Abstract
Profiles of the electron number density in the ionosphere are observed at the Arecibo Radio Observatory in Puerto Rico on a regular basis. Here, we report on recent observations showing anomalous irregularities in the density profiles at altitudes >~300 km. The irregularities occurred during a period of “mid-latitude spread F,” a space-weather phenomenon relatively common at middle latitudes in summer months characterized by instability and electron density irregularities in the bottomside of the ionospheric F layer. Remarkably, electron density irregularities extended well above the layer, through the ionization peak and into the topside which is regarded as being stable. Neither the neutral atmosphere nor the ionosphere is thought to be able to support turbulence locally at this altitude. A numerical simulation is used to illustrate how a combination of atmospheric and plasma dynamics driven at lower altitudes could explain the phenomenon.
Highlights
Profiles of the electron number density in the ionosphere are observed at the Arecibo Radio Observatory in Puerto Rico on a regular basis
One is associated with dense layers of metallic ions that form in the E region of the ionosphere at altitudes near about 110 km. (The E region is the ionospheric layer in which Hall conductivity is significant, extending from about 95 to 150 km altitude.) These “sporadic E” or “Es” layers can become patchy or billowy, suggesting a causal role for Kelvin–Helmholtz instability (KHI) in the background neutral atmosphere[15,16], plasma instability has been suggested as a cause of the patchy layers as well[17]
The results of this paper are divided into radar observations from Arecibo and numerical simulations meant to help interpret the observations
Summary
Profiles of the electron number density in the ionosphere are observed at the Arecibo Radio Observatory in Puerto Rico on a regular basis. Since the 1960s, the Earth’s ionosphere has been studied with the incoherent scatter technique that uses radar to probe weak thermal fluctuations in the gas of free electrons in the upper atmosphere. “F” refers to the Fregion ionosphere which is densest at altitudes >~250 km, and “spread” refers to spreading in visual representations of highfrequency radio soundings from the F region. This spreading was historically the earliest indication of plasma density irregularities in the mid-latitude F region This spreading was historically the earliest indication of plasma density irregularities in the mid-latitude F region (see ref. 21 for review)
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