a strong wind event on the ross ice shelf antarctica a case study of scale interactions abstractin situ observations satellite imagery numerical weather prediction and reanalysis fields are used to investigate the synoptic and mesoscale environment of a strong wind event swe at mcmurdo station ross island region on the ross ice shelf antarctica on 10 october 2003 the swe occurred during the passage of a sequence of three mesoscale low pressure systems from the central ross ice shelf to the southwest ross sea a potential vorticity pv analysis showed that the lows drew air of continental origin down the glacial valleys of the transantarctic mountains and onto the ice shelf as a katabatic drainage flow however the analysis indicated that the air mass associated with the swe was of recurved maritime origin drawn in by the second mesoscale low l2 this air mass approached mcmurdo station from the south where interactions with the orography played a critical role in the early stages of the event when the wind speed was less than 10 m s 1 the air was deflected around the topograph

importance of latent heating in mesocyclones for the decay of cold air outbreaks a numerical process study from the pacific sector of the southern ocean abstractin this study the dynamical mechanisms shaping the evolution of a marine cold air outbreak cao that occurred over the ross amundsen and bellingshausen seas in june 2010 are investigated in an isentropic framework the drainage of cold air from west antarctica into the interior ross sea its subsequent export and the formation of a dome of cold air off the sea ice edge are shown to be intimately linked to a lower tropospheric cyclone as well as the cyclonic breaking of an upper level potential vorticity trough the dome formation is accompanied by an extreme deepening of the boundary layer whose top reaches to the height of the low lying tropopause within the trough potentially allowing for deep stratosphere troposphere exchange a crucial finding of this study is that the decay of the cao is essentially driven by the circulation associated with a train of mesocyclones and the release of latent heat in their warm sectors sensitivity experiments with switched off fluxes of sensible and late

the influence of the amundsen sea low on the winds in the ross sea and surroundings insights from a synoptic climatology the amundsen sea low asl is an area of climatologically low atmospheric pressure situated over the southern ocean the depth and location of this feature have significant effects on winds temperature moisture transport and sea ice in its vicinity in this article we quantify the modulating effect of this feature on winds over the ross sea and ross ice shelf we examine composites of surface winds sampled according to extrema in asl depth longitude and latitude we employ the output of a previously developed synoptic climatology to identify the explanatory synoptic scale forcings in autumn winter and spring aws we find that the impact of the depth of the asl is smaller than that of its location the asl moves eastward when it is deep thereby reducing its influence on ross sea winds when the asl is northward we find strongly enhanced southerly flows over the ross sea and ice shelf forced by greater cyclonic activity in the north of the ross sea in summer we find increased cyclonic flow coinciding with a deeper asl despite the asl being located in the bellingshausen sea at this time the responses to the asl longitude and latitude are profoundly different to those in aws suggesting that relationships are strongly dependent on the varying seasonal location of the low we examine two metrics of the asl depth and identify that the absolute mean sea level pressure mslp has a more widespread response than that of the relative mslp

morphology and paleoclimatic significance of pleistocene lake bonneville spits abstract pleistocene lake bonneville of western utah contains a variety of spits associated with shorelines and other features that formed between 21 000 and 12 000 14 c yr bp field studies in the low lying mountain ranges of the central portion of lake bonneville identified 17 spits of various types the spits are connected to small mountain ranges and islands vary in size from 0 02 to 0 5 km 2 and are composed of coarse grained well rounded poorly sorted sedimentary material sixteen of the 17 spits have a northeasterly to southwesterly orientation implying that winds were from the northwest to northeast approximately 180 out of phase with modern winds in the eastern great basin lake bonneville spit orientation is best explained as the result of persistent northerly winds caused by the high atmospheric pressure cell of the continental ice sheet and passage of low pressure extratropical storms south of the lake similar strong persistent winds are a common feature of modern continental ice sheets and passing low pressure systems if so the north american jet stream tracked south of lake bonneville as recently as 12 000 14 c yr bp well past the height of the last glacial maximum

