Overall Strategy

Space and time scales of AMMA

To address the multiple scales that characterize the WAM, the AMMA program is structured around the following four interacting spatial scales

• The global scale: the scale at which the WAM interacts with the rest of the globe, primarily on intraseasonal-to-decadal timescales;
• The regional scale: the scale at which we consider monsoon processes and interactions between the atmosphere, land and tropical Atlantic ocean, on a very wide range of timescales, ranging from the diurnal up to seasonal and interannual;
• The mesoscale: the scale of the typical rain-producing weather systems in the WAM. Coupling between hydrology and the atmosphere at this scale is pivotal on a daily to seasonal range of timescales;
• The local scale (or sub-meso scale): from an atmospheric point of view, this is the convective rain scale (it is central to the hydrology of the Sahel and of small watersheds to the south; it is the main scale of interest for agriculture and for human impact studies in general).

Figure 1: Simplified schematic showing the characteristic space and time scales of the key phenomena to be documented by the AMMA observation program

Time scales and periods of study

Three periods of study are considered in order to sample the interannual variability and the intraseasonal variability as well as to be able to properly document the mean seasonal cycle, and possible decadal scale trends. These three periods are the Long term Observing Period (LOP: 2001-2010), the Enhanced Observing Period (EOP: 2005-2007) and the Special Observing Period (SOP: 2006) (Fig. 1).

Figure 2: The AMMA observing periods

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