Muyin Wang

Large‐scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice

Abstract Recent loss of summer sea ice in the Arctic is directly connected to shifts in northern wind patterns in the following autumn, which has the potential of altering the heat budget at the cold end of the global heat engine.With continuing loss of summer sea ice to less than 20% of its climatological mean over the next decades, we anticipate increased modification of atmospheric circulation patterns. While a shift to a more meridional atmospheric climate pattern, the Arctic Dipole (AD), over the last decade contributed to recent reductions in summer Arctic sea ice extent, the increase in late summer open water area is, in turn, directly contributing to a modification of large scale atmospheric circulation patterns through the additional heat stored in the Arctic Ocean and released to the atmosphere during the autumn season. Extensive regions in the Arctic during late autumn beginning in 2002 have surface air temperature anomalies of greater than 3 ◦C and temperature anomalies above 850 hPa of 1 ◦C. These temperatures contribute to an increase in the 1000–500 hPa thickness field in every recent year with reduced sea ice cover. While gradients in this thickness field can be considered a baroclinic contribution to the flow field from loss of sea ice, atmospheric circulation also has a more variable barotropic contribution. Thus, reduction in sea ice has a direct connection to increased thickness fields in every year, but not necessarily to the sea level pressure (SLP) fields. Compositing wind fields for late autumn 2002–2008 helps to highlight the baroclinic contribution; for the years with diminished sea ice cover there were composite anomalous tropospheric easterly winds of∼1.4ms–1, relative to climatological easterly winds near the surface and upper troposphericwesterlies of∼3 m s–1. Loss of summer sea ice is supported by decadal shifts in atmospheric climate patterns. A persistent positive Arctic Oscillation pattern in late autumn (OND) during 1988–1994 and in winter (JFM) during 1989–1997 shifted to more interannual variability in the following years. An anomalous meridional wind pattern with high SLP on the North American side of the Arctic—the AD pattern, shifted from primarily small interannual variability to a persistent phase during spring (AMJ) beginning in 1997 (except for 2006) and extending to summer (JAS) beginning in 2005.

The recent Arctic warm period

Arctic winter, spring and autumn surface air temperature (SAT) anomalies and associated sea level pressure (SLP) fields have decidedly different spatial patterns at the beginning of the 21st century (2000–2007) compared to most of the 20th century; we suggest calling this recent interval the Arctic warm period. For example, spring melt date as measured at the North Pole Environmental Observatory (2002–2007) is 7 d earlier than the records from the Russian North Pole stations (1937–1987) and statistically different at the 0.05 level. The 20th century was dominated by the two main climate patterns, the Arctic Oscillation/Northern Annular Mode (AO/NAM) and the Pacific North American-like (PNA∗) pattern. The predominately zonal winds associated with the positive phases of these patterns contribute to warm anomalies in the Arctic primarily over their respective Eastern and Western Hemisphere land areas, as in 1989–1995 and 1977–1987. In contrast, SAT in winter (DJF) and spring (MAM) for 2000–2007 show an Arctic-wide SAT anomaly of greater than +1.0◦C and regional hot spots over the central Arctic of greater than +3.0◦C. Unlike the AO and PNA∗, anomalous geostrophic winds for 2000–2007 often tended to blow toward the central Arctic, a meridional wind circulation pattern. In spring 2000–2005, these winds were from the Bering Sea toward the North Pole, whereas in 2006–2007 they were mostly from the eastern Barents Sea. A meridional pattern was also seen in the late 1930s with anomalous winter (DJFM) SAT, at Spitzbergen, of greater than +4◦C. Both periods suggest natural atmospheric advective contributions to the hot spots with regional loss of sea ice. Recent warm SAT anomalies in autumn are consistent with climate model projections in response to summer reductions in sea ice extent. The recent dramatic loss of Arctic sea ice appears to be due to a combination of a global warming signal and fortuitous phasing of intrinsic climate patterns.

