Winter Atmospheric Circulation Research Articles

Quantification of the Lateral Boundary Forcing of a Regional Climate Model Using an Aging Tracer

Abstract The present work introduces a new and useful tool to quantify the lateral boundary forcing of a regional climate model (RCM). This tool, an aging tracer, computes the time the air parcels spend inside the limited-area domain of an RCM. The aging tracers are initialized to zero when the air parcels enter the domain and grow older during their migrations through the domain with each time step in the integration of the model. This technique was employed in a 10-member ensemble of 10-yr (1980–89) simulations with the Canadian RCM on a large domain covering North America. The residency time is treated and archived as the other simulated meteorological variables, therefore allowing computation of its climate diagnostics. These diagnostics show that the domain-averaged residency time is shorter in winter than in summer as a result of the faster winter atmospheric circulation. The residency time decreases with increasing height above the surface because of the faster atmospheric circulation at high levels dominated by the jet stream. Within the domain, the residency time increases from west to east according to the transportation of the aging tracer with the westerly general atmospheric circulation. A linear relation is found between the spatial distribution of the internal variability—computed with the variance between the ensemble members—and residency time. This relation indicates that the residency time can be used as a quantitative indicator to estimate the level of control exerted by the lateral boundary conditions on the RCM simulations.

Observed impact of subtropical-midlatitude South Atlantic SST anomalies on the atmospheric circulation

[1] A maximum covariance analysis (MCA) of monthly anomaly data from the NCEP–NCAR reanalysis during 1981–2007 suggests that the atmosphere over subtropical-midlatitude South Atlantic during the austral late winter and spring is significantly correlated to the underlying sea surface temperature (SST) anomalies (SSTA) up to at least 4 months earlier. Such SST impact on the atmosphere is independent from the tropical Pacific and tropical South Atlantic influence, and is confirmed by the regression analysis based on the SSTA centers of action. The MCA pattern of SST resembles the dominant mode of SST variability and the monopole atmospheric signal is barotropic through the troposphere and hemispheric in extent. This implies predictability of the late winter and spring atmospheric circulation in the subtropical-midlatitude South Atlantic with a lead time of up to 4 months.

Atmospheric circulation features associated to Argentinean Andean rivers discharge variability

Winter atmospheric circulation patterns and their relationship to runoff variability in the Atuel and Chubut rivers of Argentina are analyzed. The most important atmospheric low levels condition associated with high (low) Atuel discharges is the weakening (strengthening) of the mean atmospheric flow, while the same feature is displaced 5° southward for Chubut. At high levels, results suggest the existence of a NW‐SE direction wave pattern extending from Australia to the South Atlantic, favoring positive (negative) pressure anomalies West of the Drake Passage, which deflect the storm tracks northward (southward) and hence increase (decrease) precipitations and subsequent Atuel discharges. In contrast, Chubut discharges are mainly controlled by a shorter wave pattern along the subtropical Pacific, which zonally crosses South America. This pattern helps to maintain low (high) pressure anomalies off the Chilean coast at the upper‐river basin latitude for high (low) Chubut runoffs.

Investigating the Impact of Reemerging Sea Surface Temperature Anomalies on the Winter Atmospheric Circulation over the North Atlantic

Abstract Extratropical SSTs can be influenced by the “reemergence mechanism,” whereby thermal anomalies in the deep winter mixed layer persist at depth through summer and are then reentrained into the mixed layer in the following winter. The impact of reemergence in the North Atlantic Ocean (NAO) upon the climate system is investigated using an atmospheric general circulation model coupled to a mixed layer ocean/thermodynamic sea ice model. The dominant pattern of thermal anomalies below the mixed layer in summer in a 150-yr control integration is associated with the North Atlantic SST tripole forced by the NAO in the previous winter as indicated by singular value decomposition (SVD). To isolate the reemerging signal, two additional 60-member ensemble experiments were conducted in which temperature anomalies below 40 m obtained from the SVD analysis are added to or subtracted from the control integration. The reemerging signal, given by the mean difference between the two 60-member ensembles, causes the SST anomaly tripole to recur, beginning in fall, amplifying through January, and persisting through the following spring. The atmospheric response to these SST anomalies resembles the circulation that created them the previous winter but with reduced amplitude (10–20 m at 500 mb per °C), modestly enhancing the winter-to-winter persistence of the NAO. Changes in the transient eddies and their interactions with the mean flow contribute to the large-scale equivalent barotropic response throughout the troposphere. The latter can also be attributed to the change in occurrence of intrinsic weather regimes.

