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Abstract
Eigenvector analysis was performed on spring, summer, fall and annual temperature and precipitation over the contiguous United States and on the frequency of occurrence of cyclonic and anticyclonic conditions over an area extending roughly from 60–130°W and 20–50°N.
The first eigenvector in all cases represents anomalies of one sign over nearly all the contiguous United States. Correspondence of the other eigenvector forms across seasons was also good. These patterns appear to be associated with latitudinal shifts in the westerlies and to the amplitude and position of the long waves.
An opposition in precipitation anomaly was found between the northwestern and southwestern United States which was mirrored in a similar pattern in variations of cyclone frequency over these two areas.
Significant changes occurred in the frequency of occurrence of individual eigenvector forms, suggesting that particular circulation regimes may become established, persist and disappear in time. The length of time that a particular regime lasts is thus connected with regional changes in climate.
Abstract
Eigenvector analysis was performed on spring, summer, fall and annual temperature and precipitation over the contiguous United States and on the frequency of occurrence of cyclonic and anticyclonic conditions over an area extending roughly from 60–130°W and 20–50°N.
The first eigenvector in all cases represents anomalies of one sign over nearly all the contiguous United States. Correspondence of the other eigenvector forms across seasons was also good. These patterns appear to be associated with latitudinal shifts in the westerlies and to the amplitude and position of the long waves.
An opposition in precipitation anomaly was found between the northwestern and southwestern United States which was mirrored in a similar pattern in variations of cyclone frequency over these two areas.
Significant changes occurred in the frequency of occurrence of individual eigenvector forms, suggesting that particular circulation regimes may become established, persist and disappear in time. The length of time that a particular regime lasts is thus connected with regional changes in climate.
Abstract
The month of March 1843 has been characterized as exhibiting the greatest temperature anomaly of any month during the period of instrumentally measured meteorological data in the United States. The March 1843 departure patterns from recent temperature normals are compared to those of February 1936 which were of the same magnitude (−30°F/−16.7°C), though perhaps of lesser areal extent. The frigidity of the air during February 1936 set some all time low temperature records that still stand today.
Abstract
The month of March 1843 has been characterized as exhibiting the greatest temperature anomaly of any month during the period of instrumentally measured meteorological data in the United States. The March 1843 departure patterns from recent temperature normals are compared to those of February 1936 which were of the same magnitude (−30°F/−16.7°C), though perhaps of lesser areal extent. The frigidity of the air during February 1936 set some all time low temperature records that still stand today.
Abstract
Areally weighted time series of temperature and precipitation have been compiled for Alaska for the period 1931–1977. Correlations of the temperature values with those of the contiguous United States indicate that, at both the monthly and seasonal time scales, the temperatures over the eastern two-thirds of the contiguous United States and Alaska are basically out of phase. However, with regard to long-term trends, the; temperatures in both Alaska and the lower 48 states exhibit a similar pattern.
Abstract
Areally weighted time series of temperature and precipitation have been compiled for Alaska for the period 1931–1977. Correlations of the temperature values with those of the contiguous United States indicate that, at both the monthly and seasonal time scales, the temperatures over the eastern two-thirds of the contiguous United States and Alaska are basically out of phase. However, with regard to long-term trends, the; temperatures in both Alaska and the lower 48 states exhibit a similar pattern.
Abstract
The spatial patterns and temporal trends of temperature and precipitation for northern North America (Alaska Canada and western Greenland) have been analyzed. Over approximately the past hundred years, three temperature regimes are identified that correspond roughly to similar climatic regimes identified in separate studies for the contiguous United States. Through 1980, warming is evident only from around the mid-1920s to about the early 1960s. No recent trends are present in winter or fall. Some cooling is evident during summer while spring shows cooling from 1963 to 1976 and warming thereafter.
Spatially, the largest changes occur in areas where variations in the amplitude of the long waves result in large advective differences; these areas are also sensitive to fluctuations in the mean position of the arctic front. Changes from one temperature regime to another occur quite abruptly and last for several years to a few decades.
There are two areas where well-defined precipitation changes coincide with temperature changes: the southern Canadian Plains near the 100°W meridian; and from the Great Lakes to James Bay northeastward toward Labrador. The location of these areas within a principal storm corridor suggests that the changes are associated with southward and northward shifts in the storm track that runs from the upper Midwest/Great Lakes region along the St. Lawrence River Valley toward the North Atlantic.
Abstract
The spatial patterns and temporal trends of temperature and precipitation for northern North America (Alaska Canada and western Greenland) have been analyzed. Over approximately the past hundred years, three temperature regimes are identified that correspond roughly to similar climatic regimes identified in separate studies for the contiguous United States. Through 1980, warming is evident only from around the mid-1920s to about the early 1960s. No recent trends are present in winter or fall. Some cooling is evident during summer while spring shows cooling from 1963 to 1976 and warming thereafter.
Spatially, the largest changes occur in areas where variations in the amplitude of the long waves result in large advective differences; these areas are also sensitive to fluctuations in the mean position of the arctic front. Changes from one temperature regime to another occur quite abruptly and last for several years to a few decades.
