Impact of abrupt stratospheric dynamical change on Tropical Tropopause Layer

We have studied the impact of stratospheric circulation change on water vapor in the Tropical Tropopause Layer (TTL) during the stratospheric sudden warming (SSW) events (e.g., Eguchi and Kodera, 2010). Increased Brewer-Dobson circulation associated with SSW produces cooling in the tropical lower stratosphere (LS). The cooling generally produces more cirrus clouds and decreases of the water vapor mixing ratio (WV) in the TTL, except for some regions over Africa and South American continents where penetrating clouds are expected. This time, we found a new stratospheric phenomenon which produces abrupt warming in the tropical stratosphere converse to the SSW event. The dynamical aspect of this phenomenon and the impact on the convective activity will be discussed. Due to the interaction between the subtropical jet and polar night jet in the upper stratosphere, tropical stratosphere warmed about two weeks in early December 2011. Accordingly, temperature in the TTL suddenly increased (approximately 0.5 K at 100 hPa) and the tropical convection ceased. Further, the downward velocity anomaly appeared from stratosphere to lower troposphere through the TTL. The present study mainly focuses on the variation of WV, temperature and cirrus clouds in the upper troposphere (UT) and LS in the period of the stratospheric dynamical change. The data from EOS MLS (Earth Observing System, Microwave Limb Sounder) is used. Before the start of abrupt warming event, the tropical convection temporarily enhanced at the south of the Equator. Then the temperature in the TTL decreased with the Kelvin wave like vertical structure: the WV at 146 hPa increased, while the WV at 100 hPa decreased, and the dryer air extended to 83 hPa with a few days lag. Following the start of the warming event, the tropical convection was suppressed. In the UT and LS, the warm and wet tendencies were found in the temperature and WV anomalies from seasonal march, respectively, and the ice cloud suddenly disappeared with increasing temperature, suggesting adiabatic heating. The result found of the present study clearly shows that the stratospheric dynamical change controls the WV variation in the UT and LS, as well as the tropical convection