37,474 research outputs found
Sea-Ice Wintertime Lead Frequencies and Regional Characteristics in the Arctic, 2003ā2015
The presence of sea-ice leads represents a key feature of the Arctic sea ice cover. Leads promote the flux of sensible and latent heat from the ocean to the cold winter atmosphere and are thereby crucial for air-sea-ice-ocean interactions. We here apply a binary segmentation procedure to identify leads from MODIS thermal infrared imagery on a daily time scale. The method separates identified leads into two uncertainty categories, with the high uncertainty being attributed to artifacts that arise from warm signatures of unrecognized clouds. Based on the obtained lead detections, we compute quasi-daily pan-Arctic lead maps for the months of January to April, 2003ā2015. Our results highlight the marginal ice zone in the Fram Strait and Barents Sea as the primary region for lead activity. The spatial distribution of the average pan-Arctic lead frequencies reveals, moreover, distinct patterns of predominant fracture zones in the Beaufort Sea and along the shelf-breaks, mainly in the Siberian sector of the Arctic Ocean as well as the well-known polynya and fast-ice locations. Additionally, a substantial inter-annual variability of lead occurrences in the Arctic is indicated
IceBird Summer 2022 Campaign - Sea ice surveys with Polar 6 from Station Nord
Changes in Arctic sea ice thickness are the result of complex interactions of the dynamic and variable ice cover with atmosphere and ocean. The availability of satellite-based estimates of Arctic-wide sea ice thickness changes is limited to the winter months. However, in light of recent model predictions of a nearly ice-free Arctic in summer and to understand the role of sea ice for the causes and consequences of a warming climate, long-term and large-scale sea ice thickness and surface observations during the melt season are more important than ever.
The AWI airborne sea ice survey program āIceBird Summerā aims to close this gap by conducting regular measurements over sea ice in summer in key regions of the Arctic Ocean. The survey program comprises and continues all airborne ice thickness measurements obtained since 2001 in the central Arctic, Fram Strait and the last ice area. The objective is to ensure the long-term availability of a unique data record of direct sea ice thickness and surface state observations (deliverable of AWI research program POFIV, Topic 2.1: Warming Climates). Sea ice thickness measurements are obtained with a tethered electromagnetic sensor, the AEM-Bird. Jointly with the ice thickness measurements, optical and laser systems are operated to derive sea ice surface models and melt pond distribution
Decadal Variability In The Arctic Ocean: Greenland-Iceland-Norwegian Seas Ice-Ocean-Atmosphere Climate System
Thesis (Ph.D.) University of Alaska Fairbanks, 2003This study investigates the decadal variability of the Arctic Ocean---Greenland, Iceland, Norwegian Seas (GIN Sea) system and possible mechanisms driving variability. The theoretical foundation of this work is the theory of Proshutinsky & Johnson [1997] that two major climate states of the Arctic---Anticyclonic Circulation Regime (ACCR) and Cyclonic Circulation Regime (CCR)---are driven by variations in the freshwater contents of the Arctic Ocean and the GIN Sea. It is hypothesized that the Arctic Ocean and the GIN Sea form an auto-oscillatory ice-ocean-atmosphere climate system with a quasi-decadal period of interannual variability. The system is characterized by two stages: (1) cold Arctic (ACCR)---warm GIN Sea with weak interaction between the basins; (2) warm Arctic (CCR)---cold GIN Sea with intense interaction between the basins. Surface air temperature and dynamic height gradients between the basins drive the auto-oscillations. This study investigates interactions between the Arctic Ocean and the GIN Sea. To test the hypothesis, a simple model of the Arctic Ocean and Greenland Sea has been developed. The Arctic shelf processes have been parameterized in a box model coupled with an Arctic Ocean module. Both the Arctic Ocean and Greenland Sea modules are coupled with a thermodynamic ice model and atmospheric models. Several model experiments have been conducted to adjust the model and to reproduce the auto-oscillatory behavior of the climate system. One of the major results of this work is the simulation of auto-oscillatory behavior of the Arctic Ocean---GIN Sea climate system. Periodical solutions obtained with seasonally varying forcing for scenarios with high and low interaction between the regions reproduce major anomalies in the ocean thermohaline structure, sea ice volume, and fresh water fluxes attributed to ACCR and CCR regimes. According to the simulation results, the characteristic time scale of the Arctic Ocean---GIN Sea system variability reproduced in the model is about 10--15 years. This outcome is consistent with theory of Proshutinsky and Johnson [1997] and shows that the Arctic Ocean---GIN Sea can be viewed as a unique auto-oscillating system
Intensified Arctic warming under greenhouse warming by vegetationāatmosphereāsea ice interaction