The recent shift in early summer Arctic atmospheric circulation

1 The last six years (2007-2012) show a persistent change in early summer Arctic wind patterns relative to previous decades. The persistent pattern, which has been previously recognized as the Arctic Dipole (AD), is characterized by relatively low sea-level pressure over the Siberian Arctic with high pressure over the Beaufort Sea, extending across northern North America and over Greenland. Pressure differences peak in June. In a search for a proximate cause for the newly persistent AD pattern, we note that the composite 700 hPa geopotential height field during June 2007-2012 exhibits a positive anomaly only on the North American side of the Arctic, thus creating the enhanced mean meridional flow across the Arctic. Coupled impacts of the new persistent pattern are increased sea ice loss in summer, long-lived positive temperature anomalies and ice sheet loss in west Greenland, and a possible increase in Arctic-subarctic weather linkages through higheramplitude upper-level flow. The North American location of increased 700 hPa positive anomalies suggests that a regional atmospheric blocking mechanism is responsible for the presence of the AD pattern, consistent with observations of unprecedented high pressure anomalies over Greenland since 2007. ©2012. American Geophysical Union. All Rights Reserved.

Seasonal and regional variation of pan-arctic surface air temperature over the instrumental record

Abstract Instrumental surface air temperature (SAT) records beginning in the late 1800s from 59 Arctic stations north of 64°N show monthly mean anomalies of several degrees and large spatial teleconnectivity, yet there are systematic seasonal and regional differences. Analyses are based on time–longitude plots of SAT anomalies and principal component analysis (PCA). Using monthly station data rather than gridded fields for this analysis highlights the importance of considering record length in calculating reliable Arctic change estimates; for example, the contrast of PCA performed on 11 stations beginning in 1886, 20 stations beginning in 1912, and 45 stations beginning in 1936 is illustrated. While often there is a well-known interdecadal negative covariability in winter between northern Europe and Baffin Bay, long-term changes in the remainder of the Arctic are most evident in spring, with cool temperature anomalies before 1920 and Arctic-wide warm temperatures in the 1990s. Summer anomalies are general...

Future climate of the north Pacific Ocean

Major changes in species distribution and abundance in North Pacific marine ecosystems are often correlated with climatic shifts in the twentieth century. Species affected in the past include halibut in the Gulf of Alaska, sardine near Japan, and various species along the Oregon/California coast [Chen and Hare, 2006; Zhang et al., 2004; Peterson and Schwing, 2003]. Because these changes can affect the fishing industry, we have investigated possible future climate patterns in the North Pacific based on the evaluation of 22 coupled atmosphere-ocean general circulation models (GCMs). These GCMs were made available to the science community for independent evaluation in preparation for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC).

Future Arctic climate changes: Adaptation and mitigation time scales

The climate in the Arctic is changing faster than in midlatitudes. This is shown by increased temperatures, loss of summer sea ice, earlier snow melt, impacts on ecosystems, and increased economic access. Arctic sea ice volume has decreased by 75% since the 1980s. Long-lasting global anthropogenic forcing from carbon dioxide has increased over the previous decades and is anticipated to increase over the next decades. Temperature increases in response to greenhouse gases are amplified in the Arctic through feedback processes associated with shifts in albedo, ocean and land heat storage, and near-surface longwave radiation fluxes. Thus, for the next few decades out to 2040, continuing environmental changes in the Arctic are very likely, and the appropriate response is to plan for adaptation to these changes. For example, it is very likely that the Arctic Ocean will become seasonally nearly sea ice free before 2050 and possibly within a decade or two, which in turn will further increase Arctic temperatures, economic access, and ecological shifts. Mitigation becomes an important option to reduce potential Arctic impacts in the second half of the 21st century. Using the most recent set of climate model projections (CMIP5), multimodel mean temperature projections show an Arctic-wide end of century increase of +13°C in late fall and +5°C in late spring for a business-as-usual emission scenario (RCP8.5) in contrast to +7°C in late fall and +3°C in late spring if civilization follows a mitigation scenario (RCP4.5). Such temperature increases demonstrate the heightened sensitivity of the Arctic to greenhouse gas forcing.

