GPS and in situ Swarm observations of the equatorial plasma density irregularities in the topside ionosphere

Abstract

Here we study the global distribution of the plasma density irregularities in the topside ionosphere by using the concurrent GPS and Langmuir probe measurements onboard the Swarm satellites. We analyze 18 months (from August 2014 till January 2016) of data from Swarm A and B satellites that flew at 460 and 510 km altitude, respectively. To identify the occurrence of the ionospheric irregularities, we have analyzed behavior of two indices ROTI and RODI based on the change rate of total electron content and electron density, respectively. The obtained results demonstrate a high degree of similarities in the occurrence pattern of the seasonal and longitudinal distribution of the topside ionospheric irregularities derived from both types of the satellite observations. Among the seasons with good data coverage, the maximal occurrence rates for the post-sunset equatorial irregularities reached 35-50 % for the September 2014 and March 2015 equinoxes and only 10-15 % for the June 2015 solstice. For the equinox seasons the intense plasma density irregularities were more frequently observed in the Atlantic sector, for the December solstice in the South American-Atlantic sector. The highest occurrence rates for the post-midnight irregularities were observed in African longitudinal sector during the September 2014 equinox and June 2015 solstice. The observed differences in SWA and SWB results could be explained by the longitude/LT separation between satellites, as SWB crossed the same post-sunset sector increasingly later than the SWA did.

Morphology of high‐latitude plasma density perturbations as deduced from the total electron content measurements onboard the Swarm constellation

“…Otherwise, the distribution of |ΔTEC| in the LOS direction space may not faithfully reflect the “morphology” of in situ perturbations but may be affected by the (possibly random) “location” of remote perturbations. As LEO‐TEC perturbations are closely correlated with in situ plasma density variations [ Zakharenkova et al , ], the effect of remote perturbations on |ΔTEC| seems small. Nevertheless, we introduce the safety measures described below to confirm that Swarm satellites are traversing in situ perturbations.…”

Climatology of GPS signal loss observed by Swarm satellites

“…Zakharenkova et al (2016) has compared Swarm in situ electron density and total electron content (TEC) measurements when irregularities were observed, and their results showed quite consistent distributions between the two datasets, which also demonstrated that most of the plasma irregularities are expected in the vicinity of the altitude of Swarm satellites. Therefore, in this study we used the in situ electron density from Langmuir probes of Swarm, to check the ionospheric background conditions when signal loss happened.…”

Coordinated Ground‐Based and Space‐Based Observations of Equatorial Plasma Bubbles

“…It is generally accepted that EPBs are triggered under a favorable condition of the generalized Rayleigh-Taylor (R-T) instability at the bottomside of the F layer, where a steep vertical density gradient forms after the E layer disappears postsunset due to high recombination rate. Furthermore, the temporal variation and occurrence distribution of irregularities/bubbles can be extracted from in situ satellite observations, such as the Defense Meteorological Satellite Program constellation Huang et al, 2002), Communications/Navigation Outrage Forecasting System (C/NOFS) satellite (Huang et al, 2014;Smith & Heelis, 2017), and Swarm constellation (Xiong et al, 2016;Zakharenkova et al, 2016). For example, the structure of EPBs can be observed from irregular traces of range-type equatorial spread F in ionograms (Abdu, 2012;Hysell, 2000;Li et al, 2018;Tsunoda, 2015).…”