Analysis And Research On The Flux Observation Of Typhoon Boundary Layer By Eddy Covariance System

The transport of momentum,energy and matter between the underlying surface and air is of vital importance to the development and dissipation of typhoons.The flux in the typhoon boundary layer is an important characteristic that characterizes this physical process.In recent years,thanks to the progress in observation technology and the development of instruments in China.The eddy covariance system and other equipment have been widely used in the flux observation and research conducted in the boundary layer.The Shanghai Typhoon Research Institute of the China Meteorological Administration(Typhoon Institute,the same below)has also carried out observation experiments on flux of typhoon boundary layer.However,the analysis and application of observation data collected by equipment such as eddy covariance system is still insufficient and urgently needs to be strengthened.In this paper,using the four eddy correlators deployed in Sansha,Pingyang,and Pingtan,their observation data during the impact of typhoons "Lekima" and "Soulik" are used to preliminarily analyze the near-surface meteorological elements change and flux exchange characteristics during the impact of the typhoon.The analysis results show that before and after the typhoon,the changes of surface meteorological elements are relatively orderly,and the near-surface meteorological elements show local effects such as sea-land breeze.the daily changes of flux are obvious with the strcture of peaks and valleys every day.During the influence period of the typhoon,the surface meteorological elements changed sharply in short time,and the momentum flux showed a "three peaks" structure during the influence period of the typhoon.The friction velocity derived from the momentum flux changes with the wind speed,using 12 m/s as the dividing line.When the wind speed is lower than 12 m/s,it shows a more obvious positive correlation,and when the wind speed is higher than 13 m/s,it gradually changes to be flat or even fallback.The drag coefficient shows an inverse relationship that continues to decrease as the wind speed increases.The energy spectrum analysis results show that the peaks mainly exist at 0.00015 Hz and 0.06 Hz,and there is a weaker peak at 0.001 Hz.As far as the contribution to energy is concerned,large-scale systems dominate,followed by mesoscale systems and turbulences.Through the sub-scale discussion,it is found that the momentum contribution of the mesoscale system accounts for about 30% of the contribution of the simultaneous turbulence,which cannot be ignored.During the influence period of the typhoon,it shows that the sensible heat flux is suppressed and the latent heat flux has increased.At the same time,both of them are affected by precipitation.The sensible heat at the moment of precipitation is show to be in a negative position,and the latent heat flux will appear high accordingly.However,when a typhoon makes landfall,the sensible heat flux will still show a weak positive value due to the heating of the warm air mass.This paper is a preliminary attempt to use the measured data of the vorticity correlator to analyze the flux characteristics of the near-surface layer during the typhoon landfall.Due to the limitation of the number of data samples,the general applicability of the conclusions and other issues still need to accumulate more data and further study to confirm.