Speaker
Woosok Moon
(SU & Nordita)
Description
Earth’s orbit and axial tilt imprint a strong seasonal cycle
on climatological data. Climate variability is typically
viewed in terms of fluctuations in the seasonal cycle
induced by higher frequency processes. We can interpret this
as a competition between the orbitally enforced monthly
stability and the fluctuations/noise induced by weather.
Here we introduce a new time-series method that determines
these contributions from monthly-averaged data. We find that
the spatio-temporal distribution of the monthly stability
and the magnitude of the noise reveal key fingerprints of
several important climate phenomena, including the evolution
of the Arctic sea ice cover, the El Nio Southern Oscillation
(ENSO), the Atlantic Nio and the Indian Dipole Mode. In
analogy with the classical destabilising influence of the
ice-albedo feedback on summertime sea ice, we find that
during some time interval of the season a destabilising
process operates in all of these climate phenomena. The
interaction between the destabilisation and the accumulation
of noise, which we term the memory effect, underlies phase
locking to the seasonal cycle and the statistical nature of
seasonal predictability.
