Renater Visio link :
https://rendez-vous.renater.fr/lobby/Seminaires_Poles_HPA_6f31a7-127173-482400
Zoom link :
https://cnrs.zoom.us/j/95003883304?pwd=MI0B5WLYiGZlzo3oAZUl5TAu4fta6q.1
Author :
Pauline Teysseyre, Doctorante au pôle HPA du LIRA.
Abstract :
----- In English -----
High Frequency (HF, 3 - 30 MHz) waves are used by various actors (civil aviation, military operations…). These waves use the ionosphere for long-distance communication. Studying the D-region (60-90 km) of the ionosphere is crucial as it controls a large part of the HF absorption, which is parametrised by the electron density.
The study of the D-region presents several challenges, amongst which its complex chemistry. The D-region’s altitude range makes continuous density monitoring impossible, entailing that the densities of the different ions and electrons are relatively unknown and data is scarce. However, the chemistry of this region is very rich. Indeed, at those altitudes, EUV, UV, X-rays, and cosmic rays ionise this medium, creating different ion species depending on different parameters such as the solar zenith angle, the altitude, or the geographic position.
I will address the D-region response to solar flares and how I model it through a simple chemistry scheme (Mitra and Rowe, 1972) that we re-developped. I will present a case study of two solar flares that happened on 2023-11-05 with almost identical solar flux and explain why the D-region response is different. Once the D-region densities are modelled, the resulting HF absorption is computed and compared to VLF measurements from Nançay.
