Vertical coupling of atmospheres: dependence on strength of sudden stratospheric warming and solar activity

Abstract

Comprehensive behavior of the low-latitude upper atmosphere during sudden stratospheric warming (SSW) events at varying levels of solar activity has been investigated. The equatorial electrojet (EEJ) strength and the total electron content (TEC) data from low latitudes over Indian longitudes during the mid-winter season in the years 2005 to 2013 are used in this study. Five major and three minor SSW events occurred in the observation duration, wherein the solar activity had varied from minimum (almost no sunspots) to mini-maximum (approximately 50 sunspots of the solar cycle 24). Spectral powers of the large-scale planetary wave (PW) features in the EEJ and the TEC have been found to be varying with solar activity and SSW strengths. Specially, the spectral powers of quasi-16-day wave variations during the three very strong SSW events in the years 2006, 2009, and 2013 were found to be very high in comparison with those of other years. For these major events, the amplitudes of the semi-diurnal tides and quasi-16-day waves were found to be highly correlated and were maximum around the peak of SSW, suggesting a strong interaction between the two waves. However, this correlation was poor and the quasi-16-day spectral power was low for the minor events. A strong coupling of atmospheres was noted during a relatively high solar activity epoch of 2013 SSW, which was, however, explained to be due to the occurrence of a strong SSW event. These results suggest that the vertical coupling of atmospheres is stronger during strong major SSW events and these events play an important role in enabling the coupling even during high solar activity.

On the variability of the diurnal tide and coupling with planetary waves in the MLT over Cachoeira Paulista (22.7°S, 45°W)

“…Mthembu et al (2013) found notable variability of the semidiurnal tide due to interactions with planetary waves of periods $ 5, 6, 23 days. Most recent study by Laskar et al (2014) observed considerable interaction between the semidiurnal tide and quasi-16-day wave during major sudden stratospheric warming and solar maximum condition. Although a number of studies have been carried out both theoretically and observationally aiming at understanding the underlying processes responsible for the tide-planetary wave interactions from various locations over the globe, our knowledge is very limited so far, especially related to the southern hemisphere, where planetary wave activities are weaker as compared to the northern hemisphere as well as least available observational studies.…”

On the latitudinal distribution of mesospheric temperatures during sudden stratospheric warming events

“…An event is considered as “major” if in addition to increased temperatures, zonal mean eastward winds reverse at these altitude and latitude regions [ McInturff , ; Labitzke , ]. SSW is attributed to the interaction of zonal winds with vertically propagating planetary waves (PWs) forced from the troposphere, and their effect in terms of quasi 16 day waves has also been seen to be present over low‐ and equatorial‐latitude E and F regions of the ionosphere [e.g., Laskar et al , ]. It has also been shown that the westward acceleration of zonal winds over northern hemispheric high latitudes occurs during SSW periods in the presence of PWs [ Matsuno , ].…”

Impact of Sudden Stratospheric Warming of 2009 on the Equatorial and Low‐Latitude Ionosphere of the Indian Longitudes: A Case Study

“…The absence of quasi 16 day periodicity around the NE stations suggests that the ionization over NE stations do not get influenced by the EEJ and the consequent fountain effect. The earlier workers also reported the presence of quasi 16 day wave during the SSW events at the low‐latitude ionosphere of the Indian zone, which are linked with the changes in the equatorial electric fields (Laskar et al, ; Patra et al, ; Sripathi & Bhattacharyya, ). The presence of quasi 16 day wave during the SSW event of 2013 was also observed over midlatitude ionosphere (Chen et al, ).…”