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Jones, Alan G., i Peter J. Savage. "North American Central Plains conductivity anomaly goes east". Geophysical Research Letters 13, nr 7 (lipiec 1986): 685–88. http://dx.doi.org/10.1029/gl013i007p00685.
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Degroot-Hedlin, Catherine, i Steven Constable. "Occam's Inversion and the North American Central Plains Electrical Anomaly." Journal of geomagnetism and geoelectricity 45, nr 9 (1993): 985–99. http://dx.doi.org/10.5636/jgg.45.985.
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Rankin, D., i F. Pascal. "A gap in the North American Central Plains conductivity anomaly". Physics of the Earth and Planetary Interiors 60, nr 1-4 (styczeń 1990): 132–37. http://dx.doi.org/10.1016/0031-9201(90)90255-v.
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Jones, Alan G., Juanjo Ledo i Ian J. Ferguson. "Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed". Canadian Journal of Earth Sciences 42, nr 4 (1.04.2005): 457–78. http://dx.doi.org/10.1139/e05-018.
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Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.
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Cook, Benjamin I., Richard Seager, Ron L. Miller i Joseph A. Mason. "Intensification of North American Megadroughts through Surface and Dust Aerosol Forcing*". Journal of Climate 26, nr 13 (1.07.2013): 4414–30. http://dx.doi.org/10.1175/jcli-d-12-00022.1.
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Abstract Tree-ring-based reconstructions of the Palmer drought severity index (PDSI) indicate that, during the Medieval Climate Anomaly (MCA), the central plains of North America experienced recurrent periods of drought spanning decades or longer. These megadroughts had exceptional persistence compared to more recent events, but the causes remain uncertain. The authors conducted a suite of general circulation model experiments to test the impact of sea surface temperature (SST) and land surface forcing on the MCA megadroughts over the central plains. The land surface forcing is represented as a set of dune mobilization boundary conditions, derived from available geomorphological evidence and modeled as increased bare soil area and a dust aerosol source (32°–44°N, 105°–95°W). In the experiments, cold tropical Pacific SST forcing suppresses precipitation over the central plains but cannot reproduce the overall drying or persistence seen in the PDSI reconstruction. Droughts in the scenario with dust aerosols, however, are amplified and have significantly longer persistence than in other model experiments, more closely matching the reconstructed PDSI. This additional drying occurs because the dust increases the shortwave planetary albedo, reducing energy inputs to the surface and boundary layer. The energy deficit increases atmospheric stability, inhibiting convection and reducing cloud cover and precipitation over the central plains. Results from this study provide the first model-based evidence that dust aerosol forcing and land surface changes could have contributed to the intensity and persistence of the central plains megadroughts, although uncertainties remain in the formulation of the boundary conditions and the future importance of these feedbacks.
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Jones, Alan G., James A. Craven, Gary W. McNeice, Ian J. Ferguson, Trevor Boyce, Colin Farquarson i Rob G. Ellis. "North American Central Plains conductivity anomaly within the Trans-Hudson orogen in northern Saskatchewan, Canada". Geology 21, nr 11 (1993): 1027. http://dx.doi.org/10.1130/0091-7613(1993)021<1027:nacpca>2.3.co;2.
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Evans, Shane, Alan G. Jones, Jessica Spratt i John Katsube. "Central Baffin electromagnetic experiment (CBEX): Mapping the North American Central Plains (NACP) conductivity anomaly in the Canadian arctic". Physics of the Earth and Planetary Interiors 150, nr 1-3 (maj 2005): 107–22. http://dx.doi.org/10.1016/j.pepi.2004.08.032.
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Cook, Benjamin I., Toby R. Ault i Jason E. Smerdon. "Unprecedented 21st century drought risk in the American Southwest and Central Plains". Science Advances 1, nr 1 (luty 2015): e1400082. http://dx.doi.org/10.1126/sciadv.1400082.
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In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for benchmarking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals. This desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100–1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.
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Garcia, Xavier, i Alan G. Jones. "Electromagnetic image of the Trans-Hudson orogen THO94 transect". Canadian Journal of Earth Sciences 42, nr 4 (1.04.2005): 479–93. http://dx.doi.org/10.1139/e05-016.
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The North American Central Plains (NACP) anomaly in enhanced electric conductivity and its relationship with the Paleoproterozoic Trans-Hudson orogen (THO) has been studied under the auspices of Lithoprobe for over a decade. The NACP anomaly was the first geophysical evidence of the existence of the THO beneath the Phanerozoic sediments of the Central Plains. This anomaly, detected geomagnetically in the late 1960s, has been the subject of a number magnetotelluric studies from the early 1980s. The PanCanadian and Geological Survey of Canada experiments in the 1980s and the Lithoprobe experiments in the 1990s together comprise four eastwest and one northsouth regional-scale profiles in Saskatchewan perpendicular to the strike of the orogen. In this paper, data from the northernmost line, coincident with seismic line S2B, are analysed and interpreted, and are shown to be key in determining the northern extension of the NACP anomaly. Dimensionality analysis confirms the rotation of deep crustal structures eastward to Hudson Bay, as earlier proposed on the basis of broad-scale geomagnetic studies. On this profile, as with the profile at the edge of the Paleozoic sediments, the NACP anomaly is imaged as lying within the La Ronge domain, in contact with the Rottenstone domain, and structurally above the Guncoat thrust, a late compressional feature. The location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds, by graphite, or by a combination of both. Our interpretation of the data is consistent with that from other profiles, and suggests that the NACP anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the THO beneath the Hearne craton. On the southern part of this profile, a resistive structure is identified as the Sask craton, suggesting that Proterozoic rocks are above Archean rocks in the THO.
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Wang, Hailan, Siegfried D. Schubert, Randal D. Koster i Yehui Chang. "Phase Locking of the Boreal Summer Atmospheric Response to Dry Land Surface Anomalies in the Northern Hemisphere". Journal of Climate 32, nr 4 (luty 2019): 1081–99. http://dx.doi.org/10.1175/jcli-d-18-0240.1.
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Past modeling simulations, supported by observational composites, indicate that during boreal summer, dry soil moisture anomalies in very different locations within the U.S. continental interior tend to induce the same upper-tropospheric circulation pattern: a high anomaly forms over west-central North America and a low anomaly forms to the east. The present study investigates the causes of this apparent phase locking of the upper-level circulation response and extends the investigation to other land regions in the Northern Hemisphere. The phase locking over North America is found to be induced by zonal asymmetries in the local basic state originating from North American orography. Specifically, orography-induced zonal variations of air temperature, those in the lower troposphere in particular, and surface pressure play a dominant role in placing the soil moisture–forced negative Rossby wave source (dominated by upper-level divergence anomalies) over the eastern leeside of the Western Cordillera, which subsequently produces an upper-level high anomaly over west-central North America, with the downstream anomalous circulation responses phase locked by continuity. The zonal variations of the local climatological atmospheric circulation, manifested as a climatological high over central North America, help shape the spatial pattern of the upper-level circulation responses. Considering the rest of the Northern Hemisphere, the northern Middle East exhibits similar phase locking, also induced by local orography. The Middle Eastern phase locking, however, is not as pronounced as that over North America; North America is where soil moisture anomalies have the greatest impact on the upper-tropospheric circulation.
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Hu, Zeng-Zhen, i Bohua Huang. "Interferential Impact of ENSO and PDO on Dry and Wet Conditions in the U.S. Great Plains". Journal of Climate 22, nr 22 (15.11.2009): 6047–65. http://dx.doi.org/10.1175/2009jcli2798.1.
