Talk:Polar mesospheric summer echoes

Untitled

The sentences "PMSE is believed to be caused by structural irregularities in the ionospheric electron density at lower altitudes. The exact cause of PMSE is not yet known, although theorists have proposed steep electron density gradients, heavy positive ions, dressed aerosols, gravity waves and turbulence as possible explanations." are awful in so many ways, I don't really know where to start. How about the beginning? PMSEs are not "believed to be caused by structural irregularities in the ionospheric electron density". There is no doubt that radar signal is reflecting off of fluctuations in the free electron density; that's how radar works. The issue is that, at that altitude, there is no way for thermal turbulence to generate structures small enough to reflect MST radar. Two things are required to generate these structures: 1) reduction in free electron diffusivity, and 2) source of turbulence. I don't believe we have definitive proof of the source of either of these, but current theories suggest that the solution to (1) is that free electrons are strongly coupled to large, negatively charged aerosols (diffusivity scales as 1/r^2). Partial reflection (e.g., off of steep electron density gradients) and hydrated (heavy) positive ions have both been shown to be incorrect explanations (and really, heavy positive ions are just a possible solution to the diffusivity issue, and not turbulence). Breaking gravity waves (and also shear instabilities) are common scapegoats for turbulence; "gravity waves and turbulence" aren't two separate "possible explanations". Rapp et al. [2003] (The role of charged ice particles for the creation of PMSE: a review of recent developments) is the most recent review article I'm aware of, but I could have missed something. The two Cho review articles are also good places to start. — Preceding unsigned comment added by 67.171.16.39 (talk • contribs) 2007-11-05T05:59:12