On the relation between extremes of midlatitude cyclones and the atmospheric circulation using ERA40

Analyzing ERA40 data there is evidence that extreme intensified midlatitude cyclones are related to the large‐scale atmospheric circulation in winter and to a minor degree for spring and autumn. Regionally different circulation patterns are related to extreme intensified cyclones, e.g., cyclones in northern Europe are linked to a slightly rotated NAO‐like pattern whereas for southern Europe a blocking‐like pattern over central to northern Europe is observed. In the Pacific a north‐south dipole pattern is related to extremes in cyclone intensity. In summer these relationships, however, collapse. In winter, depending on the considered region, changes in the meridional temperature gradient, the land‐sea temperature contrast, and to some extent changes in static stability modulate the lower to middle tropospheric baroclinicity, being important in the intensification process.

Intraseasonal Atmospheric Variability in the Extratropics and Its Relation to the Onset of Tropical Pacific Sea Surface Temperature Anomalies

Abstract Previous research has shown that seasonal-mean boreal winter variations in the subtropical/extratropical sea level pressure and wind stress fields over the central North Pacific are significantly related to the state of the El Niño–Southern Oscillation (ENSO) 12–15 months later. Results presented in this note indicate that boreal winter ENSO events are also preceded by increased intraseasonal variance in the antecedent boreal winter atmospheric circulation patterns over the extratropical central North Pacific as well. Low (high) surface pressure anomalies associated with intraseasonal variability in this region are related to intraseasonal wind stress anomalies that represent a weakening (strengthening) of the trade winds over both the north and south subtropical/tropical Pacific. There is also a concurrent increase (decrease) in the central and eastern subtropical North Pacific sea surface temperatures that projects onto the seasonal-mean SST anomalies that precede mature ENSO events by 9–12 months. Overall these results suggest that similar to seasonal-mean subtropical surface pressure and wind stress fields, enhanced transient variability in the midlatitudes can subsequently induce changes in the atmospheric and oceanic structure of the tropical Pacific that may serve as a precursor to ENSO variability.

Weichselian Late Pleniglacial surface winds over northwest and central Europe: a model–data comparison

AbstractReconstructions of the Weichselian Late Pleniglacial wind direction in northwest and central Europe are reviewed and compared with palaeoclimate simulations performed with an atmospheric general circulation model. These reconstructions are based on proxy data containing information on former wind directions, such as relic dune forms, sediments and wind‐polished rock surfaces. The objective is to investigate whether: (1) the proxy information is internally consistent; and (2) in agreement with the model simulations. We find a general consensus in the proxy‐based reconstructions, indicating a dominant westerly to northwesterly wind in winter during the Late Pleniglacial. The model results indicate over the study area an atmospheric circulation in winter that is dominated by southwesterly to west‐northwesterly winds, which are stronger than the southwesterly winds in the present‐day climate. The main driving factors behind the anomalous atmospheric circulation in the Late Pleniglacial are the Laurentide Ice Sheet and a colder North Atlantic Ocean with a relatively extensive sea‐ice cover, leading to an eastward relocation of the Icelandic Low and an enhanced pressure gradient over northwest Europe. The minor difference in Late Pleniglacial wind direction between the reconstructions and model can be explained by a combination of uncertainties in the proxy data and the relatively low spatial resolution of the applied climate model. Copyright © 2006 John Wiley & Sons, Ltd.

