Warming of waters in an East Greenland fjord prior to glacier retreat: mechanisms and connection to large-scale atmospheric conditions

Abstract. Hydrographic data acquired in Kangerlugssuaq Fjord and adjacent seas in 1993 and 2004 are used together with ocean reanalysis to elucidate water mass change and ice-ocean-atmosphere interactions in East Greenland. The hydrographic data show substantial warming of fjord waters between 1993 and 2004 and warm subsurface conditions coincide with the rapid retreat of Kangerlugssuaq Glacier in 2004–2005. The ocean reanalysis shows that the warm properties of fjord waters in 2004 are related to a major peak in oceanic shoreward heat flux into a cross-shelf trough on the outer continental shelf. The heat flux into this trough varies according to seasonal exchanges with the atmosphere as well as from deep seasonal intrusions of subtropical waters. Both mechanisms contribute to high (low) shoreward heat flux when winds from the northeast are weak (strong). The combined effect of surface heating and inflow of subtropical waters is seen in the hydrographic data, which were collected after periods when along-shore coastal winds from the north were strong (1993) and weak (2004). We show that coastal winds vary according to the pressure gradient defined by a semi-permanent atmospheric pressure system over Greenland and a persistent atmospheric low situated near Iceland. The magnitude of this pressure gradient is controlled by longitudinal variability in the position of the Icelandic Low.

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Warming of waters in an East Greenland fjord prior to glacier retreat: mechanisms and connection to large-scale atmospheric conditions

The Cryosphere ◽

10.5194/tc-5-701-2011 ◽

2011 ◽

Vol 5 (3) ◽

pp. 701-714 ◽

Cited By ~ 78

Author(s):

P. Christoffersen ◽

R. I. Mugford ◽

K. J. Heywood ◽

I. Joughin ◽

J. A. Dowdeswell ◽

...

Keyword(s):

Heat Flux ◽

Pressure Gradient ◽

Large Scale ◽

Atmospheric Conditions ◽

Outer Continental Shelf ◽

Hydrographic Data ◽

Pressure System ◽

Ocean Reanalysis ◽

East Greenland ◽

Coastal Winds

Abstract. Hydrographic data acquired in Kangerdlugssuaq Fjord and adjacent seas in 1993 and 2004 are used together with reanalysis from the NEMO ocean modelling framework to elucidate water-mass change and ice-ocean-atmosphere interactions in East Greenland. The hydrographic data show that the fjord contains warm subtropical waters and that fjord waters in 2004 were considerably warmer than in 1993. The ocean reanalysis shows that the warm properties of fjord waters in 2004 are related to a major peak in oceanic shoreward heat flux into a cross-shelf trough on the outer continental shelf. The heat flux into this trough varies according to seasonal exchanges with the atmosphere as well as from deep seasonal intrusions of subtropical waters. Both mechanisms contribute to high (low) shoreward heat flux when winds from the northeast are weak (strong). The combined effect of surface heating and inflow of subtropical waters is seen in the hydrographic data, which were collected after periods when along-shore coastal winds from the north were strong (1993) and weak (2004). The latter data were furthermore acquired during the early phase of a prolonged retreat of Kangerdlugssuaq Glacier. We show that coastal winds vary according to the pressure gradient defined by a semi-permanent atmospheric high-pressure system over Greenland and a persistent atmospheric low situated near Iceland. The magnitude of this pressure gradient is controlled by longitudinal variability in the position of the Icelandic Low.

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Extensive fires in southeastern Siberian permafrost linked to preceding Arctic Oscillation

Science Advances ◽

10.1126/sciadv.aax3308 ◽

2020 ◽

Vol 6 (2) ◽

pp. eaax3308 ◽

Cited By ~ 6

Author(s):

Jin-Soo Kim ◽

Jong-Seong Kug ◽

Su-Jong Jeong ◽

Hotaek Park ◽

Gabriela Schaepman-Strub

Keyword(s):

