| Using the NOAA OLR observed by Satellites,the NCEP/NCAR reanalysis,daily precipitation data of Chinese753stations from1979to2009and the NOAA daily SST data from1982to2011, the authors have investigated the climatological characteristics of Low-Frequency Oscillation(CLFO) in the Summer monsoon regions and their possible associations with the summer precipitation disturbances in China. The results are summarized as follows:(1) The OLR daily climatology in Indian Ocean has30-60day oscillations from April to September. These low-frequency OLR are observed to propagate eastward in latitudinal and northward propagation in meridional, which causes the change of the low-frequency circulations and heating fields, affectting the amount of precipitation in China. More obviously rainfall occurs in North China, southwestern part of China, the middle reaches of the Yangtze River, and the northern part of Heilongjiang province, and less precipitation in eastern part of northwest China, central and eastern part of China, and the South of the Changjiang River valley in the peak (Valley)phase. In transition phase from valley to peak of CLFO of OLR, more(less) precipitation is received in the upper reaches of the Yellow River, Hetao Area in China and Bohai Bay, the lower reaches of the Yangtze River and Guanxi province(in the Yellow-Huaihe River Valley and the upper and middle reaches of Yangtze River).(2) The negative correlation are found in the CLFO between Indian Ocean and MC. Similarly to the CLFO in Indian Ocean, the apparent CLFO exists in MC with a period of30～60days as derived from Outgoing Long-wave Radiation data from April to September. The CLFO of OLR is found to propagate eastward in tropic, and also have a phase propagation in meridional, exciting the EAP wave train (P-J Teleconnection) which results the position variations of Subtropical high, South Asia high and related convergence and divergence regions, leading to abnormal distribution of the summer precipitation in China. In the peak (valley)phase, less(more) precipitation can be observed in both regions of the South of the Changjiang River valley and Hetao Area in China. More(less) precipitation can be found in southwestern China, Qinghai and Gansu provinces. In transition phase from valley to peak of CLFO of OLR, the convergence takes place in the upper and middle reaches of Yangtze River and Jilin Area, which facilitates more rainfall in these regions. Meanwhile, less rainfall is received in the Yellow-Huaihe River Valley and the Yunnan-Guizhou Plateau.(3) The CLFO of convective activity in Kuroshio area are found with the strongest variance on40-90day oscillations from April to September. This CLFO shows a westward propagation in latitudinal and northward propagation in meridional. In different phases, the low-frequency circulations and heating fields indicate shifts of Rain belts in China. From phase1to4, rainbands shifts northward from the south coast of China to Huang-Huai River Basin. In period from phase5to8, the negative rainfall anomalies are observed in southern China and then the anomalous dry area enlarges and migrates northward. The abnormal distributions of rain belts as mentioned aboved are possibly induced by the variations of the CLFO circulation systems(anticyclones and cyclones) and the associated convergence and divergence. |
