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- Author or Editor: Roland A. Madden x
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Abstract
The possible relation between blocking-type flow patterns in the atmosphere and large-scale traveling waves has been investigated. A 30-yr time series of observational 500-hPa geopotential-height data was used to study the relation between westward-moving planetary-scale waves 1 and 2 and blocked flow. It was found that, depending on longitude, 20%–40% of blocks were related to traveling wave 1, whereas the percentage was smaller for wave 2. The study confirms results of earlier studies that suggest a possible important role for large-scale, westward-moving waves in many blocking episodes.
Abstract
The possible relation between blocking-type flow patterns in the atmosphere and large-scale traveling waves has been investigated. A 30-yr time series of observational 500-hPa geopotential-height data was used to study the relation between westward-moving planetary-scale waves 1 and 2 and blocked flow. It was found that, depending on longitude, 20%–40% of blocks were related to traveling wave 1, whereas the percentage was smaller for wave 2. The study confirms results of earlier studies that suggest a possible important role for large-scale, westward-moving waves in many blocking episodes.
Abstract
We describe the global correlations between a measure of the Southern Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the Northern Hemisphere for an 80-year period, and it turned out that most stable correlation coefficients were found over India, the North Pacific Ocean, the Rocky Mountains, and the central and western North Atlantic Ocean. On the Southern Hemisphere most records are too short for a similar test, but the following may tentatively be said about the Southern Oscillation in middle and high southern latitudes: when pressure is low in lower latitudes over the South Pacific Ocean it tends to be high at higher latitudes of that ocean, high over East Antarctica and low in the belt of westerlies in the Indian and South Atlantic oceans. In the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitudes than in the other extreme. The apparent large-scale sympathetic variations between the SO and temperature are shown to occur over the relatively wide range of periods dust have been attributed to the SO itself.
Abstract
We describe the global correlations between a measure of the Southern Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the Northern Hemisphere for an 80-year period, and it turned out that most stable correlation coefficients were found over India, the North Pacific Ocean, the Rocky Mountains, and the central and western North Atlantic Ocean. On the Southern Hemisphere most records are too short for a similar test, but the following may tentatively be said about the Southern Oscillation in middle and high southern latitudes: when pressure is low in lower latitudes over the South Pacific Ocean it tends to be high at higher latitudes of that ocean, high over East Antarctica and low in the belt of westerlies in the Indian and South Atlantic oceans. In the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitudes than in the other extreme. The apparent large-scale sympathetic variations between the SO and temperature are shown to occur over the relatively wide range of periods dust have been attributed to the SO itself.
Abstract
Estimates of the natural variability of monthly mean temperature data from 107 U.S. stations are made. The natural variability of monthly means is defined as those interannual fluctuations that can be attributed to the effects of statistical sampling alone. It is variability resulting from the variance and autocorrelation associated with daily weather fluctuations. It does not indicate “climate change” but rather it is the variability within an “unchanging climate”; as such it is a measure of unpredictable “climatic noise”. Comparisons between the natural and actual interannual variability are discussed in the context of potential long-range predictability. The natural variability is proposed as a lower limit for the standard error of estimate for any long-range prediction. A characteristic time between independent estimates is computed.
Abstract
Estimates of the natural variability of monthly mean temperature data from 107 U.S. stations are made. The natural variability of monthly means is defined as those interannual fluctuations that can be attributed to the effects of statistical sampling alone. It is variability resulting from the variance and autocorrelation associated with daily weather fluctuations. It does not indicate “climate change” but rather it is the variability within an “unchanging climate”; as such it is a measure of unpredictable “climatic noise”. Comparisons between the natural and actual interannual variability are discussed in the context of potential long-range predictability. The natural variability is proposed as a lower limit for the standard error of estimate for any long-range prediction. A characteristic time between independent estimates is computed.
Abstract
The correlation between seasonal mean temperatures and precipitation totals is computed at some 98 North American and European stations. Negative correlation is most frequent in summers, while negative and positive correlation appear about equally in other seasons. Normalized cospectra show that these correlation do not, in general, reflect a relationship common to a single time scale but rather one that is prevalent at all time scales.
Abstract
The correlation between seasonal mean temperatures and precipitation totals is computed at some 98 North American and European stations. Negative correlation is most frequent in summers, while negative and positive correlation appear about equally in other seasons. Normalized cospectra show that these correlation do not, in general, reflect a relationship common to a single time scale but rather one that is prevalent at all time scales.
