Morphology and possible origins of near‐range oblique HF backscatter at high and midlatitudes

• Published in: Radio science 2016-06, Vol.51 (6), p.718-730
• Main Authors: Ponomarenko, Pavlo, V., Iserhienrhien, Blessing, St.‐Maurice, Jean‐Pierre
• Format: Article
• Language: English
• Subjects: Auroral zones; Backscattering; Daytime; E region; Echoes; Electric fields; Energetic particles; Geophysics; HF backscatter; High frequencies; Irregularities; Latitude; Meteor trails; Morphology; near‐range echoes; Noon; Population (statistical); Populations; Radar; Radar networks; Scattering; Seasons; Statistical analysis; Summer; SuperDARN; Turbulence; Turbulence effects
• ISSN: 0048-6604; 1944-799X
• DOI: 10.1002/2016RS006088

High‐frequency radars (HF, ∼10–20 MHz) forming the Super Dual Auroral Radar Network (SuperDARN) regularly observe returns from very close ranges of ≤300–400 km (near‐range echoes, NREs). These echoes are conventionally attributed to backscatter from meteor trails, but other sources of NRE have been invoked, including polar mesospheric summer echoes (PMSE), and non‐field‐aligned E region irregularities leading to high‐aspect ionospheric returns. In order to relate NRE to a particular mechanism, it is essential to establish beforehand their spatiotemporal trends with respect to season, local time, and latitude. Systematic information of this kind is generally lacking from the literature, so we attempt to fill the gap by performing a statistical analysis of such echoes observed by five radars covering midlatitudes to polar latitudes over all seasons and local times. We detected two major echo populations which were observed at each radar site: (i) a nightside‐early morning returns representing the well‐known meteor backscatter and (ii) a midsummer population centered near the local noon. At high latitudes the summer daytime echoes are usually interpreted as PMSE, but the observed population extends to much lower latitudes and is centered well above the conventional PMSE height range. We hypothesize that this population could be related to neutral turbulence in the lower E region. In addition, there was a pronounced evening population restricted to the auroral region which we provisionally attribute to irregularities generated by the precipitating energetic particles and strong electric fields. Key Points Morphology of near‐range HF backscatter was established across a wide range of latitudes with three major populations being identified Midday‐midsummer echoes show characteristics incompatible with Polar Mesospheric Summer Echoes invoked previously for interpretation Based on the obtained information, these echoes are tentatively attributed to neutral turbulence effects at altitudes near 100 km