Abstract 092

Abstract ID: 092

Diagnostics of Tropical Variability in the Unified Forecast System

Lead Author: Maria Gehne
CU Boulder CIRES, United States of America

Keywords: convectively coupled equatorial waves, convection, S2S

Abstract: Tropical precipitation and circulation are often coupled and span a vast spectrum of scales from a few to several thousands of kilometers and from hours to weeks. Current operational numerical weather prediction (NWP) models struggle with representing the full range of scales of tropical phenomena. Synoptic to planetary scales are of particular importance because improved skill in the representation of tropical larger scale features such as convectively coupled equatorial waves (CCEWs) have the potential of reducing forecast error propagation from the tropics to the midlatitudes.
Here we introduce and apply diagnostics from a recently developed tropical variability diagnostics toolbox, where we focus on several versions of the subseasonal-seasonal (S2S) component of the UFS: coupled prototypes 5, 7 and 8. For comparison we also include forecasts from the ECMWF S2S database. The diagnostics include space-time coherence spectra to identify preferred scales of coupling between circulation and precipitation, pattern correlations of Hovmöller diagrams to assess model skill in zonal propagation of precipitating features, CCEW skill assessment, plus a diagnostic aimed at evaluating moisture Рconvection coupling in the tropics.
The comparison between the UFS prototypes highlights the utility of these physically based diagnostics in the pursuit of better understanding of NWP model performance in the tropics, and during model development.

Co-authors:
Brandon Wolding (CU Boulder CIRES)
Juliana Dias (NOAA PSL)
George Kiladis (NOAA PSL)