Diagnosing Convective,Large-scale Processes In Atmospheric Hydrologic Cycle Of A Coastal Mangrove During Summer Using Water Isotopes

The application of water isotopes promotes the research of atmospheric hydrologic cycle.This paper utilizes water stable isotopes to study atmospheric water cycle of a coastal mangrove during summer in Gaoqiao,Zhanjiang,Southern China,including the influences of convective rainfall and large-scale moisture transport.The research is aimed at providing detailed information about water cycle study in mangroves,helping understand deeper the atmospheric hydrologic cycle in these regions,so as to protect mangroves and make better use of the resources here.The author went to Gaoqiao Mangroves in July,2017,using Picarro CRDS to collect water vapor isotopic measurements.From q-6 diagram it is found that local vapor was influenced by rainfall reevaporation and mixing of transport moisture.Vapor isotopic ratios were highest right after noon on average,while lowest before sunrise,indicating an evident diurnal cycle.Combining information from vapor and rainfall isotopes,it is found vapor and rainfall was in near-equilibrium,while kinetic processes still existed,with relative humidity and temperature playing important roles.By analyzing rainfall rates and GPM precipitation distribution,the author finds that the rainfall events with obviously decrease of vapor isotopic ratios correspond to more organized and deeper convective systems.A typhoon is found to pass the surrounding waters and greatly reduced the vapor isotopic ratios on 15-16th in that month through analysis of wind fields and vapor distribution.Using Lagrangian method and FLEXPART model to trace the 5-day and 10-day back trajectories for the whole period and for rainfall events and applying the Sodemann method to calculate the moisture contribution,it is found that the South China Sea,the Indo-China Peninsula,lands near the site,the Indian Ocean,the Pacific Ocean were the major moisture sources during whole period,with over 90%of average overall contribution.For rainfall events,nearly 70%of moisture contribution was from above boundary layer top.The Indian Ocean as well as the Pacific Ocean contributed more than 27%and 16%,while continental contribution was almost zero,indicating the dominance of oceanic moisture sources.Through the sensitivity analysis,it is found that the number of particles has few influences on the results,while the underestimate of boundary layer height will be likely to reduce them.By projecting vapor isotopic measurements to moisture contribution,it is found that isotopes could well preserve the information of specical synoptic events.Combining data from isoGSM and FLEXPART outputs,the author calculates the isotopic variation along trajectories,finding that vapor isotopic ratios decreased dramatically with the increase of transport distance.During the study period,the South China Sea,lands near the site,the Southeast China,the Eurasian inland and the Philippine islands expressed positive isotopic contribution.The vapor from southeast Pacific ocean was of lower isotopic ratios,while southwest Indian ocean higher.Comparing the simulated isotopic values from large-scale transport and the observed ones,the author finds no obvious correlation between them.Further sensitivity studies are necessary to improve the pilot analysis of reconstructing the large-scale transport component of the local variations in isotopic composition.