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.

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