Abstract
Objective: A brief review on the effects of Sudden Stratospheric Warming (SSW) over the equatorial upper atmosphere (80-500 km) obtained using both ground and space-based measurements are presented. The emphasis is given to understand the role of semi-diurnal tidal activity during the SSW. Methods: In order to address this aspect, zonal wind data obtained using meteor wind radar over a tropical station; Trivandrum in India (8.50 N, 77.0 0 E) has been used. Wavelet analysis has been carried out to investigate the role of semi-diurnal and terdiurnal tides during the SSW event of January 2008. For characterizing the event, polar stratospheric temperature (PST) at 10 hPa, as obtained using National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) reanalysis data has been used. In order to characterize the normal behavior, the aforementioned database during December 2007 has been also looked into. Findings: It has been understood that the tropical upper atmosphere exhibits substantial changes in connection with SSW with an increase in the amplitudes of semi diurnal tides of the order of 10-15 m/s in comparison with the normal period. Over the equatorial ionosphere, the changes were observed right from the E region, extending upto the topside F region. It was noticed that the imprints of SSW were not only restricted to the neutral atmospheric parameters such as temperature, density, wind, but also found to have distinct signatures in the electrodynamic processes such as Equatorial electrojet (EEJ), Equatorial Ionization Anomaly (EIA), Equatorial Spread-F (ESF) as well. Novelty: The study, probably for the first time, has conclusively shown that it is not the terdiurnal tides, but the semi-diurnal tides, which are responsible for the SSW induced effects due to its non-linear interaction with planetary waves. Keywords: Stratospheric sudden warming; Equatorial ionosphere; waves and tides
Highlights
Sudden Stratospheric Warming (SSW) is a dramatic and large scale meteorological phenomenon in the winter polar stratosphere caused by the rapid growth of Quasi Stationary Planetary Waves (QSPW) and their interaction with the stratospheric mean circulation [1]
We have reviewed some of the important scientific results concerning the effects of SSW over the equatorial upper atmosphere 980- 500 km)
An attempt is made to understand the exact nature of the tidal forcing during the SSW event of January 2008
Summary
Sudden Stratospheric Warming (SSW) is a dramatic and large scale meteorological phenomenon in the winter polar stratosphere caused by the rapid growth of Quasi Stationary Planetary Waves (QSPW) and their interaction with the stratospheric mean circulation [1]. The resonant growth of planetary waves[2] and resonant enhancement of a barotropic mode of the polar vortex[3] are suggested to be the main reasons for the rapid growth of planetary waves, still, the complete explanation is yet to evolve. Accompanying these changes, the stratopause descends over some locations by as much as 20 km. The role of SSW over the low/equatorial ionosphere has been gleaned out[4] In this context, an attempt is made here to explore the important scientific results concerning the SSW and its effects over the other altitudes/latitudes. The case of 2008 SSW event has been investigated here in context of the tidal amplitudes as obtained using the meteor wind radar over the tropical station, Trivandrum (8.80 N, 770 E) in India
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