Simulation of the 1976/77 Climate Transition over the North Pacific: Sensitivity to Tropical Forcing

Abstract This study examines the contribution of tropical sea surface temperature (SST) forcing to the 1976/77 climate transition of the winter atmospheric circulation over the North Pacific using a combined observational and modeling approach. The National Center for Atmospheric Research (NCAR) Community Atmospheric Model version 3 (CAM3) simulates approximately 75% of the observed 4-hPa deepening of the wintertime Aleutian low from 1950–76 to 1977–2000 when forced with the observed evolution of tropical SSTs in a 10-member ensemble average. This response is driven by precipitation increases over the western half of the equatorial Pacific Ocean. In contrast, the NCAR Community Climate Model version 3 (CCM3), the predecessor to CAM3, simulates no significant change in the strength of the Aleutian low when forced with the same tropical SSTs in a 12-member ensemble average. The lack of response in CCM3 is traced to an erroneously large precipitation increase over the tropical Indian Ocean whose dynamical impact is to weaken the Aleutian low; this, when combined with the response to rainfall increases over the western and central equatorial Pacific, results in near-zero net change in the strength of the Aleutian low. The observed distribution of tropical precipitation anomalies associated with the 1976/77 transition, estimated from a combination of direct measurements at land stations and indirect information from surface marine cloudiness and wind divergence fields, supports the models’ simulated rainfall increases over the western half of the Pacific but not the magnitude of CCM3’s rainfall increase over the Indian Ocean.

Pine needles as a biomonitor for estimation of the regional-scale distribution of organic pollutants

Classic methods of the monitoring of pollutants to determine areas of their distribution from the sources have many limitations. The direct regular sampling of atmospheric air with a required number of sites in the study area is not an easy task. Results of modeling of the transport of polluted air masses often contradict experimental data. As a natural accumulative pattern, snow cover pollution characterizes the atmospheric state only during winter. Moreover, due to a distinct anticyclonic pattern of atmospheric circulation in winter, some areas of East Siberia are characterized by the localization of emission nearby the sources [1]. Therefore, we can use the data on snow cover pollution, primarily, to estimate the source capacity rather than the boundaries of polluted area. In this case, the application of biomonitors makes it possible to estimate atmospheric pollution based on results of the long-term communicative action of pollutants on the environment [2, 3]. The present paper is based on the first study of scotch pine ( Pinus sylvestris L.) needles as a bioaccumulator of persistent organic pollutants (POP) in the harsh continental climate of Central Asia. As the markers of air pollution by POP, we used the priority polycyclic aromatic hydrocarbons (PAH) that are present in both gas and aerosol phases of the atmosphere. The results show that the coefficient of PAH accumulation by pine needles ( k ac ) from the gas phase in the summer reaches 2 · 10 5 . As a result of sorption of aerosol particles, the k ac value drops to 10 3 in the winter. The maximum and background PAH accumulation levels in needles are equal to 1500‐1800 and 60‐80 ng/g, respectively. Based on the results of the simultaneous study of PAH accumulation levels and the physiological state of pine stands, we estimated the areas of POP distribution in the Baikal region.

Winter atmospheric circulation and river discharge in northwest Europe

More frequent western atmospheric circulation over Europe results in increased precipitation in winter, and could result in increasing river discharges. We made a quantitative assessment of the impact of variation in atmospheric circulation, defined by the frequency of western circulation in the Großwetterlagen classification system and the North Atlantic Oscillation (NAO) index, on variation in basin‐average precipitation and winter discharges (December–February) of eleven large river basins that drain northwest Europe. Annual winter discharges amounts are highly correlated among these rivers (up to r2 = 0.82, decreasing with increasing inter‐basin distance), which may point to a common atmospheric forcing. The number of days of western atmospheric circulation in winter as indicated by the Großwetterlagen classification system is more closely related (r2 = 0.06 to r2 = 0.28, p < 0.05 or better) to winter river discharges than the NAO index. We therefore conclude that the frequency of western atmospheric circulation over Europe is a better indicator of climate variability and climate change impacts on river discharges in northwest Europe.

Origin of dimethylsulfide, non‐sea‐salt sulfate, and methanesulfonic acid in eastern Antarctica

