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Energetic Constraints on the ITCZ Position in Idealized Simulations with a Seasonal Cycle

Wei, Ho-Hsuan and Bordoni, Simona (2018) Energetic Constraints on the ITCZ Position in Idealized Simulations with a Seasonal Cycle. Journal of Advances in Modeling Earth Systems, 10 (7). pp. 1708-1725. ISSN 1942-2466. doi:10.1029/2018MS001313.

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The atmospheric energy budget has recently been shown to provide powerful constraints on the position and shifts of the zonal and annual mean intertropical convergence zone (ITCZ), which lies close to the latitude of zero vertically integrated energy transport (energy flux equator, EFE). Relatively little work has however explored the applicability of the energetic framework to ITCZ shifts on shorter timescales. This study investigates to what extent the EFE tracks the ITCZ on subseasonal timescales in idealized aquaplanet simulations with different mixed layer depths. It is shown that the ITCZ always lags the EFE, even in the simulation with the shallowest mixed layer depth, making it possible for the EFE and the ITCZ to reside on opposite sides of the equator. At these times, which occur as the winter cross‐equatorial Hadley circulation retreats from the summer hemisphere, the required energy balance is achieved not through shifts of the Hadley cell's ascending branch and ITCZ to track the EFE but through changes in the cell's vertical structure into one of negative gross moist stability (GMS). For any given position of the ascending branch, the winter cell is much weaker as it retreats from than as it expands into the summer hemisphere and develops a shallow return flow at mid‐to‐lower tropospheric levels where the moist static energy reaches its minimum, hence favoring a negative GMS. It is argued that the asymmetry between the expanding and retreating phases of the winter Hadley cell is linked to the nonlinear seasonal evolution of near‐surface temperatures.

Item Type:Article
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URLURL TypeDescription ItemData
Wei, Ho-Hsuan0000-0002-6201-9810
Bordoni, Simona0000-0003-4771-3350
Additional Information:© 2018. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Received 5 MAR 2018; Accepted 8 MAY 2018; Accepted article online 29 MAY 2018; Published online 31 JUL 2018. This work was supported by the National Science Foundation (AGS-1462544). The numerical simulations and analyses were conducted on the Caltech’s Division of Geological and Planetary Sciences CITerra high performance computing cluster. We thank Ori Adam, Larissa Back, David Battisti, Tobias Bischoff, Tim Cronin, Aaron Donohole, Spencer Hill, and Tapio Schneider for helpful discussion. The idealized GCM and all simulations are available at
Funding AgencyGrant Number
Subject Keywords:ITCZ; aquaplanet simulation; energy flux equator; seasonal cycle; negative GMS; cross‐equatorial energy transport
Issue or Number:7
Record Number:CaltechAUTHORS:20180530-084806340
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Official Citation:Wei, H.‐H., & Bordoni, S. (2018). Energetic constraints on the ITCZ position in idealized simulations with a seasonal cycle. Journal of Advances in Modeling Earth Systems, 10, 1708–1725.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86702
Deposited By: Tony Diaz
Deposited On:30 May 2018 16:15
Last Modified:15 Nov 2021 20:41

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