Lunar tide in the equatorial electrojet in relation to stratospheric warmings

Abstract

[1] The relationship between sudden stratospheric warmings (SSWs) and large-amplitude lunar tides in the equatorial electrojet (EEJ) is studied. Analysis of ground magnetometer data shows that the lunar tide in the EEJ is maximum during the northern winter season except in the Pacific Ocean region. Since SSWs are also a northern winter phenomenon, it is suggested that the relation between the large lunar tide in the EEJ and the SSW may possibly be coincidental. The lunar tide in the geomagnetic variations at Huancayo is anomalously large compared with other EEJ stations. An examination of geomagnetic variations at EEJ stations during SSW events shows that afternoon counter-electrojets are frequently present at new moon and full moon, though the relationship is sometimes broken. The observation of large lunar EEJs when no SSW is present and of various different delay times suggests that other atmospheric processes are likely to be in play.

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…The total current intensity is largest during the Northern Hemisphere winter. The lunar modulation of the equatorial electrojet is also greatest during the northern winter, except in the West Pacific region (Rastogi and Trivedi 1970;Stening 2011). The strong L currents during the northern winter is probably contributed by the big L days in which the amplitude of L is several times larger than other normal days ( (Bartels and Johnston 1940);Onwumechili 1964).…”

“…They noted that there are some years when a lunar tidal amplification occurs without a stratospheric sudden warming event and other years when there is no lunar tidal amplification during a stratospheric sudden warming event. Stening (2011Stening ( ), analyzing equatorial data during 1960Stening ( -2009, also noted that not all stratospheric sudden warmings cause a counter electrojet event. A numerical study by Pedatella and Liu (2013) showed that the lunar tidal amplification depends on the phase of the moon relative to the timing of the stratospheric sudden warming.…”

Longitudinal, seasonal and solar cycle variation in lunar tide influence on the equatorial electrojet

“…Moreover, January is also the usual time when stratospheric sudden warming (SSW) occurs. It has been widely reported that SSW modify the mean stratospheric temperature and zonal wind conditions, leading to an enhancement of the lunar tide magnitudes (e.g., Fejer et al, 2010;Stening, 2011;Yamazaki et al, 2012;Park et al, 2012). On the other hand, in the absence of a SSW event and when the Earth is at the furthest distance from the Sun (aphelion) during June solstice, the lunar tide influence on the EEJ is very small.…”

“…Rastogi and Trivedi (1970), using limited data obtained during the International Geophysical Year and the International Geophysical Cooperation (IGY-IGC) period (on average, 1 year of data for each station), reported significant longitudinal variability in the lunar tide. Stening (2011), using magnetometer data, also reported about the relationship between sudden stratospheric warmings (SSWs) and large lunar tide amplitude at different longitudes. Recently, Lühr et al (2012), using magnetometer observations onboard the CHAMP satellite, reported longitudinal and solar cycle variability in lunar tidal wave amplitudes and found no significant longitudinal variability in the lunar tidal wave impact on the EEJ.…”

Relation between stratospheric sudden warming and the lunar effect on the equatorial electrojet based on Huancayo recordings

“…Fejer et al, 2010Fejer et al, , 2011Stening, 2011;Park et al, 2012;Yamazaki et al, 2012a, b). Stening (2011) pointed out that the relation between the large lunar tide in EEJ and SSW events could be coincidental, while Park et al (2012) confirmed a one-to-one correspondence between the lunitidal enhancement at ionospheric heights and the occurrence of SSW events between 2001-2009. Likewise, Yamazaki et al (2012a investigated the correlation between the amplitude of the geomagnetic lunar tide at Addis Ababa and lower stratospheric parameters and confirmed the occurrence correspondence between SSWs and the enhancement of the geomagnetic lunar tide for the majority of years between 1958-2007.…”