Till J W Wagner

Till J W Wagner
University of Wisconsin–Madison | UW · Department of Atmospheric and Oceanic Sciences

PhD

About

46
Publications
5,815
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536
Citations
Introduction
Till Wagner is an Assistant Professor at the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison
Additional affiliations
January 2018 - June 2021
University of North Carolina at Wilmington
Position
  • Professor (Assistant)
July 2013 - December 2017
University of California, San Diego
Position
  • PostDoc Position
October 2009 - June 2013
University of Cambridge
Position
  • PhD Student

Publications

Publications (46)
Article
Full-text available
The fate of icebergs in the polar oceans plays an important role in Earth’s climate system, yet a detailed understanding of iceberg dynamics has remained elusive. Here, the central physical processes that determine iceberg motion are investigated. This is done through the development and analysis of an idealized model of iceberg drift. The model is...
Article
The discharge of icebergs into the polar oceans is expected to increase over the coming century, which raises the importance of accurate representations of icebergs in global climate models (GCMs) used for future projections. Here, we analyze the prospects for interactive icebergs in GCMs by forcing an iceberg drift and decay model with circulation...
Article
Full-text available
Interactions between glaciers and the ocean are key for understanding the dynamics of the cryosphere in the climate system. Here we investigate the role of hydrostatic forces in glacier calving. We develop a mathematical model to account for the elastic deformation of glaciers in response to three effects: (i) marine and lake-terminating glaciers t...
Article
Full-text available
Record lows in Arctic sea ice extent have been making frequent headlines in recent years. The change in albedo when sea ice is replaced by open water introduces a nonlinearity that has sparked an ongoing debate about the stability of the Arctic sea ice cover and the possibility of Arctic “tipping points.” Previous studies identified instabilities f...
Article
Full-text available
Uncovering universal early warning signals for critical transitions has become a coveted goal in diverse scientific disciplines, ranging from climate science to financial mathematics. There has been a flurry of recent research proposing such signals, with increasing autocorrelation and increasing variance being among the most widely discussed candi...
Article
Previous studies have used coupled climate model simulations with perturbed sea ice covers to assess the impact of future Arctic sea ice loss. The results of these studies suggest that Arctic sea ice loss will cause substantial climate impacts both in the Arctic and beyond. The approaches used in these simulations can be broadly categorized into th...
Article
Full-text available
The mean seasonal cycle of Antarctic sea-ice extent is asymmetric, with the period of ice retreat being approximately two months shorter than the period of ice advance. This feature is largely consistent in observations from year to year and across different satellite products. The asymmetry is also broadly reproduced by comprehensive climate model...
Article
Full-text available
Arctic icebergs, unconstrained sea ice floes, oil slicks, mangrove drifters, lost cargo containers, and other flotsam are known to move at 2-4% of the prevailing wind velocity relative to the water, despite vast differences in the material properties, shapes, and sizes of objects. Here, we revisit the roles of density, aspect ratio, and skin and fo...
Preprint
Full-text available
Arctic icebergs, unconstrained sea ice floes, oil slicks, mangrove drifters, lost cargo containers, and other flotsam are known to move at 2-4% of the prevailing wind velocity relative to the water, despite vast differences in the material properties, shapes, and sizes of objects. Here, we revisit the roles of density, aspect ratio, and skin and fo...
Article
Full-text available
Equatorward sea ice drift can have competing impacts on the sea ice cover. On one hand, as ice reaches warmer waters it will be subject to faster melt. On the other hand, the ice near the pole will thin, causing faster ice growth when air temperatures are below freezing. This prompts the fundamental question whether equatorward ice motion increases...
Article
Full-text available
Plain Language Summary Arctic Amplification is the phenomenon by which the Arctic warms at a faster rate than the global average. Evidence for the occurrence of Arctic Amplification is widely found in climate model simulations as well as in paleo proxy reconstructions of past climate changes. In this study, we investigate the extent to which Arctic...
