Ionogram height–time–intensity observations of descending sporadic E layers at mid-latitude

Abstract

A new methodology of ionosonde height–time–intensity (HTI) analysis is introduced which allows the investigation of sporadic E layer (Es) vertical motion and variability. This technique, which is useful in measuring descent rates and tidal periodicities of Es, is applied on ionogram recordings made during a summer period from solstice to equinox on the island of Milos (36.71N; 24.51E). On the average, the ionogram HTI analysis revealed a pronounced semidiurnal periodicity in layer descent and occurrence. It is characterized by a daytime layer starting at 120km near 06 h local time (LT) and moving downward to altitudes below 100km by about 18 h LT when a nighttime layer appears above at_125 km. The latter moves also downward but at higher descent rates (1.6–2.2 km/h) than the daytime layer (0.8–1.5 km/h). The nighttime Es is weaker in terms of critical sporadic E frequencies (foEs), has a shorter duration, and tends to occur less during times close to solstice. Here, a diurnal periodicity in Es becomes dominant. The HTI plots often show the daytime and nighttime Es connecting with weak traces in the upper E region which occur with a semidiurnal, and at times terdiurnal, periodicity. These, which are identified as upper E region descending intermediate layers (DIL), play an important role in initiating and reinforcing the sporadic E layers below 120–125 km. The observations are interpreted by considering the downward propagation of wind shear convergent nodes that associate with the S2,3 semidiurnal tide in the upper E region and the S1,1 diurnal tide in the lower E region

Semidiurnal tidal signature in sporadic E occurrence rates derived from GPS radio occultation measurements at higher midlatitudes

“…As known from theory and ground-based observations (Haldoupis et al, 2006;Christakis et al, 2009) the E s layer descent follows the phase velocity of the SDT convergent node at altitudes well above about 100 km. Below, the descent velocity slows down due to enhanced ion-neutral collisions.…”

“…It is noticed that during January and October, when the wind shear maximum zones descend more quickly, the E s descend is slightly slower. This may be due to the fact that at lower altitudes formation of E s becomes too slow to remain inside the convergence zone (Haldoupis et al, 2006). During April and July, the SDT phase gradient shows a complex picture (see Fig.…”

“…This leads to the reproduction of the downward moving tidal signatures in E s ionosonde registrations (e.g. Haldoupis et al, 2006). Tides are by far the strongest oscillation within lower thermosphere dynamics.…”

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

“…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.…”

The electronic Space Weather upper atmosphere (eSWua) project at INGV: advancements and state of the art

“…For instance, it would be very interesting if the system could generate ionogram height-timeintensity analysis plots (Haldoupis et al, 2006). This work describes the technical features, software and hardware, of the whole project, as well as the state of the art.…”