variations in the age of arctic sea ice and summer sea ice extent 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

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

simulation of extreme new zealand precipitation events part i sensitivity to orography and resolution abstract the extreme precipitation events with peak observed rainfall of greater than 700 mm over the south island of new zealand were simulated using the dar hydrostatic mesoscale model nested within the ecmwf analyses the ecmwf analyses for two of the events showed a low level jet with mixing ratios greater than 12 g kg 1 crossing the south island of new zealand during the heavy precipitation near a cold front the third case which had smaller mixing ratios occurred as a low level jet and crossed the south island while a low redeveloped downstream three different orographies were used with the 30 km horizontal resolution model runs with progressively increased terrain heights the highest orography was created by artificially inserting the effective barrier of the southern alps to northwesterly flow in the model grid orography had a strong influence on the amount of precipitation the peak precipitation was related to orographic slope while the area averaged precipitation was related to the maximu

summer sea ice motion from the 18 ghz channel of amsr e and the exchange of sea ice between the pacific and atlantic sectors 1 we demonstrate that sea ice motion in summer can be derived reliably from the 18ghz channel of the amsr e instrument on the eos aqua platform the improved spatial resolution of this channel with its lower sensitivity to atmospheric moisture seems to have alleviated various issues that have plagued summer motion retrievals from shorter wavelength observations two spatial filters improve retrieval quality one reduces some of the microwave signatures associated with synoptic scale weather systems and the other removes outliers compared with daily buoy drifts uncertainties in motion are 3 4 km day using the daily motion fields we examine five years of summer ice area exchange between the pacific and atlantic sectors of the arctic ocean with the sea level pressure patterns during the summer of 2006 and 2007 favoring the export of sea ice into the atlantic sector the regional outflow is 21 and 15 of the total sea ice retreat in the pacific sector

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

spatial scaling of arctic sea ice deformation 1 arctic sea ice deformation arises from spatial gradients in the ice velocity field this deformation occurs across a wide range of spatial scales from meters to thousands of kilometers we analyze 7 years of sea ice deformation data from the radarsat geophysical processor system rgps covering the western arctic ocean we find that the mean deformation rate is related to the spatial scale over which it is measured according to a power law with exponent 0 2 over a scale range from 10 to 1000 km e g deformation rate doubles for a 30 fold reduction in scale both the exponent and the deformation rate have distinct annual cycles the exponent becomes more negative in summer as the ice pack weakens and internal stresses are not as readily transmitted over long distances the deformation rate reaches a minimum in late winter when the ice pack is strongest the deformation also exhibits considerable localization in which the largest deformation rates are confined to smaller and smaller areas as the scale of measurement decreases this supports a model for sea ice based on granular or fracture mechanics the scaling exponent in the power law relationship tends to be larger in magnitude where the concentration of multiyear ice is low consistent with a thinner and weaker ice pack with decreasing multiyear ice in the arctic and a thinning ice pack an increase in the deformation rate has already been documented from buoy data however the net effect of several deformation thickness feedbacks is still uncertain

a thickness and enthalpy distribution sea ice model abstract the theory of sea ice thickness distribution developed by thorndike et al has been extended to include sea ice enthalpy distribution the extended theory conserves both ice mass and thermal energy in the form of the heat stored in the ice by jointly solving a thickness distribution equation and an enthalpy distribution equation both equations have been implemented in a one dimensional dynamic thermodynamic sea ice model with 12 ice thickness categories following the numerical procedure of hibler the implementation of the enthalpy distribution equation allows the sea ice model to account for any changes in the ice thermal energy induced by sea ice processes as a result the model is able to conserve not only the ice mass but also its thermal energy in the presence of ice advection growth melting and ridging conserving ice thermal energy in a thickness distribution sea ice model improves the prediction of ice growth summer ice melt in particular and therefore ice thickness inability to

overview of the coordinated ground based observations of titan during the huygens mission coordinated ground based observations of titan were performed around or during the huygens atmospheric probe mission at titan on 14 january 2005 connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground based programs these observations consisted of three different categories 1 radio telescope tracking of the huygens signal at 2040 mhz 2 observations of the atmosphere and surface of titan and 3 attempts to observe radiation emitted during the huygens probe entry into titan s atmosphere the probe radio signal was successfully acquired by a network of terrestrial telescopes recovering a vertical profile of wind speed in titan s atmosphere from 140 km altitude down to the surface ground based observations brought new information on atmosphere and surface properties of the largest saturnian moon no positive detection of phenomena associated with the probe entry was reported this paper reviews all these measurements and highlights the achieved results the ground based observations both radio and optical are of fundamental importance for the interpretation of results from the huygens mission

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

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

effect of sea ice rheology in numerical investigations of climate 1 plastic sea ice rheologies that employ teardrop and parabolic lens yield curves and allow varying biaxial tensile stresses have been developed these rheologies together with the previously developed ellipse and mohr coulomb ellipse rheologies are implemented in a thickness and enthalpy distribution sea ice model to examine the rheological effect in numerical investigations of arctic climate the teardrop lens and ellipse rheologies obey a normal flow rule and result in a two peak shear stress distribution the first peak is at the zero shear stress the second is near 16 000 n m 1 for the ellipse and two lens rheologies and near 30 000 n m 1 for the two teardrop rheologies the location of the second peak depends on the fatness of the yield curve and the amount of biaxial tensile stress allowed in contrast the mohr coulomb ellipse rheology based on coulombic friction failure does not tend to create the second peak the incorporation of biaxial tensile stress tends to increase ice thickness in most of the arctic a fatter yield curve tends to increase the frequency of large shear stresses an increased frequency of large shear stresses in conjunction with the inclusion of biaxial tensile stress tends to reduce ice speed and ice export to enhance ice ridging in the arctic interior and to reduce ice ridging in the coastal areas which has a significant impact on arctic spatial ice mass distribution and the total ice budget the teardrop rheologies reduce spatial bias of modeled ice draft against submarine observations more than others by changing ice motion deformation and thickness the choice of plastic rheology also considerably affects the simulated surface energy exchanges particularly in the arctic marginal seas

