92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012: 2:30 PM
A Major Stratospheric Sudden Warming Event of January 2009 and Its Dynamical Linkage Between the Troposphere and Stratosphere
Room 355 (New Orleans Convention Center )
Hiroaki Naoe, MRI, Tsukuba, Japan; and Y. Kuroda, K. Shibata, and T. Hirooka

A seasonal march of the circulation during winter 2008/2009 is examined on the basis of the ERA-interim analysis data in connection with a stratospheric sudden warming (SSW). The SSW brings about the strong dynamical coupling of the troposphere-stratosphere system and large changes in various dynamical fields in a short time period. A prominent SSW event was observed in January 2009 after a cold and undisturbed early winter with unusual development of zonal wave number 2 along a latitude circle (wave-2). During the past 30 years there were 22 major SSW events, most of which are caused by dominant planetary waves with zonal wave number 1 (wave-1). There were only 3 SSW events caused by wave-2. In the preconditioning state of this SSW event, temperature profiles in the vicinity of the subtropical Pacific jet exhibit double tropopauses, which are associated with a characteristic break in the thermal tropopause near the subtropical jet wherein the lower latitude (tropical) tropopause extends to higher latitudes, overlying the lower tropopause. The warm double-tropopause temperature (DTT) pattern could be partly produced by the Rossby wave source, which is forced by the diabatic heating in the vicinity of the Philippines in a time of the La Niņa condition accompanied with the cold outbreak from eastern Siberia as a part of the wintertime monsoon circulation. On the basis of the analysis the formation mechanism for the wave-2 SSW is proposed as follows. The Rossby wave accompanied with warm DTT anomaly propagates along the jet stream that acts as a waveguide, and when the Rossby wave reaches in the jet exit region (near Alaska), the blocking anticyclone with warm temperature anomaly is further developed, which leads to the stratospheric warming.

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