Influence of winter and summer surface wind anomalies on summer Arctic sea ice extent (original) (raw)
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Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958–1998
Climate Dynamics, 2000
A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958±98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-toyear variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are ®rst investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is brie¯y discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait.
Recent wind driven high sea ice area export in the Fram Strait contributes to Arctic sea ice decline
The Cryosphere, 2011
Arctic sea ice area decrease has been visible for two decades, and continues at a steady rate. Apart from melting, the southward drift through Fram Strait is the main loss. We present high resolution sea ice drift across 79 • N from 2004 to 2010. The ice drift is based on radar satellite data and correspond well with variability in local geostrophic 5 wind. The underlying current contributes with a constant southward speed close to 5 cm s −1 , and drives about 33 % of the ice export. We use geostrophic winds derived from reanalysis data to calculate the Fram Strait ice area export back to 1957, finding that the sea ice area export recently is about 25 % larger than during the 1960's. The increase in ice export occurred mostly during winter and is directly connected to higher 10 southward ice drift velocities, due to stronger geostrophic winds. The increase in ice drift is large enough to counteract a decrease in ice concentration of the exported sea ice. Using storm tracking we link changes in geostrophic winds to more intense Nordic Sea low pressure systems. Annual sea ice export likely has a significant influence on the summer sea ice variability and we find low values in the 60's, the late 80's and 90's, 15 and particularly high values during 2005-2008. The study highlight the possible role of variability in ice export as an explanatory factor for understanding the dramatic loss of Arctic sea ice the last decades.
Journal of Geophysical Research: Atmospheres, 2016
Numerous studies have addressed links between summer atmospheric circulation patterns and interannual variability and the downward trend in total September Arctic sea ice extent. In general, low extent is favored when the preceding summer is characterized by positive sea level pressure (SLP) anomalies over the central Arctic Ocean north of Alaska. High extent is favored when low pressure dominates. If such atmospheric patterns could be predicted several months out, these links provide an avenue for improved seasonal predictability of total September extent. We analyze detrended September extent time series (1979-2015), atmospheric reanalysis fields, ice age and motion, and Atmospheric Infrared Sounder data, to show that while there is merit to this summer circulation framework, it has limitations. Large departures in total September extent relative to the trend line are preceded by a wide range of summer circulation patterns. While patterns for the four years with the largest positive departures in September extent have below average SLP over the central Arctic Ocean, they differ markedly in the magnitude and location of pressure and air temperature anomalies. Differences in circulation for the four years with the largest negative departures are equally prominent. Circulation anomalies preceding Septembers with ice extent close to the trend also have a wide range of patterns. In turn, years (such as 2013 and 2014) with almost identical total September extent were preceded by very different summer circulation patterns. September ice conditions can also be strongly shaped by events as far back as the previous winter or spring.
Recent wind driven high sea ice export in the Fram Strait contributes to Arctic sea ice decline
The Cryosphere Discussions, 2011
ABSTRACT Arctic sea ice area decrease has been visible for two decades, and continues at a steady rate. Apart from melting, the southward drift through Fram Strait is the main loss. We present high resolution sea ice drift across 79 • N from 2004 to 2010. The ice drift is based on radar satellite data and correspond well with variability in local geostrophic 5 wind. The underlying current contributes with a constant southward speed close to 5 cm s −1 , and drives about 33 % of the ice export. We use geostrophic winds derived from reanalysis data to calculate the Fram Strait ice area export back to 1957, finding that the sea ice area export recently is about 25 % larger than during the 1960's. The increase in ice export occurred mostly during winter and is directly connected to higher 10 southward ice drift velocities, due to stronger geostrophic winds. The increase in ice drift is large enough to counteract a decrease in ice concentration of the exported sea ice. Using storm tracking we link changes in geostrophic winds to more intense Nordic Sea low pressure systems. Annual sea ice export likely has a significant influence on the summer sea ice variability and we find low values in the 60's, the late 80's and 90's, 15 and particularly high values during 2005–2008. The study highlight the possible role of variability in ice export as an explanatory factor for understanding the dramatic loss of Arctic sea ice the last decades.
Summer minimum Arctic sea ice extent and the associated summer atmospheric circulation
Geophysical Research Letters, 2007
1] Interrelationships between year-to-year variations in September Arctic sea ice extent and summer sea level pressure and surface air temperature at high northern latitudes are examined making use of microwave satellite imagery and atmospheric data for the period 1979 -2006. Linear trends and year-to-year variability about the linear trend lines are considered separately: the latter gives a clearer indication of the physical linkages between fields. Years with low September sea ice extent tend to be characterized by anticyclonic circulation anomalies over the Arctic, with easterly wind anomalies over the marginal seas where the year-to-year variability of sea ice concentration is largest. It is hypothesized that the summer circulation anomalies cause sea ice extent principally by way of the Ekman drift in the marginal seas. The associated surface air temperature anomalies also tend to be largest over the marginal seas, with positive anomalies over the regions of reduced sea ice. Citation: Ogi, M., and J. M. Wallace , Summer minimum Arctic sea ice extent and the associated summer atmospheric circulation, Geophys. Res. Lett., 34, L12705,
Oceanographic and meteorological effects on autumn sea-ice distribution in the western Arctic
Annals of Glaciology
Oceanographic, meteorological and sea-ice data were obtained from the northern Bering Sea and Chukchi Sea during the autumns of 1987 and 1988. Ice-edge location was observed from ships and via AVHRR satellite data, and ice-drift information was obtained from ARGOS-tracked drift buoys. Meteorological data were obtained from ships, from an ARGOS-tracked meteorological station and from synoptic charts. The ice edge was significantly farther south in 1988 than during other years and impacted the Alaskan coastline. In 1987, the ice edge was, conversely, anomalously far north. Ice melt-back in certain regions, such as along the Alaskan coast and in Herald Canyon, was due to input from warm ocean currents. The larger-scale interannual differences in ice extent were, however, due to interannual differences in the regional winds. In particular, the anomalous and extreme southward extent of the ice edge during 1988 was due to northerly to northwesterly winds, which held the summer pack ice ag...
