| The characteristics of stable isotopic composition of precipitation in monsoon region reflect the formation,transport and falling process of precipitation moisture,which is the result of many factors,such as the climatic and environmental characteristics of the monsoon region,the evaporation intensity of the tropical ocean,the atmospheric circulation and so on.It covers a great deal of climate information from the tropical ocean to the interior of the continent,from the sea level to the upper air,and also records the specific models and evolution processes of the water cycle and atmospheric cycle.In-depth study of precipitation stable isotope composition and its changes in the monsoon region,provides important theoretical support and basis for inverting paleo-environmental characteristics,discussing meteorological changes and paleoclimate restoration,and also has guiding significance for dealing with global changes and the planning of ecological environment in contemporary areas.In this article,based on the continuous sampling and monitoring of stable isotopes of atmospheric precipitation in Chenggong District of Kunming City from April 2013 to September 2017,analyze the stable isotopic characteristics of precipitation in Chenggong area of Kunming City and discuss the degree of influence of some meteorological factors on the isotopes of local precipitation.At the same time,according to the precipitation data of other cities provided by GNIP,discuss the influence of different water vapor sources on the stable isotopes of precipitation in Chenggong area and resolve the characteristics of the main water vapor source paths.The preliminary conclusions are as follows.(1)The water vapor sources are different in different seasons in Chenggong area,and the difference of water vapor sources determines that the change of precipitation season is very obvious.On the whole,the isotopic composition of precipitation in rainy season(May to October each year)is negative,and that of precipitation in dry season(Every year from November to April next year)is more positive.The stable isotopes of local precipitation are influenced by meteorological factors and shows obvious precipitation effect.The precipitation effect appears on the annual scale,monthly scale and day scale,but the effect of temperature is small.(2)In the continuous precipitation event lasting two days or more,through our analysis find that there is a "reverse precipitation effect" phenomenon that the precipitation on the next day is relatively small but the precipitation isotope is more negative,which is the result of the constant depletion of isotopes of water vapor under gravity fractionation.This kind of dilution can also be seen in a day of continuous precipitation.(3)The water vapor from the Siberian monsoon in winter has lower isotope ratio and higher d-excess.Under the influence of quasi-stationary front,it is very difficult for cold air to reach Chenggong area.In the year of strong cold air,precipitation in Chenggong area is affected by Arctic water vapor,the isotopic composition is negative and it has the higherd-excess.Every summer,typhoon from the Pacific Ocean bring large amounts of precipitationto the Chenggong area,and its isotopic composition is relatively low.The influence of ENSO events on the isotopic composition of precipitation in this area is more obvious in winter than in summer.The precipitation formed by different water vapor sources has obvious differences in atmospheric waterline and d-excess.(4)Because ofthe distribution of precipitation isotopes in the southwest monsoon region has intense spatial characteristics.The isotopic composition of monsoon precipitation decreases along tropical islands,tropical coastal cities,peninsula cities and inland cities this order.It shows a more prominent continental effect,which is caused by the constant gravity fractionation of the monsoon water vapor during the migration process.(5)The water vapor in the Indian Ocean mainly comprise two water vapor channels in the Bay of Bengal and the Arabian Sea,and water vapor in the Bay of Bengal is the main source of water vapor in Chenggong region and southwest China.The water vapor of the Arabia sea channel is blocked by the mountain range,which has little influence on the precipitation in Chenggong area,besides,the precipitation in this area is more negative. |
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