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  • Recent Hadley cell expansio...
    Garfinkel, Chaim I.; Waugh, Darryn W.; Polvani, Lorenzo M.

    Geophysical research letters, 28 December 2015, Volume: 42, Issue: 24
    Journal Article

    Several studies have reported that global climate models underestimate the observed trend in tropical expansion, with the implication that such models are missing key processes of the climate system. We show here that integrations of a chemistry‐climate model forced with observed sea surface temperatures (SSTs), greenhouse gases, and ozone‐depleting substances can produce 1980 to 2009 expansion trends comparable to those found in most reanalyses data products. Correct representation of the SSTs changes is important for the Northern Hemisphere, while correct representation of stratospheric ozone changes is important for the Southern Hemisphere. The ensemble mean trend (which captures only the forced response) is nearly always much weaker than trends in reanalyses. This suggests that a large fraction of the recently observed changes may, in fact, be a consequence of internal atmospheric variability and not a response of the climate system to anthropogenic forcings. Key Points Climate models can capture recent HC expansion if internal variability is considered SSTs important for Northern Hemisphere, ozone depletion for Southern Hemisphere Models are not necessarily missing key processes