Observations and modeling studies indicate that enhanced vegetation activities over high latitudes under an elevated CO2 concentration accelerate surface warming by reducing the surface albedo. In this study, we suggest that vegetation-atmosphere-sea ice interactions over high latitudes can induce an additional amplification of Arctic warming. Our hypothesis is tested by a series of coupled vegetation-climate model simulations under 2xCO(2) environments. The increased vegetation activities over high latitudes under a 2xCO(2) condition induce additional surface warming and turbulent heat fluxes to the atmosphere, which are transported to the Arctic through the atmosphere. This causes additional sea-ice melting and upper-ocean warming during the warm season. As a consequence, the Arctic and high-latitude warming is greatly amplified in the following winter and spring, which further promotes vegetation activities the following year. We conclude that the vegetation-atmosphere-sea ice interaction gives rise to additional positive feedback of the Arctic amplification.open1188sciescopu
An Updated Assessment of the Changing Arctic Sea Ice Cover
Sea ice is an essential component of the Arctic climate system. The Arctic sea ice cover has undergone substantial changes in the past 40+ years, including decline in areal extent in all months (strongest during summer), thinning, loss of multiyear ice cover, earlier melt onset and ice retreat, and later freeze-up and ice advance. In the past 10 years, these trends have been further reinforced, though the trends (not statistically significant at p <0.05) in some parameters (e.g., extent) over the past decade are more moderate. Since 2011, observing capabilities have improved significantly, including collection of the first basin-wide routine observations of sea ice freeboard and thickness by radar and laser altimeters (except during summer). In addition, data from a year-long field campaign during 2019ā2020 promises to yield a bounty of in situ data that will vastly improve understanding of small-scale processes and the interactions between sea ice, the ocean, and the atmosphere, as well as provide valuable validation data for satellite missions. Sea ice impacts within the Arctic are clear and are already affecting humans as well as flora and fauna. Impacts outside of the Arctic, while garner-ing much attention, remain unclear. The future of Arctic sea ice is dependent on future CO2 emissions, but a seasonally ice-free Arctic Ocean is likely in the coming decades. However, year-to-year variability causes considerable uncertainty on exactly when this will happen. The variability is also a challenge for seasonal prediction
Foreword to the thematic cluster: the Arctic in Rapid Transition ā marine ecosystems
The Arctic is warming and losing sea ice. Happening at a much faster rate than previously expected, these changes are causing multiple ecosystem feedbacks in the Arctic Ocean. The Arctic in Rapid Transition (ART) initiative was developed by early-career scientists as an integrative, international, multidisciplinary, long-term pan-Arctic network to study changes and feedbacks among the physical and biogeochemical components of the Arctic Ocean and their ultimate impacts on biological productivity on different timescales. In 2012, ART jointly organized with the Association of Polar Early Career Scientists their second science workshopāOvercoming Challenges of Observation to Model Integration in Marine Ecosystem Response to Sea Ice Transitionsāat the Institute of Oceanology, Polish Academy of Sciences, in Sopot. This workshop aimed to identify linkages and feedbacks between atmosphereāiceāocean forcing and biogeochemical processes, which are critical for ecosystem function, landāocean interactions and productive capacity of the Arctic Ocean. This special thematic cluster of Polar Research brings together seven papers that grew out of workgroup discussions. Papers examine the climate change impacts on various ecosystem elements, providing important insights on the marine ecological and biogeochemical processes on various timescales. They also highlight priority areas for future research
Arctic Low Cloud Changes as Observed by MISR and CALIOP: Implication for the Enhanced Autumnal Warming and Sea Ice Loss
Retreat of Arctic sea ice extent has led to more evaporation over open water in summer and subsequent cloud changes in autumn. Studying recent satellite cloud data over the Arctic Ocean, we find that low (0.5-2 km) cloud cover in October has been increasing significantly during 2000-2010 over the Beaufort and East Siberian Sea (BESS). This change is consistent with the expected boundary-layer cloud response to the increasing Arctic evaporation accumulated during summer. Because low clouds have a net warming effect at the surface, October cloud increases may be responsible for the enhanced autumnal warming in surface air temperature, which effectively prolong the melt season and lead to a positive feedback to Arctic sea ice loss. Thus, the new satellite observations provide a critical support for the hypothesized positive feedback involving interactions between boundary-layer cloud, water vapor, temperature and sea ice in the Arctic Ocean
Modelling investigation of interaction between Arctic sea ice and storms: insights from case studies and climatological hindcast simulations
