nasa-gesdisc/es-publications-researchareas huggingface dataset:
Atmospheric conditions in the central Arctic Ocean through the melt seasons of 2012 and 2013: Impact on surface conditions and solar energy deposition into the ice-ocean system (2015)

Spectral Radiation Buoys and ice mass balance buoys were deployed on first-year ice near the North Pole in April 2012 and 2013, collecting in-band (350-800 nm) solar radiation and ice and snow mass balance data over the complete summer melt seasons. With complementary European ERA-Interim reanalysis, National Centers for Environmental Prediction (NCEP) Climate forecast system version 2 (CFSv2) analysis and satellite passive microwave data, we examine the evolution of atmospheric and surface melt conditions in the two differing melt seasons. Prevailing atmospheric conditions contributed to a longer and more continuous melt season in summer 2012 than in 2013, which was corroborated by in situ observations. ERA-Interim reanalysis data showed that longwave radiation likely played a key role in delaying the snowmelt onset in 2013. The earlier melt onset in 2012 reduced the albedo, providing a positive ice-albedo feedback at a time when solar insolation was high. Due to earlier melt onset and later freeze-up in 2012, more solar heat was deposited into the ice-ocean system than in 2013. Summer 2013 was characterized by later melt onset, intermittent freezing events and an earlier fall freeze-up, resulting in considerably fewer effective days of surface melt and a higher average albedo. Calculations for idealized seasonal albedo evolution show that moving the melt onset just 1 week earlier in mid-June increases the total absorbed solar radiation by nearly 14% for the summer season. Therefore, the earlier melt onset may have been one of the most important factors driving the more dramatic melt season in 2012 than 2013, though atmospheric circulation patterns, e.g., cyclone in early August 2012, likely contributed as well.

Research areas: Cryospheric Indicators
Persistent tracers of historic ice flow in glacial stratigraphy near Kamb Ice Stream, West Antarctica (2018)

Abstract. Variations in properties controlling ice flow (e.g., topography, accumulation
rate, basal friction) are recorded by structures in glacial stratigraphy.
When anomalies that disturb the stratigraphy are fixed in space, the
structures they produce advect away from the source and can be used to trace
flow pathways and reconstruct ice-flow patterns of the past. Here we provide
an example of one of these persistent tracers: a prominent unconformity in
the glacial layering that originates at Mt. Resnik, part of a subglacial
volcanic complex near Kamb Ice Stream in central West Antarctica. The
unconformity records a change in the regional thinning behavior seemingly
coincident (3440117 a) with stabilization of grounding-line
retreat in the Ross Sea Embayment. We argue that this feature records both
the flow and thinning history far upstream of the Ross Sea grounding line,
indicating a limited influence of observed ice-stream stagnation cycles on
large-scale ice-sheet routing over the last  5700 years.

Research areas: Cryospheric Indicators
How Well do Global Snow Products Characterize Snow Storage in High Mountain Asia? (2022)

Accurate characterization of peak snow water storage in High Mountain Asia (HMA) is essential for assessing the water supply to over 1 billion downstream residents. Currently, such characterization still relies on modeling due to measurement scarcity. Here, eight global snow products were examined over HMA using a newly developed High Mountain Asia Snow Reanalysis (HMASR) data set as a reference. The focus of intercomparison was on peak annual snow storage, the first-order determinant of warm-season water availability in snow-dominated basins. Across eight products the climatological peak storage over HMA was found to be 161 ± 102 km<SUP>3</SUP> with an average 33% underestimation relative to HMASR. The inter-product variability in cumulative snowfall (335 ± 148 km<SUP>3</SUP>) explains the majority (&gt;80%) of peak snow storage uncertainty, while significant accumulation-season snowfall loss to ablation (51% ± 9%) also reveals the critical role of ablation processes on peak snow storage.

Research areas: Cryospheric Indicators
Surge dynamics of Shisper Glacier revealed by time-series correlation of optical satellite images and their utility to substantiate a generalized sliding law (2022)

Understanding fast ice flow is key to assessing the future of glaciers. Fast ice flow is controlled by sliding at the bed, yet that sliding is poorly understood. A growing number of studies show the relationship between sliding and basal shear stress transitions from an initially rate-strengthening behavior to a rate-independent or rate-weakening behavior.  Studies that have tested a glacier sliding law with data remain rare. Surging glaciers, as we show in this study, can be used as a natural laboratory to inform sliding laws because a single glacier shows extreme velocity variations at a subannual timescale. The present study has two main goals: (1) we introduce a new workflow to produce velocity maps with a high spatiotemporal resolution from remote-sensing data, combining Sentinel-2 (S2) and Landsat 8 (L8) and using the results to describe the recent surge of Shisper Glacier, and (2) we present a generalized sliding law and substantiate the sliding-law behavior using the remote sensing dataset. The quality and spatiotemporal resolution of the velocity time series allow us to identify a gradual amplification of spring speed-up velocities in the 2 years leading up to the surge that started in November 2017. We also find that surface velocity patterns during the surge can be decomposed into three main phases, and each phase appears to be associated with hydraulic changes. Using this dataset, we are able to highlight the rate-independent and rate-weakening relationships between resistive stress and sliding during the surge. We then discuss the importance of the generalized sliding relationship to reconcile observations of fast ice flow, and in particular, different surge behaviors. The approach used in this study remains qualitative, but if coupled with better bed-elevation data and numerical modeling could lead to the widespread quantification of sliding-law parameters.

