New Research

[knocker]

The melting ice makes the sea around Greenland less saline

For the first time, ocean data from Northeast Greenland reveals the long-term impact of the melting of the Greenland ice sheet.

https://www.eurekalert.org/pub_releases/2017-10/au-tmi101317.php

[knocker]

Strong Relations Between ENSO and the Arctic Oscillation in the North American Multi-Model Ensemble†

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Arctic Oscillation (AO) variability impacts climate anomalies over the mid-to-high latitudes of the Northern Hemisphere. Recently, state-of-the-art climate prediction models have proved capable of skillfully predicting the AO during the winter, revealing a previously unrealized source of climate predictability. Hindcasts from the North American Multi-Model Ensemble (NMME) show that the seasonal, ensemble mean 200-hPa AO index is skillfully predicted up to seven months in advance and that this skill, especially at longer leads, is coincident with previously unknown and strong relations (r > 0.9) with the El Niño-Southern Oscillation (ENSO). The NMME is a seasonal prediction system that comprises eight models and up to 100 members with forecasts out to 12 months. Observed ENSO-AO correlations are within the spread of the NMME member correlations, but the majority of member correlations are stronger than observed, consistent with too high predictability in the model, or over-confidence.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074854/abstract

[knocker]

Skillful prediction of northern climate provided by the ocean

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It is commonly understood that a potential for skillful climate prediction resides in the ocean. It nevertheless remains unresolved to what extent variable ocean heat is imprinted on the atmosphere to realize its predictive potential over land. Here we assess from observations whether anomalous heat in the Gulf Stream's northern extension provides predictability of northwestern European and Arctic climate. We show that variations in ocean temperature in the high latitude North Atlantic and Nordic Seas are reflected in the climate of northwestern Europe and in winter Arctic sea ice extent. Statistical regression models show that a significant part of northern climate variability thus can be skillfully predicted up to a decade in advance based on the state of the ocean. Particularly, we predict that Norwegian air temperature will decrease over the coming years, although staying above the long-term (1981–2010) average. Winter Arctic sea ice extent will remain low but with a general increase towards 2020.

https://www.nature.com/articles/ncomms15875 (open access)

[knocker]

Missing Arctic temperature data, not Mother Nature, created the seeming slowdown of global warming from 1998 to 2012, according to a new study in the journal Nature Climate Change.

https://phys.org/news/2017-11-added-arctic-global-didnt.html#jCp

[knocker]

A couple of recent La Nina research papers.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075034/abstract;jsessionid=BC86673D77C6229F82E8158347526705.f03t02?systemMessage=Wiley+Online+Library+usage+report+download+page+will+be+unavailable+on+Friday+24th+November+2017+at+21%3A00+EST+%2F+02.00+GMT+%2F+10%3A00+SGT+(Saturday+25th+Nov+for+SGT+

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074904/abstract?systemMessage=Wiley+Online+Library+usage+report+download+page+will+be+unavailable+on+Friday+24th+November+2017+at+21%3A00+EST+%2F+02.00+GMT+%2F+10%3A00+SGT+(Saturday+25th+Nov+for+SGT+

Article

https://phys.org/news/2017-11-la-nina-drought-years-advance.html

[knocker]

Observational evidence of European summer weather patterns predictable from spring

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Forecasts of summer weather patterns months in advance would be of great value for a wide range of applications. However, seasonal dynamical model forecasts for European summers have very little skill, particularly for rainfall. It has not been clear whether this low skill reflects inherent unpredictability of summer weather or, alternatively, is a consequence of weaknesses in current forecast systems. Here we analyze atmosphere and ocean observations and identify evidence that a specific pattern of summertime atmospheric circulation––the summer East Atlantic (SEA) pattern––is predictable from the previous spring. An index of North Atlantic sea-surface temperatures in March–April can predict the SEA pattern in July–August with a cross-validated correlation skill above 0.6. Our analyses show that the sea-surface temperatures influence atmospheric circulation and the position of the jet stream over the North Atlantic. The SEA pattern has a particularly strong influence on rainfall in the British Isles, which we find can also be predicted months ahead with a significant skill of 0.56. Our results have immediate application to empirical forecasts of summer rainfall for the United Kingdom, Ireland, and northern France and also suggest that current dynamical model forecast systems have large potential for improvement.