Article
Full-text available
Nearly half of the freshwater flux from the Antarctic Ice Sheet into the Southern Ocean occurs in the form of large tabular icebergs that calve off the continent’s ice shelves. However, because of difficulties in adequately simulating their breakup, large Antarctic icebergs to date have either not been represented in models or represented but with...
Article
Full-text available
The Antarctic Ice Sheet loses mass via its ice shelves predominantly through two processes: basal melting and iceberg calving. Iceberg calving is episodic and infrequent, and not well parameterized in ice-sheet models. Here, we investigate the impact of hydrostatic forces on calving. We develop two-dimensional elastic and viscous numerical framewor...
Article
Full-text available
Polar amplification is a widely discussed phenomenon, and a range of mechanisms have been proposed to contribute to it, many of which involve atmospheric and surface processes. However, substantial questions remain regarding the role of ocean heat transport. Previous studies have found that ocean heat transport into the Arctic increases under globa...
Article
Full-text available
Winds are thought to play a significant role in driving the asymmetric seasonal cycle of Antarctic sea ice growth and melt. https://eos.org/editors-vox/antarctic-seasonal-sea-ice-melts-faster-than-it-grows
Article
Full-text available
Over the 40‐year satellite record, there has been a slight increasing trend in total annual mean Antarctic sea ice extent of approximately 1.5% per decade that is made up of the sum of significantly larger opposing regional trends. However, record increases in total Antarctic sea ice extent were observed during 2012‑2014, followed by record lows (f...
Presentation
Full-text available
Nearly 16 million km 2 of sea ice grows and subsequently melts each year in the seas surrounding Antarctica. This sixfold increase in sea ice extent effectively doubles the size of the continent each winter. The modest increase in Antarctic sea ice cover observed in the satellite record (1.5 % per decade, 1981–2010) masks substantial interannual an...
Article
Full-text available
The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution...
Poster
Full-text available
Sea ice is a critical component of the climate system. It affects global climate dynamics through its interplay with planetary albedo, atmospheric circulation, ocean productivity and the thermohaline circulation. Nearly 16 million square kilometres of sea ice grows and subsequently melts each year in the seas surrounding Antarctica, effectively dou...
Article
Recent acceleration of Greenland's ocean-terminating glaciers has substantially amplified the ice sheet's contribution to global sea level. Increased oceanic melting of these tidewater glaciers is widely cited as the likely trigger, and is thought to be highest within vigorous plumes driven by freshwater drainage from beneath glaciers. Yet melting...
Article
Full-text available
We investigate the frontal mass budget of a medium-sized tidewater glacier in western Greenland. This is done by comparing the seasonal retreat of the glacier to ice advection and ablation along the front. Frontal ablation is partitioned into calving and submarine melting, both of which are estimated from in situ observations. We observe large spat...
Article
Full-text available
Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of low-permeability layers and barometr...
Article
Full-text available
Ancient air trapped in ice core bubbles has been paramount to developing our understanding of past climate and atmospheric composition. Before air bubbles become isolated in ice, the atmospheric signal is altered in the firn column by transport processes such as advection and diffusion. However, the influence of impermeable layers and barometric pu...
Article
Although iceberg models have been used for decades, they have received far more widespread attention in recent years, in part due to efforts to explicitly represent icebergs in climate models. This calls for increased scrutiny of all aspects of typical iceberg models. An important component of iceberg models is the representation of iceberg capsizi...
Code
Code to accompany ”An Analytical Model of Iceberg Drift”, Wagner, Dell, Eisenman (JPO, in press)
Poster
Full-text available
- Iceberg meltwater fluxes are computed using an iceberg model forced with climate conditions from (i) GCM output and (ii) an observational state estimate. - Large-scale differences in meltwater fluxes are found to be driven by relatively small-scale differences in ocean currents. - The impact of a high wind bias in the GCM is reduced through compe...
Poster
Full-text available