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Abstract The influence of the El Niño–Southern Oscillation (ENSO) and Pacific decadal oscillation (PDO) interference on the dry and wet conditions in the Great Plains of the United States has been examined using monthly observational datasets. It is shown that both ENSO and PDO can generate a similar pattern of atmospheric and oceanic anomalies over the eastern part of the North Pacific and western North America that has significant impact on the climate over the Great Plains. Furthermore, the relationship between ENSO–PDO and climate anomalies in the Great Plains is intensified when ENSO and PDO are in phase (El Niño and warm PDO or La Niña and cold PDO). On average, anomalies over the Great Plains favor wet (dry) conditions when both ENSO and PDO are in the positive (negative) phase. However, when ENSO and PDO are out of phase, the relationship is weakened and the anomalies over the Great Plains tend toward neutral. Without ENSO, PDO alone does not affect the North American climate significantly. The relationship is quite robust for different seasons, with the strongest effects for the months of spring and the weakest effects for the months of autumn, whereas the months of winter and summer fall in between. The seasonality of the relationship may be associated with the seasonal dependence of the anomalies of general circulation and the pattern of mean seasonal cycle in the North Pacific. The contrasting impact of the interference of ENSO and PDO on the climate anomalies in the Great Plains is associated with differences in the ocean–atmosphere anomalies. When ENSO and PDO are in phase, the sea surface temperature (SST) anomalies extend from the equatorial Pacific to the higher latitudes of the North Pacific via the eastern ocean. The distribution of the corresponding anomalies of sea level pressure (SLP) and the wind at 1000 hPa form an ellipse with a southeast–northwest orientation of the long axis because the SST anomalies promote coherent changes in SLP in the central North Pacific. In the upper troposphere, a similar teleconnection pattern with the same sign generated by ENSO and PDO is overlapped and enhanced, which favors anomaly (dry and wet) conditions in the Great Plains. However, when ENSO and PDO are out of phase, the SST anomalies have the same sign in the tropical and central North Pacific, which is opposite to the anomalies near the west coast of North America. The anomalously cyclonic circulation over the North Pacific is weaker in the out-of-phase situation than in the in-phase situation. The distribution of the anomalies of SLP and the wind at 1000 hPa resembles a circle. Meanwhile, in the upper troposphere, ENSO and PDO generate a similar teleconnection pattern with opposite sign, causing cancellation of the anomalous circulation and favoring neutral climate in the Great Plains.
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Yu, Wandi, Andrew E. Dessler, Mijeong Park i Eric J. Jensen. "Influence of convection on stratospheric water vapor in the North American monsoon region". Atmospheric Chemistry and Physics 20, nr 20 (27.10.2020): 12153–61. http://dx.doi.org/10.5194/acp-20-12153-2020.
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Abstract. We quantify the connection between deep convective occurrence and summertime 100 hPa water vapor anomaly over the North American (NA) region and find substantial consistency between their interannual variations and also that the water vapor mixing ratio over the NA region is up to ∼1 ppmv higher when deep convection occurs. We use a Lagrangian trajectory model to demonstrate that the structure and the location of the NA anticyclone, as well as the tropical upper tropospheric temperature, mediate the moistening impact of convection. The deep convection mainly occurs over the Central Plains region. Most of the convectively moistened air is then transported to the center of the NA anticyclone, and the anticyclonic structure helps maintain high water vapor content there. This explains both the summer seasonal cycle and interannual variability of the convective moistening efficiency in the NA region and can provide valuable insight into modeling stratospheric water vapor.
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Liang, Xin-Zhong, Jinhong Zhu, Kenneth E. Kunkel, Mingfang Ting i Julian X. L. Wang. "Do CGCMs Simulate the North American Monsoon Precipitation Seasonal–Interannual Variability?" Journal of Climate 21, nr 17 (1.09.2008): 4424–48. http://dx.doi.org/10.1175/2008jcli2174.1.
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Abstract This study uses the most recent simulations from all available fully coupled atmosphere–ocean general circulation models (CGCMs) to investigate whether the North American monsoon (NAM) precipitation seasonal–interannual variations are simulated and, if so, whether the key underlying physical mechanisms are correctly represented. This is facilitated by first identifying key centers where observed large-scale circulation fields and sea surface temperatures (SSTs) are significantly correlated with the NAM precipitation averages over the core region (central–northwest Mexico) and then examining if the modeled and observed patterns agree. Two new findings result from the analysis of observed NAM interannual variations. First, precipitation exhibits significantly high positive (negative) correlations with 200-hPa meridional wind centered to the northwest (southeast) of the core region in June and September (July and August). As such, wet conditions are associated with strong anomalous southerly upper-level flow on the northwest flank during the monsoon onset and retreat, but with anomalous northerly flow on the southeast flank, during the peak of the monsoon. They are often identified with a cyclonic circulation anomaly pattern over the central Great Plains for the July–August peak monsoon and, reversely, an anticyclonic anomaly pattern centered over the northern (southern) Great Plains for the June (September) transition. Second, wet NAM conditions in June and July are also connected with a SST pattern of positive anomalies in the eastern Pacific and negative anomalies in the Gulf of Mexico, acting to reduce the climatological mean gradient between the two oceans. This pattern suggests a possible surface gradient forcing that favors a westward extension of the North Atlantic subtropical ridge. These two observed features connected to the NAM serve as the metric for quantitative evaluation of the model performance in simulating the important NAM precipitation mechanisms. Out of 17 CGCMs, only the Meteorological Research Institute (MRI) model with a medium resolution consistently captures the observed NAM precipitation annual cycle (having a realistic amplitude and no phase shift) as well as interannual covariations with the planetary circulation patterns (having the correct sign and comparably high magnitude of correlation) throughout the summer. For the metric of correlations with 200-hPa meridional wind, there is general agreement among all CGCMs with observations for June and September. This may indicate that large-scale forcings dominate interannual variability for the monsoon onset and retreat, while variability of the peak of the monsoon in July and August may be largely influenced by local processes that are more challenging for CGCMs to resolve. For the metric of correlations with SSTs, good agreement is found only in June. These results suggest that the NAM precipitation interannual variability may likely be determined by large-scale circulation anomalies, while its predictability based on remote signals such as SSTs may not be sufficiently robust to be well captured by current CGCMs, with the exception of the June monsoon onset which is potentially more predictable.
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Jones, Alan G., i James A. Craven. "The North American Central Plains conductivity anomaly and its correlation with gravity, magnetic, seismic, and heat flow data in Saskatchewan, Canada". Physics of the Earth and Planetary Interiors 60, nr 1-4 (styczeń 1990): 169–94. http://dx.doi.org/10.1016/0031-9201(90)90260-5.
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Flanagan, Paul X., Jeffrey B. Basara, Jason C. Furtado, Elinor R. Martin i Xiangming Xiao. "Role of Sea Surface Temperatures in Forcing Circulation Anomalies Driving U.S. Great Plains Pluvial Years". Journal of Climate 32, nr 20 (23.09.2019): 7081–100. http://dx.doi.org/10.1175/jcli-d-18-0726.1.
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Abstract In the U.S. Great Plains (GP), diagnosing precipitation variability is key in developing an understanding of the present and future availability of water in the region. Building on previous work investigating U.S. GP pluvial years, this study uses ERA twentieth century (ERA-20C) reanalysis data to investigate key circulation anomalies driving GP precipitation anomalies during a subset of GP pluvial years (called in this paper Pattern pluvial years). With previous research showing links between tropical Pacific sea surface temperature (SST) anomalies and GP climate variability, this study diagnoses the key circulation anomalies through an analysis of SSTs and their influence on the atmosphere. Results show that during Pattern southern Great Plains (SGP) pluvial years, central tropical Pacific SST anomalies are coincident with key atmospheric anomalies across the Pacific basin and North America. During northern Great Plains (NGP) Pattern pluvial years, no specific pattern of oceanic anomalies emerges that forces the circulation anomaly feature inherent in specific NGP pluvial years. Utilizing the results for SGP pluvial years, a conceptual model is developed detailing the identified pathway for the occurrence of circulation patterns that are favorable for pluvial years over the SGP. Overall, results from this study show the importance of the identified SGP atmospheric anomaly signal and the potential for predictability of such events.
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Cook, Benjamin I., Jason E. Smerdon, Richard Seager i Edward R. Cook. "Pan-Continental Droughts in North America over the Last Millennium*". Journal of Climate 27, nr 1 (1.01.2014): 383–97. http://dx.doi.org/10.1175/jcli-d-13-00100.1.