http://www.pnas.org/content/early/2017/12/12/1713146114

Article

http://novafm.co.uk/2017/12/18/new-approach-promises-early-warnings-of-soggy-summers/

[knocker]

Industrial-age doubling of snow accumulation in the Alaska Range linked to tropical ocean warming

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Future precipitation changes in a warming climate depend regionally upon the response of natural climate modes to anthropogenic forcing. North Pacific hydroclimate is dominated by the Aleutian Low, a semi-permanent wintertime feature characterized by frequent low-pressure conditions that is influenced by tropical Pacific Ocean temperatures through the Pacific-North American (PNA) teleconnection pattern. Instrumental records show a recent increase in coastal Alaskan precipitation and Aleutian Low intensification, but are of insufficient length to accurately assess low frequency trends and forcing mechanisms. Here we present a 1200-year seasonally- to annually-resolved ice core record of snow accumulation from Mt. Hunter in the Alaska Range developed using annual layer counting and four ice-flow thinning models. Under a wide range of glacier flow conditions and layer counting uncertainty, our record shows a doubling of precipitation since ~1840 CE, with recent values exceeding the variability observed over the past millennium. The precipitation increase is nearly synchronous with the warming of western tropical Pacific and Indian Ocean sea surface temperatures. While regional 20^th Century warming may account for a portion of the observed precipitation increase on Mt. Hunter, the magnitude and seasonality of the precipitation change indicate a long-term strengthening of the Aleutian Low.

https://www.nature.com/articles/s41598-017-18022-5

[knocker]

Reanalysing the impacts of atmospheric teleconnections on cold-season weather using multivariate surface weather types and self-organizing maps

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While regional- to hemispheric-scale oscillations in oceanographic and atmospheric variables have long been known to have teleconnective impacts on the surface weather at distant locations, the impacts of these teleconnections and their interactions on multivariate weather types (WTs) are relatively under-researched. Using a recently developed gridded weather typing classification (GWTC) and a self-organizing maps-based clustering of five different teleconnection indices, this research aims to explore the impacts of teleconnections on surface weather in the United States and Canada. Individual teleconnections have a predictable impact on GWTC WTs, with the Pacific/North American pattern, the Western Pacific (WP) pattern and the North Atlantic Oscillation showing the most widespread significant correlations with cool and warm WTs, in agreement with previous research. While many teleconnection clusters are dominated by one teleconnection's WT correlations, certain clusters reveal surprising regional- to continental-scale impacts considering many teleconnections are in a relatively neutral phase. Furthermore, some expected impacts of the Southern Oscillation Index and WP are offset when considered in tandem with neutral phases of the other teleconnections examined. Overall, the clustering results highlight the importance of examining multiple teleconnections simultaneously when researching teleconnection impacts on surface weather and making statistically based monthly- to seasonal-range climate projections.

http://onlinelibrary.wiley.com/doi/10.1002/joc.4950/abstract

[knocker]

Frost fairs, sunspots and the Little Ice Age

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Where spin doctors, politicians and newspaper editors understand well that a name alters how something is perceived, scientists know that a name does not change the reality one iota. By virtue of the name awarded to it, the “Little Ice Age” has been associated with full ice ages. The name Little Ice Age has also become almost synonymous with the Maunder minimum in solar activity in the minds of many people. Hence it has even become possible to build semantic arguments that imply there is some sort of link between solar activity and ice ages – and evidence for major control of climate by solar activity is often offered in the form of the occurrence of frost fairs on the Thames in London (figure 1). This paper discusses the true relationships, or lack of them, between these different events.

https://academic.oup.com/astrogeo/article/58/2/2.17/3074082

[knocker]

The importance of including variability in climate change projections used for adaptation

