Analysis of tropical cyclone activity in three recent versions of the Canadian global numerical weather prediction system

In June 2009, the Canadian Meteorological Centre (CMC) made important changes to its global mid-range forecast system. Changes to the model included raising the model lid to 0.1 hPa (64 km); replacing sigma-like (or eta) vertical coordinates with a new hybrid coordinate; adding a non-orographic gravity wave drag scheme; and a new radiative transfer scheme leading to improvements in tropospheric temperature forecasts. Changes to the data assimilation system included assimilation of higher level atmospheric data from ATOVS, AMSU-A channels, GPS radio occultation data; as well as new observation and background error statistics. It has been shown that the new system does not overpredict tropical storms and tropical cyclones (TC) as much as the previous global system. A new version of the CMC global model is currently under development. The main objective of this project has been to further reduce the TC false alarm ratio in the CMC mid-range forecasts. An adjustment to the trigger function in the deep convection scheme over tropical oceans proved sufficient to reduce the TC false alarm ratio, while keeping other forecast scores practically unchanged. This adjustment is part of a new version of the global prediction system expected to become operational in June 2010. In this talk, we present results from the study of various TC properties -- e.g. false alarm ratio, detection rate, central pressure and position error, genesis distribution, potential intensity, genesis potential index – of the three latest versions of the CMC global forecasting system.