Targeted Observation Experiments Using High Temporal Geostationary Sounder GIIRS On Board FY-4A: Typhoon Ambil Case

Targeted observation is a technique to reduce rapidly growing forecast errors with the assimilation of observations in the sensitive regions at initial time. The efforts of using targeted observations to improve numerical forecasts of high-impact weather events has been carried out over the past two decades, particularly during the THORPEX era (2005–14).The target regions were often of synoptic scale, which is usually beyond the range of coverage of a single aircraft mission.For the first time, a hyperspectral IR sounder call GIIRS (Geosynchronous Interferometric Infrared Sounder) is stationed in geostationary orbit, it is onboard the first satellite (FengYun-4A) of Chinese second generation FengYun-4 series. FengYun-4A has the capability on providing GIIRS observations every 15 minutes for selected regions where active weather events occur. The GIIRS measurements have been calibrated, geo-located and processed for real-time applications. In this study for typhoon Ambil case, the target observing experiments and forecasts was conducted in real-time. The target region was determined using GRAPES global singular vector (SV) framework and then GIIRS was controlled to observe the target area every 30 minutes. The high temporal GIIRS soundings were assimilated in GRAPES global 4D-Var. The results were sent to chief weather forecaster of CMA on time and showed a positive impact on Typhoon forecasts, especially on the track and associated precipitation , which demonstrate the potential added value from high temporal sounding information on high impact weather forecast with target observation from geostationary sounder.