P1.4
East African temperature variations and their possible causes
J. R. Christy, Earth System Science Center, Huntsville, AL; and W. B. Norris and R. T. McNider
Surface temperatures have been observed in East Africa for more than a hundred years but heretofore have not been subjected to a rigorous climate analysis. To pursue this goal monthly averages of maximum (TMax), minimum (TMin), and mean (Tmean) temperatures were obtained for Kenya and Tanzania. After the data were organized into time series for specific sites (60 in Kenya and 58 in Tanzania), the series were adjusted for breakpoints and merged into individual grid-cell squares of 1.25°, 2.5° and 5.0°.
The results for the 5° cell that contains the most data and includes Nairobi, Mt. Kilimanjaro, and Mt. Kenya indicate that since 1905, and even recently, the trend of TMax is negligible. However, TMin results suggest an accelerating temperature rise of +0.17 ± 0.05 C° decade-1 for 1979-2004. Uncertainty estimates are based on parametric variations in the construction process and may not reflect complete uncertainty.
The difference between TMax and TMin trends, especially recently, are likely a response to complex changes in the boundary-layer dynamics. TMax reflects the significantly greater daytime vertical connection to the deep atmosphere, whereas TMin often represents only a shallow layer whose temperature is more dependent on the turbulent state than on the temperature aloft. The turbulent state is highly dependent on local land-use and locally produced aerosols. It is suggested that Tmax is a more appropriate proxy variable for assessing climate changes affecting the deep troposphere such as those induced by the enhanced greenhouse effect. A consensus of tropospheric trends above Nairobi, showing near zero values, is consistent with this hypothesis.
Poster Session 1, African Climate Poster Session
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
Previous paper Next paper