Abstract
Since 1999 radar continuous observations of polar mesospheric echoes have been conducted on the Norwegian island of Andøya (69.30°N, 16.04°E), with the ALWIN radar (1999–2008) and MAARSY (since 2011). Traditionally these observations have been named after their seasonal occurrence, i.e., Polar Mesosphere Summer Echoes (PMSE) and Polar Mesosphere Winter Echoes (PMWE). PMSE are much stronger than PMWE and are known to be due to contributions of charged-dust (ice) particles and turbulence. On the other hand, most PMWE are mainly due to turbulence. Both echoes depend on electron density and its gradients. The use of MAARSY, more 17 dB sensitive than the ALWIN radar, makes it possible to observe turbulence-dominated echoes, usually below 80 km, all year round with a mean seasonal occurrence frequency of about 14%. Their minimum occurrence rate is 2% in July and August, while there are two maxima, one in March/April (22%) and the second one in October (26%). On average the dust-dominated summer echoes starts on 14 May and ends on 26 August (i.e. 105 days) with an average occurrence in June/July of 95%. These summer echoes occur mainly between 80 and 90 km, and present a maximum daily occurrence around 13:00 LT. On the other hand, the turbulence-dominated winter echoes occur mainly between 55 and 80 km with maximum daily occurrence around 11:30 LT. Besides the seasonal and daily occurrence of these echoes, we present the variability of occurrence frequency rates for the summer layers since 1994. After eliminating the effects of geomagnetic and/or solar activity the occurrence of the summer dust-dominated echoes show a positive trend of about 0.32%̇/yr over the last twenty seven years which might be related to the observed negative mesospheric temperature trends at polar latitudes.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
More From: Journal of Atmospheric and Solar-Terrestrial Physics
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.