Thesis (Ph.D.) University of Alaska Fairbanks, 2019The goal of this study is to improve understanding of atmosphere, sea ice, and ocean interactions in the context of Arctic storm activities. The reduction of Arctic sea ice extent, increase in ocean water temperatures, and changes of atmospheric circulation have been manifested in the Arctic Ocean along with the large surface air temperature increase during recent decades. All of these changes may change the way in which atmosphere, sea ice, and ocean interact, which may in turn feedback to Arctic surface air warming. To achieve the goal, we employed an integrative approach including analysis of modeling simulation results and conducting specifically designed model sensitivity experiments. The novelty of this study is linking synoptic scale storms to large-scale changes in sea ice and atmospheric circulation. The models were used in this study range from the regional fully coupled Arctic climate model HIRHAM-NAOSIM to the ocean-sea ice component model of the Community Earth System Model CESM and the Weather Research and Forecasting (WRF) model. Analysis of HIRHAM-NAOSIM simulation outputs shows regionally dependent variability of storm count with a higher number of storms over the Atlantic side than over the Pacific side. High-resolution simulations also reproduce higher number of storms than lower resolution reanalysis dataset. This is because the high-resolution model may capture more shallow and small size storms. As an integrated consequence, the composite analysis shows that more numerous intense storms produce low-pressure systems centered over the Barents-Kara-Laptev seas and the Chukchi-East Siberian seas, leading to anomalous cyclonic circulation over the Atlantic Arctic Ocean and Pacific Arctic Ocean. Correspondingly, anomalous sea ice transport occurs, enhancing sea ice outflow out of the Barents-Kara-Laptev sea ice and weakening sea ice inflow into the Chukchi-Beaufort seas from the thick ice area north of the Canadian Archipelago. This change in sea ice transport causes a decrease in sea ice concentration and thickness in these two areas. However, energy budget analysis exhibits a decrease in downward net sea ice heat fluxes, reducing sea ice melt, when more numerous intense storms occur. This decrease could be attributed to increased cloudiness and destabilized atmospheric boundary layer associated with intense storms, which can result in a decrease in downward shortwave radiation and an increase in upward turbulent heat fluxes. The sea ice-ocean component CICE-POP of Community Earth System Model (CESM) was used to conduct sensitivity experiment to examine impacts of two selected storms on sea ice. CICE-POP is generally able to simulate the observed spatial distribution of the Arctic sea-ice concentration, thickness, and motion, and interannual variability of the Arctic sea ice area for the period 1979 to 2011. However, some biases still exit, including overestimated sea-ice drift speeds, particularly in the Transpolar Drift Stream, and overestimated sea-ice concentration in the Atlantic Arctic but slightly underestimated sea ice concentration in the Pacific Arctic. Analysis of CICE-POP sensitivity experiments suggests that dynamic forcing associated with the storms plays more important driving role in causing sea ice changes than thermodynamics does in the case of storm in March 2011, while both thermodynamic and dynamic forcings have comparable impacts on sea ice decrease in the case of the August 2012. In case of March 2011 storm, increased surface winds caused the reduction of sea ice area in the Barents and Kara Seas by forcing sea ice to move eastward. Sea ice reduction was primarily driven by mechanical processes rather than ice melting. On the contrary, the case study of August 2012 storm, that occurred during the Arctic summer, exemplified the case of equal contribution of mechanical sea ice redistribution of sea ice in the Chukchi - East Siberian - Beaufort seas and melt in sea ice reduction. To understand the impacts of the changed Arctic environment on storm dynamics, we carried out WRF model simulations for a selected Arctic storm that occurred in March 2011. Model output highlight the importance of both increased surface turbulent heat fluxes due to sea ice retreat and self-enhanced warm and moist air advection from the North Atlantic into the Arctic. These external forcing factor and internal dynamic process sustain and even strengthen atmospheric baroclinicity, supporting the storm to develop and intensify. Additional sensitivity experiments further suggest that latent heat release resulting from condensation/precipitation within the storm enhances baroclinicity aloft and, in turn, causes a re-intensification of the storm from its decaying phase.NSF Grant #1023592 and ONR-Glable Grant #N62909-13-1-V219Chapter 1: Introduction and motivation -- 1.1: Arctic climate system: current state and mechanisms of ongoing change -- 1.2: Arctic climate system feedbacks -- 1.3: Motivations -- 1.4: Implications of Arctic climate change to socio-economic activity -- 1.5: Research goal and objectives -- 1.6: Methods and research approach -- 1.7: Thesis structure. Chapter 2: Climatology of Arctic cyclones and impacts on sea ice: results from regional fully coupled model hindcast simulations -- 2.1: Introduction -- 2.2: Data and methods -- 2.2.1: Model data -- 2.2.2: Cyclone identification algorithm -- 2.2.3: Composite analysis -- 2.3: Results and discussion -- 2.3.1: Arctic