Observation impact estimation and TC relocation - Developments on the global EnKF

Yoichiro Ota
JMA Visiting Scientist


In this seminar, I will present works during my two-year stay in the NCEP/EMC, especially focusing on two topics: observation impact estimation, and better representation of Tropical Cyclone (TC) in the Ensemble Kalman Filter (EnKF).

The first part of the talk will be about the observation impact estimation technique using the ensembles. The method of Kalnay et al. (2012) has been applied to the GFS/EnKF system assimilating almost all observation types used in the operational Global Data Assimilation System (GDAS). The basic idea is similar to the adjoint-based observation impact estimation proposed by Langland and Baker (2004). Ensemble-based method can be used without an adjoint model so that it is convenient for the ensemble-based data assimilation system. Observation impact estimation can be a powerful tool to monitor and investigate the observation quality and data assimilation system. The example of the application of the impact estimates as well as key issues using ensembles will be presented.

The second part of the talk will focus on the representation of TCs in the EnKF analysis and ensemble forecast. Current operational global EnKF analysis does not apply any TC relocation procedure. This could cause a problem on the TC structure in the EnKF analysis and high resolution GDAS analysis through the ensemble-based background error covariance. On the other hand, future Global Ensemble Forecasting System (GEFS) is planned to utilize the EnKF 6 hour forecast perturbations for its initial perturbations. Thus, the TC relocation is also necessary in the ensemble forecasting purpose. I will briefly review the current operational GEFS TC relocation method and propose a new approach allowing more consistent initial uncertainty on TCs. Results from a preliminary experiment will be shown.