Hemispheric asymmetry of dust shifts the latitude of tropical precipitation

Abstract:

Mineral dust is emitted primarily from arid regions, which may shrink or expand in one or both hemispheres, producing a complex and asymmetric pattern of radiative forcing that varies on interannual to millennial timescales. We assess the impact of hemispheric dust asymmetry on tropical precipitation via the dust radiative effect. Using the GFDL coupled climate model CM3 to simulate dust emission, we vary dust source strength in each hemisphere individually by factors of 0, 1, 2, or 5. Hemispherically asymmetric dust emission produces asymmetric dust load and radiative forcing. The hemispheric radiative forcing drives a cross-equatorial heat flux which shifts the ITCZ away from the hemisphere with enhanced dust load. We find significant linear relationships between the hemispheric dust forcing imbalance and the latitude of tropical precipitation globally, in the Pacific, and especially in the Atlantic basin. In addition we quantify the precipitation shift due to relative changes in hemispheric dust emission, so as to better compare with records of paleodust. This relationship offers a first-order estimation of dust effects on the hydrological cycle when investigating paleoclimate, and for accurately predicting dust effects and feedbacks on future climate.