Researchers have noted a very significant increase in special continuous oscillations with pearl-type structures called Geomagnetic Pc1 pearl oscillations on the Earth’s surface during the recovery phase of geomagnetic storms.
This study is significant for investigating precipitation particles during geomagnetic storms and may help us understand the radiation risk to satellites and astronauts.
Earth’s magnetic field creates a protective shield around us, and various plasma waves are generated in this magnetic field cavity. However, geomagnetic storms often dent this protection. Energetic particles are either accelerated or lost from Earth’s radiation belts during these storms.
This is responsible for changes in the plasma environment leading to the growth of low-frequency waves called electromagnetic ion-cyclotron (EMIC) wave instability, which manifests as magnetic field oscillations (0.1-5 Hz) called Pc1 pulsations.
Geomagnetic pearl oscillations Pc1
Geomagnetic pearl oscillations Pc1 are amplitude modulated structured narrowband signals that are signatures of low-frequency EMIC waves generated by resonant wave-particle interactions in the Earth’s magnetosphere. Observation of these oscillations is a proxy for measuring particle collisions in the Earth’s magnetosphere.
Evidence of these pulsations is abundant in the mid- and high-latitude regions. However, this is not common at very low latitude stations. These waves are an important part of space weather in the near-Earth environment.
A team of scientists from IIG, an autonomous institute of the Department of Science and Technology, along with various Indian and global organizations, investigated the long-term variability of these pulsations in relation to solar cycles 20-21 and the descending phase of solar cycle 24 from the very low latitude region of India.
In the study published in the Journal of Atmospheric and Solar-Terrestrial Physics, the researchers used 13 years of archived records covering solar cycle 20–21 from the equatorial site Choutuppal (CPL, L = 1.03) and 5 years of digital coil magnetometer data. covering the descending phase of solar cycle 24 from the low-latitude Desalpar site (DSP, L = 1.07) to investigate the Pc1 wave structure.
Morphological changes during quiescent and active geomagnetic conditions were investigated, and the role of the ionosphere in high-latitude to low-latitude EMIC wave transmission through the ionosphere was modeled.
A clear increase in the number of Pc1 was observed at night compared to the day. This is because the attenuation of Pc1 waves when propagating through the ionospheric waveguide towards lower latitudes is weaker during the nighttime hours. Similarly, during the period of solar maximum, the transmission speed of Pc1 waves to the equator decreased than during solar minimum.
The annual and seasonal patterns of Pc1 occurrence showed an inverse relationship with the number of sunspots at both stations. The association of these pulsations with active geomagnetic conditions showed that the occurrence of Pc1 increases significantly in the recovery phase of geomagnetic storms.
The understanding of the radiation hazard to satellites and astronauts that the study offers is a great necessity in an era highly dependent on satellite-based communication systems.
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