Abstract. Steady state spectral features of stimulated electromagnetic emissions (SEEs) for their major emission components (DM, NC, BC, BUM, and BUS) are studied in a wide pump wave frequency range, from 4.3 to 9.5 MHz, i.e., from slightly above the 3 rd to slightly above the 7 th gyroharmonic frequency. Based on these systematic experimental data, new peculiarities in the behaviour of the SEE intensity and of the spectral properties, in relation to the gyroharmonic mode number, have been found. The experimental results, discussed in the paper, were collected during the years 1996-2000 at the Sura heating fa,cility in Russia by modification of the ionospheric F region, using ordinary mode HF pump waves.

This paper presents observations of electromagnetic ion cyclotron (EMIC) waves from multiple data sources during the four Geospace Environment Modeling challenge events in 2013 selected by the Geospace Environment Modeling Quantitative Assessment of Radiation Belt Modeling focus group: 17 and 18 March (stormtime enhancement), 31 May to 2 June (stormtime dropout), 19 and 20 September (nonstorm enhancement), and 23–25 September (nonstorm dropout). Observations include EMIC wave data from the Van Allen Probes, Geostationary Operational Environmental Satellite, and Time History of Events and Macroscale Interactions during Substorms spacecraft in the near‐equatorial magnetosphere and from several arrays of ground‐based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low‐altitude Polar Operational Environmental Satellite spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patterns and reveals some events that would not be identified as significant using near‐equatorial spacecraft alone. Relativistic and ultrarelativistic electron flux observations, phase space density data, and pitch angle distributions based on data from the Relativistic Electron‐Proton Telescope and Magnetic Electron Ion Spectrometer instruments on the Van Allen Probes during these events show two cases during which EMIC waves are likely to have played an important role in causing major flux dropouts of ultrarelativistic electrons, particularly near L* ~4.0. In three other cases, identifiable smaller and more short‐lived dropouts appeared, and in five other cases, these waves evidently had little or no effect.

We study the properties of a broadband spectral maximum (BSM) of the background noise at frequencies 2-6 Hz using the data of mid-latitude observations. We find that the parameters of the maximum depend on the local ionosphere properties and that small scales (several tens of km) are absent in the field distribution at the BSM frequencies. We propose a mechanism forming the BSM, which is related to the large gradients of the refractive indices of normal ionosphericplasma waves at altitudes from 70 to 300 km. The performed simulation of BSM spectra for a plane-stratified model of anisotropic inhomogeneous ionosphere allowed us to explain the main experimentally observed BSM properties.

No abstract