a case study of a ross ice shelf airstream event a new perspective abstract a case study illustrating cloud processes and other features associated with the ross ice shelf airstream ras in antarctica is presented the ras is a semipermanent low level wind regime primarily over the western ross ice shelf linked to the midlatitude circulation and formed from terrain induced and large scale forcing effects an integrated approach utilizes moderate resolution imaging spectroradiometer modis satellite imagery automatic weather station aws data and antarctic mesoscale prediction system amps forecast output to study the synoptic scale and mesoscale phenomena involved in cloud formation over the ross ice shelf during a ras event a synoptic scale cyclone offshore of marie byrd land draws moisture across west antarctica to the southern base of the ross ice shelf vertical lifting associated with flow around the queen maud mountains leads to cloud formation that extends across the ross ice shelf to the north the low level cloud has a warm signature in thermal infrare

distribution and characteristics of mesoscale cyclones in the antarctic ross sea eastward to the weddell sea abstract the mesoscale cyclone activity observed in the portion of antarctica that faces the south pacific ocean and weddell sea area is summarized from a study of 1991 in general area normalized results reveal much greater mesoscale cyclonic activity over the ross sea ross ice shelf and southern marie byrd land than on both sides of the antarctic peninsula more than 50 of the observed mesoscale vortices are of the comma cloud type the average diameter of mesoscale vortices is approximately 200 km near terra nova bay 270 km near byrd glacier and 280 km near siple coast near the antarctic peninsula the average diameter is about 370 km over the bellingshausen sea and 380 km on the weddell sea side the largest percentage of deep vortices occurs over the bellingshausen sea sector 38 of all cases where convective instability frequently occurs over the ross sea ross ice shelf and weddell sea sectors the majority of the mesoscale vortices are low cloud features that probably do not exceed the 700

cyclonically forced barrier winds along the transantarctic mountains near ross island abstract the effect of the transantarctic mountains on cyclonically forced boundary layer winds in the vicinity of ross island antarctica 77 5 s 167 e is discussed when cyclones are present over the western ross ice shelf and ross sea the low level easterly airflow is toward the mountains a barrier wind regime is set up as the flow is turned northward and becomes parallel to the mountain range it is found that cyclonically forced barrier winds occurred around 5 and 8 of the time during 1984 and 1985 respectively the case histories of two well defined barrier wind events lasting for 24 h are discussed in detail with regional analyses based on satellite photographs and automatic weather station data one case is for a katabatic wind forced mesoscale cyclone forming to the north of ross island and the other is for a synoptic scale cyclone moving through the western ross ice shelf ross sea region a numerical model for the vertically integrated boundary layer flow that calculates two horizontal

modeling the enso modulation of antarctic climate in the late 1990s with the polar mm5 abstract the polar fifth generation pennsylvania state university ncar mesoscale model mm5 is employed to examine the el nino southern oscillation enso modulation of antarctic climate for july 1996 june 1999 which is shown to be stronger than for the mean modulation from 1979 to 1999 and appears to be largely due to an eastward shift and enhancement of convection in the tropical pacific ocean this study provides a more comprehensive assessment than can be achieved with observational datasets by using a regional atmospheric model adapted for high latitude applications polar mm5 the most pronounced enso response is observed over the ross ice shelf marie byrd land and over the weddell sea ronne filchner ice shelf in addition to having the largest climate variability associated with enso these two regions exhibit anomalies of opposite sign throughout the study period which supports and extends similar findings by other investigators the dipole structure is observed in surface temperature meridio

a dynamical investigation of the may 2004 mcmurdo antarctica severe wind event using amps on 15 16 may 2004 a severe windstorm struck mcmurdo antarctica the antarctic mesoscale prediction system amps is used along with available observations to analyze the storm a synoptic scale cyclone weakens as it propagates across the ross ice shelf toward mcmurdo flow associated with the cyclone initiates a barrier jet along the transantarctic mountains forcing terms from the horizontal equations of motion are computed in the barrier wind to show that the local time tendency and momentum advection terms are key components of the force balance the barrier jet interacts with a preexisting near surface radiation inversion over the ross ice shelf to set up conditions favorable for the development of large amplitude mountain waves leading to a downslope windstorm in the ross island area hydraulic theory can explain the structure of the downslope windstorms with amplification of the mountain waves possibly caused by wave breaking events the underestimation of amps wind speed at mcmurdo is caused by the misplacement of a hydraulic jump downstream of the downslope windstorms the dynamics associated with the cyclone barrier jet and downslope windstorms are analyzed to determine the role of each in development of the severe winds

