Abstract
Polar Mesosphere Summer Echoes (PMSEs) are very strong radar echoes observed at altitudes near the polar summer mesopause. One of the essential properties of these radar echoes is that they can give useful diagnostic information about the physics of the scattering process. In this paper, the related characteristics of PMSEs measured with the European Incoherent SCATter Very High Frequency (EISCAT VHF) 224 MHz radar on 13–15 July 2010 are studied at different elevation angles from 78° to 90°. It is found that the PMSEs peak power and strongest PMSEs average power occur at the same elevation angles. Also interesting is that the strongest PMSEs occur at off-vertical angles when a PMSEs has a layered (multilayer) structure. And reflection may have more significant effects on PMSEs when there are double or multilayer PMSEs. Possible explanations regarding these observations are discussed.
Highlights
Polar Mesosphere Summer Echoes (PMSEs) are extremely strong radar echoes observed from 80 to 90 km at high latitudes in the Northern and Southern Hemispheres during summer
In order to study in more detail the characteristics of PMSEs with different elevation angles, on 14 and 15 July we expanded the range of elevation angles for the experiments; the elevation angle was changed by 4° increments to yield observations starting from and returning to 90°, i.e. 90°→86°→82°→78°→82°→86°→90°
By exploring the experimental results, we have found that the PMSEs peak power and maximum PMSEs average power occur at the same elevation angles
Summary
Polar Mesosphere Summer Echoes (PMSEs) are extremely strong radar echoes observed from 80 to 90 km at high latitudes in the Northern and Southern Hemispheres during summer. Nowadays it is known that PMSEs are due to scattering from fluctuations in electron density caused by atmospheric turbulence in the presence of ice particles formed from water vapor and ice particles in noctilucent clouds forming at low temperatures in the local summer mesopause. On the angular dependence of PMSEs, the obtained radar observations in the mesosphere have not been consistent with the two classical extreme models: turbulent volume isotropic scattering and Specular Fresnel reflection. In view of these empirical observations, Swarnalingam et al (2011) suggested a new model for anisotropic turbulence and Fresnel scattering. The characteristics of PMSEs with different elevation angles are a property of the scatterer, and describe the variation of scattered power with respect to the incident angle
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