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Radar cross sections (RCS) of mesospheric layers at 50 MHz observed atJicamarca, Peru, range from 10−18 to 10−16 m−1, three ordersof magnitudes smaller than cross sections reported for polar mesosphericwinter echoes during solar proton events and six orders of magnitude smallerthan polar mesospheric summer echoes. Large RCS are found in thick layersaround 70 km that also show wide radar spectra, which is interpreted asturbulent broadening. For typical atmospheric and ionospheric conditions,volume scattering RCS for stationary, homogeneous, isotropic turbulence at 3 mare also in the range 10−18 to 10−16 m−1, in reasonableagreement with measurements. Moreover, theory predicts maximum crosssections around 70 km, also in agreement with observations. Theoreticalvalues are still a matter of order-of-magnitude estimation, since the Braggscale of 3 m is near or inside the viscous subrange, where the form ofthe turbulence spectrum is not well known. In addition, steep electrondensity gradients can increase cross-sections significantly. For thin layerswith large RCS and narrow spectra, isotropic turbulence theory fails andscattering or reflection from anisotropic irregularities may gain relevance

Radar cross sections for mesospheric echoes at Jicamarca