Atmospheric Circulation Characteristics Of Extreme Cool Event Over The Northeastern China In The Summer And Related Physics Processes

In this study, the1948-2009daily NCEP/NACR reanalysis daily data andtemperature data from150meteorological stations in the Northeast China are employed.Definition of synoptic and climatic extreme cool events were given. The space-timestructure of extreme cool event were given on the daily, monthly and seasonal time scale.The variation characteristics of atmospheric circulation and sea surface temperature inprophase and simultaneous time were analyzed, meanwhile the dynamic mechanism ofextreme cool event in the Northeast China were researched too, some results were foundas following:1. Owing to the150observatory stations temperature in Northeast China of Junecorrelated significantly with that of the whole summer, also, correlated significantly withthe average temperature of July and August, therefore, the various temperature of June canbe used as a predictor to the whole summer in Northeast China. Besides, the second andthe third kind of synoptic extreme cool events were the major kind in these events, whichmeant that large-scale extreme cool events played a dominant role among them. Therewere total31years occurred synoptic extreme cool events,29years occurred extrememonthly cool events, and11years occurred extreme cool seasonal events, which meantthat the event of extreme cool monthly event needed more fastidious conditions than thatof extreme cool synoptic events, and the extreme cool seasonal event was in a more lowfrequency among them.2. The influence scope and strength of extreme cool events was determined by theplace disposition of blocking high and cold vortex. There is closely relationship betweenOkhotsk blocking high and extreme cool event occurred in Heilongjiang province. On thecondition that Baikal and Okhotsk blocking high matched very well, and cold vortex wasfurther south, the third kind cool extreme event was liable to occur. On the climate meanstate, a dipole of north blocking high and south cold vortex prevailed in the region ofNortheast Asia. Due to the in phase force of Rossby wave perturbation, a wave train ofnorth “+” and south “-” was strengthened which benefited for occurrence of anomalouscirculation over local region, in addition, a pattern of trough-range-trough occurred overthe area from Northeast Asia to Northwest Pacific. Basing on the favorable conditions mentioned above, the extreme cool event was liable to occur. Vertical profile showed thatthere was a strong ascending motion in troposphere once extreme cool events happenedespecially in the third kind cool event, yet, the cold advection was the main factor to thefirst and second kind cool events. As refer to mechanism of the warm event, it wascontrary to the cool mentioned above.3. The year1964that reported high cool summer incidence and the year1993thatsaw low cool summer incidences are different only in basic atmospheric modeconfiguration, with their major North Pacific SST phases close to one another. Comparedwith the preceding winter, the spring of1964reported a reversed phase realignment of thePacific polar vortex index, NPO/NAO, westerly drift zone, and the central and easternequatorial Pacific SSTA. However,1993enjoyed a consistent picture in both the precedingwinter and in the spring followed. As a result, the opposite phases of major air-sea systemmodes in the spring of two individual years would naturally produce an evolution (fromthe spring to the summer) that cannot see eye to eye. For example, the spring of1964reported a very weak Pacific polar vortex, with NPO in a typical negative phase, thewesterly drift zone in a strong warm phase, and the central and eastern equatorial PacificSSTA in La Nina phase. The spring of1993, however, told a different story, where thepolar vortex was strong, and NPO sat in a typical positive phase, with the westerly driftzone in a zero phase and the central and eastern equatorial Pacific SSTA in an El Ninophase. Entering the summer, the westerly drift zone was positioned in a noticeably coldphase and the central and eastern equatorial Pacific SSTA in a weakened El Nino phase.However, unusually cool summer occurred all the same in both individual years,regardless of the difference between the two. It is worth mentioning, however, that in thespring of1964, a weak polar vortex and a typical negative NPO worked with the warmwesterly drift zone and the La Nina oriented central and eastern equatorial Pacific SSTA tocreate a dominating Okhotsk blocking high (eastern blocking) in the coupled air-seaprocess from the spring to the summer. The northeast cold vortex had its positive vorticitymainly from the western path, and from the low-latitude transport as well. However, in thespring of1993, the strong polar vortex area and positive NPO phase collaborated with thezero phase of westerly drift zone SSTA and the El Nino oriented central and easternequatorial Pacific SSTA to stage a Ural blocking high (western blocking), with thenortheast cold vortex having its positive vorticity mainly from the westbound retreatingultra long-wave disturbance trough (eastern path) in the central North Pacific, and fromhigh latitude transport as well.