| Water vapor and precipitation participate in the global water cycle,which has become a hot topic.The latent heat energy released during the phase transition changes the general circulation,absorbs long-wavelength radiation and affects Earth's radiation budget.Precipitable water(PW)describes the column-integrated water vapor.Studying atmospheric PW is a way to understand the distribution of water resource in the air and PW is a good indicator of precipitation.Atmospheric temperature and humidity are the foundation of PW and precipitation during water cycle.Moreover,temperature and humidity interact with PW and precipitation.On the other hand,East Asia is located in a special region.The climate is controlled by monsoon,which leads to the variability of PW and precipitation in this region.At present,the research on atmospheric parameters(atmospheric temperature and humidity),PW and precipitation needs to be further explored,particularly in mainland China which is closely related with our life.Therefore,climatic characteristics of temperature,humidity,PW and precipitation are systematically analyzed in this paper.Meanwhile,linear trend and correlation among atmospheric parameters,PW and precipitation is investigated.Additionally,in order to understand the thermal and dynamic structure of climate in mainland China,the characteristics of frequent extreme precipitation in recent decades and the response to atmosphere are discussed.1.Characteristics and trends of atmospheric precipitable water distributionVariations and trends of atmospheric precipitable water(APW)are examined using radiosonde data from Integrated Global Radiosonde Archive(IGRA)and China Meteorological Administration(CMA)from 1995 to 2012 in mainland China.The spatial distribution of the climatological mean APW shows that APW gradually decreases from the southern to the northern regions of mainland China.The seasonal mean pattern of APW shows clear regional difference,except for higher APW in summer(June-August)and lower APW in winter(December-February).Four regions show significantly downward trends in APW.Moreover,the trends of APW calculated using reanalysis datasets are consistent with the results of radiosonde data.Furthermore,the relationship between APW and the general circulation is investigated.The summer East Asian monsoon intensity and El Nino events show positive correlations with APW,whereas the North Atlantic Oscillation shows negative correlation with APW.The downward trend of APW is in accordance with the downward trend of mean column temperature(1000-300 hPa)at most stations,which suggests that decreasing mean column temperature results in decreasing APW in mainland China.Additionally,statistical analysis has revealed the regional trends in APW are not consistent with the regional trends in precipitation,implying that not all the variation of precipitation can be explained by APW.2.Structural characteristics of different precipitation types corresponding to atmospheric temperature and humidityA merged dataset constructed from Tropical Rainfall Measuring Mission precipitation radar(TRMM PR)rain products and IGRA data is used to investigate the thermal structural characteristics of convective and stratiform precipitation in the rainy season(May-August)of 1998-2012 in three regions(Sichuan basin,Southeast China and middle-eastern China)of mainland China and adjacent ocean region(Northwest Pacific).The results show that the storm tops for convective precipitation are higher than those for stratiform precipitation,because of the more unstable atmospheric motions for convective precipitation.Moreover,the storm tops are higher at 1200 UTC than at 0000 UTC over land regions for both convective and stratiform precipitation,and vice versa for ocean region.Additionally,temperature anomaly patterns inside convective and stratiform precipitating clouds show a negative anomaly of about 0-2 K,which results in cooling effects in the lower troposphere.This cooling is more obvious at 1200 UTC for stratiform precipitation.The positive anomaly that appears in the middle troposphere is more than 2 K,with the strongest warming at 300 hPa.Relative humidity anomaly patterns show a positive anomaly in the middle troposphere(700-500 hPa)prior to the occurrence of the two types of precipitation,and the increase in moisture is evident for stratiform precipitation.3.Characteristics of extreme precipitation corresponding atmospheric temperature and humidity distributionDistribution characteristics of multi-year mean precipitation and corresponding temperature and relative humidity structure are studied comprehensively over mainland China(26°-34°N,85°-125°E).Moreover,the characteristics of extreme precipitation and corresponding temperature and humidity structure are analyzed and compared.The result shows that precipitation occurs mainly in the central,eastern China and the southern Tibet Plateau.Besides,the distribution of near-surface precipitation intensity is relatively uniform over above regions(about 4 mm/h).According to the near-surface temperature,the temperature increases from west to east(280-290 K),especially the temperature is larger than 295 K over southern Tibet Plateau.Relative humidity is higher over southern Tibet Plateau and eastern Sichuan basin,which reaches 95%.The distribution pattern of extreme precipitation sample and intensity is similar to those of multi-year mean precipitation.The percentage of extreme precipitation in precipitation mainly appears in the central,eastern China and south of Tibet Plateau,which reaches about 8%.In addition,the percentage of extreme precipitation in precipitation shows a significant change in monthly mean variation,whereas the monthly mean intensity of extreme precipitation is not obvious.Through the trend analysis,it is found that the frequent of extreme precipitation in recent 15 years has an upward trend.4.Relationship between extreme precipitation intensity and near-surface temperatureThe radiosonde data derived from IGRA,co-located rain gauge observations provided by CMA and TRMM PR observation are used to investigate the relationship between extreme precipitation intensity and near-surface temperature in middle-east China(MEC)and east Tibet Plateau(TP)during 1998-2012.How the extreme precipitation intensity responds to the change of temperature is studied in two regions.It is found that the variation of the daily extreme precipitation intensity and temperature shows a peak structure both in MEC and TP.That is,extreme precipitation intensity increases with temperature at an approximate Clausius-Clapeyron(C-C)rate below the temperature transition value.Moreover,the more intense precipitation corresponds to the closer C-C rate relationship between precipitation intensity and temperature.However,extreme precipitation intensity decreases with the increasing temperature after temperature transition value.From a thermodynamic point of view,the pattern for extreme precipitation intensity and atmospheric humidity implies that the variation of humidity dominantly affects the change of extreme precipitation with temperature in MEC and TP.In contrast,the temperature transition value differs between MEC(25 ?)and TP(15 ?).The increasing rate(regression slope)between extreme precipitation intensity and the temperature is larger in TP than that in MEC,which is probably due to different types of precipitation in two regions.Furthermore,the change of atmospheric humidity is more sensitive to temperature in TP than in MEC. |
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