The representation of Föhn events to the east of the Antarctic Peninsula in simulations by the Antarctic Mesoscale Prediction System (AMPS)

2020 ◽  
Author(s):  
Amélie Kirchgaessner ◽  
John King ◽  
Alan Gadian
Keyword(s):  
Antarctic Peninsula ◽  
Weather Research And Forecasting ◽  
Mountain Range ◽  
Prediction System ◽  
Atmospheric Conditions ◽  
Ice Shelf ◽  
Cloud Properties ◽  
Surface Melt ◽  
Mixed Phase Clouds ◽  
The Antarctic

<p>We examine the representation of Föhn events across the Antarctic Peninsula Mountains during 2011 as they were observed in measurements by an Automatic Weather Station, and in simulations with the Weather Research and Forecasting Model (WRF) as run for the Antarctic Mesoscale Prediction System (AMPS). On the Larsen Ice Shelf (LIS) in the lee of this mountain range Föhn winds are thought to provide the atmospheric conditions for significant warming over the ice shelf thus leading to the initial firn densification and subsequently providing the melt water for hydrofracturing. This process has led to the dramatic collapse of huge parts of the LIS in 1995 and 2002 respectively.</p><p>We find that, while the model generally simulates meteorological parameters very well, and shows good skills in capturing the occurrence, frequency and duration of Föhn events realistically, it underestimates the temperature increase and the humidity decrease during the Föhn significantly, and may thus underestimate the contribution of Föhn to driving surface melt on the LIS. Our results indicate that the misrepresentation of cloud properties and particularly the absence of mixed phase clouds in AMPS, affects the quality of weather simulation under normal conditions to some extent, and to a larger extent the model’s capability to simulate the strength of Föhn conditions - and thus their contribution to driving surface melt on the LIS - adequately.</p>

Simulations of Föhn in Antarctica with WRF for the Antarctic Mesoscale Prediction System AMPS

2021 ◽  
Author(s):  
Amélie Kirchgaessner ◽  
John King ◽  
Alan Gadian ◽  
Phil Anderson
Keyword(s):  
Weather Research And Forecasting ◽  
Mountain Range ◽  
Prediction System ◽  
Atmospheric Conditions ◽  
Ice Shelf ◽  
Cloud Properties ◽  
Surface Melt ◽  
Mixed Phase Clouds ◽  
The Antarctic

<p>We examine the representation of Föhn events across the Antarctic Peninsula Mountains during 2011 as they were observed in measurements by an Automatic Weather Station, and in simulations with the Weather Research and Forecasting Model (WRF) as run for the Antarctic Mesoscale Prediction System (AMPS). On the Larsen Ice Shelf (LIS) in the lee of this mountain range Föhn winds are thought to provide the atmospheric conditions for significant warming over the ice shelf thus leading to the initial firn densification and subsequently providing the melt water for hydrofracturing. This process has led to the dramatic collapse of huge parts of the LIS in 1995 and 2002 respectively.</p><p>Measurements obtained at a crest AWS on the Avery Plateau (AV), and the analysis of conditions upstream using the Froude number help to put observations at CP into a wider context. We find that, while the model generally simulates meteorological parameters very well, and shows good skills in capturing the occurrence, frequency and duration of Föhn events realistically, it underestimates the temperature increase and the humidity decrease during the Föhn significantly, and may thus underestimate the contribution of Föhn to driving surface melt on the LIS.</p><p>Our results indicate that the misrepresentation of cloud properties and particularly the absence of mixed phase clouds in AMPS, affects the quality of weather simulation under normal conditions to some extent, and to a larger extent the model’s capability to simulate the strength of Föhn conditions - and thus their contribution to driving surface melt on the LIS - adequately. Most importantly our data show that Föhn conditions can raise the air temperature to above freezing, and thus trigger melt/sublimation even in winter.</p>

scholarly journals Centuries of intense surface melt on Larsen C Ice Shelf

2017 ◽  
Author(s):  
Suzanne Bevan ◽  
Adrian Luckman ◽  
Bryn Hubbard ◽  
Bernd Kulessa ◽  
David Ashmore ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
18Th Century ◽  
Warm Period ◽  
Ice Shelf ◽  
Equivalent Age ◽  
Melt Distribution ◽  
Last 300 Years ◽  
Surface Melt ◽  
The 1960S ◽  
The Antarctic

