A Climatology of Midlatitude Low Clouds from the ARM SGP Site: Part I: Macrophysical, Microphysical and Radiative Properties
Dong, X.(a), Minnis, P.(b), and Xi, B.(a), University of North Dakota (a), NASA Langley Research Center (b)
Fourteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting
A record of single-layer and overcast low cloud properties has been generated using data collected from January 1997 to December 2002 at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) research site. Here in part I of a series of papers examining the climatological properties of the low clouds studied over the ARM SGP site, ~2163 hours of daytime data and ~1839 hours of nighttime data have been collected during the 6-yr period. The cloud properties include liquid-phase and liquid dominant mixed-phase low cloud macrophysical, microphysical, and radiative properties. The macrophysical properties consist of cloud-base and -top heights and temperatures, and cloud physical thickness derived from a ground-based radar and lidar pair, and rawinsonde sounding. The microphysical properties include cloud liquid water path (LWP) and content (LWC), and cloud-droplet effective radius (re) and number concentration (N) obtained from microwave radiometer brightness temperature measurements, and the parameterization. The radiative properties contain cloud optical depth (tau), effective solar transmission (gama), and cloud/top-of-atmosphere albedos (Rcldy/RTOA) derived from the parameterization and standard Eppley precision spectral pyranometers. The cloud properties have been processed in terms of their seasonal, monthly, and hourly means and variabilities. In general, there are more low clouds in winter and spring than in summer. Cloud-layer altitudes and physical thicknesses were higher and greater in summer than in winter with averaged physical thicknesses of 0.85 km and 0.73 km for day and night, respectively. The seasonal variations of LWP, LWC, N,tau, and Rcldy/RTOA for both day and night basically have the same pattern: they are max-min-max from winter-summer-winter. This suggests that the low cloud microphysical and radiative properties may be affected by different air masses and synoptic weather patterns from different seasons. There is no significant variation in re, however. Although a considerable degree of variability exists, the 6-yr average values of LWP, LWC, re, N, tau, gama, Rcldy and RTOA are 151 gm-2 (138), 0.245 gm-3 (0.268), 8.7 um (8.5), 213 cm-3 (238), 26.8 (24.8), 0.331, 0.672, 0.563 for daytime (nighttime). The diurnal cycle of low clouds peaks around the local noon (from 10 am to 1 pm), however there are no strong diurnal cycles in low cloud macrophysical and microphysical properties.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
