[1] Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

/pdf/evidence-linking-arctic-amplification-to-extreme-weather-in-3kdkxe89pm.pdf

Evidence linking Arctic amplification to extreme weather in mid‐latitudes

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.

/pdf/a-reconciled-estimate-of-ice-sheet-mass-balance-tca0inf12m.pdf

A reconciled estimate of ice-sheet mass balance

Supplementary Materials for A Reconciled Estimate of Ice-Sheet Mass Balance

[1] Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time-variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.

/pdf/acceleration-of-the-contribution-of-the-greenland-and-1561m4lbkp.pdf

Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise

Modelling the evolution of the Antarctic ice sheet since the last interglacial

[1] The atmospheric circulation patterns over the Greenland ice sheet and its surrounding seas are studied by explicitly calculating the momentum budget components, using data of a high-resolution regional atmospheric climate model. In winter (DJF), the katabatic pressure gradient force (PGF) dominates the momentum budget of the atmospheric boundary layer (ABL) over the ice sheet. Over the western slopes of the ice sheet, the large-scale PGF acts in the same direction as the katabatic PGF, resulting in a strong southerly jet of up to 12 m s−1. In winter, the accumulation of cold air over the sea ice along the northeast coast leads to a thermally induced northerly flow. This circulation facilitates southward sea ice transport in this area and is enhanced by the large-scale circulation. Along the west coast, a similar west-east temperature gradient also forces a northerly flow. In the summer months, sea ice is absent, and thermal wind forcing is largely reduced over the ocean. Summer insolation also reduces katabatic forcing; the large-scale forcing dominates the ABL momentum budget over the ice sheet. Heating of the ABL over the snow-free tundra induces thermal contrasts with the ice sheet and ocean, forcing barrier winds in the coastal regions. Throughout the year, strong surface layer winds along the southeast coast of Greenland are forced by the large-scale PGF.

/pdf/momentum-budget-of-the-atmospheric-boundary-layer-over-the-jg94crx230.pdf

Momentum Budget of the atmospheric boundary layer over the Greenland ice sheet and its surrounding seas

Received 19 April 2005; revised 20 December 2005; accepted 24 January 2006; published 27 May 2006. [1] A vertically integrated two-dimensional ice flow model was coupled to an elastic lithosphere-Earth model to study the effects of lateral variations in lithospheric strength on local bedrock adjustment. We used a synthetic bedrock profile and a synthetic climate to model a characteristic ice sheet through an ice age cycle. Realistic differences in lithospheric strength altered the local bedrock adjustment up to 100 m, the ice extent by tens of kilometers, and the ice volume by several percent. Hence, when modeling ice sheets, it is essential to include information on lithospheric structure. In addition, we used the coupled ice flow–lithosphere model to construct synthetic bedrock motion time series to assess their potential in resolving lithospheric structure. Inverse experiments showed that the model can resolve lateral variations in lithospheric strength from these bedrock motion time series, provided that we have data from both sides of a lateral transition in lithospheric strength. The inversion that solved for a lateral transition was able to find a solution that was consistent with all data, even if they were noisy. In the presence of lateral variations in lithospheric strength, there was no solution to the inverse problem for which all data were modeled correctly by a uniform lithospheric model. The synthetic data showed no significant sensitivity to the location of the transition. Hence we require information from independent sources, such as seismology or gravity, about the locations of transitions in lithospheric strength.

/pdf/recovering-lateral-variations-in-lithospheric-strength-from-w5nccg0gf6.pdf

Recovering lateral variations in lithospheric strength from bedrock motion data using a coupled ice sheet‐lithosphere model

[1] The heat budget of the lower East Antarctic atmosphere is calculated using output from a regional atmospheric climate model. The climatology of this model compares well with observations, although the surface energy budget shows an underestimation of the downwelling longwave radiation and an overestimation of the sensible heat flux. The winter atmospheric boundary layer over Antarctica is characterized by a strong surface inversion, due to longwave cooling of the surface. The longwave radiation loss is balanced by heat extracted from the atmosphere by turbulent mixing, which in turn is compensated by large-scale horizontal and vertical heat advection. Above the boundary layer, net longwave cooling is balanced by subsidence. In the coastal margin, latent heat release from condensation is a significant heat budget component. In summer, the surface is near radiative balance, resulting in a weak surface inversion. As a result, cooling by turbulent mixing and heating by advection in the atmospheric boundary layer are largely reduced. Absorption of shortwave radiation is a small heating source throughout the atmosphere, reducing the importance of advection above the boundary layer. Net longwave cooling and heating by condensation remain unchanged compared to winter.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007JD008613

Heat budget of the East Antarctic lower atmosphere derived from a regional atmospheric climate model

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020GL090471

W. J. van de Berg

Papers

Modelling the evolution of the Antarctic ice sheet since the last interglacial

Momentum Budget of the atmospheric boundary layer over the Greenland ice sheet and its surrounding seas

Recovering lateral variations in lithospheric strength from bedrock motion data using a coupled ice sheet‐lithosphere model

Heat budget of the East Antarctic lower atmosphere derived from a regional atmospheric climate model

A 21st Century Warming Threshold for Sustained Greenland Ice Sheet Mass Loss