the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

atmospheric impact of arctic sea ice loss in a coupled ocean atmosphere simulation the atmospheric response to an idealized decline in arctic sea ice is investigated in a novel fully coupled climatemodel experiment in this experimenttwo ensembles of single year model integrations are performed starting on 1 april the approximate start of the ice melt season by perturbing the initial conditions of sea ice thickness sit declines in both sea ice concentration and sit which result in sea ice distributions that are similar to the recent sea ice minima of 2007 and 2012 are induced in the ice loss regions there are strong 3k local increasesin sea surface temperature sst additionally there are remoteincreases in sst in the central north pacific and subpolar gyre in the north atlantic over the central arctic there are increases in surface air temperature sat of 8k due to increases in ocean atmosphere heatfluxes there are increases in sat over continental north america that are in good agreement with recent changes as seen by reanalysis data it is estimated that up to two thirds of the observed increase in sat in this region could be related to arctic sea ice loss in early summer there is a significant but weak atmospheric circulation response that projects onto the summer north atlantic oscillation nao in early summer and early autumn there is an equatorward shift of the eddy driven jet over the north atlantic as a result of a reduction in the meridional temperature gradients in winter there is no projection onto a particular phase of the nao

dynamic and thermodynamic characteristics of atmospheric response to anomalous sea ice extent in the sea of okhotsk abstract influence of sea ice extent anomalies within the sea of okhotsk on the large scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea ice cover significant response appears not only around the sea of okhotsk but also downstream over the bering sea alaska and north america in the form of a stationary wave train in the troposphere this remote response associated with wave activity flux emanating from the okhotsk area to the downstream is regarded as a stationary rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea ice cover the pacific storm track in the model that extends zonally at 35 n is located too far south of the sea of okhotsk to exert substantial feedback forcing on the local and remote response since a similar stationary wave train is identified in the composite di

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part i main features and storm track characteristics of the response observed multidecadal trends in extratropical atmospheric flow such as the positive trend in the north atlantic oscillation nao index may be attributable to a number of causes this study addresses the question of whether the atmospheric trends may be caused by observed trends in oceanic boundary forcing experiments were carried out using the ncar atmospheric general circulation model with specified sea surface temperature sst and sea ice anomalies confined to the north atlantic sector the spatial pattern of the anomalous forcing was chosen to be realistic in that it corresponds to the recent 40 yr trend in sst and sea ice but the anomaly amplitude was exaggerated in order to make the response statistically more robust the wintertime response to both types of forcing resembles the nao to first order even for an exaggerated amplitude the atmospheric response to the sst anomaly is quite weak compared to the observed positive trend in the nao but has the same sign indicative of a weak positive feedback the anomalies in sea ice extent are more efficient than sst anomalies at exciting an atmospheric response comparable in amplitude to the observed nao trend however this atmospheric response has the opposite sign to the observed trend indicative of a significant negative feedback associated with the sea ice forcing additional experiments using sst anomalies with opposite sign to the observed trend indicate that there are significant nonlinearities associated with the atmospheric response the transient eddy response to the observed sst trend is consistent with the positive nao response with the north atlantic storm track amplifying downstream and developing a more pronounced meridional tilt in contrast the storm track response to the observed sea ice trend corresponds to a weaker southward shifted more zonal storm track which is consistent with the negative nao response

role for eurasian arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century a hypothesized low frequency climate signal propagating across the northern hemisphere through a network of synchronized climate indices was identified in previous analyses of instrumental and proxy data the tempo of signal propagation is rationalized in terms of the multidecadal component of atlantic ocean variability the atlantic multidecadal oscillation through multivariate statistical analysis of an expanded database we further investigate this hypothesized signal to elucidate propagation dynamics the eurasian arctic shelf sea region where sea ice is uniquely exposed to open ocean in the northern hemisphere emerges as a strong contender for generating and sustaining propagation of the hemispheric signal ocean ice atmosphere coupling spawns a sequence of positive and negative feedbacks that convey persistence and quasi oscillatory features to the signal further stabilizing the system are anomalies of co varying pacific centered atmospheric circulations indirectly related to dynamics in the eurasian arctic these anomalies appear to negatively feed back onto the atlantic s freshwater balance earth s rotational rate and other proxies encode traces of this signal as it makes its way across the northern hemisphere

