Are There 150 km Echoes at Mid-Latitudes? An Arecibo Survey
Abstract
150 km VHF echoes are a ubiquitous feature of equatorial radar surveys that continues to puzzle the ionospheric physics community. The origin of these echoes are not well understood. Recent work suggests the possibility of photoelectron enhancement of thermal fluctuations playing a role whereas the fine structuring of the echoing layers seem to suggest a resonance effect that can only operate at equatorial latitudes with magnetic flux lines terminated at both ends in the nearby E regions to the north and south of the equator. In an effort to sort out the importance of the photoelectron and resonance mechanisms it may be useful to survey the 150 km region (between 130 and 180 km altitudes) at mid-latitudes where the described resonance effect will be absent. The Arecibo incoherent scatter radar(ISR) at 430 MHz is the ideal high sensitivity instrument to conduct such a survey. The survey will attempt to answer the following questions: (1) Can Arecibo detect fine structured 150 km echoes like those observed at the equator? (2) Can Arecibo detect any photoelectron caused enhancement of ISR echoes from the 150 km region (whether fine structured or not)? The answer to question (2) will be important to assess the accuracy of the photoelectron-based enhancement mechanism proposed as a potential solution of the 150-km puzzle. The answer to question (1) on the other hand can potentially falsify the need for a resonance mechanism if fine structured 150-km echoes can be identified above Arecibo. The survey will be conducted using historical (from the Madrigal database) and newly acquired Arecibo ISR data. New observations were conducted in June 2018 with this survey in mind. Different modes of data collection including ion line and plasma line features of ISR returns will be examined in search of enhanced and/or fine structured echoing regions distinct from well understood descending layers caused by tidal shears in the same altitude region (See Figure 1).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSA31B3433R
- Keywords:
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- 2415 Equatorial ionosphere;
- IONOSPHEREDE: 2435 Ionospheric disturbances;
- IONOSPHEREDE: 2437 Ionospheric dynamics;
- IONOSPHEREDE: 2441 Ionospheric storms;
- IONOSPHERE