Impact of the Radiosonde Observations of Cold Surge over the Philippine Sea on the Tropical Region and the Southern Hemisphere in December 2012

The impact of the radiosonde observations of cold surge over the Philippine Sea on the tropical region and the Southern Hemisphere has been investigated by the assimilation of radiosonde data obtained during the R/V Hakuho Maru cruise KH–12–6 in late December 2012. After assimilating the observation data, the modified surface winds of the cold surge were generally stronger than those before the assimilation. In addition, cyclonic rotations around the 4 developing tropical cyclones in the Northern and Southern Hemispheres were more intensified. Furthermore, the analysis errors over the Indian Ocean and the Pacific Ocean in the Northern and Southern Hemispheres were reduced by 1 to 10%.The impacts of the additional radiosonde observations in the cold surge immediately propagated up to the updraft region near the equator and to the mid-latitude downdraft regions through the local Hadley circulation. After the impact spread in the lower troposphere, large impacts were deepened around the tropical cyclones and depressions within 2 days. The propagation process of the additional observation impact over the Philippine Sea suggested that the cold surge could affect large-scale circulation, including typhoons and tropical depressions in the tropics and the mid-latitude regions.