Inter-model spread of the climatological annual mean Hadley circulation and its relationship with the double ITCZ bias i
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Inter-model spread of the climatological annual mean Hadley circulation and its relationship with the double ITCZ bias in CMIP5 Chenggong Wang1 · Yongyun Hu1 · Xinyu Wen1 · Chen Zhou2 · Jiping Liu3 Received: 9 April 2020 / Accepted: 7 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In the present paper, we study the climatological annual mean Hadley circulation simulated by 47 coupled atmospheric and ocean general circulation models (AOGCMs) of the phase 5 of the Coupled Model Intercomparison Project (CMIP5). Our results show that the climatological annual mean states of the Hadley circulation, i.e., strength, central line, and poleward boundaries of the Hadley cells, have a large inter-model spread. The strength of the Hadley cells, i.e., the maximum value of mean meridional streamfunction (MMS), varies from 7.0 × 1010 to 11.1 × 1010 kg s− 1. The variation range is about half of the multi-model ensemble mean strength of about 8.7 × 1010 kg s − 1. The central line location between the two Hadley cells varies from 3.7° S to 7.8° N, and the poleward boundary latitudes have a variation range of 5.5° in latitude. In contrast, intermodel spreads of the Hadley circulation are much smaller in reanalyses. Using a method of inter-model empirical orthogonal function (EOF) analysis of annual-mean MMS, we show that the first principal component (PC1) is closely correlated with the central line latitudes of the Hadley cells, and that the second principal component (PC2) has a high correlation with the poleward boundaries. Both PC1 and PC2 are significantly correlated with the strength of the Hadley cells. Regressions of sea surface temperatures (SSTs) and precipitation on PC1 and PC2 show that EOF1 is associated with the well-known double intertropical convergence zone (ITCZ) problem in AOGCMs, and that EOF2 is related to the cold tongue bias. The results suggest that the large inter-model spread of the climatological mean Hadley circulation is largely due to the double ITCZ and cold tongue biases, and that the key for improving the simulation performance of the Hadley circulation is to reduce the double ITCZ and cold tongue bias in AOGCMs. Keywords The Hadley circulation · AOGCMs · Double ITCZ · Cold tongue · Climate
1 Introduction The Hadley circulation has been a classical topic in atmospheric dynamics for a few centuries (Lorenz 1967, 1983). The dynamical framework for the Hadley circulation was well established by the pioneer works of scaling theories and idealized modeling (Phillips 1956; Lorenz 1967; Held and * Yongyun Hu [email protected] 1
Laboratory for Climate and Ocean‑Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
2
School of Atmospheric Sciences, Nanjing University, Nanjing 210023, Jiangsu, China
3
Department of Atmospheric and Environmental Sciences, State University of New York, University at Albany, Albany, NY 12222, USA
Hou 1980; Held 2000). In these early idealized models, the
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