[M-GI26] Data assimilation: A fundamental approach in geosciences

[MGI26-P09] Estimation of AMSU-A radiance observation impacts in an AGCM-LETKF data assimilation system: Comparison with EFSO and observing system experiments

*山崎 哲¹、寺崎 康児²、三好 建正^3,1、野口 峻佑⁴ (1.海洋研究開発機構 アプリケーションラボ、2.気象庁 気象研究所、3.理化学研究所、4.九州大学 理学研究院 地球惑星科学部門)

キーワード：AMSU-A放射輝度観測、観測インパクト、観測に対する予報感度

The impacts of assimilating AMSU-A satellite radiances with sensitive channels to the upper troposphere and the lower stratosphere were evaluated using an AGCM–local ensemble transform Kalman filter (LETKF) data assimilation system. Two streams of data-denial experiments for the AMSU-A observations have been performed for about a month in the Northern and Southern Hemisphere (SH) winters. Accumulating observation impact (OI) effects by cycling (repeating) data denials were quantified through the data assimilation system's tropospheric and stratospheric general circulation. It was discovered that adding the AMSU-A observations aided in reducing total OI by all observations of each data assimilation cycle; this is the opposite of the estimation of AMSU-A OI by the ensemble-based forecast sensitivity to observations (EFSO); however, such contributions could stabilize the data assimilation cycles. In both experiments, the accumulated AMSU-A OI was most evident in the upper troposphere, particularly in the SH midlatitudes where the westerly jets exist, and observations of the other types are sparse. The estimated AMSU-A OI by EFSO was also the most valuable (beneficial) in a similar space. Results demonstrated that AMSU-A OI tended to accumulate just downstream where EFSO estimated beneficial OI signals and that the accumulation of AMSU-A OI was tied to dynamic processes in the upper-tropospheric and general stratospheric circulation. Therefore, EFSO helps estimate the beneficial distributions of accumulated AMSU-A OI by considering their dynamical propagation.