The Relationship between ITCZ Location and Cross-Equatorial Atmospheric Heat Transport: From the Seasonal Cycle to the Last Glacial Maximum

• Published in: Journal of climate 2013-06, Vol.26 (11), p.3597-3618
• Main Authors: Donohoe, Aaron, Marshall, John, Ferreira, David, Mcgee, David
• Format: Article
• Language: English
• Subjects: Annual; Asymmetry; Atmosphere; Atmospheric models; Atmospherics; Carbon dioxide; Climate; Climate change; Climate models; Coefficients; Convergence zones; Cooling; Earth sciences; Earth, ocean, space; Energy; Equator; Exact sciences and technology; Greenhouse gases; Hadley cells; Heat; Heat transport; Holocene; Intertropical convergence zone; Last Glacial Maximum; Marine; Marine and continental quaternary; Meteorology; Mixed layer; Mixed layer depth; Ocean mixed layer; Oceans; Paleoclimatology; Perturbation; Position (location); Precipitation; Regression analysis; Regression coefficients; Sea transportation; Seasonal variation; Seasonal variations; Simulation; Summer; Surficial geology; Tropical climates; Winter
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-12-00467.1

The authors quantify the relationship between the location of the intertropical convergence zone (ITCZ) and the atmospheric heat transport across the equator (AHTEQ) in climate models and in observations. The observed zonal mean ITCZ location varies from 5.3°S in the boreal winter to 7.2°N in the boreal summer with an annual mean position of 1.65°N while the AHTEQvaries from 2.1 PW northward in the boreal winter to 2.3 PW southward in the boreal summer with an annual mean of 0.1 PW southward. Seasonal variations in the ITCZ location and AHTEQare highly anticorrelated in the observations and in a suite of state-of-the-art coupled climate models with regression coefficients of −2.7° and −2.4° PW−1respectively. It is also found that seasonal variations in ITCZ location and AHTEQare well correlated in a suite of slab ocean aquaplanet simulations with varying ocean mixed layer depths. However, the regression coefficient between ITCZ location and AHTEQdecreases with decreasing mixed layer depth as a consequence of the asymmetry that develops between the winter and summer Hadley cells as the ITCZ moves farther off the equator. The authors go on to analyze the annual mean change in ITCZ location and AHTEQin an ensemble of climate perturbation experiments including the response to CO₂ doubling, simulations of the Last Glacial Maximum, and simulations of the mid-Holocene. The shift in the annual average ITCZ location is also strongly anticorrelated with the change in annual mean AHTEQwith a regression coefficient of −3.2° PW−1, similar to that found over the seasonal cycle.