Oceanographic and meteorological effects on autumn sea-ice distribution in the western Arctic (original) (raw)
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A 5-year satellite climatology of winter sea ice leads in the western Arctic
Journal of Geophysical Research, 1998
The distribution of openings (leads and polynyas) in polar sea ice is not well known. This study estimates the large-scale distribution and variability of leads in the Arctic of the western hemisphere in winter, using a 5-year record of Defense Meteorological Satellite Program thermal-and visible-band imagery. The occurrence (density) and orientation of leads are derived from gridded maps made at 1 O-day intervals. Their mean value and interannual, seasonal, and monthly variabilities are estimated. Lead densities are observed to be highest in early winter, decreasing 20% from November through April. The highest densities are observed in the central Canada Basin, and the lowest are in the East Siberian Sea. There is limited interannual variability in the positions of maximum and minimum densities. Preferred lead orientations are identified as generally north-south in the Beaufort Sea sector and east-west in the East Siberian Sea sector, with transitional orientations in the intermediate area. The mean distributions of lead density and orientation are observed to be associated with large-scale mean fields of ice divergence and shear, respectively. 1. Introduction Sea ice is an important, interactive component of the Earth's climate system, both affecting and reflecting climate variability through a number of feedback mechanisms. The most important climatological aspects of sea ice arc, in probable order of significance: (1) its spatial extent (the total area within the ice margins), (2) its thickness distribution, and (3) the open water area within the ice cover. Variations in the ice extent affect and reflect climate variability and arc considered important factors in global climate change [c.g., Johannessen et al., 1995]
Theoretical and Applied Climatology, 2010
A reliable data set of Arctic sea ice concentration based on satellite observations exists since 1972. Over this time period of 36 years western arctic temperatures have increased; the temperature rise varies significantly from one season to another and over multi-year time scales. In contrast to most of Alaska, however, on the North Slope the warming continued after 1976, when a circulation change occurred, as expressed in the PDO index. The mean temperature increase for Barrow over the 36-year period was 2.9°C, a very substantial change. Wind speeds increased by 18% over this time period, however, the increase were non-linear and showed a peak in the early 1990s. The sea ice extent of the Arctic Ocean has decreased strongly in recent years, and in September 2007 a new record in the amount of open water was recorded in the Western Arctic. We observed for the Southern Beaufort Sea a fairly steady increase in the mean annual amount of open water from 14% in 1972 to 39% in 2007, as deduced from the best linear fit. In late summer the decrease is much larger, and September has, on average, the least ice concentration (22%), followed by August (35%) and October (54%). The correlation coefficient between mean annual values of temperature and sea ice concentration was 0.84. On a monthly basis, the best correlation coefficient was found in October with 0.88. However, the relationship between winter temperatures and the sea ice break-up in summer was weak. While the temperature correlated well with the CO 2 concentration (r=0.86), the correlation coefficient between CO 2 and sea ice was lower (r=−0.68).
Acta Oceanologica Sinica, 2012
Sea-ice physical characteristics were investigated in the Arctic section of 143 • -180 • W during August and early September 2008. Ship-based observations show that both the sea-ice thickness and concentration recorded during southward navigation from 30 August to 6 September were remarkably less than those recorded during northward navigation from 3 to 30 August, especially at low latitudes. Accordingly, the marginal ice zone moved from about 74.0 • N to about 79.5 • N from mid-August to early September. Melt-pond coverage increased with increasing latitude, peaking at 84.4 • N, where about 27% of ice was covered by melt ponds. Above this latitude, melt-pond coverage decreased evidently as the ice at high latitudes experienced a relatively short melt season and commenced its growth stage by the end of August. Regional mean ice thickness increased from 0.8 (±0.5) m at 75.0 • N to 1.5 (±0.4) m at 85.0 • N along the northward navigation while it decreased rapidly to 0.6 (±0.3) m at 78.0 • N along the southward navigation. Because of relatively low ice concentration and thin ice in the investigated Arctic sector, both the short-term ice stations and ice camp could only be set up over multiyear sea ice. Observations of ice properties based on ice cores collected at the short-term ice stations and the ice camp show that all investigated floes were essentially isothermal with high temperature and porosity, and low density and salinity. Most ices had salinity below 2 and mean density of 800-860 kg/m 3 . Significant ice loss in the investigated Arctic sector during the last 15 a can be identified by comparison with the previous observations.
Mechanisms in the development of anomalous sea ice extent in the western Arctic: A case study
Journal of Geophysical Research: Atmospheres, 2001
Interannual cycles and trends in Arctic ice cover are dominated by strong regional variability. Arctic sea ice extent exhibited a record minimum within the Arctic Basin during September 1990, dominated by a rapid retreat in the Chukchi, East Siberian, and Laptev Seas. Simulations using a coupled regional model reproduced the enhanced cyclonic activity and enhanced ice melt which led to this large retreat in sea ice cover. Sensitivity experiments showed that accurate initial ice conditions are crucial for a realistic simulation of the ice anomaly, pointing to the need for adequate spin-up in coupled model experiments. It was also found that thermodynamic melt can account for the bulk of the total loss in ice mass over the summer season in 1990, but without dynamics, the spatial patterns characteristic of the ice reductions are not reproduced well. Also, transport of ice was crucial to initiate the formation of the anomaly, even if the formation was delayed until later in the season. The ice-albedo feedback is important in allowing the continued formation of the ice anomaly throughout the summer. Interannual variations in atmospheric circulation that yield regional differences in ice thickness provide a preconditioning that significantly affected development of the ice anomaly. This suggests that circulation modes play an important role in determining ice severity along the Siberian coast.
