A Further Study of Inner-Core Data Assimilation Using GSI-Based Hybrid System for Hurricane Intensity Predictions: Impacts of HWRF Model Physics and Resolution for Patricia (2015)

Early work showed the newly developed GSI-based, continuously cycled, dual-resolution hybrid 3DEnVar DA (data assimilation) system for HWRF (Lu and Wang, 2017) can produce realistic three-dimensional analyses after assimilating the field campaign observations from the ONR TCI and NOAA IFEX (including TCI dropsondes, IFEX TDR, SFMR and flight level data) in addition to the CIMSS AMVs (Atmospheric Motion Vectors) during hurricane Patricia (2015). However, significant intensity spin-down occurred in the forecasts initialized from the realistic DA analysis. Additionally, none of the experiments can capture the unprecedentedly strong peak intensity of real Patricia during the RI (rapid intensification).

Therefore, in this study, experiments and diagnostics were first conducted to understand how and why the significant spin-down issue occurs even initialized with the realistic analysis. We found the spin down issue is largely attributed to the errors in HWRF model physics. In particular, the modified turbulent mixing parameterization scheme was found to significantly alleviate the spin-down issue. Further detailed diagnostics showed that the modified turbulent mixing parameterization scheme allows mixing in the cloud above the boundary layer top, which induces more stronger vertical mixing and convections in the eyewall region. The resultant stronger secondary circulation eventually leads to realistically rapid storm intensification.

Although the spin-down issue is alleviated with improved physics and therefore the peak simulated intensity is significantly improved, there is still a large gap between the simulated maximum intensity and the observed peak intensity for Patricia. Additional experiments showed that the peak simulated intensity was further improved by increasing the model resolution. These findings together with further diagnostics will be presented at the conference.