Radar-radiometer retrievals of cloud number concentration and dispersion parameter in nondrizzling marine stratocumulus

[摘要] The retrieval of cloud microphysical properties from remote sensorsis challenging. In the past, ground-based radar-radiometermeasurements have been successfully used to retrieve the liquidwater content profile in nondrizzling clouds but offer littleconstraint in retrieving other moments of the cloud particle sizedistribution (PSD). Here, a microphysical condensational model understeady-state supersaturation conditions is utilized to provideadditional constraints to the well-established radar-radiometerretrieval techniques. The coupling of the model with theobservations allows the retrieval of the three parameters ofa lognormal PSD, with two of them being height dependent. Twoperiods of stratocumulus from the Azores are used to evaluate thenovel technique. The results appear reasonable in two nondrizzling periods: continental-likenumber concentrations are retrieved, in agreement with thedrizzle-free cloud conditions. The cloud optical depth derived fromthe retrieved distributions compares well in magnitude andvariability with the one derived independently from a narrow fieldof view zenith radiometer. Uncertainties coming from themeasurements are propagated to the retrieved quantities to estimatetheir errors. In general, errors smaller than 20% should beattainable for most parameters, demonstrating the added value of thenew technique.

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