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
A space-time spectral analysis of a long time series of observed geopotential heights for each season at several levels and latitudes of the Northern Hemisphere was performed as part of a continuing investigation of large-scale traveling waves. The data set that is analyzed consists of the first six zonal wavenumbers. A discussion emphasizes westward traveling wave 1 with periods near 16 and 5 days which we argue are consistent with external Rossby warm. An additional outstanding feature is an eastward propagating wave 6 which may result from baroclinic instability.
Abstract
A space-time spectral analysis of a long time series of observed geopotential heights for each season at several levels and latitudes of the Northern Hemisphere was performed as part of a continuing investigation of large-scale traveling waves. The data set that is analyzed consists of the first six zonal wavenumbers. A discussion emphasizes westward traveling wave 1 with periods near 16 and 5 days which we argue are consistent with external Rossby warm. An additional outstanding feature is an eastward propagating wave 6 which may result from baroclinic instability.
Abstract
Eastward phase propagation, at speed faster than 30 m s−1, of a signal in the equatorial troposphere of the Eastern Pacific is detected, first in historical meteorological observations and then in more recent data. A first baroclinic mode vertical structure is identified with this signal in separate analyses based on linear theory and complex empirical orthogonal functions, respectively. This rapid, eastward signal is conceptualized as a far-field dispersion product of strong convection associated with the intraseasonal tropical oscillation in the Indian Ocean and Western Pacific.
Abstract
Eastward phase propagation, at speed faster than 30 m s−1, of a signal in the equatorial troposphere of the Eastern Pacific is detected, first in historical meteorological observations and then in more recent data. A first baroclinic mode vertical structure is identified with this signal in separate analyses based on linear theory and complex empirical orthogonal functions, respectively. This rapid, eastward signal is conceptualized as a far-field dispersion product of strong convection associated with the intraseasonal tropical oscillation in the Indian Ocean and Western Pacific.
Abstract
Seasonally varying spectral and cross-spectral calculations are carried out on multiyear time series of vertically and zonally averaged daily zonal wind fields to describe the seasonal cycle of the 40–50-day oscillation of atmospheric angular momentum. Intraseasonal variability (including 40–50-day fluctuations) of global momentum is largest in late boreal winter and smallest in boreal autumn; however, the 40–50-day spectral peak is most pronounced in boreal summer when lower-frequency intraseasonal variance is depressed. The 40–50-day spectral peak in global momentum is much less pronounced and apparently is restricted to a narrower frequency band, than corresponding peaks in zonal wind spectra from individual tropical rawinsonde stations. Contributions to global momentum fluctuations from three near-equal-area latitude bands (tropics, Northern Hemisphere, and Southern Hemisphere) are compared, confirming that intraseasonal momentum fluctuations are tropical in origin. The variance of extratropical momentum at this time scale is about an order of magnitude less than the tropical momentum variability. Coherent tropical–extratropical interactions are found principally in boreal winter, with the highest coherence between the tropics and Northern Hemisphere. The corresponding phase difference between tropical and Northern Hemisphere momentum is suggestive of poleward propagation of momentum out of the tropics.
Abstract
Seasonally varying spectral and cross-spectral calculations are carried out on multiyear time series of vertically and zonally averaged daily zonal wind fields to describe the seasonal cycle of the 40–50-day oscillation of atmospheric angular momentum. Intraseasonal variability (including 40–50-day fluctuations) of global momentum is largest in late boreal winter and smallest in boreal autumn; however, the 40–50-day spectral peak is most pronounced in boreal summer when lower-frequency intraseasonal variance is depressed. The 40–50-day spectral peak in global momentum is much less pronounced and apparently is restricted to a narrower frequency band, than corresponding peaks in zonal wind spectra from individual tropical rawinsonde stations. Contributions to global momentum fluctuations from three near-equal-area latitude bands (tropics, Northern Hemisphere, and Southern Hemisphere) are compared, confirming that intraseasonal momentum fluctuations are tropical in origin. The variance of extratropical momentum at this time scale is about an order of magnitude less than the tropical momentum variability. Coherent tropical–extratropical interactions are found principally in boreal winter, with the highest coherence between the tropics and Northern Hemisphere. The corresponding phase difference between tropical and Northern Hemisphere momentum is suggestive of poleward propagation of momentum out of the tropics.
