The Pacific Sector Hadley and Walker Circulation in Historical Marine Wind Analyses

Abstract

We investigate the historical variation of the wintertime Pacific marine sector meridional atmospheric circulation, using simple diagnostics calculated from a statistical analysis of 140 years of surface wind data. Intensity of the wintertime expression of the Hadley circulation, as expressed by a wind divergence index, varies interannually and secularly. In agreement with previous studies, interannual variation is associated with variations in the Walker circulation; e.g., El Nino/Southern Oscillation (ENSO) activity. The secular variation, most likely affected by systematic measurement biases, is nevertheless consistent with results from simulation of the Indo-Pacific-sector Hadley circulation variability in the NCEP/NCAR reanalysis (see Chapter 3, “Change of the Tropical Hadley Cell since 1950,” Quan et al., this volume; and Chapter 5, “Interannual to Interdecadal Variations of the Hadley and Walker Circulations,” Minobe, this volume) and model simulations of the global atmospheric response to anthropogenic forcing (see Chapter 14, “The Response of the Hadley Circulation to Climate Changes, Past and Future,” Rind and Perlwitz, this volume; and Chapter 17, “Mechanisms of an Intensified Hadley Circulation in Response to Solar Forcing in the Twentieth Century,” Meehl et al., this volume). A proxy network tracking Hadley intensity as mirrored in sea surface temperature (SST), precipitation, surface winds, and/or ocean upwelling might be used to further study processes underlying long-term variability in the Hadley circulation over the past several hundred years.