Data Assimilation Study for TC intensity


In consultation with EMC, the DTC AOP 2014 T&E activities related to the application of the GSI-hybrid system for the HWRF application focused on diagnostics for the 2014 HWRF spin-down issue and investigating the current two-way GSI-hybrid capabilities.

As a first step, the DTC completed baseline tests for the HWRF 2014 pre-implementation cases to "reproduce" the HWRF pre-implementation results. The DTC then performed further diagnostics and, subsequently, selected Hurricane Irene (2011) for more detailed study. This detailed study indicated the spin-down behavior stems from an imbalance between the vortex initialization and the DA steps. The inner core DA and its interaction with the vortex initialization are the key components for this spin-down issue.

During AOP 2014, the DTC also investigated ways to improve how the flow-dependent background error is prescribed. A quick study performed by the DTC indicated using the HWRF regional ensemble (instead of GFS ensemble) in the one-way hybrid DA to define the flow-dependent portion of the background error may improve the TC intensity forecasts. Cycling update of the regional ensemble may further improve the forecasts. Therefore, the DTC continued to build a complete two-way hybrid system for HWRF and conducted experiments with both one-way and two-way hybrid techniques and examined their impacts on the inner core DA.