Accumulation and hoar effects on microwave emission in the Greenland ice-sheet dry-snow zones

The relationships between accumulation and microwave emissivity in the dry-snow regions of the Greenland ice sheet are studied with special focus on hear formation. With the use of a discrete-ordinate radiative-transfer model, the relative contributions of hear and accumulation to microwave emission are examined. The results show that the link between microwave emission and accumulation rates in the dry-snow area of the Greenland ice sheet is significant; however, the emissivity is also dependent on the extent of boar development. As a result, accumulation estimates based on passive microwave observations in the low-accumulation dry-snow areas will require successful parameterization of hear formation. Furthermore, the increasing Tb trends that were observed during the 1980s, which have been hypothesized to be related to accumulation changes, may be strongly related to variations in hoar development. Other possible explanations for these observed trends, such as slight surface melt or atmospheric conditions, are also discussed.