Type of Document Thesis Author States, Julie Author's Email Address firstname.lastname@example.org URN etd-10122005-162126 Title An Analysis of Temporal Variations in the Surface Albedo of Africa Degree Master of Science Department Meteorology, Department of Advisory Committee
Advisor Name Title G. Liu Committee Member Jon Ahlquist Committee Member Sharon E. Nicholson Committee Member Keywords
- Surface Albedo
Date of Defense 2005-09-15 Availability unrestricted AbstractABSTRACT
Surface albedo is defined as the ratio of the reflected to the incident solar radiation on the earth’s surface. Some general circulation model simulations indicate that an increase in albedo due to desertification and deforestation may lead to reduction in precipitation and evapotranspiration. The monthly mean of an earlier surface albedo dataset and MODIS are used to examine the surface albedo spatial and temporal variations of Africa. In order to study surface albedo temporal variations the African continent is divided into three regions: northern, equatorial and southern. Even though every month is analyzed, only the four months of February, April, July and November are discussed.
In the northern region both the earlier dataset and MODIS the surface albedo showed the largest annual range in surface albedo in the semi-arid and arid areas. It is in these areas where the Meteosat surface albedo values were highest. While MODIS also showed a similar annual range in these areas, however this range was over a much smaller area. The spatial variations in surface albedo in the northern region depict the geographical features of the region.
Also in the semi-arid and arid areas of the northern region is where the two datasets most differed. The largest differences between the datasets occur in February, which is during the dry season. It is in these areas where the largest surface albedo values were found and these areas are near or are west of major dust sources.
In the southern region as was the case in the northern region the semi-arid and arid areas had the largest annual ranges. In the southern region the actual surface albedo for the semi-arid and arid region are lower than the surface albedo in the northern region for the same areas. The two datasets differ the most in the semi-arid and arid areas.
To further understand the temporal and spatial variations of surface albedo, two land cover classification schemes were examined. MODIS uses the International Geosphere-Biosphere Programme 17-land cover scheme. A second land cover dataset was created from White/UNESCO vegetation map to be used with the earlier surface albedo dataset. In some areas the maximum albedo occur in the wet season while in other areas maximum albedo occur in the dry season. In the areas where maximum albedo occurs in the wet season, vegetation tended to be the major factor in determining surface albedo. In Charney’s classic 1975 paper he theorized that a reduction in vegetation would lead to an increase in surface albedo, which in turn would lead to a reduction in precipitation. In this for a majority of the vegetation groups minima in surface albedo and NDVI occur at the same time of year. These findings do not support Charney’s theory that a reduction in vegetation will lead to an increase in surface albedo. Surface albedo may be influenced by an increase in reflective surfaces.
One of the objectives of understanding the spatial and temporal variations in surface albedo is to compare model calculated surface albedo to satellite derived surface albedo. A Comparison of Biosphere-Atmosphere Transfer Scheme, Land Surface Model to Advanced Very High Resolution Radiometer lead to the parameterized albedo in the Community Land Model version 2 to be adjusted. As satellite instrumentation improves so must the land surface process of general circulation models. This study shows that the parameterized surface albedo in Community Land Model version 2 still may not correctly represent the semi-arid and arid regions of Africa. The parameterized vegetation and soil albedo values are still too low.
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access finalbw.pdf 1.36 Mb 00:06:18 00:03:14 00:02:50 00:01:25 00:00:07