Abstract. Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula, Larsen C Ice Shelf is the focus of ongoing investigation regarding its future stability. The ice shelf is known to be experience surface melt, and commonly features surface meltwater ponds. Here, we use a flowline model and a firn density model to date and interpret observations of melt-affected ice layers found within five 90 m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice in two boreholes in Cabinet Inlet, close to the Antarctic Peninsula mountains – a region currently affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flowline model shows that, whilst preconditioning of the ice began in the late 1960s, it was probably not until the early 1990s that twentieth-century ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, in one of the Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, in a mid-shelf borehole, formed at the same time in an area which now experiences significant annual melt. Further south on the shelf, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west–east and north–south gradient in past melt distribution resembles current spatial patterns of surface melt intensity. Using flowlines to trace the advection and submergence of continental ice identified in boreholes, we demonstrate that, even by the time the ice reaches the calving front, only the upper 40 to 50 % of the shelf is composed of meteoric ice accumulated on the shelf. This vertical composition implies that basal crevasses must be confined within continental and/or basally accreted ice, and therefore will be unaffected by current climate-induced firn compaction.

scholarly journals Centuries of intense surface melt on Larsen C Ice Shelf

2017 ◽  
Vol 11 (6) ◽  
pp. 2743-2753 ◽  
Author(s):  
Suzanne L. Bevan ◽  
Adrian Luckman ◽  
Bryn Hubbard ◽  
Bernd Kulessa ◽  
David Ashmore ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
18Th Century ◽  
Flow Line ◽  
Warm Period ◽  
Ice Shelf ◽  
Line Model ◽  
Melt Distribution ◽  
Surface Melt ◽  
The 1960S ◽  
The Antarctic

Abstract. Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula (AP), Larsen C Ice Shelf (LCIS) has become the focus of ongoing investigation regarding its future stability. The ice shelf experiences surface melt and commonly features surface meltwater ponds. Here, we use a flow-line model and a firn density model (FDM) to date and interpret observations of melt-affected ice layers found within five 90 m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal dry compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice measured in two boreholes in Cabinet Inlet, which is close to the Antarctic Peninsula mountains – a region affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flow-line model shows that, whilst preconditioning of the snow began in the late 1960s, it was probably not until the early 1990s that the modern period of ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, at 61 m in one of our Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, at 69 m in a mid-shelf borehole, formed at the same time on the edge of the pond area. Further south, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west–east and north–south gradient in the past melt distribution resembles current spatial patterns of surface melt intensity.

Modelling perennial firn aquifers in the Antarctic Peninsula

2020 ◽  
Author(s):  
Jan Melchior van Wessem ◽  
Michiel van den Broeke ◽  
Christian Steger ◽  
Nander Wever ◽  
Stefan Ligtenberg
Keyword(s):  
Antarctic Peninsula ◽  
Climate Model ◽  
Cold Wave ◽  
Mountain Range ◽  
Polar Regions ◽  
Ice Shelf ◽  
Surface Mass ◽  
Surface Energy Fluxes ◽  
Mass Fluxes ◽  
The Antarctic

