The selection of atmospheric sample profiles is one of the key factors affecting the accuracy of the fast simulation of satellite channels, but the mechanism of the influence has not been conclusively established. In this paper, the mechanism of atmospheric sample profile selection and its contribution in the forward modeling are discussed through the analysis of the role of transmittance predictors in RTTOV model. The CO2 absorption channel at 15 μm in the infrared band of FY-3C IRAS (InfraRed Atmospheric Sounder) is used as the study object, and the IRAS laminar channel transmittance factor is established based on the TIGR43 profile database. The comparison tests between the profile temperature anomaly and simulation accuracy in the cold and warm scenarios show that the root mean square error (RMSE) of the simulation for the IRAS temperature detection channel is 0.2 K when all the profiles are involved in the regression calculation, compared with the simulation results of LBL. Within the detection height range of the selected CO2 detection channels, there is a strong linear correlation between the profile temperature anomaly and the simulation accuracy in the warm scenario due to the higher order residual term in the Taylor expansion, and more significant accuracy improvement can be obtained if the profile with larger temperature anomaly is removed from the forward modeling.
This study introduces the construction of the satellite observation cycling assimilation system in national satellite
meteorological center (NSMC). A typhoon case (1209 Saola ) is chosen to be performed as a testing experiment to check
the operation of the cycling assimilation, with a low resolution . Three experiments are designed: control, ATOVS
microwave observation assimilation and forecasting with cold starting, assimilation and forecasting with warm starting.
Compared with the cold start forecasting, cycling forecasting showed advance in describing more information of the
Tropical Cyclones in detail. As for track and intensity prediction, both the two assimilation experiments were prior to
control experiment. Especially, the cycling experiment is better than cold experiment in the first one day and third day
and the day before landing, but not act well in its peak period, which may suggest that the model couldn’t not match the
description of the typhoon Saola at the full developing period or upgrading develop period, with the low resolution in the
testing experiments, but also can demonstrate well when it develop slowly or in a relatively steady period.
The Vertical Atmospheric Sounding Suits (VASS) onboard FY-3C satellite includes The Infrared Atmospheric
Sounder (IRAS), Microwave Temperature Sounder (MWTS) and Microwave Temperature and moisture sounder
(MWTHS-II). The IRAS is similar to that onboard FY-3A/B, while the MWTS-II/MWTHS-II is more sophisticated
than their precursors. MWTS has 13 channels mainly at the window region and 57 O2 absorption band, and
MWTHS has 15 channels mainly at the 118 O2 absorption band and the 183 H2O absorption band. A package has
been developed to retrieve the atmospheric temperature profile, moisture profile, atmospheric total ozone, and
other parameters in both clear and cloudy atmospheres from the VASS measurements, which is remap to IRAS
Field of view. The algorithm that retrieves these parameters contains four steps: 1) cloud and precipitation
detection, 2) bias adjustment for VASS measurements, 3) regression retrieval processes, and 4) a nonlinear iterative
physical retrieval. The package does not process precipitation FOV, and for non-precipitation cloud FOV, the
measurements from middle to low channels of IRAS are excluded. Till now all instruments are under orbit
examination stage, and the primary results show that temperature soundings can be produced under partial cloud
cover with RMS errors on the order of, or better than, 2.0 K in 1-km-thick layers from the surface to 700 mb, 1-km
layers from 700–300 mb, 3-km layers from 300–30 mb, and 5-km layers from 30–1 mb; and moisture profiles can
be obtained with an accuracy better than 20% absolute errors in 2-km layers from the surface to nearly 300 mb.
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