The impact of resolution on Met Office model predictions of tropical cyclone track and intensity

Increases in the horizontal and vertical resolution of the various configurations of the Met Office Unified Model (MetUM) have been made at regular intervals over the years as computing power has permitted. At the beginning of 2009 the global configuration of the MetUM was running at a horizontal resolution of approximately 40 km at mid-latitudes and with 50 vertical levels. By comparison, twenty years earlier the resolution was 150 km and 15 levels. By Spring 2010 the global MetUM will be running at a resolution of 25 km and with 70 levels.

In recent years various regional configurations of the MetUM have also been set up and run over areas that experience tropical cyclones – some on an ad hoc basis and some running regularly in real time. These models have been run at a resolution of 17 km in the horizontal with 38 vertical levels. By Spring 2010, one such model (covering the North Indian Ocean) will be running at 12 km resolution and with 70 levels.

This paper will review the impact of resolution on forecasts of the track and intensity of tropical cyclones and severe tropical rainfall events in both the global and regional configurations of the MetUM. It will also explore how changes to data assimilation techniques and physics tunings combine with resolution changes to impact on the forecast performance.