Sensitivity of stationary wave amplitude to regional changes in Laurentide ice sheet topography

1999 ◽  
pp. 329-337
Author(s):  
Charles Jackson
Keyword(s):  
Wave Amplitude ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Laurentide Ice Sheet ◽  
Ice Sheet Topography

Terminating the Last Interglacial: The Role of Ice Sheet–Climate Feedbacks in a GCM Asynchronously Coupled to an Ice Sheet Model

2011 ◽  
Vol 25 (6) ◽  
pp. 1871-1882 ◽  
Author(s):  
Adam R. Herrington ◽  
Christopher J. Poulsen
Keyword(s):  
Ice Sheet ◽  
Stationary Wave ◽  
Rapid Expansion ◽  
Laurentide Ice Sheet ◽  
Interglacial Period ◽  
Climate Feedbacks ◽  
Last Interglacial ◽  
Ice Volume ◽  
Ice Cap

Abstract Climatic deterioration in northeastern Canada following the last interglacial resulted in the formation and abrupt expansion of the Laurentide Ice Sheet. However, the physical mechanisms leading to rapid ice sheet expansion are not well understood. Here, the authors report on experiments using an ice sheet model asynchronously coupled to a GCM to investigate the role of ice sheet–climate feedbacks in terminating the last interglacial period. In agreement with simpler models, the experiments indicate that a specific type of ice–albedo feedback, the small ice cap instability, is the dominant process controlling rapid expansion of the Laurentide Ice Sheet. As ice elevations increase in northeastern Canada, a stationary wave forms and strengthens over the Laurentide Ice Sheet, which acts to hinder further expansion of the ice margin and reduce the effect of the small ice cap instability. The sensitivity of these feedbacks to ice topography results in a reduction in simulated ice volume when the communication interval between the GCM and ice sheet model is lengthened since this permits larger gains in ice elevation between GCM updates and biases the simulation toward a stronger stationary wave feedback. The shortest communication interval (500 yr) leads to a Laurentide ice volume of 6 × 106 km3 in 10 kyr, which is less than ice volume estimates based on the geological record but is a substantial improvement over previous GCM studies. The authors discuss potential improvements to the asynchronous coupling scheme that would more accurately resolve ice sheet–climate feedbacks, potentially leading to greater simulated ice volume.

Dynamic Effect of Last Glacial Maximum Ice Sheet Topography on the East Asian Summer Monsoon

2020 ◽  
Vol 33 (16) ◽  
pp. 6929-6944 ◽  
Author(s):  
Yu Gao ◽  
Zhengyu Liu ◽  
Zhengyao Lu
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Westerly Jet ◽  
Asian Summer ◽  
Ice Sheet Topography

AbstractThe effect of ice sheet topography on the East Asian summer monsoon (EASM) during the Last Glacial Maximum is studied using CCSM3 in a hierarchy of model configurations. It is found that receding ice sheets result in a weakened EASM, with the reduced ice sheet thickness playing a major role. The lower ice sheet topography weakens the EASM through shifting the position of the midlatitude jet, and through altering Northern Hemisphere stationary waves. In the jet shifting mechanism, the lowering of ice sheets shifts the westerly jet northward and decreases the westerly jet over the subtropics in summer, which reduces the advection of dry enthalpy and in turn precipitation over the EASM region. In the stationary wave mechanism, the lowering of ice sheets induces an anomalous stationary wave train along the westerly waveguide that propagates into the EASM region, generating an equivalent-barotropic low response; this leads to reduced lower-tropospheric southerlies, which in turn reduces the dry enthalpy advection into East Asia, and hence the EASM precipitation.

scholarly journals The impact of topographically forced stationary waves on local ice-sheet climate

2010 ◽  
Vol 56 (197) ◽  
pp. 534-544 ◽  
Author(s):  
Johan Liakka ◽  
Johan Nilsson
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Atmospheric Model ◽  
Stationary Waves ◽  
Local Cooling ◽  
Ice Volume ◽  
Wave Induced ◽  
The Impact ◽  
Ice Sheet Topography

