Experimental assimilation of synthetic bogus tropical cyclone pressure observations into a high-resolution rapid-update NWP model

Abstract

The effect of synthetic ‘bogus’ tropical cyclone (TC) central pressure observations on TC Owen was tested in a convective-scale numerical weather prediction (NWP) system with hourly 4D-Var assimilation. TC Owen traversed the Gulf of Carpentaria over 10–14 December 2018, entering from the east and briefly making landfall on the western edge before reversing course and retracing its path east to cross the northern tip of Queensland. The Australian Bureau of Meteorology runs a high-resolution NWP model centred over Darwin, which covers much of the Gulf of Carpentaria. The next-generation developmental version of this model includes data assimilation. Therefore, when TC Owen presented the opportunity to investigate the simulation of a TC within the domain, the developmental system was run as a case study. The modelled cyclone initially failed to intensify. The case study was then repeated including assimilation of bogus central pressure observations. This new run showed a large improvement in the intensity throughout the simulation; however, the TC track was not substantially improved. This demonstration of the potential impact of using synthetic observations may guide whether the development of a bogus observation source with sufficiently low latency for use in an hourly-cycling system should be prioritised.