|
Atmos. Chem. Phys. Discuss., 12, 20007-20032, 2012
www.atmos-chem-phys-discuss.net/12/20007/2012/ doi:10.5194/acpd-12-20007-2012 © Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License. |
Simultaneous occurrence of polar stratospheric clouds and upper-tropospheric clouds caused by blocking anticyclones
1Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
Abstract. This study statistically examines the simultaneous appearance of polar stratospheric clouds (PSCs) and upper tropospheric clouds (UCs) using satellite lidar observations for five austral winters of 2007–2011. The time series of PSC occurrence in the height range of 15–25 km are significantly correlated with those of UC in 9–11 km. The UCs observed simultaneously with PSCs reported in previous case studies are possibly located around and slightly above the tropopause (~7–8 km) rather than in the troposphere. It is shown that the simultaneous occurrence of PSCs and UCs is frequently associated with blocking highs having large horizontal scales (several thousand kilometers) and tall structure (up to a~height of ~15 km). The longitudinal variation of blocking high frequency accords well with that of the simultaneous occurrence frequency of PSCs and UCs. This coincidence is clearer when the analysis is limited to the latitudinal regions inside the stratospheric polar vortex. This fact suggests that the blocking highs provide a~preferable condition for the simultaneous occurrence of PSCs and UCs. Moreover, PSC compositions are investigated as a~function of relative-longitude of the anticyclones including blocking highs. It is seen that relatively high proportions of STS (super-cooled ternary solutions), Ice, and Mix2 (mixture of nitric acid trihydrate and STS) types are distributed to windward of, around, and to leeward of the anticyclones in the westerly background flows, respectively.
Citation: Kohma, M. and Sato, K.: Simultaneous occurrence of polar stratospheric clouds and upper-tropospheric clouds caused by blocking anticyclones, Atmos. Chem. Phys. Discuss., 12, 20007-20032, doi:10.5194/acpd-12-20007-2012, 2012.