Ocean-atmospheric state dependence of the atmospheric response to Arctic sea ice loss

This is the final version of the article. Available from American Meteorological Society via the DOI in this record.The Arctic is warming faster than the global average. This disproportionate warming – known as Arctic amplification – has caused significant local changes to the Arctic system and more uncertain remote changes across the Northern Hemisphere midlatitudes. Here, we use an atmospheric general circulation model (AGCM) to test the sensitivity of the atmospheric and surface response to Arctic sea ice loss to the phase of the Atlantic Multidecadal Oscillation (AMO), which varies on (multi-)decadal timescales. Four experiments are performed, combining low and high sea ice states with global sea surface temperature (SST) anomalies associated with opposite phases of the AMO. A trough-ridge-trough response to wintertime sea ice loss is seen in the PacificNorth America sector in the negative phase of the AMO. We propose that this is a consequence of an increased meridional temperature gradient in response to sea ice loss, just south of the climatological maximum, in the central midlatitude North Pacific. This causes a southward shift in the North Pacific storm track, which strengthens the Aleutian Low with circulation anomalies propagating into North America. While the climate response to sea ice loss is sensitive to AMO-related SST anomalies in the North Pacific, there is little sensitivity to larger magnitude SST anomalies in the North Atlantic. With background ocean-atmospheric states persisting for a number of years, there is the potential to improve predictions of the impacts of Arctic sea ice loss on decadal timescalesThis work was supported by the Natural Environment Research Council grants NE/M006123/1 and NE/J019585/1. The HadGAM2 simulations were performed on the ARCHER UK National Supercomputing Service. For the provision of observed and reanalysis data the Met Office Hadley Centre and NOAA ESRL are thanked. Model data are available from the authors upon request

New climate models reveal faster and larger increases in Arctic precipitation than previously projected

As the Arctic continues to warm faster than the rest of the planet, evidence mounts that the region is experiencing unprecedented environmental change. The hydrological cycle is projected to intensify throughout the twenty-first century, with increased evaporation from expanding open water areas and more precipitation. The latest projections from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) point to more rapid Arctic warming and sea-ice loss by the year 2100 than in previous projections, and consequently, larger and faster changes in the hydrological cycle. Arctic precipitation (rainfall) increases more rapidly in CMIP6 than in CMIP5 due to greater global warming and poleward moisture transport, greater Arctic amplification and sea-ice loss and increased sensitivity of precipitation to Arctic warming. The transition from a snow- to rain-dominated Arctic in the summer and autumn is projected to occur decades earlier and at a lower level of global warming, potentially under 1.5 °C, with profound climatic, ecosystem and socio-economic impacts

Atmospheric precursors of and response to anomalous Arctic sea ice in CMIP5 models

This is the final version of the article. Available from Springer Verlag via the DOI in this record.This study examines pre-industrial control simulations from CMIP5 climate models in an effort to better understand the complex relationships between Arctic sea ice and the stratosphere, and between Arctic sea ice and cold winter temperatures over Eurasia. We present normalized regressions of Arctic sea-ice area against several atmospheric variables at extended lead and lag times. Statistically significant regressions are found at leads and lags, suggesting both atmospheric precursors of, and responses to, low sea ice; but generally, the regressions are stronger when the atmosphere leads sea ice, including a weaker polar stratospheric vortex indicated by positive polar cap height anomalies. Significant positive midlatitude eddy heat flux anomalies are also found to precede low sea ice. We argue that low sea ice and raised polar cap height are both a response to this enhanced midlatitude eddy heat flux. The so-called “warm Arctic, cold continents” anomaly pattern is present one to two months before low sea ice, but is absent in the months following low sea ice, suggesting that the Eurasian cooling and low sea ice are driven by similar processes. Lastly, our results suggest a dependence on the geographic region of low sea ice, with low Barents–Kara Sea ice correlated with a weakened polar stratospheric vortex, whilst low Sea of Okhotsk ice is correlated with a strengthened polar vortex. Overall, the results support a notion that the sea ice, polar stratospheric vortex and Eurasian surface temperatures collectively respond to large-scale changes in tropospheric circulation.This work was supported by the Natural Environment Research Council (Grant No. NE/M006123/1)

Multimodel Analysis of the Atmospheric Response to Antarctic Sea Ice Loss at Quadrupled CO2

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordAntarctic sea ice cover is projected to significantly decrease by the end of the twenty-first century if greenhouse gas concentrations continue to rise, with potential consequences for Southern Hemisphere weather and climate. Here we examine the atmospheric response to projected Antarctic sea ice loss at quadrupled CO2, inferred from 11 Coupled Model Intercomparison Project phase 5 models. Our study is the first multimodel analysis of the atmospheric response to Antarctic sea ice loss. Projected sea ice loss enhances the negative phase of the Southern Annular Mode, which slightly damps the positive Southern Annular Mode response to increased CO2, particularly in spring. The negative Southern Annular Mode response largely reflects a weakening of the eddy-driven jet, and to a lesser extent, an equatorward shift of the jet. Sea ice loss induces near-surface warming over the high-latitude Southern Ocean, but warming does not penetrate over the Antarctic continent. In spring, we find multimodel evidence for a weakened polar stratospheric vortex in response to sea ice loss.NER

Contribution of sea-ice loss to Arctic amplification is regulated by Pacific Ocean decadal variability

