Gareth W. Perry

Automatically determining the origin direction and propagation mode of high‐frequency radar backscatter

Elevation angles of returned backscatter are calculated at Super Dual Auroral Radar Network radars using interferometric techniques. These elevation angles allow the altitude of the reflection point to be estimated, an essential piece of information for many ionospheric studies. The elevation angle calculation requires knowledge of the azimuthal return angle. This directional angle is usually assumed to lie along a narrow beam from the front of the radar, even though the signals are known to return from both in front of and behind the radar. If the wrong direction of return is assumed, large uncertainties will be introduced through the azimuthal return angle. This paper introduces a means of automatically determining the correct direction of arrival and the propagation mode of backscatter. The application of this method will improve the accuracy of backscatter elevation angle data and aid in the interpretation of both ionospheric and ground backscatter observations.

Low‐Altitude Ion Heating, Downflowing Ions, and BBELF Waves in the Return Current Region

Heavy (O+) ion energization and field-aligned motion in and near the ionosphere are still not well understood. Based on observations from the CASSIOPE Enhanced Polar Outflow Probe (e-POP) at altitudes between 325 km and 730 km over one year, we present a statistical study (24 events) of ion heating and its relation to field-aligned ion bulk flow velocity, low-frequency waves and field-aligned currents (FACs). The ion temperature and field-aligned bulk flow velocity are derived from 2-D ion velocity distribution functions measured by the suprathermal electron imager (SEI) instrument. Consistent ion heating and flow velocity characteristics are observed from both the SEI and the rapid-scanning ion mass spectrometer (IRM) instruments. We find that transverse O+ ion heating in the ionosphere can be intense (up to 4.5 eV), confined to very narrow regions (∼ 2 km across B), is more likely to occur in the downward current region, and is associated with broadband extremely low frequency (BBELF) waves. These waves are interpreted as linearly polarized perpendicular to the magnetic field. The amount of ion heating cannot be explained by frictional heating, and the correlation of ion heating with BBELF waves suggest that significant wave-ion heating is occurring and even dominating at altitudes as low as 350 km, a boundary that is lower than previously reported. Surprisingly, the majority of these heating events (17 out 24) are associated with core ion downflows rather than upflows. This may be explained by a downward-pointing electric field in the low-altitude return current region.

Citizen Radio Science: An Analysis of Amateur Radio Transmissions With e‐POP RRI

We report the results of a radio science experiment involving citizen scientists conducted on 28 June 2015, in which the Radio Receiver Instrument (RRI) on the Enhanced Polar Outflow Probe (e-POP) tuned-in to the 40 and 80 m Ham Radio bands during the 2015 American Radio Relay League (ARRL) Field Day. We have aurally decoded the Morse coded call signs of 14 Hams (amateur operators) from RRI’s data to help ascertain their locations during the experiment. Through careful analysis of the Hams’ transmissions, and with the aid of ray tracing tools, we have identified two notable magnetoionic effects in the received signals: plasma cutoff and single-mode fading. The signature of the former effect appeared approximately 30 seconds into the experiment, with the sudden cessation of signals received by RRI despite measurements from a network of ground-based receivers showing that the Hams’ transmissions were unabated throughout the experiment. The latter effect, single-mode fading, was detected as a double-peak modulation on the individual “dots” and “dashes” of one the Ham’s Morse coded transmissions. We show that the modulation in the Ham’s signal agrees with expected fading rate for singlemode fading. The results of this experiment demonstrate that Ham Radio transmissions are a valuable tool for studying radio wave propagation and remotely sensing the ionosphere. The analysis and results provide a basis for future collaborations in radio science between traditional researchers in academia and industry, and citizen scientists in which novel and compelling experiments can be performed. Plain Language Summary We report the results of an experiment in which we used a satellite-based radio receiver to eavesdrop on Ham radio communications as the satellite passed over the United States. We identified 14 Ham radio users by their call signs, and used this information to determine their location during the experiment. We were able to identify unique signatures in the Hams’ signals that are directly related to the nature of the how the Hams’ radio waves traveled through the Earth’s ionosphere up to the satellite. Furthermore, we used our knowledge of the position of the spacecraft, and the location of the Hams and their broadcast frequencies to deduce the structure of the Earth’s ionosphere over the United States during the experiment. This experiment and its results show that Ham radio transmissions and Hams (amateur radio operators) can be valuable assets in determining the structure of the ionosphere over large geographic regions.