Time series of satellite radar backscatter coefficients of the ERS-1/2 scatterometer are presented for perennial ice regions in the Antarctic from June 1991 to June 1999. There is a pronounced seasonal cycle, with higher backscatter in summer than in winter. On average, backscatter increases from spring values of 16.3 dB to summer values of 10.7 dB within 96 days. This rapid rise, and the summer maximum, are occasionally interrupted by sudden strong signal drops. After late summer/early fall, backscatter decreases again and slowly approaches winter values. The seasonal cycle is interpreted in terms of processes at the ice surface. The spring backscatter rise is associated with internal snow melt and the formation of superimposed ice. This process commences once the surface energy balance becomes positive. Sudden backscatter drops are caused by temporary melt water saturation of the snow during episodic events of warm air advection. In fall, when superimposed ice formation ceases due to surface cooling, gradual surface flooding with seawater becomes the dominating process. This causes the observed decreasing backscatter. The re-occurrence of the seasonal backscatter cycle in most regions points to the widespread formation of superimposed ice on perennial Antarctic sea ice.
AWI Organizations > Climate Sciences > Climate Dynamics
AWI Organizations > Climate Sciences > Sea Ice Physics