Improvements in the representation of the Indian Summer Monsoon in the NCEP Climate Forecast System version 2
Friday, 19 December 2014: 5:00 PM
A new triggering mechanism for deep convection named Heated Condensation Framework (HCF) is implemented into the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). The new trigger is implemented as an additional criterion in the Simplified Arakawa-Schubert scheme for deep convection. Seasonal forecasts are performed to evaluate the influence of the new triggering mechanism in the representation of the Indian Summer Monsoon in the CFSv2. The HCF trigger improves the seasonal representation of precipitation over the Indian Subcontinent. Although the improvement is small in comparison to the overall precipitation bias in the CFSv2, there is a significant improvement. In addition, the new trigger improves the representation of the annual precipitation cycle of the Indian monsoon, including onset dates. The mechanism whereby the HCF improves convection over India seems to be related not only to a better representation of the background state of atmospheric convection but also to a reduction in the frequency in which the convective scheme is triggered. When the convection scheme is triggered less often, the convective available potential energy can build up. Once the convective scheme is triggered, intense precipitation occurs.