Reference:

Phipps, S. J., and J. N. Brown: Understanding ENSO dynamics through
the exploration of past climates, IOP Conference Series: Earth and
Environmental Science, 9, 012010, doi:10.1088/1755-1315/9/1/012010,
2010.


Abstract:

The palaeoclimate record shows that significant changes in ENSO
characteristics took place during the Holocene. Exploring these
changes, using both data and models, provides a means of understanding
ENSO dynamics. Previous modelling studies have suggested a mechanism
whereby changes in the Earth’s orbital geometry explain the
strengthening of ENSO over the Holocene. Decreasing summer insolation
over the Asian landmass resulted in a weakening of the Asian monsoon
system. This led to a weakening of the easterly trade winds in the
western Pacific, creating conditions more favourable for El Niño
development. To explore this hypothesised forcing mechanism, we use a
climate system model to conduct a suite of simulations of the climate
of the past 8,000 years. In the early Holocene, we find that the Asian
summer monsoon system is intensified, resulting in an amplification of
the easterly trade winds in the western Pacific. The stronger trade
winds represent a barrier to the eastward propagation of westerly wind
bursts, therefore inhibiting the onset of El Niño events. The
fundamental behaviour of ENSO remains unchanged, with the major change
over the Holocene being the influence of the background state of the
Pacific on the susceptibility of the ocean to the initiation of El
Niño events.


Variables:

psl     Mean sea level pressure (hPa)
sftlf   Land area fraction (%)
sst     Sea surface temperature (degrees Celsius)
tauu    Zonal wind stress (N m-2)
tauv    Meridional wind stress (N m-2)
tax     Surface stress east (N m-2)
tay     Surface stress north (N m-2)
tsc     Screen temperature (Kelvin)


Contact:

Steven Phipps <Steven.Phipps@utas.edu.au>