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Abstract Regional droughts are common in North America, but pan-continental droughts extending across multiple regions, including the 2012 event, are rare relative to single-region events. Here, the tree-ring-derived North American Drought Atlas is used to investigate drought variability in four regions over the last millennium, focusing on pan-continental droughts. During the Medieval Climate Anomaly (MCA), the central plains (CP), Southwest (SW), and Southeast (SE) regions experienced drier conditions and increased occurrence of droughts and the Northwest (NW) experienced several extended pluvials. Enhanced MCA aridity in the SW and CP manifested as multidecadal megadroughts. Notably, megadroughts in these regions differed in their timing and persistence, suggesting that they represent regional events influenced by local dynamics rather than a unified, continental-scale phenomena. There is no trend in pan-continental drought occurrence, defined as synchronous droughts in three or more regions. SW, CP, and SE (SW+CP+SE) droughts are the most common, occurring in 12% of all years and peaking in prevalence during the twelfth and thirteenth centuries; patterns involving three other regions occur in about 8% of years. Positive values of the Southern Oscillation index (La Niña conditions) are linked to SW, CP, and SE (SW+CP+SE) droughts and SW, CP, and NW (SW+CP+NW) droughts, whereas CP, NW, and SE (CP+NW+SE) droughts are associated with positive values of the Pacific decadal oscillation and Atlantic multidecadal oscillation. While relatively rare, pan-continental droughts are present in the paleo record and are linked to defined modes of climate variability, implying the potential for seasonal predictability. Assuming stable drought teleconnections, these events will remain an important feature of future North American hydroclimate, possibly increasing in their severity in step with other expected hydroclimate responses to increased greenhouse gas forcing.
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Weaver, Scott J., Siegfried Schubert i Hailan Wang. "Warm Season Variations in the Low-Level Circulation and Precipitation over the Central United States in Observations, AMIP Simulations, and Idealized SST Experiments". Journal of Climate 22, nr 20 (15.10.2009): 5401–20. http://dx.doi.org/10.1175/2009jcli2984.1.
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Abstract Sea surface temperature (SST) linkages to central U.S. low-level circulation and precipitation variability are investigated from the perspective of the Great Plains low-level jet (GPLLJ) and recurring modes of SST variability. The observed and simulated links are first examined via GPLLJ index regressions to precipitation, SST, and large-scale circulation fields in the NCEP–NCAR and North American Regional Reanalysis (NARR) reanalyses, and NASA’s Seasonal-to-Interannual Prediction Project (NSIPP1) and Community Climate Model, version 3 (CCM3) ensemble mean Atmospheric Model Intercomparison Project (AMIP) simulations for the 1949–2002 (1979–2002 for NARR) period. Characteristics of the low-level circulation and its related precipitation are further examined in the U.S. Climate Variability and Predictability (CLIVAR) Drought Working Group idealized climate model simulations (NSIPP1 and CCM3) forced with varying polarities of recurring modes of SST variability. It is found that the observed and simulated correlations of the GPLLJ index to Atlantic and Pacific SST, large-scale atmospheric circulation, and Great Plains precipitation variability for 1949–2002 are robust during the July–September (JAS) season and show connections to a distinct global-scale SST variability pattern, one similar to that used in forcing the NSIPP1 and CCM3 idealized simulations, and a subtropical Atlantic-based sea level pressure (SLP) anomaly with a maximum over the Gulf of Mexico. The idealized simulations demonstrate that a warm Pacific and/or a cold Atlantic are influential over regional hydroclimate features including the monthly preference for maximum GPLLJ and precipitation in the seasonal cycle. Furthermore, it appears that the regional expression of globally derived SST variability is important for generating an anomalous atmospheric low-level response of consequence to the GPLLJ, especially when the SST anomaly is positioned over a regional maximum in climatological SST, and in this case the Western Hemisphere warm pool.
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Maidens, J. M., i K. V. Paulson. "A magnetotelluric investigation under the Williston Basin of southeastern Saskatchewan". Canadian Journal of Earth Sciences 25, nr 1 (1.01.1988): 60–67. http://dx.doi.org/10.1139/e88-006.
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A magnetotelluric (MT) survey using naturally occurring ultra low frequency (ULF) and extremely low frequency (ELF) sources was conducted in the frequency range of 0.5 mHz to 20 Hz in order to locate the western edge and the depth of the North American Central Plains (NACP) conductivity anomaly in the Bengough area of southeastern Saskatchewan. The data base was also used to evaluate the complex singular-value decomposition (CSVD) method of MT processing and to corroborate certain geologic interpretations in this part of the Williston Basin.Modelling of the resulting impedance tensors revealed a deep (10–15 km) zone with resistivity (35–85 Ω∙m) significantly lower than typical values (1000–1500 Ω∙m) obtained from a borehole resistivity log of the top 30 m of the Precambrian at a depth of 2.3 km. An increase in depth (to 20 km) and resistivity (150–275 Ω∙m) of this deep zone measured at the survey's west end was interpreted as indicating the anomaly's western edge. The CSVD processing of the data did not show any particular advantages over the conventional cross-spectral method.
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Linkin, Megan E., i Sumant Nigam. "The North Pacific Oscillation–West Pacific Teleconnection Pattern: Mature-Phase Structure and Winter Impacts". Journal of Climate 21, nr 9 (1.05.2008): 1979–97. http://dx.doi.org/10.1175/2007jcli2048.1.
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Abstract The North Pacific Oscillation (NPO) in sea level pressure and its upper-air geopotential height signature, the west Pacific (WP) teleconnection pattern, constitute a prominent mode of winter midlatitude variability, the NPO/WP. Its mature-phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the Pacific–North American variability pattern. NPO/WP variability, primarily on subseasonal time scales, is characterized by a large-scale meridional dipole in SLP and geopotential height over the Pacific and is linked to meridional movements of the Asian–Pacific jet and Pacific storm track modulation. The hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing. The NPO/WP divergent circulation is thermal wind restoring, pointing to independent forcing of jet fluctuations. Intercomparison of sea level pressure, geopotential height, and zonal wind anomaly structure reveals that NPO/WP is a basin analog of the NAO, which is not surprising given strong links to storm track variability in both cases. The NPO/WP variability is influential: its impact on Alaskan, Pacific Northwest, Canadian, and U.S. winter surface air temperatures is substantial—more than that of PNA or ENSO. It is likewise more influential on the Pacific Northwest, western Mexico, and south-central Great Plains winter precipitation. Finally, and perhaps, most importantly, NPO/WP is strongly linked to marginal ice zone variability of the Arctic seas with an influence that surpasses that of other Pacific modes. Although NPO/WP variability and impacts have not been as extensively analyzed as its Pacific cousins (PNA, ENSO), it is shown to be more consequential for Arctic sea ice and North American winter hydroclimate.
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Li, Funing, Daniel R. Chavas, Kevin A. Reed i Daniel T. Dawson II. "Climatology of Severe Local Storm Environments and Synoptic-Scale Features over North America in ERA5 Reanalysis and CAM6 Simulation". Journal of Climate 33, nr 19 (1.10.2020): 8339–65. http://dx.doi.org/10.1175/jcli-d-19-0986.1.
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AbstractSevere local storm (SLS) activity is known to occur within specific thermodynamic and kinematic environments. These environments are commonly associated with key synoptic-scale features—including southerly Great Plains low-level jets, drylines, elevated mixed layers, and extratropical cyclones—that link the large-scale climate to SLS environments. This work analyzes spatiotemporal distributions of both extreme values of SLS environmental parameters and synoptic-scale features in the ERA5 reanalysis and in the Community Atmosphere Model, version 6 (CAM6), historical simulation during 1980–2014 over North America. Compared to radiosondes, ERA5 successfully reproduces SLS environments, with strong spatiotemporal correlations and low biases, especially over the Great Plains. Both ERA5 and CAM6 reproduce the climatology of SLS environments over the central United States as well as its strong seasonal and diurnal cycles. ERA5 and CAM6 also reproduce the climatological occurrence of the synoptic-scale features, with the distribution pattern similar to that of SLS environments. Compared to ERA5, CAM6 exhibits a high bias in convective available potential energy over the eastern United States primarily due to a high bias in surface moisture and, to a lesser extent, storm-relative helicity due to enhanced low-level winds. Composite analysis indicates consistent synoptic anomaly patterns favorable for significant SLS environments over much of the eastern half of the United States in both ERA5 and CAM6, though the pattern differs for the southeastern United States. Overall, our results indicate that both ERA5 and CAM6 are capable of reproducing SLS environments as well as the synoptic-scale features and transient events that generate them.
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Fowler, C. MR, D. Stead, B. I. Pandit, B. W. Janser, E. G. Nisbet i G. Nover. "A database of physical properties of rocks from the Trans-Hudson Orogen, Canada". Canadian Journal of Earth Sciences 42, nr 4 (1.04.2005): 555–72. http://dx.doi.org/10.1139/e05-006.