Research areas: Cryospheric Indicators
Dark Glacier Surface of Greenland's Largest Floating Tongue Governed by (2020)

Surface melt, driven by atmospheric temperatures and albedo, is a strong contribution of mass loss of the Greenland Ice Sheet. In the past, black carbon, algae and other light-absorbing impurities were suggested to govern albedo in Greenlands ablation zone. Here we combine optical (MODIS/Sentinel-2) and radar (Sentinel-1) remote sensing data with airborne radar and laser scanner data, and engage firn modelling to identify the governing factors leading to dark glacier surfaces in Northeast Greenland. After the drainage of supraglacial lakes, the former lake ground is a clean surface represented by a high reflectance in Sentinel-2 data and aerial photography. These bright spots move with the ice flow and darken by more than 20% over only two years. In contrast, sites further inland do not exhibit this effect. This finding suggests that local deposition of dust, rather than black carbon or cryoconite formation, is the governing factor of albedo of fast-moving outlet glaciers. This is in agreement with a previous field study in the area which finds the mineralogical composition and grain size of the dust comparable with that of the surrounding soils.

Research areas: Cryospheric Indicators
Modelled glacier dynamics over the last quarter of a century at Jakobshavn Isbræ (2016)

Abstract. Observations over the past 2 decades show substantial ice loss associated with the speed-up of marine-terminating glaciers in Greenland. Here we use a regional three-dimensional outlet glacier model to simulate the behaviour of Jakobshavn Isbr (JI) located in western Greenland. Our approach is to model and understand the recent behaviour of JI with a physical process-based model. Using atmospheric forcing and an ocean parametrization we tune our model to reproduce observed frontal changes of JI during 19902014. In our simulations, most of the JI retreat during 19902014 is driven by the ocean parametrization used and the glacier's subsequent response, which is largely governed by bed geometry. In general, the study shows significant progress in modelling the temporal variability of the flow at JI. Our results suggest that the overall variability in modelled horizontal velocities is a response to variations in terminus position. The model simulates two major accelerations that are consistent with observations of changes in glacier terminus. The first event occurred in 1998 and was triggered by a retreat of the front and moderate thinning of JI prior to 1998. The second event, which started in 2003 and peaked in the summer 2004, was triggered by the final break-up of the floating tongue. This break-up reduced the buttressing at the JI terminus that resulted in further thinning. As the terminus retreated over a reverse bed slope into deeper water, sustained high velocities over the last decade have been observed at JI. Our model provides evidence that the 1998 and 2003 flow accelerations are most likely initiated by the ocean parametrization used but JI's subsequent dynamic response was governed by its own bed geometry. We are unable to reproduce the observed 20102012 terminus retreat in our simulations. We attribute this limitation to either inaccuracies in basal topography or to misrepresentations of the climatic forcings that were applied. Nevertheless, the model is able to simulate the previously observed increase in mass loss through 2014.

Research areas: Cryospheric Indicators
Ice Shelf Basal Melt Rates in the Amundsen Sea at the End of the 21st Century (2022)

Antarctic Ice Sheet projections show the highest sensitivity to increased basal melting in the Amundsen Sea. However, little is known about the processes that control future increase in melt rates. We build an ensemble of three ocean-sea-ice-ice-shelf simulations for both the recent decades and the late 21st century, constrained by regional atmosphere simulations and the multi-model mean climate change of the fifth Climate Model Intercomparison Project under the RCP8.5 scenario. The ice-shelf melt rates are typically multiplied by 1.4-2.2 from present day to future, for a total basal mass loss increased by 346 Gt yr<SUP>-1</SUP> on average. This is equally explained by advection of warmer water from remote locations and regional changes in Ekman downwelling and in the ice-shelf melt-induced circulation, while increased iceberg melt plays no significant role. Our simulations suggest that high-end melt projections previously used to constrain recent sea level projections may have been significantly overestimated.

