Nonmigrating tidal signatures in the magnitude and the inter-hemispheric asymmetry of the equatorial ionization anomaly

Xiong, Chao; Lühr, Hermann

doi:10.5194/angeo-31-1115-2013

Cited by 36 publications

(41 citation statements)

References 35 publications

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“…The tidal amplitude is much enhanced during the period of high solar flux compared to the solar minimum years around the end of the year. Xiong and Lühr (2013) reported similar results about the SW3 tidal effect on the intensity of the equatorial ionisation anomaly. They also find a strong dependence of SW3 on solar activity during the later months of the year but no dependence on magnetic activity.…”

Section: Discussionsupporting

confidence: 62%

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

Lühr

Manoj²

2013

Ann. Geophys.

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Abstract. Based on 10 yr of magnetic field measurements by the CHAMP satellite we draw a detailed picture of the equatorial electrojet (EEJ) tidal variations. For the first time the complete EEJ spectrum related to average solar tides has been compiled. A large fraction of the resulting spectrum is related to the switch on/off of the EEJ between day and night. This effect has carefully been considered when interpreting the results. As expected, largest amplitudes are caused by the migrating tides representing the mean diurnal variation. Higher harmonics of the daily variations show a 1/f fall-off in amplitude. Such a spectrum is required to represent the vanishing of the EEJ current at night. The migrating tidal signal exhibits a distinct annual variation with large amplitudes during December solstice and equinox seasons but a depression by a factor of 1.7 around June–July. A rich spectrum of non-migrating tidal effects is deduced. Most prominent is the four-peaked longitudinal pattern around August. Almost 90% of the structure can be attributed to the diurnal eastward-propagating tide DE3. In addition the westward-propagating DW5 is contributing to wave-4. The second-largest non-migrating tide is the semi-diurnal SW4 around December solstice. It causes a wave-2 feature in satellite observations. The three-peaked longitudinal pattern, often quoted as typical for the December season, is significantly weaker. During the months around May–June a prominent wave-1 feature appears. To first order it represents a stationary planetary wave SPW1 which causes an intensification of the EEJ at western longitudes beyond 60° W and a weakening over Africa/India. In addition, a prominent ter-diurnal non-migrating tide TW4 causes the EEJ to peak later, at hours past 14:00 local time in the western sector. A particularly interesting non-migrating tide is the semi-diurnal SW3. It causes largest EEJ amplitudes from October through December. This tidal component shows a strong dependence on solar flux level with increasing amplitudes towards solar maximum. We are not aware of any previous studies mentioning this behaviour of SW3. The main focus of this study is to present the observed EEJ spectrum and its relation to tidal driving. For several of the identified spectral components we cannot offer convincing explanations for the generation mechanisms.

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Section: Discussionsupporting

confidence: 62%

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

Lühr

Manoj²

2013

Ann. Geophys.

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“…Hagan et al (2009) reported the existence of stationary planetary wave-4 (SPW4) oscillation in the upper mesosphere and lower thermosphere (MLT) region, caused by the nonlinear interaction between DE3 and the migrating tide DW1. Since then, the importance of stationary planetary waves, SPW4/SPW3, contributing to the longitudinal WN4/WN3 patterns in the upper atmosphere, has also been supported by both model simulations (e.g., Oberheide et al, 2011a;Pancheva et al, 2012) and in situ observations (e.g., Kil et al, 2010;Lühr and Manoj, 2013;Xiong and Lühr, 2013;Chang et al, 2013).…”

