ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 44 Issue 10 > 2018,44(10):1295-1305. DOI:10.7519/j.issn.1000-0526.2018.10.006 Prev Next
Spatio-Temporal Variations of Summer Rainfall over Yellow River Valley and Its Association with Atmospheric Circulation
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Abstract:
With the recent 58 summers data from 1958-2015, including precipitation from 55 observing stations over the Yellow River Valley and height field of NCEP/NCAR reanalysis 1 data etc., the characteristics of interannual variations for the summer rainfall in the Yellow River Valley and their causes associated with the synchronous variations of atmospheric circulations are analyzed by MannKendall test, composite analysis and MonteCarlo test methods in this paper. The results show that the reasons why the summer rainfall in the Yellow River Valley has been decreasing since 1958, in particular, significantly decreasing trend in the northern bend of Yellow River, are derived from the rising isobaric surface and weakened westerlies over the midhigh latitude of Eurasia. The climatic changes of the 58year rainfall in Yellow River Valley is divided into three different periods by two abrupt points in 1975 and 1996 according to natural changes in itself. During the period of 1958-1975, the low pressure circulations with stronger cold air dominated the Yellow River Valley and led to the larger interannual variations of anomalous precipitation whatever the above and below normal. In the phase 1976-1995, the reasons why the above normal rainfall happened to most sections of Yellow River Valley, are the development of Ural blocking high, and the negative height anomalies in troposphere dominated the regions from Baikal to Okhotsk, creating a deep trough over the Yellow River Valley. In addition, the warm and moist flow from South became stronger. In the recent 20 years, 1996-2015, most regions of Yellow River Valley suffered less rainfall, mainly due to the decreased heights of circulations over the northern Ural, and meanwhile the isobaric surface rising together over the areas from Caspian Sea to Baikal and to Okhotsk accompanied with weakened westerlies, which resulted in the weakened cold air and enhanced high pressure circulations controlling the Yellow River Valley. Moreover, the correlation analyses of rainfall in four basins of the Yellow River Valley with midhigh latitude blocking highs and the subtropical high in three different decades evidence the above conclusion further.
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