Research areas: Cryospheric Indicators
Evolution of debris flow and moraine failure in the Gangotri Glacier region, Garhwal Himalaya: Hydro-geomorphological aspects (2019)

A debris flow occurred in the foreland of Gangotri Glacier by its former tributary, Meru (Bamak) Glacier between 16 and 19 July 2017. We investigated the debris flow using pre- and post-event field observations; hydro-meteorological data along with remote sensing assessments to understand the mechanism and evolution of the debris flow. A large volume of sediments (7.9  106 m3  0.1  106 m3) moved from the Meru Bamak and adjoining Neela Taal (4380 m a.s.l) during the debris flow, depositing 6.5  106 m3  0.1  106 m3 of sediments in the frontal region (4050 m a.s.l) of the Gangotri Glacier. This event transported sediments up to 1.5 km downstream, as a debris flow fan-type feature. During the event, ~18% of the sediments were transferred by the meltwater stream. The stream of the Meru Bamak completely dissected and exposed the ice-cored left lateral moraine of the Gangotri Glacier. This event comprehensively reworked the morainic material and entirely changed the morphology of the pro-glacial area. A small pro-glacial lake (area: 5075 m2) is also observed at the snout of Gangotri Glacier because of the blockage by morainic material and sediments. A sharp increase in the concentration of suspended sediments (SSC), reaching 11,370 and 10,605 mg/l on July 18 and 19, respectively was recorded at Bhojwasa (~3 km downstream). Multiple factors such as recession of Gangotri Glacier, degraded ice-cored moraine, loose sediments at the front of the Meru Bamak, and continuous rainfall created favourable conditions for the debris flow. Therefore, geomorphic hazards associated with glacial retreat need to be investigated intensively in the Himalaya especially, in areas where significant glacial retreat is observed, lateral moraines are exposed, and the unstable slopes are occupied by the tributary glaciers.

Research areas: Cryospheric Indicators
A 120 000-year record of sea ice in the North Atlantic? (2019)

Abstract. Although it has been demonstrated that the speed and magnitude of the recent Arctic sea ice decline is unprecedented for the past 1450 years, few records are available to provide a paleoclimate context for Arctic sea ice extent. Bromine enrichment in ice cores has been suggested to indicate the extent of newly formed sea ice areas. Despite the similarities among sea ice indicators and ice core bromine enrichment records, uncertainties still exist regarding the quantitative linkages between bromine reactive chemistry and the first-year sea ice surfaces. Here we present a 120 000-year record of bromine enrichment from the RECAP (REnland ice CAP) ice core, coastal east Greenland, and interpret it as a record of first-year sea ice. We compare it to existing sea ice records from marine cores and tentatively reconstruct past sea ice conditions in the North Atlantic as far north as the Fram Strait (5085 N). Our interpretation implies that during the last deglaciation, the transition from multi-year to first-year sea ice started at 17.5 ka, synchronously with sea ice reductions observed in the eastern Nordic Seas and with the increase in North Atlantic ocean temperature. First-year sea ice reached its maximum at 12.411.8 ka during the Younger Dryas, after which open-water conditions started to dominate, consistent with sea ice records from the eastern Nordic Seas and the North Icelandic shelf. Our results show that over the last 120 000 years, multi-year sea ice extent was greatest during Marine Isotope Stage (MIS) 2 and possibly during MIS 4, with more extended first-year sea ice during MIS 3 and MIS 5. Sea ice extent during the Holocene (MIS 1) has been less than at any time in the last 120 000 years.

Research areas: Cryospheric Indicators
Recent strengthening of snow and ice albedo feedback driven by Antarctic sea-ice loss (2021)

The decline of the Arctic cryosphere during recent decades has lowered the regions surface albedo, reducing its ability to reflect solar radiation back to space. It is not clear what role the Antarctic cryosphere plays in this regard, but new remote-sensing-based techniques and datasets have recently opened the possibility to investigate its role. Here, we leverage these to show that the surface albedo reductions from sustained post-2000 losses in Arctic snow and ice cover equate to increasingly positive snow and ice albedo feedback relative to a 19821991 baseline period, with a decadal trend of +0.08  0.04 W m2 decade1 between 1992 and 2015. During the same period, the expansion of the Antarctic sea-ice pack generated a negative feedback, with a decadal trend of 0.06  0.02 W m2 decade1. However, substantial Antarctic sea-ice losses during 20162018 completely reversed the trend, increasing the three-year mean combined Arctic and Antarctic snow and ice albedo feedback to +0.26  0.15 W m2. This reversal highlights the importance of Antarctic sea-ice loss to the global snow and ice albedo feedback. The 19922018 mean feedback is equivalent to approximately 10% of anthropogenic CO2 emissions over the same period; the share may rise markedly should 20162018 snow and ice conditions become common, although increasing long-wave emissions will probably mediate the impact on the total radiative-energy budget.