<p>We predict the location of perennial firn aquifers (PFAs) in the Antarctic Peninsula using the updated regional atmospheric climate model RACMO2.3p2, that is specifically adapted for use over the polar regions. With RACMO2 output we force two sophisticated firn models, IMAU-FDM and SNOWPACK, with surface mass fluxes and surface energy fluxes, respectively. These firn models explicitly calculate processes in the snowpack, such as densification, meltwater penetration, refreezing, retention and runoff.</p><p>In this presentation, we focus on the Antarctic Peninsula (AP), where conditions are favorable for the formation of PFAs: there is both sufficient meltwater production and snowfall to store the meltwater in the firn during winter without refreezing, as the fresh snow insulates the meltwater from the winter cold wave. These conditions are similar to those locations where PFAs were discovered in Greenland and Svalbard.</p><p>While slightly different in behavior, both firn models calculate PFAs on Wilkins ice shelf and the northwestern AP mountain range, but also near the grounding lines of unstable or disintegrated ice shelves such as Prince Gustav, Larsen B and Wordie. The PFAs exist in different forms, e.g. long-lasting, shallow, deep or multi-layer, and are sensitive to the magnitude and timing of atmospheric forcing conditions. We carefully explore processes controlling their formation and/or longevity, discuss their implications for ice shelf stability, and their potential to exist elsewhere in Antarctica.</p>

scholarly journals Estimating surface melt and runoff on the Antarctic Peninsula using ERA-Interim reanalysis data

2018 ◽  
Vol 30 (6) ◽  
pp. 379-393 ◽  
Author(s):  
Juliana Costi ◽  
Jorge Arigony-Neto ◽  
Matthias Braun ◽  
Bulat Mavlyudov ◽  
Nicholas E. Barrand ◽  
...  
Keyword(s):  
Specific Surface ◽  
Antarctic Peninsula ◽  
Surface Runoff ◽  
Field Measurements ◽  
Reanalysis Data ◽  
Degree Days ◽  
Ice Shelf ◽  
Surface Melt ◽  
The Antarctic ◽  
Maximum Runoff

AbstractUsing the positive degree days approach and ERA-Interim reanalysis downscaled data, the researchers ran a melt model spatially gridded at 200 m with annual temporal resolution over 32 years and estimated surface melt (SM) and surface runoff (SR) on the Antarctic Peninsula. The model was calibrated and validated independently by field measurements. The maximum surface melt values occurred in 1985 (129 Gt), and the maximum runoff (40 Gt) occurred in 1993; both parameters showed minimum values in 2014 (26 Gt and 0.37 Gt, respectively). No significant trends are present. Two widespread positive anomalies occurred in 1993 and 2006. The results reveal that the floating ice areas produce an average of 68% of runoff and 61% of surface melt, emphasizing their importance to coastal hydrography. During the seven years preceding the Larsen B collapse, surface melt retention was higher than 95% on floating ice areas, and negative runoff anomalies persisted. Excluding the islands, the vicinity of this former ice shelf exhibits the highest specific surface melt and runoff across the studied area.

scholarly journals Clouds drive differences in future surface melt over the Antarctic ice shelves

2021 ◽  
Author(s):  
Christoph Kittel ◽  
Charles Amory ◽  
Stefan Hofer ◽  
Cécile Agosta ◽  
Nicolas C. Jourdain ◽  
...  
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Longwave Radiation ◽  
Surface Energy Budget ◽  
Atmospheric Conditions ◽  
Ice Shelves ◽  
Cloud Properties ◽  
High Emission ◽  
Surface Melt ◽  
The Antarctic

Abstract. Recent warm atmospheric conditions have damaged the ice shelves of the Antarctic Peninsula through surface melt and hydrofracturing, and could potentially initiate future collapse of other Antarctic ice shelves. However, model projections with similar greenhouse gas scenarios suggest large differences in cumulative 21st century surface melting. So far it remains unclear whether these differences are due to variations in warming rates in individual models, or whether local surface energy budget feedbacks could also play a notable role. Here we use the polar-oriented regional climate model MAR to study the physical mechanisms that will control future melt over the Antarctic ice shelves in high-emission scenarios RCP8.5 and SSP585. We show that clouds enhance future surface melt by increasing the atmospheric emissivity and longwave radiation towards the surface. Furthermore, we highlight that differences in meltwater production for the same climate warming rate depend on cloud properties and particularly cloud phase. Clouds containing a larger amount of liquid water lead to stronger melt, subsequently favouring the absorption of solar radiation due to the snow-melt-albedo feedback. By increasing melt differences over the ice shelves in the next decades, liquid-containing clouds could be a major source of uncertainties related to the future Antarctic contribution to sea level rise.

