Relationship between summer rainfall anomalies and sub-seasonal oscillation intensity in the ChangJiang Valley in China |
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| Affiliation: | 1. Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical Weather Prediction, China Meteorological Administration, Guangzhou 510080, China;2. IPRC/AORC and Department of Atmospheric Sciences, University of Hawaii, Honolulu, HI, USA;3. International Laboratory on Climate and Environment Change and Key Laboratory of Meteorological Disaster, Nanjing University of Information Science and Technology, Nanjing, China;1. School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Ave, Singapore 639798, Singapore;2. Dept. of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020, USA;3. PUB, Singapore''s National Water Agency, 40 Scotts Road #07-01 Environment Building, Singapore 228231, Singapore;1. Department of Civil Engineering, The University of Texas at Arlington, Arlington, TX, United States;2. Office of Hydrologic Development, National Weather Service, Silver Spring, MD, United States;3. Remote Sensing Application Division, National Climatic Data Center, Asheville, NC, United States;1. Dipartimento di Fisica e Centro di Nanomedicina, Università degli Studi di Milano-Bicocca, Milan, Italy;2. CNR-ISASI, Center for Complex Systems, Pozzuoli, Italy;1. Laboratoire de Physique des Oceans, UMR 6523, CNRS/IFREMER/IRD/UBO, Brest, France;2. ICEMASA, Department of Oceanography, University of Cape Town, South Africa;3. CNRS-CERFACS, Toulouse, France;1. International Pacific Research Center, University of Hawaii, Honolulu, HI, USA;2. APL, JAMSTEC, Yokohama, Japan |
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| Abstract: | Sub-seasonal variability of summer (May–October) rainfall over the ChangJiang Valley exhibits two dominant timescales, one with a quasi-biweekly (QBW) period (10–20 days) and the other with an intraseasonal oscillation (ISO) period (20–60 days). A significant positive correlation (at a 99% confidence level) was found between the summer precipitation anomaly and the intensity of the QBW and ISO modes in the region. By examining the composite structure and evolution characteristics, we note that the QBW mode is characterized by a northwest–southeast oriented wave train pattern, moving southeastward. The perturbations associated with the ISO mode propagate northwestward in strong ISO years but southeastward in weak ISO years. A marked feature is the phase leading of low-level moisture to convection in both the QBW and ISO mode. When the summer rainfall is strong in the ChangJiang Valley, large-scale atmospheric conditions in the strong QBW/ISO activity region are characterized by deeper moist layer, convectively more unstable stratification and greater ascending motion. Such mean conditions favor the growth of the QBW and ISO perturbations. Thus, a significant positive correlation between the summer precipitation and the strength of sub-seasonal variability arises from the large-scale control of the summer mean flow to perturbations. |
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| Keywords: | Interannual variation of summer rainfall Quasi-biweekly oscillation Intraseasonal oscillation |
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