A study of composite cirrus morphology using data from a 94-GHz radar and correlations with temperature and large-scale vertical motion

In order to improve the representation of clouds in climate models, we require a better understanding of the relationship among cloud properties and the synoptic-scale state of the atmosphere. In order to investigate this issue as it pertains to a specific class of cirrus clouds, we have combined a 2 month data set of radar reflectivities observed at State College, Pennsylvania, using a W-band radar with output from a mesoscale model that uses 3-hourly data assimilation. Products of the analysis include statistical distributions of fundamental cirrus cloud properties, such as frequency of occurrence, base, top and midcloud height, and layer thickness. We also consider the relationships between cirrus reflectivity and the large-scale meteorological state defined by area-averaged temperature and vertical velocity. Overall, cirrus clouds are observed 32% of the time, and 51% of those events occur in conjunction with lower-level clouds. Most of the cirrus occur in thin layers (<1.5 km thickness). Cirrus occurrence appears to be related to large-scale meteorological factors but the relationships are complex. The majority of the cirrus we observed occurred at temperatures lower than -35°C and there is little correlation between radar reflectivity and temperature. We also used this data set to examine the usefulness of a satellite-borne W-band radar.