摘要
Using the 1979-2009 NCEP/NACR reanalysis data and precipitation records in East China, research is performed of the climatological features of low-frequency oscillation(LFO) in OLR over the Maritime Continent(MC) as well as their associations with precipitation disturbance in the eastern part of China. Results suggest that in the MC there is significant climatological low-frequency oscillation(CLFO) in outgoing long-wave radiation(OLR), with the intraseasonal oscillation(30-60 days) being the strongest for April-September, and the MC acting as a high-value region of percentage contributions of low-frequency OLR variance. On the low-frequency time scale there occur four events of more intense active OLR during this time interval. In the January-April(May-August) phase, MC convection is relatively weak(vigorous). The CLFO makes pronounced eastward displacement at tropics, with phase propagation seen longitudinally, too. There occur low-frequency disturbance circulations similar to the EAP wavetrain or P-J teleconnection,starting from the MC via the South China Sea and the Philippines to the Yangtze valley of China. At different phases,the variation in the low-frequency circulations and heating fields shows that the rainfall disturbance in eastern China is likely to be under possible effects of the CLFO from the MC in April-September, and the low-frequency heating variation exhibits a meridional pattern as an EAP wavetrain or P-J teleconnection. As the OLR CLFO is in a peak(valley)phase the low-level divergence or convergence with the reversal at high levels over the MC is related to relatively feeble(robust) low frequency convection, thereby exciting an EAP or P-J wavetrain from the MC to the Sea of Japan. At the higher levels, the South-Asian high is eastward(westward) of normal due to effects of low-frequency cyclones(anticyclones), resulting in less(more) rainfall in the Jiangnan(areas in the middle and lower reaches of Yangtze and to the south of the river) and Hetao(the Great Bend of Yellow River) areas, and increased(decreased) rainfall in SW China,Qinghai Plateau and Gansu. At the conversion phases, low-frequency convection becomes more active in parts of the MC, consequently exciting low-frequency wavetrain of cyclones-anticyclones-cyclones at low levels, making the South-Asian high southward of the mean, so that strong convergent zones emerge in the upper and middle Yangtze basins and Jilin of NE China, responsible for plentiful precipitation there in sharp contrast to the rainfall over the band between the Yellow and Huaihe Rivers and the Yunnan-Guizhou Plateau. These results help understand in depth the climatological LFO characteristics and the phase-locked feature, thereby further improving our understanding of the causes of rainfall disturbances in different parts of the country.
Using the 1979-2009 NCEP/NACR reanalysis data and precipitation records in East China, research is per- formed of the climatological features of low-frequency oscillation （LFO） in OLR over the Maritime Continent （MC） as well as their associations with precipitation disturbance in the eastern part of China. Results suggest that in the MC there is significant climatological low-frequency oscillation （CLFO） in outgoing long-wave radiation （OLR）, with the in- traseasonal oscillation （30-60 days） being the strongest for April-September, and the MC acting as a high-value region of percentage contributions of low-frequency OLR variance. On the low-frequency time scale there occur four events of more intense active OLR during this time interval. In the January-April （May-August） phase, MC convection is relative- ly weak （vigorous）. The CLFO makes pronounced eastward displacement at tropics, with phase propagation seen longi- tudinally, too. There occur low-frequency disturbance circulations similar to the EAP wavetrain or P-J teleconnection, starting from the MC via the South China Sea and the Philippines to the Yangtze valley of China. At different phases, the variation in the low-frequency circulations and heating fields shows that the rainfall disturbance in eastern China is likely to be under possible effects of the CLFO from the MC in April-September, and the low-frequency heating varia- tion exhibits a meridional pattern as an EAP wavetrain or P-J teleconnection. As the OLR CLFO is in a peak （valley） phase the low-level divergence or convergence with the reversal at high levels over the MC is related to relatively fee- ble （robust） low frequency convection, thereby exciting an EAP or P-J wavetrain from the MC to the Sea of Japan. At the higher levels, the South-Asian high is eastward （westward） of normal due to effects of low-frequency cyclones （anti- cyclones）, resulting in less （more） rainfall in the Jiangnan （areas in the middle and lower reaches of Yangtze and to the south of the river） and Hetao （the Great Bend of Yellow River） areas, and increased （decreased） rainfall in SW China, Qinghai Plateau and Gansu. At the conversion phases, low-frequency convection becomes more active in parts of the MC, consequently exciting low-frequency wavetrain of cyclones-anticyclones-cyclones at low levels, making the South-Asian high southward of the mean, so that strong convergent zones emerge in the upper and middle Yangtze basins and Jilin of NE China, responsible for plentiful precipitation there in sharp contrast to the rainfall over the band between the Yellow and Huaihe Rivers and the Yunnan-Guizhou Plateau. These results help understand in depth the cli- matological LFO characteristics and the phase-locked feature, thereby further improving our understanding of the causes of rainfall disturbances in different parts of the country.
基金
Natural Science Foundation of China(41330425,41175062,40475028)
Jiangsu PAPD Project
Jiangsu"Qinglan"Project for Activating Research Teams
