Impacts of Variations in the Width of the Tropics

Abstract:

The implications of tropical width variations for the oceans, the cryosphere, the hydrological cycle, human society, and ecosystems are reviewed. Over the oceans, meridional shifts in the subtropical highs modify surface winds and, thereby, surface currents. Large-scale impacts on the ocean gyres, including the western boundary currents, as well as regional-scale changes in coastal currents and upwelling, are possible. Over the tropical continents, the close coupling between land-based precipitation and the upbranch of the Hadley circulation suggests implications for monsoon systems and tropical rainforests, and potential shifts in the partitioning between Walker and Hadley circulations. The poleward edge of the Hadley circulation defines the location of deserts, with possible regional associations with monsoon circulations. Variations in the width of the tropics can modify the distribution of deserts and/or the climatology of drought in marginal ecosystems. Ocean salinity maxima are also located in the subtropics, with close association to the hydrological cycle, so shifts in the width of the tropics can have implications for the thermohaline circulation, deep water formation, and sea ice distributions. The mid-latitude eddy-driven westerly flow is inextricably connected to the poleward edge of the tropics, so shifts in the width of the tropics will be accompanied by changes in the storm tracks and, therefore, the midlatitude hydrological cycle.