mechanisms determining the winter atmospheric response to the atlantic overturning circulation abstractin climate models an intensification of the atlantic meridional overturning circulation amoc precedes a warming in the north atlantic subpolar basin by a few years in the ipsl cm5a lr model this warming may explain the atmospheric response to the amoc observed in winter which resembles a negative phase of the north atlantic oscillation nao to firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in this model ensembles of atmosphere only simulations are conducted prescribing the sst and sea ice anomalies that follow an amoc intensification in late winter the north atlantic sst and sea ice anomalies drive atmospheric circulation anomalies similar to those found in the coupled model simulations only driven by the sst anomalies related to the amoc show that the largest oceanic influence is due to the warm subpolar sst anomaly which enhances the oceanic heat release and decreases the lower tropospheric baroclinicity in the reg

intra seasonal relationship between the northern hemisphere sea ice variability and the north atlantic oscillation 1 an intra seasonal relationship including a possible feedback is investigated between the north atlantic oscillation nao and a hemispheric scale seesaw like pattern dominant in sea ice variability over the wintertime northern hemisphere with one polarity in the bering and labrador seas and the other in the okhotsk and greenland barents seas statistical analysis using observational data suggests that a particular phase of nao and anomalous atmospheric circulation in the pacific during early winter contribute toward the development of the midwinter hemispheric sea ice seesaw in contrast the ice seesaw tends to damp the preexisting nao signal during late winter indicating a reversal of the phase relation between them this nao damping may be triggered by the pacific sea ice anomalies results from numerical experiments generally support this notion and further suggests a stationary rossby wave train emanated from the north pacific as a dynamical mechanism for damping the nao signal

empirical relationships between summertime oceanic heat anomalies in the nordic seas and large scale atmospheric circulation in the following winter a lagged regression analysis between an index of observed summertime atlantic water temperature awt variability at the entrance to the barents sea in the period 1982 2005 and year round atmospheric ncep ncar reanalysis data is used to show that subsurface oceanic heat anomalies in high latitudes are significant precursors of wintertime atmospheric variability in middle latitudes in particular positive awt anomalies precede predominantly westerly wind anomalies in high latitudes and easterly wind anomalies in middle latitudes the mid latitude wind anomalies while being generally equivalent barotropic in the upper troposphere have a strong low level baroclinic contribution over eurasia the near surface easterly wind anomalies in this area are locally deflected southward maintaining cold spots near orography the summertime oceanic anomalies explain about 40 of the variance in the surface air temperature averaged over eurasia from 35 to 45 n and about 50 of the variance in surface winds over the far east asia in the following winter we suggest that the remote connections arise from reorganization of the mid latitude storm tracks the awt anomalies explain about 60 of the variance in the upper tropospheric storm track activity averaged over the pacific and eurasia from 35 to 55 n and in the lower tropospheric poleward synoptic eddy heat flux over western eurasia finally we show that the awt associated wintertime atmospheric anomalies appear in quadrature with the concurrent anomalies associated with the north atlantic oscillation these findings suggest that oceanic heat anomalies in high latitudes may be a useful predictor of atmospheric variability

month to month variability of winter temperature over northeast china linked to sea ice over the davis strait baffin bay and the barents kara sea abstractthis study focuses on the month to month variability of winter temperature anomalies over northeast china necta especially the out of phase change between december and january february

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

interdecadal variability of the warm arctic and cold eurasia pattern and its north atlantic origin abstractthis study investigates the origin of the interdecadal variability in the warm arctic and cold eurasia wace pattern which is defined as the second empirical orthogonal function of surface air temperature sat variability over eurasian continent in northern winter by analyzing the twentieth century reanalysis dataset while previous studies highlight recent enhancement of the wace pattern ascribing it to anthropogenic warming we found that the wace pattern has experienced a seemingly periodic interdecadal variation over the twentieth century this long term variation in the eurasian sat is attributable to the altered coupling between the siberian high sh and intraseasonal rossby wave emanating from the north atlantic as the local wave branch interacts with the sh and consequentially enhances the continental temperature perturbation it is further identified that these atmospheric circulation changes in eurasia are largely controlled by the decadal amplitude modulation of the climatological

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

snow n ao teleconnection and its modulation by the quasi biennial oscillation abstractthis study explores the wintertime extratropical atmospheric response to siberian snow anomalies in fall using observations and two distinct atmospheric general circulation models the role of the quasi biennial oscillation qbo in modulating this response is discussed by differentiating easterly and westerly qbo years the remote influence of siberian snow anomalies is found to be weak in the models especially in the stratosphere where the holton tan effect of the qbo dominates the simulated snow influence on the polar vortex at the surface discrepancies between composite analyses from observations and model results question the causal relationship between snow and the atmospheric circulation suggesting that the atmosphere might have driven snow anomalies rather than the other way around when both forcings are combined the simulations suggest destructive interference between the response to positive snow anomalies and easterly qbo and vice versa at odds with the hypothesis that the s

seasonal prediction of the northern and southern temperature modes of the east asian winter monsoon the importance of the arctic sea ice previous research work found that two distinct surface air temperature sat modes the northern n and the southern s modes dominate the east asian winter monsoon eawm region the inter annual variations of these two modes were mainly attributed to preceding siberian snow cover anomalies and el nino southern oscillation enso observed evidence in this study shows that sea ice anomalies on barents kara bk and laptev seas and those on chukchi beaufort cb sea in autumn have co mingled effects on the two abnormal eawm modes if negative sea ice anomalies appear in the bk and northern cb sea in september october so the following winter sat anomaly over east asia is featured by an obvious cooling north of 40 n which highly resembles the sat n mode of eawm if negative sea ice anomalies occur in bk laptev sea but positive anomalies in the southern cb sea the east asia winter sat anomaly exhibits a salient cold condition over the south of 40 n and corresponds to the eawm s mode the above results indicate that autumn arctic sea ice can provide another predictability source for the eawm besides siberian snow cover and enso to further verify its contribution to seasonal prediction of the eawm a series of physical empirical models are established using the combinations of so arctic sea ice autumn siberian snow cover and enso hindcast experiment output shows when adding autumn arctic sea ice into the predictors the cross validated prediction skill is significantly improved the possible physical mechanisms on how preceding arctic sea ice anomalies impact on the n and s modes are also discussed

regionality of record breaking low temperature events in china and its associated circulation extreme cold events frequently occur around the world in recent several years and arouse widespread concern in this study 17 record breaking event processes rbeps of low temperature during 1981 2012 are identified by using daily minimum temperature at 1897 meteorological stations in china these rbeps are classified into two types based on the occurring area at northern or southern china to compositely examine the associated circulations although the correspondence between arctic oscillation ao and rbeps is not linearly stable there still exist relationship between them i e under ao negative phase the rbeps tend to occur at northern china nor the southern part where the rbeps prefer to happen under ao positive phase in the rbeps occurring at southern china the continent high pressure over mongolia area is extremely intensified and the east asian polar front jet stream is enhanced accompanied with strong synoptic scale eddy kinetic energy transports correspondingly the cold air masses break out and unobstructed southward intrude to low latitudes causing severe cooling effect in southern china in the rbeps occurring at northern china however the extremely intensified high pressure over northern siberian area combining with the northward enhanced subtropical jet stream lead to the cold air mass accumulation and blockage at mid latitudes and therefore rbeps of low temperature at this area further study implies that interdecadal change of the ao phase and differences of synoptic scale eddy activity might synthetically attribute to the different regional preference of those rbeps of low temperature that are mostly located at southern china in 1990s but concentrated in northern china in 2000s

atmospheric response to anomalous autumn surface forcing in the arctic basin data from four reanalyses are analyzed to evaluate the downstream atmospheric response both spatially and temporally to anomalous autumn surface forcing in the arctic basin running weekly mean skin temperature anomalies were classified using the self organizing map algorithm the resulting classes were used to both composite the initial atmospheric state and determine how the atmosphere evolves from this state the strongest response was to anomalous forcing positive skin temperature and total surface energy flux anomalies and reduced sea ice concentration in the barents and kara seas analysis of the evolution of the atmospheric state for 12 weeks after the initial forcing showed a persistence in the anomalies in this area which led to a buildup of heat in the atmosphere this resulted in positive 1000 500 hpa thickness and high pressure circulation anomalies in this area which were associated with cold air advection and temperatures over much of central and northern asia evaluation of days with the opposite forcing i e negative skin temperature anomalies and increased sea ice concentration in the barents and kara seas showed a mirrored opposite downstream atmospheric response other patterns with positive skin temperature anomalies in the arctic basin did not show the same response most likely because the anomalies were not as strong nor did they persist for as many weeks following the initial forcing

variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks abstract the heat and vorticity transports by synoptic scale eddies at various levels between 1000 and 100 mb have been compiled for each winter month of the 1966 84 period using time filtered daily analyses produced by the u s national meteorological center these circulation statistics were used to compute the three dimensional distributions of the quasigeostrophic geopotential tendency and vertical motion induced by baroclinic and barotropic eddy processes in individual months the latter fields serve as the basis for describing the synoptic scale eddy forcing associated with the leading modes of month to month variability of the storm tracks over the north pacific and north atlantic these modes are associated with the meridional displacements of the storm track axes from their climatological positions the placement of a storm track at a certain latitude in a certain month is accompanied by enhanced convergence of eddy heat fluxes poleward of in the tropospheric column poleward of the storm tra

observed evidence of an impact of the antarctic sea ice dipole on the antarctic oscillation abstracta lagged maximum covariance analysis mca is applied to investigate the linear covariability between monthly sea ice concentration sic and 500 mb geopotential height z500 in the southern hemisphere sh the dominant signal is the atmospheric forcing of sic anomalies throughout the year but statistically significant covariances are also found between austral springtime z500 and prior sic anomalies up to four months earlier the mca pattern is characterized by an antarctic dipole adp like pattern in sic and a positively polarized antarctic oscillation aao in z500 such long lead time covariance suggests the forcing of the aao by persistent adp like sic anomalies the leading time of sic anomalies provides an implication for skillful predictability of springtime atmospheric variability

interdecadal variation of winter cold surge path in east asia and its relationship with arctic sea ice abstractthe paths of winter cold surge cs events in east asia ea from 1979 to 2017 are tracked by the flexible particle flexpart model using era interim daily datasets and the probability de

the atmospheric response to realistic arctic sea ice anomalies in an agcm during winter abstract the influence of realistic arctic sea ice anomalies on the atmosphere during winter is investigated with version 3 6 of the community climate model ccm3 6 model experiments are performed for the winters with the most 1982 83 and least 1995 96 arctic ice coverage during 1979 99 when ice concentration estimates were available from satellites the experiments consist of 50 member ensembles using large ensembles proved critical to distinguish the signal from noise the local response to ice anomalies over the subpolar seas of both the atlantic and pacific is robust and generally shallow with large upward surface heat fluxes 100 w m 2 near surface warming enhanced precipitation and below normal sea level pressure where sea ice receded and the reverse where the ice expanded the large scale response to reduced enhanced ice extent to the east west of greenland during 1982 83 resembles the negative phase of the arctic oscillation north atlantic oscillation ao nao with a ridge over t

