Abstract
In the present study, we investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb wave activity fluxes to study the two and three dimensional aspects of wave propagation, respectively. The 2013 SSW event is excited by the combined influence of wavenumber 1 (WN1) and wavenumber 2 (WN2) planetary waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013.
Highlights
We investigate the impact of stratospheric planetary wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event
We explore vertical wave propagation and coupling during the 2013 SSW, an event excited by the combined influence of wavenumber 1 (WN1) and later wavenumber 2 (WN2) in the prewarming stage of the SSW
In the last 36 years there are only three cases; e.g. 1985/86, 1987/88 and 2012/13 which are due to the combined influence of WN1 and WN2
Summary
Eurasia: Role of planetary wave received:06October2015 accepted: 21 March 2016 reflection Published: 07April 2016. The wave packets propagated upward and were reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. In some cases, during a SSW event ( induced by WN1), the upper stratospheric zonal mean zonal wind is weakened substantially, while the lower stratospheric jet remains strong This creates a negative vertical wind shear in the upper stratosphere and provides a favorable background for the reflection of upward propagating planetary waves. While Kodera et al.[17] considered the total wavenumber field to demonstrate the reflection of planetary waves during the final warming of March 2007, in which upward propagating waves from Eurasia were reflected back to the North American sector, resulting in very cold weather over the Northeast coast of the North American continent[17]. Am is the amplitude and φ is the phase, estimated by means of LSF analysis
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