Abstract
Nearly ten years of daily rawinsonde data for Canton Island (3S, 172W) have been subjected to spectrum and cross-spectrum analysis. In the course of this analysis a very pronounced maximum was noted in the co-spectrum of the 850- and 150-mb zonal wind components in the frequency range 0.0245–0.0190 day−1 (41–53 days period). Application of a posteriori sampling theory resulted in a significance level of ∼6% (0.1% prior confidence level). This type of significance test is appropriate because no prior evidence or reason existed for expecting such a spectral feature. Subsequent analysis revealed the following structure of the oscillation. Peaks in the variance spectra of the zonal wind are strong in the low troposphere, are weak or non-existent in the 700–400 mb layer, and are strong again in the upper troposphere. No evidence of this feature could be found above 80 mb, or in any of the spectra of the meridional component. The spectrum of station pressure possesses a peak in this frequency range and the oscillation is in phase with the low tropospheric zonal wind oscillation, and out of phase with that in the upper troposphere. The tropospheric temperatures exhibit a similar peak and are highly coherent with the station pressure oscillation; positive station pressure anomalies are associated with negative temperature anomalies throughout the troposphere. Thus, the lower-middle troposphere appears to be a nodal surface with u and P oscillating in phase but 180° out of phase above and below this surface. Evidence for this phenomenon was found in shorter records at Kwajalein (9N, 168E) but not at Singapore (1N, 104E) or Balboa, Canal Zone (9N, 79w). We speculate that the oscillation is a large circulation cell oriented in zonal planes and centered in the mid-Pacific.
Abstract
Nearly ten years of daily rawinsonde data for Canton Island (3S, 172W) have been subjected to spectrum and cross-spectrum analysis. In the course of this analysis a very pronounced maximum was noted in the co-spectrum of the 850- and 150-mb zonal wind components in the frequency range 0.0245–0.0190 day−1 (41–53 days period). Application of a posteriori sampling theory resulted in a significance level of ∼6% (0.1% prior confidence level). This type of significance test is appropriate because no prior evidence or reason existed for expecting such a spectral feature. Subsequent analysis revealed the following structure of the oscillation. Peaks in the variance spectra of the zonal wind are strong in the low troposphere, are weak or non-existent in the 700–400 mb layer, and are strong again in the upper troposphere. No evidence of this feature could be found above 80 mb, or in any of the spectra of the meridional component. The spectrum of station pressure possesses a peak in this frequency range and the oscillation is in phase with the low tropospheric zonal wind oscillation, and out of phase with that in the upper troposphere. The tropospheric temperatures exhibit a similar peak and are highly coherent with the station pressure oscillation; positive station pressure anomalies are associated with negative temperature anomalies throughout the troposphere. Thus, the lower-middle troposphere appears to be a nodal surface with u and P oscillating in phase but 180° out of phase above and below this surface. Evidence for this phenomenon was found in shorter records at Kwajalein (9N, 168E) but not at Singapore (1N, 104E) or Balboa, Canal Zone (9N, 79w). We speculate that the oscillation is a large circulation cell oriented in zonal planes and centered in the mid-Pacific.
Abstract
Long time series (5–10 years) of station pressure and upper air data from stations located in the tropics are subjected to spectral and cross-spectral analysis to investigate the spatial extent of a previously detected oscillation in various variables with a period range of 40–50 days. In addition, time series of station pressure from two tropical stations for the 1890's are examined and indicate that the oscillation is a stationary feature. The cross-spectral analysis suggests that the oscillation is of global scale but restricted to the tropics: it possesses features of an eastward-moving wave whose characteristics change with time. A mean wave disturbance, constructed with data from the IGY, provides additional descriptive material on the spatial and temporal behavior of the oscillation. The manifestation in station pressure consists of anomalies which appear between 10N and 10S in the Indian Ocean region and propagate eastward to the Eastern Pacific. Zonal winds participate in the oscillation and, in general, are out-of-phase between the upper and lower troposphere. Mixing ratios and temperatures are also investigated. The sum total of evidence indicates that the oscillation is the result of an eastward movement of large-scale circulation cells oriented in the equatorial (zonal) plane.
Abstract
Long time series (5–10 years) of station pressure and upper air data from stations located in the tropics are subjected to spectral and cross-spectral analysis to investigate the spatial extent of a previously detected oscillation in various variables with a period range of 40–50 days. In addition, time series of station pressure from two tropical stations for the 1890's are examined and indicate that the oscillation is a stationary feature. The cross-spectral analysis suggests that the oscillation is of global scale but restricted to the tropics: it possesses features of an eastward-moving wave whose characteristics change with time. A mean wave disturbance, constructed with data from the IGY, provides additional descriptive material on the spatial and temporal behavior of the oscillation. The manifestation in station pressure consists of anomalies which appear between 10N and 10S in the Indian Ocean region and propagate eastward to the Eastern Pacific. Zonal winds participate in the oscillation and, in general, are out-of-phase between the upper and lower troposphere. Mixing ratios and temperatures are also investigated. The sum total of evidence indicates that the oscillation is the result of an eastward movement of large-scale circulation cells oriented in the equatorial (zonal) plane.