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A physical properties database of rock types from the Trans-Hudson Orogen provides information for interpretation of geophysical surveys over the Trans-Hudson Orogen. Measurements have been made on 320 samples (all reduced to core) representing metamorphosed Archaean and juvenile Proterozoic orogenic rocks. Water saturated densities were generally between 2600 and 3100 kg m3. In most cases, the porosity was < 1%. Except for a few samples, magnetic susceptibility ranged from 20 to 4000 × 106 SI units. P- and S-wave velocities were made under maximum uniaxial stress and triaxial stresses equivalent to depths of ca. 4 km. P- and S-wave velocities measured were 57 km s1 and 34 km s1, respectively. Electrical resistivity measurements were made at room temperature from 5 Hz to 10 kHz after samples were oven dried and after saturation in solutions with salinity between 0.0 and 1.0 mol/L. Increasing salinity caused a reduction in resistivity. The porosityresistivity data is in reasonable overall agreement with Archie's Law for all rock types. A minimum value of 50 Ω m was obtained from samples not containing significant sulphide minerals or graphite. For sulphide and graphite-bearing samples, resistivity was as low as 1 Ω m. The resistivity data are consistent with the hypothesis that North American Central Plains (NACP) conductivity anomaly could be due to the presence of graphite- and (or) sulphide-rich bodies or saline pore fluids in the crust. Thermal conductivity measurements made using a "divided-bar" apparatus yielded values between 1 and 5 W m1 K1.
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Halpert, Michael S., i Gerald D. Bell. "Climate Assessment for 1996". Bulletin of the American Meteorological Society 78, nr 5s (1.05.1997): S1—S50. http://dx.doi.org/10.1175/1520-0477-78.5s.s1.
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The climate of 1996 can be characterized by several phenomena that reflect substantial deviations from the mean state of the atmosphere persisting from months to seasons. First, mature cold-episode conditions persisted across the tropical Pacific from November 1995 through May 1996 and contributed to large-scale anomalies of atmospheric circulation, temperature, and precipitation across the Tropics, the North Pacific and North America. These anomalies were in many respects opposite to those that had prevailed during the past several years in association with a prolonged period of tropical Pacific warm-episode conditions (ENSO). Second, strong tropical intraseasonal (Madden–Julian oscillations) activity was observed during most of the year. The impact of these oscillations on extratropical circulation variability was most evident late in the year in association with strong variations in the eastward extent of the East Asian jet and in the attendant downstream circulation, temperature, and precipitation patterns over the eastern North Pacific and central North America. Third, a return to the strong negative phase of the atmospheric North Atlantic oscillation (NAO) during November 1995–February 1996, following a nearly continuous 15-yr period of positive-phase NAO conditions, played a critical role in affecting temperature and precipitation patterns across the North Atlantic, Eurasia, and northern Africa. The NAO also contributed to a significant decrease in wintertime temperatures across large portions of Siberia and northern Russia from those that had prevailed during much of the 1980s and early 1990s. Other regional aspects of the short-term climate during 1996 included severe drought across the southwestern United States and southern plains states during October 1995–May 1996, flooding in the Pacific Northwest region of the United States during the 1995/96 and 1996/97 winters, a cold and extremely snowy 1995/96 winter in the eastern United States, a second consecutive year of above-normal North Atlantic hurricane activity, near-normal rains in the African Sahel, above-normal rainfall across southeastern Africa during October 1995–April 1996, above-normal precipitation for most of the year across eastern and southeastern Australia following severe drought in these areas during 1995, and generally nearnormal monsoonal rains in India with significantly below-normal rainfall in Bangladesh and western Burma. The global annual mean surface temperature for land and marine areas during 1996 averaged 0.21°C above the 1961–90 base period means. This is a decrease of 0.19°C from the record warm year of 1995 but was still among the 10 highest values observed since 1860. The global land-only temperature for 1996 was 0.06°C above normal and was the lowest anomaly observed since 1985 (−0.11°C). Much of this relative decrease in global temperatures occurred in the Northern Hemisphere extratropics, where land-only temperatures dropped from 0.42°C above normal in 1995 to 0.04°C below normal in 1996. The year also witnessed a continuation of near-record low ozone amounts in the Southern Hemisphere stratosphere, along with an abnormally prolonged appearance of the “ozone hole” into early December. The areal extent of the ozone hole in November and early December exceeded that previously observed for any such period on record. However, its areal extent at peak amplitude during late September–early October was near that observed during the past several years.
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Seager, Richard, i Martin Hoerling. "Atmosphere and Ocean Origins of North American Droughts*". Journal of Climate 27, nr 12 (5.06.2014): 4581–606. http://dx.doi.org/10.1175/jcli-d-13-00329.1.
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Abstract The atmospheric and oceanic causes of North American droughts are examined using observations and ensemble climate simulations. The models indicate that oceanic forcing of annual mean precipitation variability accounts for up to 40% of total variance in northeastern Mexico, the southern Great Plains, and the Gulf Coast states but less than 10% in central and eastern Canada. Observations and models indicate robust tropical Pacific and tropical North Atlantic forcing of annual mean precipitation and soil moisture with the most heavily influenced areas being in southwestern North America and the southern Great Plains. In these regions, individual wet and dry years, droughts, and decadal variations are well reproduced in atmosphere models forced by observed SSTs. Oceanic forcing was important in causing multiyear droughts in the 1950s and at the turn of the twenty-first century, although a similar ocean configuration in the 1970s was not associated with drought owing to an overwhelming influence of internal atmospheric variability. Up to half of the soil moisture deficits during severe droughts in the southeast United States in 2000, Texas in 2011, and the central Great Plains in 2012 were related to SST forcing, although SST forcing was an insignificant factor for northern Great Plains drought in 1988. During the early twenty-first century, natural decadal swings in tropical Pacific and North Atlantic SSTs have contributed to a dry regime for the United States. Long-term changes caused by increasing trace gas concentrations are now contributing to a modest signal of soil moisture depletion, mainly over the U.S. Southwest, thereby prolonging the duration and severity of naturally occurring droughts.
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MORSE, Caleb A., i Douglas LADD. "Staurothele nemorum sp. nov. (Ascomycota: Verrucariaceae), with a revised key to North American Staurothele s. lat." Lichenologist 51, nr 6 (listopad 2019): 495–506. http://dx.doi.org/10.1017/s0024282919000410.
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AbstractStaurothele nemorum is described as new to science from the southern Great Plains of central North America. The species is characterized by a thin, areolate, epilithic thallus, sessile perithecia, globose to oblong hymenial algal cells and 8-spored asci. Staurothele hymenogonia is restored to the North American flora, based on material from the south-western Great Plains. An updated key to North American members of Staurothele s. lat. is provided.
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Thomas, M. D., V. L. Sharpton i R. A. F. Grieve. "Gravity patterns and Precambrian structure in the North American Central Plains". Geology 15, nr 6 (1987): 489. http://dx.doi.org/10.1130/0091-7613(1987)15<489:gpapsi>2.0.co;2.
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Ting, Mingfang, i Hailan Wang. "The Role of the North American Topography on the Maintenance of the Great Plains Summer Low-Level Jet*". Journal of the Atmospheric Sciences 63, nr 3 (1.03.2006): 1056–68. http://dx.doi.org/10.1175/jas3664.1.
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Abstract Summer precipitation over the central United States depends strongly on the strength of the Great Plains low-level jet (LLJ). The Geophysical Fluid Dynamics Laboratory’s new generation of the atmospheric general circulation model (GCM) and the linear and nonlinear stationary wave models are used in this study to examine the role of North American topography in maintaining the Great Plains summer mean LLJ and precipitation. Atmospheric GCM experiments were first performed with and without the North American topography and with prescribed climatological sea surface temperatures. Results show that the Great Plains LLJ disappears completely in the experiment when the North American topography is removed, while the summer seasonal mean LLJ is well simulated in the experiment with full earth topography. In the absence of the North American topography, the summer precipitation is significantly reduced over the central United States and increased along the Gulf States and northeast Mexico. Linear and nonlinear stationary wave models are used to determine the physical mechanisms through which the North American topography maintains the Great Plains time mean LLJ. Possible mechanisms include the physical blocking of the topography and the induced flow over and around the mountains, the thermal effect due to the elevation of the topography, and the transient thermal and vorticity forcing due to the modification of transient eddy activities in the presence of the topography. The linear and nonlinear model results indicate that the dominant mechanism for maintaining the time mean Great Plains LLJ is through the nonlinear effect of the trade wind along the southern flank of the North Atlantic subtropical high encountering the east slope of the Sierra Oriental and causing the flow to turn northward. As the flow turns north along the east slope of the North American topography, it obtains anticyclonic shear vorticity and thus the LLJ. The effect of the thermal forcing is negligible, while the effect of transient forcing is only important in extending the jet farther northward and eastward. The results suggest that variations in the strength of the North Atlantic subtropical anticyclone and the associated trade wind over the Caribbean Sea and the Gulf of Mexico may be important for understanding the interannual variation of the Great Plains LLJ and U.S. precipitation.
