Global distribution of the migrating terdiurnal tide seen in sporadic E occurrence frequencies obtained from GPS radio occultations

Abstract

Global Positioning System radio occultation measurements by FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate satellites were used to analyse the characteristics of the 8-h oscillation in sporadic E (E S) layers. Six-year averages based on the 3-monthly mean zonal means from December 2006 to November 2012 were constructed for the amplitude of the terdiurnal oscillation in the occurrence frequency of E S. A global distribution from 60°S to 60°N is given, revealing two peaks above 100 km during solstice with one maximum at low and midlatitudes (approximately 10°to 40°) in each hemisphere. During equinox, the global distribution is marked by two dominant peaks centred at midlatitudes, while an additional weak maximum is located at very low southern latitudes. The seasonal characteristics around 110 km reveal large values during equinox at low and midlatitudes (<40°N), while further peaks occur in April at >40°S and in July near 30°S. The pattern around 90 km is dominated by a broad peak between 20°and 30°S from March to September. Comparisons with the terdiurnal oscillation in the neutral atmosphere derived from zonal wind and vertical zonal wind shear simulated with a circulation model of the middle atmosphere, as well as with satellite observations of the terdiurnal tide in temperature, fit quite well for the results above 100 km, but do not show agreement for lower altitudes.

Daytime twin-peak structures observed at southern African and European middle latitudes on 8–13 April 2012

“…They suggested that tidal activity may have an influence on the generation of these structures because descending Es layers reflect wind shear, produced when winds at heights above the Es layer have changed directions, due to migrating tides. This seems to be supported by Haldoupis et al (2004), Arras et al (2009) andFytterer et al (2014), who have shown that diurnal, semi-diurnal and terdiurnal tides are the main drivers of Es layers by providing large vertical wind gradients, i.e. wind shear.…”

“…In the presence of the magnetic field the dynamo electric field results in vertical plasma drift, where ions converge into thin and dense plasma layers known as Es layers. Tide-like structures, especially diurnal and semidiurnal tidal components, have been observed in downward-propagating Es layers, confirming that thermal tides are the primary source of wind shear (Haldoupis et al, 2006;Arras et al, 2009;Fytterer et al, 2014). It is also important to note that the E-region dynamo electric field reaches into the F region via the magnetic field lines, where they drive vertical and horizontal plasma drifts.…”

“…In this theory it was shown that horizontal wind shear, mainly generated as solar tides propagate upwards, leads to the formation of Es layers through an interaction between the Earth's magnetic field and the ions (Fytterer et al, 2014). This is because nonmigrating tides at low and middle latitudes modify the general wind circulation and can cause partially ionised plasma to move across the Earth's magnetic field lines while the electrons remain fixed to the magnetic field because of their large gyro frequency / collision frequency ratio, which results in an electromotive force with ensuing electric currents and dynamo electric fields (Oberheide et al, 2015).…”

Dependence of mesospheric Na and Fe distributions on electron density at Arecibo

“…This is consistent with the ISR observations of sporadic-E layer on both the nights. Recent studies by Fytterer et al (2014) revealed that the amplitude of 8-h E s maximizes during equinox at low and mid-latitudes in both hemispheres.…”

Coupling between parameters of Es layer and planetary waves during SSW 2008, 2010

“…There are a number of different ionosphere sounding techniques that provide information about the morphology of the sporadic-E (e.g., Incoherent Scatter Radar (ISR), Radiometric Observation, transionospheric propagation of radio-navigation system signals and GPS radio occultation (e.g., Arras et al, 2009;Fytterer et al, 2014). However, the vertical-incidence ionosonde is still the benchmark and the main data-source about Es variability.…”