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.
Highlights
The Greenland ice sheet is the largest ice mass in the Northern Hemisphere with a glaciated surface area of about 1 800 000 km2, a thickness of up to 3 km and a stored water volume of about 2 900 000 km3, which is enough to raise the mean sea level by about 7.2 m (Aschwanden et al, 2019)
We only applied the correction to Scanning Multichannel Microwave Radiometer (SMMR), and we did not apply the linear regression to the sensor microwave/imager (SSM/I)-F08–SSM/I-F11, SSM/I-F11–SSM/I-F13 and SSM/I-F13–SSMI/S-F17 datasets as, in this case, the linear correction worsened the agreement between the two sets of measurements
We compared surface melting detected from Passive microwave (PMW) enhanced-resolution data with that estimated from automatic weather stations (AWSs) air temperature data and the outputs of the Modèle Atmosphérique Régional (MAR) regional climate model
Summary
The Greenland ice sheet is the largest ice mass in the Northern Hemisphere with a glaciated surface area of about 1 800 000 km, a thickness of up to 3 km and a stored water volume of about 2 900 000 km, which is enough to raise the mean sea level by about 7.2 m (Aschwanden et al, 2019). In this regard, estimating mass losses from Greenland is crucial in order to better understand climate system variability and the contribution of Greenland to current and future sea level rise (Mouginot et al, 2019). The contribution of the Greenland ice sheet to sea level rise accelerated at a rate of 21.9 ± 1 Gt yr−2 over the period from 1992 to 2010 (Rignot et al, 2011), indicating that monitoring the Greenland ice sheet and the Antarctic ice sheet is crucial to assess the impact of global warming on sea level rise and the global water balance (Kargel et al, 2005, 2014; Le Meur et al, 2018)
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