Topside Ionosphere And Inner Plasmasphere At Low Solar Flux

Download or read book Topside Ionosphere and Inner Plasmasphere at Low Solar Flux written by Sevag Derghazarian and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents several detailed observations of the upper portion of the topside ionosphere and inner plasmasphere during low solar flux conditions using Jicamarca's VHF radar. This is followed by theoretical derivations and numerical simulations that aim to present the reader with valuable information and insights into this layer of the upper atmosphere. Measurements of ionospheric parameters are first presented followed by observations of a new class of non-thermal plasma density irregularities that manifest in the equatorial topside ionosphere and inner plasmasphere above Jicamarca in the nighttime and post-midnight sectors. Measurements of ionospheric parameters such as topside density, temperature, ion composition and transition height were acquired during the recent deep solar minimum and correspond to experiments run in October, 2019, February, 2020, and September, 2020. The main features observed are a large and extended decrease in noontime temperatures unlike that seen in studies at moderate solar flux levels, predawn ionospheric heating as early as 0300 LT, large day-to-day variability in the O+/H+ transition height, and negligible helium ion concentration at all altitudes. We also analyze the data in light of the SAMI2-PE model which shows less agreement with the data than at higher solar flux. The main areas of discrepancy with the data are outlined, such as the absence of significant predawn heating, less pronounced decreases in noontime temperatures, and much higher O+ fractions at high altitudes, particularly in September. A discussion is presented on bridging the discrepancies in future model runs. Novel techniques of clutter removal and noise power bias correction are introduced and described in Appendix A. The new class of plasma density irregularities observed in the topside ionosphere and inner plasmasphere in the nighttime and post-midnight sectors are distinct from equatorial spread (ESF) in terms of their morphology and because they exhibit strong spectral sidebands at the lower-hybrid frequency. The coherent echoes were observed in a series high-altitude radar experiments performed at Jicamarca utilizing long- and coded double-pulse modes and a dual-beam mode between the years of 2018 - 2022, overlapping both the deep solar minimum of 2019 - 2020, and a subsequent period of moderately low solar flux. Observations from archival long pulse topside experiments are also presented. Doppler shifts, zonal drifts, and longitudinal dimensions of the echoes are calculated. The coded double-pulse mode was used to measure the low-frequency characteristics of the echoes with fine range resolution. The long-pulse mode was employed for high-frequency spectral analysis which revealed the presence of strong spectral sidelobes at the lower-hybrid frequency. The mechanism underlying lower hybrid waves associated with these lines is subsequently investigated. We present numerical simulations which demonstrate the feasibility of an inverse energy cascade coupled with a short wavelength instability, i.e. the lower hybrid drift instability, in explaining the waves. An inverse cascade is required for short wavelength lower hybrid waves to extend to the 3 m wavelengths measured by the Jicamarca radar. The simulations were able to reproduce multiple features of the measurements.