Antarctic summer sea ice concentration and extent: comparison of ODEN 2006 ship observations, satellite passive microwave and NIC sea ice charts

摘要

Antarctic sea ice cover has shown a slight increase (<1%/decade) inoverall observed ice extent as derived from satellite mapping from 1979 to2008, contrary to the decline observed in the Arctic regions. Spatial andtemporal variations of the Antarctic sea ice however remain a significantproblem to monitor and understand, primarily due to the vastness andremoteness of the region. While satellite remote sensing has provided andhas great future potential to monitor the variations and changes of sea ice,uncertainties remain unresolved. In this study, the National Ice Center(NIC) ice edge and the AMSR-E (Advanced Microwave Scanning Radiometer-Earth Observing System) ice extent are examined, while the ASPeCt (AntarcticSea Ice Process and Climate) ship observations from the Oden expedition inDecember 2006 are used as ground truth to verify the two products duringAntarctic summer. While there is a general linear trend between ASPeCt andAMSR-E ice concentration estimates, there is poor correlation (R2=0.41)and AMSR-E tends to underestimate the low ice concentrations. We also foundthat the NIC sea ice edge agrees well with ship observations, while theAMSR-E shows the ice edge further south, consistent with its poorerdetection of low ice concentrations. The northward extent of the ice edge atthe time of observation (NIC) had mean values varying from 38 km to 102 kmgreater on different days for the area as compared with the AMSR-E sea iceextent. For the circumpolar area as a whole in the December period examined,AMSR-E therefore may underestimate the area inside the ice edge at this timeby up to 14% or, 1.5 million km2 less area, compared to the NIC icecharts. Preliminary comparison of satellite scatterometer data however,suggests better resolution of low concentrations than passive microwave, andtherefore better agreement with ship observations and NIC charts of the areainside the ice edge during Antarctic summer. A reanalysis data set forAntarctic sea ice extent that relies on the decade long scatterometer andhigh resolution satellite data set, instead of passive microwave, maytherefore give better fidelity for the recent sea ice climatology.