The Southern Hemisphere semiannual oscillation and circulation variability during the Mid-Holocene National Institute of Water and Atmospheric Research Ltd, Private Bag 14901, Kilbirnie, Wellington, New Zealand
Received: 09 February 2010 – Published in Clim. Past Discuss.: 22 February 2010 Abstract. The Paleoclimate Modelling Intercomparison Project (PMIP) was undertaken to
assess the climatic effects of the presence of large ice-sheets and changes
in the Earth's orbital parameters in fully coupled Atmosphere-Ocean General
Circulation Models (AOGCMs). Much of the previous literature has focussed on
the tropics and the Northern Hemisphere during the last glacial maximum and
Mid-Holocene whereas this study focuses only on the Southern Hemisphere. This
study addresses the representation of the Semiannual Oscillation (SAO) in the
PMIP2 models and how it may have changed during the Mid-Holocene. The output
from the five models suggest a weakening of the (austral) autumn circumpolar
trough (CPT) and (in all but one model) a strengthening of the spring CPT.
The effects of changing the orbital parameters are to cause warming and
drying during spring over New Zealand and a cooling and moistening during
autumn. The amount of spring warming/drying and autumn cooling/moistening is
variable between the models and depends on the climatological locations of
surface pressure anomalies associated with changes in the SAO. This study
also undertakes an Empirical Orthogonal Function (EOF) analysis of the
leading modes of atmospheric variability during the control and Mid-Holocene
phases for each model. Despite the seasonal changes, the overall month by
month and interannual variability was simulated to have changed little from
the Mid-Holocene to present.
Revised: 21 June 2010 – Accepted: 22 June 2010 – Published: 05 July 2010
Citation: Ackerley, D. and Renwick, J. A.: The Southern Hemisphere semiannual oscillation and circulation variability during the Mid-Holocene, Clim. Past, 6, 415-430, doi:10.5194/cp-6-415-2010, 2010.