimilation Research Testbed as coupled to the Advanced Research Weather Research and Forecasting model is used to initialize two nearly identical thirty-member ensembles of short-range forecasts for each case: one initial condition set that incorporates MPEX dropsonde observations and one that excludes these observations. All forecasts for a given mission begin at 1500 UTC and are integrated for 15 h on a convection-permitting grid encompassing much of the conterminous United States. Forecast verification is conducted probabilistically using fractions skill score and deterministically using a 2 x 2 contingency table approach at multiple neighborhood sizes and spatiotemporal event matching thresholds to assess forecast skill and support hypothesis testing. The probabilistic verification represents the first of its kind for numerical CI forecasts. Forecasts without MPEX observations have high fractions skill score and probabilities of detection on the meso-α-scale but exhibit a considerable high bias for forecast CI event count. Assimilating MPEX observations has a negligible impact upon forecast skill for the cases considered, independent of verification metric, as the MPEX observations result in only subtle differences primarily manifest in the position and intensity of atmospheric features responsible for focusing and/or triggering deep, moist convection.

Journal

Monthly Weather ReviewAmerican Meteorological Society

Published: Oct 5, 2017

References

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