Ignoring the origin of atmospheric chemicals is often a strong limitation to the full interpretation of their measurement. In this article, this question is addressed in the case of the sulfur species in Antarctica, with an original method of retrotransport of tracers. The retrotransport model is derived from the Laboratoire de Météorologie Dynamique Zoom‐Tracers (LMD‐ZT) atmospheric general circulation model, optimized for polar climate and expanded to simulate atmospheric sulfur chemistry. For two East Antarctic scientific stations (Dumont d'Urville and Vostok) the effects of transport and chemistry and the influence of oceanic, volcanic, and anthropogenic sources on dimethylsulfide (DMS), non‐sea‐salt (nss) sulfate, and methanesulfonic acid (MSA) concentrations are evaluated in summer and winter. The oceanic source largely dominates, but other sources can episodically be significant. The meridional origin and the age of DMS, MSA, and biogenic nss sulfate are also estimated. The latitudes of origin of MSA and nss sulfate are similar in summer, but they differ markedly in winter. This is a signature of their different chemical production scheme. Also, the interannual variability of the origin of the sulfur species at Vostok is weak compared to that at Dumont d'Urville. Acknowledging that the DMS concentrations in the ocean have no interannual variability in the model, this result suggests unsurprisingly that inland Antarctic stations may be better observation sites to monitor large‐scale DMS bioproductivity variability than coastal sites are. The combination of slower chemistry and more intense atmospheric circulation in winter leads to unexpected results, such as a younger DMS in winter than in summer at Vostok.

The impact of Greenland's deglaciation on the Arctic circulation

The influence of Greenland's deglaciation on the atmospheric winter and summer circulation of the Arctic have been quantified with the high‐resolution regional atmospheric model HIRHAM4. Greenland's deglaciation exerts a pronounced influence on the atmospheric winter circulation of the Arctic. The land areas over Siberia and the Canadian archipelago are warmed by up to 5°C. Parts of the Atlantic and the Arctic Ocean are cooled by up to 3°C. A north‐eastward shift of the storm tracks occurs over the North Atlantic as well as an increase of synoptic activity over Alaska. The pronounced P‐E changes connected with shifts in the synoptic storm tracks during winter would have important consequences for the atmospheric freshwater input into the Arctic Ocean and the Nordic sea with the potential to cause variability in the Arctic Ocean dynamics on centennial to millennial time scales. The significant differences between simulations with and without Greenland result in a decrease of the geopotential height and a dominant barotropic response of the Arctic atmosphere. These changes correspond to an enhanced winter polar vortex and stratospheric conditions more favorable for large Arctic ozone losses.

Trend in Northern Hemisphere Winter Atmospheric Circulation during the Last Half of the Twentieth Century

Abstract During the last half century, the trend in the Northern Hemisphere tropospheric circulation has been associated with a deepening of both the Aleutian and Icelandic lows, a pattern akin to the “Cold Ocean Warm Land” (COWL) pattern. A simplified dynamical model is used to show that the observed simultaneous deepening trend in both the Aleutian and Icelandic lows can be largely explained as a hemispheric planetary wave response to tropical diabatic forcing in the Indo–Pacific region. In the model, the extratropical storm tracks play a role in modulating the wave train, tending to enhance (weaken) the anomalous Icelandic (Aleutian) low in the North Atlantic (North Pacific) sector. The model results also suggest two ways in which the circulation trend over the North Atlantic sector could have been influenced by tropical forcing: one a direct, linear planetary wave response from the eastern tropical Pacific and the other an indirect response of the North Atlantic storm track to tropical forcing over th...

Polar MM5 Simulations of the Winter Climate of the Laurentide Ice Sheet at the LGM*

Optimized regional climate simulations are conducted using the Polar MM5, a version of the fifth-generation Pennsylvania State University‐NCAR Mesoscale Model (MM5), with a 60-km horizontal resolution domain over North America during the Last Glacial Maximum (LGM, 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). The objective is to describe the LGM annual cycle at high spatial resolution with an emphasis on the winter atmospheric circulation. Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. Polar MM5 produces a substantially different atmospheric response to the LGM boundary conditions than CCM3 and other recent GCM simulations. In particular, from November to April the upper-level flow is split around a blocking anticyclone over the LIS, with a northern branch over the Canadian Arctic and a southern branch impacting southern North America. The split flow pattern is most pronounced in January and transitions into a single, consolidated jet stream that migrates northward over the LIS during summer. Sensitivity experiments indicate that the winter split flow in Polar MM5 is primarily due to mechanical forcing by LIS, although model physics and resolution also contribute to the simulated flow configuration. Polar MM5 LGM results are generally consistent with proxy climate estimates in the western United States, Alaska, and the Canadian Arctic and may help resolve some long-standing discrepancies between proxy data and previous simulations of the LGM climate.

