Impacts of aerosols on ITCZ position with different autoconversion schemes and cumulus parameterizations

Many studies have found that the latitudinal displacement of the Intertropical Convergence Zone (ITCZ) induced by disturbing the interhemispheric contrast of energy was influenced greatly by how to treat the cloud-precipitation processes, and that aerosols could cause ITCZ shifts because of their asymmetrical distribution about the equator. This study explores the impacts of black carbon (BC) and sulfate (SO₄) aerosols on the latitudinal position of the ITCZ with five different autoconversion schemes and three cumulus parameterizations, within a single climate model. We homogeneously perturb the emissions of BC and SO₄in the year 2000 by 10 (10BC) and 5 (5SO₄) times, respectively, in order to amplify their impacts. It is found that altering autoconversion schemes influences the simulated effective radiative forcings (ERFs) of 10BC and 5SO₄greatly, through modulating the rapid adjustments of clouds. For example, the global-annual-mean ERFs of 10BC simulated with different autoconversion schemes can have different signs; and the global-annual-mean ERF of 5SO₄simulated with one autoconversion scheme can be as three times as that with the other one. The ITCZ shifts caused by 5SO₄with different autoconversion schemes can be very diverse in magnitude, as altering autoconversion scheme can not only affect the total (atmospheric + oceanic) interhemispheric energy imbalance caused by 5SO₄, but also modulate the role the atmosphere plays in the 5SO₄-induced total cross-equatorial heat transport anomaly. It is found that with the increase of the 5SO₄-induced cloud rapid adjustment, more and more percentage of the 5SO₄-induced total cross-equatorial heat transport anomaly is undertaken in the atmosphere. For the 10BC case, altering autoconversion scheme can even change the direction of the 10BC-induced oceanic cross-equatorial heat transport anomaly, that is the larger the 10BC-induced cloud rapid adjustment, the more likely that the corresponding oceanic cross-equatorial heat transport anomaly shifts from southward to northward. Compared with changing autoconversion scheme, it seems that altering cumulus parameterization has relatively small influence on the 10BC- and 5SO₄-induced interhemispheric energy imbalances and the consequent ITCZ shifts.