Ice concentration retrieval in mixed-phase stratiform clouds (MSCs) using radar reflectivity and 1D ice growth model

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Description

Ice nucleation has significant impacts on the radiative property and precipitation efficiency of atmospheric clouds. However, the primary ice nucleation process is still poorly understood. Stratiform mixed-phase clouds (SMCs) provide a “simple scenario” for studying ice nucleation characteristics in clouds. Due to the weak updrafts and turbulence in SMCs, ice crystals are primarily formed in the upper part of the supercooled cloud layer, grow large in a water-saturated environment, and fall out of the mixed-phase layer. Below the liquid-dominated mixed-phase cloud layer, ice crystals continue to grow and fall until they reach the level below the ice-saturation condition. Under similar meteorological conditions in terms of cloud top temperature (CTT) and liquid water path (LWP), ice crystal growths in SMCs are expected to be statistically identical. We confirm this with in situ data.

This simple ice generation and growth pattern offers opportunities to use radar reflectivity (Ze) measurements and other cloud properties to quantitatively infer the ice concentration. To remove the strong temperature dependency of ice growth, we developed a 1D ice growth model to calculate the ice diffusional growth along its fall trajectory in SMCs. The radar reflectivity and fall velocity profiles of ice particles calculated from the 1D ice growth model are evaluated with ARM Facility ground-based high- vertical-resolution radar measurements. Combining Ze measurements and 1D ice growth model simulations, we can retrieve the ice concentrations in MSCs at given CTT and LWP. The retrieved ice concentrations in SMCs are evaluated with in situ measurements and 3D cloud resolving model simulations. These comparisons show that the retrieved ice concentrations are within an uncertainty of a factor of two, statistically.