Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

Abstract

The polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarm mission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities. We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

Dayside Field‐Aligned Current Impacts on Ionospheric Irregularities

“…In this study, we use plasma density measurements from the Langmuir Probe on the Electric Field Instrument (EFI) (Knudsen et al, 2017) and magnetic field measurements from the Vector Field Magnetometer (VFM, Olsen et al, 2013). From the Ionospheric Plasma IRregularities (IPIR) product (Jin et al, 2019), we use vertical total electron content (VTEC) as well as ROTI, which is the rate of change of VTEC index. We also include the rate of change of density index (RODI), which is the standard deviation of the rate of change of density computed in a 10 s running window.…”

“…The VTEC, ROTI, and RODI all have a resolution of 1 Hz. For a detailed explanation of the IPIR data set, see Jin et al (2019).…”

Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites

“…This creates a sharp vertical gradient of plasma density directed upwards, contrary to the gravitational force's direction of action. For such unstable arrangement, irregularities in the F region at the bottom intensify and drift up, creating more complex plasma structures that extend to higher altitudes along magnetic field lines (Woodman and La Hoz, 1976;Abdu, 2005;Kelley, 2009). In general, ionospheric irregularities are more intense at the equatorial ionization anomaly belts (±15 • QLat) than at the geomagnetic equator as observed in Fig.…”

“…2 (dN e > 0.25 × 10 10 m −3 and dN e /N e > 0.01) to identify plasma density structures, these depletions are ionospheric irregularities. The RTI is the most known mechanism that causes irregularities in low latitudes (Kelley, 2009;Kintner et al, 2007). The lowerionospheric layer declines rapidly during the night compared to the top layer.…”

“…They may be identified as density decrease along satellite passes referred to as equatorial plasma bubbles (EPBs) or range and frequency spread signatures on ionograms commonly called equatorial spread F (ESF) (Woodman and La Hoz, 1976;Burke et al, 2004). The generalized Rayleigh-Taylor instability (RTI) is the suggested mechanism which can explain how ionospheric irregularities occur in the low latitudes (Woodman and La Hoz, 1976;Gentile et al, 2006;Portillo et al, 2008;Kelley, 2009;Schunk and Nagy, 2009). They may cause disruptions in trans-ionospheric radio signals of frequencies ranging from a few hundred kilohertz to several gigahertz, which in turn degrade the performance of communication and navigation systems (Kil and Heelis, 1998;Kintner et al, 2007).…”