scholarly journals Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

2017 ◽  
Vol 63 (238) ◽  
pp. 309-323 ◽  
Author(s):  
DONALD SLATER ◽  
PETER NIENOW ◽  
ANDREW SOLE ◽  
TOM COWTON ◽  
RUTH MOTTRAM ◽  
...  
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Time Lapse ◽  
Atmospheric Temperature ◽  
Recent Change ◽  
Grounding Line ◽  
Tidewater Glacier ◽  
Spatially Distributed ◽  
Basal Sliding ◽  
Catchment Runoff

ABSTRACTUnderstanding the drivers of recent change at Greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming. A poorly constrained component of tidewater glacier processes is the near-terminus subglacial hydrology. Here we present a novel method for constraining near-terminus subglacial hydrology with application to marine-terminating Kangiata Nunata Sermia in South-west Greenland. By simulating proglacial plume dynamics using buoyant plume theory and a general circulation model, we assess the critical subglacial discharge, if delivered through a single compact channel, required to generate a plume that reaches the fjord surface. We then compare catchment runoff to a time series of plume visibility acquired from a time-lapse camera. We identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface, yet we observe no plume. We attribute these observations to spatial spreading of runoff across the grounding line. Persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers, potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration.

scholarly journals An estimate of the impact of transient luminous events on the atmospheric temperature

2008 ◽  
Vol 13 ◽  
pp. 37-43 ◽  
Author(s):  
E. Arnone ◽  
P. Berg ◽  
N. F. Arnold ◽  
B. Christiansen ◽  
P. Thejll
Keyword(s):  
General Circulation ◽  
Middle Atmosphere ◽  
Statistical Significance ◽  
Magnitude Estimate ◽  
Circulation Model ◽  
Atmospheric Temperature ◽  
Order Estimate ◽  
Transient Luminous Events ◽  
Non Linear ◽  
The Impact

Abstract. We present an order of magnitude estimate of the impact of sprites and other transient luminous events (TLEs) on the atmospheric temperature via ozone changes. To address the effects of expected TLE-ozone changes of at most a few percent, we first study the linearity of the radiatively driven response of a stratosphere-mesosphere model and of a general circulation model (GCM) to a range of uniform climatological ozone perturbations. The study is limited to Northern Hemisphere winter conditions, when planetary wave activity is high and the non linear stratosphere-troposphere coupling can be strong. Throughout most of the middle atmosphere of both models, the radiatively driven temperature response to uniform 5% to 20% ozone perturbations shows a close-to linear relationship with the magnitude of the perturbation. A mid-latitude stratopause ozone perturbation is then imposed as an idealised experiment that mimics local temperature gradients introduced by the latitudinal dependence of TLEs. An unrealistically high 20% magnitude is adopted for the regional ozone perturbation to obtain statistical significance in the model response. The local linearity of the radiatively driven response is used to infer a first order estimate of TLE-induced temperature changes of the order of 0.015 K under typical conditions, and less than a peak temperature change of 0.3 K at 60–70 km height in coincidence of extraordinarily active TLE-producing thunderstorms before horizontal mixing quickly occurs. In the latter case, dedicated mesoscale modelling is needed to study the relevance of regional non linear processes which are expected to impact these radiatively driven responses.

Secondary Volcanically-Induced Lunar Atmosphere and Lunar Volatiles: 3-D Modeling and Analysis

2020 ◽  
Author(s):  
Igor Aleinov ◽  
Michael Way ◽  
Kostas Tsigaridis ◽  
Eric Wolf ◽  
Chester Harman ◽  
...  
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Atmospheric Temperature ◽  
Atmospheric Composition ◽  
Polar Regions ◽  
The Moon ◽  
Modeling And Analysis ◽  
Orbital Parameters ◽  
Atmospheric Escape ◽  
Major Eruption

