The paper deals with a unique 3-cm radar observation in which echoes arranged in cellular and striated patterns were detected out to a maximum range of ninety miles. The cellular structure closely resembles a Benard convection pattern and the cell scale is consistent with that to be expected when convection is restricted to a layer of the observed depth. The echoes cannot be attributed to clouds or precipitation, which were absent. Birds, insects, or other particulate matter are also illogical targets. Direct back scatter or angel echoes from atmospheric inhomogeneities are also precluded except at very short ranges because of the restricted echo heights and great ranges. The echoes can only be attributed to a mechanism of forward scatter by atmospheric eddies to ground targets and back via the same path. The resulting echo structure is then that of the convectively patterned atmospheric ‘mirror’ upon which are superimposed the more prominent features of the topography. Theoretical analysis indicates that the magnitude of the forward-scatter intensity function must be extremely high. However, extrapolation of the frequencies with which smaller scatter intensities have been observed indicates that the required magnitude might be expected to occur with a frequency which is in general accord with the rarity of the present phenomenon. Although the required index irregularities are extremely sharp, they are physically conceivable.
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David Atlas (1959) studied this question.