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Improving Analyses and Predictions of a Tropical Squall Line Using Upper-Tropospheric Infrared Satellite Observations

Presentation Date
Wednesday, January 13, 2021 at 1:15pm
Authors

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Abstract

The intense convective activity over the Maritime Continent (MC) influences the Earth’s general circulation. It is thus important to accurately analyze and predict convective systems over the MC. However, the MC’s complex terrain and sparse in-situ observations make it challenging to produce accurate analyses and forecasts of convection over the MC. One solution is to supplement in-situ observation with modern geostationary satellite observations. Current geostationary satellite infrared brightness temperature (BT) observations have the spatiotemporal resolution to resolve the rapid evolution of meso-γ, or larger, convective systems. Furthermore, atmospheric motion vectors (AMV) produced from these satellites often have a spatial resolution of 10 km over cloudy regions. The assimilation of AMV and BT observations thus have the potential to constrain mesoscale convective systems over the MC.

In this study, we explored the impacts of assimilating these satellite observations during a MC tropical squall line. Specifically, we tested assimilating all-sky BT observations from the upper tropospheric water vapor channel of the Advanced Himawari Imager (channel 8; ch08-BT), as well as AMV produced by the Cooperative Institute for Meteorological Satellite Studies. In-situ observations were assimilated in all experiments. When ch08-BT observations were assimilated every three hours, the ensemble’s cloud fields showed noticeable improvement. Increasing the ch08-BT assimilation frequency to half-hourly not only amplified the cloud field improvements, but also improved the squall line’s lower tropospheric cold pool and outflow boundary. The assimilation of half hourly ch08-BT and three hourly AMV together observations further improved the cold pool and outflow boundary. Finally, deterministic short-term forecasts from experiments that assimilated either ch08-BT alone or ch08-BT and AMV observations produced better cloud features than those from an experiment that only assimilated in-situ observations.

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