Observations of long period HF Doppler oscillations over the dip equatorial ionosphere in the Indian longitudinal sector

S G Susanth

doi:10.17485/ijst/v14i6.2023

Abstract

Background/ Objective: The signatures of long period High Frequency Doppler (HFD) oscillations over a dip equatorial station, Trivandrum (8.33◦N, 77◦E, dip 0.4◦N) in the Indian longitudinal sector have been investigated. Methods: High cadence vertical plasma drift measurements obtained using a Multi frequency HF Doppler Radar over Trivandrum along with ground based magnetometer observations over several latitudes/longitudes have been used to address this very aspect. Findings: It has been observed that long period (~15 min.) oscillations of high latitude origin can instantaneously reflect over the equatorial latitudes in the form of coherent HFD oscillations. The study is very important as it provided a unique opportunity not only to understand various characteristics of HFD oscillations, but also expected to have significant implications in the understanding of equatorial ionospheric variability in context of solar wind-magnetosphere-ionosphere coupling. Novelty: In a complementary point of view, the study also highlights the potential of HF Doppler measurements to capture such transient events originating from interplanetary medium with an unprecedented temporal resolution. Keywords: HF Doppler radar; equatorial ionosphere; HF Doppler oscillations

Highlights

HF Doppler radar over Trivandrum has provided significant results concerning the equatorial electrodynamics and associated phenomena
The High Frequency Doppler (HFD) oscillations observed are found to be in phase with the geomagnetic field oscillations of high latitude origin
It is evident from the above discussion that, long period HFD oscillations(~15 min.) are plausible in the equatorial latitudes coherent with geomagnetic disturbances originating from high latitudes

Summary

Introduction

HF Doppler radar over Trivandrum has provided significant results concerning the equatorial electrodynamics and associated phenomena. High latitude magnetic disturbances can manifest as the correlated fluctuations in HF Doppler signals due to either the (i) electric field generated in the E region influencing the F-region as ExB drift or (ii) motion of F-region due to magnetohydrodynamic (MHD) wave[2] These HFD oscillations are generally observed during various occasions such as geomagnetic storms, pulsation events, sudden storm commencements (SC) etc. Long period (5-15 min.) pulsations are common over auroral latitudes, their counterpart HFD oscillations over equatorial/low latitudes have not been properly understood so far, mainly due to the paucity of observations In this context, in the present study, an attempt is made to understand the effects of long period oscillations (~15 min) of high latitude origin in the HF Doppler signals over the dip equator. The plausible mechanism for these observations is explored in detail

Experiment

Results and Discussion

Concluding remarks