Bo Huang-April 19- Convective Meteorology Seminar

Name:     Bo Huang

Title:    Development of the Multi-scale Hybrid 4DEnVar System for NCEP FV3GFS: Scale-dependent-localization with and without Cross-band Correlations

Location: NWC 5600

Date:     2019/04/19

Time:     03:30 PM

Series:   Convective Meteorology (Mesoscale Dynamics)

Abstract: A uniform spatial localization for all scales is commonly applied in the ensemble-based data assimilation (DA) systems to treat sampling errors. Early studies suggest that the optimal effective localization length for the large scale is broader than that for the small scale. Therefore, the improved performance of the ensemble-based DA systems could be potentially gained by applying different amounts of localization to different ranges of scales. This study explores two variants of the scale-dependent-localization (SDL) method. The first SDL variant assumes that the cross-scale correlation is zero (referred to as the SDL-NoCross). The second variant takes into account the cross-scale correlation (referred to as the SDL-Cross).

The four-dimensional ensemble-variational (4DEnVar) hybrid DA system based on the gridpoint statistical interpolation (GSI) system is being transitioned to the next generation global prediction system FV3GFS at NCEP. These two SDL variants are mathematically demonstrated and implemented in the GSI-based 4DEnVar system. In this study, the impacts of these two SDL variants are examined for the FV3GFS global NWP. The results from a single observation experiment using a hurricane example show that these two SDL variants produce the analysis increments that are distinguishable from each other and consistent with their theoretical expectation. Results from the two-week cycled DA experiments show that SDL-NoCross and SDL-Cross generally improve the global forecasts and hurricane track forecasts, especially for SDL-Cross at longer lead times.