Polar mesosphere summer echoes (PMSE) studied at Bragg wavelengths of 2.8 m, 67 cm,and 16 cm |
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| Institution: | 1. Department of Optical Soundings and Sounding Rockets, Leibniz-Institute of Atmospheric Physics, 18225 Kühlungsborn, Germany;2. Norwegian Defence Research Establishment, Kjeller, Norway;3. EISCAT Scientific Association, Sweden;1. Centre of Studies in Resources Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India;2. Indian Institute of Geomagnetism, Mumbai 400005, India;3. Indian Institute of Geomagnetism, Navi Mumbai 410218, India;1. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA;2. Center for Space Science and Engineering Research, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA 24060, USA;3. GATS Inc., Driggs, ID 83422, USA;4. Institute of Physics, Ernst-Moritz-Arndt-University of Greifswald, Greifswald, Germany;1. Wroclaw University of Technology, Wybrze?e St. Wyspiańskiego 27, Wroc?aw, Poland;2. budowlaniec.net, ul. Pi?sudskiego 14 b, Nowa Ruda, Poland;1. Deutsches Zentrum für Luft- und Raumfahrt, Deutsches Fernerkundungsdatenzentrum, Oberpfaffenhofen, Germany;2. Umweltforschungsstation Schneefernerhaus, Zugspitze, Germany;3. Universität Augsburg, Institut für Physik, Augsburg, Germany;4. Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD, USA;5. NASA Langley Research Center, Hampton, USA;6. Center for Atmospheric Sciences, Hampton, USA;1. School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia;2. INESC Coimbra, Department of Civil Engineering, University of Coimbra, Rua Luís Reis Santos, 3030–788 Coimbra, Portugal;3. ICIST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;4. Polytechnic Institute of Coimbra, Rua Pedro Nunes – Quinta da Nora, 3030-199 Coimbra, Portugal;5. CEPAC, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal;6. Department of Civil Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal |
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| Abstract: | We present observations of radar volume reflectivities under conditions of polar mesosphere summer echoes (PMSE) at three frequencies, i.e., 53.5, 224, and 930 MHz corresponding to Bragg wavelengths of 2.8, 0.67, and 0.16 m. These measurements were made with the ALWIN radar in Andenes and the EISCAT VHF and UHF radars in Tromsø. Contributions to the signal at 930 MHz by incoherent scatter are used to estimate electron number densities and their gradient at PMSE altitudes, and spectral width measurements of Doppler spectra recorded at 224 MHz are used to estimate the turbulent energy dissipation rate. We further derive a theoretical expression for the radar volume reflectivity for the case of turbulent scatter aided by a large Schmidt number (i.e., the current standard theory of PMSE) and show that our observations quantitatively agree with this theory if Schmidt numbers between 2500 and 5000 are assumed. We then show that these Schmidt numbers correspond to ice particles with radii in the range 20–30 nm which should frequently occur in the polar summer mesopause region. In addition, we show that for the short period when PMSE was observed at UHF frequencies the volume reflectivity is proportional to a factor determined by the turbulent energy dissipation rate, electron number density, and the electron number density gradient in agreement with theory. We consider our findings as strong support that PMSE at all considered frequencies is indeed created by turbulent scatter in the presence of a large Schmidt number. We finally highlight that ultimate proof of this concept will require the direct measurement of ice particle sizes in a PMSE environment probed by radars covering frequencies between 50 MHz and 1 GHz. |
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