Spatial And Temporal Analysis Of850hPa And500hPa North Pacific Subtropical High In Summer

North Pacific subtropical high (referred to as NPSH) is closely related to weather, climatechange of China.Northern Hemisphere subtropical high layers have the unique nature of theannual and seasonal scales.Early research aimed at500hPa NPSH,due to the850hPa NPSH isthe main channel for the transportation of water vapor to the East Asia, so in-depth study on850hPa NPSH is also very important. The paper selects850hPa and500hPa NPSH as a clue,defining the area index(referred to as IA), intensity index (referred to as II), the ridge lineindex (referred to as IR) and the northernmost position index (referred to as IN) of NPSH,using the moving average, wavelet analysis, correlation analysis methods to analyze of annualmean, monthly mean, annual variation and decadal variations characteristics of the NPSH inthe summer of1951-2010. Since then, combined with four classifications of850hPa and500hPa NPSH II anomaly:500hPa and850hPa are both larger,500hPa and850hPa are bothsmaller,500hPa is larger while850hPa is smaller,500hPa is smaller while850hPa is larger(referred to as LL, SS, LS, SL type), This work uses the composite analysis, T-test methods tofocus on the characteristics of atmospheric circulation and the North Pacific SST configurationwhen850hPa and500hPa NPSH II are in-phase and anti-phase.The conclusions are asfollows:1. Annual variation characteristics: the area index and intensity index of middle-leveland low-level NPSH are single peak, the peak is in July,850hPa (500hPa) NPSH in July andAugust (June and July) are stronger; the peaks of IR and IN index appears in August.Theclimatic characteristics of850hPa (500hPa) NPSH in July and August (June and July) aresimilar.2. The standard deviation characteristics: in JJA the standard deviations of500hPaNPSH geopotential height are larger, indicating that500hPa NPSH is more active in summer.In summer, the standard deviations of850hPa (500hPa) NPSH are significantly different,which are both most similar to the seasonal mean in July, the NPSH in JJA need to bediscussed separately. 3. The decadal variation characteristics: in June and July, mutations of IA and II indicesof500hPa NPSH are in1978, the phase of IR index is contrary, however, these features of850hPa NPSH are not obvious.4. NPSH indices characteristics: the changes of IA and II of NPSH are very consistent inJJA. The IA(II) between850hPa and500hPa NPSH are positive correlation,however,thecorrelation of their IR(IN) is not significant. The500hPa NPSH IA is crucial in June, becauseit will affect the IA in JJA and IR in June and July of850hPa NPSH.5. The periods characteristics of IA: the periods of850hPa NPSH are2~3a,5a and8~10a in June,2~3a and10a in July and2~4a in August; In addition, the periods of500hPaNPSH are3~5a in June, most significant in July including3~5a and3.3~5a and2~3a,2.5~4.5a and5~7a. in August.6. Zonal winds characteristics: in the Western Pacific equatorial region,850hPa and500hPa NPSH are positively correlated with the200hPa zonal winds in JJA.850hPa zonalwinds just are negatively correlated with850hPa NPSH; The200hPa (850hPa) zonal winds inJJA in Nino regions are mainly negatively (positively) correlated with500hPa NPSH, thecorrelation is the most significant in July; When it’s LL (SS) type, in the mid-latitude region ofWestern Pacific there is positive (negative) westerly anomaly, subtropical easterlies (westerlies)enhance at200hPa; furthermore, when LS (SL) type occurs, westerlies (easterlies) enhance at200hPa in the mid-latitude region of Northern Pacific in JJA, in Nino regions at200hPa thereare westerly anomalies in June, easterly (westerly) anomalies in July, easterly anomalies inAugust.7. Vector winds distribution: When500hPa NPSH strengthen(weaken) in JJA, Meiyufront strengthens (weakens) and moves to the north. In JJA, the cyclonical (anti-cyclonical)circulation is notable in southeastern equatorial Pacific, accompanied with strengthening(weakening) of the westerly in western equatorial Pacific, and the weakening (strengthening)of cross-equatorial flow. At low altitude, upwelling is found in Nino regions in June, whileEast Asian Monsoon strengthens (weakens) during July~August accompanied with increasingof upwelling (downwelling).8. Vertical movement: when LL(SS) type occurs in JJA, NPSH relates to downwelling(upwelling) at middle and low altitude Nino region and ITCZ. When LL(SS) type occurs during July~August, upwelling (downwelling) intensifies at tropical area in eastern Pacific, therain bands in China, and the western Pacific warm pool. In August, downwelling (upwelling)of low altitude in Nino3region is mainly related to the strengthening (weakening) of850hPaNPSH.9. Sea surface temperature (SST) distribution: when LL(SS) type occurs duringJune~August, SST in southeastern Asia and western Pacific warm pool denotes positive(negative) anomaly, and the positive and negative anomaly in middle North Pacific showshorseshoe pattern. Vertical zonal circulation with ‘’ pattern generates at equator in June,which is clockwise (anti-clockwise) in the west and opposite in the east, while ‘W’ pattern isrecognized in July and August.10. Sea surface temperature (SST) in Nino region: Nino indices are not correlated wellwith the850hPa NPSH during June~July.Positive SSTA with lead of6~16months andsynchronous negative SSTA at Nino region both tend to strengthen the850hPa NPSH inAugust of the same year.In JJA,500hPa NPSH is revealed to positively lag-correlate withNino indeices with peak correlation coefficient at September~October the year before.11. Sea surface temperature (SST) in other area:In spring, increasing of SST in westernPacific warm pool and decreasing of SST in middle and low latitude area in middle NorthPacific both strengthen the subtropical high at middle and low altitude in summer (850hPaNPSH only found during July~August). During July~August, the strengthening of500hPaNPSH will bring up the SST of western Pacific warm pool in September, and also the SST ofwesterly drift region during October~December.The strengthening of NPSH at middle and lowaltitude in summer will lead to decreasing of SST in western Pacific warm pool at the nextOctober.The positive feedback mechanism is still under investigation.