Considerations in the Selection of Global Climate Models for Regional Climate Projections: The Arctic as a Case Study*

Abstract Climate projections at regional scales are in increased demand from management agencies and other stakeholders. While global atmosphere–ocean climate models provide credible quantitative estimates of future climate at continental scales and above, individual model performance varies for different regions, variables, and evaluation metrics—a less than satisfying situation. Using the high-latitude Northern Hemisphere as a focus, the authors assess strategies for providing regional projections based on global climate models. Starting with a set of model results obtained from an “ensemble of opportunity,” the core of this procedure is to retain a subset of models through comparisons of model simulations with observations at both continental and regional scales. The exercise is more one of model culling than model selection. The continental-scale evaluation is a check on the large-scale climate physics of the models, and the regional-scale evaluation emphasizes variables of ecological or societal rele...

Recent Temperature Changes in the Western Arctic during Spring

The lower troposphere of the western Arctic (eastern Siberia to northern Canada) was relatively warm during spring in the 1990s. Based on the NCEP‐NCAR reanalysis, supplemented by the Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) Polar Pathfinder dataset, this warmth is a result of a recent increase in the frequency of warm months, compared to the previous four decades. The primary difference between four notably warm springs in the 1990s and four cold springs in the 1980s was the sense of the horizontal advection term in a lower-tropospheric heat budget for northern Alaska/southern Beaufort Sea. While the horizontal advection of heat was highly episodic, it was related to changes in the mean circulation at low levels, in particular a shift from anomalous northeasterly flow in the 1980s to anomalous southwesterly flow in the 1990s during March and April. This change in the low-level winds in the western Arctic coincided with a systematic shift in the Arctic Oscillation (AO) near the end of the 1980s, and reflects the equivalent barotropic nature of the AO. The stratospheric temperature anomalies associated with the AO were greatest in March; the low-level wind anomalies brought about near-surface temperature anomalies in northern Alaska that peaked in April. In addition to substantial decadal differences, there was considerable month-to-month and yearto-year variability within the last two decades.

Recent Extreme Arctic Temperatures are due to a Split Polar Vortex

AbstractThere were extensive regions of Arctic temperature extremes in January and February 2016 that continued into April. For January, the Arctic-wide averaged temperature anomaly was 2.0°C above the previous record of 3.0°C based on four reanalysis products. Midlatitude atmospheric circulation played a major role in producing such extreme temperatures. Extensive low geopotential heights at 700 hPa extended over the southeastern United States, across the Atlantic, and well into the Arctic. Low geopotential heights along the Aleutian Islands and a ridge along northwestern North America contributed southerly wind flow. These two regions of low geopotential height were seen as a major split in the tropospheric polar vortex over the Arctic. Warm air advection north of central Eurasia reinforced the ridge that split the flow near the North Pole. Winter 2015 and 2016 geopotential height fields represented an eastward shift in the longwave atmospheric circulation pattern compared to earlier in the decade (2010...

Increased Variability in the Early Winter Subarctic North American Atmospheric Circulation

AbstractThe last decade shows increased variability in the Arctic Oscillation (AO) index for December. Over eastern North America such increased variability depended on amplification of the climatological longwave atmospheric circulation pattern. Recent negative magnitudes of the AO have increased geopotential thickness west of Greenland and cold weather in the central and eastern United States. Although the increased variance in the AO is statistically significant based on 9-yr running standard deviations from 1950 to 2014, one cannot necessarily robustly attribute the increase to steady changes in external sources (sea temperatures, sea ice) rather than a chaotic view of internal atmospheric variability; this is due to a relatively short record and a review of associated atmospheric dynamics. Although chaotic internal variability dominates the dynamics of atmospheric circulation, Arctic thermodynamic influence can reinforce the regional geopotential height pattern. Such reinforcement suggests a conditio...