著者

QIN Zhengkun ZOU Xiaolei

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-064, (Released:2019-09-13)

被引用文献数

10

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The Tibetan Plateau (TP) and the atmospheric conditions over it strongly affect downstream regional weather. Advanced Microwave Sounding Unit-A (AMSU-A) brightness temperature observations provide temperature sounding information and have been long assimilated successfully for numerical weather prediction. AMSU-A brightness temperatures observed from the polar-orbiting NOAA-15 and -18 satellites in July and August 2016 were collected. During these months, the equator crossing time of these particular satellites was around 0600 local time. Observations collected within the three-hour periods centered at 0000 UTC and 1200 UTC, covering the TP, were assimilated. The weighting coefficients for mid-tropospheric AMSU-A channels 6 and 7 were significantly reduced over areas with terrain heights greater than 2 km and 4 km, respectively, in the National Centers for Environmental Prediction Gridpoint Statistical Interpolation system. The assimilation of AMSU-A observations was improved to better exploit the role of AMSU-A channels 6 and 7 over the TP. This was achieved by not decreasing the weighting coefficients of the two channels over the grassy surface of the TP’s high terrain so that they were consistent with the inverse error variances. This modification produced larger positive impacts of satellite data assimilation on the 48-h forecasts of the mid-tropospheric trough, water vapor, and quantitative precipitation forecasts downstream of the TP. This study also suggests the importance of having AMSU-A observations from early-morning satellite orbits for numerical weather prediction downstream of the TP.

著者

ZHUGE Xiaoyong ZOU Xiaolei

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2018-041, (Released:2018-04-13)

被引用文献数

19

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Convective initiation (CI) nowcasting often has a low probability of detection (POD) and a high false-alarm ratio (FAR) at sub-tropical regions where the warm-rain processes often occur. Using the high spatial- and temporal-resolution and multi-spectral data from the Advanced Himawari Imager (AHI) on board Japanese new-generation geostationary satellite Himawari-8, a stand-alone CI nowcasting algorithm is developed in this study. The AHI-based CI algorithm utilizes the reflectance observations from channels 1 (0.47 μm) and 7 (3.9 μm), brightness temperature observations from infrared window channel 13 (10.4 μm), the dual-spectral differences between channels 10 (7.3 μm) and 13, 13 and 15 (12.4 μm), as well as a tri-spectral combination of channels 11, 15 and 13, as CI predictors without relying on any dynamic ancillary data (e.g., cloud type and atmospheric motion vector products). The proposed AHI-based algorithm is applied to CI cases over Fujian province in the Southeastern China. When validated by S-band radar observations, the CI algorithm produced a POD as high as 93.33 %, and a FAR as low as 33.33 % for a CI case day that occurred on 1 August 2015 over Northern Fujian. For over 216 CI events that occurred in a three-month period from July to September 2015, the CI nowcasting lead time has a mean value of ~64 minutes, with a longest lead time over 120 minutes. It is suggested that false-alarm nowcasts that occur in the presence of capping inversion require further investigation and algorithm enhancements.