Relationships between Sea Ice Concentration and Wind Speed over the Arctic Ocean during 1979–2015
Journal of Climate, 2019
NCEP CFSR reanalysis 6-hourly fields from 1979 to 2015 were used to investigate the relationships of sea ice concentration (SIC), atmospheric stratification, surface roughness, and wind speed at 10-m height (W10) and 850-hPa level (W850). We found that in autumn (September–November), winter (December–February), and spring (March–May) a lower SIC favors less-stable stratification and a higher W10. In autumn, the decrease in SIC is strongest, and SIC has its strongest correlation with the atmospheric stratification, W10, and the ratio of W10 and W850 (WSR). W10 and WSR have increased in autumn, and the negative trends in SIC typically are collocated with positive trends in W10 and WSR. In winter, W850 has negative trends over the Arctic Ocean, which, together with the lack of decrease of SIC in the central Arctic, has prevented W10 from increasing in winter. The winter trends are notably different from those for autumn, but the correlations are fairly similar. In autumn, winter, and s...
Clues to variability in Arctic minimum sea ice extent
Geophysical Research Letters, 2005
Perennial sea ice is a primary indicator of Arctic climate change. Since 1980 it has decreased in extent by about 15%. Analysis of new satellite-derived fields of winds, radiative forcing, and advected heat reveals distinct regional differences in the relative roles of these parameters in explaining variability in the northernmost ice edge position. In all six peripheral seas studied, downwelling longwave flux anomalies explain the most variabilityapproximately 40%-while northward wind anomalies are important in areas north of Siberia, particularly earlier in the melt season. Anomalies in insolation are negatively correlated with perennial ice retreat in all regions, suggesting that the effect of solar flux anomalies is overwhelmed by the longwave influence on ice edge position.
Springtime atmospheric energy transport and the control of Arctic summer sea-ice extent
2013
The summer sea-ice extent in the Arctic has decreased in recent decades, a feature that has become one of the most distinct signals of the continuing climate change 1-4. However, the interannual variability is large-the ice extent by the end of the summer varies by several million square kilometres from year to year 5. The underlying processes driving this year-to-year variability are not well understood. Here we demonstrate that the greenhouse effect associated with clouds and water vapour in spring is crucial for the development of the sea ice during the subsequent months. In years where the end-of-summer sea-ice extent is well below normal, a significantly enhanced transport of humid air is evident during spring into the region where the ice retreat is encountered. This enhanced transport of humid air leads to an anomalous convergence of humidity, and to an increase of the cloudiness. The increase of the cloudiness and humidity results in an enhancement of the greenhouse effect. As a result, downward long-wave radiation at the surface is larger than usual in spring, which enhances the ice melt. In addition, the increase of clouds causes an increase of the reflection of incoming solar radiation. This leads to the counterintuitive effect: for years with little sea ice in September, the downwelling shortwave radiation at the surface is smaller than usual. That is, the downwelling shortwave radiation is not responsible for the initiation of the ice anomaly but acts as an amplifying feedback once the melt is started. The sea-ice extent in the Arctic has been steadily decreasing during the satellite remote-sensing era, 1979 to present (Fig. 1a). The highest rate of retreat is found in September 5 , which coincides with the month of the annual cycle that has the lowest ice extent. Factors that are believed to cause the ice retreat are, among others: changes in surface air temperature 6-8 , ice circulation in response to winds/pressure patterns 7-11 , and ocean currents 8 , as well as changes in radiative fluxes (for example, due to changes in cloud cover) 7,10,12-15 , and ocean conditions (for example, ocean warming 16). However, large interannual variability is superimposed onto the declining trend (Fig. 1a). The year-to-year deviation of the ice extent in September relative to the trend line varies by, on average, ±0.5 × 10 6 km 2 , but can reach 1.75 × 10 6 km 2 , which is around 25% of the mean September extent for 1979-2010. The magnitude of the variability shows considerable regional differences: a comparison of years with an anomalously large September sea-ice extent (HIYs-high ice years) with years showing an anomalously small ice extent (LIYs-low ice years) reveals that the variability is most pronounced in the Arctic Ocean north of Siberia (Fig. 1b,c). Significant ice-concentration anomalies of ∼±30% are observed for LIYs and HIYs in this area, which is chosen as the study area for the following analyses. In 2007 and 2012-the years showing the first and second lowest Arctic ice extent since the satellite observations began-a large part of this area became entirely ice free 17-19 .
Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice
Tellus Series A-dynamic Meteorology and Oceanography, 2010
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 ∼1.4 m s–1, relative to climatological easterly winds near the surface and upper tropospheric westerlies 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.