Large Scale ◽

Arctic Oscillation ◽

Ground Surface ◽

Fire Season ◽

Burned Area ◽

Late Winter ◽

Atmospheric Conditions ◽

Pressure System ◽

Southeastern Siberia ◽

Carbon Release

Carbon release through boreal fires could considerably accelerate Arctic warming; however, boreal fire occurrence mechanisms and dynamics remain largely unknown. Here, we analyze fire activity and relevant large-scale atmospheric conditions over southeastern Siberia, which has the largest burned area fraction in the circumboreal and high-level carbon emissions due to high-density peatlands. It is found that the annual burned area increased when a positive Arctic Oscillation (AO) takes place in early months of the year, despite peak fire season occurring 1 to 2 months later. A local high-pressure system linked to the AO drives a high-temperature anomaly in late winter, causing premature snowmelt. This causes earlier ground surface exposure and drier ground in spring due to enhanced evaporation, promoting fire spreading. Recently, southeastern Siberia has experienced warming and snow retreat; therefore, southeastern Siberia requires appropriate fire management strategies to prevent massive carbon release and accelerated global warming.

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Extensive fires in southeastern Siberian permafrost linked to preceding Arctic Oscillation

10.5194/egusphere-egu2020-6502 ◽

2020 ◽

Author(s):

Jin-Soo Kim ◽

Jong-Seong Kug ◽

Su-Jong Jeong ◽

Hotaek Park ◽

Gabriela Schaepman-Strub

Keyword(s):

Large Scale ◽

Arctic Oscillation ◽

Climate Feedback ◽

Fire Season ◽

Burned Area ◽

Late Winter ◽

Atmospheric Conditions ◽

Pressure System ◽

Southeastern Siberia ◽

Carbon Release

Terrestrial Arctic is a critical region for positive carbon-climate feedback because of the release of considerable organic carbon from the permafrost buried in the soil. Fires rapidly transfer carbon to the atmosphere. Thus, carbon release through boreal fires could considerably accelerate Arctic warming; however, boreal fire occurrence mechanisms and dynamics remain largely unknown. Here, we analyze fire activity and relevant large-scale atmospheric conditions over southeastern Siberia, which has the largest burned area fraction in the circumboreal and high-level carbon emissions due to high-density peatlands. It is found that the annual burned area increased when a positive Arctic Oscillation (AO) takes place in early months of the year, despite peak fire season occurring 1 to 2 months later. A local high-pressure system linked to the AO drives a high-temperature anomaly in late winter, causing premature snowmelt. This causes earlier ground surface exposure and drier ground in spring due to enhanced evaporation, promoting fire spreading. Recently, southeastern Siberia has experienced warming and snow retreat; therefore, southeastern Siberia requires appropriate fire management strategies to prevent massive carbon release and accelerated global warming.

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Observed local drivers of rainfall variability and changes in the Rio Santa Basin, Tropical Andes of Peru

10.5194/egusphere-egu2020-19981 ◽

2020 ◽

Author(s):

Cornelia Klein ◽

Wolfgang Gurgiser ◽

Fabien Maussion

Keyword(s):

Large Scale ◽

Dynamical Downscaling ◽

Rainfall Variability ◽

Small Scale ◽

Climate Projections ◽

Atmospheric Conditions ◽

Tropical Andes ◽

Wet Season ◽

Pressure System ◽

Local Conditions

The climate in the Rio Santa basin (Peruvian Andes) is characterized by a strong seasonality, with a wet season reaching its maximum intensity from December to March. Understanding the characteristics and variability of rainfall during the wet season is fundamental for small-scale farmers based on rain-fed agriculture, and is one of the main objectives of the recently started AgroClim-Huaraz project (http://agroclima-huaraz.info). Based on a combination of rain gauge observations and ERA5 reanalysis data, we demonstrate that the occurrence of local wet and dry spells in the Rio Santa basin is strongly connected to large scale circulation patterns that are known to drive such rainfall variability in the wider tropical Andes. Changes in upper-tropospheric zonal wind and the location of the Bolivian High pressure system therefore crucially affect the local water availability.&#160;On large spatio-temporal scales, this connection was claimed to have already caused a decrease in precipitation in the Central Andes in response to global warming and could be associated with a projected four-fold increase of dry years by 2100. Consequently, it is of great importance to (i) evaluate the validity of this drying by trend analyses from different sources and (ii) understand the implications of a potential large-scale trend from a local perspective that takes into account the heterogeneity of rainfall distributions in complex terrain.&#160;We therefore use ERA5 to evaluate whether and how observed changes in this teleconnection affect local atmospheric conditions and convective environments. In addition, we infer associated potential trends in rainfall frequency and extremes, cloud cover and convective intensity for the Rio Santa Basin from CHIRPS rainfall estimates and GRIDSAT brightness temperatures down to a resolution of 4-7km for 1983-2019.Based on observations, our results illustrate how large-scale climatic changes may translate into smaller scales. This will in further steps not only help to validate and constrain regional dynamical downscaling attempts but also inform about the representativeness of coarser-scale climate projections for local conditions in Andean valleys.&#160;

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Climatology and Meteorological Evolution of Major Wildfire Events over the Northeast United States

Weather and Forecasting ◽

10.1175/waf-d-12-00009.1 ◽

2013 ◽

Vol 28 (1) ◽

pp. 175-193 ◽

Cited By ~ 9

Author(s):

Joseph B. Pollina ◽

Brian A. Colle ◽

Joseph J. Charney

Keyword(s):

United States ◽

Coastal Plain ◽

Large Scale ◽

Trajectory Analysis ◽

Synoptic Pattern ◽

Pressure System ◽

Northeast United States ◽

The North ◽

North American Regional Reanalysis ◽

Regional Reanalysis

Abstract This study presents a spatial and temporal climatology of major wildfire events, defined as >100 acres burned (>40.47 ha, where 1 ha = 2.47 acre), in the northeast United States from 1999 to 2009 and the meteorological conditions associated with these events. The northeast United States is divided into two regions: region 1 is centered over the higher terrain of the northeast United States and region 2 is primarily over the coastal plain. About 59% of all wildfire events in these two regions occur in April and May, with ~76% in region 1 and ~53% in region 2. There is large interannual variability in wildfire frequency, with some years having 4–5 times more fire events than other years. The synoptic flow patterns associated with northeast United States wildfires are classified using the North American Regional Reanalysis. The most common synoptic pattern for region 1 is a surface high pressure system centered over the northern Appalachians, which occurred in approximately 46% of all events. For region 2, the prehigh anticyclone type extending from southeast Canada and the Great Lakes to the northeast United States is the most common pattern, occurring in about 46% of all events. A trajectory analysis highlights the influence of large-scale subsidence and decreasing relative humidity during the events, with the prehigh pattern showing the strongest subsidence and downslope drying in the lee of the Appalachians.

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Atmospheric Conditions Associated with Labrador Sea Deep Convection: New Insights from a Case Study of the 2006/07 and 2007/08 Winters

Journal of Climate ◽

10.1175/jcli-d-15-0527.1 ◽

2016 ◽

Vol 29 (14) ◽

pp. 5281-5297 ◽

Cited By ~ 10

Author(s):

Who M. Kim ◽

Stephen Yeager ◽

Ping Chang ◽

Gokhan Danabasoglu

Keyword(s):

North America ◽

North Atlantic ◽

Large Scale ◽

Initial Conditions ◽

Deep Convection ◽

La Niña ◽

Labrador Sea ◽

Atmospheric Conditions ◽

Circulation Anomaly ◽

La Nina

Abstract Deep convection in the Labrador Sea (LS) resumed in the winter of 2007/08 under a moderately positive North Atlantic Oscillation (NAO) state. This is in sharp contrast with the previous winter with weak convection, despite a similar positive NAO state. This disparity is explored here by analyzing reanalysis data and forced-ocean simulations. It is found that the difference in deep convection is primarily due to differences in large-scale atmospheric conditions that are not accounted for by the conventional NAO definition. Specifically, the 2007/08 winter was characterized by an atmospheric circulation anomaly centered in the western North Atlantic, rather than the eastern North Atlantic that the conventional NAO emphasizes. This anomalous circulation was also accompanied by anomalously cold conditions over northern North America. The controlling influence of these atmospheric conditions on LS deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and/or initial conditions are modified. An extended analysis for the 1949–2009 period shows that about half of the winters with strong heat losses in the LS are associated with such a west-centered circulation anomaly and cold conditions over northern North America. These are found to be accompanied by La Niña–like conditions in the tropical Pacific, suggesting that the atmospheric response to La Niña may have a strong influence on LS deep convection.