The pace of Arctic warming is about double that at lower latitudes – a robust phenomenon known as Arctic amplification (AA)1. Many diverse climate processes and feedbacks cause AA2-7, including positive feedbacks associated with diminished sea ice6,7. However, the precise contribution of sea-ice loss to AA remains uncertain7,8. Through analyses of both observations and model simulations, we show that the contribution of sea-ice loss to wintertime AA appears dependent on the phase of the Pacific Decadal Oscillation (PDO). Our results suggest that for the same pattern and amount of sea-ice loss, consequent Arctic warming is larger during the negative PDO phase, relative to the positive phase, leading to larger reductions in the poleward gradient of tropospheric thickness and to more pronounced reductions in the upper-level westerlies. Given the oscillatory nature of the PDO, this relationship has the potential to increase skill in decadal-scale predictability of Arctic and sub-Arctic climate. Our results indicate that Arctic warming in response to the ongoing long-term sea-ice decline9,10 is greater (reduced) during periods of negative (positive) PDO phase. We speculate that the observed recent shift to the positive PDO phase, if maintained and all other factors being equal, could act to temporarily reduce the pace of wintertime Arctic warming in the near future.J.A.S. was funded by a UK Natural Environment Research Council (NERC) grants NE/J019585/1 and NE/M006123/1. J.A.F. was supported by an NSF/ARCSS grant (1304097) and NASA grant (NNX14AH896). The model simulations were performed on the ARCHER UK National Supercomputing Service. We thank the NOAA ESRL and Met Office Hadley Centre for provision of observational and reanalysis data sets. We also thank D. Ackerley for helping to diagnose the cause of model crashes, C. Deser for commenting on the manuscript prior to submission, and two anonymous reviewers for constructive criticism

A Combined Spectrophotometer and Fluorometer to Demonstrate the Principles of Absorption Spectroscopy

A dual-function student-crafted instrument is described as part of a laboratory activity aimed to teach both the principles and practical aspects of absorption spectroscopy to secondary and introductory undergraduate students. Using minimal changes in an arrangement that is based on interlocking bricks and low-cost components, both a fluorometer and photometer have been constructed. The former demonstrates the principles of the Beer–Lambert law visually and quantitatively by acquiring the spatial light attenuation through a fluorescent sample. The latter then demonstrates its practical application in a visible-light spectrometer by measuring the absorption spectrum of an aqueous permanganate solution

The dynamics of temperature extremes

Changes in the occurrence of atmospheric circulation patterns are not well understood. A study finds that these have been a big factor in observed changes in regional temperature extremes during recent decades

Collisional depolarization of NO(A) by He and Ar studied by quantum beat spectroscopy

Zeeman and hyperfine quantum beat spectroscopies have been used to measure the total elastic plus inelastic angular momentum depolarization rate constants at 300 K for NO (A 2 σ+) in the presence of He and Ar. In the case of Zeeman quantum beats it is shown how the applied magnetic field can be used to allow measurement of depolarization rates for both angular momentum orientation and alignment. For the systems studied here, collisional loss of alignment is more efficient than loss of orientation. In the case of NO (A) with He, and to a lesser extent NO (A) with Ar, collisional depolarization is found to be a relatively minor process compared to rotational energy transfer, reflecting the very weak long-range forces in these systems. Detailed comparisons are made with quantum mechanical and quasiclassical trajectory calculations performed on recently developed potential energy surfaces. For both systems, the agreement between the calculated depolarization cross sections and the present measurements is found to be very good, suggesting that it is reasonable to consider the NO (A) bond as frozen during these angular momentum transferring collisions. A combination of kinematic effects and differences in the potential energy surfaces are shown to be responsible for the differences observed in depolarization cross section with He and Ar as a collider. © 2009 American Institute of Physics

Consistency and discrepancy in the atmospheric response to Arctic sea-ice loss across climate models

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordThe decline of Arctic sea ice is an integral part of anthropogenic climate change. Sea-ice loss is already having a significant impact on Arctic communities and ecosystems. Its role as a cause of climate changes outside of the Arctic has also attracted much scientific interest. Evidence is mounting that Arctic sea-ice loss can affect weather and climate throughout the Northern Hemisphere. The remote impacts of Arctic sea-ice loss can only be properly represented using models that simulate interactions among the ocean, sea ice, land and atmosphere. A synthesis of six such experiments with different models shows consistent hemispheric-wide atmospheric warming, strongest in the mid-to-high-latitude lower troposphere; an intensification of the wintertime Aleutian Low and, in most cases, the Siberian High; a weakening of the Icelandic Low; and a reduction in strength and southward shift of the mid-latitude westerly winds in winter. The atmospheric circulation response seems to be sensitive to the magnitude and geographic pattern of sea-ice loss and, in some cases, to the background climate state. However, it is unclear whether current-generation climate models respond too weakly to sea-ice change. We advocate for coordinated experiments that use different models and observational constraints to quantify the climate response to Arctic sea-ice loss.J.A.S. and R.B. were funded by the Natural Environment Research Council (NE/P006760/1). C.D. acknowledges the National Science Foundation (NSF), which sponsors the National Center for Atmospheric Research. D.M.S. was supported by the Met Office Hadley Centre Climate Programme (GA01101) and the APPLICATE project, which is funded by the European Union’s Horizon 2020 programme. X.Z. was supported by the NSF (ARC#1023592). P.J.K. and K.E.M. were supported by the Canadian Sea Ice and Snow Evolution Network, which is funded by the Natural Science and Engineering Research Council of Canada. T.O. was funded by Environment and Climate Change Canada (GCXE17S038). L.S. was supported by the National Oceanic and Atmospheric Administration’s Climate Program Office