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- Author or Editor: Henry F. Diaz x
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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
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
The 1976–77 winter season is compared with earlier winters with respect to temperature and beating degree days. Comparisons are based on 1) station data; 2) composite indices derived from a combination of a few very long-term station records; 3) areally weighted state and regional temperature averages; and 4) population weighted beating degree days. Major conclusions are as follows:
1) January 1977 was possibly the coldest month experienced in the eastern half of the country in the past 200 years.
2) The 1976–77 winter was not a record-breaker for temperature for the contiguous 48 states as a whole, but set a new record for fuel demand because of the extreme cold in highly populated areas.
3) Relatively coarse networks of stations can be used for monitoring large-scale anomalous weather features; they allow use of continuous records covering more than 100 years for which dense networks do not exist. They also allow near-real-time assessment of anomalous weather events at a small fraction of the time and money needed to process data from a large number of stations.
Abstract
The 1976–77 winter season is compared with earlier winters with respect to temperature and beating degree days. Comparisons are based on 1) station data; 2) composite indices derived from a combination of a few very long-term station records; 3) areally weighted state and regional temperature averages; and 4) population weighted beating degree days. Major conclusions are as follows:
1) January 1977 was possibly the coldest month experienced in the eastern half of the country in the past 200 years.
2) The 1976–77 winter was not a record-breaker for temperature for the contiguous 48 states as a whole, but set a new record for fuel demand because of the extreme cold in highly populated areas.
3) Relatively coarse networks of stations can be used for monitoring large-scale anomalous weather features; they allow use of continuous records covering more than 100 years for which dense networks do not exist. They also allow near-real-time assessment of anomalous weather events at a small fraction of the time and money needed to process data from a large number of stations.
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.
Abstract
Analysis of monthly-mean temperature and precipitation data for each of the 48 contiguous United States for the 1976–77 through 1978–79 winter seasons shows that the temperature and precipitation departures from the long-term means were extreme. The consecutive occurrence of such severely cold winters is unprecedented in the available 85-year record.
Variability of temperature and precipitation has increased in the past 5-year period, compared to previous pentads, mainly as a result of much greater frequency of extreme anomalies. An “extreme anomaly”is defined as a mean monthly or seasonal value exceeding two standard deviations from the long-term mean.
Statistical estimates of average return periods of winter mean temperatures equal to or lower than the actual values recorded for the past three seasons are close to the empirical values. However, the implausibly low probabilities for the occurrence of consecutive severe winters suggest that the development of large-scale anomalies in atmospheric circulation, which these low temperatures represent, may have a common dynamical forcing and that these forcing mechanisms possess time scales on the order of several years.
Abstract
Analysis of monthly-mean temperature and precipitation data for each of the 48 contiguous United States for the 1976–77 through 1978–79 winter seasons shows that the temperature and precipitation departures from the long-term means were extreme. The consecutive occurrence of such severely cold winters is unprecedented in the available 85-year record.
Variability of temperature and precipitation has increased in the past 5-year period, compared to previous pentads, mainly as a result of much greater frequency of extreme anomalies. An “extreme anomaly”is defined as a mean monthly or seasonal value exceeding two standard deviations from the long-term mean.
Statistical estimates of average return periods of winter mean temperatures equal to or lower than the actual values recorded for the past three seasons are close to the empirical values. However, the implausibly low probabilities for the occurrence of consecutive severe winters suggest that the development of large-scale anomalies in atmospheric circulation, which these low temperatures represent, may have a common dynamical forcing and that these forcing mechanisms possess time scales on the order of several years.
