Meteoric smoke particles: Evidence from rocket and radar techniques

We review the available in situ evidence for the existence of charged meteoric smoke particles (MSPs) which are thought to be key players in a variety of important atmospheric processes. We show that there is now strong evidence that these particles do exist at mesopause altitudes. Importantly, different measurement techniques applied at different geographical locations and under different geophysical conditions all provide undisputable evidence for the ubiquitous presence of these particles in the upper atmosphere, even though admittedly some of the specific features like the detailed altitude distribution and the charging characteristics are not completely understood. Given these findings, it is also clear that MSPs must be considered as an important part of the D-region charge balance and hence, that they are expected to influence the scattering of radar waves from the D-region plasma. We then discuss the potential influence of charged MSPs on the spectral characteristics of incoherent scatter radar (ISR) spectra and demonstrate that particles larger than ∼0.5 nm should lead to a significant spectral narrowing and change of the observed spectral shape. We hence propose a strategy to identify the presence of charged MSPs in ISR spectra by simultaneously considering the spectral width and the spectral shape and we use measurements obtained with the EISCAT UHF radar in January 2005 to demonstrate that this is indeed a promising approach. However, our measurements also imply that very good signal quality is needed to derive quantitative results.