Alaska landfast sea ice: Links with bathymetry and atmospheric circulation
2007
1] Using Radarsat Synthetic Aperture Radar (SAR) imagery of northern Alaska and northwestern Canada, we calculated a mean climatology of the annual landfast ice cycle for the period 1996-2004. We also present the monthly minimum, mean, and maximum landfast ice extents throughout the study area. These data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events. Stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge (SLIE) into waters around 18 m deep. Isobaths near this depth are a good approximation for midseason landfast ice extent. Comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the Arctic, due to later formation and earlier breakup. This will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities, which are intimately linked to the timing of marine mammal migration patterns. Interannually, landfast ice formation correlates with the incursion of pack ice into coastal waters, suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge. The timing of breakup correlates well with onset of thawing air temperatures. Analysis of regional data shows a multidecadal trend toward earlier thaw onset, which suggests that the observed change in breakup dates may be part of a longer-term trend.
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.
Influence of winter and summer surface wind anomalies on summer Arctic sea ice extent
Geophysical Research Letters, 2010
Based on a statistical analysis incorporating 925-hPa wind fields from the NCEP/NCAR Reanalyses, it is shown that the combined effect of winter and summer wind forcing accounts for 50% of the variance of the change in September Arctic sea ice extent from one year to the next ( Δ SIE) and it also explains roughly 1/3 of the downward linear trend of SIE over the past 31 years. In both seasons meridional wind anomalies to the north and east of Greenland are correlated with September SIE, presumably because they modulate the export of ice through Fram Strait. Anticyclonic wind anomalies over the Beaufort Sea during summer favor low September SIE and have contributed to the record-low values in recent summers, perhaps by enhancing the flux of ice toward Fram Strait in the trans-polar drift.
Seasonal variations in sea ice motion and effects on sea ice concentration in the Canada Basin
Journal of Geophysical Research, 1989
Drifting buoy data, surface pressure, and geostrophic wind analyses from the Arctic Ocean Buoy Program are used to examine seasonal features of the sea ice motion in the Canada Basin for 1979-1985. Although the 7-year annual mean motion in this region is clockwise, the month-to-month motion is highly variable. In late summer to early autumn, the circulation can become net anticlockwise for periods lasting at least 30 days. Results from a linear model demonstrate that these "reversals" of ice motion in the Beaufort Gyre are a wind-driven response to persistent cyclonic activity that contrasts sharply with the predominantly anticyclonic regimes of spring, late autumn, and winter. Model-predicted ice divergences of 0.5% or more per day which can occur during periods of anticlockwise ice motion are in good agreement with values calculated from optimally interpolated velocity gradient fields. Visible band imagery and passive microwave data confirm associated large areal reductions in ice concentration of approximately 20%. Data from under-ice submarine sonar transects and surface pressure records prior to the study period point to frequent recurrences of these late summer to early autumn ice conditions. 1980; Thomas, 1983; Thorndike 1986] even noted influences, over 70% of the variance in the daily ice occasional reversals but regarded them as motion is explained by the local geostrophic wind. anomalies. Variance spectra of ice drift data show peaks at 4-10 days [Coachman and Aagaard, 1974; During early August 1958 and 1970, the submarines USS Nautilus (SSN-571) and USS Thorndike, 1986], indicative of the effects of Queenfish (SSN-651), respectively, continuously synoptic-scale weather systems, superimposed on recorded the under-ice topography of the Canada longer-term effects. As wind fields are strongly Basin along the 155øW meridian between latitudes organized on such scales, and the Arctic 72 ø and 90øN as they crossed the Arctic Basin. atmospheric circulation is strongly seasonal Subsequent analysis of the acoustically recorded [Keegan, 1958; Reed and Kunkel, 1960; Walsh, under-ice thickness data demonstrated that within the lower Canada Basin, ice drains were moderate and the under-ice topography was quite uniform
Inter-annual climatic response of the sea ice edge latitudinal displacement in the Arctic to variability of the large-scale atmospheric circulation (the Arctic Oscillation and North Atlantic Oscillation), location of the Gulf Stream northern boundary and solar activity in 1969–2012 is studied. It is noted that the most significant ice edge latitudinal displacements in the intra-annual cycle were observed westward of Novaya Zemlya and in the Bering Strait area. It is shown that, depending on the longitudinal sector, response of the edge geographical position to changes of the atmospheric circulation and the Gulf Stream indices can be manifested both quasi-synchronously and with a delay. Exceptions are the Greenland Sea and the Norwegian Sea areas as well as the Barents Sea western part where ice edge displacements advance the Gulf Stream index variation. The correlation between the edge latitudinal displacement along its perimeter and the Wolf numbers variation is assessed. It is received that the oscillations of cross-correlation functions with a period which is close to 11-year one (Schwabe Cycle) are observed on each longitude at that. In the variations of cross-correlation functions from their average position, solar activity variation is manifested in the edge position displacement with up to two-year delay.
Variations in the age of Arctic sea-ice and summer sea-ice extent
Geophysical Research Letters, 2004
1] Three of the past six summers have exhibited record low sea-ice extent on the Arctic Ocean. These minima may have been dynamically induced by changes in the surface winds. Based on results of a simple model that keeps track of the age of ice as it moves about on the Arctic Ocean, we show that the areal coverage of thick multi-year ice decreased precipitously during 1989 -1990 when the Arctic Oscillation was in an extreme ''high index'' state, and has remained low since that time. Under these conditions, younger, thinner ice anomalies recirculate back to the Alaskan coast more quickly, decreasing the time that new ice has to ridge and thicken before returning for another melt season. During the 2002 and 2003 summers this anomalously younger, thinner ice was advected into Alaskan coastal waters where extensive melting was observed, even though temperatures were locally colder than normal. The age of sea-ice explains more than half of the variance in summer sea-ice extent.