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Publication Date
23 June 2015

Black Carbon Aerosol-Induced Northern Hemisphere Tropical Expansion



Global Climate Models (GCMs) underestimate the observed trend in tropical expansion. Recent studies partly attribute it to black carbon aerosols (BC), which are poorly represented in GCMs. We conduct a suite of idealized experiments with the Community Atmosphere Model (CAM4) coupled to a slab ocean model forced with increasing BC concentrations covering a large swath of the estimated range of current BC radiative forcing while maintaining their spatial distribution. The Northern Hemisphere (NH) tropics expand polewards nearly linearly as BC radiative forcing increases (0.70 W-1 m2), indicating that a realistic representation of BC could reduce GCM biases. We find support for the mechanism where BC induced midlatitude tropospheric heating shifts the maximum meridional tropospheric temperature gradient polewards resulting in tropical expansion. We also find that the NH poleward tropical edge is nearly linearly correlated with the location of the inter- tropical convergence zone (ITCZ), which shifts northwards in response to increasing BC.

“Black Carbon Aerosol-Induced Northern Hemisphere Tropical Expansion”. 2015. Geophysical Research Letters 42: 4964-4972. doi:10.1002/2015GL064559.
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