dynamics of the foehn mechanism in the mcmurdo dry valleys of antarctica from polar wrf foehn events over the mcmurdo dry valleys mdvs the largest ice free region of antarctica promote glacial melt that supports biological activity in the lakes streams rocks and soils although mdvs foehn events are known to depend upon the synoptic scale circulation the physical processes responsible for foehn events are unknown a polar optimized version of the weather research and forecasting model polar wrf is used for a case study of a representative summer foehn event from 29 december 2006 to 1 january 2007 in order to identify and explain the mdvs foehn mechanism pressure differences across an elevated mountain gap upstream of the mdvs provide forcing for southerly flow into the western upvalley entrance of the mdvs complex terrain over the elevated gap and the mdvs leads to mountain wave effects such as leeside acceleration hydraulic jumps wave breaking and critical layers these mountain wave effects depend on the ambient geostrophic wind direction pressure driven channelling then brings the warm dry foehn air downvalley to eastern mdv sites brief easterly intrusions of maritime air into the eastern mdvs during foehn events previously have been attributed to either a sea breeze effect in summer or local cold pooling effects in winter in this particular case the easterly intrusions result from blocking effects of nearby ross island and the adjacent antarctic coast temperature variability during the summer foehn event which is important for meltwater production and biological activity when it exceeds 0 c primarily depends on the source airmass rather than differences in foehn dynamics

strong wind speed events over antarctica and its surrounding oceans abstractstrong wind events swes over antarctica and its surrounding oceans are investigated using gridded surface wind data from the era interim for the 1979 2017 period throughout the year swe

tip jets and barrier winds a quikscat climatology of high wind speed events around greenland the high topography of greenland results in a number of orographically induced high wind speed flows along its coast that are of interest from both a severe weather and climate perspective here the surface wind field dataset from the nasa jpl seawinds scatterometer on board the quick scatterometer quikscat satellite is used to develop a wintertime climatology of these flows the high spatial resolution and the twice daily sampling of the seawinds instrument allows for a much more detailed view of the surface winds around greenland than has been previously possible three phenomena stand out as the most distinctive features of the surface wind field during the winter months the previously identified tip jets and reverse tip jets as well as the hitherto unrecognized barrier flows along its southeast coast in the vicinity of the denmark strait peak surface wind speeds associated with these phenomena can be as large as 50 m s 1 with winds over 25 m s 1 occurring approximately 10 15 of the time at each location a compositing technique is used to show that each type of flow is the result of an interaction between a synoptic scale parent cyclone and the high topography of greenland in keeping with previous work it is argued that tip jets are caused by a combination of conservation of the bernoulli function during orographic descent and acceleration due to flow splitting as stable air passes around cape farewell while barrier winds are a geostrophic response to stable air being forced against high topography it is proposed that reverse tip jets occur when barrier winds reach the end of the topographic barrier and move from a geostrophic to a gradient wind balance becoming supergeostrophic as a result of their anticyclonic curvature

a description of the ross ice shelf air stream ras through the use of self organizing maps soms 1 the low level wind field across the ross ice shelf region antarctica is studied through the method of self organizing maps soms emphasis is placed on identifying and characterizing the ross ice shelf air stream ras the ras is a dominant northward stream of air resulting in significant transport of atmospheric mass from the interior of antarctica two soms are created for the lowest model level 13 m and the 5th lowest model level 150 m from archived real time numerical weather prediction output of the antarctic mesoscale prediction system amps a verification of the som for the lowest model level is completed by comparing select nodes to automatic weather station wind rose plots the winds depicted in the lowest model level som are dominated by the position of the cyclone in the ross sea and the changes in wind speeds on the antarctic plateau the 5th lowest model level provides a better depiction of the ras the ras is found to be present primarily when associated with a cyclone in the ross sea there is a strong seasonality to the ras with the ras occurring frequently during the winter months and rarely during the summer months the structure and position of the ras is strongly dependent on the position of the ross sea cyclone