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Adair, Mary J., Neil A. Duncan, Danielle N. Young, Steven R. Bozarth i Robert K. Lusteck. "Early Maize (Zea mays) in the North American Central Plains: The Microbotanical Evidence". American Antiquity 87, nr 2 (kwiecień 2022): 333–51. http://dx.doi.org/10.1017/aaq.2021.152.
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Artifacts, including ceramics, ground stone, and soil samples, as well as dental calculus, recovered from sites in the eastern North American central Plains were submitted to multiple laboratories for analysis of microbotanical remains. Direct accelerator mass spectrometer (AMS) dates of 361–197 cal BC provide evidence for the earliest use of maize (Zea mays ssp. mays) in this region. Squash (Cucurbita sp.), wild rice (cf. Zizania spp.), and palm (Arecaceae sp.) microremains were also found. This research adds to the growing evidence of the importance of microbotanical analysis in documenting plant use and in the identification of early maize. The combined data on early maize from the eastern Plains adds to our understanding of the timing and dispersal of this crop out of the American Southwest. Alternative explanations for the adoption and early use of maize by eastern central Plains communities include its value as a secondary resource, as an addition to an existing farming strategy, or as a component of Middle Woodland rituals.
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Hu, Qi, i Michael C. Veres. "Atmospheric Responses to North Atlantic SST Anomalies in Idealized Experiments. Part II: North American Precipitation". Journal of Climate 29, nr 2 (11.01.2016): 659–71. http://dx.doi.org/10.1175/jcli-d-14-00751.1.
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Abstract This is the second part of a two-part paper that addresses deterministic roles of the sea surface temperature (SST) anomalies associated with the Atlantic multidecadal oscillation (AMO) in variations of atmospheric circulation and precipitation in the Northern Hemisphere, using a sequence of idealized model runs at the spring equinox conditions. This part focuses on the effect of the SST anomalies on North American precipitation. Major results show that, in the model setting closest to the real-world situation, a warm SST anomaly in the North Atlantic Ocean causes suppressed precipitation in central, western, and northern North America but more precipitation in the southeast. A nearly reversed pattern of precipitation anomalies develops in response to the cold SST anomaly. Further examinations of these solutions reveal that the response to the cold SST anomaly is less stable than that to the warm SST anomaly. The former is “dynamically charged” in the sense that positive eddy kinetic energy (EKE) exists over the continent. The lack of precipitation in its southeast is because of an insufficient moisture supply. In addition, the results show that the EKE of the short- (2–6 day) and medium-range (7–10 day) weather-producing processes in North America have nearly opposite signs in response to the same cold SST anomaly. These competing effects of eddies in the dynamically charged environment (elevated sensitivity to moisture) complicate the circulation and precipitation responses to the cold SST anomaly in the North Atlantic and may explain why the model results show more varying precipitation anomalies (also confirmed by statistical test results) during the cold than the warm SST anomaly, as also shown in simulations with more realistic models. Results of this study indicate a need to include the AMO in the right context with other forcings in an effort to improve understanding of interannual-to-multidecadal variations in warm season precipitation in North America.
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Ladwig, William C., i David J. Stensrud. "Relationship between Tropical Easterly Waves and Precipitation during the North American Monsoon". Journal of Climate 22, nr 2 (15.01.2009): 258–71. http://dx.doi.org/10.1175/2008jcli2241.1.
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Abstract Relationships between tropical easterly waves (TEWs) and precipitation over Mexico and the United States are examined during the North American monsoon (NAM). The National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data are used to identify 137 TEWs that cross Mexico north of 20°N after monsoon onset over a 31-yr period from 1975 to 2005. Mean precipitation anomalies over two-day periods both before and after TEW passage are determined using Climate Prediction Center daily precipitation analyses. Results indicate that positive precipitation anomalies occur along the west coast of Mexico and extending into the west-central United States in association with TEW passage. Negative precipitation anomalies are found in the south-central United States. These precipitation anomaly patterns share many similarities to precipitation anomaly patterns previously defined in association with gulf surge events. On longer time scales, correlations between the total number of these northern TEWs crossing Mexico and 90-day monsoon period precipitation anomalies are also examined. An out-of-phase relationship is found between monsoon period precipitation anomalies in the southwestern and south-central United States, suggesting that increasing the number of northern TEWs crossing Mexico leads to enhanced monsoon period rainfall in Arizona and New Mexico and reduced monsoon period rainfall in Texas and Oklahoma. Thus, these northern TEWs likely play an important role in producing the distribution of precipitation throughout the NAM region and the south-central United States during the monsoon season, and extended-range predictions of northern TEW frequency may lead to improved seasonal rainfall anomaly forecasts in these regions.
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Meltzer, David J. "Human Responses to Middle Holocene (Altithermal) Climates on the North American Great Plains". Quaternary Research 52, nr 3 (listopad 1999): 404–16. http://dx.doi.org/10.1006/qres.1999.2067.
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The climate of the Great Plains during the middle Holocene varied considerably, but overall it was marked by a north–south gradient of increasingly warmer and drier conditions, with a reduction in effective moisture, surface water, and resource abundance, and an increase in resource patchiness, sediment weathering, erosion, and aeolian activity. Pronounced drought conditions were most evident on the Southern High Plains. Understanding the human responses to middle Holocene climates is complicated by a lack of archaeological data, which is partly a result of geomorphic processes that removed or deeply buried sites of this age, and by the varying adaptive responses of hunter-gatherers during this period. On the Southern High Plains, where drought was most severe, surface and groundwater sources dried and bison populations were diminished, prompting substantial adaptive changes, including local abandonment, well-digging to tap underground water, and a widening of the diet breadth to incorporate higher-cost, lower-return seed and plant resources. Sites of this age on the Central and Northern Plains also show a possible increase in diet breadth (with the incorporation of plant foods in the diet), and perhaps changes in settlement mobility (including possible shift into higher elevation areas, or mapping-on to extant rivers and springs). But linking those changes to middle Holocene drought is less straightforward.
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Harding, Keith J., i Peter K. Snyder. "The Relationship between the Pacific–North American Teleconnection Pattern, the Great Plains Low-Level Jet, and North Central U.S. Heavy Rainfall Events*". Journal of Climate 28, nr 17 (1.09.2015): 6729–42. http://dx.doi.org/10.1175/jcli-d-14-00657.1.
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Abstract This study demonstrates the relationship between the Pacific–North American (PNA) teleconnection pattern and the Great Plains low-level jet (GPLLJ). The negative phase of the PNA, which is associated with lower heights over the Great Plains and ridging in the southeastern United States, enhances the GPLLJ by increasing the pressure gradient within the GPLLJ on 6-hourly to monthly time scales. Strong GPLLJ events predominantly occur when the PNA is negative. Warm-season strong GPLLJ events with a very negative PNA (<−1) are associated with more persistent, longer wavelength planetary waves that increase the duration of GPLLJ events and enhance precipitation over the north central United States. When one considers the greatest 5-day north central U.S. precipitation events, a large majority occur when the PNA is negative, with most exhibiting a very negative PNA. Stronger moisture transport during heavy rainfall events with a very negative PNA decreases the precipitation of locally derived moisture compared to events with a very positive PNA. The PNA becomes negative 2–12 days before heavy rainfall events and is very negative within two weeks of 78% of heavy rainfall events in the north central United States, a finding that could be used to improve medium-range forecasts of heavy rainfall events.
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Xu, Min, Xin-Zhong Liang, Arthur Samel i Wei Gao. "MODIS Consistent Vegetation Parameter Specifications and Their Impacts on Regional Climate Simulations". Journal of Climate 27, nr 22 (4.11.2014): 8578–96. http://dx.doi.org/10.1175/jcli-d-14-00082.1.
