P-11

Data assimilation experiment of GNSS derived water vapor data using a nested LETKF system

M. Oigawa (Kyoto University), T. Tsuda (Kyoto University), H. Seko (Meteorological Research Institute), Y. Shoji (Meteorological Research Institute), K. Sato (JAXA), R. Eugenio (Geomatics Research & Development)

Strong horizontal gradient of PWV (Precipitable Water Vapor), i.e. about 9 mm/3.5 km, was observed by a hyper-dense GNSS (Global Navigation Satellite System) receiver network around south of Kyoto, Japan, with a resolution of about 1 km (Sato et al., 2013) when a meso-scale convective system (MCS) generated over the network at 2 JST on 14 August 2012, which was difficult to observe by the nationwide network called GEONET (GNSS Earth Observation Network), which has a resolution of about 20 km. The objective of this study is to investigate the formation mechanism of the PWV gradient by conducting a experiment using the Japan Meteorological Agency non-hydrostatic model and a nested Local Ensemble Transform Kalman Filter (LETKF) system (Seko et al., 2013) which consists of outer and inner LETKFs with horizontal grid intervals of 15 km and 1.875 km, respectively.

Thirty ensemble members were used. Although the MCS was reproduced well when GEONET-derived PWV for the outer LETKF and GEONET-derived slant water vapor and radial wind velocity by Doppler radars for the inner LETKF were assimilated, the observed PWV gradient was not reproduced. In future, additional experiment will be conducted by changing assimilation settings such as localization scale used in LETKF.