Passive microwave-derived spatial and temporal variations of summer melt on the Greenland ice sheet

Abstract

Passive microwave-brightness temperatures over the Greenland ice sheet are examined during the melt season in order to develop a technique for determining surface-melt occurrences. Time series of Special Sensor Microwave/ Imager (SSM/I) data are examined for three locations on the ice sheet, two of which are known to experience melt. These two sites demonstrate a rapid increase in brightness temperatures in late spring to early summer, a prolonged period of elevated brightness temperatures during the summer, and a rapid decrease in brightness temperatures during late summer. This increase in brightness temperatures is associated with surface snow melting. An objective technique is developed to extract melt occurrences from the brightness-temperature time series. Of the two sites with summer melt, the site at the lower elevation had a longer period between the initial and final melt days and had more total days classified as melt during 1988 and 1989. The technique is then applied to the entire Greenland ice sheet for the first major surface-melt event of 1989. The melt-zone signal is mapped from late May to early June to demonstrate the advance and subsequent retreat of one “melt wave”. The use of such a technique to determine melt duration and extent for multiple years may provide an indication of climate change.

Spatiotemporal variations of snowmelt in Antarctica derived from satellite scanning multichannel microwave radiometer and Special Sensor Microwave Imager data (1978–2004)

“…In the past 25 years, about 17% of the Antarctic snow surface in total has experienced surface melting. This is in strong contrast to Greenland where melt normally occurred over 40% of the ice sheet each year, and cumulatively about 66% of the Greenland ice sheet has experienced surface melt during 1979–1991 [ Mote et al , 1993]. The limited melt extent on the Antarctic ice sheet is mainly due to its high latitude and relatively high surface slope in the coastal zone, which limits the expansion of melt zones toward the interior of the ice sheet.…”

“…In the past decade, various algorithms have been proposed for extracting snowmelt information from multichannel satellite passive microwave data. To detect snowmelt occurrence, many researchers have employed a single channel brightness temperature and a threshold empirically determined by field observations or physical experiments [e.g., Mote et al , 1993; Mote and Anderson , 1995; Ridley , 1993; Zwally and Fiegles , 1994; Torinesi et al , 2003]. Some researchers have also used a composite index derived from two channels of passive microwave data, including the normalized gradient ratio (GR) [ Steffen et al , 1993] and the cross polarization gradient ratio (XPGR) [e.g., Abdalati and Steffen , 1997, 2001; Fahnestock et al , 2002].…”

“…The availability of spatially coherent and temporally continuous passive microwave data provides a viable means for investigating the intra‐annual and interannual variability of surface melt. Using SMMR and SSM/I data, surface melt over the Greenland Ice Sheet has been thoroughly examined by various researchers [ Mote et al , 1993; Mote and Anderson , 1995; Abdalati and Steffen , 1995, 1997, 2001; Joshi et al , 2001]. However, only a limited number of studies have reported on Antarctic surface melt.…”

Greenland surface melt trends 1973–2007: Evidence of a large increase in 2007

“…[3] Passive microwave satellite sensors have been used to map the spatial extent and frequency of melting on the Greenland ice sheet, and the data have been a useful indicator of changing melt given the continuous time series of data available since October 1978 [Mote et al, 1993;Mote and Anderson, 1995;Steffen, 1997, 2001;Mote, 2003;Steffen et al, 2004;Tedesco, 2007aTedesco, , 2007b. Infrared instruments also have been used to assess ice sheet temperature and melt, including the Advanced Very High Resolution radiometer (AVHRR) [Comiso, 2006b] and the Moderate Resolution Imaging Spectroradiometer (MODIS) [Hall et al, 2007].…”

Enhanced Identification of Snow Melt and Refreeze Events From Passive Microwave Brightness Temperature Using Air Temperature

“…While the presence of liquid water complicates estimation of snow depth and SWE from passive microwave observations, it is possible to use its impact on the microwave signal as an advantage to determine when snow melting occurs. Early melt detection methods focused on wet snow detection on large ice sheets (e.g., Greenland: Mote et al, ; Antarctica: Zwally & Fiegles, ; Steffen et al, ; Abdalati & Steffen, ) using brightness temperature ( T b ) from the Special Sensor Microwave Imager (SSM/I) series of satellite instruments and various thresholding techniques. Walker and Goodison () used SSM/I data from the Canadian prairies to determine that a difference of greater than 10 K between the horizontal and vertical polarizations at 37 GHz, along with a difference of 0 K between the 37 and 19 GHz frequencies at vertical polarization, indicates the presence of wet snow.…”