Exploring the Impacts of Aerosols on ITCZ Position Through Altering Different Autoconversion Schemes and Cumulus Parameterizations

Abstract

AbstractTo disentangle the mechanisms how different types of aerosols influence the position of the Intertropical convergence zone (ITCZ), this study explores the impacts of black carbon (BC) and sulfate (SO4) aerosols on the ITCZ latitudinal position through altering different autoconversion schemes and cumulus parameterizations within a single climate model. To investigate their impacts with a detectable magnitude, we homogeneously perturb the emissions of BC and SO4 in the year 2000 by 10 and 5 times, respectively. It is found that for 5SO4 cases, altering the autoconversion scheme not only affects the total (atmosphere plus ocean) anomalous cross‐equatorial heat transport, but also modulates the atmospheric portion in it, and thus influences the magnitude of the corresponding ITCZ shift. The atmospheric portion in the 5SO4‐induced total anomalous cross‐equatorial heat transport increases with the cloud adjustment to 5SO4, as longer cloud lifetime can suppress more surface evaporation in the northern hemisphere and increase southern‐northern hemispheric energy contrast in the atmosphere. For 10BC cases, it is found that with the increase of cloud adjustment, the corresponding oceanic anomalous cross‐equatorial heat transport tends to shift from southward to northward, as larger cloud adjustment means more increase (decrease) of low (high) cloud fraction and less net downward radiation both at the top of the atmosphere and the surface in the northern hemisphere. However, the atmospheric anomalous cross‐equatorial heat transport and the consequent ITCZ shift caused by 10BC are affected little. Compared with the altering autoconversion scheme, altering cumulus parameterization has relatively small influences on the 10BC‐ and 5SO4‐induced anomalous cross‐equatorial heat transports and the consequent ITCZ shifts.