Home > climate, climate models, Research Papers > Kang: Uncertainty in climate change projections of the Hadley circulation: the role of internal variability

Kang: Uncertainty in climate change projections of the Hadley circulation: the role of internal variability

2013 April 29


Fig. 1. (a,c) CCSM3 40-member ensemble mean ψ climatology (black contours) and trends
(colors). Positive values (red shading and solid contours) indicate clockwise circulation; negative
values (blue shading and dashed contours) contour-clockwise circulation. Black contour
interval: 51010 kg/s. (b,d) Nmin, the minimum number of ensemble members needed to
detect a signi cant trends. Gray areas indicate locations where trends are not signi cant at
the 95% con dence level. In all panels the climatological latitudes max are marked with a
“x”, Φψ=0 with a “+”, and Pt with a horizontal line segment in each hemisphere.
Left panels show DJF, right panels JJA.

Uncertainty in climate change projections of the Hadley circulation: the role of internal variability

The uncertainty arising from internal climate variability in climate change projections of the Hadley circulation (HC) is presently unknown. In this paper it is quantified by analyzing a 40-member ensemble of integrations of the Community Climate System Model, Version 3 (CCSM3) under the SRES A1B scenario over the period 2000–2060. An additional set of 100 year-long, time-slice integrations with the atmospheric component of the same model (CAM3) is also analyzed.

Focusing on simple metrics of the HC – its strength, width and height – three key results emerge from our analysis of the CCSM3 ensemble. First, the projected weakening of the HC is almost entirely confined to the Northern Hemisphere, and is stronger in winter than summer. Second, the projected widening of the HC occurs only in the winter season, but in both hemispheres. Third, the projected rise of the tropical tropopause occurs in all hemispheres and in all seasons and is, by far, the most robust of the three metrics.

We show further that uncertainty in future trends of HC width is largely controlled by extratropical variability, while those of HC strength and height are associated primarily with tropical dynamics. Comparison of the CCSM3 and CAM3 integrations reveals that ocean-atmosphere coupling is the dominant source of uncertainty in future trends of HC strength and height, and of the tropical mean meridional circulation in general. Finally, we show that uncertainty in future trends of the hydrological cycle is largely captured by the uncertainty in future trends of the mean meridional circulation

Uncertainty in climate change projections of the Hadley circulation: the role of internal variability
Sarah M. Kang, Clara Deser, Lorenzo M. Polvani

Journal of Climate 2013 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-12-00788.1

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