Use of cloud and radiation testbed measurements to evaluate cloud cover and convective parameterizations
Conference
·
OSTI ID:83207
- State Univ. of New York, Albany, NY (United States)
We have used temperature and humidity soundings and radiation measurements from the Atmospheric Radiation Measurement (ARM) Cloud and Radiation Testbed (CART) site in northern Oklahoma to evaluate an improved cloud cover algorithm. We have also used a new single-column model cumulus parameterization to estimate convective heating and moistening tendencies at the CART site. Our earlier analysis of cloud cover showed that relatively dry atmospheres contain small cloud amounts. We have found numerous periods during 1993 where maximum relative humidities within any layer of the atmosphere over the CART site are well below 60-80%, yet clouds are clearly reducing shortwave irradiance measured by a rotating shadowband radiometer. These ARM measurements support our earlier findings that most current climate models probably underestimate cloud coverage when relative humidities fall below the threshold humidities where clear skies are assumed. We have applied a {open_quotes}detraining-plume{close_quotes} model of cumulus convection to the June 1993 intensive observation period (16-25 June 1993). This model was previously verified with GARP Atlantic Tropical Experiment (GATE) measurements. During the June intensive observing period (IOP), relative humidities over the CART site are typically 20% less than tropical Atlantic GATE relative humidities. Our convective model calculates that evaporation of convectively induced cloud and rainwater plays a much more important role in the heating and moistening convective tendencies at the drier CART location. In particular, we predict that considerable cooling and moistening in the lower troposphere should occur due to the evaporation of convectively initiated precipitation.
- Research Organization:
- USDOE Office of Energy Research, Washington, DC (United States). Environmental Sciences Div.
- OSTI ID:
- 83207
- Report Number(s):
- CONF-940277--; ON: DE95009951
- Country of Publication:
- United States
- Language:
- English
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