Occurrence frequencies of polar mesosphere summer echoes observed at 69° N during a full solar cycle

[摘要] Polar mesosphere summer echoes (PMSE) are strong enhancements of receivedsignal power at very high radar frequencies occurring at altitudes betweenabout 80 and 95 km at polar latitudes during summer. PMSE are caused byinhomogeneities in the electron density of the radar Bragg scale within theplasma of the cold summer mesopause region in the presence of negativelycharged ice particles. Thus the occurrence of PMSE contains information aboutmesospheric temperature and water vapour content but also depends on theionisation due to solar wave radiation and precipitating high energeticparticles. Continuous and homogeneous observations of PMSE have been done onthe North-Norwegian island Andøya (69.3° N, 16.0° E) from1999 until 2008 using the ALWIN VHF radar at 53.5 MHz. In 2009 theLeibniz-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 becontinued in spring 2010 starting with an initial stage of expansion ofMAARSY and is carried out with the completed installation of the radar sinceMay 2011. Since both the ALWIN radar and MAARSY are calibrated, the receivedecho strength of PMSE from 14 yr of mesospheric observations could beconverted to absolute signal power. Occurrence frequencies based on differentcommon thresholds of PMSE echo strength were used for investigations of thesolar and geomagnetic control of the PMSE as well as of possible long-termchanges. The PMSE are positively correlated with the solar Lyman αradiation and the geomagnetic activity. The occurrence frequencies of thePMSE show slightly positive trends but with marginal significance levels.

[学科分类] 电子、光学、磁材料