Using EnOI Data Assimilation Method To Assimilate Ocean Fields Under Typhoon Conditions

So far,most research on ocean data assimilation targets at circumstances under normal conditions instead of ocean influenced by typhoon.As a most powerful weather phenomena,typhoon forces ocean in its unique way——the stirring and pumping may change salinity and temperature of deep ocean.Therefore,EnOI scheme may be different when typhoon is involved,especially it is rare to do data assimilation beneath subsurface of ocean.Furthermore,researchers always be faced with lacking of ocean observing data under typhoon conditions,here we have observations of South China Sea Intensified Buoys Array launched by 973 national project of “The phenomenon and mechanism of unusual changes before and after typhoon landing”.And the 15 th typhoon in2014——typhoon Kalmaegi happened to pass the center of South China Sea Intensified Buoys Array,which provide us advantage to carry out data assimilation.This paper imported data assimilation system from Institute of Atmospheric Physics and calculated a new inflation coefficient scheme from model static samples simulated under typhoon conditions.And then we assimilated satellite observing sea surface temperature data.The analysis fields were verified by observations of South China Sea Intensified Buoys Array and then analyzed deeply.The result indicates that new coefficient differs from traditional coefficient in many ways which mainly manifest as new coefficient increases faster when depth varies from 0 to 200 meters,thus reaches higher values,and then decreases faster when depth ranges from 200 to 350 meters.The result also showed that new EnOI scheme improved efficiently the analysis fields of upper ocean under typhoon conditions,and the standard deviation between analysis fields and observation reduced0.49 ?,the standard deviation between analysis fields using old inflation coefficient scheme reduced 0.11?.On the other hand,Second,to better simulate the dynamic process of ocean influenced by typhoon,a new drag coefficient scheme of C_D considering sea spay layer on sea surface was established.It is found that the new scheme of C_D increases slowly and even decreases slightly under high wind condition,which is consistent with recent observations.Then,a new C_D scheme and traditional C_D scheme were applied to POMnumerical experiments and the results showed that the responses of upper ocean on temperature are more reasonable with weaker cooling rate of sea temperature and thermocline strength,smaller depth deepening of mixed layer in the upper ocean if using the new drag coefficient scheme.