PNNL

Abstract

Employing a new approach based on combined Raman lidar and millimeter-wave radar measurements and a parameterization of the infrared absorption coefficient ??(km-1) in terms of retrieved cloud microphysics, we derive a statistical relation between ??and cirrus cloud temperature. The relations ??= 0.3949 + 5.3886x10-3 T + 1.526x10-5 T2 for ambient temperature (T, ?aC), and ??= 0.2896 + 3.409x10-3 Tm for midcloud temperature (Tm, ?aC), are found using a second order polynomial fit. Comparison with two ??versus Tm relations obtained primarily from midlatitude cirrus using the combined lidar/infrared radiometer (LIRAD) approach reveals significant differences. However, we show that this reflects both the previous convention used in curve fitting (i. e., ???_ 0 at ~-80?aC), and the types of clouds included in the datasets. Without such constraints, convergence is found in the three independent remote sensing datasets within the range of conditions considered valid for cirrus (i.e., cloud optical depth