Passive microwave satellite data are effective for monitoring the polar sea ice cover. Two decades of data have now been obtained from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I). These data are processed into space-time series of sea ice concentration and derived parameters such as ice extent. Analyses of such time series to the mid-1990s have established reductions in the extent of arctic sea ice of about 3% per decade. Here, we update the record into 1998. In addition, we produce and analyze time series of multi-year ice (i.e., ice having survived a summer melt season) in winter. This is the first time that the variability and trends of this parameter have been studied using SMMR and SSM/I data. It is found that the total ice area in the Arctic has decreased about 6% during the two decades, consistent with the reduction rate found in previous studies. More remarkably, the multi-year ice area in winter has decreased over 15% during the period, such that an increasing proportion of the winter ice cover is first-year ice. These findings show an arctic ice cover in apparent transformation.