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New Conceptual Model (new + conceptual_model)
Selected AbstractsA conceptual model for understanding rainfall variability in the West African Sahel on interannual and interdecadal timescalesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2001S.E. Nicholson Abstract This article describes and validates a new conceptual model for understanding Sahel rainfall variability. This conceptual model provides a framework that can readily incorporate and synthesize the roles played by the oceans, the African landmass and local meteorological factors. The most important ,local' factors are the location of the African Easterly Jet (AEJ) and the associated shears. The position of the AEJ helps to distinguish between a ,wet mode' and a ,dry mode' in the Sahel, while other factors determine which of two spatial patterns prevail during years of the dry regime. We test the paradigm by contrasting selected circulation parameters for the years 1958,1967 (representing the wet mode) and 1968,1997 (representing the dry mode). In doing so, we have identified several changes in the general atmospheric circulation that have accompanied the shift to drier conditions. The AEJ is further southward and more intense, the Inter-tropical Convergence Zone (ITCZ) is further south, the Tropical Easterly Jet (TEJ) is weaker, the equatorial westerlies are shallower and weaker, the southwesterly monsoon flow is weaker, and the relative humidity is lower (but not consistently so). The results of this study suggest that the key factor controlling the occurrence of the ,wet Sahel' mode versus the ,dry' mode is the presence of deep, well-developed equatorial westerlies. These displace the AEJ northward into Sahelian latitudes and increase the shear instabilities. The westerlies appear to be at least partially responsible for the well-known association between a weaker AEJ and wetter conditions in the Sahel, because the thermal wind induced by the Sahara/Atlantic temperature gradient is imposed upon a westerly basic state. Since one of the strongest contrasts between the ,wet Sahel' and ,dry Sahel' modes is the strength of the TEJ, the TEJ probably also plays a pivotal role in rainfall variability. In the dry mode, the equatorial westerlies are poorly developed and the core of the AEJ lies well to the south of the Sahel. The dry mode consists of two basic spatial patterns, depending on whether the Guinea Coast Region is anomalously wet or dry (the well-known dipole and no-dipole patterns, respectively). Which occurs is determined by other factors acting to reduce the intensity of the rainbelt. One of the relevant factors appears to be sea-surface temperatures (SSTs) in the Gulf of Guinea. Copyright © 2001 Royal Meteorological Society [source] Developing a theory-driven model of community college student engagementNEW DIRECTIONS FOR COMMUNITY COLLEGES, Issue 144 2008Pam Schuetz This chapter describes development and testing of a new conceptual model of community college student engagement that can be used to guide and strengthen institutional leverage over student outcomes. [source] Measuring competencies of higher education graduatesNEW DIRECTIONS FOR INSTITUTIONAL RESEARCH, Issue 126 2005Jim Allen This chapter describes a new conceptual model for measuring competencies of higher education graduates. The proposed instrument can become a valuable tool for higher education quality management, policy evaluation, and scientific research. [source] A new conceptual model for forest fires based on percolation theoryCOMPLEXITY, Issue 3 2008Allen Hunt First page of article [source] | ||||||||||