We develop an idealized model to account for the elastic deformation of glaciers in response to three effects: 1. Marine and lake-terminating glaciers tend to enter the water with a nonzero slope which results in upward flexure around the grounding line. 2. Horizontal pressure imbalances at the glacier front are known to cause hydrostatic in-plane...
Article
Full-text available
In August 2010, a 253 km^2 ice island calved from the floating glacial tongue of Petermann Glacier in Northwest Greenland. Petermann Ice Island (PII)-B, a large fragment of this original ice island, is the most intensively observed ice island in recent decades. We chronicle PII-B’s deterioration over four years while it drifted more than 2,400 km s...
Poster
Full-text available
In order to avoid impending catastrophic shifts in the climate system, drastic measures such as geoengineering interventions are currently being considered. The profound consequences such measures may have for the planet make it imperative that we accurately identify the approach of such “tipping points”. Here, we show that a leading candidate to a...
Article
Temperature and salinity data collected around grounded tabular icebergs in Baffin Bay in 2011, 2012 and 2013 indicate wind-induced upwelling at certain locations around the icebergs. These data suggest that along one side of the iceberg, wind forcing leads to Ekman transport away from the iceberg, which causes upwelling of the cool saline water fr...
Poster
Full-text available
Record lows in Arctic sea ice extent have been making frequent headlines in recent years. The change in albedo when sea ice is replaced by open water introduces a nonlinearity that has sparked an ongoing debate about the stability of the Arctic sea ice cover and the possibility of Arctic ‘‘tipping points.’’ Previous studies identified instabilities...
Article
We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg water...
Thesis
Full-text available
This thesis is concerned with the deformation and adhesion of thin elastic sheets that come into contact with an underlying substrate. The focus of this work is on the interplay between material and geometric properties of a system and how this interplay determines the equilibrium states of sheet and substrate, particularly in the regime of geometr...
Article
Full-text available
We present a theoretical investigation of stiction in nanoscale electromechanical contact switches. We develop a mathematical model to describe the deflection of a cantilever beam in response to both electrostatic and van der Waals forces. Particular focus is given to the question of whether adhesive van der Waals forces cause the cantilever to rem...
Article
Full-text available
We consider the form of an elastic loop adhered to a rigid substrate: the ‘Sticky Elastica’. In contrast to previous studies of the shape of delamination ‘blisters’, the theory developed accounts for deflections with large slope (i.e. geometrically nonlinear). Starting from the classical Euler Elastica we provide numerical results for the dimension...
Article
Full-text available
We study theoretically the deposition of few layer graphene sheets onto a grooved substrate incorporating adhesion between substrate and sheet. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives physical insight into recent observations of “snap-through” from flat...
Conference Paper
Understanding the interaction between graphene flakes and various substrates is of crucial importance for nanoelectromechanical systems (NEMS) applications, among others. The `snap-through' instability of graphene flakes placed onto corrugated substrates has recently received much attention as a potential assay for the study of this interaction. A...
Conference Paper
Understanding of Antarctic sea ice processes, both small and large scale, have been hampered by our inability to reliably monitor ice thickness distribution from space, primarily due to the confounding role of its snow cover. This is highlighted by a large discrepancy between recent ice thickness estimates from ICESat and ship-based observations. W...
Conference Paper
Sea ice is a critical component of the Earth's climate system and is a highly complex media. The physical characteristics are important in interpretation of remote sensing data. Sea ice characteristics such as snow surface topography, snow depth and ice thickness were derived from in situ measurements obtained during the J.C. Ross (ICEBell) and Ode...
Article
Full-text available
We investigate the deformation of a thin elastic sheet floating on a liquid surface and subject to a uniaxial compression. We show that at a critical compression the sheet delaminates from the liquid over a finite region forming a delamination "blister." This blistering regime adds to the wrinkling and localized folding regimes that have been studi...

