Impacts of assimilating measurements of different state variables with a simulated supercell storm and three-dimensional variational method

Abstract

This paper investigates the impacts of assimilating measurements of different state variables, which can be potentially available from various observational platforms, on the cycled analysis and short-range forecast of supercell thunderstorms by performing a set of observing system simulation experiments (OSSEs) using a storm-scale three-dimensional variational data assimilation (3DVAR) method. The control experiments assimilate measurements every 5 min for 90 min. It is found that the assimilation of horizontal wind Vh can reconstruct the storm structure rather accurately. The assimilation of vertical velocity w, potential temperature u, or water vapor qy can partially rebuild the thermodynamic and precipitation fields but poorly retrieves the wind fields. The assimilation of rainwater mixing ratio qr can build up the precipitation fields together with a reasonable cold pool but is unable to properly recover the wind fields. Overall, Vh data have the greatest impact, while qy have the second largest impact. The impact of qr is the smallest. The impact of assimilation frequency is examined by comparing results using 1-, 5-, or 10-min assimilation intervals. When Vh is assimilated every 5 or 10 min, the analysis quality can be further improved by the incorporation of additional types of observations. When Vh are assimilated every minute, the benefit from additional types of observations is negligible, except for qv. It is also found that for Vh, w, and qr measurements, more frequent assimilation leads to more accurate analyses. For qv and u, a 1-min assimilation interval does not produce a better analysis than a 5-min interval. © 2013 American Meteorological Society.