December 2, 2009
Strong Regional Climatic Fluctuations In The Tropics
Distinct long-term variations of wet and dry phases in the tropics of East Africa
Climatic fluctuations close to the equator show a different pattern to climate change in the Arctic and Antarctic. In the tropics distinct 11500 year fluctuations between wet and dry periods can be clearly identified which do not occur in temperature reconstructions of polar ice cores. The investigations of the climate of the last 25000 years in tropical Africa show that dry phases prevailed during lower solar radiation in March and September, which caused the following rain period to be less intensive. This emphasizes the significance of hydrological variations in regional climate change, as was formulated by a European consortium of earth scientists under the direction of Professor Dirk Verschuren (University of Gent, Belgium) in the latest issue of the science magazine "Nature" (Vol. 462, 7273).
The results show that the changes from wet to dry phases vary on the same temporal sample as fluctuations in the solar radiation, which are caused by cyclic changes in the Earth's orbit around the sun. In particular the rotating of the Earth's axis at a rhythm of 23000 years becomes obvious, which consequently leads to an alternating maximum solar radiation every 11500 years in the southern tropics and in northern tropics. These radiation maxima in turn steer the position and the intensity of the inner-tropical convergence zone(ITCZ), the rain-rich cloud belt close to the equator. The ITCZ is strongest there, where the radiation is intense and evaporation is high.
It can, thus, be proven that Earth's orbit around the sun and associated regional fluctuations of solar radiation, even if these are relatively weak, have a large influence on the climate at the equator. The question as to whether these tropical climatic fluctuations have influenced the global climatic history still remains open.
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