A comparison between SSM/I passive microwave melt onset dates and satellite-derived albedo melt onset dates in the Arctic

Arctic sea ice undergoes a very strong annual cycle. This study sets out to look at the transition when the Arctic sea ice starts to melt using satellite-obtained passive microwave brightness temperatures and satellite-derived albedo data for 13 points within the Arctic, including both first-year and multiyear ice locations, for 1995-2000. SSM/I brightness temperature differences are used to determine melt onset dates once surface temperatures approach freezing. Independently, satellite-derived albedo data are obtained and a melt onset date is derived. Generally, the two methods produce the same date for melt onset with optimum conditions. However, in most cases there are clouds present, which for the albedo data restrict observations and generates melt dates that are several days later than the passive microwave melt onset which is not affected by cloud cover. Melt onset dates determined from the passive microwave brightness temperatures are compared to those from the albedo observation to determine differences between the two methods. For first-year ice locations, the average differences in melt onset dates for the study locations between the passive microwave and albedo-derived methods are +/ 3 days. The average difference for multiyear ice locations melt onset dates is around eight days, slightly longer than the first-year ice locations, however, this is due to more cloudy conditions. The results indicate that the passive microwave-derived melt onset dates and albedo-derived dates are very close and either method could be used to determine melt. The advantage of using microwave data would be the independence of having to have cloud free conditions.