A comparison of the Hadley circulation in modern reanalyses
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Previous studies using reanalysis data suggest an intensification and poleward expansion of the tropical Hadley circulation (HC) throughout the twentieth century, yet the HC climatology and trends remain undocumented for many of the newest reanalyses. An intercomparison of eight reanalyses is presented to better elucidate the mean state variability and trends concerning HC intensity and width. Significant variability between reanalyses was found in the mean HC intensity with less variability in HC width. Certain reanalyses (e.g., ERA40 and the Climate Forecast System Reanalysis) tend to produce stronger meridional overturning, while others (National Centers for Environmental Prediction-National Center for Atmospheric Research and Modern-Era Retrospective-Analysis for Research and Applications) are constantly weaker. The NOAA-Cooperative Institute for Research in Environmental Sciences Twentieth Century Reanalysis best matched the ensemble averages with the exception of a poleward shift in the subtropical terminus. Ensemble trends regarding HC intensity and width are broadly consistent with previous work, indicating a 0.40 (0.07) 1010 kg s-1 decade-1 intensification in the northern (southern) cell and a 1.1 decade -1 widening in the past 30 years, although some uncertainty remains regarding the intensity of the southern cell. Longer-term ensemble trends (i.e., 1958-2008) containing fewer ensemble members suggest a weaker northern cell intensification but stronger southern cell intensification and a more modest widening of the HC (i.e., 0.53 decade-1) compared to the last 30 years. Separation of the seasonally averaged stream function magnitudes by the El Nio-Southern Oscillation (ENSO) phase revealed a weak clustering and statistically significant strengthening of the mean circulation for El Nio compared to ENSO neutral and La Nia events for the winter cell with little difference in the summer cell intensity. Copyright 2011 by the American Geophysical Union.