AbstractA linear two-level atmospheric model is employed to study the influence of ice-sheet topography on atmospheric stationary waves. In particular, the stationary-wave-induced temperature anomaly is considered locally over a single ice-sheet topography, which is computed using the plastic approximation. It is found that stationary waves induce a local cooling which increases linearly with the ice volume for ice sheets of horizontal extents smaller than ∼1400 km. Beyond this horizontal scale, the dependence of stationary-wave-induced cooling on the ice volume becomes gradually weaker. For a certain ice-sheet size, and for small changes of the surface zonal wind, it is further shown that the strength of the local stationary-wave-induced cooling is proportional to the basic state meridional temperature gradient multiplied by the vertical stratification in the atmosphere. These results are of importance for the nature of the feedback between ice sheets and stationary waves, and may also serve as a basis for parameterizing this feedback in ice-sheet model simulations (e.g. through the Pleistocene glacial/interglacial cycles).

scholarly journals Assessing the impact of Laurentide Ice Sheet topography on glacial climate

2014 ◽  
Vol 10 (2) ◽  
pp. 487-507 ◽  
Author(s):  
D. J. Ullman ◽  
A. N. LeGrande ◽  
A. E. Carlson ◽  
F. S. Anslow ◽  
J. M. Licciardi
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Ice Sheet ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Laurentide Ice Sheet ◽  
Global Circulation Model ◽  
Northeastern Asia ◽  
The Impact ◽  
Ice Sheet Topography

Abstract. Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets caused profound changes in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotope-enabled fully coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition. We present this comparison at two equilibrium time slices: the LGM, when differences in ice-sheet topography are maximized, and 14 ka, when differences in maximum ice-sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic Meridional Overturning Circulation and warmer surface air temperatures, particularly over northeastern Asia and the North Pacific. These up- and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over northeastern Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may significantly impact the results of paleoclimate simulations and their ability to successfully simulate past climates, with implications for estimating climate sensitivity to greenhouse gas forcing utilizing past climate states.

scholarly journals Assessing the impact of Laurentide Ice-Sheet topography on glacial climate

2013 ◽  
Vol 9 (3) ◽  
pp. 3239-3306 ◽  
Author(s):  
D. J. Ullman ◽  
A. N. LeGrande ◽  
A. E. Carlson ◽  
F. S. Anslow ◽  
J. M. Licciardi
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Northeast Asia ◽  
Ice Sheet ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Laurentide Ice Sheet ◽  
Global Circulation Model ◽  
The Impact ◽  
Ice Sheet Topography

Abstract. Simulations of past climates require altered boundary conditions to account for known shifts in the Earth system. For the Last Glacial Maximum (LGM) and subsequent deglaciation, the existence of large Northern Hemisphere ice sheets provides a profound change in surface topography and albedo. While ice-sheet extent is fairly well known, numerous conflicting reconstructions of ice-sheet topography suggest that precision in this boundary condition is lacking. Here we use a high-resolution and oxygen-isotope-enabled fully-coupled global circulation model (GCM) (GISS ModelE2-R), along with two different reconstructions of the Laurentide Ice Sheet (LIS) that provide maximum and minimum estimates of LIS elevation, to assess the range of climate variability in response to uncertainty in this boundary condition. We present this comparison at two equilibrium time slices: the LGM, where differences in ice sheet topography are maximized, and 14 ka, where differences in maximum ice sheet height are smaller but still exist. Overall, we find significant differences in the climate response to LIS topography, with the larger LIS resulting in enhanced Atlantic meridional overturning circulation and warmer surface air temperatures, particularly over Northeast Asia and the North Pacific. These up and downstream effects are associated with differences in the development of planetary waves in the upper atmosphere, with the larger LIS resulting in a weaker trough over Northeast Asia that leads to the warmer temperatures and decreased albedo from snow and sea-ice cover. Differences between the 14 ka simulations are similar in spatial extent but smaller in magnitude, suggesting that climate is responding primarily to the larger difference in maximum LIS elevation in the LGM simulations. These results suggest that such uncertainty in ice-sheet boundary conditions alone may greatly impact the results of paleoclimate simulations and their ability to successfully simulate past climates, with implications for estimating climate sensitivity to greenhouse gas forcing utilizing past climate states.

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