Twentieth century changes in winter climatic regions (original) (raw)
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Cluster analysis of Southeastern U.S. climate stations
Theoretical and Applied Climatology, 1991
A two-step cluster analysis of 449 Southeastern climate stations is used to objectively determine general climate clusters (groups of climate stations) for eight southeastern states. The purpose is objectively to define regions of climatic homogeneity that should perform more robustly in subsequent climatic impact models. This type of analysis has been successfully used in many related climate research problems including the determination of corn/climate districts in Iowa (Ortiz-Valdez, 1985) and the classification of synoptic climate types .
Journal of Climate, 2009
The observed climate trends over the United States during 1950–2000 exhibit distinct seasonality and regionality. The surface air temperature exhibits a warming trend during winter, spring, and early summer and a modest countrywide cooling trend in late summer and fall, with the strongest warming occurring over the northern United States in spring. Precipitation trends are positive in all seasons, with the largest trend occurring over the central and southern United States in fall. This study investigates the causes of the seasonality and regionality of those trends, with a focus on the cooling and wetting trends in the central United States during late summer and fall. In particular, the authors examine the link between the seasonality and regionality of the climate trends over the United States and the leading patterns of sea surface temperature (SST) variability, including a global warming (GW) pattern and a Pacific decadal variability (PDV) pattern. A series of idealized atmosph...
Journal of Great Lakes Research, 1999
Many studies have identified continental-scale atmospheric circulation regimes, and some have been employed for various regions, but none have involved a regional categorization of circulation around the Great Lakes basin. Such an analysis is important not only because of the economic and recreational importance of the lakes, but in an effort to relate the regional circulation types to the broaderscale modes of atmospheric circulation, such as that forced by El Niño (ENSO). In this study, rotated principal components analysis (RPCA) is performed on the monthly mean sea-level pressure field around the Great Lakes basin, and in a separate analysis, on the mean 700 hPa field in eastern North America. An average-linkage clustering algorithm is applied to the RPCA scores to classify the monthly surface circulation in the Great Lakes region and the 700 hPa circulation over eastern North America. The classification is used to determine whether the various categories of regional circulation patterns are coincident with distinct hemispheric-scale flow regimes. To do this, indices of the modes of variability in some of the most well-known atmospheric teleconnections during months that fall within each circulation mode are subjected to ANOVA tests by cluster. Results suggest that the regional atmosphere over the Great Lakes basin undergoes long-term shifts in preferred modes of circulation. Furthermore, flow variability associated with the 700 hPa North Atlantic Oscillation (NAO) and Pacific/North American (PNA) teleconnections are more strongly tied to variability in both the Great Lakes regional surface circulation and the 700 mb eastern North American flow regimes than is the ENSO-forced Southern Oscillation.
Theoretical and Applied Climatology - THEOR APPL CLIMATOL, 1999
Summary Much literature has reported on the concept of increased surface temperature variability during cool periods, although analyses on temperature records have rendered inconsistent results. In addition, temperature variability during transition periods has been rarely investigated. This study examines temperature variability during wintertime cooling (1947–1977) and warming (1978–1992) periods for the conterminous United States to determine both whether temperature variability is different during warming or cooling periods, and whether the change in variability is supported by midtropospheric circulation conditions. Our results indicate that regions with high temperature variability are mostly found below the troughs in the midtropospheric pressure fields. The direction of change in temperature variability corresponding to cooling or warming conditions, however, varied spatially. For the southeastern and northeastern United States, winter temperatures were more variable durin...
The climate velocity of the contiguous United States during the 20th century
Global Change Biology, 2013
Rapid climate change has the potential to affect economic, social, and biological systems. A concern for species conservation is whether or not the rate of on-going climate change will exceed the rate at which species can adapt or move to suitable environments. Here we assess the climate velocity (both climate displacement rate and direction) for minimum temperature, actual evapotranspiration, and climatic water deficit (deficit) over the contiguous US during the 20th century . Vectors for these variables demonstrate a complex mosaic of patterns that vary spatially and temporally and are dependent on the spatial resolution of input climate data. Velocities for variables that characterize the climatic water balance were similar in magnitude to that derived from temperature, but frequently differed in direction resulting in the divergence of climate vectors through time. Our results strain expectations of poleward and upslope migration over the past century due to warming. Instead, they suggest that a more full understanding of changes in multiple climatic factors, in addition to temperature, may help explain unexpected or conflicting observational evidence of climate-driven species range shifts during the 20th century.
Proceedings of the National Academy of Sciences, 2009
Changes in climate during the 20th century differ from region to region across the United States. We provide strong evidence that spatial variations in US temperature trends are linked to the hydrologic cycle, and we also present unique information on the seasonal and latitudinal structure of the linkage. We show that there is a statistically significant inverse relationship between trends in daily temperature and average daily precipitation across regions. This linkage is most pronounced in the southern United States (30-40°N) during the May-June time period and, to a lesser extent, in the northern United States (40-50°N) during the July-August time period. It is strongest in trends in maximum temperatures (Tmax) and 90th percentile exceedance trends (90PET), and less pronounced in the Tmax 10PET and the corresponding Tmin statistics, and it is robust to changes in analysis period. Although previous studies suggest that areas of increased precipitation may have reduced trends in temperature compared with drier regions, a change in sign from positive to negative trends suggests some additional cause. We show that trends in precipitation may account for some, but not likely all, of the cause point to evidence that shows that dynamical patterns (El Niñ o/Southern Oscillation, North Atlantic Oscillation, etc.) cannot account for the observed effects during May-June. We speculate that changing aerosols, perhaps related to vegetation changes, and increased strength of the aerosol direct and indirect effect may play a role in the observed linkages between these indices of temperature change and the hydrologic cycle.
