Application of WRF 3DVAR to operational typhoon prediction in Taiwan: Impact of outer loop and partial cycling approaches
Journal
Weather and Forecasting
Journal Volume
27
Journal Issue
5
Pages
1249-1263
Date Issued
2012
Author(s)
Abstract
In this paper, the impact of outer loop and partial cycling with the Weather Research and Forecasting Model's (WRF) three-dimensional variational data assimilation system (3DVAR) is evaluated by analyzing 78 forecasts for three typhoons during 2008 for which Taiwan's Central Weather Bureau (CWB) issued typhoon warnings, including Sinlaku, Hagupit, and Jangmi. The use of both the outer loop and the partial cycling approaches in WRF 3DVAR are found to reduce typhoon track forecast errors by more than 30%, averaged over a 72-h period. The improvement due to the outer loop approach, which can be more than 42%, was particularly significant in the early phase of the forecast. The use of the outer loop allows more observations to be assimilated and produces more accurate analyses. The assimilation of additional nonlinear GPS radio occultation (RO) observations over the western North Pacific Ocean, where traditional observational data are lacking, is particularly useful. With the lack of observations over the tropical and subtropical oceans, the error in the first-guess field (which is based on a 6-h forecast of the previous cycle) will continue to grow in a full-cycling limited-area data assimilation system. Even though the use of partial cycling only shows a slight improvement in typhoon track forecast after 12 h, it has the benefit of suppressing the growth of the systematic model error. A typhoon prediction model using the Advanced Research core of the WRF (WRF-ARW) and the WRF 3DVAR system with outer loop and partial cycling substantially improves the typhoon track forecast. This system, known as TyphoonWRF (TWRF), has been in use by CWB since 2010 for operational typhoon predictions. © 2012 American Meteorological Society.
Subjects
Data assimilation; Hurricanes/typhoons; Model initialization; Numerical weather prediction/forecasting; Regional models
SDGs
Other Subjects
Accurate analysis; Advanced researches; Central weather bureaux; Data assimilation; Data assimilation systems; Forecast errors; Model initialization; Numerical weather prediction; Observational data; Outer loop; Partial cycling; Prediction model; Radio occultations; Regional model; Subtropical ocean; Systematic models; Variational data assimilation system; Weather research and forecasting models; Western North Pacific; Data processing; Hurricanes; Three dimensional; Weather forecasting; accuracy assessment; data assimilation; error analysis; GPS; hurricane; numerical model; regional climate; storm track; typhoon; variance analysis; weather forecasting; Pacific Ocean; Pacific Ocean (North); Taiwan
Type
journal article