This article discusses how pyrgeometers, pyranometers, and some basic weather parameters can be used to evaluate cloud base height, cloud base temperature, and cloud coverage at the local scale throughout the year. Ground-based laser beam ceilometers are used at Automated Surface Observing Systems (ASOS) in major airports in the United States to measure cloud base height and report sky conditions hourly or at shorter intervals. These are fixed-type laser ceilometers, with transmitters and receivers pointing straight up at the cloud (if any) base. They can’t detect clouds that aren’t directly above the sensor. Many of these are used to report cloudiness at the local scale. Various types of ceilometers are required. A single cloud hanging over the sensor will result in overcast readings, whereas a hole in the clouds above the sensor may result in a clear reading. To address this issue, we have operated a ventilated radiation station at Logan – Cache Airport in Utah, United States of America, since 1995. This airport has one of the above-mentioned ceilometers. Throughout the year, this radiation station (composed of pyranometers and pyrgeometers with fields of view of 150o) and net radiometer provide continuous measurements of incoming and outgoing shortwave and longwave radiation, as well as net radiation. Taking into account the additional longwave radiation captured by the facing-up pyrgeometer during cloudy skies, which comes from the cloud in the wave band (8-13 m) that gaseous emission lacks, we developed an algorithm that provides continuous cloud information (cloud base height, cloud base temperature, and percent of skies covered by cloud) at the local scale throughout the day and night. This article reports on comparisons between ASOS and model data for the month of June, 2004. The proposed algorithm is a promising approach for evaluating cloud base temperature and height, as well as the percentage of the sky covered by cloud and its effects on aviation throughout the year. With enough pyrgeometers and surface weather parameters, the study can be expanded to a regional scale for continuous cloud evaluation.

Author(s) Details

Dr. Esmaiel Malek
Department of Applied Sciences, Embry-Riddle Aeronautical University, Worldwide Campus, 1 Aerospace Boulevard, Daytona Beach, FL 32114Port Orange, Florida, United States.

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