jurassic to palaeogene tectono magmatic evolution of northern chile and adjacent bolivia from detrital zircon u pb geochronology and heavy mineral provenance heavy mineral provenance data presented in this article reinforce evidence for significant late palaeogene deformation and relief formation along the western margin of the central andean plateau late eocene oligocene onset of molasse type sedimentation records initial range uplift strikingly different basement sources of sediments deposited to the east and west of the late palaeogene range indicate that initial relief development was governed by a bivergent thrust system significantly higher sediment accumulation rates to the east of the range compared to the west suggest that the generated relief acted already as an effective orographic barrier at that time higher precipitation and denudation along the eastern slope facilitated deeper erosion of the trust belt

case study of a barrier wind corner jet off the coast of the prince olav mountains antarctica abstractthe ross ice shelf airstream ras is a barrier parallel flow along the base of the transantarctic mountains previous research has hypothesized that a combination of katabatic flow barrier winds and mesoscale and synoptic scale cyclones drive the ras within the ras an area of maximum wind speed is located to the northwest of the protruding prince olav mountains in this region the sabrina automatic weather station aws observed a september 2009 high wind event with wind speeds in excess of 20 m s 1 for nearly 35 h the following case study uses in situ aws observations and output from the antarctic mesoscale prediction system to demonstrate that the strong wind speeds during this event were caused by a combination of various forcing mechanisms including katabatic winds barrier winds a surface mesocyclone over the ross ice shelf an upper level ridge over the southern tip of the ross ice shelf and topographic influences from the prince olav mountains these forcing mechanisms induced a b

influence of the orographic roughness of glacier valleys across the transantarctic mountains in an atmospheric regional model glacier valleys across the transantarctic mountains are not properly taken into account in climate models because of their coarse resolution nonetheless glacier valleys control katabatic winds in this region and the latter are thought to affect the climate of the ross sea sector frsater formation to snow mass balance the purpose of this paper is to investigate the role of the production of turbulent kinetic energy by the subgrid scale orography in the transantarctic mountains using a 20 km atmospheric regional model a classical orographic roughness length parametrization is modified to produce either smooth or rough valleys a one year simulation shows that katabatic winds in the transantarctic mountains are strongly improved using smooth valleys rather than rough valleys pressure and temperature fields are affected by the representation of the orographic roughness specifically in the transantarctic mountains and over the ross ice shelf a smooth representation of escarpment regions shows better agreement with automatic weather station observations than a rough representation this work stresses the need to improve the representation of subgrid scale orography to simulate realistic katabatic flows this paper also provides a way of improving surface winds in an atmospheric model without increasing its resolution

ice volume and sea level during the last interglacial during the last interglacial period 125 000 years ago sea level was at least several meters higher than at present with substantial variability observed for peak sea level at geographically diverse sites speculation that the west antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice sheet dynamics during this time interval we provide an internally consistent database of coral u th ages to assess last interglacial sea level observations in the context of isostatic modeling and stratigraphic evidence these data indicate that global eustatic sea level peaked 5 5 to 9 meters above present sea level requiring smaller ice sheets in both greenland and antarctica relative to today and indicating strong sea level sensitivity to small changes in radiative forcing

a high resolution numerical simulation of the wind flow in the ross island region antarctica abstract a detailed description of the characteristics of the three dimensional wind flow for the ross island region of antarctica is presented this region of antarctica has complex topographic features and the wind flow is dependent on the topography and the local meteorological conditions high resolution nonhydrostatic numerical simulations are conducted over a high resolution domain in the ross island region two simulations are performed corresponding to the two dominant wind flow patterns in the ross island region the first simulation is a light wind case with a stable lower atmosphere and the second is a high wind speed event froude number calculations along with a study of the equation of motion are included for a more complete understanding of the dynamics of the wind flow the results of the simulations show a favorable correlation to past research results and observations and provide a more complete understanding of the three dimensional wind flow in the region in addition to a more tho

