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

Fig. 4 Spectra of PMSE measured at the almostthe same time in the same range gateswith the SSR (left side) and the ESR (rightside) on 53.5 MHz and 500 MHz, respectively.In the upper range gate thecorresponding width in fluctuating velocityunits is about equal, whereas this is not thecase in the lower range gate 86.1 km. In thelower two range gates spectra on 500 MHzare extremely narrow, and the spectrum on53.5 MHz show several spikes. This seems toindicate that thescattering medium or the coherentscattering process is different on thetwo spatial scales of 0.3 cm and 3.8 m,respectively. We also notice that the noiselevel on 500 MHz is much higher than theone on 53.5 MHz. This provides a gross estimate of the scatter cross section, which is muchsmaller on 500 MHz than on 53.5 MHz. A quantitative estimate of scatter cross section andSchmidt number was deduced by Röttger et al. (2000). In Fig. 5 we show the results of suchdeductions which first of all need the radar reflectivity on both frequencies, which is obtainedfrom the signal power, the turbulence energy dissipation from the spectrum width of thenarrow-beam ESR spectra (assuming a reasonable BV frequency) and the electron densityfrom the ESR incoherent scatter as well. Schmidt numbers as high as 100 are needed, if wecan assume that the scattering mechanism is the same on both radar wavelengths.Recognizing the results shown in Figs. 6 and 7, this may be questioned.Fig. 5 Models of radar volume reflectivity as function of spatial wavenumberk for different Schmidt numbers, which are determined by theelectron diffusivity and reflectivity values measured on 53.5 MHz with theSSR and on 500 MHz with the ESR (see Röttger, 2000, for details andreferences).108