Occurrence characteristics of electromagnetic ion cyclotron waves at sub-auroral Antarctic station Maitri during solar cycle 24

Abstract

We present a statistical study of electromagnetic ion cyclotron (EMIC) waves observed at Antarctic station (geographic 70.7 • S , 11.8 • E , L = 5) on quiet and disturbed days during 2011-2017. The data span a fairly good period of both ascending and descending phases of the solar cycle 24, which has witnessed extremely low activity. We noted EMIC wave occurrence by examining wave power in different frequency ranges in the spectrogram. EMIC wave occurrence during ascending and descending phases of solar cycle 24, its local time, seasonal dependence and durations have been examined. There are total 2367 days for which data are available. Overall, EMIC waves are observed for 3166.5 h (≈ 5.57% of total duration) which has contributions from 1263 days. We find a significantly higher EMIC wave occurrence during the descending phase (≈ 6.83%) as compared to the ascending phase (≈ 4.08%) of the solar cycle, which implies nearly a twofold increase in EMIC wave occurrence. This feature is attributed to the higher solar wind dynamic pressure during descending phase of solar activity. There is no evident difference in the percentage occurrence of EMIC waves on magnetically disturbed and quiet days. On ground, EMIC waves show marginally higher occurrence during winter as compared to summer. This seasonal tendency is attributed to lower electron densities and conductivities in the ionosphere, which can affect the propagation of EMIC waves through ionospheric ducts. In local time, the probability distribution function of EMIC wave occurrence shows enhancement during 11.7-20.7 LT (i.e., afternoon-dusk sector). Daily durations of EMIC waves are in the range of 5-1015 min and it is noted that the longer duration (240-1015 min) events are prevalent on quiet days and are mostly seen during the descending phase of solar cycle.

A Statistical Study of Modulation of Electromagnetic Ion Cyclotron Waves Observed on Ground

“…In Equation , the local time (LT) is taken as 14, where the EMIC wave occurrence is most likely as reported by Upadhyay et al. (2020). The ambient ion density is assumed to be same as the electron density to fulfill quasi‐neutrality condition, n e 0 ≈ n i 0 .…”

A Case Study of Pc1 Waves Observed at the Polar Cap Associated with Proton Precipitation at Subauroral Latitudes

“…On the ground, Pc1 pulsations are commonly observed from subauroral to polar latitudes [10,18,19]. Under very quiet geomagnetic conditions (Kp ≤ 1), the occurrence peak is usually in the prenoon sector, but it shifts to afternoon for increasing geomagnetic activity [19,20].…”

Statistical Study of EMIC Wave Propagation Using Space‐Ground Conjugate Observations

“…In addition, Upadhyay et al. (2020) reported a statistical study of ground EMIC wave observations at the Maitri station ( L = 5.0). They found a higher occurrence rate of the EMIC wave event during the winter season than the summer season, although they did not incorporate the frequency dependence of the wave.…”

“…They also found a seasonal dependence of the wave frequency that shows predominant observation of higher frequency (f > 0.4 Hz) waves in the winter season when the ionospheric density is relatively low. In addition, Upadhyay et al (2020) reported a statistical study of ground EMIC wave observations at the Maitri station (L = 5.0). They found a higher occurrence rate of the EMIC wave event during the winter season than the summer season, although they did not incorporate the frequency dependence of the wave.…”