Long term observations of PMSE using SuperDARN SANAE HF radar measurements

  • Author(s): Olakunle Ogunjobi, Venkataraman Sivakumar, Judy Ann Elizabeth Stephenson, and Zolile Mtumela
  • DOI: 10.3319/TAO.2016.09.19.01
  • Keywords: SuperDARN SANAE radar, PMSE, Mesosphere
  • Multiple–filter technique isemployedtoextractlongterm PMSE fromSuperDARNradar
  • Seasonalanddiurnal PMSE inrelation togeomagnetic activity wereexamined
  • PMSE peakscoincidedwithlowermesopause temperatureandlowered activity
Abstract

It has been known thatthe presence ofnanometre–scaleiceparticlesand neutralair turbulencein the Polar summer mesospheremodify the plasma ofthe D–region, resultinginstrong backscatters.These strongbackscattersare referred toasPolar Mesosphere SummerEchoes (PMSE).Althoughstudies onPMSE havebeenongoingforoverthree decades, aspectsrevealed byvarious instrumentsarestillsubjectofdiscussion. Sequeltothepaper ofOgunjobietal.(2015), wereportthelongterm trendsandvariationsofPMSE occurrence probabilityfromSuper DualAuroralRadarNetwork (SuperDARN)Highfrequency (HF) radar measurements overSouth AfricanNationalAntarcticExpeditionIV(SANAE IV).Inthiscurrentpaper, simplemultiple–filter techniqueisemployed toobtaintheoccurrenceprobabilityrate ofSuperDARN–PMSEduring thesummer periodsoftheyear1998to2007. TheSuperDARN–PMSEoccurrenceprobabilityrate inrelationtogeomagnetic activityisexamined. Also, the trendofmesospheric neutralwinds and temperature,during these periods, are furtherstudiedand presentedinthis paper. Both the monthlyand diurnalvariationsofoccurrenceare consistentwith previous reports,confirming the presence ofPMSE fromSuperDARNSANAE IVradarmeasurementsand the influence ofpoletopolemesospherictransport circulation.The special mesosphericmean flowobserved prior to the year 2002isascribed to the influence ofsolar activity. The SuperDARN–PMSE occurrenceprobabilitypeaks with lowered geomagneticactivity.These presentresults supportthe hypothesisthattheparticleprecipitationalsoplays animportantroleinSuperDARN-PMSEoccurrence.

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