Spatiotemporal Distributions Of Extreme Hourly Precipitation And Its Cloud Properties Over The Mongolian Plateau

The Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change(IPCC)points out that,against the background of global warming,the global water cycle will continue to strengthen,and extreme hourly precipitation events will become more frequent,widespread and intense,with record-breaking precipitation events occurring repeatedly.The spatial and temporal characteristics of extreme hourly precipitation(EXHP)and its formation mechanism have become a hot issue in weather and climate research,and clouds,as an important climate factor,are the main cause of precipitation changes.The observation of cloud macro-and microscopic characteristics plays an important role in the observation of high altitude clouds and precipitation on the plateau and the global water cycle.The occurrence and intensity of extreme hourly precipitation events on the Mongolian plateau are influenced by a variety of factors,and an in-depth study and exploration of the role of these factors can help to better understand and address the challenges posed by climate change.The Mongolian Plateau is one of the highly sensitive regions to global climate change,with a complex geography and diverse climate types,influenced by a variety of monsoonal climates,and highly susceptible to a variety of extreme precipitation events.Using the GPM satellite precipitation data(Global Preciptation Measurement)and ground observations as the main data sources,the extreme hourly precipitation index is defined based on the calculation of extreme hourly precipitation thresholds through the percentile method,Sen’s slope,MK test method,principal component analysis and multiple stepwise regression.Based on the analysis of the distribution characteristics of different precipitation indicators of extreme hourly precipitation on the Mongolian Plateau,the spatial distribution characteristics and long-term trends of extreme hourly precipitation events on the Mongolian Plateau are revealed.The GPM hourly satellite precipitation data are matched with the Himawari-8 cloud parameter data to analyze the spatial and temporal distribution of the total precipitation(PRCPTOT),maximum hourly precipitation(Rx1hr),intense precipitation(R95pw1hr)and very intense precipitation(R99pw1hr)and their cloud characteristic parameters such as cloud effective particle radius,cloud optical thickness,cloud top height and cloud top temperature.We also analyze the correlation between the extreme hourly precipitation index,the regional average precipitation and the extreme hourly precipitation index,and the cloud characteristics,and investigate the influence of water vapor sources,wind speed and direction,and atmospheric circulation on the extreme hourly precipitation index,and draw the following main conclusions:(1)The multi-year average extreme hourly precipitation intensity index on the Mongolian plateau from 2001 to 2020 shows a fluctuating increasing trend,and the frequency index shows a fluctuating increasing trend in the interannual variation,and its variation characteristics are similar to the extreme hourly precipitation intensity;there are three peaks in the interannual variation of both the hourly precipitation intensity(SDII)and the severity index(EPSI),and the extreme hourly precipitation The severity of extreme hourly precipitation events increases year by year.The extreme hourly precipitation shows obvious seasonal and regional distribution characteristics,with precipitation mainly concentrated in summer,slightly increasing in spring,and decreasing in winter,reaching the lowest level among the four seasons.The extreme hourly precipitation indices all show a decreasing trend from northeast to southwest,and the intensity index in Inner Mongolia is significantly higher than that in Mongolia,and the Daxinganling region is always the most dramatic zone in terms of average hourly precipitation intensity and severity changes.(2)The extreme hourly precipitation intensity index and its cloud effective particle radius(CLER_P),cloud optical thickness(CLOTP),cloud top height(CLTH_P),and cloud top temperature(CLTT_P)on the time scale of the Mongolian plateau from 2016 to 2020 increase with the precipitation index,while the cloud optical thickness,cloud top height,and The trends of cloud effective particle radius,cloud optical thickness,cloud top height and cloud top temperature are similar for the same seasons,while cloud top temperature decreases with the increase of precipitation intensity(except for hourly maximum precipitation).The spatial scale has obvious regional and seasonal characteristics,and the precipitation intensity index shows a decreasing trend from northeast to southwest,with the Inner Mongolia region being significantly higher than Mongolia,and all reaching larger values in summer and lowest levels in winter in all seasons.(3)The extreme hourly precipitation on the Mongolian plateau is influenced by several factors,including the interaction between the extreme hourly precipitation indices,the regional average precipitation,cloud characteristics parameters and water vapor originated from the atmospheric circulation.It was found that there were significant positive correlations among the extreme hourly precipitation indices and with the annual average precipitation,and positive correlations between the total precipitation and the cloud characteristics parameters.Through multiple stepwise regression analysis,it is found that the cloud top height of cloud characteristics has a greater influence on the extreme hourly precipitation index.The distribution of highland water vapor shows obvious regional and seasonal characteristics,with the highest distribution of highland water vapor in summer and the lowest in winter.It is also found that the extreme hourly precipitation index has a significant negative correlation with some circulation indices,and a significant positive correlation with the East Asian trough intensity index and the Tibetan plateau-2 index.