Is there a causal relationship between cosmic noise absorption and PMSE

Abstract

We report on the first Southern Hemisphere comparison between polar mesosphere summer echoes (PMSE) and cosmic noise absorption (CNA). Observations were obtained during the austral summer of 2003-2004 from a 55 MHz MST radar, a 38.2 MHz imaging riometer and a 30 MHz standard riometer all co-located at Davis, Antarctica (68.6°S). Case study PMSE events suggest that CNA plays a role in the intensification of established dayside PMSE possibly linked with soft electron precipitation from the polar cusp, and indeed with a similar effect and moreover with the creation of night-side PMSE connected with hard auroral electron precipitation. Although Pearson correlation coefficients are not that high (i.e., 0.423), Spearman rank correlation coefficients of 0.315, with 123 degrees of freedom well above the 99% confidence limits, established that a weak correlation between CNA and PMSE intensity exists. We use this result to discuss two unexplained properties of PMSE: (i) diurnal minimum near ∼15-21 UT; and (ii) non-linear intensity variation as a function of latitude. Surprisingly, this study presents only the second analysis of this kind using co-located instruments. Copyright 2005 by the American Geophysical Union.