Impact of rain rate initialization, cloud microphysics and angular momentum torques on hurricane intensity

The modulation of hurricane intensity forecast in a high resolution mesoscale model is investigated in terms of its sensitivity to rain rate initialization, microphysical parameters and cloud torques. This study is carried out using WRF-ARW mesoscale model at a cloud resolving resolution of 2.7 kilometer. The numerical simulations were performed in a triply nested fashion for hurricane Dennis of year 2005. However, all the experiment results would be shown for the innermost grid with finest resolution and integrated with explicit microphysics. The rain rate initialize model results show that there is a profound improvement in hurricane forecast (48hours) both in terms of intensity as well as structural characteristics of a hurricane inner core in compared to the forecast obtained from the control initial condition (i.e. without invoking rain rate initialization). The microphysics sensitivity experiments show that enhancing the ice mass concentration in the explicit scheme and making the intercept parameter independent of temperature produced the strongest storm and the weakest storm respectively. We are now investigating in more detail on the impact of microphysical changes on the hurricane precipitation forecast and hydrometeor distributions. The third component of this study to evaluate the hurricane intensity changes in terms of angular momentum and cloud torque budget. The backward trajectories following a parcel were constructed throughout the hurricane simulation period for all the experiments and for every segment of the parcel trajectory path the changes in angular momentum and cloud torques were computed. We note that the main factors responsible for the depletion of angular momentum influx within the storm are cloud torques. And it is possible to predict the short term intensity changes (for an air parcel) by carrying out the balance budget study of these two key parameters (i.e. angular momentum and cloud torques) across the individual trajectory segments during the storm life cycle.