Variability of atmospheric winds and waves in the Arctic polar mesosphere during a stratospheric sudden warming

101

Abstract. The present study demonstrates the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events and the reversal in the afternoon equatorial electrojet (EEJ), often called the counter-electrojet (CEJ), during the winter months of 1998-1999, 2001-2002, 2003-2004 and 2005-2006. As the EEJ current system is driven by tidal winds, an investigation of tidal variabilities in the MF radar observed zonal winds during the winters of 1998-1999 and 2005-2006 at 88 km over Tirunelveli, a site close to the magnetic equator, shows that there is an enhancement of semi-diurnal tidal amplitude during the days of a major SSW event and a suppression of the same immediately after the event. The significance of the present results lies in demonstrating the latitudinal coupling between the high latitude SSW phenomenon and the equatorial ionospheric current system with clear evidence for major SSW events influencing the day-to-day variability of the CEJ.

Section: Resultsmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 97%

Variabilities of mesospheric tides and equatorial electrojet strength during major stratospheric warming events

Sridharan

Sathishkumar²,

Gurubaran³

2009

101

“…of eastward zonal winds happened several days before temperature maximum in the stratospheric polar cap during the SSW event in February 2001 (Bhattacharya et al, 2004). MLT winds observed at three other stations located at Castle Eaton, 52 • N; Collm,52 • N and Esrange,68 • N showed that both zonal and meridional winds changed directions in the mesopause region when the SSW event happened (Jacobi et al, 2003).…”

Section: Chen Et Al: Mlt Winds and Waves Over Mid-latitude Duringmentioning

confidence: 89%

Variability of MLT winds and waves over mid-latitude during the 2000/2001 and 2009/2010 winter stratospheric sudden warming

Chen

Cunying

2012

winter are examined to reveal the effects of stratospheric sudden warming (SSW) in mid-low-latitude MLT region. The result shows that the MLT daily zonal wind over these two sites reversed from eastward wind to westward wind for several days during the SSW events. The reversals were almost coincident with the polar stratospheric temperature reaching its maximum at 10 hPa, 90 • N and were about ten days prior to the reversal of high latitude stratospheric zonal wind at 10 hPa, 60 • N. The temporal variations of tides, gravity waves and 2-day planetary waves in the mid-latitude MLT showed different behavior during the two SSW events. During the 2001 SSW event, MLT diurnal tide reached its maximum when the MLT zonal wind decreased rapidly and SSW event began in polar stratosphere; the activity of 2-day waves decreased after the onset of the 2001 SSW, while the gravity wave increased when the 2001 SSW developed into a major warming. However, in the 2009/2010 winter, the semidiurnal tide and 2-day wave in MLT over Langfang reached a peak about two days earlier than zonal wind reversal at 10 hPa, 60 • N; no significant features were found in diurnal tides, terdiurnal tides and gravity waves related to the 2010 SSW event.

“…Winds obtained by Doppler-shifting techniques from both emission layers showed reversals around the times of SSW (Bhattacharya et al, 2004). Spectral analyses of the data indicated that during the periods of cold or undisturbed stratospheric temperatures the amplitudes of oscillations with periods from 6 h to 2 days decreased.…”

mentioning

confidence: 90%

Polar vortex evolution during Northern Hemispheric winter 2004/05

Chshyolkova

Manson²,

Meek³

et al. 2007

Abstract. As a part of the project "Atmospheric Wave Influences upon the Winter Polar Vortices (0-100 km)" of the CAWSES program, data from meteor and Medium Frequency radars at 12 locations and MetO (UK Meteorological Office) global assimilated fields have been analyzed for the first campaign during the Northern Hemispheric winter of 2004/05. The stratospheric state has been described using the conventional zonal mean parameters as well as Q-diagnostic, which allows consideration of the longitudinal variability.The stratosphere was cold during winter of 2004/05, and the polar vortex was relatively strong during most of the winter with relatively weak disturbances occurring at the end of December and the end of January. For this winter the strongest deformation with the splitting of the polar vortex in the lower stratosphere was observed at the end of February. Here the results show strong latitudinal and longitudinal differences that are evident in the stratospheric and mesospheric data sets at different stations. Eastward winds are weaker and oscillations with planetary wave periods have smaller amplitudes at more poleward stations. Accordingly, the occurrence, time and magnitude of the observed reversal of the zonal mesospheric winds associated with stratospheric disturbances depend on the local stratospheric conditions. In general, compared to previous years, the winter of 2004/05 could be characterized by weak planetary wave activity at stratospheric and mesospheric heights.