Abstract
A possible driver of precipitation of magnetospheric energetic electrons in the high-latitude atmosphere is represented by electromagnetic ion-cyclotron (EMIC) magnetospheric waves. The precipitating particles produce variations, by collision, in the ionized component of the atmosphere, altering its chemistry and electrical conductivity, with a significant impact on the atmospheric processes. In this framework, it would be significant to find experimental evidence of a correspondence between ionospheric electron density irregularities and the occurrence of Ultra-Low-Frequency (ULF) Pc1 geomagnetic pulsations, i.e., the ground signatures of EMIC waves, at high latitudes. In this work, we face this subject by considering a specific case study occurred on 22 February 2007 during quiet magnetospheric conditions. The study is based on the analysis of simultaneous ULF geomagnetic field and Total Electron Content (TEC) measurements recorded at Mario Zucchelli Station in Antarctica. We show that Pc1 pulsations occur in correspondence to solar wind pressure increases and that, at the same time, the ionosphere is characterized by the presence of ionospheric irregularities. We suggest that a possible link between the Pc1 activity and the ionospheric irregularities may be energetic electron precipitations, driven by EMIC waves generated in the compressed magnetosphere, which produce density variations in the ionized component of the atmosphere.
Highlights
Ultra-Low-Frequency (ULF) Pc1 waves (f ~ 0.2–5.0 Hz) are known to be generated by the electromagnetic ioncyclotron (EMIC) resonance in the equatorial magnetospheric regions with unstable, energetic ions, such as ring current and plasma sheet ions during disturbed geomagnetic conditions (Menk 2011)
We focused our attention on the time interval 02-14 universal time (UT) (18-06 magnetic local time (MLT) at Mario Zucchelli station (MZS), i.e., between the local magnetic evening and the local magnetic morning), excluding hours close to the magnetic noon when the region of interest approaches the polar cusp and measurements are characterized by large broadband fluctuations
Pc1 activity roughly corresponds to an enhanced solar wind dynamic pressure, suggesting that the Pc1 pulsations could represent the ground signatures of EMIC waves generated just inside the magnetopause by magnetosphere compressions
Summary
Ultra-Low-Frequency (ULF) Pc1 waves (f ~ 0.2–5.0 Hz) are known to be generated by the electromagnetic ioncyclotron (EMIC) resonance in the equatorial magnetospheric regions with unstable, energetic ions, such as ring current and plasma sheet ions during disturbed geomagnetic conditions (Menk 2011). Such waves are transmitted as Alfven waves along geomagnetic field lines into the auroral ionosphere and after being converted into compressional waves, they propagate horizontally in the waveguide represented by the ionosphere, becoming linearly polarized well far from the injection region (Greifinger and Greifinger 1968; Greifinger 1972; Fraser 1975; Fujita and Tamao 1988). A statistical study based on experimental measurements from an Antarctic magnetometer array over a very large range of geomagnetic latitudes (−62° to −87°, spanning 2920 km geographically) showed that they propagate from the injection region with power attenuation factors of 10–14 dB/1000 km (Kim et al 2011). The results of a numerical modeling presented by Fedorov et al (2018) indicate that, at distances smaller than 600 km from the injection point, the wave amplitude decreases by ~ 1 dB/100 km during nighttime and by ~ 10 dB/100 km during daytime, while at distances larger than 600 km the nighttime and daytime attenuation rates are approximately the same, ~ 1 dB/100 km
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