scholarly journals Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

2010 ◽  
Vol 51 (55) ◽  
pp. 97-102 ◽  
Author(s):  
J. Wendt ◽  
A. Rivera ◽  
A. Wendt ◽  
F. Bown ◽  
R. Zamora ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Regional Climate ◽  
Airborne Lidar ◽  
Similar Data ◽  
Ice Shelf ◽  
International Polar Year ◽  
Ice Flow ◽  
Ice Shelves ◽  
Elevation Changes ◽  
The Antarctic

AbstractRegional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

scholarly journals Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

2013 ◽  
Vol 7 (3) ◽  
pp. 797-816 ◽  
Author(s):  
T. O. Holt ◽  
N. F. Glasser ◽  
D. J. Quincey ◽  
M. R. Siegfried
Keyword(s):  
Antarctic Peninsula ◽  
Structural Changes ◽  
Surface Elevation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
The North ◽  
Surface Elevation Change ◽  
Elevation Changes ◽  
Negative Surface ◽  
The Antarctic

Abstract. George VI Ice Shelf (GVIIS) is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat), radar (ERS 1/2 SAR) and laser altimetry (GLAS) datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010) are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009) to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to ongoing atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.

scholarly journals Surface melt magnitude retrieval over Ross Ice Shelf, Antarctica using coupled MODIS near-IR and thermal satellite measurements

2009 ◽  
Vol 3 (3) ◽  
pp. 1069-1107 ◽  
Author(s):  
D. J. Lampkin ◽  
C. C. Karmosky
Keyword(s):  
Meteorological Data ◽  
Temporal Variations ◽  
Katabatic Wind ◽  
Ice Shelf ◽  
Water Fraction ◽  
Ross Ice Shelf ◽  
Near Ir ◽  
Coarse Spatial Resolution ◽  
Surface Melt ◽  
The Antarctic

Abstract. Surface melt has been increasing over recent years, especially over the Antarctic Peninsula, contributing to disintegration of shelves such as Larsen. Unfortunately, we are not realistically able to quantify surface snowmelt from ground-based methods because there is sparse coverage of automatic weather stations. Satellite based assessments of melt from passive microwave systems are limited in that they only provide an indication of melt occurrence and have coarse spatial resolution. An algorithm was developed to retrieve surface melt magnitude using coupled near-IR/thermal surface measurements from MODIS were calibrated by estimates of liquid water fraction (LWF) in the upper 1 cm of the firn derived from a one-dimensional physical snowmelt model (SNTHERM89). For the modeling phase of this study, SNTHERM89 was forced by hourly meteorological data from automatic weather station data at reference sites spanning a range of melt conditions across the Ross Ice Shelf during a relatively intense melt season (2002). Effective melt magnitude or LWF<eff> were derived for satellite composite periods covering the Antarctic summer months at a 4 km resolution over the entire Ross Ice Shelf, ranging from 0–0.5% LWF<eff> in early December to areas along the coast with as much as 1% LWF<eff> during the time of peak surface melt. Spatial and temporal variations in the magnitude of surface melt are related to both katabatic wind strength and advection during onshore flow.

scholarly journals Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula

2013 ◽  
Vol 7 (1) ◽  
pp. 373-417 ◽  
Author(s):  
T. O. Holt ◽  
N. F. Glasser ◽  
D. J. Quincey ◽  
M. R. Siegfried
Keyword(s):  
Antarctic Peninsula ◽  
Structural Changes ◽  
Surface Elevation ◽  
Ice Shelf ◽  
Ice Shelves ◽  
The North ◽  
Surface Elevation Change ◽  
Elevation Changes ◽  
Negative Surface ◽  
The Antarctic

Abstract. George VI Ice Shelf (GVIIS) is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat), radar (ERS 1/2 SAR) and laser altimetry (GLAS) datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010) are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009) to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to on-going atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.

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