Proceedings with Extended Abstracts (single PDF file) - Radio ...

ABOUT MULTIPLE LAYERING ANDASPECT SENSITIVITY OF POLAR MESOSPHERE SUMMER ECHOESJ. RöttgerMax-Planck-Institut, 37191 Katlenburg-Lindau, GermanyIt is frequently noticed that the Polar Mesosphere Summer Echoes (PMSE) are occurring in adouble-layer structure as reported by Röttger (1994), Rüster et al. (2001) and other authors.Although this seems to be dominating on the average if one averages the power profiles, asshown in the upper panel of Fig. 1, we can show that multiple layering is the most commonstatus, but is usually eliminated by averaging over too long time periods. The separation ofsuch persistent sheet-like layers can be as small as one kilometer or less. These thin sheets areexplained to occur in regions of lowered temperature due to long-period gravity waves(Röttger, 1994), where heavy ions and ice particle can be formed. These interact with theionospheric plasma and cause sheet-like PMSE irregularities. Here we show some evidentexamples and propose how the PMSE irregularities can be created and make a suggestion toexplain the PMSE aspect sensitivity, which is observed frequently in the lower PMSE heights.Scatter plot of PMS E (+ noi se) powerHTI of PM SEAverage powerMaxi ma ofPMS ESeparationof PMS E15 :16 21 :59Fig. 1 Typical PMSE plots covering the period of 6.74 hours and altitudes between 80 kmand 91 km. These observations were done with the SOUSY Svalbard Radar (Röttger, 2001).on 7 June 2001, 15:16-21:59 UT. The upper panel shows the scatter plot of the signal plusnoise power in linear units; the second panel is a common height-time intensity (HTI) plot,the third panel shows the maxima of layers and the lower panel their height-normalizedposition. The right-hand-side shows the averages over the given period.To avoid averaging as it is done in the upper panels of Figs. 1 and 2, we have introduced anew method, namely finding the peak (maximum in power) of the thin sheet-like layer. This isplotted in the center panels of Figs. 1 and 2 and we notice that it clearly enhances the sheetlikestructure of PMSE. Taking the height of the lowest layer as reference, we have a possibilityto measure the distance between the sheet-like layers, namely their separations, shown inthe lower panels of Figs. 1 and 2. The right-hand-side plots show the corresponding averages.We recognize that the average power shows the often-referred double peak (Rüster et al.,2001) but tends to smears out the fine structure, which we still recognize when applying themaxima-selection procedures. In particular, Fig. 2 shows that there are more than two layers.This can be shown for almost all observations of PMSE. Although we have analyzed onlydata from observations with the SOUSY Svalbard Radar, we assume that this multiply layeredstructure with vertical separations of some kilometer is universal for all PMSE observations.54