1. A Statistical Study of Modulation of Electromagnetic Ion Cyclotron Waves Observed on Ground.
- Author
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Upadhyay, Aditi, Kakad, Bharati, Kakad, Amar, and Rawat, Rahul
- Subjects
ION acoustic waves ,INDUCTION coils ,RADIATION belts ,NONLINEAR theories ,RELATIVISTIC electrons ,CYCLOTRONS ,SCATTERING (Physics) ,GEOMAGNETISM - Abstract
The modulation of electromagnetic ion cyclotron (EMIC) waves by different geomagnetic pulsations is known to us from both ground and satellite observations. However, their dependence on the EMIC wave characteristics is not well explored. We report a statistical analysis of modulation of EMIC waves by short and long periodicities at the Indian Antarctic station, Maitri (L ≈ 5). We have analyzed the induction coil magnetometer data for the period of 2011–2017 and identified 6,845 EMIC wave events, out of which 5,502 events (80%) clearly showed the presence of short period modulation. These short period modulations are associated with repetitive rising tone EMIC wave emissions. Among these 5,502 EMIC wave events only 2,413 events showed presence of long period modulation, in addition to the short period modulation. Next we have examined the characteristics like start time, end time, peak frequency, frequency extent, maximum power, and dominant short and long periodicities present in each EMIC wave event. Based on the statistical analysis, we found that the dominant short and long periodicities in the EMIC waves are in the range of 1.5–3 min and 10–60 min, respectively. These short period decreases with an increase in the peak frequency of the EMIC wave. It is attributed to the decrease in magnetic field line oscillation period at lower L‐shells. Additionally, we noticed that the stronger EMIC wave events are likely to have a higher peak frequency. All these observed tendencies are examined in light of nonlinear theory, and they are found to be in good agreement. Plain Language Summary: The electromagnetic ion cyclotron (EMIC) waves play an important role in the precipitation of relativistic electrons from the outer radiation belt to the upper atmosphere. Thus, it forms an important component of the magnetospheric research. The modulation of the EMIC waves by different geomagnetic pulsations is known to us from both ground and satellite observations. It is believed that the modulation of the EMIC wave is governed through the modulation of the source region ambient plasma parameters by the ULF geomagnetic pulsations. Therefore it is possible that the modulation periodicities are linked to the EMIC wave characteristics. We examined this aspect using long‐term EMIC wave observations from Indian Antarctic ground station and validated the observed trends using nonlinear theory. Such study is important to improve our understanding about the EMIC wave modulation. Key Points: Short and long periodicities in the electromagnetic ion cyclotron (EMIC) waves are in the range of 1.5–3 min and 10–60 min, respectivelyShort period modulation is common and dependent on EMIC wave frequency such that it has larger values at higher L‐shellsStronger EMIC waves likely to have higher frequency, which is in agreement with nonlinear theory [ABSTRACT FROM AUTHOR]
- Published
- 2022
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