Inter-Hemispheric Albedo, the ITCZ and the West African Monsoon

Abstract:

Multiple studies show a relationship between the location of the ITCZ and the difference in albedo in the two hemispheres of Earth. In observations, the two hemispheres exhibit symmetry in their albedo but this symmetry is not reproduced in many models. Biases in cloud cover in the Southern Hemisphere storm track are one of the key drivers of inter-hemispheric albedo biases in models and many of the same models exhibit biases in their representation of the monsoons and the ITCZ. Here, we examine one such model, HadGEM2-ES, using a spectrum of idealised and bias correction experiments. We show that simplified corrections to the albedo in the Southern Hemisphere are capable of improving the representation of the monsoons. However, as the bias corrections are made more realistic and targeted at the Southern Ocean, the response in the cross-equatorial tropical energy transport changes. Albedo perturbations lead to adjustments in the partitioning of the meridional heat transport between the atmosphere and ocean. We examine the mechanisms through which these adjustments occur, both locally and through teleconnections, and how they determine the spatial pattern of the energy transport and associated precipitation response. The impact on the fidelity with which the ITCZ and monsoons are represented, with a particular focus on West Africa, are investigated.