<p>The fact that the Moon could have a transient secondary atmosphere due to volcanic outgassing has been known for some time, though typically such an atmosphere was believed to be extremely thin (~10<sup>-8</sup> bar) [1]. But recent research by Needham and Kring (NK) [2] suggests that during the peak of volcanic activity ~3.5 Ga such a volcanically-outgassed atmosphere could reach ~10<sup>-2</sup> bar of surface pressure. In similar research Wilson et al. [3] proposed a more conservative estimate, arguing that the thickness of such an atmosphere would depend on the intervals between major eruptions and may not exceed microbar densities. In either case a collisional atmosphere could be present, which would control transport of outgassed volatiles (such as H<sub>2</sub>O) and their deposition in polar regions, where they could be preserved until modern day frozen in permanently shadowed regions (PSR) or buried beneath the regolith.</p><p>Here we study such a hypothetical atmosphere to investigate its stability, meteorological properties and the effect on transport of volatiles. We use the ROCKE-3D planetary 3-D General Circulation Model (GCM)[4]. The insolation and orbital parameters were set to conditions 3.5 Ga. The atmospheric composition, based on the list of outgassed species presented by NK in combination with our estimates for atmospheric escape, condensation and the results from our 1-D chemistry model, was chosen to be either CO-dominated or CO<sub>2</sub>-dominated (depending on atmospheric temperature). In this study we restricted ourselves to relatively "thick" lunar atmospheres of 1-10 mb, though we believe that our results will scale to thinner atmospheres as well.</p><p>We present the results for ground and atmospheric temperature for modeled atmospheres over a wide parameter space. In particular we consider  different atmospheric compositions (CO or CO<sub>2</sub> dominated), a set of atmospheric pressures from 1 mb to 10 mb and a set of obliquities from 0<sup>o</sup> to 40<sup>o</sup>. We also present an experiment of a single major eruption [5] and show that in just 3 years ~80% of the outgassed water is deposited in polar regions. This demonstrates the efficiency of such an atmosphere in delivering volatiles. We argue that a secondary lunar atmosphere could play a significant role in forming volatile deposits currently observed in the polar regions of the Moon. </p><p>References:<br>[1] Stern S. A. (1999) Rev. of Geophysics, 37, 453-492.<br>[2] Needham D. H. and Kring D. A. (2017) Earth and Planetary Sci. Lett., 478, 175-178.<br>[3] Wilson L. et al. (2019) LPSC 50, Abstract 1343. <br>[4] Way M. J. et al. (2017) ApJS, 231, 12.<br>[5] Wilson L. and Head J. W. (2018) GRL, 45, 5852-5859.</p><p> </p>

scholarly journals Assimilation of Mars Global Surveyor atmospheric temperature data into a general circulation model

2001 ◽  
Vol 106 (E12) ◽  
pp. 32863-32877 ◽  
Author(s):  
Kate Q. Zhang ◽  
Andrew P. Ingersoll ◽  
David M. Kass ◽  
John C. Pearl ◽  
Michael D. Smith ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Atmospheric Temperature ◽  
Temperature Data ◽  
Mars Global Surveyor

Modelling the impact of iceberg melt on glacier-ocean interaction, east Greenland

2020 ◽  
Author(s):  
Ben Davison ◽  
Tom Cowton ◽  
Finlo Cottier ◽  
Andrew Sole
Keyword(s):  
Surface Waters ◽  
General Circulation ◽  
Circulation Model ◽  
Freshwater Flux ◽  
Near Surface ◽  
Distributed Source ◽  
East Greenland ◽  
Tidewater Glacier ◽  
Modelling Studies ◽  
The Impact

<p>The melting of icebergs within Greenland’s iceberg-choked fjords provides a large and distributed source of liquid freshwater throughout the year. However, the impact of this freshwater flux on fjord properties and circulation remains unclear, in part because icebergs have typically been neglected in modelling studies that seek to examine interaction between glacier and fjord processes. Here, we modify a general circulation model to simulate the impact of iceberg submarine melting within Kangerdlugssuaq and Sermilik fjords in east Greenland, home to two of Greenland’s largest glaciers. We find that iceberg submarine melting results in cooling of up to 5°C and freshening of up to 0.6 psu throughout the upper 100-200 metres of both fjords, compared to experiments without icebergs. The resulting freshwater flux, which is of the order of hundreds of cumecs, is capable of driving a weak overturning circulation. This augments the runoff-driven circulation at depth but can oppose the up-fjord flow of warm near-surface waters, resulting in an increase in up-fjord heat flux at depth but a decrease near the surface. By increasing subsurface iceberg melt rates, ocean warming will therefore expedite iceberg deterioration within ice mélange and may further increase ocean thermal forcing of tidewater glacier grounding lines. Our results highlight the significant impact that icebergs have on fjord water properties and circulation in Greenland’s iceberg-choked fjords, demonstrating the importance of including these processes in studies that seek to examine interactions between the ice sheet and the ocean.</p>

scholarly journals Spatio-temporal variations in seasonal ice tongue submarine melt rate at a tidewater glacier in southwest Greenland

2019 ◽  
Vol 65 (252) ◽  
pp. 523-530 ◽  
Author(s):  
A. N. MOYER ◽  
P. W. NIENOW ◽  
N. GOURMELEN ◽  
A. J. SOLE ◽  
D. A. SLATER ◽  
...  
Keyword(s):  
Dynamic System ◽  
Time Lapse ◽  
Temporal Variations ◽  
Flow Paths ◽  
Tidewater Glaciers ◽  
Grounding Line ◽  
Tidewater Glacier ◽  
Spatio Temporal ◽  
Southwest Greenland

