Water Vapor Transport Characteristics Of Atmospheric Precipitation In Jinhua Area From 2016 To 2018

Based on NCEP reanalysis data of 2016-2018 and precipitation data of the same period as well as HYSPLIT 4.9 model,this paper analyzes the water vapor sources and transport characteristics of monthly precipitation and their effects on precipitation in Jinhua area from 2016 to 2018,and quantitatively calculates the water vapor transport channels and their contribution rates of precipitation in different periods in Jinhua area.In addition,combined with the characteristics of 850 hPa transport flux field,this paper discusses the differences of water vapor transport in different periods.At the same time,in order to deepen the understanding of extreme precipitation,the water vapor transport characteristics of typical abnormal precipitation events are analyzed by taking two rainstorm events in the Mei-yu period of 2017 in Jinhua area as an example.The main conclusions are as follows:(1)The water vapor source and migration path of the monthly precipitation in the study area from 2016 to 2018 were closely related to the monsoon circulation,and there were differences in water vapor source and migration trajectory at different altitudes.The water vapor source and migration path of the low-level 700m-high precipitation had obvious seasonal changes.In winter,the water vapor mainly caame from the cold air mass from the south of the mainland;in summer,the water vapor mainly came from the South China Sea and the Western Pacific Ocean.The airflow trajectory in the 1500m-altitude layer was more complicated,and the water vapor originating from the coastal waters and local areas in China was relatively large,while the water vapor in the 3000m-altitude layer was greatly affected by the southern branch airflow of the westerly belt and the South Asian monsoon transport.In addition,the change of monthly precipitation during the monitoring period was closely related to the source and trajectory of water vapor.The increase and decrease of water vapor transport in the low latitude sea(South China Sea-Bay of Bengal and Western Pacific Sea)directly affected the amount of precipitation in the same period.(2)There are four main water vapor transport channels for precipitation in the study area from 2016 to 2018,namely,the Western Pacific,the South China Sea-Bay of Bengal,Eurasia and local channels.However,there were differences in water vapor transport channels and their contribution rates in different periods.During the transition period of winter and summer monsoon(April-May),the main water vapor channels of precipitation in 2016 and 2018 were the West Pacific and the South China Sea-Bay of Bengal;while the main water vapor channels of precipitation in 2017 were the Northwest Pacific and local channels,and the transport of warm and wet currents from South China Sea monsoon and Indian southwest monsoon was less than that in the same period of 2016 and 2018,which also led to a significant reduction of precipitation in April-May of that year.In summer(June-August),the South Asian monsoon and the South China Sea monsoon had strong influence on the study area.The South China Sea-Bay of Bengal was the main water vapor channel,but the water vapor contribution rate of this channel was different in 2016-2018,67.35%,71.8% and 55.40% respectively,which were consistent with the changes of precipitation in the same period.During the transition period of summer and winter monsoon,influenced by typhoons,the western Pacific Ocean was the main water vapor channel of precipitation in the study area in 2016,with a contribution rate of 60.25%.The main water vapor channels of precipitation in 2017 were the South China Sea-Bay of Bengal and the Northwest Pacific,with contributions of 46.07% and 41.22%,respectively.The water vapor channels of precipitation in 2018 were the South China Sea and Eurasia,with contributions of 56.82% and 43.18%,respectively.In 2018,the influence of Mongolian-Siberian downward cold air mass was enhanced,that is,the transition time of summer and winter monsoon was earlier in the study area in 2018,and the influence of winter monsoon was stronger.(3)Through the analysis of the two rainstorms in the Mei-yu period of 2017 in the study area,it was found that the water vapor channels of the two rainstorms were the Western Pacific,the South China Sea-Bay of Bengal and the local channel respectively.Among them,the ocean water vapor from the West Pacific and the South China Sea-Bay of Bengal was mainly concentrated in the lower troposphere,which was the main water vapor source area of heavy rain;while the water vapor in the local channel was concentrated in the middle troposphere or above,and the specific humidity of air flow was low,and its contribution rate of water vapor was low.In addition,there were differences in water vapor sources and transport processes between the two rainstorms.During the 6.12 rainstorm,due to the influence of typhoon “Miaobai” and the airflow transport of the western edge of Subtropical High,the east-leaning water vapor from the tropical western Pacific and the South China Sea transported anomalous airflow,and enough water vapor was transported into the study area,indicating that water vapor transport of the East Asian monsoon was strong;during the 6.24 rainstorm,the strong southwest airflow from the Arabian Sea-Bay of Bengal and the airflow on the west side of the Subtropical High converged in the northern South China Sea and transported into the study area,indicating that the southwest airflow affected by the South Asian monsoon provided sufficient water vapor for the heavy rainfall,while the influence of the East Asian monsoon was relatively weak.