Hectometric Continuum Radiation Observations on Different Temporal Scales in Near-Earth Space

Abstract

This study analyzes data from the ERG (Arase) satellite over a period of nearly 7 years (2017–2023). During this time, about 1,000 cases of hectometric continuum (HMC) radiation in near-Earth space were detected, which made it possible to identify characteristic features on different time scales. On a daily scale, it was established that HMC is observed at night and is completely absent during the day. There is also an asymmetric shift (different delay before the end and start of HMC generation during sunrise and sunset, respectively) of 1–3 hr relative to sunrise and sunset. Most likely, this is due to the fact that at night, when there is no solar radiation and the plasma density in the upper ionosphere is reduced, HMC is generated. On larger scales, seasonal and annual variations in HMC were detected. A predominance of HMC cases was observed during the summer months, with the fewest cases occurring during the autumn and spring equinoxes. In addition, starting from the second half of 2022, the HMC ceased to be observed, which may be associated with the approach to the peak of the 25th solar activity cycle, as indicated by the increase in the F10.7 index, Wolf numbers and Lyman-alpha radiation, which traditionally characterize solar activity.