Determining electron temperature in the ionosphere is a fundamentally important measurement for space science. Obtaining measurements of electron temperatures at high altitudes (>700 km) is difficult because of limitations on ground‐based radar and classic spacecraft instrumentation. In light of these limitations, the rocket‐borne Electron Retarding Potential Analyzer (ERPA) was developed to allow for accurate in situ measurement of ionospheric electron temperature with a simple and low‐resource instrument. The compact ERPA, a traditional retarding potential analyzer with multiple baffle collimators, allows for a straightforward calculation of electron temperature. Since its first mission in 2004, it has amassed significant flight heritage and obtained data used in multiple studies investigating a myriad of phenomena related to magnetosphere‐ionosphere coupling. In addition to highlighting the scientific contributions of the ERPA instrument, this paper outlines its theory and operation, the methodology used to obtain electron temperature measurements, and a comparative study suggesting that the ERPA can also provide electron density measurements.
Narrow bandwidth, whistler-like spectral features in the extremely low frequency (ELF) range were recorded at South Pole Station over the duration of 2004.A full year of observation shows a distinct lack of activity over the Antarctic winter season. A calculation of solar zenith angle at the time of detection illustrates a connection between the occurrence of ELF whistlers and a sunlit ionosphere. ELF whistlers detected at low latitude follow a similar general trend between ELF whistler occurrence rate and changing solar zenith angle, but with an additional persistence of detections after local sunset. Temporal profiles from the International Reference Ionosphere 2016 show that the peaks in ELF whistler occurrence align with times of changing ionospheric composition. Correlation with solar activity per the F 10.7 index shows no connection to daily variations in activity, and the consistency of solar flux levels throughout 2004 appears insufficient to explain the absence of events during the winter blackout. These observations place new physical constraints on the conditions necessary for detecting ELF whistlers and suggest the potential for localized generating mechanisms due to plasma instabilities in the ionosphere.
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