Bibliography

Climatology of global, hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.

Younas, Waqar; Amory-Mazaudier, C.; Khan, Majid; Amaechi, Paul;

Published by: Advances in Space Research      Published on: jul

YEAR: 2022     DOI: 10.1016/j.asr.2022.07.029

annual variation; global electron content; Ionosphere; semi-annual variation; total electron content

Theoretical tools for studies of low-frequency thermospheric variability

[1]\ This paper supports studies of low-frequency variability (LFV) within the thermosphere by deriving approximate integral and closed-form solutions of a nontrivial model of thermospheric temperature, density, and composition depending on altitude and time. We also provide a paradigm for applying dimensional analysis in such studies. The domain is the region between the mesopause and the exobase. The solutions emphasize the connectedness of the thermosphere, i.e., nonlocal influences of LFV in key physical parameters and phenomena. The present focus is seasonal variability, within which the origin of a sizable semiannual variation in the thermosphere remains under active investigation. Following from the thermodynamic differential equation for temperature is a filtered, integral solution consistent with the Π theorem of dimensional analysis. A key result is the explicit demonstration that lower thermospheric boundary conditions affect low-frequency variability throughout the thermosphere, making accurate boundary conditions essential to modeling LFV. In addition, LFV of the temperature varies inversely with variability of the net heating profile and has directly and inversely proportional contributions from variations in the thermal conductivity profile, which can include an \textquotedbllefteddy diffusivity\textquotedblright component. Given a temperature profile, diffusive equilibrium defines model composition. For rapid calculations and transparency, we develop an approximate, closed-form solution for temperature, density, and composition depending only on a minimal set of observable parameters, and from that, we demonstrate the essential role of the phase and amplitude profile of the temperature LFV in determining the corresponding profile of variability in composition and density.

Picone, J.; Meier, R.; Emmert, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2013

YEAR: 2013     DOI: 10.1002/jgra.v118.910.1002/jgra.50472

dimensional analysis; low frequency variation; Pi Theorem; seasonal variation; semi-annual variation; thermospheric variability