Clouds and Aerosols

[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.

More Evidence Linking Arctic Amplification to Extreme Weather in Mid-Latitudes

The areal extent, concentration and thickness of sea ice in the Arctic Ocean and adjacent seas have strongly decreased during the recent decades, but cold, snow-rich winters have been common over mid-latitude land areas since 2005. A review is presented on studies addressing the local and remote effects of the sea ice decline on weather and climate. It is evident that the reduction in sea ice cover has increased the heat flux from the ocean to atmosphere in autumn and early winter. This has locally increased air tempera- ture, moisture, and cloud cover and reduced the static stability in the lower troposphere. Several studies based on observations, atmospheric reanalyses, and model experiments suggest that the sea ice decline, together with increased snow cover in Eurasia, favours circulation patterns resembling the negative phase of the North Atlantic Oscillation and Arctic Oscillation. The suggested large-scale pressure patterns include a high over Eurasia, which favours cold winters in Europe and northeastern Eurasia. A high over the western and a low over the eastern North America have also been suggested, favouring advection of Arctic air masses to North America. Mid-latitude winter weather is, however, affected by several other factors, which generate a large inter-annual variability and often mask the effects of sea ice decline. In addition, the small sample of years with a large sea ice loss makes it difficult to distinguish the effects directly attributable to sea ice conditions. Several studies suggest that, with advancing global warming, cold winters in mid-latitude continents will no longer be common during the second half of the twenty-first century. Recent studies have also suggested causal links between the sea ice decline and summer precipitation in Europe, the Mediterranean, and East Asia.

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Effects of Arctic Sea Ice Decline on Weather and Climate: A Review

The loss of Arctic sea ice has emerged as a leading signal of global warming. This, together with acknowledged impacts on other components of the Earth system, has led to the term “the new Arctic.” Global coupled climate models predict that ice loss will continue through the twenty-first century, with implications for governance, economics, security, and global weather. A wide range in model projections reflects the complex, highly coupled interactions between the polar atmosphere, ocean, and cryosphere, including teleconnections to lower latitudes. This paper summarizes our present understanding of how heat reaches the ice base from the original sources—inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiative fluxes at the ocean/ice surface—and speculates on how such processes may change in the new Arctic. The complexity of the coupled Arctic system, and the logistic and technological challenges of working in the Arctic Ocean, require a coordinated ...

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Toward Quantifying the Increasing Role of Oceanic Heat in Sea Ice Loss in the New Arctic

The polar regions have been attracting more and more attention in recent years, fueled by the perceptible impacts of anthropogenic climate change. Polar climate change provides new opportunities, such as shorter shipping routes between Europe and East Asia, but also new risks such as the potential for industrial accidents or emergencies in ice-covered seas. Here, it is argued that environmental prediction systems for the polar regions are less developed than elsewhere. There are many reasons for this situation, including the polar regions being (historically) lower priority, with fewer in situ observations, and with numerous local physical processes that are less well represented by models. By contrasting the relative importance of different physical processes in polar and lower latitudes, the need for a dedicated polar prediction effort is illustrated. Research priorities are identified that will help to advance environmental polar prediction capabilities. Examples include an improvement of the p...

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Advancing Polar Prediction Capabilities on Daily to Seasonal Time Scales

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020JD033389

Evaluation of Three Numerical Weather Prediction Models for the Weddell Sea Region for the Austral Winter 2013

T. Vihma1,2, R. Pirazzini1, I. Fer3, I. A. Renfrew4, J. Sedlar5,6, M. Tjernstrom5,6, C. Lupkes7, T. Nygard1, D. Notz8, J. Weiss9, D. Marsan10, B. Cheng1, G. Birnbaum7, S. Gerland11, D. Chechin12, and J. C. Gascard13 1Finnish Meteorological Institute, Helsinki, Finland 2The University Centre in Svalbard, Longyearbyen, Norway 3University of Bergen, Bergen, Norway 4University of East Anglia, Norwich, UK 5Bert Bolin Center for Climate Research, Stockholm, Sweden 6Department of Meteorology, Stockholm University, Stockholm, Sweden 7Alfred-Wegener-Institut Helmholtz-Zentrum fur Polarund Meeresforschung, Bremerhaven, Germany 8Max Planck Institute for Meteorology, Hamburg, Germany 9LGGE, Universite de Grenoble, CNRS, Grenoble, France 10ISTerre, Universite de Savoie, CNRS, Le Bourget-du-Lac, France 11Norwegian Polar Institute, Tromso, Norway 12A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia 13Universite Pierre et Marie Curie, Paris, France

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Corrigendum to "Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review" published in Atmos. Chem. Phys., 14, 9403–9450, 2014

Abstract. Despite the general warming trend, wintertime cold air outbreaks in Europe have remained nearly as extreme and as common as decades ago. In this study, we identify six principal 850 hPa cold anomaly types over Europe in 1979–2020 using self-organizing maps (SOMs). Based on extensive analysis of atmospheric large-scale circulation patterns combined with nearly two million kinematic backward trajectories, we show the origins and contributions of various physical processes to the formation of cold wintertime 850-hPa air masses. The location of the cold anomaly region is closely tied to the location of blocking; if the block is located farther in the east, also the cold anomaly is displaced eastwards. Considering air-mass evolution along the trajectories, the air parcels are typically initially (5–10 d before) colder than at their arrival in Europe, but also initially warmer air parcels sometimes lead to cold anomalies over Europe. Most commonly the effect of adiabatic warming on the temperature anomalies is overcompensated by advection from regions that are climatologically colder than the target region, supported by diabatic cooling along the pathway. However, there are regional differences: cold anomalies over western Europe and southeastern Europe are dominantly caused by advection, and over eastern Europe by both advective and diabatic processes. The decadal-scale warming in the site of air mass origin has been partly compensated by enhanced diabatic (radiative) cooling along the pathway to Europe. There have also been decadal changes in large-scale circulation patterns and air mass origin. Our results suggest that understanding future changes in cold extremes will require in-depth analyses on both large-scale circulation and the physical (adiabatic and diabatic) processes. 

Tiina Nygård

Papers

Evaluation of Three Numerical Weather Prediction Models for the Weddell Sea Region for the Austral Winter 2013

Corrigendum to "Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review" published in Atmos. Chem. Phys., 14, 9403–9450, 2014

Cold wintertime air masses over Europe: Where do they come from and how do they form?

Impact of assimilation of radiosonde and UAV observations on numerical weather prediction analyses and forecasts in the Arctic and Antarctic