Wintertime surface temperature in Egypt in relation to the associated atmospheric circulation

AbstractMean wintertime temperatures (December, January, February) recorded during the period 1905–2000 at 18 weather stations distributed across Egypt were analysed to reveal spatial and temporal patterns of long‐term trends. The relationship between winter atmospheric circulation indices and winter temperature in Egypt is examined using correlation analysis. The atmospheric circulation is represented by four indices: the well‐known El Niño–southern oscillation (ENSO), North Atlantic oscillation (NAO) index, East Atlantic–West Russia (EAWR) index, and East Atlantic (EA) index.Surface temperature is a stable climatic element whose coefficient of variation (COV) is lower during winter. A statistically significant relation between COV and latitude indicates that stations in the south, Upper Egypt, are more variable than stations in the north, Lower Egypt. Increasing and decreasing winter surface temperature trends were found. In general, wintertime temperature has increased (warming) at most stations. Decreasing trends (cooling) are observed mainly over Upper Egypt. The upward trends in mean winter temperature during the 1910s–30s, mid 1970s, and early 1980s–2000 and the downward trends during the 1940s and 1960s are prominent features of the temporal distributions. The warming period that occurred early in the century may be explained by changes in circulation. Striking upward trends are most remarkable during the last 20 years. This could be attributed not only to human activities, but also to atmospheric circulation changes. No detectable connection between Egypt temperature and either ENSO or EA index was found during winter. A statistically significant negative relationship between winter temperature and winter NAO index can be observed. The NAO index is more dominant in determining winter temperature than ENSO circulation. A significantly stronger negative relationship between temperature over Egypt and the winter EAWR index values is detected. Copyright © 2004 Royal Meteorological Society

Simulating the winter North Atlantic Oscillation: the roles of internal variability and greenhouse gas forcing

Analysis of simulations with seven coupled climate models demonstrates that the observed variations in the winter North Atlantic Oscillation (NAO), particularly the increase from the 1960s to the 1990s, are not compatible with either the internally generated variability nor the response to increasing greenhouse gas forcing simulated by these models. The observed NAO record can be explained by a combination of internal variability and greenhouse gas forcing, though only by the models that simulate the strongest variability and the strongest response. These models simulate inter-annual variability of the NAO index that is significantly greater than that observed, and can no longer explain the observed record if the simulated NAO indices are scaled so that they have the same high-frequency variance as that observed. It is likely, therefore, that other external forcings also contributed to the observed NAO index increase, unless the climate models are deficient in their simulation of inter-decadal NAO variability or their simulation of the response to greenhouse gas forcing. These conclusions are based on a comprehensive analysis of the control runs and transient greenhouse-gas-forced simulations of the seven climate models. The simulations of mean winter circulation and its pattern of inter-annual variability are very similar to the observations in the Atlantic half of the Northern Hemisphere. The winter atmospheric circulation response to increasing greenhouse gas forcing shows little inter-model similarity at the regional scale, and the NAO response is model-dependent and sensitive to the index used to measure it. At the largest scales, however, sea level pressure decreases over the Arctic Ocean in all models and increases over the Mediterranean Sea in six of the seven models, so that there is an increase of the NAO in all models when measured using a pattern-based index.

Predicting East Coast Winter Storm Frequencies from Midtropospheric Geopotential Height Patterns

Abstract Relationships between a previously developed U.S. East Coast winter storm (ECWS) climatology and atmospheric circulation patterns derived from the NCEP–NCAR reanalysis data during 1958–97 have been investigated. Composites of normalized height difference, defined as the difference in monthly mean standardized 500-mb height anomalies between active and inactive ECWS seasons, reveal two dipoles, one over the eastern North Pacific Ocean and the other over the central North Atlantic Ocean, which may have seasonal forecasting utility. An October-mean dipolar pattern yielding stronger (weaker) than normal 500-mb geostrophic westerlies over the eastern Pacific (North Atlantic) skillfully predicts, in the data, greater than normal ECWS activity during the following November–April period. Active ECWS seasons follow other combinations of October-mean dipoles in the data, depending upon the phase of the El Nino–Southern Oscillation. On shorter time scales, 7-day-mean ECWS activity was positively (negatively...