Projects

Projects (3)
Project
This session aims at showcasing recent research progress and augmenting existing knowledge in polar meteorology and climate and the atmosphere-land ice-sea ice coupling in both the Northern and Southern Hemispheres. It will provide a setting to foster discussion and help identify gaps, tools, and studies that can be designed to address these open questions. It is also the opportunity to convey newly acquired knowledge to the community. We invite contributions on all observational and numerical modelling aspects of Arctic and Antarctic meteorology and climatology, that address atmospheric interactions with the cryosphere. This may include but is not limited to studies on past, present and future of: - Atmospheric processes that influence sea-ice (snow on sea ice, sea ice melt, polynya formation and sea ice production and transport) and associated feedbacks, - The variability of the polar large-scale atmospheric circulation (such as polar jets, the circumpolar trough and storm tracks) and impact on the cryosphere (sea ice and land ice), - Atmosphere-ice interactions triggered by synoptic and meso-scale weather phenomena such as cold air outbreaks, katabatic winds, extratropical cyclones, polar cyclones, atmospheric rivers, Foehn winds and heatwaves, - Role of clouds in polar climate and impact on the land ice and sea ice through interactions with radiation, - Teleconnections and climate indices and their role in land ice/sea ice variability. Presentations including new observational (ground and satellite-based) and modelling methodologies specific to polar regions are encouraged. Contributions related to results from recent field campaigns in the Arctic and in the Southern Ocean/Antarctica are also welcomed. Share: https://meetingorganizer.copernicus.org/EGU21/session/39062
Project
Dear colleagues, I would like to bring to your attention that there will be a co-organised session AS2.9/CR7.10 on 'Polar meteorology and climatology and their link to changes in the cryosphere' at the EGU 2020 General Assembly on 3-8 May 2020 in Vienna (Austria). We would like to invite contributions on all observational and modelling aspects of Arctic and Antarctic meteorology and climatology that address atmospheric interactions with the cryosphere. The deadline to submit an abstract is 14 January 2020 via this link: https://meetingorganizer.copernicus.org/EGU2020/sessionprogramme Here is the session description: The polar climate system is strongly affected by interactions between the atmosphere and the cryosphere. Feedback mechanisms between snow, land ice, sea ice and the atmosphere, such as blowing snow, ice melt, polynya formation, and sea ice production play an important role. Atmosphere-ice interactions are also triggered by synoptic weather phenomena such as cold air outbreaks, katabatic winds, polar lows, atmospheric rivers, Foehn winds and heatwaves. However, our understanding of these processes is still incomplete, and to fully capture how atmosphere, land ice and sea ice are coupled on different spatial and temporal scales, remains a major challenge. This session will provide a setting to foster discussion on the atmosphere-ice coupling in both the Northern and Southern Hemispheres. It will offer the opportunity to review newly acquired knowledge, identify gaps, and which instruments, tools, and studies can be designed to address these open questions. We invite contributions on all observational and modelling aspects of Arctic and Antarctic meteorology and climatology that address atmospheric interactions with the cryosphere. This may include studies of atmospheric dynamics that influence sea-ice dynamics or ice-sheet mass balance, or investigations into the variability of the atmospheric circulation such as polar jets, the circumpolar trough, storm tracks and their link to changes in the cryosphere. Looking forward to receive your abstracts! Best, Diana, Amelie and Till.
Project
Dear colleagues, I would like to bring to your attention that there will be a co-organised session AS1.16/CR3.09 on 'Polar meteorology and climatology and their link to changes in the cryosphere' at the EGU 2019 General Assembly in April in Vienna (Austria). We would like to invite contributions on all observational and modelling aspects of Arctic and Antarctic meteorology and climatology that address atmospheric interactions with the cryosphere. The deadline to submit an abstract is 10 January 2019 via this link: https://meetingorganizer.copernicus.org/EGU2019/session/31170 Here are the session details: Session number: AS1.16/CR3.09 Session title: Polar meteorology and climatology and their link to changes in the cryosphere Convener: Diana Francis Co-conveners: Amélie Kirchgaessner, Till Wagner Description: The polar climate system is strongly affected by interactions between the atmosphere and the cryosphere. Feedback mechanisms between snow, land ice, sea ice and the atmosphere, such as blowing snow, ice melt, polynya formation, and sea ice production play an important role. Atmosphere-ice interactions are also triggered by synoptic weather phenomena such as cold air outbreaks, katabatic winds, polar lows, atmospheric rivers, Foehn winds and heatwaves. However, our understanding of these processes is still incomplete, and to fully capture how atmosphere, land ice and sea ice are coupled on different spatial and temporal scales, remains a major challenge. This session will provide a setting to foster discussion on the atmosphere-ice coupling in both the Northern and Southern Hemispheres. It will offer the opportunity to review newly acquired knowledge, identify gaps, and which instruments, tools, and studies can be designed to address these open questions. We invite contributions on all observational and modelling aspects of Arctic and Antarctic meteorology and climatology that address atmospheric interactions with the cryosphere. This may include studies of atmospheric dynamics that influence sea-ice dynamics or ice-sheet mass balance, or investigations into the variability of the atmospheric circulation such as polar jets, the circumpolar trough, storm tracks and their link to changes in the cryosphere. Looking forward to receive your abstracts! Best, Diana, Amelie and Till.