Morning Overshoot of Electron Temperature as Observed by the Swarm Constellation and the International Space Station

Abstract

The rapid increase of electron temperature in the early morning hours at low latitudes is a well‐known ionospheric phenomenon called morning overshoot. In this study, we extensively investigate the dependence of morning overshoot on local time, season, latitude/longitude/altitude, and magnetic activity. The electron temperature and density data set used in this study are obtained from (1) the Swarm constellation at two different altitudes of 470 and 520 km with identical payloads and (2) the Floating Potential Measurement Unit onboard International Space Station at an altitude of 400 km. Based on the data between 2014 and 2019, the main findings of this study are as follows: (1) on a global average, morning overshoot generally weakens with decreasing altitudes. (2) Morning overshoot is stronger around the dip equator than at midlatitude regions. As latitude increases, the overshoot decreases gradually and shifts to later local times. (3) In off‐equatorial regions the overshoot is stronger in the winter than in the summer hemisphere, especially at higher altitudes. (4) Lastly, the morning overshoot shows multiday oscillations, which are negatively correlated with plasma density and affected by geomagnetic activity.

On the Electron Temperature in the Topside Ionosphere as Seen by Swarm Satellites, Incoherent Scatter Radars, and the International Reference Ionosphere Model

“…A difference between long-term and short-term T e variations with F10.7 has also been noted [14], which further complicates the modeling of T e . Empirical models still struggle to describe small-scale structures such as the morning overshoot [15][16][17] and its dependence on solar and magnetic activity or the mid-latitude T e enhancement [18,19]. The dependence on the magnetic activity and the choice of an appropriate magnetic activity proxy for T e modeling is still an open problem; for example, Brace and Theis [20] found no clear dependence of T e on the ap index, with exception of perhaps a slight systematic increase of T e with ap at polar latitudes.…”

“…As a consequence, the present dataset of Swarm LP T e measurements is that large to cover different latitudes, local times, seasons, and also solar activity levels. Contrary to the electron density, T e data have not been extensively exploited so far; only a few and rather narrowly focused studies have been published, such as [17,24]. In this context, we aimed to investigate the main climatological trends of T e in the topside ionosphere by taking advantage of seven full years (from the beginning of 2014 to the end of 2020) of Swarm T e observations by comparing the corresponding spatial, diurnal, and seasonal trends with those modeled by IRI.…”

“…Figure 4 shows how equatorial values at Jicamarca are characterized by the presence of a remarkable morning peak between 5 and 8 MLT, with median values from ISR exceeding 3000 K; this phenomenon is often referred as morning overshoot [15][16][17]42]. Overall, daytime values stand at about 1000-1300 K, while nighttime ones at about 700-1000 K, in a quite steady fashion.…”

Observations and Validation of Plasma Density, Temperature, and Abundance From a Langmuir Probe Onboard the International Space Station

“…(2003). The plasma density and temperature data products returned by FPMU have been used in past studies addressing ionospheric variability during geospace events (Coffey et al., 2017; Yang et al., 2020). They have also aided data assimilation for models (Hartman et al., 2019), as well as model‐data comparisons (Broadwater, 2013; Willis & Pour, 2018).…”

Reply on RC1

“…The morning overshoot consists in a rapid increase of electron temperature in the early morning hours at low latitudes. Its dependence on geographic regions, local time, seasons and geomagnetic activity has been presented by Yang et al (2020), by using Swarm data and ISS/FPMU (International Space Station/Floating Potential Measurement Unit) measurements (Coffey et al, 2008). Plasma density and temperature hemispherical asymmetries have been largely investigated in ionospheric physics, and recently discussed by Hatch et al (2020).…”