Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes

[摘要] We present small scale variations of electron number densities andparticle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the smallscale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scalesobserved. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we findthatthe radar profile is well described by the power spectral density of both electrons and charged particles at the radar halfwavelength (=the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and findthat both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on thedistribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results areconsistent with the theoretical ideas by Rappand Lübken (2003)suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavycharged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHFradar when small scale fluctuations are present.

[学科分类] 大气科学