HR: 0800h
AN: A41A-0018    [Abstracts]
TI: Effects of Cloudiness on the Daily and Annual Radiation Balance: Elaboration on the Shartwave and Longwave Radiation
AU: * Malek, E
EM: emalek@mendel.usu.edu
AF: Utah State University, 4820 Old Main Hill, Logan, Uta 84322-4820, United States
AB: Clouds are visible masses of condensed droplets and frozen crystals of water in the atmosphere above the Earth. They make changes in the energy balance at local, regional, and planetary scales. They affect the climate by positive and negative feedback. To study these effects at local scale, we set up a radiation station which uses two CM21 Kipp & Zonen pyranometers (one inverted), and two CG1 Kipp & Zonen pyrgeometers (one inverted) in a semi-arid mountainous valley in Logan, Utah, U.S.A. The pyranometers and pyrgeometers were ventilated using four CV2 Kipp & Zonen ventilation systems. Ventilation of pyranometers and pyrgeometers prevents dew and frost and snow accumulation which otherwise would disturb the measurement. All sensors were installed at about 3 m above the ground, which is covered with natural vegetation during the growing season (May - September). The incoming (Rsi) and outgoing (Rso) solar or shortwave radiation, the incoming (Rli, atmospheric) and outgoing (Rlo, terrestrial) longwave radiation, along with the 2-m air temperature, humidity, and pressure have been continuously measured since 1995. We also measured the 3-m wind speed and direction, the surface temperature (using an IR thermometer) and precipitation (using a heated rain gauge). These parameters have been measured every 2 seconds and averaged into 20 minutes. For this study we chose three days: 6 April (a partially cloudy day), 29 July (a cloudless day), and 29 November (an overcast day), 2005, along with continuous study throughout the year 2005. We developed an algorithm for evaluation of cloudless-sky incoming (atmospheric) longwave radiation. Equations for cloudless-sky incoming shortwave and atmospheric longwave radiation were applied to compare the cloud-free measurements with the actual ones. Cloudless – measured incoming shortwave (solar) radiation is an indication of how much less radiation was received due to cloudiness (if any). Measured – cloudless incoming longwave (atmospheric) radiation shows the cloud (if any) contribution to the radiation budget. The results indicate that for the partial cloudy day of 6 April, 2005, cloudiness caused less shortwave radiation 23.29 – 13.76 = 9.53 MJ m-2 d-1 received at the surface. On the same day cloud contributed an additional radiation of 25.44 – 23.44 = 2.00 MJ m-2 d-1. On 29 November, 2005, these values were 9.37 – 1.98 = 7.39 and 28.82 – 23.86 = 4.96 MJ m-2 d-1, respectively. On the annual basis, the 2005 cloudiness caused a reduction of 7279 – 5800 = 1479 MJ m-2 y-1 for the shortwave radiation, while the additional longwave radiation due to cloudiness amounted to 9976 – 9573 = 403 MJ m-2 y-1. The cloudiness in 2005 caused a negative feedback on the climate in this valley.
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0350 Pressure, density, and temperature
DE: 0360 Radiation: transmission and scattering
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting