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Abstract
Lag one-year autocorrelations and spectra for summer and winter seasons are estimated from 64-Year time series at 87 North American stations. Linear trends are first removed from the data to eliminate the effects of very long-period (longer than 64 years) variations. Summer season temperatures appear to have more year-to-year correlation and “redder” spectra than those of winter seasons. High correlations and red spectra are not necessarily found more frequently at near-ocean stations than at interior stations. Excepting variance near the quasi-biennial period, which is not judged because of its proximity to the folding frequency, no spectral “peaks” are found. Because of their differing autocorrelations and spectra it is concluded that evidence for potential long-range (more than two but less than 32 years) predictability is greater in summer than in winter, and that this is due, at least in part, to less natural variability or climatic noise in summer than in winter.
Abstract
Lag one-year autocorrelations and spectra for summer and winter seasons are estimated from 64-Year time series at 87 North American stations. Linear trends are first removed from the data to eliminate the effects of very long-period (longer than 64 years) variations. Summer season temperatures appear to have more year-to-year correlation and “redder” spectra than those of winter seasons. High correlations and red spectra are not necessarily found more frequently at near-ocean stations than at interior stations. Excepting variance near the quasi-biennial period, which is not judged because of its proximity to the folding frequency, no spectral “peaks” are found. Because of their differing autocorrelations and spectra it is concluded that evidence for potential long-range (more than two but less than 32 years) predictability is greater in summer than in winter, and that this is due, at least in part, to less natural variability or climatic noise in summer than in winter.
Abstract
A method for gridding scanning radiometer (SR) data is outlined in complete detail. This gridding method, coupled with a suggested display technique, enables one to produce a real-time quantitative display of APT service SR data with only minimal computer capability.
Abstract
A method for gridding scanning radiometer (SR) data is outlined in complete detail. This gridding method, coupled with a suggested display technique, enables one to produce a real-time quantitative display of APT service SR data with only minimal computer capability.
Abstract
The standard error of yearly and seasonally time-averaged station pressure values is estimated directly from a 49-year time series. The results compare well with similar estimates inferred from the autocorrelation character of the pressure data. The effect of seasonal variability in the autocorrelation on this standard error is indicated and a possible implication for numerical climatic-change experiments proposed.
Abstract
The standard error of yearly and seasonally time-averaged station pressure values is estimated directly from a 49-year time series. The results compare well with similar estimates inferred from the autocorrelation character of the pressure data. The effect of seasonal variability in the autocorrelation on this standard error is indicated and a possible implication for numerical climatic-change experiments proposed.
Abstract
Cross spectra between long time series (5–10 years) of pressure data from 27 stations and that from Canton Island show peaks in the coherence squares near 5-day periods. Phase angles indicate that these peaks are manifestations of a westward propagating, zonal wavenumber 1 disturbance. Sea-level pressures and 500-mb heights recorded during the IGY are filtered in time and harmonically analyzed in space revealing the westward propagating 5-day waves. A composite wave based on the IGY sea-level pressure data suggests that the amplitude of the disturbance increases with increasing latitude. The observed characteristics of the 5-day pressure wave are shown to he not inconsistent with those of a planetary wave, or wave mode of the second class, theoretically predicted by Laplace's tidal equations.
Abstract
Cross spectra between long time series (5–10 years) of pressure data from 27 stations and that from Canton Island show peaks in the coherence squares near 5-day periods. Phase angles indicate that these peaks are manifestations of a westward propagating, zonal wavenumber 1 disturbance. Sea-level pressures and 500-mb heights recorded during the IGY are filtered in time and harmonically analyzed in space revealing the westward propagating 5-day waves. A composite wave based on the IGY sea-level pressure data suggests that the amplitude of the disturbance increases with increasing latitude. The observed characteristics of the 5-day pressure wave are shown to he not inconsistent with those of a planetary wave, or wave mode of the second class, theoretically predicted by Laplace's tidal equations.
Abstract
Atmospheric angular momentum (M), friction (TF ), and mountain torques (TM ) are estimated from a 13-month period of European Centre for Medium-Range Weather Forecasts (ECMWF) data. Cross-spectrum analysis between M and total torques results in high coherence and one-quarter cycle phase angles (TF + TM leading M) for timescales between 5 and 66 days, suggesting that variations of the total torque are reasonably well estimated for these slower variations. However, cross spectra between M and TF , and TM separately reveal that the relatively high coherence is present between M and TF only at periods longer than 20 days. Also comparison with other published values and the considerable lack of balance between TF + TM and M over a full year implies that our estimates of TF , based on the parameterization of surface wind stress in short-term forecasts of the ECMWF, are negatively biased. For the 13-month period, the average bias is about −15.2 Hadleys (1018 kg m2 s−2).
During the period there are a few near 50-day oscillations in the M. Similar variations have been reported before and related to tropical intraseasonal oscillations of the same timescale. Two oscillations in M that are coincident with eastward-propagating cloud complexes of tropical intraseasonal oscillations are examined more closely. It is found that TF and TM work together to alter the M on the 50-day timescale, but that TM 's contribution is three times larger than that of TF . During the two oscillations TF , reaches maxima when cloud complexes of tropical intraseasonal oscillations are in the vicinity of 90°E. It then declines but maintains positive anomalies at least until the cloud complexes reach the Central Pacific. The M reaches its maxima shortly thereafter. TM has sharp minima shortly before the cloud complexes are strongly developed in the Indian Ocean. Contributors to these minima are strong cast to west pressure gradients primarily across the Rocky Mountains.
Abstract
Atmospheric angular momentum (M), friction (TF ), and mountain torques (TM ) are estimated from a 13-month period of European Centre for Medium-Range Weather Forecasts (ECMWF) data. Cross-spectrum analysis between M and total torques results in high coherence and one-quarter cycle phase angles (TF + TM leading M) for timescales between 5 and 66 days, suggesting that variations of the total torque are reasonably well estimated for these slower variations. However, cross spectra between M and TF , and TM separately reveal that the relatively high coherence is present between M and TF only at periods longer than 20 days. Also comparison with other published values and the considerable lack of balance between TF + TM and M over a full year implies that our estimates of TF , based on the parameterization of surface wind stress in short-term forecasts of the ECMWF, are negatively biased. For the 13-month period, the average bias is about −15.2 Hadleys (1018 kg m2 s−2).
During the period there are a few near 50-day oscillations in the M. Similar variations have been reported before and related to tropical intraseasonal oscillations of the same timescale. Two oscillations in M that are coincident with eastward-propagating cloud complexes of tropical intraseasonal oscillations are examined more closely. It is found that TF and TM work together to alter the M on the 50-day timescale, but that TM 's contribution is three times larger than that of TF . During the two oscillations TF , reaches maxima when cloud complexes of tropical intraseasonal oscillations are in the vicinity of 90°E. It then declines but maintains positive anomalies at least until the cloud complexes reach the Central Pacific. The M reaches its maxima shortly thereafter. TM has sharp minima shortly before the cloud complexes are strongly developed in the Indian Ocean. Contributors to these minima are strong cast to west pressure gradients primarily across the Rocky Mountains.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
Observational aspects of the 40–50-day oscillation are reviewed. The oscillation is the result of large-scale circulation cells oriented in the equatorial plane that move eastward from at least the Indian Ocean to the central Pacific. Anomalies in zonal winds and the velocity potential in the upper troposphere often propagate the full circumference of the globe. Related, complex convective regions also show an eastward movement. There is a zonally symmetric component to the oscillation. It is manifest in changes in surface pressure and in the relative atmospheric angular momentum. The oscillation is an important factor in the timing of active and break phases of the Indian and Australian monsoons. It affects ocean waves, currents, and air-sea interaction. The oscillation was particularly active during the First GARP (Global Atmospheric Research Program) Global Experiment year, and some features that were evident during the Monsoon Experiment are described.
Abstract
Observational aspects of the 40–50-day oscillation are reviewed. The oscillation is the result of large-scale circulation cells oriented in the equatorial plane that move eastward from at least the Indian Ocean to the central Pacific. Anomalies in zonal winds and the velocity potential in the upper troposphere often propagate the full circumference of the globe. Related, complex convective regions also show an eastward movement. There is a zonally symmetric component to the oscillation. It is manifest in changes in surface pressure and in the relative atmospheric angular momentum. The oscillation is an important factor in the timing of active and break phases of the Indian and Australian monsoons. It affects ocean waves, currents, and air-sea interaction. The oscillation was particularly active during the First GARP (Global Atmospheric Research Program) Global Experiment year, and some features that were evident during the Monsoon Experiment are described.
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.
