题目：Nonlinear interaction and saturation of planetary waves in the stratosphere

报告人：Prof. Pogoreltsev A.I.

单位：Russian State Hydrometeorological University

时间：2010年11月17日（星期三）上午9：30

地点：科研楼303会议室

摘要：

The analysis of observations shows that there exists a strong variability of stationary planetary wave (SPW) amplitudes during winter-time in the Northern hemisphere. Using a numerical model of the general circulation, the nonlinear response to an increase of the SPW amplitudes at the lower boundary is investigated. The results obtained show that nonlinear wave-wave and wave-mean flow interactions lead to the saturation of the SPW1 (planetary wave with zonal wave number one). Further increase of the SPW1 forcing at the lower boundary cased a substantial change of the mean flow in the lower stratosphere that limit the vertical penetration of the forced wave into the stratosphere. In result the SPW1 amplitude in the upper stratosphere and mesosphere becomes even smaller in comparison with case of a weak forcing. The analysis of the SPW2 sensitivity in the stratosphere to an increase of the lower boundary forcing shows that in this case the response is approximately linear at least for the realistic (observed) SPW2 amplitudes. A possible application of the results obtained to the problems of the sudden stratospheric warmings, stratospheric vacillations, and spring-time transition is shortly discussed.

题目：Influence of the QBO, NAM and ENSO on planetary wave-driven interannual variability of the spring transition

报告人：Dr. Kanukhina A.Yu

单位：Russian State Hydrometeorological University

时间：2010年11月17日（星期三）上午10：30

地点：科研楼303会议室

摘要：

The analysis of data assimilated in the UK Met Office and NCEP models shows that there exists a sufficiently strong (in the range of about two months) interannual variability of the spring-time breakup date of stratospheric circulation. The preliminary results show also that spring-time transition depends on the planetary-wave activity in the stratosphere and during the last decades there is a tendency of the shift of the breakup to the later date. The main purpose of the present paper is to investigate the possible reasons of observed interannual variability of the spring-time breakup date. Increase of the amplitude of stationary planetary wave with zonal wave number 1 (SPW1) observed during the last decades in February leads to a substantial decrease of the SPW1 amplitude in March that can explain the observed shift to the later spring-time breakup date. Scatter plot between NAM and the spring-time breakup date shows a positive correlation, which is stronger for the early spring-time transition. Under east-QBO taken at 40-50 hPa according to the established classification, growth of the SPW1 amplitude is accompanied with the early spring-time transition. Under west-QBO conditions the correlation between the SPW1 amplitude and the date of spring-time transition is positive. Statistically significant positive correlation between MEI index of ENSO and spring-time breakup has been obtained under east-QBO conditions. This means that cold ENSO leads to early occurrence of spring-time transition in spite of the stronger polar vortex.