Tentative analysis on multi-typhoon characteristics and atmospheric circulation background in the midsummer of 2012

Tentative analysis on multi-typhoon characteristics and atmospheric circulation background in China between July and August in 2012 is performed with the data of serially numbered typhoons in northwestern Pacific,outgoing long-wave radiation(OLR) data from NOAA,sea surfer temperature(SST) data and NCEP/NCAR reanalysis dataset.Conclusions are drawn that the typhoons originated and landed mainly in the period from mid-July to the end of August in China,and it is unusual that the percentage of typhoon landing is high and the area affected by typhoon is large.Atmospheric circulation characteristics in the period mainly show the stronger South Asian High,the two ridges and one trough pattern with a ridge in the Northeast China over the mid-and high-latitudes and the western Pacific subtropical high(WPSH) stabilized with increased intensity and more westward and more northward location.The ridge of WPSH locating in the north of 30°N is in favor of the genesis of typhoon and its south border moving northerly is in favor of formation of some typhoons in the higher latitudes,and more typhoons make landfall easily when the western extension index is continuously higher.The strengthen of East Asian summer monsoon,position changes of ITCZ,positive anomalies of SST over western Pacific and negative anomalies of OLR may be the reason to lead to the frequent occurrence of typhoon.And the extending northerly of north border of anomaly regions results in the origination of typhoons at the northerly latitudes probably.