intraseasonal and interdecadal jet shifts in the northern hemisphere the role of warm pool tropical convection and sea ice abstractthis study uses cluster analysis to investigate the interdecadal poleward shift of the subtropical and eddy driven jets and its relationship to intraseasonal teleconnections for this purpose self organizing map som analysis is applied to the ecmwf interim re analysis era interim zonal mean zonal wind the resulting som patterns have time scales of 4 8 5 7 days and undergo notable interdecadal trends in their frequency of occurrence the sum of these trends closely resembles the observed interdecadal trend of the subtropical and eddy driven jets indicating that much of the interdecadal climate forcing is manifested through changes in the frequency of intraseasonal teleconnection patterns two classes of jet cluster patterns are identified the first class of som pattern is preceded by anomalies in convection over the warm pool followed by changes in the poleward wave activity flux the second class of patterns is preceded by sea ice and stratospheric polar vortex anomalies when the arctic se

record of latest barremian cenomanian environmental change in tectonically controlled depressions from the jura burgundy threshold jura mountains eastern france and western switzerland abstract the area of the western jura mountains constitutes the former jura burgundy threshold between the tethys ocean and the epicontinental paris basin sea during the barremian the area was covered by a shallow water urgonian carbonate platform tectonic processes influenced the architecture of the urgonian platform and were notably responsible for the formation of fault related depressions on top of the urgonian series which were subsequently transformed into incised valleys and then to marine depocenters their sedimentary infills are mostly represented by the perte du rhone formation and record stepwise environmental change on the innermost platform which was strongly influenced by the nearby landmass from the latest barremian onward sedimentation progressively changed from i predominantly oncoidal and detrital charophyte rich marly limestones to ii heterozoan marly limestones and marls followed by iii detrital sediments interspersed with numerous phosphatic conglomerates these changes are linked with the onset of the latest barremian taxy episode and with the following oceanic anoxic episodes oae s 1a to d in the neighbouring basins the sedimentary changes are associated with sedimentary sequences which formed during 2nd order transgressions and which express the effect of sea level fall followed by drowning events the presence of a rich ammonite fauna allowed a precise biostratigraphical dating of these events during the latest barremian to cenomanian time interval

subsidence of the gulf of papua in the cenozoic abstract the gulf of papua between papua new guinea and the northeastern australian margin contains thick cenozoic strata we have examined the subsidence history using data from eight wells in the gulf of papua four are in the western gulf region overlying paleozoic basement and four are in the eastern gulf near the aure trough backstripping results show two subsidence episodes for the western wells the first episode from early cenozoic to oligocene may be due to a small amount of lithospheric stretching associated with the opening of the coral sea the second from early miocene to the present has a substantially higher subsidence rate which cannot be explained by a paleocene rifting event the late oligocene late miocene episode of rapid subsidence in the aure trough to the east appears to be a significant factor affecting the subsidence of the western gulf of papua during this period to test this we computed the expected deflection from flexure due to the load of the aure trough strata and find a profile similar to that observed the model used had an effective elastic thickness similar to those for rifted continental margins thus implying a relatively weak lithosphere in addition the predicted position of the forebulge in the western gulf occurs where oligocene strata are absent suggesting post depositional uplift and hence facilitating the growth of early miocene reefs

patterns of asian winter climate variability and links to arctic sea ice abstractthis paper describes two dominant patterns of asian winter climate variability the siberian high sh pattern and the asia arctic aa pattern the former depicts atmospheric variability closely associated with the intensity of the siberian high and the latter characterizes the teleconnection pattern of atmospheric variability between asia and the arctic which is distinct from the arctic oscillation ao the aa pattern plays more important roles in regulating winter precipitation and the 850 hpa meridional wind component over east asia than the sh pattern which controls surface air temperature variability over east asia in the arctic ocean and its marginal seas sea ice loss in both autumn and winter could bring the positive phase of the sh pattern or cause the negative phase of the aa pattern the latter corresponds to a weakened east asian winter monsoon eawm and enhanced winter precipitation in the midlatitudes of the asian continent and east asia for the sh pattern sea ice loss in the