Section: Introductionmentioning

confidence: 79%

Tidal signatures of the thermospheric mass density and zonal wind at midlatitude: CHAMP and GRACE observations

et al. 2015

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Abstract. By using the accelerometer measurements from CHAMP and GRACE satellites, the tidal signatures of the thermospheric mass density and zonal wind at midlatitudes have been analyzed in this study. The results show that the mass density and zonal wind at southern midlatitudes are dominated by a longitudinal wave-1 pattern. The most prominent tidal components in mass density and zonal wind are the diurnal tides D0 and DW2 and the semidiurnal tides SW1 and SW3. This is consistent with the tidal signatures in the F region electron density at midlatitudes as reported by Xiong and Lühr (2014). These same tidal components are observed both in the thermospheric and ionospheric quantities, supporting a mechanism that the non-migrating tides in the upper atmosphere are excited in situ by ion-neutral interactions at midlatitudes, consistent with the modeling results of Jones Jr. et al. (2013). We regard the thermospheric dynamics as the main driver for the electron density tidal structures. An example is the in-phase variation of D0 between electron density and mass density in both hemispheres. Further research including coupled atmospheric models is probably needed for explaining the similarities and differences between thermospheric and ionospheric tidal signals at midlatitudes.

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“…The phase of the SPW defines the longitude where the wave crest occurs. At low and equatorial latitudes the WN4/WN3 patterns of the ionospheric and thermospheric quantities and the related tidal components have been widely studied (Sagawa et al, 2005;Immel et al, 2006;England et al, 2006England et al, , 2010Lühr et al, 2008Lühr et al, , 2012Kil et al, 2007;Häusler and Lühr, 2009;Zhang et al, 2010;Xiong and Lühr, 2013;. These tides originate from the lower atmosphere and can propagate upward to the upper atmosphere, either by direct propagation or through the E region wind dynamo coupling mechanism (e.g.…”

Section: Y-l Zhou Et Al: Solar Activity Dependence Of Nonmigratingmentioning

confidence: 99%

“…The related tidal components and the possible coupling mechanisms between the mesosphere and lower thermosphere (MLT) and the upper atmosphere have also been proposed (e. g. Sagawa et al, 2005;Immel et al 2006;England et al, 2006England et al, , 2010Lühr et al, , 2012Xiong and Lühr, 2013). These tides are usually excited by thermal sources, stationary planetary wave- tide (e.g., Angelats i Coll and and tide-tide interactions (Hagan et al, 2009;Oberheide et al, 2011).…”

Section: Nonmigrating Tides At Low Latitudesmentioning

confidence: 99%

The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE

et al. 2016

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Abstract. In this paper we use more than a decade of in situ electron density observations from CHAMP and GRACE satellites to investigate the solar activity dependence of nonmigrating tides at both low and middle latitudes. The results indicate that the longitudinal patterns of F region electron density vary with season and latitude, which are exhibiting a wavenumber 4 (WN4) pattern around September equinox at low latitudes and WN1/WN2 patterns during local summer at the southern/northern middle latitudes. These wave patterns in the F region ionosphere can clearly be seen during both solar maximum and minimum years. At low latitudes the absolute amplitudes of DE3 (contributing to the WN4 pattern) are found to be highly related to the solar activity, showing larger amplitudes during solar maximum years. Similarly a solar activity dependence can also be found for the absolute amplitudes of D0, DW2 and DE1 (contributing to the WN1 and WN2 pattern) at middle latitudes. The relative amplitudes (normalized by the zonal mean) of these nonmigrating tides at both low and middle altitudes show little dependence on solar activity. We further found a clear modulation by the quasi-biennial oscillation (QBO) of the relative DE3 amplitudes in both satellite observations, which is consistent with the QBO dependence as reported for the E region temperatures and zonal wind. It also supports the strong coupling of the low-latitude nonmigrating tidal activity between the E and F regions. However, the QBO dependence cannot be found for the relative amplitudes of the nonmigrating tides at middle latitudes, which implies that these tides are generated in situ at F region altitudes.

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Nonmigrating tidal signatures in the magnitude and the inter-hemispheric asymmetry of the equatorial ionization anomaly

Cited by 36 publications

References 35 publications

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

Tidal signatures of the thermospheric mass density and zonal wind at midlatitude: CHAMP and GRACE observations

The solar activity dependence of nonmigrating tides in electron density at low and middle latitudes observed by CHAMP and GRACE

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