Temporal Characteristics of Energetic Magnetospheric Electron Precipitation as Observed During Long‐Term Balloon Observations

Abstract

The paper summarizes the properties of precipitation of magnetospheric electrons with energy above several hundred keV recorded by observing X-ray bremsstrahlung in the polar stratosphere above the Murmansk region, Russia, in 1961-2019. Precipitation occurrence rate demonstrates a clear dependence on the solar activity with a maximum at the decay phase of the 11-year solar cycle, similarly to the variability in occurrences of the high-speed solar wind streams (HSSWS). The energetic electron precipitation (EEP) event series is often initiated by a moderate geomagnetic storm caused by a HSSWS and continues during geomagnetic storm recovery. EEP demonstrates the seasonal rate variation with the maxima in occurrence rate around the spring and the autumn solstices and correlates with fluences of relativistic electrons in the outer radiation belt. For 59 years, 589 events of precipitation were observed. Analysis of the long-term time series revealed a growing trend in the rate of precipitation occurrence, especially in the 1990s to 2000s that is not properly explained yet.

Estimation of Energy Spectrum of Precipitating Magnetospheric Electrons Based on Bremsstrahlung X‐Ray Fluxes Recorded in the Atmosphere

“…Balloon measurements are carried out at Apatity (67.55°N, 33.33°E). During the flight, the radiosonde can move ∼100 km away from the launch site in latitude but not in longitude due to the direction of the winds in the observation region (Bazilevskaya et al., 2020). We use 1 min data of the radiosonde.…”

“…Measuring the X‐ray bremsstrahlung at different levels in the atmosphere enables us to derive the precipitating electron fluxes at the atmosphere boundary. Actually, in the world there is no other long‐term (for several solar activity cycles) homogeneous experimental data base of electron precipitation events in polar regions recorded directly in the atmosphere well below satellite orbits (Bazilevskaya et al., 2020; Makhmutov et al., 2006, 2016).…”

Energetic Electron Precipitation via Satellite and Balloon Observations: Their Role in Atmospheric Ionization

“…One of the EEP observation methods is the measurement on balloons of bremsstrahlung generated by precipitating electrons in the altitudes of stratosphere [17][18][19]. In our previous studies [15,20], we estimated the ion pair production into the atmosphere based on the results of selected EEP balloon observations in Apatity (N67.55, E33.33, the McIlwain parameter L = 5.3).…”