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Abstract A consistent set of Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation parameters, including leaf and stem area index (LAI and SAI, respectively), land-cover category (LCC), fractional vegetation cover (FVC), and albedo parameterization are developed, and their impacts on North American regional climate are evaluated based on 10-yr Climate–Weather and Research Forecasting Model (CWRF) simulations. As compared with the previous Advanced Very High Resolution Radiometer (AVHRR) set, MODIS LCC increases grassland and cropland fractions in the central Great Plains and Midwest, respectively. Evergreen needleleaf forest converts to mixed forest in the Southeast, and mixed forest converts to evergreen needleleaf in Canada. FVC decreases by 0.05–0.3 over the central Great Plains but increases by 0.1–0.35 over the northern Rocky Mountains, Canada, and the U.S. Southeast. MODIS LAI is less than AVHRR by 2–6, except in the central Great Plains, eastern Rocky Mountains, and central Mexico. LCC and FVC changes over the central Great Plains reduce CWRF warm biases by 0.71°C and wet biases by 0.36 mm day−1. Large LAI reductions cause latent and sensible heat fluxes to decrease by 0.78–5.81 and 0.91–6.54 W m−2, respectively. They also lessen cold biases over the Gulf States and Southeast and wet biases over the North American monsoon region and Canada during summer. In densely vegetated regions including eastern Canada, the Ohio Valley, and the mid-Atlantic region, spring and summer precipitation decreases and temperature increases result from LAI reductions that cause positive evapotranspiration–precipitation–soil moisture feedbacks. Conversely, precipitation and temperature decreases in sparely vegetated regions, such as the Great Plains, result from FVC reductions that cause negative albedo–evapotranspiration–precipitation–soil moisture feedbacks.
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Hill, Matthew E. "A Moveable Feast: Variation in Faunal Resource Use among Central and Western North American Paleoindian Sites". American Antiquity 72, nr 3 (lipiec 2007): 417–38. http://dx.doi.org/10.2307/40035854.
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In the Great Plains and Rocky Mountains of North America, researchers have debated the degree to which Paleoindian foragers relied on large-game hunting to fulfill their subsistence needs. This study reviews the zooarchaeological record from 60 sites to test predictions drawn from prey choice models. Results indicate that different site types provide different perspectives on Paleoindian faunal use. Data from kill assemblages can only inform on the exploitation of large game, while the full variety of prey used by Paleoindian foragers is represented at camp localities. In addition, prehistoric foragers varied prey choice based on habitat setting. In the low diversity grasslands of the High Plains and Rolling Hills, prehistoric groups hunted large game almost exclusively. In the more diverse environments of the alluvial valleys and foothill/mountain environments, foragers show higher diversity of faunal use. During the early Holocene, small game made a greater contribution in the diet of Paleoindians, possibly in response to changing environmental conditions and/or increased hunting pressure.
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Hu, Qi, Song Feng i Robert J. Oglesby. "Variations in North American Summer Precipitation Driven by the Atlantic Multidecadal Oscillation". Journal of Climate 24, nr 21 (1.11.2011): 5555–70. http://dx.doi.org/10.1175/2011jcli4060.1.
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Abstract Understanding the development and variation of the atmospheric circulation regimes driven by the Atlantic multidecadal oscillation (AMO) is essential because these circulations interact with other forcings on decadal and interannual time scales. Collectively, they determine the summer (June, July, and August) precipitation variations for North America. In this study, a general circulation model (GCM) is used to obtain such understanding, with a focus on physical processes connecting the AMO and the summertime precipitation regime change in North America. Two experimental runs are conducted with sea surface temperature (SST) anomalies imposed in the North Atlantic Ocean that represent the warm and cold phases of the AMO. Climatological SSTs are used elsewhere in the oceans. Model results yield summertime precipitation anomalies in North America closely matching the observed anomaly patterns in North America, suggesting that the AMO provides a fundamental control on summertime precipitation in North America at decadal time scales. The impacts of the AMO are achieved by a chain of events arising from different circulation anomalies during warm and cold phases of the AMO. During the warm phase, the North Atlantic subtropical high pressure system (NASH) weakens, and the North American continent is much less influenced by it. A massive body of warm air develops over the heated land in North America from June–August, associated with high temperature and low pressure anomalies in the lower troposphere and high pressure anomalies in the upper troposphere. In contrast, during the cold phase of the AMO, the North American continent, particularly to the west, is much more influenced by an enhanced NASH. Cooler temperatures and high pressure anomalies prevail in the lower troposphere, and a frontal zone forms in the upper troposphere. These different circulation anomalies further induce a three-cell circulation anomaly pattern over North America in the warm and cold phases of the AMO. In particular, during the cold phase, the three-cell circulation anomaly pattern features a broad region of anomalous low-level southerly flow from the Gulf of Mexico into the U.S. Great Plains. Superimposed with an upper-troposphere front, more frequent summertime storms develop and excess precipitation occurs over most of North America. A nearly reversed condition occurs during the warm phase of the AMO, yielding drier conditions in North America. This new understanding provides a foundation for further study and better prediction of the variations of North American summer precipitation, especially when modulated by other multidecadal variations—for example, the Pacific decadal oscillation and interannual variations associated with the ENSO and the Arctic Oscillation.
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Hu, Qi, Jose Abraham Torres-Alavez i Matthew S. Van Den Broeke. "Land-Cover Change and the “Dust Bowl” Drought in the U.S. Great Plains". Journal of Climate 31, nr 12 (czerwiec 2018): 4657–67. http://dx.doi.org/10.1175/jcli-d-17-0515.1.
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The North American Dust Bowl drought during the 1930s had devastating environmental and societal impacts. Comprehending the causes of the drought has been an ongoing effort in order to better predict similar droughts and mitigate their impacts. Among the potential causes of the drought are sea surface temperature (SST) anomalies in the tropical Pacific Ocean and strengthened local sinking motion as a feedback to degradation of the land surface condition leading up to and during the drought. Limitations on these causes are the lack of a strong tropical SST anomaly during the drought and lack of local anomaly in moisture supply to undercut the precipitation in the U.S. Great Plains. This study uses high-resolution modeling experiments and quantifies an effect of the particular Great Plains land cover in the 1930s that weakens the southerly moisture flux to the region. This effect lowers the average precipitation, making the Great Plains more susceptible to drought. When drought occurs, the land-cover effect enhances its intensity and prolongs its duration. Results also show that this land-cover effect is comparable in magnitude to the effect of the 1930s large-scale circulation anomaly. Finally, analysis of the relationship of these two effects suggests that while lowering the precipitation must have contributed to the Dust Bowl drought via the 1930s land-cover effect, the initiation of and recovery from that drought would likely result from large-scale circulation changes, either of chaotic origin or resulting from combinations of weak SST anomalies and other forcing.
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Morrow, Juliet E., i Toby A. Morrow. "Geographic Variation in Fluted Projectile Points: A Hemispheric Perspective". American Antiquity 64, nr 2 (kwiecień 1999): 215–30. http://dx.doi.org/10.2307/2694275.
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This paper examines geographic variation in fluted point morphology across North and South America. Metric data on 449 North American points, 31 Central American points, and 61 South American points were entered into a database. Ratios calculated from these metric attributes are used to quantify aspects of point shape across the two continents. The results of this analysis indicate gradual, progressive changes in fluted point outline shape from the Great Plains of western North America into adjacent parts of North America as well as into Central and South America. The South American “Fishtail” form of fluted point is seen as the culmination of incremental changes in point shape that began well into North America. A geographically gradual decline in fluting frequency also is consistent with the stylistic evolution of the stemmed “Fishtail” points. Although few in number, the available radiocarbon dates do suggest that “Fishtail” fluted points in southern South America are younger than the earliest dates associated with Clovis points in western North America. All of these data converge on the conclusion that South American “Fishtail” points evolved from North American fluted points.
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Taylor, William Timothy Treal, Pablo Librado, Mila Hunska Tašunke Icu, Carlton Shield Chief Gover, Jimmy Arterberry, Anpetu Luta Wiƞ, Akil Nujipi i in. "Early dispersal of domestic horses into the Great Plains and northern Rockies". Science 379, nr 6639 (31.03.2023): 1316–23. http://dx.doi.org/10.1126/science.adc9691.
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The horse is central to many Indigenous cultures across the American Southwest and the Great Plains. However, when and how horses were first integrated into Indigenous lifeways remain contentious, with extant models derived largely from colonial records. We conducted an interdisciplinary study of an assemblage of historic archaeological horse remains, integrating genomic, isotopic, radiocarbon, and paleopathological evidence. Archaeological and modern North American horses show strong Iberian genetic affinities, with later influx from British sources, but no Viking proximity. Horses rapidly spread from the south into the northern Rockies and central plains by the first half of the 17th century CE, likely through Indigenous exchange networks. They were deeply integrated into Indigenous societies before the arrival of 18th-century European observers, as reflected in herd management, ceremonial practices, and culture.
