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5 September 2002 Signature of cloud-base-height skewness in ARM microwave water radiometer data: implications for cloud radiative parameterizations in GCMs
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Abstract
The statistics of ground-based retrievals of cloud liquid water path using the microwave water radiometer (MWR) are typically assumed to be independent of the cloud's absolute position in the column. Furthermore, translational invariance implies statistical parity, i.e. invariance under reflection, of cloud-base height (zbot) and cloud-top height distributions. This symmetry is necessarily broken, especially under conditions of high boundary-layer relative humidity for which a minimum large-scale lifting condensation level leads to the generation of a significant positive skewness in the distribution function of zbot. We suggest that the signature of this boundary effect is visible in ARM MWR time-series collected at the TWP site. Motivated by the MWR analysis, we incorporate a minimum lifting condensation level into the analytic model of unresolved low-cloud optical variability developed by Jeffery & Austin (J. Atmos. Sci., to appear). Preliminary results indicate that the effect of cloud-base height skewness on mean oceanic low-cloud reflectivity averaged over GCM spatial scales (order 100 km) is significant.
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Christopher A. Jeffery and Anthony B. Davis "Signature of cloud-base-height skewness in ARM microwave water radiometer data: implications for cloud radiative parameterizations in GCMs", Proc. SPIE 4815, Atmospheric Radiation Measurements and Applications in Climate, (5 September 2002); https://doi.org/10.1117/12.482314
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