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Quantifying the uncertainty of the annular mode time scale and the role of the stratosphere |
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| Authors: | Junsu Kim Thomas Reichler |
| Institution: | 1. West African Science Service Center on Climate Change and Adapted Landuse (WASCAL), WASCAL Competence Center, 06 PO BOX 9705, Ouagadougou, Burkina Faso 2. Department of Civil Engineering and Environmental Science, Loyola Marymount University, Los Angeles, CA, USA 3. Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT, USA 4. Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA |
| Abstract: | The impact of high resolution modern vegetation cover on the West African climate is examined using the International Centre for Theoretical Physics Regional Climate Model implementing the NCAR Community Land Model. Two high resolution 25 km long-term simulations driven by the output from a coarser 50-km resolution simulation are performed for the period 1998–2010. One high resolution simulation uses an earlier and coarser-resolution version of plant functional type distribution and leaf area index, while the other uses a more recent, higher-quality, and finer-resolution version of the data. The results indicate that the new land cover distribution substantially alters the distribution of temperature with warming in Central Nigeria, northern Gulf of Guinea and part of the Sahel due to the replacement of C4 grass with corn; and cooling along the coastlines of the Gulf of Guinea and in Central Africa due to the replacement of C4 grass with tropical broadleaf evergreen trees. Changes in latent heat flux appear to be largely responsible for these temperature changes with a net decrease (increase) in regions of warming (cooling). The improved land cover distribution also results in a wetter monsoon season. The presence of corn tends to favor larger precipitation amounts via more intense events, while the presence of tropical broadleaf evergreen trees tends to favor the occurrence of both more intense and more frequent events. The wetter conditions appear to be sustained via (1) an enhanced soil moisture feedback; and (2) elevated moisture transport due to increased low-level convergence in regions south of 10N where the most substantial land cover differences are present. Overall the changes induced by the improved vegetation cover improve, to some extent, the performance of the high resolution regional climate model in simulating the main West African summer monsoon features. |
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