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Trabert, Sarah. "Reframing the Protohistoric Period and the (Peri)Colonial Process for the North American Central Plains". World Archaeology 50, nr 5 (20.10.2018): 820–34. http://dx.doi.org/10.1080/00438243.2019.1576539.
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Fan, Majie, Ran Feng, John W. Geissman i Christopher J. Poulsen. "Late Paleogene emergence of a North American loess plateau". Geology 48, nr 3 (3.01.2020): 273–77. http://dx.doi.org/10.1130/g47102.1.
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Abstract The relative roles of tectonics and global climate in forming the hydroclimate for widespread eolian deposition remain controversial. Oligocene loess has been previously documented in the interior of western United States, but its spatiotemporal pattern and causes remain undetermined. Through new stratigraphic record documentation and data compilation, we reveal the time transgressive occurrence of loess beginning in the latest Eocene in the central Rocky Mountains, that expands eastward to the Great Plains across the Eocene-Oligocene transition (EOT). Our climate simulations show that moderate uplift of the southern North America Cordillera initiated drying in the Cordilleran hinterland and immediate foreland, forming a potential dust source and sink, and global cooling at the EOT expanded the drying and eolian deposition eastward by causing retreat of the North American Monsoon. Therefore, the eolian deposition reflects continental aridification induced both by regional tectonism and global climate change during the late Paleogene.
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Yu, B., H. Lin, V. V. Kharin i X. L. Wang. "Interannual Variability of North American Winter Temperature Extremes and Its Associated Circulation Anomalies in Observations and CMIP5 Simulations". Journal of Climate 33, nr 3 (1.02.2020): 847–65. http://dx.doi.org/10.1175/jcli-d-19-0404.1.
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AbstractThe interannual variability of wintertime North American surface temperature extremes and its generation and maintenance are analyzed in this study. The leading mode of the temperature extreme anomalies, revealed by empirical orthogonal function (EOF) analyses of December–February mean temperature extreme indices over North America, is characterized by an anomalous center of action over western-central Canada. In association with the leading mode of temperature extreme variability, the large-scale atmospheric circulation features an anomalous Pacific–North American (PNA)-like pattern from the preceding fall to winter, which has important implications for seasonal prediction of North American temperature extremes. A positive PNA pattern leads to more warm and fewer cold extremes over western-central Canada. The anomalous circulation over the PNA sector drives thermal advection that contributes to temperature anomalies over North America, as well as a Pacific decadal oscillation (PDO)-like sea surface temperature (SST) anomaly pattern in the midlatitude North Pacific. The PNA-like circulation anomaly tends to be supported by SST warming in the tropical central-eastern Pacific and a positive synoptic-scale eddy vorticity forcing feedback on the large-scale circulation over the PNA sector. The leading extreme mode–associated atmospheric circulation patterns obtained from the observational and reanalysis data, together with the anomalous SST and synoptic eddy activities, are reasonably well simulated in most CMIP5 models and in the multimodel mean. For most models considered, the simulated patterns of atmospheric circulation, SST, and synoptic eddy activities have lower spatial variances than the corresponding observational and reanalysis patterns over the PNA sector, especially over the North Pacific.
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Hoard, Robert J., William E. Banks, Rolfe D. Mandel, Michael Finnegan i Jennifer E. Epperson. "A Middle Archaic Burial from East Central Kansas". American Antiquity 69, nr 4 (październik 2004): 717–39. http://dx.doi.org/10.2307/4128445.
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In late 2001, investigators excavated a solitary Middle Archaic burial from the Plains-Prairie border in east-central Kansas. The burial was contained in a dissected colluvial apron at the foot of the valley wall, in a soil horizon that began accumulating around 9000 B.P. Burial goods include deer bone, a drill, and a side-notched projectile point/knife, the morphology of which is consistent with side-notched Middle Archaic points of the North American Central Plains and Midwest. Use-wear analysis shows that the stone tools were used before being placed with the burial and were not manufactured specifically as burial goods. A radiocarbon assay of the deer bone in direct association with the burial yielded a radiocarbon age of 6160 ± 35 B.P. This is one of only a few burials older than 5,000 years in the region. Comparison of this burial to other coeval regional burials shows similarities in burial practices.
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Liang, Xin-Zhong, Min Xu, Kenneth E. Kunkel, Georg A. Grell i John S. Kain. "Regional Climate Model Simulation of U.S.–Mexico Summer Precipitation Using the Optimal Ensemble of Two Cumulus Parameterizations". Journal of Climate 20, nr 20 (15.10.2007): 5201–7. http://dx.doi.org/10.1175/jcli4306.1.
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Abstract The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5)-based regional climate model (CMM5) simulations of U.S.–Mexico summer precipitation are quite sensitive to the choice of Grell or Kain–Fritsch convective parameterization. An ensemble based on these two parameterizations provides superior performance because distinct regions exist where each scheme complementarily captures certain observed signals. For the interannual anomaly, the ensemble provides the most significant improvement over the Rockies, Great Plains, and North American monsoon region. For the climate mean, the ensemble has the greatest impact on skill over the southeast United States and North American monsoon region, where CMM5 biases associated with the individual schemes are of opposite sign. Results are very sensitive to the specific methods used to generate the ensemble. While equal weighting of individual solutions provides a more skillful result overall, considerable further improvement is achieved when the weighting of individual solutions is optimized as a function of location.
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Klingaman, Nicholas P., Brian Hanson i Daniel J. Leathers. "A Teleconnection between Forced Great Plains Snow Cover and European Winter Climate". Journal of Climate 21, nr 11 (1.06.2008): 2466–83. http://dx.doi.org/10.1175/2007jcli1672.1.
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Abstract Anomalies in Siberian snow cover have been shown to affect Eurasian winter climate through the North Atlantic Oscillation (NAO). The existence of a teleconnection between North American snow cover and the NAO is far less certain, particularly for limited, regional snow cover anomalies. Using three ensembles of the Community Atmosphere Model, version 2 (CAM2), the authors examined teleconnections between persistent, forced snow cover in the northern Great Plains of the United States and western Eurasian winters. One ensemble allowed the model to freely determine global snow cover, while the other two forced a 72-cm snowpack centered over Nebraska. Of the forced ensembles, the “early-season” (“late season”) simulations initiated the snowpack on 1 November (1 January). The additional snow cover generated lower (higher) sea level pressures and geopotential heights over Iceland (the Azores) and warmer (cooler) temperatures over northern and western (eastern and southeastern) Europe, which suggests the positive NAO phase. Differences between the free-snow-cover and early-season ensembles were never significant until January, which implied either that the atmospheric response required a long lag or that the late-winter atmosphere was particularly sensitive to Great Plains snow. The authors rejected the former hypothesis and supported the latter by noting similarities between the early- and late-season ensembles in late winter for European 2-m temperatures, transatlantic circulation, and an NAO index. Therefore, a regional North American snow cover anomaly in an area of high inter- and intra-annual snow cover variability can show a stronger teleconnection to European winter climate than previously reported for broader snow cover anomalies. In particular, anomalous late-season snow in the Great Plains may shift the NAO toward the positive phase.
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Wang, Shih-Yu, i Tsing-Chang Chen. "The Late-Spring Maximum of Rainfall over the U.S. Central Plains and the Role of the Low-Level Jet". Journal of Climate 22, nr 17 (1.09.2009): 4696–709. http://dx.doi.org/10.1175/2009jcli2719.1.
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Abstract The seasonal rainfall over the U.S. central plains features a late-spring maximum. A spring–fall annual mode revealed from the empirical orthogonal function analysis on rainfall delineates a maximum center over the central plains that coincides with the large late-spring rainfall. This paper examines the large-scale dynamical and hydrological processes in forming the rainfall center. The NCEP–Department of Energy (DOE) reanalysis 2 data reveal that the baroclinic structure of the continental-scale circulation during late spring (May and June) induces a vertically out-of-phase divergent circulation forming strong convergence of water vapor flux over the central plains. Such circulation features generate concentrated convective activity in this region. The upper-level anticyclone development with the North American monsoon in July replaces the late-spring baroclinic structure and, in turn, reduces the convective activity. The Great Plains low-level jet (LLJ) plays a role in the downscaling process that connects the continental-scale circulation to rainfall. The LLJ coupled with approaching baroclinic waves leads to stronger moisture convergence in the central plains than that occurring under the upper-level anticyclone. The former type of the LLJ occurs most frequently in late spring and contributes to more than 60% of the rainfall. During midsummer (July and August), such a coupling is hindered by the well-developed upper-level anticyclone, subsequently decreasing the rainfall.
