Abstract
Abstract. Polar mesosphere summer echoes (PMSE) are strong enhancements of received signal power at very high radar frequencies occurring at altitudes between about 80 and 95 km at polar latitudes during summer. PMSE are caused by inhomogeneities in the electron density of the radar Bragg scale within the plasma of the cold summer mesopause region in the presence of negatively charged ice particles. Thus the occurrence of PMSE contains information about mesospheric temperature and water vapour content but also depends on the ionisation due to solar wave radiation and precipitating high energetic particles. Continuous and homogeneous observations of PMSE have been done on the North-Norwegian island Andøya (69.3° N, 16.0° E) from 1999 until 2008 using the ALWIN VHF radar at 53.5 MHz. In 2009 the Leibniz-Institute of Atmospheric Physics in Kühlungsborn, Germany (IAP) started the installation of the Middle Atmosphere Alomar Radar System (MAARSY) at the same location. The observation of mesospheric echoes could be continued in spring 2010 starting with an initial stage of expansion of MAARSY and is carried out with the completed installation of the radar since May 2011. Since both the ALWIN radar and MAARSY are calibrated, the received echo strength of PMSE from 14 yr of mesospheric observations could be converted to absolute signal power. Occurrence frequencies based on different common thresholds of PMSE echo strength were used for investigations of the solar and geomagnetic control of the PMSE as well as of possible long-term changes. The PMSE are positively correlated with the solar Lyman α radiation and the geomagnetic activity. The occurrence frequencies of the PMSE show slightly positive trends but with marginal significance levels.
Highlights
The phenomenon of strong radar echoes from the mesopause region during summer is well known from VHF radar observations at frequencies between ∼ 2 MHz and ∼ 1 GHz at polar and middle latitudes for more than 30 yr
The results indicate a generally low dependence of Polar mesosphere summer echoes (PMSE) occurrence on solar activity and confirms the conclusion by Bremer et al (2009) that various processes caused by solar radiation, reduce the influence of increasing electron density due to increasing ionisation which should increase PMSE
The investigation is based on occurrence rates derived from radar volume reflectivity of the received echoes considering the differences in technical performance and experimental operation of the radars ALWIN and Middle Atmosphere Alomar Radar System (MAARSY) used at the same site during the long period of observation
Summary
The phenomenon of strong radar echoes from the mesopause region during summer is well known from VHF radar observations at frequencies between ∼ 2 MHz and ∼ 1 GHz at polar and middle latitudes for more than 30 yr. These so called Polar Mesosphere Summer Echoes (PMSE) are caused by inhomogeneities in the electron density of a size comparable to the radar Bragg scale (about 3 m at 50 MHz radar frequency) in the presence of negatively charged aerosol particles. The basis of radar volume reflectivity which allows the comparison of observations from different radar systems
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