Surface melting over the Greenland ice sheet derived from enhanced resolution passive microwave brightness temperatures (1979–2019)

Abstract

Abstract. Surface melting is a major component of the Greenland ice sheet surface mass balance, and it affects sea level rise through direct runoff and the modulation of ice dynamics and hydrological processes, supraglacially, englacially and subglacially. Passive microwave (PMW) brightness temperature observations are of paramount importance in studying the spatial and temporal evolution of surface melting due to their long temporal coverage (1979–present) and high temporal resolution (daily). However, a major limitation of PMW datasets has been the relatively coarse spatial resolution, which has historically been of the order of tens of kilometers. Here, we use a newly released PMW dataset (37 GHz, horizontal polarization) made available through a NASA “Making Earth System Data Records for Use in Research Environments” (MeASUREs) program to study the spatiotemporal evolution of surface melting over the Greenland ice sheet at an enhanced spatial resolution of 3.125 km. We assess the outputs of different detection algorithms using data collected by automatic weather stations (AWSs) and the outputs of the Modèle Atmosphérique Régional (MAR) regional climate model. We found that sporadic melting is well captured using a dynamic algorithm based on the outputs of the Microwave Emission Model of Layered Snowpack (MEMLS), whereas a fixed threshold of 245 K is capable of detecting persistent melt. Our results indicate that, during the reference period from 1979 to 2019 (from 1988 to 2019), surface melting over the ice sheet increased in terms of both duration, up to 4.5 (2.9) d per decade, and extension, up to 6.9 % (3.6 %) of the entire ice sheet surface extent per decade, according to the MEMLS algorithm. Furthermore, the melting season started up to 4.0 (2.5) d earlier and ended 7.0 (3.9) d later per decade. We also explored the information content of the enhanced-resolution dataset with respect to the one at 25 km and MAR outputs using a semi-variogram approach. We found that the enhanced product is more sensitive to local-scale processes, thereby confirming the potential of this new enhanced product for monitoring surface melting over Greenland at a higher spatial resolution than the historical products and for monitoring its impact on sea level rise. This offers the opportunity to improve our understanding of the processes driving melting, to validate modeled melt extent at high resolution and, potentially, to assimilate these data in climate models.

Ice Sheet Surface and Subsurface Melt Water Discrimination Using Multi‐Frequency Microwave Radiometry

“…The measurement record at these frequencies has now reached a climatologically meaningful record of surface melt statistics (e.g., Fettweis et al., 2011). Continuing observations are now routinely used to track current melt status (e.g., NSIDC, 2021) as well as long‐term trends in melt extent (e.g., Colosio et al., 2021).…”

“…The measurement record at these frequencies has now reached a climatologically meaningful record of surface melt statistics (e.g., Fettweis et al, 2011). Continuing observations are now routinely used to track current melt status (e.g., NSIDC, 2021) as well as long-term trends in melt extent (e.g., Colosio et al, 2021). However, while significant progress is being made using these approaches, our understanding of ice sheet melt is limited by current observational melt products.…”

Flood Monitoring Using Enhanced Resolution Passive Microwave Data: A Test Case over Bangladesh

“…We continue evaluating the capability of the PMW algorithm outputs in describing the temporal evolution of the flood event by comparing them with water level data measured by a selected hydrometric station. Then, we report the results of a semi-variograms analysis to study the scale lengths and the spatial autocorrelation of the PMW and MODIS-based products [17], aiming at evaluating the consistency of the PMW datasets with respect to the higher resolution MODIS reference. Lastly, we make use of a global permittivity dataset to retrieve the water fractional area within each PMW pixel and compare it with that obtained with MODIS.…”

Impact of runoff temporal distribution on ice dynamics

“…The changes in the melt season are clearly observed in the distribution of the melt (Zwally et al, 2011;Sasgen et al, 2012) culminating in the 2012 season when the whole surface of the Greenland ice sheet experienced melt at some point during the year (Nghiem et al, 2012;Tedesco et al, 2013a). But even if it is less visible, the length of the melt season has been increasing since the late 70's (Colosio et al, 2021) and that lengthening has a large impact on the overall melt of the ice sheet, this has been clearly pointed out during the exceptionally long 2010 melt season which lead to a large amount of total melt (Tedesco et al, 2011).…”