Cryospheric and Polar Processes Seminar

Modelling the Annual Cycle of Antarctic Sea ice Extent by Marilyn Raphael, UCLA Department of Geography

Satellite-observed, total Antarctic sea ice extent (SIE) experiences a distinct annual cycle, peaking
in September and troughing in March on average. The amplitude and phase of the annual cycle
also varies regionally. What forces the observed annual cycle and its variations is not completely
understood. The annual cycle may be calculated by simply taking the average SIE for each day of
the year. However, while simple and transparent, this method produces a value that is subject to
substantial variation since it is based on fewer than 40 numbers, one for each year of observed
data. It also disguises the fact that the annual cycle might be slowly changing phase and that the
amplitude as well as shape of the daily extent might vary. Here, we present a model that allows the
mathematical and stochastic representation of the proximate forces that lead to the observed
annual cycle of sea ice extent. These mathematical and stochastic methods allow amplitude and
phase dilation and contraction. Thus, the annual cycle is not constrained to be a fixed cyclical
pattern rather, it is a pattern that allows both temporal dilation and contraction as well as amplitude
modulation. We use this model in an ensemble interpolation to reconstruct missing daily data in
the early part of the satellite- observed sea ice data set. Results are presented and discussed.