internal layer tracing and age depth accumulation relationships for the northern greenland ice sheet clues to previous ice sheet structure and long term glaciological processes are preserved in the internal layering configuration of the greenland ice sheet information about these internal layers has been retrieved over many parts of the ice sheet with the university of kansas ice penetrating radar we report on the coherence of these layers over very large distances describe a method of tracing these layers along thousands of kilometers of flight line and do so for one flight during the 1999 program for arctic regional climate assessment parca aircraft campaign we determine the ages of these layers based on information at the grip ice core site and extend these ages along the flight line to camp century where they are compared to modeled derived age estimates these ages agree with each other to between 2 and 15 differences that can be substantially reduced with minor changes to the model parameters accumulation rate and shear layer depth finally we are able to derive estimates of accumulation rates along the flight line by fitting the age depth data from layer tracing to a dansgaard johnsen model with a minimization technique providing estimates that match recent accumulation patterns within a few centimeters per year

interdecadal change in the north atlantic storm track during boreal summer around the mid 2000s role of the atmospheric internal processes the first eof mode eof1 of summer storm track activity over the north atlantic is characterized by a dipole structure with negative storm track anomalies over the south coast of greenland extending northeast across iceland to the norwegian sea and positive anomalies over coastal western europe this study shows that a significant interdecadal change in the north atlantic storm track during boreal summer occurred around the mid 2000s after the mid 2000s the eof1 occurs more frequently at its positive phase which is associated with an interdecadal increase in the geopotential height anomalies around greenland on the intra seasonal timescale the anticyclonic anomalies around greenland are crucial for the occurrence of positive eof1 events via triggering eastward propagating rossby waves therefore the interdecadal increase in the geopotential height anomalies around greenland tends to facilitate the occurrence of the positive eof1 event and is therefore a key driver of the interdecadal change in the summer storm track activity over the north atlantic further analysis indicates that the development of anticyclonic anomalies around greenland is maintained by the self interaction among the low and high frequency transients themselves moreover the anomalous synoptic eddy activities associated with the change in storm tracks can in turn amplify and maintain the rossby waves triggered by the anticyclonic anomalies around greenland in the synoptic scale eddy feedback process

change in relationship between the east asian winter monsoon and the east asian jet stream during the 1998 99 regime shift abstracta composite analysis was conducted on the reanalysis dataset for 1979 2016 along with an idealized model experiment to show that the relationship between the east asian jet stream eajs a

wind and wave influences on sea ice floe size and leads in the beaufort and chukchi seas during the summer fall transition 2014 sea ice floe size distribution and lead properties in the beaufort and chukchi seas are studied in the summer fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves floe size distributions are analyzed from medea landsat8 and radarsat 2 imagery with a resolution span of 1 100 m landsat8 imagery is also used to identify the orientation and spacing of leads the study period centers around three large wave events during august september 2014 identified by swift buoys and wavewatch iii model data the range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness all cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes the overall slopes in the cumulative floe size distribution curves from landsat8 images are lower than while those from radarsat 2 are similar to previously reported results in the same region and seasonal period the medea floe size distributions appeared to be sensitive to the passage of storms lead orientations regardless of length correlate slightly better with the peak wave direction than with the mean wave direction their correlation with the geostrophic wind is stronger than with the surface wind the spacing between shorter leads correlates well with the local incoming surface wavelengths obtained from the model peak wave frequency the information derived shows promise for a coordinated multisensor study of storm effects in the arctic marginal ice zone

the role of summer surface wind anomalies in the summer arctic sea ice extent in 2010 and 2011 1 strong summertime anticyclonic wind anomalies over the arctic ocean with anomalous flow toward the fram strait during summer months of 2007 contributed to the record low the arctic sea ice extent observed in september of that year had the summer winds over the arctic during the summers of 2010 and 2011 been the same as those in 2007 september sea ice extent would have reached new record lows in those years as well by regulating the flow of ice toward and through the fram strait variations in low level winds over the arctic have contributed to the month to month year to year and decade to decade variability of sea ice extent

north american snow depth and climate teleconnection patterns abstract snow atmosphere relationships have been studied for nearly half a century but the primary focus has been on snow extent variability largely because of the relative scarcity of snow depth data a recently released north american snow depth dataset with extensive spatial coverage and multidecadal temporal duration provides a new opportunity to compare snow depth climate relationships with snow extent climate relationships over north america robust concurrent lead and lag correlations are observed between snow depth and two major climate modes the pacific decadal oscillation pdo and the pacific north america pna pattern across north america and throughout the snow season in contrast snow extent exhibits a less coherent relationship with pdo and pna except in late spring which can be interpreted as a residual of the snow depth climate mode relationship a regional signature for the snow depth pdo pna relationship is also identified centered over interior central western north america

