Abstract
AbstractIn this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.
Highlights
Irregularities in the ionospheric plasma density impact the propagation of radio waves (Hey et al, 1946)
These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals, and inside the polar caps
We focus on in situ density measurements and use the following parameters, which are a part of the Ionospheric Plasma Irregularities (IPIR) data product: rate of change of density (ROD) and rate of change of density index (RODI)
Summary
Irregularities in the ionospheric plasma density impact the propagation of radio waves (Hey et al, 1946). They can lead to rapid fluctuations in the amplitude and phase of trans‐ionospheric radio waves received on the ground. These effects are termed as ionospheric scintillations (e.g., Basu & Groves, 2001; Yeh & Liu, 1982). The phase screen theory relates scintillations to plasma irregularities, where, for example, the variance of phase fluctuations σφ is proportional to the variance in the electron density fluctuations σΔn2 (Booker et al, 1950; Rino, 1979; Yeh & Liu, 1982), where Δn is the variation of the electron density. Amplitude scintillations depend on both the thickness of the scintillation layer and the structuring of the ionosphere in that layer
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