automated surface observing systems (asos)

Atmospheric Monitoring has been assigned as the primary responsibility for Utah State University in the Telescope

Array Low Energy Extension (TALE) Project

TA/TAE US-Japan-ROC Collaboration

An Algorithm for Evaluation of Cloud

Esmaiel Malek (Biometeorologist)

Department of Plants, Soils and Biometeorology, Utah State University, Logan, UT 84322-4820, U.S.A.

emalek@mendel.usu.edu

Clouds affect the radiation budget of our planet by:

- Reflecting, - Absorbing, and

- Scattering of solar radiation - Re-emission of the terrestrial

radiation. They affect the weather and

climate by positive or negative feedbacks.

Automated Surface Observing Systems (ASOS)

The Vaisala model CT-12K laser beam ceilometer is used at the ASOS to

measure the cloud base height and report the sky conditions on an hourly

basis or at shorter intervals. This laser ceilometer is a fixed-type

whose transmitter and receiver point straight up at the cloud (if any) base.

- It is unable to measure clouds that are not above the sensor.

- A single cloud hanging overhead the sensor will cause overcast readings, whereas, a hole in the clouds could

cause a clear reading to be reported. To report cloudiness at the local scale, many of these type of ceilometers are needed. This is not a perfect method

for cloud measurement.

To overcome this problem, we have set up a ventilated radiation station at Cache-Logan Airport, Utah, U.S.A., since 1995, along

with an algorithm for evaluation of the

-cloud base temperature, - cloud base height, and

- percent of skies covered by cloud at the local scale.