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

an effective elastic thickness map of australia from wavelet transforms of gravity and topography using forsyth s method 1 we have developed a wavelet version of forsyth s coherence method for estimating the effective elastic thickness te of the lithosphere from gravity and topography we have previously shown that the fan wavelet is particularly well suited to making localised coherence estimates and here we progress the method by showing how the coherence can be modelled by using the wavelet transforms of gravity and topography to infer the initial loads that flex the plate the effectiveness of the method is demonstrated on synthetic data from a model having a rectangular area of large te embedded in a uniform low te surrounding and a load ratio that increases with wave number the results for the australia region show a core of high te under north and central australia with much lower values to the east and also unexpectedly under the western parts of the yilgarn and pilbara cratons

implications of fractured arctic perennial ice cover on thermodynamic and dynamic sea ice processes decline of the arctic summer minimum sea ice extent is characterized by large expanses of open water in the siberian laptev chukchi and beaufort seas and introduces large fetch distances in the arctic ocean long waves can propagate deep into the pack ice thereby causing flexural swell and failure of the sea ice this process shifts the floe size diameter distribution smaller increases floe surface area and thereby affects sea ice dynamic and thermodynamic processes the results of radarsat 2 imagery analysis show that a flexural fracture event which occurred in the beaufort sea region on 6 september 2009 affected 40 000 km2 open water fractional area in the area affected initially decreased from 3 7 to 2 7 but later increased to 20 following wind forced divergence of the ice pack energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed layer of the ocean following flexural fracture 11 54 mj m 2 of additional energy for lateral melting of ice floes was identified in affected areas the impact of this process in future arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season and is discussed in context with ocean heat fluxes atmospheric mixing of the ocean mixed layer and declining sea ice cover we conclude that this process is an important positive feedback to arctic sea ice loss and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

autumn atmospheric response to the 2007 low arctic sea ice extent in coupled ocean atmosphere hindcasts the autumn and early winter atmospheric response to the record low arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent made with the european centre for medium range weather forecasts state of the art coupled ocean atmosphere seasonal forecast model robust warm anomalies over the pacific and siberian sectors of the arctic as high as 10 c at the surface are found in october and november a regime change occurs by december characterized by weaker temperatures anomalies extending through the troposphere geopotential anomalies extend from the surface up to the stratosphere associated to deeper aleutian and icelandic lows while the upper level jet is weakened and shifted southward over the continents it is intensified over both oceanic sectors especially over the pacific ocean on the american and eurasian continents intensified surface highs are associated with anomalous advection of cold warm polar air on their eastern western sides bringing cooler temperatures along the pacific coast of asia and northeastern north america transient eddy activity is reduced over eurasia intensified over the entrance and exit regions of the pacific and atlantic storm tracks in broad qualitative agreement with the upper level wind anomalies potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the arctic in autumn but also along the pacific coast of asia in december when the observed sea ice extent from 2007 is prescribed throughout the autumn a higher correlation of surface temperatures with meteorological re analyses is found at high latitudes from october until mid november this further emphasises the relevance of sea ice for seasonal forecasting in the arctic region in the autumn

what drove the dramatic retreat of arctic sea ice during summer 2007 1 a model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007 it is found that preconditioning anomalous winds and ice albedo feedback are mainly responsible for the retreat arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate during summer 2007 atmospheric changes strengthened the transpolar drift of sea ice causing more ice to move out of the pacific sector and the central arctic ocean where the reduction in ice thickness due to ice advection is up to 1 5 m more than usual some of the ice exited fram strait and some piled up in part of the canada basin and along the coast of northern greenland leaving behind an unusually large area of thin ice and open water thin ice and open water allow more surface solar heating because of a much reduced surface albedo leading to amplified ice melting the arctic ocean lost additional 10 of its total ice mass in which 70 is due directly to the amplified melting and 30 to the unusual ice advection causing the unprecedented ice retreat arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing

