P3.17
Cirrus observations in the tropical tropopause layer over the western Pacific
Masatomo Fujiwara, Hokkaido University, Sapporo, Hokkaido, Japan; and S. Iwasaki, A. Shimizu, M. Shiotani, H. Matsuura, Y. Inai, F. Hasebe, I. Matsui, N. Sugimoto, H. Okamoto, K. Yoneyama, A. Hamada, N. Nishi, and F. Immler
Cirrus clouds in the tropical tropopause layer (TTL), between ~14 and ~17 km, are keys for the dehydration of the air entering the stratosphere and for the Earth's radiation budget. In this presentation, we will discuss the three-campaign results of ship-borne lidar measurements over the western Pacific, and emphasize the important role of equatorial Kelvin waves in controlling the TTL cirrus. Diurnal variation of TTL cirrus will also be documented.
A polarization lidar at the wavelengths of 1064 nm and 532 nm was continuously operated on the Japanese research vessel Mirai in three one-month campaigns. The locations and time periods are (1) 2.0N, 138.0E, 9 Nov. to 9 Dec. 2001, (2) 2.0N, 138.5E, 15 Nov. to 14 Dec. 2002, and (3) 7.5N, 134.0E, close to Palau, 14 Dec. 2004 to 11 Jan. 2005. Three hourly intensive radiosonde soundings were also made on the vessel during all these campaigns.
Meteorological data analyses show that in the TTL, a packet of equatorial Kelvin waves propagated over the vessel at least during the campaigns (2) and (3). In general, the lidar captured corresponding variations in the TTL cirrus, which appeared in the cold phases of the large-scale waves and disappeared in their warm phases. For the case of campaign (3), clouds suddenly appeared when the cold phase of the wave came over the vessel in late December 2004, and in early January 2005, after the cold phase had passed, rather thick clouds still remained in the TTL. Trajectory analysis shows that in early January 2005, the observed air parcels came from the east where they had experienced coldest conditions only a few days before. This is the reason why the observed air parcels were rich in cloud particles. In this period, the thick TTL cirrus also showed a clear diurnal variation, an apparent descending motion at night. Radiosonde data analysis shows that this motion may be due to periodic growth and sedimentation in association with the diurnal cycle of radiation condition.
Poster Session 3, Recent Field Investigations of TTL
Tuesday, 21 August 2007, 1:30 PM-3:30 PM, Holladay
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