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Our understanding of mankind’s influence on the climate is largely based on computer simulations^1,2. Model output is typically averaged over several decades³ so that the anthropogenic climate change signal stands out from the largely unpredictable ‘noise’ of climate variability. Similar averaging periods (30-year) are used for regional climate projections^4,5,6 to inform adaptation. According to two such projections, UKCIP02 (ref. 4) and UKCP09 (ref. 6), the UK will experience ‘hotter drier summers and warmer wetter winters’^7,8 in the future. This message is about a typical rather than any individual future season, and these projections should not be compared directly to observed weather as this neglects the sizeable contribution from year-to-year climate variability. Therefore, despite the apparent contradiction with the messages, it is a fallacy to suggest the recent cold UK winters like 2009/2010 disprove human-made climate change⁹. Nevertheless, such claims understandably cause public confusion and doubt¹⁰. Here we include year-to-year variability to provide projections for individual seasons. This approach has two advantages. First, it allows fair comparisons with recent weather events, for instance showing that recent cold winters are within projected ranges. Second, it allows the projections to be expressed in terms of the extreme hot, cold, wet or dry seasons that impact society, providing a better idea of adaptation needs.

https://www.nature.com/articles/nclimate2705

[knocker]

Ice Loss and the Polar Vortex: How a Warming Arctic Fuels Cold Snaps

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When winter sets in, "polar vortex" becomes one of the most dreaded phrases in the Northern Hemisphere. It's enough to send shivers even before the first blast of bitter cold arrives.

New research shows that some northern regions have been getting hit with these extreme cold spells more frequently over the past four decades, even as the planet as a whole has warmed. While it may seem counterintuitive, the scientists believe these bitter cold snaps are connected to the warming of the Arctic and the effects that that warming is having on the winds of the stratospheric polar vortex, high above the Earth's surface.

https://insideclimatenews.org/news/27092017/polar-vortex-cold-snap-arctic-ice-loss-global-warming-climate-change

[knocker]

 

[knocker]

The mind-bending physics of Scandinavian sea-level change

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The Greenland ice sheet is a poster child of climate change. But in the Nordics, what happens in West Antarctica and Alaska has a more profound impact on local sea level rise. Sounds strange? Here’s how it works.

http://sciencenordic.com/mind-bending-physics-scandinavian-sea-level-change

[knocker]

Jet stream response to Arctic temperature swings

https://usclivar.org/research-highlights/jet-stream-response-arctic-temperature-swings

[knocker]

Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation

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Satellite observations over the past two decades have revealed increasing loss of grounded ice in West Antarctica, associated with floating ice shelves that have been thinning. Thinning reduces an ice shelf’s ability to restrain grounded-ice discharge, yet our understanding of the climate processes that drive mass changes is limited. Here, we use ice-shelf height data from four satellite altimeter missions (1994–2017) to show a direct link between ice-shelf height variability in the Antarctic Pacific sector and changes in regional atmospheric circulation driven by the El Niño/Southern Oscillation. This link is strongest from the Dotson to Ross ice shelves and weaker elsewhere. During intense El Niño years, height increase by accumulation exceeds the height decrease by basal melting, but net ice-shelf mass declines as basal ice loss exceeds ice gain by lower-density snow. Our results demonstrate a substantial response of Amundsen Sea ice shelves to global and regional climate variability, with rates of change in height and mass on interannual timescales that can be comparable to the longer-term trend, and with mass changes from surface accumulation offsetting a significant fraction of the changes in basal melting. This implies that ice-shelf height and mass variability will increase as interannual atmospheric variability increases in a warming climate

https://www.nature.com/articles/s41561-017-0033-0

[knocker]

Arctic sea-ice loss in different regions leads to contrasting Northern Hemisphere impacts†

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To explore the mechanisms linking Arctic sea-ice loss to changes in mid-latitude surface temperatures, we conduct idealized modeling experiments using an intermediate general circulation model and with sea-ice loss confined to the Atlantic or Pacific sectors of the Arctic (Barents-Kara or Chukchi-Bering Seas). Extending previous findings, there are opposite effects on the winter stratospheric polar vortex for both large-magnitude (late twenty-first century) and moderate-magnitude sea-ice loss. Accordingly, there are opposite tropospheric Arctic Oscillation (AO) responses for moderate-magnitude sea-ice loss. However, there are similar strength negative AO responses for large-magnitude sea-ice loss, suggesting that tropospheric mechanisms become relatively more important than stratospheric mechanisms as the sea-ice loss magnitude increases. The mid-latitude surface temperature response for each loss region and magnitude can be understood as the combination of an ‘indirect’ part induced by the large-scale circulation (AO) response, and a residual ‘direct’ part that is local to the loss region.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076433/full

[knocker]

Why Do Hurricanes Have Eyes? Scientists Still Don't Really Know

https://www.livescience.com/61415-hurricane-eye-wall-how-form.html

[knocker]

Disentangling global warming, multi-decadal variability, and El Niño in Pacific temperatures†

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A key challenge in climate science is to separate observed temperature changes into components due to internal variability and responses to external forcing. Extended integrations of forced and unforced climate models are often used for this purpose. Here we demonstrate a novel method to separate modes of internal variability from global warming based on differences in timescale and spatial pattern, without relying on climate models. We identify uncorrelated components of Pacific sea-surface temperature (SST) variability due to global warming, the Pacific Decadal Oscillation (PDO), and the El Niño–Southern Oscillation (ENSO). Our results give statistical representations of PDO and ENSO that are consistent with their being separate processes, operating on different timescales, but are otherwise consistent with canonical definitions. We isolate the multi-decadal variability of the PDO and find that it is confined to midlatitudes; tropical SSTs and their teleconnections mix in higher-frequency variability. This implies that midlatitude PDO anomalies are more persistent than previously thought.

http://onlinelibrary.wiley.com/wol1/doi/10.1002/2017GL076327/abstract

[knocker]

The Arctic sea ice cover of 2016: a year of record-low highs and higher-than-expected lows

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Abstract. The Arctic sea ice cover of 2016 was highly noteworthy, as it featured record low monthly sea ice extents at the start of the year but a summer (September) extent that was higher than expected by most seasonal forecasts. Here we explore the 2016 Arctic sea ice state in terms of its monthly sea ice cover, placing this in the context of the sea ice conditions observed since 2000. We demonstrate the sensitivity of monthly Arctic sea ice extent and area estimates, in terms of their magnitude and annual rankings, to the ice concentration input data (using two widely used datasets) and to the averaging methodology used to convert concentration to extent (daily or monthly extent calculations). We use estimates of sea ice area over sea ice extent to analyse the relative "compactness" of the Arctic sea ice cover, highlighting anomalously low compactness in the summer of 2016 which contributed to the higher-than-expected September ice extent. Two cyclones that entered the Arctic Ocean during August appear to have driven this low-concentration/compactness ice cover but were not sufficient to cause more widespread melt-out and a new record-low September ice extent. We use concentration budgets to explore the regions and processes (thermodynamics/dynamics) contributing to the monthly 2016 extent/area estimates highlighting, amongst other things, rapid ice intensification across the central eastern Arctic through September. Two different products show significant early melt onset across the Arctic Ocean in 2016, including record-early melt onset in the North Atlantic sector of the Arctic. Our results also show record-late 2016 freeze-up in the central Arctic, North Atlantic and the Alaskan Arctic sector in particular, associated with strong sea surface temperature anomalies that appeared shortly after the 2016 minimum (October onwards). We explore the implications of this low summer ice compactness for seasonal forecasting, suggesting that sea ice area could be a more reliable metric to forecast in this more seasonal, "New Arctic", sea ice regime.

https://www.the-cryosphere.net/12/433/2018/

[knocker]

Skilful seasonal predictions of Summer European rainfall

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076337/abstract?utm_content=buffera4eb1&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

[knocker]

Claim of solar influence is on thin ice: are 11-year cycle solar minima associated with severe winters in Europe?

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A recent paper in Geophysical Research Letters, 'Solar influence on winter severity in central Europe', by Sirocko et al (2012 Geophys. Res. Lett. 39 L16704) claims that 'weak solar activity is empirically related to extremely cold winter conditions in Europe' based on analyses of documentary evidence of freezing of the River Rhine in Germany and of the Reanalysis of the Twentieth Century (20C). However, our attempt to reproduce these findings failed. The documentary data appear to be selected subjectively and agree neither with instrumental observations nor with two other reconstructions based on documentary data. None of these datasets show significant connection between solar activity and winter severity in Europe beyond a common trend. The analysis of Sirocko et al of the 20C circulation and temperature is inconsistent with their time series analysis. A physically-motivated consistent methodology again fails to support the reported conclusions. We conclude that multiple lines of evidence contradict the findings of Sirocko et al.

http://iopscience.iop.org/article/10.1088/1748-9326/8/2/024014

[knocker]

The stratospheric pathway for Arctic impacts on midlatitude climate

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Recent evidence from both observations and model simulations suggests that an Arctic sea ice reduction tends to cause a negative Arctic Oscillation (AO) phase with severe winter weather in the Northern Hemisphere, which is often preceded by weakening of the stratospheric polar vortex. Although this evidence hints at a stratospheric involvement in the Arctic-midlatitude climate linkage, the exact role of the stratosphere remains elusive. Here we show that tropospheric AO response to the Arctic sea ice reduction largely disappears when suppressing the stratospheric wave mean flow interactions in numerical experiments. The results confirm a crucial role of the stratosphere in the sea ice impacts on the midlatitudes by coupling between the stratospheric polar vortex and planetary-scale waves. Those results and consistency with observation-based evidence suggest that a recent Arctic sea ice loss is linked to midlatitudes extreme weather events associated with the negative AO phase.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL068330/full

[Gray-Wolf]

Very timely knock's esp. for a paper from 2016!

I am equally as sure that the 'energy' that halted the switch east of the QBO the other year was tied into some pretty wild 10mb waves that a wonky polar night Jet was throwing around? Yesterdays wacked out GFS MJO medium range forecast showed us that the last major departure ,and splitting/relocating of the polar night Jet has left a lot of energy in the atmosphere to augment the atmospheric angular momentum and give us some extreme deviations from the norm!

But where does all this play out?

Unlike my youth ,when there was no way ( barring a direct asteroid impact!) we were going to see a blue ocean over the pole, now a repeat of the 07' summer will bring just that?

At present we have two areas that are seasonally ice free ( that used to be ice covered), our side of the basin ( Karas/Barentsz) and the Pacific side (Bering/part Beaufort) so their heat shedding in Autumn/early winter is what messes up the polar night jat formation and positioning. What happens the year of the Blue Ocean's appearance when the whole basin ( for a short period) is pumping heat into the atmosphere above? What of the formation /positioning of the polar night jet then?

Edited March 7, 2018 by Gray-Wolf

[knocker]

Solar Constant: Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to the Present

Introduction

Solar irradiance is the fundamental driver of all climate processes on Earth. Past climate changes can be related to variations in TSI while human activity has had an increasing effect on Earth’s climate over the past ~150 years. High-accuracy TSI measurements help to assess solar forcing on global temperatures in order to distinguish between anthropogenic and natural climate change. TSI has been continuously measured in space since the late 1970’s, and towards the end of the 1990’s, the scatter between different radiometers decreased. The current best estimate of TSI is ~1361 W.m-2.

https://www.pmodwrc.ch/en/research-development/solar-physics/tsi-composite/

[knocker]

Increased wind risk from sting-jet windstorms with climate change

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Extra-tropical cyclones dominate autumn and winter weather over western Europe. The strongest cyclones, often termed windstorms, have a large socio-economic impact on landfall due to strong surface winds and coastal storm surges. Climate model integrations have predicted a future increase in the frequency of, and potential damage from, European windstorms and yet these integrations cannot properly represent localised jets, such as sting jets, that may significantly enhance damage. Here we present the first prediction of how the climatology of sting-jet-containing cyclones will change in a future warmer climate, considering the North Atlantic and Europe. A proven sting-jet precursor diagnostic is applied to 13 year present-day and future (~2100) climate integrations from the Met Office Unified Model in its Global Atmosphere 3.0 configuration. The present-day climate results are consistent with previously-published results from a reanalysis dataset (with around 32% of cyclones exhibiting the sing-jet precursor), lending credibility to the analysis of the future-climate integration. The proportion of cyclones exhibiting the sting-jet precursor in the future-climate integration increases to 45%. Furthermore, while the proportion of explosively-deepening storms increases only slightly in the future climate, the proportion of those storms with the sting-jet precursor increases by 60%. The European resolved-wind risk associated with explosively-deepening storms containing a sting-jet precursor increases substantially in the future climate; in reality this wind risk is likely to be further enhanced by the release of localised moist instability, unresolved by typical climate models.

http://iopscience.iop.org/article/10.1088/1748-9326/aaae3a/meta (open access)

Article

http://www.reading.ac.uk/news-and-events/releases/PR760896.aspx