Selected related publications:

Hwang, Y.-T. and D. M. W. Frierson. A new look at the double ITCZ problem: Connections to cloud bias over Southern Ocean.^ in revision, Proc. Nat. Acad. Sci.

Frierson, D. M. W., and Y.-T. Hwang. Extratropical influence on ITCZ shifts in slab ocean simulations of global warming.** J. Climate, 25, 720-733, 2012. official link

Here, the theoretical framework is combined with other simple models (12) and attribution techniques (13, 14) that allow us to address the problem using observation data and outputs from a large suite of global climate models (GCMs) simulations and idealized GCMs experiments. We attempt to fill in gaps between observations, GCMs, and idealized simulations through exploring the following four topics related with the tropical rain belt location/displacement:

  1. (1)Observed shift: What was the primary cause of the southward shift in the tropical rain belt during the latter half of the 20th century?

  2. (2)Future projection: What is the future projection of the shift? Do GCMs agree? What are the sources of GCMs’ spread?

  3. (3)GCMs’ biases: What is the cause of the double ITCZ problem in GCMs? Are biases in extratropics responsible? How can it be improved?

Friedman, A. R., Hwang, Y.-T., Chiang, J. C. H. and D. M. W. Frierson. The interhemispheric thermal gradient over the 20th century and in future projections.*  in revision, J. Climate.


  1. 1.Xie, 2005: The shape of continents, air-sea interaction, and the rising branch of the Hadley Circulation. The Hadley Circulation: Present, Past and Future, H. F. Diaz and R. S. Bradley, Eds., Kluwer Academic, 121–152.

  2. 2.Xie and S. G. H. Philander, 1994: A coupled ocean-atmosphere model of relevance to the ITCZ in the eastern Pacific. Tellus, 46A, 340–350.

3, Klein, S. A., and D. L. Hartmann, 1993: The seasonal cycle of low stratiform clouds. J. Climate, 6, 1587–1606.

  1. 4.Philander, S.G.H., D. Gu, D. Halpern, G. Lambert, N.-C. Lau, T. Li, and R.C. Pacanowski. 1996. Why the ITCZ is mostly north of the equator. Journal of Climate 9: 2958– 2972.

  2. 5.Kang, S. M., I. M. Held, D. M. W. Frierson, and M. Zhao, 2008: The response of the ITCZ to extratropical thermal forcing: idealized slab-ocean experiments with a GCM. J. Climate, 21, 3521– 3532.

  3. 6.Kang S M, Frierson D M W, Held I M, 2009: The tropical response to extratropical thermal forcing in an idealized GCM: The importance of radiative feedbacks and convective parameterization. J Atmos Sci 66, 2812-282

  4. 7.Chiang J. C. H., Friedman A. R., 2012: Extratropical Cooling, Interhemispheric Thermal Gradients, and Tropical Climate Change. Ann Rev Earth Planet Sci 40, 383-412.

  5. 8.Chiang J. C. H., Bitz, C. M., 2005: Influence of high latitude ice cover on the marine Intertropical Convergence Zone. Climate Dyn 25, 477–496.

  6. 9. Zhang R., Delworth, T. L., 2005: Simulated tropical response to a substantial weakening of the Atlantic thermohaline circulation. J Climate 18, 1853–1860.

  7. 10. Broccoli A. J., Dahl, K. A., Stouffer, R. J. 2006: Response of the ITCZ to Northern Hemisphere cooling. Geophys Res Lett 33, L01702.

  8. 11.Rotstayn, L. D., Lohmann, U. 2002: Tropical Rainfall Trends and the Indirect Aerosol Effect. J Climate 15, 2103–2116.

  9. 12. Hwang, Y.-T., Frierson, D. M. W. 2010: Increasing atmospheric poleward energy transport with global warming. Geophys Res Lett 37, L24807.

  10. 13. Soden, B. J., I. M. Held, R. Colman, K. M. Shell, J. T. Kiehl, and C. A. Shields, 2008: Quantifying climate feedbacks using ra- diative kernels. J. Climate, 21, 3504–3520.

  11. 14. Taylor, K. E., M. Crucifix, P. Braconnot, C. D. Hewitt, C. Doutriaux, A. J. Broccoli, J. F. B. Mitchell, and M. J. Webb, 2007: Estimating shortwave radiative forcing and response in climate models. J. Climate, 20, 2530–2543.

Figure 1. Annual mean precipitation, 1985 - 2004 from Global Precipitation Climatology Project (GPCP) Version 2.1 (top) and the ensemble mean of historical simulations of 20 CMIP5 GCMs (bottom).