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Dodsworth, Paul. "The distribution of dinoflagellate cysts across a Late Cenomanian carbon isotope (<i>δ</i><sup>13</sup>C) anomaly in the Pulawy borehole, central Poland". Journal of Micropalaeontology 23, nr 1 (1.05.2004): 77–80. http://dx.doi.org/10.1144/jm.23.1.77.
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Abstract. Late Cenomanian dinoflagellate cyst assemblages in the Pulawy borehole, central Poland, exhibit similarities with those from west European and North American localities. A comparable change in assemblage composition around the base of a positive carbon isotope (δ13C) anomaly occurs in all three areas.
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Scott Van Pelt, R., Matthew C. Baddock, Ted M. Zobeck, Alan J. Schlegel, Merle F. Vigil i Veronica Acosta-Martinez. "Field wind tunnel testing of two silt loam soils on the North American Central High Plains". Aeolian Research 10 (wrzesień 2013): 53–59. http://dx.doi.org/10.1016/j.aeolia.2012.10.009.
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Roos, Christopher I., María Nieves Zedeño, Kacy L. Hollenback i Mary M. H. Erlick. "Indigenous impacts on North American Great Plains fire regimes of the past millennium". Proceedings of the National Academy of Sciences 115, nr 32 (23.07.2018): 8143–48. http://dx.doi.org/10.1073/pnas.1805259115.
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Fire use has played an important role in human evolution and subsequent dispersals across the globe, yet the relative importance of human activity and climate on fire regimes is controversial. This is particularly true for historical fire regimes of the Americas, where indigenous groups used fire for myriad reasons but paleofire records indicate strong climate–fire relationships. In North American grasslands, decadal-scale wet periods facilitated widespread fire activity because of the abundance of fuel promoted by pluvial episodes. In these settings, human impacts on fire regimes are assumed to be independent of climate, thereby diminishing the strength of climate–fire relationships. We used an offsite geoarchaeological approach to link terrestrial records of prairie fire activity with spatially related archaeological features (driveline complexes) used for intensive, communal bison hunting in north-central Montana. Radiocarbon-dated charcoal layers from alluvial and colluvial deposits associated with driveline complexes indicate that peak fire activity over the past millennium occurred coincident with the use of these features (ca. 1100–1650 CE). However, comparison of dated fire deposits with Palmer Drought Severity Index reconstructions reveal strong climate–fire linkages. More than half of all charcoal layers coincide with modest pluvial episodes, suggesting that fire use by indigenous hunters enhanced the effects of climate variability on prairie fire regimes. These results indicate that relatively small, mobile human populations can impact natural fire regimes, even in pyrogeographic settings in which climate exerts strong, top-down controls on fuels.
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Hanberry, Brice B. "Climate Envelopes Do Not Reflect Tree Dynamics after Euro-American Settlement in Eastern North America". Land 11, nr 9 (11.09.2022): 1536. http://dx.doi.org/10.3390/land11091536.
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Tree distributions and densities have been dynamic since Euro-American settlement in North America. Historically dominant fire-tolerant tree species have decreased, and fire-sensitive, successional species have increased, and tree species have expended westward since the 1800s into the central Great Plains grasslands. Divergent compositional trajectories and the westward expansion of tree species may be explained by climate change. To establish patterns expected by climate change, I predicted climate envelopes in eastern North America during 7 intervals, from the 1500s to 1961–1990, of 16 wide-ranging fire-tolerant and fire-sensitive species. The climate envelopes demonstrated that suitable climate area has remained relatively stable for all species: compared with the 1500s, areal extents during the 1900s increased 104% for fire-sensitive species and 106% for fire-tolerant species. Additionally, a pattern of northeastern shifts (i.e., following the North American land mass) resulted from climate change. Climate envelopes demonstrated northeastern shifts with slight expansion for all species, which did not accord with realized dynamics of westward tree expansion or increases in fire-sensitive species. In accordance with other lines of evidence, land use disturbance change, incorporating fire exclusion, likely has caused the divergent trajectories of fire-tolerant and fire-sensitive species and westward expansion into the Great Plains grasslands.
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Chan, Steven C., i Vasubandhu Misra. "Dynamic Downscaling of the North American Monsoon with the NCEP–Scripps Regional Spectral Model from the NCEP CFS Global Model". Journal of Climate 24, nr 3 (1.02.2011): 653–73. http://dx.doi.org/10.1175/2010jcli3593.1.
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Abstract The June–September (JJAS) 2000–07 NCEP coupled Climate Forecasting System (CFS) global hindcasts are downscaled over the North and South American continents with the NCEP–Scripps Regional Spectral Model (RSM) with anomaly nesting (AN) and without bias correction (control). A diagnosis of the North American monsoon (NAM) in CFS and RSM hindcasts is presented here. RSM reduces errors caused by coarse resolution but is unable to address larger-scale CFS errors even with bias correction. CFS has relatively weak Great Plains and Gulf of California low-level jets. Low-level jets are strengthened from downscaling, especially after AN bias correction. The RSM NAM hydroclimate shares similar flaws with CFS, with problematic diurnal and seasonal variability. Flaws in both diurnal and monthly variability are forced by erroneous convection-forced divergence outside the monsoon core region in eastern and southern Mexico. NCEP reanalysis shows significant seasonal variability errors, and AN shows little improvement in regional-scale flow errors. The results suggest that extreme caution must be taken when the correction is applied relative to reanalyses. Analysis also shows that North American Regional Reanalysis (NARR) NAM seasonal variability has benefited from precipitation data assimilation, but many questions remain concerning NARR’s representation of NAM.
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Schumacher, Philip N., Gregory Frosig, Jason L. Selzler i Robert A. Weisman. "Precipitation Regimes during Cold-Season Central U.S. Inverted Trough Cases. Part II: A Comparative Case Study". Weather and Forecasting 23, nr 4 (1.08.2008): 617–43. http://dx.doi.org/10.1175/2007waf2006058.1.
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Abstract This is the second of two papers that examine the organization of the precipitation field during central U.S. cold-season cyclones involving inverted troughs (ITs). The first paper (Part I) used a climatology and composites to find synoptic-scale differences between storms with precipitation located ahead of the IT (ahead cases) and those with precipitation located behind the IT (behind cases). This paper expands the conclusions in Part I through the use of a comparative case study between two cyclones. The first cyclone, on 29 October 1996, was an ahead case that produced heavy rainfall and was associated with a potential vorticity (PV) anomaly moving across the central plains. The IT formed in the lee of the Rockies prior to 0600 UTC 29 October and moved east into the northern plains over the next 18 h. The trough itself was coincident with the limiting streamline, which separated moist air rising over the warm front from dry air subsiding behind the cyclone. The second cyclone, on 17–18 January 1996, had precipitation on both sides of the IT and was associated with heavy snow and blizzard conditions in the northern plains and significant ice accumulation in the western Great Lakes. The IT was associated with large frontogenesis over the snow area. The ascent was further enhanced by a jet streak moving across southern Canada. Dynamically, the IT resembled a warm front, with veering winds with height and a strong frontal inversion. The mechanism that appeared to control the different precipitation organization between the two systems was the orientation of the PV anomalies and the airstreams associated with their secondary circulations. This resulted in a differing orientation of the baroclinicity north and east of the cyclone. In the ahead case, the rising branches of the secondary circulations forced by the northern and southern anomalies remained separate. This allowed the baroclinicity to develop along the traditional warm front, while the IT never developed a thermal gradient as it moved east. In the both sides case, the southern stream anomaly helped to fix the northern anomaly-forced jet streak in place, so that a strong temperature gradient developed along the IT with strong frontogenesis and warm-air advection observed behind the IT. As the frontal circulation developed, the direct circulation associated with the right entrance region of a jet streak enhanced the ascent to the west of the IT. A conceptual model is proposed based upon the case studies and the results of Part I. This model can be used by forecasters to differentiate between the precipitation regimes in cyclones associated with ITs.