ABSTRACTSubmarine melting of tidewater glaciers is proposed as a trigger for their recent thinning, acceleration and retreat. We estimate spring submarine melt rates (SMRs) of Kangiata Nunaata Sermia in southwest Greenland, from 2012 to 2014, by examining changes in along-fjord freeboard and velocity of the seasonal floating ice tongue. Estimated SMRs vary spatially and temporally near the grounding line, with mean rates of 1.3 ± 0.6, 0.8 ± 0.3 and 1.0 ± 0.4 m d−1across the tongue in 2012, 2013 and 2014, respectively. Higher melt rates correspond with locations of emerging subglacial plumes and terminus calving activity observed during the melt season using time-lapse camera imagery. Modelling of subglacial flow paths suggests a dynamic system capable of rapid re-routing of subglacial discharge both within and between melt seasons. Our results provide an empirically-derived link between the presence of subglacial discharge plumes and areas of high spring submarine melting and calving along glacier termini.

scholarly journals Past and present dynamics of Skelton Glacier, Transantarctic Mountains

2016 ◽  
Vol 28 (5) ◽  
pp. 371-386 ◽  
Author(s):  
R.S. Jones ◽  
N.R. Golledge ◽  
A.N. Mackintosh ◽  
K.P. Norton
Keyword(s):  
Ice Sheets ◽  
Atmospheric Temperature ◽  
Ice Thickness ◽  
Surface Slope ◽  
Flow Sensitivity ◽  
The Past ◽  
Transantarctic Mountain ◽  
Grounding Line ◽  
Basal Sliding ◽  
Transantarctic Mountains

AbstractAny future changes in the volume of Antarctica’s ice sheets will depend on the dynamic response of outlet glaciers to shifts in environmental conditions. In the Transantarctic Mountains, this response is probably heavily dependent on the geometry of the system, but few studies have quantified the sensitivity of these glaciers to environmental forcings. Here we investigated the controls, along-flow sensitivity and time-dependent dynamics of Skelton Glacier. Three key outcomes were: i) present-day flow is governed primarily by surface slope, which responds to reduced valley width and large bed undulations, ii) Skelton Glacier is more susceptible to changes in atmospheric temperature than precipitation through its effect on basal sliding near the grounding line, and iii) under conditions representative of Pliocene and Quaternary climates large changes in ice thickness and velocity would have occurred in the lower reaches of the glacier. Based on these new quantitative predictions of the past and present dynamics of Skelton Glacier, we suggest that similar Transantarctic Mountain outlet glaciers could experience greater ice loss in their confined, lower reaches through increased basal sliding and ocean melt under warmer-than-present conditions. These effects are greatest where overdeepenings exist near the grounding line.

Pemanfaatan CFSRv2 untuk Statistical Downscaling menggunakan Principal Component Regression dan Partial Least Square

2019 ◽  
Vol 8 (1) ◽  
Author(s):  
Khairunnisa Khairunnisa ◽  
Rizka Pitri ◽  
Victor P Butar-Butar ◽  
Agus M Soleh
Keyword(s):  
Statistical Downscaling ◽  
General Circulation ◽  
Principal Component Regression ◽  
Circulation Model ◽  
Principal Component ◽  
Meteorological Station ◽  
Grid Size ◽  
Partial Least Square ◽  
Least Square ◽  
Output Data

This research used CFSRv2 data as output data general circulation model. CFSRv2 involves some variables data with high correlation, so in this research is using principal component regression (PCR) and partial least square (PLS) to solve the multicollinearity occurring in CFSRv2 data. This research aims to determine the best model between PCR and PLS to estimate rainfall at Bandung geophysical station, Bogor climatology station, Citeko meteorological station, and Jatiwangi meteorological station by comparing RMSEP value and correlation value. Size used was 3×3, 4×4, 5×5, 6×6, 7×7, 8×8, 9×9, and 11×11 that was located between (-40) N - (-90) S and 1050 E -1100 E with a grid size of 0.5×0.5 The PLS model was the best model used in stastistical downscaling in this research than PCR model because of the PLS model obtained the lower RMSEP value and the higher correlation value. The best domain and RMSEP value for Bandung geophysical station, Bogor climatology station, Citeko meteorological station, and Jatiwangi meteorological station is 9 × 9 with 100.06, 6 × 6 with 194.3, 8 × 8 with 117.6, and 6 × 6 with 108.2, respectively.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

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