modeling the formation and fate of the near surface temperature maximum in the canadian basin of the arctic ocean 1 a numerical model is used to investigate the time and space extent of the near surface temperature maximum nstm of the canadian basin of the arctic ocean over the years 2000 2009 the nstm is formed from local summertime absorption of solar radiation which in some circumstances descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer we find that winter survival of this layer is confined largely to the beaufort gyre of the canadian basin where ekman convergence and downwelling push the summer warm layer down below the winter mixing depth in recent years summer stratification has increased downwelling has accelerated and the nstm has warmed as the sea ice cover in the beaufort gyre has thinned the result is a strengthening nstm which contained enough heat by the end of winter 2007 2008 to melt about 20 cm of sea ice northwest of alaska the model also simulates a second deeper temperature maximum layer that forms from advection of saltier summer pacific water however this layer is difficult to adequately resolve and maintain given the model s resolution

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

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

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

whither arctic sea ice a clear signal of decline regionally seasonally and extending beyond the satellite record the arctic sea ice has been pointed to as one of the first and clearest indicators of climate change satellite passive microwave observations from 1979 through 2005 now indicate a significant 8 4 1 5 decade 1 trend 99 confidence level in september sea ice extent a larger trend than earlier estimates due to acceleration of the decline over the past 41 years there are differences in regional trends with some regions more stable than others not all regional trends are significant the largest trends tend to occur in months where melt is at or near its peak for a given region a longer time series of september extents since 1953 was adjusted to correct biases and extended through 2005 the trend from the longer time series is 7 7 0 6 decade 1 99 slightly less than from the satellite derived data that begin in 1979 which is expected given the recent acceleration in the decline

did unusually sunny skies help drive the record sea ice minimum of 2007 1 we conduct experiments with an ice ocean model to answer the question whether and to what degree unusually clear skies during the summer of 2007 contributed to the record sea ice extent minimum in the arctic ocean during september of 2007 anomalously high pressure over the beaufort sea during summer 2007 appears associated with a strong negative cloud anomaly this anomaly is two standard deviations below the 1980 2007 average established from a combination of two different satellite based records cloud anomalies from the modis sensor are compared with anomalies from the ncep ncar reanalysis and are found in good agreement in spatial patterns and magnitude however these experiments establish that the negative cloud anomaly and increased downwelling shortwave flux from june through august did not contribute substantially to the record sea ice extent minimum this finding eliminates one aspect of the unusual weather that may have contributed to the record minimum

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

the arctic ice thickness anomaly of the 1990s a consistent view from observations and models 1 observations of sea ice draft from submarine cruises in much of the arctic ocean show that the ice cover was unusually thin in the mid 1990s here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11 year span comparisons of our modeled draft with observed draft show good agreement in the temporal change comparing average draft over entire cruises the rms discrepancy between modeled and observed draft is 0 3 m and the correlation is 0 98 agreement in the spatial patterns of draft is somewhat lower the rms discrepancy of 50 km averages of draft is 0 7 m and the correlation is 0 73 we review reports of interannual variations of ice thickness or volume from other model studies all models agree that thickness decreased by between 0 6 and 0 9 m from 1987 to 1996 our model shows a modest recovery in thickness from 1996 to 1999 for the 1950s 1960s and 1970s models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations

impact of reduced arctic sea ice on greenland ice sheet variability in a warmer than present climate a global climate model with interactive vegetation and a coupled ice sheet shelf component is used to test the response of the greenland ice sheet gis to increased sea surface temperatures ssts and reduced sea ice si cover during the mid pliocene warm period 3 ma as reconstructed from proxy records seasonally open water in the arctic and north atlantic are shown to alter regional radiation budgets storm tracks and moisture and heat advection into the greenland interior with increases in temperature rather than precipitation dominating the ice sheets response when applied to an initially glaciated greenland the presumed warm ice free pliocene ocean conditions induce rapid melting of nearly the entire ice sheet and preclude a modern like gis from re growing regardless of orbital forcing the sensitivity of greenland to imposed pliocene ocean conditions may have serious implications for the future response of the ice sheet to continued warming in the arctic basin

antarctic sea ice parameters from amsr e data using two techniques and comparisons with sea ice from ssm i 1 we use two algorithms to process advanced microwave scanning radiometer for the earth observing system amsr e data in order to determine algorithm dependence if any on the estimates of sea ice concentration ice extent and area and trends and to evaluate how amsr e data compare with historical special sensor microwave imager ssm i data the monthly ice concentrations derived from the two algorithms from amsr e data the amsr e bootstrap algorithm or aba and the enhanced nasa team algorithm or nt2 differ on average by about 1 3 with data from the consolidated ice region being comparable for aba and nt2 retrievals while data in the marginal ice zones and thin ice regions show slightly higher values when the nt2 algorithm is used the iceextents and areas derived separately from amsr e using these two algorithms are however in good agreement with the differences aba nt2 being about 0 07 106 km2 on average for ice extents and 0 07 106 km2 for ice area which are small compared with mean seasonal values of 10 5 106 and 9 8 106 for ice extent and area respectively likewise extents and areas derived from the same algorithm but from amsr e and ssm i data are consistent but differ by about 0 24 106 km2 and 0 14 106 km2 respectively the discrepancies are larger with the estimates of extents than area mainly because of differences in channel selection and sensor resolutions trends in extent during the amsr e era were also estimated and results from all three data sets are shown to be in good agreement within errors