Lunar and solar tidal variabilities in mesospheric winds and EEJ strength over Tirunelveli (8.7°N, 77.8°E) during the 2009 major stratospheric warming

Abstract

[1] Mesospheric wind observations by the medium frequency radar and geomagnetic field observations at Tirunelveli (8.7 N, 77.8 E, 1.75 N dip angle) are used to study the relative importance of solar and lunar influences in the variabilities of mesospheric tides and equatorial electrojet (EEJ) strength during the unprecedented major stratospheric sudden warming (SSW) of 2009. It is observed that the afternoon reversal in the EEJ, popularly known as counter electrojet, occurs consecutively for several days during the SSW event, when there is an enhancement of solar semidiurnal tide in both zonal wind at 90 km and EEJ strength over Tirunelveli. Although the amplitude of lunar tides also shows enhancement, it is much less than that of solar. The diurnal tidal amplitude in zonal wind and EEJ strength also shows large enhancement just before the onset of SSW. However, solar semidiurnal tide dominates diurnal tide during the SSW. The diurnal tidal phase in zonal wind shifts to a few hours earlier during the SSW. The lunar semidiurnal tidal phase shifts to later hours in both zonal wind and EEJ strength. The main observation of the present study is that the large semidiurnal tide observed during the SSW 2009 is mostly solar driven and only partly lunar driven, although tidal planetary wave interaction also may play a vital role. Although a similar behavior is noticed during the SSW 2006 also, the large lunar semidiurnal tide observed in the EEJ strength without having large lunar semidiurnal tide in the underlying mesospheric winds needs further investigation.Citation: Sathishkumar, S., and S. Sridharan (2013), Lunar and solar tidal variabilities in mesospheric winds and EEJ strength over Tirunelveli (8.7 N, 77.8 E) during the 2009 major stratospheric warming,

Coupling between mesosphere and ionosphere over Beijing through semidiurnal tides during the 2009 sudden stratospheric warming

“…That means the vertical wavelength of solar semidiurnal tide is quite large. The tidal phase in meridional wind is 2–6 h lead to that in zonal wind as many other observations [ Sathishkumar and Sridharan , ]. From 15 January, the phase of both zonal and meridional tides drop 3–4 h and then recover at about 10 February.…”

“…All of the lunar tidal amplitudes of zonal wind, meridional wind, and TEC perturbation at 20°N are enhanced during 15 January and 15 February. The lunar tide in the EEJ in low‐latitude ionosphere enhances during the similar period as shown by [ Sathishkumar and Sridharan , ]. Comparing with the lunar tide in the low latitude, the lunar tide in wind is much stronger but with very similar variation during SSW.…”

“…The observation in low latitude does not show such significant phase variation in solar semidiurnal tide. The variation of phases of semidiurnal solar tide in zonal and meridional wind is not the same before and after SSW [ Sathishkumar and Sridharan , ]. Figure b shows the phase variation of semidiurnal lunar tide at 96 km.…”

“…The semidiurnal lunar tide in the Brazilian sector in the MLT region is observed to enhance during 2006 SSW [ Paulino et al ., ]. Recently, based on the mesospheric winds and EEJ observation at Tirunelveli (8.7°N, 77.8°E), Sathishkumar and Sridharan [] demonstrated that the large semidiurnal tide during 2009 SSW is mostly solar driven and only partly lunar driven in the low latitude. Forbes and Zhang [] demonstrated that the enhanced semidiurnal lunar tides in the mesosphere during 2009 SSW resulted from the resonance between lunar tides and a normal mode named Pekeris peak ,which shifted its peak to the lunar tidal period with strongly changed neutral winds during the SSW.…”

The Comparison of Lunar Tidal Characteristics in the Low‐Latitudinal Ionosphere Between East Asian and American Sectors During Stratospheric Sudden Warming Events: 2009–2018

“…The well-known 2008-2009 SSW has been studied in a lot of works (Fang et al, 2012;Fejer et al, 2010;Fuller-Rowell et al, 2011;Liu et al, 2011;Pedatella & Forbes, 2010;Sathishkumar & Sridharan, 2013;Siddiqui et al, 2017). It draws attention because it is not only a recordbreaking major event but also that the year 2009 is in a prolonged solar minimum period, and the geomagnetic conditions are relatively quiet.…”