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Characters of Low Frequency Oscillation and Its Relationship with Summer Precipitation of Middle and Low Reaches of Yangtze Rivers

Author: ZhangXiuLi
Tutor: HeJinHai
School: Nanjing Institute of Meteorology
Course: Meteorology
Keywords: Low-frequency oscillation The middle and lower reaches of the Yangtze River Summer rainfall Drought and flood forecast
CLC: P426.616
Type: Master's thesis
Year: 2002
Downloads: 206
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Abstract


The application of wavelet transform and bandpass filtering method to analyze the differences of the summer 8 Typical Drought Year OLR field in the middle and lower reaches of the Yangtze River since the 1980s, the low-frequency characteristics of the wind field and droughts and years geopotential height field. The results show that: (1) regardless of droughts and floods in Year of the middle and lower reaches of the Yangtze River, the low frequency oscillation characteristics of OLR and wind fields are very significant. Focus on drought, floods, four each year analysis showed that 30 to 60 days of flood years OLR field oscillation is more significant than the drought year. (2) the flood year zonal wind and OLR field corresponding relationship either in phase or amplitude configuration are better, the peak pre precipitation in the middle and lower reaches of the Yangtze River, 20 ~ 30 ° N latitude band always appears westerly peak associated with EASM north; drought year, the main period of oscillation of the zonal wind and OLR always inconsistent, poor co-ordination between the two. (3) flood year low OLR exist in the meridional direction by the low-latitude north and the spread of Chinese and high latitudes south between 20 ~ 30 ° N, the two intersection. Dry years is not a significant convergence of area. (4) The impact of low-frequency cyclone and anticyclone sources in the northern mid-latitude Pacific and low latitudes of eastern China near the Philippines. In the flood years, and lower latitudes have low frequency cyclone / anticyclone generated, and the low-latitude low-frequency cyclone / anti-cyclone moving north and in the high-latitude low-frequency cyclone / anticyclone southwest to move more obvious, both the configuration good, easy to form a wide range of the cyclone or anticyclone belt, and cause airflow convergence or divergence more precipitation occurs, so that the middle and lower reaches of the Yangtze River. In dry years, low-latitude low-frequency cyclone / anticyclone go northward and mid-latitude low-frequency cyclone / anticyclone westward extension is not obvious, is not conducive to large-scale convergence and divergence zone formation of the Yangtze River basin, and thus not conducive to the precipitation occurs. (5) from the geopotential height field of view, droughts and floods in years corresponding circulation situation is exactly the opposite the 500hPa East Asian high latitudes to low latitudes in the flood year \negative - positive - negative anomaly type. Correlation analysis, spring Okhotsk area with high pressure area in Australia, and the middle and lower reaches of the Yangtze River in summer OLR values ??showed a positive correlation and negative correlation, indicating that the changes in the two areas geopotential height field and Yangtze precipitation in the middle and lower reaches how many have a close relationship.

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CLC: > Astronomy,Earth Sciences > Atmospheric science (meteorology ) > Meteorological elements,atmospheric phenomenon > Water vapor,condensation,and precipitation > Precipitation > Ordinary precipitation > Precipitation caused by the disaster
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