storm analysis -- 2.3.2: Impact on sea ice and ocean. Chapter 3: Processes associated with cyclone impacts on sea ice: a case study using sea ice-ocean model simulations -- 3.1: Introduction -- 3.1.1: Dynamic forcing of Arctic cyclones on sea ice -- 3.1.2: Thermodynamic impact of Arctic storms on sea ice -- 3.1.3: Sea ice momentum and mass balance -- 3.1.4: Sea ice surface heat budget -- 3.2: Data and methods -- 3.2.1: Model description -- 3.2.2: Forcing and initialization -- 3.2.3: Experimental design -- 3.2.4: Model validation -- 3.3: March 2011 cyclone -- 3.3.1: Dynamic vs thermodynamic forcing on sea ice -- 3.4: August 2012 cyclone -- 3.4.1: Dynamic and thermodynamic forcing on sea ice -- 3.5: Comparison of March 2011 and August 2012 storms. Chapter 4: Possible processes and forcing in Arctic cyclone development: a case study with WRF model simulations -- 4.1: Introduction -- 4.2: Synoptic analysis for March 16 - 22, 2011 -- 4.3: Model configuration -- 4.4: Model experimental design -- 4.5: Model validation -- 4.6: Results and discussions -- 4.6.1: Baroclinic instability -- 4.6.2: Sensitivity to decreased sea ice concentration and elevated SST -- 4.6.3: Sensitivity to latent heat release. Chapter 5: Conclusions and discussions -- References
Interannual variability in Transpolar Drift summer sea ice thickness and potential impact of Atlantification
Changes in Arctic sea ice thickness are the result of complex interactions of the dynamic and variable ice cover with atmosphere and ocean. Most of the sea ice exiting the Arctic Ocean does so through Fram Strait, which is why long-term measurements of ice thickness at the end of the Transpolar Drift provide insight into the integrated signals of thermodynamic and dynamic influences along the pathways of Arctic sea ice. We present an updated summer (JulyāAugust) time series of extensive ice thickness surveys carried out at the end of the Transpolar Drift between 2001 and 2020. Overall, we see a more than 20ā% thinning of modal ice thickness since 2001. A comparison of this time series with first preliminary results from the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) shows that the modal summer thickness of the MOSAiC floe and its wider vicinity are consistent with measurements from previous years at the end of the Transpolar Drift. By combining this unique time series with the Lagrangian sea ice tracking tool, ICETrack, and a simple thermodynamic sea ice growth model, we link the observed interannual ice thickness variability north of Fram Strait to increased drift speeds along the Transpolar Drift and the consequential variations in sea ice age. We also show that the increased influence of upward-directed ocean heat flux in the eastern marginal ice zones, termed Atlantification, is not only responsible for sea ice thinning in and around the Laptev Sea but also that the induced thickness anomalies persist beyond the Russian shelves and are potentially still measurable at the end of the Transpolar Drift after more than a year. With a tendency towards an even faster Transpolar Drift, winter sea ice growth will have less time to compensate for the impact processes, such as Atlantification, have on sea ice thickness in the eastern marginal ice zone, which will increasingly be felt in other parts of the sea-ice-covered Arctic
Advances in understanding and parameterization of small-scalephysical processes in the marine Arctic climate system: a review
The Arctic climate system includes numerous highly interactive small-scale physical processes in the atmosphere, sea ice, and ocean. During and since the International Polar Year 2007ā2009, significant advances have been made in understanding these processes. Here, these recent advances are reviewed, synthesized, and discussed. In atmospheric physics, the primary advances have been in cloud physics, radiative transfer, mesoscale cyclones, coastal, and fjordic processes as well as in boundary layer processes and surface fluxes. In sea ice and its snow cover, advances have been made in understanding of the surface albedo and its relationships with snow properties, the internal structure of sea ice, the heat and salt transfer in ice, the formation of superimposed ice and snow ice, and the small-scale dynamics of sea ice. For the ocean, significant advances have been related to exchange processes at the iceāocean interface, diapycnal mixing, double-diffusive convection, tidal currents and diurnal resonance. Despite this recent progress, some of these small-scale physical processes are still not sufficiently understood: these include waveāturbulence interactions in the atmosphere and ocean, the exchange of heat and salt at the iceāocean interface, and the mechanical weakening of sea ice. Many other processes are reasonably well understood as stand-alone processes but the challenge is to understand their interactions with and impacts and feedbacks on other processes. Uncertainty in the parameterization of small-scale processes continues to be among the greatest challenges facing climate modelling, particularly in high latitudes. Further improvements in parameterization require new year-round field campaigns on the Arctic sea ice, closely combined with satellite remote sensing studies and numerical model experiments.publishedVersio
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