On the statistical correlation between polar mesospheric cloud occurrence and enhanced mesospheric radar echoes

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Abstract
Using data from the Poker Flat MST radar and the Solar Mesosphere Explorer Satellite (SME), we demonstrate the existence of a statistically significant correlation between the occurrence of Polar Mesospheric Clouds (PMC) and enhanced VHF radar echoes near the high‐latitude summer mesopause. We propose three physical conditions which could explain the coexistence of strong summertime echoes and PMC. First, both the enhanced echoes and the PMC are most likely to occur in the presence of very low mesopause temperatures and associated steep temperature gradients. Second, the presence of PMC ice particles could induce a strong gradient in the electron density profile, which would produce enhancements in the radar echo strength. Third, it is likely that heavy water cluster ions, indicative of PMC particle nucleation, can alter the ambipolar diffusion coefficient, thus allowing the electron density fluctuations to extend down to much smaller vertical scales. Under these conditions, the turbulent power at the 3 meter scale required for the occurrence of the MST radar echoes could be greatly enhanced. Finally, we discuss the possibility of using MST radars as instruments for PMC detection.