Journal Article

Plasma Structure Decay Rates in the Equatorial Ionosphere Are Strongly Coupled by Turbulence

Klenzing, J., Lee, W., Park, J., Jin, Y., Ivarsen, M. F., St‐Maurice, J.‐P.

2024

Overview

Equatorial plasma irregularities in the ionospheric F‐region proliferate after sunset, causing the most apparent radio scintillation “hot‐spot” in geospace. These irregularities are caused by plasma instabilities, and appear mostly in the form of under‐densities that rise up from the F‐region's bottomside. After an irregularity production peak at sunset, the amplitude of the resulting turbulence decays with time. Analyzing a large database of irregularity spectra observed by one of the European Space Agency's Swarm satellites, we have applied a novel but conceptually simple statistical analysis to the data, finding that turbulence in the F‐region tends to decay with a uniform, scale‐independent rate, thereby confirming and extending the results from an earlier case study. We find evidence for two regimes, one valid post‐sunset (1.4 hr decay rate) and one valid post‐midnight (2.6 hr). Our results should be of utility for large‐scale space weather modeling efforts that are unable to resolve turbulent effects. Plain Language Summary After sunset in the equatorial region of Earth, GPS devices frequently experience service interruption due to space weather. The signal disruptions that cause these interruptions are in turn caused by plasma turbulence in Earth’s ionosphere, a layer of ionized gas that covers Earth like a blanket of electrical currents. The growth of such turbulence has been studied for decades, but little is still known about how such plasma irregularity structures decay with time. We elucidate the topic, showing that turbulence cause structures to decay at the same rate regardless of size. This important result will have consequences for large‐scale space weather modeling efforts, since such models rarely have the capability to resolve turbulence. Turbulence is an enigmatic chaotic behavior often that is often present in astrophysical processes, but also on Earth’s oceans and in its atmosphere. Key Points Turbulence forces equatorial irregularities to decay with a scale‐independent rate Equatorial irregularities of scale‐sizes between 500 m and 75 km are not dissipating by chemical recombination or perfect ambipolar diffusion Decay rates depend on solar local time, with post‐sunset decay rates around 1.4 hr, increasing to 2.6 hr post‐midnight

• Publisher: John Wiley & Sons, Inc
• Subject: Astronomical models / Atmospheric turbulence / Decay / Decay rate / Earth / Equatorial ionosphere / equatorial plasma bubbles / Equatorial regions / Global positioning systems / GPS / GPS scintillations / Ionosphere / Irregularities / irregularity dissipation / Magnetohydrodynamic stability / Modelling / Oceanic turbulence / Oceans / Plasma / Plasma instabilities / Plasma turbulence / Satellite observation / Space weather / Statistical analysis / Statistical methods / Sunset / Swarm / Turbulence / Weather