Observations of F layer electron density profiles modulated by planetary wave type oscillations in the equatorial ionospheric anomaly region

Abstract

A digital ionosonde of the type known as the Canadian Advanced Digital Ionosonde (CADI) is operational at São José dos Campos (23.2°S, 45.9°W), Brazil. This ionospheric sounding station is located under the southern crest of the ionospheric equatorial anomaly. The F layer electron density profile presents considerable day‐to‐day variability, even during undisturbed conditions, and this variability is still one of the less understood aspects of the physics of the ionosphere. The propagation of waves into the ionosphere may play an important role in this day‐to‐day ionospheric variability. In this paper we present a new technique that uses multifrequency virtual height variations, from ionospheric sounding observations at this low‐latitude station, to investigate how the F layer is modulated by planetary wave type oscillations. We have also considered the possible influence of oscillations due to solar origin (solar rotation variation). In the present study, observations during the months of June to September 2003 (season of low‐range type equatorial spread F occurrence at this location) have been used. The present study indicates the presence of 2‐day (the observed 3‐day periods are possibly associated with the quasi 2‐day oscillations), 5‐day, 10‐day, and 16‐day periods related to planetary wave type oscillations due to tropospheric sources during all the day. Also, it appears that during the day and dusk times, the longer periods 24–30 days are related to solar rotation (27 days), whereas the shorter periods 9–17 days have possibly some influence from half solar rotation (13.5 days). During the nighttime, possibly the short period oscillations 3–9 days may have some influence from the geomagnetic disturbances.

Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector

“…These waves are strongly connected with the ionospheric day-to-day variability in the equatorial and low latitudes and are important topics of investigation. Considerable research has gone into understanding the physics behind the observed high variability, particularly in the F2 layer [Fagundes et al, 2005Klausner et al, 2009;MacDougall et al, 2009;Rishbeth et al, 2009]. For many years, it was thought that during geomagnetic quiet conditions, the equatorial and low-latitude F2 layer was mainly perturbed by waves or electric fields generated by the equatorial electroject (EEJ), via tidal winds, which are transmitted along the magnetic field lines to equatorial F-region altitudes .…”

IRI-2001 model predictions compared with ionospheric data observed at Brazilian low latitude stations

“…Ionospheric F-region parameters such as the critical frequency (foF2), minimum virtual height (h F), true height of the electron density peak (hmF2), and virtual height at a frequency of 83.4% of foF2 (hpF2 -an estimate of the true height density peak) were scaled and averaged for the 5-selected days during each month (representing a particular season). The scaling of ionograms used the software developed at Universidade do Vale do Paraíba (UNIVAP) called the UNIVAP Digital Ionosonde Data Analysis (UDIDA) (Fagundes et al, 2005). The digital ionospheric data registered by the CADIs are displayed on a PC monitor screen for scaling of ionograms.…”

“…In the present study, POLAN was run under the software UDIDA (Fagundes et al, 2005), to obtain the true height electron density profiles by conveniently choosing points in the ionograms. The profiles were calculated on an hourly basis.…”

On the Features of Magnetogradient Planetary Waves in the Approximation of the Spherical Symmetry of the Ionosphere

“…Below we will not take into account the effects of viscosity, compressibility and temperature stratification [3,15,16]. Experimental verifications of existence of the magnetogradient planetary waves at the ionospheric levels are given in [7,9,[17][18][19].…”

“…Numerous experimental observations show [3,9,19] that in case of influence on the ionosphere from below (during the earthquakes, man-made explosions, launching of spacecrafts) and from above (during the magnetic storms, substorms, etc) planetary waves are often registered in the ionosphere. Wavelength of these waves equals or exceeds the Earth radius.…”