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    Cold surge event observed by radiosonde observation from the research vessel “Hakuho-maru” over the Philippine Sea in December 2012

    Ogino S-Y, Wu P, Hattori M, Endo N, Kubota H, Inoue T, Matsumoto J

    Cold surge, Air-sea interaction, Air mass transformation, Hakuho-maru, Philippine Sea, VPREX2012, AMY2007-2012

    A cold surge event observed with radiosondes from the research vessel Hakuho-maru. Horizontal map of the NCEP Reanalysis II geopotential height (color shading), temperature (black contours, in Kelvin), horizontal wind (arrows) at the 925 hPa level, and TRMM 3B42 rainfall (gray shading) at 0600 UT on December 23, 2012. The launch sites of the radiosondes from Hakuho-maru are indicated by red pluses.

    The thermal energy transfer from the sea surface to the atmosphere associated with a cold surge event was investigated with observations from radiosondes on the research vessel “Hakuho-maru” over the Philippine Sea in December 2012. These observations were analyzed, and the results were compared with those obtained from observations over the East China Sea in the Air Mass Transformation Experiment in 1974 (AMTEX ‘74). The horizontal advection of cold and dry air associated with the cold surge dominated at heights below 850 hPa. In spite of this strong advection, the local temporal variations in the temperature and moisture were small, because the advection was balanced by the transfer of heat and moisture from the sea surface, which is qualitatively the same behavior as observed during the cold surge event in AMTEX ‘74. The eddy transport of the total heat energy from the sea surface to the atmosphere was estimated at about 410 W/m2, which is about half of the maximum value of 780 W/m2 observed during AMTEX ‘74. This result shows the existence of considerable heat transfer from the sea surface to the atmosphere over the Philippine Sea, which is the downstream region of the cold surge, after it passed through the East China Sea.