There are two areas where well-defined precipitation changes coincide with temperature changes: the southern Canadian Plains near the 100°W meridian; and from the Great Lakes to James Bay northeastward toward Labrador. The location of these areas within a principal storm corridor suggests that the changes are associated with southward and northward shifts in the storm track that runs from the upper Midwest/Great Lakes region along the St. Lawrence River Valley toward the North Atlantic.
Abstract
The separate contribution of December, January and February temperature to the net seasonal anomaly for the 1975–76 through 1981–82 winter seasons is analyzed. It is found that the January departures contributed by far the most toward making these seven winter seasons well below average in much of the contiguous United States, particularly in the eastern half of the country.
Each of these Januaries averaged from below to much-below the long-term average. By contrast, the Decembers and Februaries ranged from much-below to much-above the long-term mean.
Intraseasonal relationships were explored to see what role monthly persistence may have played during these seven winters. It was found that although there was a general tendency for anomalies to persist in sign from one month to the next, particularly in the eastern third and the far West of the United States, the coldness of the Januaries appears to be the result of an intensified meridional circulation occurring for the most part, during the calendar month of January.
Abstract
The separate contribution of December, January and February temperature to the net seasonal anomaly for the 1975–76 through 1981–82 winter seasons is analyzed. It is found that the January departures contributed by far the most toward making these seven winter seasons well below average in much of the contiguous United States, particularly in the eastern half of the country.
Each of these Januaries averaged from below to much-below the long-term average. By contrast, the Decembers and Februaries ranged from much-below to much-above the long-term mean.
Intraseasonal relationships were explored to see what role monthly persistence may have played during these seven winters. It was found that although there was a general tendency for anomalies to persist in sign from one month to the next, particularly in the eastern third and the far West of the United States, the coldness of the Januaries appears to be the result of an intensified meridional circulation occurring for the most part, during the calendar month of January.
Abstract
Using state monthly values of the Palmer Drought Index from January 1895 through April 1981, thespatial and temporal features of dry and wet episodes over the contiguous United States were analyzed. Thevariance spectrum of the area under both drought and wet spells in the western United States (17 westernmoststates) was also investigated.
The main results are as follows. Consistent with the findings of previous investigators, the interior andwestern portions of the United States are found to be more drought-prone than other parts of the country.By contrast, the likelihood of drought occurrence in states near coastal areas is considerably less. Prolongedmoisture abnormalities also tend to occur over the more drought-prone states indicating a tendency towardbimodality (either too dry or too wet).
The variance spectrum of the area under drought in the western United States exhibits a red-type spectrum,whereas the wet spell area exhibits relatively greater variance at the highest and intermediate frequencies(2 and 3-9 years). In a few regions of the United States, the initiation and termination of drought episodestend to occur more often at certain times of the year. For most regions, however, this preference is onlymarginal or non-existent.
Abstract
Using state monthly values of the Palmer Drought Index from January 1895 through April 1981, thespatial and temporal features of dry and wet episodes over the contiguous United States were analyzed. Thevariance spectrum of the area under both drought and wet spells in the western United States (17 westernmoststates) was also investigated.
The main results are as follows. Consistent with the findings of previous investigators, the interior andwestern portions of the United States are found to be more drought-prone than other parts of the country.By contrast, the likelihood of drought occurrence in states near coastal areas is considerably less. Prolongedmoisture abnormalities also tend to occur over the more drought-prone states indicating a tendency towardbimodality (either too dry or too wet).
The variance spectrum of the area under drought in the western United States exhibits a red-type spectrum,whereas the wet spell area exhibits relatively greater variance at the highest and intermediate frequencies(2 and 3-9 years). In a few regions of the United States, the initiation and termination of drought episodestend to occur more often at certain times of the year. For most regions, however, this preference is onlymarginal or non-existent.
Abstract
A comparison of the 1877–78 and 1982–83 El Niño/Southern Oscillation (ENSO) events was made using monthly and seasonal values of sea surface temperature (SST) and station pressure in the tropics, sea level pressure (SLP) in North America and the North Atlantic, temperature in North America and precipitation in several key areas around the globe.
SST anomalies in the eastern tropical Pacific, heavy rains in coastal Peru and extreme pressure anomalies across the Pacific and Indian Oceans during 1877–78 indicate an ENSO event of comparable magnitude to that during 1982–83. Both events were also associated with drought conditions in the Indonesian region, India, South Africa, northeastern Brazil and Hawaii. Wintertime teleconnections in the midlatitudes of the Northern Hemisphere were similar in terms of SLP from the North Pacific to Europe, resulting in significantly higher than normal temperatures over most of the United States and extreme rains in California.
Abstract
A comparison of the 1877–78 and 1982–83 El Niño/Southern Oscillation (ENSO) events was made using monthly and seasonal values of sea surface temperature (SST) and station pressure in the tropics, sea level pressure (SLP) in North America and the North Atlantic, temperature in North America and precipitation in several key areas around the globe.
