Climatology of tropical cyclones in WRF-NRCM simulations

Many studies have shown that high resolution climate models can reproduce with some success both the structure and the climatology of tropical cyclones (TCs). These models have also been used to infer future climatologies of TCs. In keeping with this philosophy, we have extended a mesoscale model to run as a Nested Regional Climate Model (NRCM) to test its ability to reproduce tropical modes of variability.

The Weather Research and Forecasting Model (WRF) was run in tropical channel mode with a grid spacing of 36km. Three sets of simulations were conducted to simulate the period of 1996 – 2005: first simulation covering 1996 – 2000 with latitudinal extent of 30S – 45N, the second simulation covering 2000 – 2005 for latitudes 45S – 45N, and the third simulation covering May through November of 2005 with two-way nesting to 12km grid spacing over the tropical North Atlantic. Observed sea-surface temperatures were used throughout the integrations.

The climatology of tropical cyclones as produced by the WRF-NCRM is examined by total number, location of genesis, and monthly and yearly variability. WRF-NRCM is able to capture the overall climatology of TCs but tends to over-produce TCs in all TC regions. The impact of two-way nesting is examined by comparing the nested and non-nested simulations of the 2005 Atlantic hurricane season. Tropical cyclones are detected using a new objective numerical scheme. Reasons of the model's over-production of cyclones are also discussed.