characteristics of the ross ice shelf air stream as depicted in antarctic mesoscale prediction system simulations 1 streamlines of the mean annual near surface winds over the antarctic continent suggest a confluent channeling of the drainage flows off the ice sheets and onto the ross ice shelf a persistent cyclonic circulation to the north of the ice shelf supports a large scale pressure field that reinforces the continental drainage flows owing to these two processes an enhanced low level airflow is present along the southern and western sections of the ross ice shelf the resulting air stream known as the ross ice shelf air stream ras is one of the persistent and prominent low level wind features seen in the antarctic real time mesoscale simulations of the antarctic atmosphere and high southern latitudes using a modified version of the pennsylvania state university national center for atmospheric research mesoscale modeling system have been ongoing since the 1999 2000 austral field season model results from the 1 year period november 2001 to october 2002 have been analyzed to investigate the mean structure and modulation of the ross ice shelf air stream analyses of model results show the low level air stream over the western ross ice shelf has a wind speed maxima that is linked to the steep topography to the west individual cases of strong wind events appear to contain a significant barrier wind component that arises from cold air damming against the transantarctic mountains cyclones that frequently form in the ross sea are shown to establish conditions that promote barrier wind dynamics and thus significantly modulate the intensity of the ras

gale force winds over the irminger sea to the east of cape farewell greenland 1 high wind events that occur over the irminger sea to the east of cape farewell greenland are of interest as a result of the significant hazard they represent to maritime activity as well as their potential role in forcing deep ocean convection in the region in this paper the ncep reanalysis is used to develop a climatology of gale force wind events over the irminger sea in addition to the previously identified tip jet events that are characterized by strong westerly flow we show that there also exist reverse tip jet events that are characterized by strong easterly flow both types of events are associated with deep extra tropical cyclones that are undergoing an interaction with the high topography of southern greenland we also show that the frequency of both types of events is highest in the winter months and is modulated by the phase of the north atlantic oscillation nao

an analysis of low level jets in the greater ross ice shelf region based on numerical simulations abstract an analysis of the presence and location of low level jets lljs across the ross ice shelf region in antarctica is presented based on the analysis of archived output from the real time antarctic mesoscale prediction system amps the method of self organizing maps soms is used to objectively identify different patterns in column averaged wind speed over the approximately lowest 1200 m of the atmosphere as an identifier to the location of lljs the results indicate three primary lljs in the region the largest and most dominant llj is along the transantarctic mountains by the siple coast and the southern end of the ross ice shelf the second llj extends from the base of byrd glacier and curves to the north passing by the eastern extremes of ross island the third llj extends from the base of reeves glacier and curves to the north across the western ross sea a strong seasonality is observed in the frequency and intensity of the lljs with the highest values for wind speed and the size of the

met office unified model high resolution simulations of a strong wind event in antarctica during winter much of the antarctic coast is susceptible to severe and hazardous strong wind events swes associated with the enhancement of katabatic winds by synoptic weather systems in this study a swe that occurred at mawson east antarctica involving a hurricane force wind speed of 39 m s 1 is simulated by the met office unified model at high horizontal resolutions with grid lengths between 12 and 1 5 km it is shown that all the simulations capture the qualitative evolution of the swe but underestimate its peak wind speed the extent of the underestimate is dependent on horizontal resolution with the 4 and 1 5 km 12 km models underforecasting the peak wind speed by around 15 36 in addition to a strengthening of the katabatic flow the simulated low level cyclonic winds associated with the depression responsible for the swe caused the formation of a barrier type jet parallel to the coast resulting in strong wind convergence interaction at the coastline and suggesting a strong topographic influence on the dynamics responsible for swe formation moreover it suggests that mawson is influenced by small scale gravity waves that formed in response to the stronger winds and that representation of this was particularly sensitive to horizontal resolution additional experiments suggest that the met office unified model simulation of the swe is most sensitive to the representation of turbulent mixing under stable conditions this study is important to identify shortcomings in the performance of the met office unified model near antarctica s coastal regions as well as to improve understanding of the processes responsible for swes

a validation of the antarctic mesoscale prediction system using self organizing maps and high density observations from snowweb abstractthis study compares high resolution output 1 1 km horizontal grid length from twice daily forecasts produced by the antarctic mesoscale prediction system amps with a dense observational network east of ross island covering 10 000 km2 15 snowweb stations significantly increased the number of observation stations in the area to 19 during the 2014 15 austral summer collocated virtual stations created from amps output are combined with observations producing a single dataset of zonal and meridional wind components used to train a self organizing map som the resulting som is used to individually classify the observational and amps datasets producing a time series of classifications for each dataset directly comparable to the other analysis of class composites shows two dominant weather patterns low but directionally variable winds and high but directionally constant winds linked to the ross ice shelf airstream ras during ras events the amps and snowweb data displayed good temporal cl