Comparison of Passive Microwave-Derived Early Melt Onset Records on Arctic Sea Ice

Angela Bliss,Walter Meier,Jeffrey Miller

doi:10.3390/rs9030199

Abstract

Two long records of melt onset (MO) on Arctic sea ice from passive microwave brightness temperatures (Tbs) obtained by a series of satellite-borne instruments are compared. The Passive Microwave (PMW) method and Advanced Horizontal Range Algorithm (AHRA) detect the increase in emissivity that occurs when liquid water develops around snow grains at the onset of early melting on sea ice. The timing of MO on Arctic sea ice influences the amount of solar radiation absorbed by the ice–ocean system throughout the melt season by reducing surface albedos in the early spring. This work presents a thorough comparison of these two methods for the time series of MO dates from 1979 through 2012. The methods are first compared using the published data as a baseline comparison of the publically available data products. A second comparison is performed on adjusted MO dates we produced to remove known differences in inter-sensor calibration of Tbs and masking techniques used to develop the original MO date products. These adjustments result in a more consistent set of input Tbs for the algorithms. Tests of significance indicate that the trends in the time series of annual mean MO dates for the PMW and AHRA are statistically different for the majority of the Arctic Ocean including the Laptev, E. Siberian, Chukchi, Beaufort, and central Arctic regions with mean differences as large as 38.3 days in the Barents Sea. Trend agreement improves for our more consistent MO dates for nearly all regions. Mean differences remain large, primarily due to differing sensitivity of in-algorithm thresholds and larger uncertainties in thin-ice regions.

Highlights

Satellite-based passive microwave observations have been used to monitor sea ice continuously since late 1978 [1], resulting in a long record of the annual growth and retreat cycle of Arctic sea ice consisting of multiple measures such as extent [2,3], melt season length [4,5], and sea ice season length [6]
The Advanced Horizontal Range Algorithm (AHRA) Snowmelt Onset on Arctic Sea Ice Version 3 melt onset (MO) dates [15] are distributed by the National Snow and Ice Data Center (NSIDC)
The AHRA and the early MO date from the Passive Microwave (PMW) method are consistent with the “early melt” transition season defined by Livingstone et al [27]

Summary

Introduction

Satellite-based passive microwave observations have been used to monitor sea ice continuously since late 1978 [1], resulting in a long record of the annual growth and retreat cycle of Arctic sea ice consisting of multiple measures such as extent [2,3], melt season length [4,5], and sea ice season length [6]. During the spring and summer months, sea ice transitions from a cold, winter-like surface at the beginning of spring to the onset of melt and more advanced melting stages when melt ponds develop on the sea ice and sea ice extent retreats [7]. The spring transition period is known to be important for the annual surface energy budget of the Arctic. Modest reductions in surface albedo occur when melting begins [8] and liquid water develops between snow grains [9], contributing to increased absorption of solar radiation that enhances the ice–albedo feedback mechanism [10]. Melting on the sea ice reduces surface albedo earlier in the year, increasing the total amount of solar radiation absorbed

Methods

Results

Discussion

Conclusion