sipex 2012 extreme sea ice and atmospheric conditions off east antarctica abstract in 2012 antarctic sea ice coverage was marked by weak annual mean climate anomalies that consisted of opposing anomalies early and late in the year some setting new records which were interspersed by near average conditions for most of the austral autumn and winter here we investigate the ocean ice atmosphere system off east antarctica prior to and during the sea ice physics and ecosystems experiment sipex 2012 by exploring relationships between atmospheric and oceanic forcing together with the sea ice and snow characteristics during august and september 2012 just prior to sipex 2012 atmospheric circulation over the southern ocean was near average setting up the ocean ice atmosphere system for near average conditions however below average surface pressure and temperature as well as strengthened circumpolar winds prevailed during june and july 2012 this led to a new record 19 48 10 6 km 2 in maximum antarctic sea ice extent recorded in late september in contrast to the weak circum antarctic conditions the east antarctic sector including the sipex 2012 region experienced positive sea ice extent and concentration anomalies during most of 2012 coincident with negative atmospheric pressure and sea surface temperature anomalies heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east this increased westward ice flux is likely linked to the break up of nearly 80 of the mertz glacier tongue in 2010 which strongly modified the coastal configuration and hence the width of the westward coastal current combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141 145 e in addition a westward propagating positive anomaly of sea ice extent from the western ross sea during austral winter 2012 has been identified to have fed into the westward current of the sipex 2012 region a pair of large grounded icebergs appears to have modified the local stress state as well as the structure of the ice pack upstream and also towards the dalton glacier tongue together with the increased influx of sea ice into the regions this contributed to the difficulties in navigating the sipex 2012 region

abrupt evolution of the summer northern hemisphere annular mode and its association with blocking 1 using reanalysis data from the national centers for environmental prediction national center for atmosperic research boulder colorado for the period from 1958 to 2005 we statistically analyzed the relationships of the summer northern hemisphere annular mode summer nam with hemispheric scale anomalous summer weather and the occurrence of blocking highs the anomalous positive nam low pressure anomaly in the arctic and high pressure anomaly in midlatitudes accounts well for the hemispheric scale weather associated with anomalous blocking between the polar and subtropical jets whereas blocking rarely occurs during negative nam periods the double jet stream structure is more evident during periods of anomalous positive nam than during periods of negative nam the surface temperatures associated with the anomalous positive nam clearly show europe to be hot and east asia to be cool as was the case during the anomalous summer of 2003 the occurrence of a positive summer nam is therefore consistent with the hemispheric scale anomalous summer weather associated with blocking in 2003 we investigated the abrupt evolution of atmospheric patterns and the geographic distribution of blocking highs associated with the development maintenance and decay periods of an anomalous positive nam during the development period blocking tends to occur over europe and the atlantic ocean but no significant blocking signature is evident over eastern eurasia during the maintenance stage blocking tends to occur in the far east during the decay stage blocking over the pacific region is obvious this longitudinal migration of blocking phenomena may be used to predict the evolution through time of the nam

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

warm season subseasonal variability and climate extremes in the northern hemisphere the role of stationary rossby waves abstractthis study examines the nature of boreal summer subseasonal atmospheric variability based on the new nasa modern era retrospective analysis for research and applications merra for the period 1979 2010 an analysis of the june july and august subseasonal 250 hpa meridional wind anomalies shows distinct rossby wave like structures that appear to be guided by the mean jets on monthly subseasonal time scales the leading waves the first 10 rotated empirical orthogonal functions reofs of the 250 hpa wind explain about 50 of the northern hemisphere wind variability and account for more than 30 60 of the precipitation surface temperature variability over a number of regions of the northern middle and high latitudes including the u s northern great plains parts of canada europe and russia the first reof in particular consists of a rossby wave that extends across northern eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability and

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

regional dependence in the timing of onset of rapid decline in arctic sea ice concentration arctic sea ice concentration from satellite passive microwave measurements is analyzed to assess the form and timing of the onset of decline of recent ice loss and the regional dependence of the response the timing of the onset is estimated using an objective method and suggests differences of up to 20 years between the various subregions a clear distinction can be drawn between the recent onset times of the atlantic sector beginning in 2003 and the much earlier onset times associated with the pacific sector where the earliest transition to rapid loss is found in 1992 rates of decline prior to and following the transition points are calculated and suggest that the postonset rate of loss is greatest in the barents sea and weakest in the pacific sector covariability between the seasons is noted in the sic response both at interannual and longer time scales for two case regions potential mechanisms for the onset time transitions are briefly analyzed in the barents sea the onset time coincides with a redistribution of the pathways of ice circulation in the region while along the alaskan coast the propagation of the regional signal can be traced in the age of the sea ice the results presented here indicate a series of spatially self consistent regional responses and may be useful in understanding the primary drivers of recent sea ice loss

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

arctic sea ice retreat in 2007 follows thinning trend the minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record a coupled ice ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective it is found that even though the 2007 ice extent was strongly anomalous the loss in total ice mass was not rather the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987 since then the simulated mean september ice thickness within the arctic ocean has declined from 3 7 to 2 6 m at a rate of 0 57 m decade 1 both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing the combined impact of these two trends caused a large reduction in the september mean ice concentration in the arctic ocean this created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the pacific side to the atlantic side of the basin and more than usual into the greenland sea this exposed large areas of open water resulting in the record ice extent anomaly