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Seasonal,annual, and interannual variability in MLT quasi-two-day waves over the low-latitude region Kolhapur (16.8°N; 74.2°E)
Authors:HP Gaikwad  AK Sharma  OB Gurav  GA Chavan  DP Nade  PT Patil  SS Nikte  GP Naniwadekar
Institution:1. Space and Earth Science Laboratory, Department of Physics, Shivaji University, Kolhapur, Maharashtra, India;2. School of Physics, Shri Mata Vaishno Devi University, Kakryal, Katra 182320 (J&K), India;3. Department of Physics, Ahmednagar College Ahmednagar, Maharashtra, India;4. Department of Physics, Sanjay Ghodawat University, Kolhapur, Maharashtra, India;5. MF Radar, Indian Institute of Geomagnetism, Shivaji University Campus, Vidyanagar, Kolhapur, Maharashtra, India;6. Department of Basic Sciences and Humanities, Fabtech Technical Campus, College of Engineering And Research, Sangola, Maharashtra, India;7. Shivaji University, Kolhapur, Maharashtra, India
Abstract:This study presents the quasi-two-day wave (Q2DW) characteristics of the mesosphere and lower thermosphere (MLT) region obtained by taking hourly mean values of horizontal wind velocities for 4? years (August 2013–July 2017) through continuous measurements using a medium-frequency (MF) radar (operating frequency – 1.98?MHz) located at the low-latitude Indian station Kolhapur (16.8°N; 74.2°E). The MF radar located at Kolhapur was upgraded in 2013, and these results of Q2DW have been reported for the first time after upgrading. The present study investigated variability in seasonal, annual, interannual, and solar indices of Q2DWs traveling in zonal (EW) and meridional (NS) components in the MLT region. The Q2DW activity is observed to be stronger during austral summer (January–February) (EW?=?~5?m/s and NS?=?~8–10?m/s) than during boreal summer (June–July) (EW = ~5 m/s and NS = ~6–8?m/s). The Q2DW amplitudes are larger in the meridional component than in the zonal one. A strong semiannual oscillation (SAO) has been observed in Q2DWs, with peak during January–February and June–July. In addition, small enhancement is seen in meridional Q2DW in October (~5–6?m/s). It is observed that the entire spectrum (40–60?h) measured between 86 and 94?km contributes to the SAO amplitudes during January–February and June–July, whereas the waves measured between 42?h and 52?h contribute to enhancement in October similar to that reported elsewhere. In general, the Q2DW amplitude shows large interannual variability. The easterlies developed in the global circulation model in Northern hemisphere during May intensify up to around summer solstice. Q2DW activity peaks during westerly shear zone and intensifies with time at a lower thermospheric altitude (above 90?km). Small positive correlations (r?=?0.2 for sunspot number and r?=?0.1 for 10.7?cm solar flux) have been observed between Q2DW amplitudes and solar activity.
Keywords:Quasi-two-day waves  MF radar  Low latitude
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