Solar Flare

Solar Flare impact on HF communication & the Ionosphere-Thermosphere system

Solar flares pose a significant threat to High Frequency (HF) radio wave propagation, particularly in the frequency range of 3-30 MHz. This research delved into the intricate impact of solar flares on trans-ionospheric signals. A notable consequence of solar flares is the heightened absorption of HF signals at the D-region heights, resulting in what is commonly known as shortwave fadeout (SWF). Leveraging observations from the SuperDARN HF radar and employing first-principle-based modeling, this study characterized and modeled this flare-induced HF absorption.

Beyond absorption, solar flares induce dynamic disruptions in the HF signal frequency, causing sudden phase and frequency shifts. This phenomenon, termed the ‘Doppler flash,’ precedes the HF absorption effect. Investigations have done into the sources of these abrupt shifts involved utilizing the NCAR/WACCM-X physical model and HF raytracing techniques. These efforts aimed at comprehending the underlying mechanisms of flare-driven alterations in signal characteristics, contributing to a nuanced understanding of the intricate dynamics involved.

Data-model comparison for SuperDARN Blackstone radar measurements at the peak of the Doppler flash (22:08 UT). Field-of-view scan plots showing: (a) Doppler velocity simulated using the model and (b) observations from the Blackstone radar. Doppler velocity is color coded according to the scale on the right. Root-median-squared-error and mean percentage error between modeled and observed Doppler velocity is provided in panel (b). The region enclosed by the red dashed lines represents beam 7 of the radar.

In addition to these investigations, study revisited a less-explored ionospheric property known as sluggishness, an inertial aspect of the ionosphere. Research scrutinized its variations with solar flare intensity and provided insights into D-region ion chemistry through simulation studies. This holistic approach to studying solar flare impacts on HF communication, encompassing absorption, Doppler shifts, and ionospheric properties, contributes to a comprehensive understanding of the challenges posed by space weather phenomena. Such insights are crucial for developing effective mitigation and prediction strategies to safeguard communication systems reliant on HF radio waves.

Ionospheric sluggishness in Ottawa (OTT) riometer measurement during a solar flare event on March 11, 2015, estimated using (a) conventional, (b) peak time derivative, and (c) correlation methods. Red and black colors represent SXR irradiance from GOES and CNA observations from the riometer, respectively. The solid and dashed vertical lines in panels (a) and (b) represent peaks and peak time derivative in both data sets, respectively. The dashed red curve in panel (c) represents time delayed GOES SXR irradiance data. Sluggishness values estimated using the three different methods are provided inside each panel.

In recent times, this study has pivoted towards a more focused exploration of the impact of solar flares on ionospheric electrodynamics. This shift involves a detailed examination of the impulse signatures within ionospheric electrojets, with a particular emphasis on addressing the following question.

  • How does solar flare create the impulse in the ionospheric electrodynamics (Sq, Equatorial, and Auroral Electrojets)?

Ground-based HF radar observations have revealed the abrupt emergence of ionospheric backscatters, indicative of decameter-scale field-aligned irregularities, in close temporal proximity to the dawn terminator and after a substantial X9.3 solar flare. These irregularities, exhibiting radar line-of-sight Doppler velocities nearing 300 m/s, were aligned with equatorward reverse convection flow. To further investigate this phenomenon, Chakraborty have been honored with the esteemed ‘Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowship (Short-term)’ and the ‘ISEE International Joint Research Fellowship from Nagoya University.’ These prestigious fellowships support my engagement in international collaborative research in Japan, where Chakraborty will delve into the intricate dynamics and implications of these ionospheric irregularities, contributing to the global understanding of space weather phenomena.