| The IPCC’s Fifth Assessment Report claims that the global mean surface air temperature hasremained flat for the past15years, termed the global warming hiatus period. And some research resultssuggest that there is a chance that the current observed hiatus could extend for several more years. Undermentioned backgrounds, analyzing the interdecadal changes of the surface air temperature (SAT) overChina mainland anew is a potential scientific value and practical significance. Considering that thewintertime SAT is characterized by the significant interdecadal time scale, the study on which will deepthe present understanding of the global warming and promote the predictability of the future SAT. Theconclusions are derived as follows:(1) Based on the daily air surface temperature data of468meteorological observation stations inthe mainland of China from1960~2013, the spatial and temporal characteristics of winter temperatureare analyzed. Firstly, the linear regression and regime shift detection methods are used to identify thetendency and abrupt point. The result is that the winter temperature shows an interdecadal variabilitysuperimposed on the long-term warming trend, with the cold period in1960/61~1985/86, the warmperiod in1986/87~2005/06and the hiatus period in2006/07~2012/13. To understand the underlyingmechanism for the formation of the three periods, the atmospheric circulation systems are compared byusing the NCEP/NCAR reanalysis data. It is found that the cold/hiatus (warm) period is characterizedby weak (strong) zonal wind in the middle and high latitude of the Northern Hemisphere, strong (weak)East Asian Trough on500hPa geopotential height field, strong (weak) downdraft after the trough, strong (weak) Siberian High and enhanced (weakened) northeast surface wind over Asian continent.These provide favorable circulation conditions for cold (warm) winter in the mainland of China.Furthermore, by influencing the East Asian winter monsoon circulations the Northern HemisphereAnnular Mode (NAM)/Arctic Oscillation (AO) puts an impact on the winter temperature, especially thewinter minimum temperature on the interdecadal timescale.On the other hand, the Pacific Decadal Oscillation (PDO) is positively correlated to the wintertemperature on the interdecadal timescale. Subsequently, the results indicate that with the modulation ofthe interdecadal variability of the PDO the combined effects of the NAM/AO and ENSO not onlyinfluence the first EOF1mode that has an identical signal in whole China, but also influence the secondEOF mode that has a seesaw pattern between southern and northern China. In addition, thesuperimposition of EOF1and EOF2probably causes persistent warming winters in the1980s and1990s and may be responsible for the significant cooling trend during the last seven years in NorthwestChina and Northeast China. The results also point out that the NAM/AO tends to be at negative phaseduring negative phase of the PDO.(2) The paper confirms that the NAM/AO is an important factor affecting winter SAT over China.This is because that on the synoptic time scale the NAM/AO has an influence on the movement of thenear surface cold air in the Arctic, which is very important in the outbreak of the cold wave. The paperfocuses on analyzing the superior trajectory of the near surface cold air in the Arctic during the abnormalNAM/AO index events and how these cold airs can affect the SAT over China. The results show thatduring the positive NAM/AO index event, the near surface air is restricted in the Arctic and high latitudeareas, characterized by cyclonical trajectory. In this case, the Arctic cold air seldom sweeps down overnorth China so that the winter SAT is warmer than normal. During the NAM/AO index descentingphase, the circulation pattern is beneficial to intrusions of the cold air from mid-high latitudes of Europeto southern China and transporting of the water vapor from the Bay of Bengal to South China with the East European Trough and the southern branch trough deepening, which provide favorable atmosphericconditions for the low temperature weather, for example the cold wave or even snow calamity. On thecontrary, during the negative NAM/AO index event, the near surface air flows out the Arctic in theanticyclonical trajectory. At the same time, the meridional circulation pattern is intensified in themid-high latitudes. During the NAM/AO index descenting phase, the cold air can directly affect thenortheast part of China and the Mongolia Cold Wave key area. The latter cooperates with otheratmospheric circulation systems can induce cold waves in the eastern China.(3) However, the NAM/AO is not the single factor that modulating the outbreak of cold wave andother low temperature weather that are subject to many other circulation patterns. The paper analyzesthe different patterns of the strong regional prolonged low temperature events (RPLTE) in China. Theresults show the frequency and intensity of the RPLTE is higher and stronger in the cold period, whilethe frequency and intensity is lower and weaker in the warm period. So far the frequency of the RPLTEis increasing during the hiatus period. In general the NAM/AO index is negative during early andmature stage of the Northeastern type and the Eastern type of the RPLTE, while the relationshipbetween the other types of the RPLTE and the NAM/AO index is uncertain.(4) The simulated capability of6global system modes released by Coupled ModelIntercomparison Project Phase5(CMIP5) is tested for the wintertime SAT over China. The6modelscan reasonably reproduce the evolution of wintertime SAT over China during the1960~2005incapturing the long term trend of warming especially in the North China. Also, the6models can almostcapture the spatiotemporal structures of the second EOF mode that has a seesaw pattern betweensouthern and northern China. The models of BCC-CSM1.1can detect the regime shift in the EOF1corresponding normalized time coefficient of the wintertime SAT over China.6model scenarioprojections of future climate change during2006~2035indicate that the wintertime SAT over Chinawould continue to rise, while the intensities are scenario-dependent. The results indicate that the wintertemperature shows an interdecadal variability superimposed on the long-term warming trend, with thehiatus period ending around2010~2025. After that the wintertime SAT over China will increase warming. |
PDF Full Text Request