In search of an elusive Antarctic circumpolar wave in sea ice extents: 1978-1996

For ease in discerning an Antarctic circumpolar wave in the perimeter of th e ice pack, we construct a time series of the sea ice extents (essentially the area within the ice perimeter) in 1-degree longitudinal sectors for the period 1978-1996, as observed with the multichannel microwave imagers on b oard the NASA Nimbus 7 and the DOD (Dept. of Defense) DMSP (Defense Meteoro logical Satellite Program) F8, F11, and F13 satellites. After converting th e time series into complex numbers by means of a Hilbert transform, we deco mpose the time series of the 360 sectors into its complex principal compone nts (CPCs), effectively separating the spatial and temporal values. Then we decompose the real and imaginary parts of the temporal portions of the fir st three CPCs (complex principal compenents) by Empirical Mode Decompositio n into their intrinsic modes, each representing a narrow frequency band, re sulting in a collection of three CPCs for each intrinsic mode. Finally, we reconstruct the data in two different ways. First, we low-pass filter the d ata by combining all of the intrinsic modes of each CPC with periods longer than two years, which we designate as lowpass filtered. Next, we select th e intrinsic mode of each CPC with periods of approximately four years, whic h we designate the quasiquadrennial (QQ) modes. The low-pass filtered time series shows eastward propagating azimuthal motion in the Ross and Weddell Seas, but no clearly circumpolar motion. The QQ time series, on the other h and, clearly shows eastward propagating circumpolar waves, but with occasio nal retrograde motion to the west.