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    Session convener-recommended article JpGU Meeting 2013

    201409201409

    A numerical experiment on the formation of the tropopause inversion layer associated with an explosive cyclogenesis: Possible role of gravity waves

    Otsuka S, Takeshita M, Yoden S

    Tropopause inversion layer, Extratropical cyclone, Gravity wave

    Vertical cross sections of∂w/∂z andN2. Vertical cross sections of ∂w/∂z (color, s -1) and N2 (contour, s −2) at t=27 h (development stage of the cyclone). Tropopause is denoted by the green line. The dashed-dotted line shows the 260 hPa level.

    The tropopause inversion layer (TIL) is a persistent layer with high static stability. Although some mechanisms for the formation of the TIL have been proposed, the time evolution of the TIL under realistic conditions especially when factoring in the contribution of small-scale processes such as gravity waves is not well understood. To gain an understanding of this factor, we conducted a numerical experiment on an explosive cyclogenesis in mid-latitudes using a nonhydrostatic regional atmospheric model. Although the TIL in the model is consistent with previous observations in the sense that it is stronger in the negative vorticity areas, the relationship is clear only in the development and mature stages of a cyclone, suggesting that the evolution of the cyclone plays an important role in the formation of the TIL. To ascertain the effects of gravity waves on the TIL, vertical convergence at the tropopause is analyzed. Histograms of maximum buoyancy frequency squared (N2max) within the TIL show that regions of vertical convergence have higher N2max , in addition to regions with high ∂w/∂z, implying that waves having downward phase propagation also play an important role in the dynamical formation of the TIL. This tendency is clearer in regions of negative relative vorticity at the tropopause. By taking account of the fact that the gravity wave activities associated with the cyclone and the jet streak are enhanced during the development and mature stages of the cyclone, vertical convergence due to gravity waves associated with synoptic weather systems can be seen to be a key process in the formation of the negative correlation between the strength of the TIL and the local relative vorticity at the tropopause.