scholarly journals Climate Noise Influences Ice Sheet Mean State

2019 ◽  
Vol 46 (16) ◽  
pp. 9690-9699 ◽  
Author(s):  
Lu Niu ◽  
Gerrit Lohmann ◽  
Evan J. Gowan
Keyword(s):  
Ice Sheet ◽  
Mean State ◽  
Climate Noise

scholarly journals The key role of topography in altering North Atlantic atmospheric circulation during the last glacial period

2011 ◽  
Vol 7 (4) ◽  
pp. 1089-1101 ◽  
Author(s):  
F. S. R. Pausata ◽  
C. Li ◽  
J. J. Wettstein ◽  
M. Kageyama ◽  
K. H. Nisancioglu
Keyword(s):  
Greenhouse Gases ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Ice Sheet ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Mean State ◽  
Ice Sheet Topography ◽  
The Last Glacial

Abstract. The Last Glacial Maximum (LGM; 21 000 yr before present) was a period of low atmospheric greenhouse gas concentrations, when vast ice sheets covered large parts of North America and Europe. Paleoclimate reconstructions and modeling studies suggest that the atmospheric circulation was substantially altered compared to today, both in terms of its mean state and its variability. Here we present a suite of coupled model simulations designed to investigate both the separate and combined influences of the main LGM boundary condition changes (greenhouse gases, ice sheet topography and ice sheet albedo) on the mean state and variability of the atmospheric circulation as represented by sea level pressure (SLP) and 200-hPa zonal wind in the North Atlantic sector. We find that ice sheet topography accounts for most of the simulated changes during the LGM. Greenhouse gases and ice sheet albedo affect the SLP gradient in the North Atlantic, but the overall placement of high and low pressure centers is controlled by topography. Additional analysis shows that North Atlantic sea surface temperatures and sea ice edge position do not substantially influence the pattern of the climatological-mean SLP field, SLP variability or the position of the North Atlantic jet in the LGM.

scholarly journals The key role of topography in altering North Atlantic atmospheric circulation during the last glacial period

2011 ◽  
Vol 7 (1) ◽  
pp. 575-599 ◽  
Author(s):  
F. S. R. Pausata ◽  
C. Li ◽  
J. J. Wettstein ◽  
M. Kageyama ◽  
K. H. Nisancioglu
Keyword(s):  
Greenhouse Gases ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Ice Sheet ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Mean State ◽  
Ice Sheet Topography ◽  
The Last Glacial

Abstract. The Last Glacial Maximum (LGM; 21 000 years before present) was a period of low atmospheric greenhouse gas concentrations, when vast ice sheets covered large parts of North America and Eurasia. Paleoclimate reconstructions and modeling studies suggest that the atmospheric circulation was substantially altered compared to today, both in terms of its mean state and its variability. Here we present a suite of coupled model simulations designed to investigate both the separate and combined influences of the main LGM boundary condition changes (greenhouse gases, ice sheet topography and ice sheet albedo) on the mean state and variability of the atmospheric circulation as represented by sea level pressure (SLP), 200-hPa zonal wind in the North Atlantic sector. We find that ice sheet topography accounts for most of the simulated change during the LGM. Greenhouse gases and ice sheet albedo affect the SLP gradient in the North Atlantic, but the overall placement of high and low pressure centers is controlled by topography. We also show that North Atlantic sea surface temperatures do not substantially influence the pattern of the climatological-mean SLP field, SLP variability or the position of the North Atlantic jet in the LGM.

Moisture sources for Greenland ice core sites: Seasonality and land/ocean contributions

2020 ◽  
Author(s):  
Anne-Katrine Faber ◽  
Harald Sodemann ◽  
Hans Christian Steen-Larsen
Keyword(s):  
Moisture Transport ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Near Surface ◽  
Surface Mass ◽  
Moisture Source ◽  
Moisture Sources ◽  
The Mean ◽  
Mean State