Research areas: Cryospheric Indicators
Controls on water storage and drainage in crevasses on the Greenland Ice Sheet (2021)

Surface crevasses on the Greenland Ice Sheet (GrIS) capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention relative to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behavior at a fast-moving, marine-terminating sector of the GrIS. We map surface meltwater, crevasses, and surface-parallel stress across a ∼2,700 km<SUP>2</SUP> region using satellite data and contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017 to 2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection. We find that the spatial distribution of ponded crevasses does not relate to previously proposed controls on the distribution of supraglacial lakes (elevation and topography) or crevasses (von Mises stress thresholds), suggesting the operation of some other physical control(s). Ponded crevasse fields were preferentially located in regions of compressive surface-parallel mean stress, which we interpret to result from the hydraulic isolation of these systems. This contrasts with unponded crevasse fields, which we suggest are readily able to transport meltwater into the wider supraglacial and englacial network. UAV observations show that ponded crevasses can drain episodically and rapidly, likely through hydrofracture. We therefore propose that the surface stress regime influences a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with consequences for processes, such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater.

Research areas: Cryospheric Indicators
Elevation change of the Antarctic Ice Sheet: 1985 to 2020 (2022)

Abstract. The largest uncertainty in future projections of sea level change comes from the uncertain response of the Antarctic Ice Sheet to the warming oceans and atmosphere. The ice sheet gains roughly 2000 km3 of ice from precipitation each year and loses a similar amount through solid ice discharge into the surrounding oceans. Numerous studies have shown that the ice sheet is currently out of long-term equilibrium, losing mass at an accelerated rate and increasing sea level rise. Projections of sea level change rely on accurate estimates of the contribution of land ice to the contemporary sea level budget. The longest observational record available to study the mass balance of the Earth's ice sheets comes from satellite altimeters. This record, however, consists of multiple satellite missions with different life spans and inconsistent measurement types (radar and laser) of varying quality. To fully utilize these data, measurements from different missions must be cross-calibrated and integrated into a consistent record of change. Here, we present a novel approach for generating such a record that implies improved topography removal, cross-calibration, and normalization of seasonal amplitudes from different mission. We describe in detail the advanced geophysical corrections applied and the processes needed to derive elevation change estimates. We processed the full archive record of satellite altimetry data, providing a seamless record of elevation change for the Antarctic Ice Sheet that spans the period 1985 to 2020. The data are produced and distributed as part of the NASA MEaSUREs ITS_LIVE (Making Earth System Data Records for Use in Research Environments Inter-mission Time Series of Land Ice Velocity and Elevation) project (Nilsson et al., 2021, DOI: https://doi.org/10.5067/L3LSVDZS15ZV).

Research areas: Cryospheric Indicators
Sensing the Nighttime EconomyHousing Imbalance from a Mobile Phone Data Perspective: A Case Study in Shanghai (2022)

Sensing the nighttime economyhousing imbalance is of great importance for urban planning and commerce. As an efficient tool of social sensing and human observation, mobile phone data provides an effective way to address this issue. In this paper, an indicator, mobile phone data-based nighttime economyhousing imbalance intensity, is proposed to measure the degree of the nighttime economyhousing imbalance. This indicator can distinguish vitality variations between sleep periods and nighttime activity periods, which are highly related to the nighttime economyhousing imbalance. The spatial pattern of the nighttime economyhousing imbalance was explored, and its association with the built environment was investigated through city-scale geographical regression analysis in Shanghai, China. The results showed that the sub-districts of Shanghai with high-positive-imbalance intensities displayed structures with superimposed rings and striped shapes, and the sub-districts with negative imbalance intensities were distributed around high positive-intensity areas. There were significant linear correlations between imbalance intensity and the built environment. The multiple influences of built environment factors and related mechanisms were explored from a geographical perspective. Our study utilized the social sensing data to provide a more comprehensive understanding of the nighttime economyhousing imbalance. These findings will be useful for fostering the nighttime economy and supporting urban renewal.

Research areas: Habitat Conversion/Fragmentation
Strategic Forest Reserves can protect biodiversity in the western United States and mitigate climate change (2021)

Forest preservation is crucial for protecting biodiversity and mitigating climate change. Here we assess current forest preservation in the western United States using spatial data and find that beyond the 18.9% (17.5 Mha) currently protected, an additional 11.1% (10.3 Mha) is needed to achieve 30% preservation by 2030 (30  30). To help meet this regional preservation target, we developed a framework that prioritizes forestlands for preservation using spatial metrics of biodiversity and/or carbon within each ecoregion. We show that meeting this preservation target would lead to greater protection of animal and tree species habitat, current carbon stocks, future carbon accumulation, and forests that are important for surface drinking water. The highest priority forestlands are primarily owned by the federal government, though substantial areas are also owned by private entities and state and tribal governments. Establishing Strategic Forest Reserves would help protect biodiversity and carbon for climate adaptation and mitigation.

Research areas: Land Surface/Agriculture Indicators, Ecosystems, Habitat Conversion/Fragmentation