Data Assimilation Meetings at Reading
Date | Meeting type | Speakers |
25 June 2014 | Invited speaker |
Yuanfu Xie (NOAA ESRL)
Impact of Control Variables in Variational Data Assimilation Systems The new, variational version of the Local Analysis and Prediction System (LAPS) has a number of unique features. This presentation will focus on the choice of velocity related control variables. For wind analysis, stream function and velocity potential (commonly used), U and V wind components, and vorticity and divergence can be used as control variables. We will present theoretical analysis regarding the choice of wind-related control variables and discuss the issues of using stream function and velocity potential, such as tendency of introducing analysis errors, heavy analysis weights on unresolvable scales from observations, ill-condition minimization, and complexity in regional applications. Recently, WRF DA has been implemented using U and V as control variables. Several high impact weather events were studied by using stream function and velocity potential versus U and V as control variables. The numerical results confirm our theory and show much improved analysis and forecast when U and V are used as control variables. |