<div> <div>The interpretation of the climate ice core isotope signal relies on the knowledge on the underlying moisture transport and variability hereof. From ice core records from Greenland and Antarctica we have access to unique climate archives that provide knowledge of past climate changes and variability.  Availability of water vapor, formation of clouds and precipitation are all essential for shaping the radiative and hydrological conditions of the polar climate system. Understanding the mean state and the spatiotemporal variability of moisture transport towards the polar ice sheets is thus vital for exploring moisture and cloud processes affecting the energy and surface mass balance of the Greenland Ice sheet.   </div> <div> </div> </div><p>This study identifies moisture sources for  both Greenland precipitation and near-surface vapor using a combination of backward trajectories and moisture source diagnostics. Using the Lagrangian moisture source diagnostic WaterSip, based on a global transport climatology calculated with the FLEXPART model, and spanning the entire ERA-Interim dataset, we identify Greenland moisture sources for present-day conditions (1980-2018). We focus on six deep ice core sites and identify the key moisture source areas and their patterns of variability. The role of land vs. ocean moisture sources are investigated, with a particular focus on land sources from North America and Greenland. Further, we evaluate moisture transport in relation to Greenland ice core isotopic composition observations of snow and ice, and explore how moisture sources of precipitation and near-source vapor can differ.</p><div> <p>Results show that the deep ice core sites have different spatial patterns of moisture sources. Seasonality is important and large spatial variability with season exists due to precipitation seasonality.  Land-sources are found to be dominating the full moisture uptake budget during summer for some ice core sites.Differences are found between transport patterns for sources of near-surface vapor and sources of precipitation at the same site. This finding highlight that sources and transport of  respectively near-surface moisture and precipitation at the Greenland Ice Sheet are not necessarily comparable.  This suggest that the atmospheric drivers and variability of moisture sources over the Greenland Ice Sheet  can be different for near-surface vapor and precipating clouds at higher altitudes.  This is relevant for a better understanding of  isotope surface processes  related to how the climate signal gets imprinted in the snow. Furthermore these results elucidate the mean state and variability of Greenland moisture sources at different altitudes above the ice surface. This analysis of drivers of Greenland moisture transport therefore contribute to the understanding on how moisture variability influences the energy budget and  surface mass balance of the Greenland Ice sheet. </p> </div><p> </p>

A topological approach to the strain-rate pattern of ice sheets

1993 ◽  
Vol 39 (131) ◽  
pp. 10-14 ◽  
Author(s):  
J. F. Nye
Keyword(s):  
Strain Rate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Point Of View ◽  
Principal Strain ◽  
Topological Approach ◽  
Contour Maps ◽  
Isotropic Point ◽  
Horizontal Strain

AbstractThe pattern of horizontal strain rate in an ice sheet is discussed from a topological point of view. In a circularly symmetric ice sheet, the isotropic point for strain rate at its centre is degenerate and structurally unstable. On perturbation the degenerate point splits into two elementary isotropic points, each of which has the lemon pattern for the trajectories of principal strain rate. Contour maps of principal strain-rate values are presented which show the details of the splitting.

Satellite Altimeter Results Over East Antarctica

1982 ◽  
Vol 3 ◽  
pp. 32-35 ◽  
Author(s):  
R. L. Brooks
Keyword(s):  
Tracking System ◽  
Ice Sheet ◽  
East Antarctica ◽  
Satellite Altimeter ◽  
Ice Shelves ◽  
Ice Surface ◽  
Operational Lifetime ◽  
Waveform Retracking ◽  
Better Than

During the operational lifetime of the Seasat altimeter from 3 July to 10 October 1978, more than 450 overflights were made over East Antarctica inland to latitude 72°S. An analysis of selected passes over a variety of ice features demonstrates that the oceanographic altimeter performed surprisingly well over the ice sheet and ice shelves, acquiring useful measurements during approximately 70% of each pass. The altimeter's onboard tracking system dampened out the ice-surface elevations, but post-flight retracking of the stored return waveforms reveals excellent ice-surface details. After waveform retracking, the altimeter repeatability is better than ±1 m.

Analysis and Simulation of Altimeter Performance for the Production of Ice Sheet Topographic Maps

1986 ◽  
Vol 8 ◽  
pp. 141-145 ◽  
Author(s):  
K.C. Partington ◽  
C.G. Rapley
Keyword(s):  
High Precision ◽  
Systems Analysis ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Data Interpretation ◽  
Topographic Maps ◽  
Error Signal ◽  
Tracking Systems ◽  
Tracking Mode ◽  
Non Linear

Satellite-borne, radar altimeters have already demonstrated an ability to produce high-precision, topographic maps of the ice sheets. Seasat operated in a tracking mode, designed for use over oceans, but successfully tracked much of the flatter regions of the ice sheet to ± 72° latitude. ERS-1 will extend coverage to ± 82° latitude and will be equipped with an ocean mode similar to that of Seasat and an ice mode designed to permit tracking of the steeper, peripheral regions. The ocean mode will be used over the flatter regions, because of its greater precision.Altimeter performance over the ice sheets has been investigated through a study of Seasat tracking behaviour and the use of an altimeter performance simulator, with a view to assessing the likely performance of ERS-1 and the design of improved tracking systems. Analysis of Seasat data shows that lock was frequently lost, as a result of possessing a non-linear height error signal over the width of the range window. Having lost lock, the tracker frequently failed to transfer rapidly and effectively to track mode. Use of the altimeter performance simulator confirms many of the findings from Seasat data and it is being used to facilitate data interpretation and mapping, through the modelling of waveform sequence.

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