PNNL

Abstract

A long-term climatology of classified cloud types has been generated for 13 years (1997-2009) over the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site for 7 cloud categories: low clouds, congestus, deep convection, altocumulus, altostratus, cirrostratus/anvil, and cirrus. The classification was based on the cloud macro-physical quantities of cloud top, cloud base, and physical thickness of cloud layers, as measured by active sensors such as the millimeter wavelength cloud radar (MMCR) and micropulse lidar (MPL). Climate variability of cloud characteristics has been examined using the 13-year cloud type retrieval. Low clouds and cirrus showed distinct diurnal and seasonal cycles. Total cloud occurence followed the variation of low clouds, with a diurnal peak in early afternoon and a seasonal maximum in late winter. Additionally, further work has been done to identify fair-weather shallow cumulus (FWSC) events for 9 years (2000-2008). Periods containing FWSC, a sub-category of clouds classified as low clouds, were produced using cloud fraction information from a total sky imager and ceilometer. The identified FWSC periods in our study show good agreement with manually identified FWSC, missing only 6 cases out of 70 possible events during the spring to summer season (May-August).