Solar Influences on the Return Direction of High-Frequency Radar Backscatter

• Published in: Radio Science
• Main Authors: Burrell, Angeline G., Perry, Gareth W., Yeoman, Timothy K., Milan, Stephen E. Milan, Stoneback, Russell
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU),Wiley, International Union of Radio Science 2018
• Subjects: Science & Technology; Physical Sciences; Technology; Astronomy & Astrophysics; Geochemistry & Geophysics; Meteorology & Atmospheric Sciences; Remote Sensing; Telecommunications; high-frequency radar; SuperDARN; ground backscatter; long-term variations; groundscatter; ionospheric propagation; HF-RADARS; NETWORK SUPERDARN; Arctic; Canada; Norway; New Zealand; Scripps; Omni; Canadian High Arctic Ionospheric Network
• Online Access: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017RS006512; http://hdl.handle.net/2381/42700; https://doi.org/10.1002/2017RS006512

The file associated with this record is under embargo until six months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above. Coherent‐scatter, high‐frequency, phased‐array radars create narrow beams through the use of constructive and destructive interference patterns. This formation method leads to the creation of a secondary beam, or lobe, that is sent out behind the radar. This study investigates the relative importance of the beams in front of and behind the high‐frequency radar located in Hankasalmi, Finland, using observations taken over a solar cycle, as well as coincident observations from Hankasalmi and the Enhanced Polar Outflow Probe Radio Receiver Instrument. These observations show that the relative strength of the front and rear beams is frequency dependent, with the relative amount of power sent to the front lobe increasing with increasing frequency. At the range of frequencies used by Hankasalmi, both front and rear beams are always present, though the main beam is always stronger than the rear lobe. Because signals are always transmitted to the front and rear of the radar, it is always possible to receive backscatter from both return directions. Examining the return direction as a function of local time, season, and solar cycle shows that the dominant return direction depends primarily on the local ionospheric structure. Diurnal changes in plasma density typically cause an increase in the amount of groundscatter returning from the rear lobe at night, though the strength of this variation has a seasonal dependence. Solar cycle variations are also seen in the groundscatter return direction, modifying the existing local time and seasonal variations. A. G. Burrell, S. E. Milan, and T. K. Yeoman were supported by NERC grant NE/K011766/1. The research at the University of Calgary was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant Program and Discovery Accelerator Supplement Program. The development and operations of the CASSIOPE/e-POP mission were supported by the Industrial Technologies Office (ITO), Canadian Space Agency (CSA), and MacDonald, Dettwiler and Associates (MDA), respectively. R. Stoneback was supported by NSF grant 1259508. e-POP RRI data can be accessed at http://epop-data.phys.ucalgary.ca. The authors acknowledge the use of IDL GEOPACK DLM in the production of the RRI data products used in this work. The authors acknowledge the use of SuperDARN data. SuperDARN is a collection of radars funded by the national scientific funding agencies of Australia, Canada, China, France, Italy, Japan, Norway, South Africa, the United Kingdom, and the United States. The Virginia Tech SuperDARN database (described at http://vt.superdarn.org/) provides up-to-date public access to the Hankasalmi observations, which were analyzed with the aid of DaViTpy. We acknowledge use of NASA/GSFC’s Space Physics Data Facility’s OMNIWeb service and OMNI data. Galactic Cosmic Ray data were obtained from the Sodankyla Geophysical Observatory at http://cosmicrays.oulu.fi. GPS TEC data products and access through the Madrigal distributed data system are provided to the community by the Massachusetts Institute of Technology under support from U.S. National Science Foundation grant AGS-1242204. Data for the TEC processing is provided by the following organizations: UNAVCO, Scripps Orbit and Permanent Array Center, Institut Geographique National, France, International GNSS Service, The Crustal Dynamics Data Information System (CDDIS), National Geodetic Survey, Instituto Brasileiro de Geografia e Estatística, RAMSAC CORS of Instituto Geográfico Nacional del la República Agentina, Arecibo Observatory, Low-Latitude Ionospheric Sensor Network (LISN), Topcon Positioning Systems, Inc., Canadian High Arctic Ionospheric Network, Institute of Geology and Geophysics, Chinese Academy of Sciences, China Meterorology Administration, Centro di Ricerche Sismogiche, Système d’Observation du Niveau des Eaux Littorales (SONEL), RENAG : REseau NAtional GPS permanent, and GeoNet— the official source of geological hazard information for New Zealand. Peer-reviewed Publisher Version