Forcing of Northern Hemisphere Climate Trends

The impact of observed global SST trends during the second half of the twentieth century on the Northern Hemisphere extratropical winter atmospheric circulation is investigated using ensembles of simulations with the Center for Ocean‐Land‐Atmosphere Studies (COLA) atmospheric GCM. In contrast to some other studies, the simulated ensemble mean 500-hPa trends in the North Atlantic sector do not resemble the observed trend. However, the intraensemble variability of the trends is large, with the dominant structure of that variability resembling the Arctic Oscillation ‘‘annular mode.’’ The model results are consistent with the interpretation that the observed trend is dominated by the forced signal in the Pacific‐North America sector, while over the rest of the Northern Hemisphere, and especially the North Atlantic sector, the trend is primarily interdecadal timescale internal atmospheric noise with an annular structure. In order to diagnose the origins of the forced component of the model trend, a series of equilibrium response simulations is performed using constant-in-time SST anomalies with the structure of the trend superimposed on the annually varying climatological SST. It is found that the SST trend in the latitude belt from 20 8 St o 208N is responsible for forcing much of the extratropical trend, and that the dominant tropical forcing is the SST trend in the Indian Ocean/western Pacific and eastern Pacific sectors. The idealized experiments show that the precipitation response in the Tropics is linearly related to the SST trend, and that the NH December‐January‐ February height response to SST anomalies in various regions is quasi-linear. Some additional analysis and interpretation is given. The extratropical response to low-latitude SST trends in the idealized experiments has characteristics reminiscent of Rossby wave trains forced by tropical deep convection. The intraensemble variability in the model’s extratropical zonal mean height trend, which cannot be explained by external forcing, appears to be due to variability in the trends of midlatitude eddy stirring. The observed zonal mean trend also shows evidence of forcing by trends in the eddy stirring.

The interpretation of non‐homogeneous hydrometeorological time series: a case study

AbstractLong records of hydrological and hydrometeorological variables are of inestimable value for the planning, design and management of water resource systems. Unfortunately, such long series invariably exhibit inconsistencies and non‐homogeneities arising from a wide variety of causes –for example, changes in instruments and observation practices, and alterations to the general environment of the instruments themselves. Both non‐parametric and parametric statistical tests are available to detect the presence of long‐term movements in recorded time series, but the interpretation of results from such testing has often to be carried out in the absence of sufficient station metadata. A case study of precipitation records for 20 stations in Scotland over the period from 1961–99 has demonstrated that the results from statistical testing for inconsistency and non‐homogeneity should also be interpreted in the context of prevailing weather systems. In particular, the increases in both annual and winter (Dec–Feb) rainfall totals recorded during this period at sites in western Scotland appear to reflect the changes in the winter atmospheric circulation over the Northern Hemisphere as encapsulated in the North Atlantic Oscillation Index (NAOI). Sustained periods of positive values of the NAOI, albeit less severe than during those of the 1970s and 1980s, are evident in the historical record of this index. The trends in rainfall totals identified could therefore be interpreted as arising from natural variability or even greenhouse gas forcing rather than from any inconsistency and non‐homogeneity. Copyright © 2003 Royal Meteorological Society

Late glacial–Holocene atmospheric circulation and precipitation in the northeast United States inferred from modern calibrated stable oxygen and carbon isotopes

As global climate changes because of anthropogenic influences, it has become critical to better understand past climate and its various forcing mechanisms as a baseline for future comparison. To this end, we present a continental isotopic record from an 11.2-m-long wetland piston core sampled at 10‐50 yr resolution; the core was taken in the heavily populated, economically vibrant northeastern United States (adjacent to Fayetteville Green Lake) and spans 14,600‐3200 cal. yr B.P. We use a historically based correlation between d 18 Ocalcite obtained from individual varves in a box core from Fayetteville Green Lake and winter atmospheric circulation over the northeast United States to examine the way in which changes in winter circulation have influenced d 18 O in precipitation from 14,600 to 3200 cal. yr B.P. Our correlation analysis suggests that in periods during which the circumpolar westerlies are expanded, storms track more frequently from the Gulf of Mexico region, delivering precipitation with relatively high d 18 O values to the study site. By contrast, contracted westerlies result in more frequent low-d 18 Oprecipitation cross-continental storms. By using this relationship we model winter-vortex latitudes over the northeast United States for the prehistoric oxygen isotope record, focusing on millennial-scale