East Coast Of Japan Sea Surface Temperature Anomaly On The Early Summer Okhotsk High-pressure Impact

Using NCEP/NCAR monthly reanalysis geopotential height data and Sea SurfaceTemperature(SST) data from Hadley Centre, we analyzed the large scale circulationbackground in favor of the formation and the maintenance of the Okhotsk high andthe relationship between which and the preceding and simultaneous SST over thenorth Pacific with the method of the SVD and correlation technique. Then, basedupon the diagnostic results, we simulated the impact of the anomaly of the SeaSurface temperature (SSTA) off the east coast of Japan on the Okhotsk high in earlysummer using NCAR CAM3 AGCM model. At last, we selected the Okhotsk high inJun 1998 as a typical example, diagnosed the abnormal circulation characterstics andthe relationship between which and the simultaneous SSTA, and simulated itcombined with numerical model. The main results as follows:(1) There is a close relationship between the Europe-Asia atmospheric circulationin Jun and the preceding and simultaneous SST over the north Pacific. the "+-+" pattern of geopotential height anomaly crossing Eurasia in themid-high latitudes is the typical spatial distribution pattern. In the precedingautumn and winter, the SSTA distribution with the El Nino pattern has theclose relation with the later abnormal atmospheric circulation in June. But,during the period from preceding spring to simultaneous time, the SSTA offthe east coast of Japan might contribute to the formation and the developmentof the Okhotsk high in June.(2) The index of Okhotsk high(OKHI) has an obvious inter-annual andinter-decadal variations. During the period from 1951 to 2000 AD, there arenine blocking years and eight anti-blocking years. During the period prophaseof 1950s and after 1980s, the OKHI is positive, and Okhotsk high is active.Then, from late 1950s to early 1980s, the OKHI shows negative value i.e. thefrequency of Okhotsk high occurred is low. When the Okhotsk high maintains,there is an evident positive geopotential height anomaly and the anticyclonicabnormal atmospheric circulation around the Okhotsk sea and the contraryabnormal circulation off east coast of Japan. The results indicat that the "+-+" pattern of geopotential height anomaly crossing Eurasia in themid-high latitudes and from high to low latitudes over the East Asia are infavor of the formation and the maintenance of the Okhotsk high.(3) The analytic results of OKHI in June and the preceding and simultaneousSSTA over north Pacific show that there is a close relationship between theOkhotsk high and the SSTA over the tropical middle-east Pacific, aroundPhilippines and the east coast of Japan. In the preceding autumn and winter,the SSTA over the tropical middle-east Pacific is evident. But, during theperiod of preceding spring and simultaneous time, The influence of the SSTAoff the east coast of Japan to the Okhotsk high becoming evident. Afteranalyzed the relationship between the SSTA off the east coat of Japan and thesimultaneous Okhotsk high in detail, it indicated that the large negative SSTAmight bring the positive geopotential height anomaly over the Okhotsk sea,which might contribute to the formation and the development of the Okhotskhigh.(4) In order to confirm the analysis results, using NCAR CAM3 model, wedesigned the control and sensitive experiments. Through the comparebetween the control experiment and NCEP/NCAR data, it indicated that theCAM3 model could describe the global large scale atmospheric circulation inJune preferably, and the mid-high latitude condition better. The results of thesensitive experiments showed that the negative SSTA off the east coast ofJapan could result in the significant positive 40-60gpm 500hPa geopotentialheight anomaly over the Okhotsk Sea and the negative anomaly off the eastcost of Japan which might contribute to the formation and the development ofthe Okhotsk high in June.(5) In Jun 1998, there was strong blocking high around the Okhotsk sea, and theatmospheric circulation was identical to the compositive results of blockingyears. In the field of the simultaneous SSTA over the north Pacific, there wasobvious negative SSTA whose maximum was above 1.5℃ off the east coastof Japan, and we add which on the climatic SST in the model to design a newsensitive experiment. The simulation showed that there were evident positivegeopotential height anomaly and the anticyclonic circulation anomaly aroundthe Okhotsk sea from high level to lower, but the situation off the east coastof Japan was reversed, which accord to the condition of blocking years couldavail the formation and development to the Okhotsk high in June.