Interannual and interdecadal variability in United States surface-air temperatures, 1910-87
Climatic Change, 1995
Monthly mean surface-air temperatures at 870 sites in the contiguous United States were analyzed for interannual and interdecadal variability over the time interval 1910-87. The temperatures were analyzed spatially by empirical-orthogonal-function analysis and temporally by singularspectrum analysis (SSA). The dominant modes of spatio-temporal variability are trends and nonperiodic variations with time scales longer than 15 years, decadal-scale oscillations with periods of roughly 7 and 10 years, and interannual oscillations of 2.2 and 3.3 years. Together, these modes contribute about 18% of the slower-than-annual United States temperature variance. Two leading components roughly capture the mean hemispheric temperature trend and represent a long-term warming, largest in the southwest, accompanied by cooling of the domain's southeastern quadrant. The extremes of the 2.2-year interannual oscillation characterize temperature differences between the Northeastern and Southwestern States, whereas the 3.3-year cycle is present mostly in the Western States. The 7- to 10-year oscillations are much less regular and persistent than the interannual oscillations and characterize temperature differences between the western and interior sectors of the United States. These continental- or regional-scale temperature variations may be related to climatic variations with similar periodicities, either global or centered in other regions; such variations include quasi-biennial oscillations over the tropical Pacific or North Atlantic and quasi-triennial oscillations of North Pacific sea-surface temperatures.
1981
An objectively derived catalogue of daily pressure patterns for 11199-1974 has been prepared for the western Uoited States. The temperature and precipitation characteristics of the major types are described and a more detailed analysis for Colorado in extreme cold and warm months shows that the sign of the anomalies for each type is generally consistent with expectation hased Oil the prohable airflow patterns. A regression analysis of type frequencies versus temperature and precipitation anomalies for 1899-1970 at stations east and west of the Continental Divide in the Rocky Mountain states shows that useful explanation of variance is obtained only for temperatures in the transition seasons and for precipitation west of the Divide in winter and east of the Divide in spring. Within-type variahility of the climatic characteristics is one source of the discrepancy. The results underline the problems encountered in trying to. link climatic anomalies with atmospheric circulation characteristics. KEY WORDS Synoptic ciimatology Western United States Recent climatic fluctuations Climatic anomalies * The time take on the University of Colorado CDC 6400 for the 60-month sample was approximately 122 min. compared with only 60 min. for classification of the 75 years.
Atmosphere, 2019
A meridional Northern Hemisphere (NH) circulation epoch, which began in 1957, is marked by changes in the temperature and precipitation regimes over southwest Russia and central USA depending on the occurrence of NH atmospheric circulation regimes. A classification scheme proposed in 1968, and studied later put forth 13 NH circulation types, fitting more broadly into four groups, two of which are more zonal type flows and two of which are more meridional flows. Using the results of a previous study that showed four distinct sub-periods during the 1957–2017 epoch, the temperature and precipitation regimes of both regions were studied across all seasons in order to characterize modern day climate variability and their suitability for vegetation growth. Then the Hydrologic Coefficient, which combined the temperature and precipitation variables, was briefly studied. The most optimal conditions for vegetation growth, positive temperature and precipitation anomalies, were noted during the...
Climatic changes in western North America, 1950-2005
International Journal of Climatology, 2011
The rate of climatic change over western North America (WNA) is quantified for 485 climate stations for the period 1950-2005. Additionally, six stations with quality long-term records were selected and analysed for the period 1906-2005. The indicators used were developed by the World Meteorological Organization (WMO) and the World Climate Research Program's Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI). From the 27 core indices, 4 temperature-based and 4 precipitation-based indicators were selected for in-depth analysis. The 8 million km 2 study area is comprised of the 22 contiguous US states and 4 Canadian provinces west of the Mississippi River and Great Lakes. The results were divided into six general regions for interpretation and presentation. GIS interpolation of station-specific statistical output was completed to further aid in the identification of spatially coherent trends across WNA. Mean slopes were calculated over the whole study area, and by region, for each index, and then tested to determine if they were significantly different from zero. Results of the study show statistically significant historical climate trends across the study area. As expected in a region as geographically diverse as WNA, results differed between, and within, regions. Overall, temperature-based indicators showed a general warming trend over the entire study area, with the greatest increases along the North American Cordillera. The trends in precipitation-based indicators were more varied. General trends indicate moderately increasing precipitation volume and intensity over much of WNA. The strongest precipitation trends were found in areas with climate largely controlled by air masses originating over the Gulf of Mexico. Copyright 2011 Royal Meteorological Society KEY WORDS climate change; climate indices; extreme temperature; extreme precipitation; North America