SST anomalies in the eastern tropical Pacific, heavy rains in coastal Peru and extreme pressure anomalies across the Pacific and Indian Oceans during 1877–78 indicate an ENSO event of comparable magnitude to that during 1982–83. Both events were also associated with drought conditions in the Indonesian region, India, South Africa, northeastern Brazil and Hawaii. Wintertime teleconnections in the midlatitudes of the Northern Hemisphere were similar in terms of SLP from the North Pacific to Europe, resulting in significantly higher than normal temperatures over most of the United States and extreme rains in California.
Abstract
Monthly stream flow series from 1345 sites around the world are used to characterize geographic differences in the seasonality and year-to-year variability of stream flow. Stream flow seasonality varies regionally, depending on the timing of maximum precipitation, evapotranspiration, and contributions from snow and ice. Lags between peaks of precipitation and stream flow vary smoothly from long delays in high-latitude and mountainous regions to short delays in the warmest sectors. Stream flow is most variable from year to year in dry regions of the southwest United States and Mexico, the Sahel, and southern continents, and it varies more (relatively) than precipitation in the same regions. Tropical rivers have the steadiest flows. El Niño variations are correlated with stream flow in many parts of the Americas, Europe, and Australia. Many stream flow series from North America, Europe, and the Tropics reflect North Pacific climate, whereas series from the eastern United States, Europe, and tropical South America and Africa reflect North Atlantic climate variations.
Abstract
Monthly stream flow series from 1345 sites around the world are used to characterize geographic differences in the seasonality and year-to-year variability of stream flow. Stream flow seasonality varies regionally, depending on the timing of maximum precipitation, evapotranspiration, and contributions from snow and ice. Lags between peaks of precipitation and stream flow vary smoothly from long delays in high-latitude and mountainous regions to short delays in the warmest sectors. Stream flow is most variable from year to year in dry regions of the southwest United States and Mexico, the Sahel, and southern continents, and it varies more (relatively) than precipitation in the same regions. Tropical rivers have the steadiest flows. El Niño variations are correlated with stream flow in many parts of the Americas, Europe, and Australia. Many stream flow series from North America, Europe, and the Tropics reflect North Pacific climate, whereas series from the eastern United States, Europe, and tropical South America and Africa reflect North Atlantic climate variations.
Abstract
Using eigenvector methods, the principal anomaly patterns of winter temperature, precipitation and cyclone/anticyclone frequency over the contiguous United States are described. The period of record used is 1894/95–1977/78; the data consist of state averages for temperature and precipitation and 10° × 10° grid counts for the cyclone/anticyclone analysis.
The first three temperature eigenvectors (out of a possible 48) account for 86% of the total seasonal variance; the principal seasonal precipitation eigenvectors account for proportionally smaller variance, with 67% being contained in the first five eigenvectors. An even smaller variance reduction is effected with the variation of cyclone and anticyclone centers over the United States. Nevertheless, the first three components (out of a possible 12) account for 46 and 48%, respectively, of the variance in the series of cyclone and anticyclone frequency counts.
The principal modes of variation of mean winter temperature and precipitation appear to be associated with the season-to-season positioning (both in terms of the amplitude and phase) of the major long-wave trough in eastern North America. Principally over the eastern two-thirds of the United States, this results in a predominance of cold/dry and warm/wet winter types. For the western United States the tendency is for colder and wetter versus warmer and drier regimes.
Variations in synoptic-scale system frequencies appear to be associated with latitudinal shifts in the mean position of the jet stream from season to season, with land-sea contrasts along the Atlantic Coast, and with changes that take place over the eastern Pacific.
Abstract
Using eigenvector methods, the principal anomaly patterns of winter temperature, precipitation and cyclone/anticyclone frequency over the contiguous United States are described. The period of record used is 1894/95–1977/78; the data consist of state averages for temperature and precipitation and 10° × 10° grid counts for the cyclone/anticyclone analysis.
The first three temperature eigenvectors (out of a possible 48) account for 86% of the total seasonal variance; the principal seasonal precipitation eigenvectors account for proportionally smaller variance, with 67% being contained in the first five eigenvectors. An even smaller variance reduction is effected with the variation of cyclone and anticyclone centers over the United States. Nevertheless, the first three components (out of a possible 12) account for 46 and 48%, respectively, of the variance in the series of cyclone and anticyclone frequency counts.
The principal modes of variation of mean winter temperature and precipitation appear to be associated with the season-to-season positioning (both in terms of the amplitude and phase) of the major long-wave trough in eastern North America. Principally over the eastern two-thirds of the United States, this results in a predominance of cold/dry and warm/wet winter types. For the western United States the tendency is for colder and wetter versus warmer and drier regimes.
Variations in synoptic-scale system frequencies appear to be associated with latitudinal shifts in the mean position of the jet stream from season to season, with land-sea contrasts along the Atlantic Coast, and with changes that take place over the eastern Pacific.
Abstract
No abstract available.
Abstract
No abstract available.
