Schwartz, Craig S.., Zhiquan Liu, Chris Snyder,
So-Young Ha, National Center for Atmospheric Research, Stuart A. McKeen, NOAA
A limited-area ensemble
adjustment Kalman filter (EAKF) was employed to study tropical cyclones (TCs)
over the Atlantic basin. Between
11 August and 13 September 2008, a new EAKF analysis was produced every six
hours from a 96-member ensemble.
The mean analyses initialized 72-hr Advanced Research Weather Research
and Forecasting (WRF) model forecasts.
This month-long period was very active in the tropics, as five TCs (Fay,
Gustav, Hanna, Ike, and Josephine) developed, and all except Josephine made
landfall.
One particularly unique
aspect of this study was the direct assimilation of microwave satellite
radiances with the EAKF. Although
radiance assimilation is an important component of many operational global
analysis systems, the impact of assimilating radiances within a regional domain
is less understood. Thus, output
from a configuration with radiance DA was compared to output from a parallel
experiment where radiances were not assimilated. This design permitted a robust assessment of analysis and
forecast sensitivity to limited-area radiance assimilation for several TC
cases.
Assimilating radiances
yielded improved WRF model track and intensity forecasts compared to the
experiment where radiances were not assimilated, especially for mid-range lead
times. These results will be presented
in addition to a discussion of challenges associated with assimilating
radiances using an ensemble data assimilation system.