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Atmospheric Circulation Effects on Wind Speed Variability at Turbine Height

Journal of Applied Meteorology and Climatology ◽

10.1175/jam2466.1 ◽

2007 ◽

Vol 46 (4) ◽

pp. 445-456 ◽

Cited By ~ 50

Author(s):

Katherine Klink

Keyword(s):

Wind Speed ◽

Pressure Gradient ◽

Large Scale ◽

Ground Level ◽

The Arctic ◽

Circulation Index ◽

Regression Equations ◽

Change Models ◽

Wind Speeds ◽

The North

Abstract Mean monthly wind speed at 70 m above ground level is investigated for 11 sites in Minnesota for the period 1995–2003. Wind speeds at these sites show significant spatial and temporal coherence, with prolonged periods of above- and below-normal values that can persist for as long as 12 months. Monthly variation in wind speed primarily is determined by the north–south pressure gradient, which captures between 22% and 47% of the variability (depending on the site). Regression on wind speed residuals (pressure gradient effects removed) shows that an additional 6%–15% of the variation can be related to the Arctic Oscillation (AO) and Niño-3.4 sea surface temperature (SST) anomalies. Wind speeds showed little correspondence with variation in the Pacific–North American (PNA) circulation index. The effect of the strong El Niño of 1997/98 on the wind speed time series was investigated by recomputing the regression equations with this period excluded. The north–south pressure gradient remains the primary determinant of mean monthly 70-m wind speeds, but with 1997/98 removed the influence of the AO increases at nearly all stations while the importance of the Niño-3.4 SSTs generally decreases. Relationships with the PNA remain small. These results suggest that long-term patterns of low-frequency wind speed (and thus wind power) variability can be estimated using large-scale circulation features as represented by large-scale climatic datasets and by climate-change models.

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Domain-Adversarial Training of Self-Attention-Based Networks for Land Cover Classification Using Multi-Temporal Sentinel-2 Satellite Imagery

Remote Sensing ◽

10.3390/rs13132564 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2564

Author(s):

Mauro Martini ◽

Vittorio Mazzia ◽

Aleem Khaliq ◽

Marcello Chiaberge

Keyword(s):

Land Cover ◽

Large Scale ◽

Domain Adaptation ◽

Learning Approaches ◽

Atmospheric Conditions ◽

Practical Applications ◽

Area Of Interest ◽

Multi Temporal ◽

Significant Performance ◽

Adversarial Training

The increasing availability of large-scale remote sensing labeled data has prompted researchers to develop increasingly precise and accurate data-driven models for land cover and crop classification (LC&CC). Moreover, with the introduction of self-attention and introspection mechanisms, deep learning approaches have shown promising results in processing long temporal sequences in the multi-spectral domain with a contained computational request. Nevertheless, most practical applications cannot rely on labeled data, and in the field, surveys are a time-consuming solution that pose strict limitations to the number of collected samples. Moreover, atmospheric conditions and specific geographical region characteristics constitute a relevant domain gap that does not allow direct applicability of a trained model on the available dataset to the area of interest. In this paper, we investigate adversarial training of deep neural networks to bridge the domain discrepancy between distinct geographical zones. In particular, we perform a thorough analysis of domain adaptation applied to challenging multi-spectral, multi-temporal data, accurately highlighting the advantages of adapting state-of-the-art self-attention-based models for LC&CC to different target zones where labeled data are not available. Extensive experimentation demonstrated significant performance and generalization gain in applying domain-adversarial training to source and target regions with marked dissimilarities between the distribution of extracted features.

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Pumping power and heating area dependence of thermal resistance for a large-scale microchannel heat sink under extremely high heat flux

Heat and Mass Transfer ◽

10.1007/s00231-021-03104-y ◽

2021 ◽

Author(s):

Bo Sun ◽

Huiru Wang ◽

Zhongshan Shi ◽

Ji Li

Keyword(s):

Heat Flux ◽

Thermal Resistance ◽

Heat Sink ◽

Large Scale ◽

High Heat ◽

High Heat Flux ◽

Microchannel Heat Sink ◽

Pumping Power

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Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe

10.5194/egusphere-egu21-11134 ◽

2021 ◽

Author(s):

Alvise Aranyossy ◽

Sebastian Brune ◽

Lara Hellmich ◽

Johanna Baehr

Keyword(s):

North Atlantic ◽

Large Scale ◽

Jet Stream ◽

Cyclonic Activity ◽

Max Planck ◽

Pressure System ◽

Wind Speeds ◽

Average Lifespan ◽

The North ◽

The North Atlantic

We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones.&#160;Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.&#160; Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.

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