Comparative analysis of spread‐F signature and GPS scintillation occurrences at Tucumán, Argentina

Abstract

We analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24th solar cycle, from an Advanced Ionospheric Sounder‐Istituto Nazionale di Geofisica e Vulcanologia ionosonde and a GPS Ionospheric Scintillation and total electron content (TEC) monitor scintillation receiver, colocated at low latitude in the Southern American longitudinal sector (Tucumán, 26.9°S, 294.6°E, magnetic latitude 15.5°S, Argentina). The site offers the opportunity to perform spread‐F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread‐F signatures, classified into four types (strong range spread‐F (SSF), range spread‐F, frequency spread‐F (FSF), and mixed spread‐F), the phase and amplitude scintillation index (σΦ and S4, respectively), the TEC, and the rate of TEC parameter, marker of the TEC gradients, that can cause scintillations, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread‐F is higher in summer and lower in winter, while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter. The correspondence between SSF and scintillations seems to be systematic, and a possible correlation between S4 and FSF peaks is envisaged at the terminator. The investigation focused also on two particular periods, from 12 to 16 March 2011 and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena, allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities.

Spread F occurrence and drift under the crest of the equatorial ionization anomaly from continuous Doppler sounding and FORMOSAT-3/COSMIC scintillation data

“…Spread F occurred at night generally in the local summer half of the year and propagated roughly eastward at typical velocities of ~100-160 m s . This result is consistent with those other reports based on airglow, ionosonde, and GPS measurements (Terra et al 2004;Haase et al 2011;Alfonsi et al 2013). The advantage of continuous Doppler sounding compared with optical measurements is its independence of tropospheric weather conditions.…”

“…Moreover, equatorial and low-latitude spread F is often associated with plasma bubbles and scintillations of global positioning system (GPS) signals (Chen et al 2006;Shi et al 2011;Alfonsi et al 2013), which may cause inaccuracies in position determination. It is generally accepted that equatorial spread F (ESF) and plasma bubbles result from Rayleigh-Taylor instability triggered during the uplift of the F layer owing to the prereversal enhancement of the eastward (zonal) electric field and development of the steep plasma density gradient as the bottomside ionosphere becomes depleted after sunset (Fejer et al 1999;Stolle et al 2006;Abdu et al 2009a;Kelley 2009).…”

Comparison between IRI and preliminary Swarm Langmuir probe measurements during the St. Patrick storm period

“…These irregularities can grow to become large ionospheric depletions that are usually called equatorial plasma bubbles (e.g., Whalen 2000). The fact that very low values of N e are detected along the magnetic equator only during quiet conditions could be an additional confirmation that ionospheric irregularities can be either inhibited or triggered during disturbed periods, possibly depending on the phase of the storm and local time of occurrence of D st maximum excursion (Aarons 1991;Alfonsi et al 2013;Dabas et al 2003).…”

Daytime gigahertz scintillations near magnetic equator: relationship to blanketing sporadic E and gradient-drift instability

“…In order to account for varying geometrical effects on the measurements made at different elevation angles, the amplitude scintillation index is projected to the vertical according to the formulae described in (Alfonsi et al 2013). The elevation and azimuth of every GPS satellite signal that is received are recorded every 60 s. We focus our attention on an infinitely thin layer within the E layer at an altitude of 110 km above the Earth's surface.…”

“…Nevertheless, daytime GHz scintillation studies attracted as much attention as nighttime scintillation studies, perhaps because daytime scintillation have a relatively lower rate of occurrence and milder nature (Patel et al 2009). For the most part, scintillations are generally believed to be associated with the F layer at night and the blanketing sporadic E (E sb ) layer during the day (Kumar et al 2007;Zou and Wang 2009;Zou 2011;Seif et al 2012;Alfonsi et al 2013). …”