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- Author or Editor: Wan-Cheng Chiu x
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Abstract
The wind and temperature spectra of the upper troposphere and lower stratosphere over selected North American stations are constructed, by means of Tukey's method, from rawinsonde and radiosonde data taken by these stations. The variation of the spectral intensity with frequency (or period) and with height is fully discussed. The conclusions drawn from this study are given at the end of the paper.
Abstract
The wind and temperature spectra of the upper troposphere and lower stratosphere over selected North American stations are constructed, by means of Tukey's method, from rawinsonde and radiosonde data taken by these stations. The variation of the spectral intensity with frequency (or period) and with height is fully discussed. The conclusions drawn from this study are given at the end of the paper.
Abstract
From about five years (1952 to 1956) of radiosonde data over the United States, taken by fifteen radiosonde stations that had been conducting four observations a day, the mean temperatures at the four observational hours were obtained separately for winter and summer at the 200-mb, 150-mb, 100-mb, and 50-mb levels of the stratosphere. At each season and level (except the 50-mb level in winter), a diurnal temperature variation was detected by plotting these mean temperatures for all the stations on one diagram against their appropriate local times of observations. After all the physical factors or errors in observations that might induce or influence the observed diurnal temperature variation were carefully examined, it was estimated that about one quarter of the observed variation was real and the rest of it due to radiation error in observation.
Abstract
From about five years (1952 to 1956) of radiosonde data over the United States, taken by fifteen radiosonde stations that had been conducting four observations a day, the mean temperatures at the four observational hours were obtained separately for winter and summer at the 200-mb, 150-mb, 100-mb, and 50-mb levels of the stratosphere. At each season and level (except the 50-mb level in winter), a diurnal temperature variation was detected by plotting these mean temperatures for all the stations on one diagram against their appropriate local times of observations. After all the physical factors or errors in observations that might induce or influence the observed diurnal temperature variation were carefully examined, it was estimated that about one quarter of the observed variation was real and the rest of it due to radiation error in observation.
Abstract
The mean monthly wind fields at five different levels from the 300-mb surface to the 30-mb surface were constructed from rawinsonde data taken by stations in North America and adjacent waters over the four year period from 1951 to 1954. These wind fields are represented by streamlines and isotachs on isobaric maps. The general features of these wind fields at January and July as revealed by these maps are discussed. The detailed features of these fields, such as the variation of the mean wind components with latitude, longitude or time, are scrutinized and made obvious by diagrams.
Abstract
The mean monthly wind fields at five different levels from the 300-mb surface to the 30-mb surface were constructed from rawinsonde data taken by stations in North America and adjacent waters over the four year period from 1951 to 1954. These wind fields are represented by streamlines and isotachs on isobaric maps. The general features of these wind fields at January and July as revealed by these maps are discussed. The detailed features of these fields, such as the variation of the mean wind components with latitude, longitude or time, are scrutinized and made obvious by diagrams.
Abstract
The spectra of large-scale eddy transfer of angular momentum and heat were constructed for seven levels, ranging from 700 mb to 50 mb over Belmar, N. J., and at the 300-mb and 200-mb levels over Cocoa, Florida. It is found that the frequencies of motion which were largely responsible for the eddy transport of heat shift toward lower frequencies with height. There was no such frequency shift indicated in the case of momentum transfer. The spectral intensity for the transport of angular momentum, when plotted against frequency, in general decreases with increasing frequency. The disturbances of long periods (say, longer than 20 days) were found to play a role as important as those of shorter periods in contributing to the total eddy transport of both heat and momentum.
Abstract
The spectra of large-scale eddy transfer of angular momentum and heat were constructed for seven levels, ranging from 700 mb to 50 mb over Belmar, N. J., and at the 300-mb and 200-mb levels over Cocoa, Florida. It is found that the frequencies of motion which were largely responsible for the eddy transport of heat shift toward lower frequencies with height. There was no such frequency shift indicated in the case of momentum transfer. The spectral intensity for the transport of angular momentum, when plotted against frequency, in general decreases with increasing frequency. The disturbances of long periods (say, longer than 20 days) were found to play a role as important as those of shorter periods in contributing to the total eddy transport of both heat and momentum.
Abstract
The motion of the atmosphere, with its climatological trend and periodic components excluded, is considered to be a stationary random process, under the control of macroscopic factors such as the solar constant, the rate of earth's rotation, the distribution and physical natures of land and sea, etc. In an effort to develop understanding of the statistical features of this process, the Eulerian frequency energy spectra of the large-scale atmospheric motions were constructed at 12 North American and nearby island stations from lengthy wind data. Examination of these spectra reveals that: 1) they are red-noise in character, 2) there is no systematic relationship between the shape of the spectrum and the local rate of earth's rotation, 3) there is a cut-down of spectral energy at low frequencies at 950 mb at some stations, 4) the shape of the spectrum is very much the same at levels in the mid and high troposphere, and 5) a spectral peak at some stations may correspond to the frequency of cyclone occurrence.
Abstract
The motion of the atmosphere, with its climatological trend and periodic components excluded, is considered to be a stationary random process, under the control of macroscopic factors such as the solar constant, the rate of earth's rotation, the distribution and physical natures of land and sea, etc. In an effort to develop understanding of the statistical features of this process, the Eulerian frequency energy spectra of the large-scale atmospheric motions were constructed at 12 North American and nearby island stations from lengthy wind data. Examination of these spectra reveals that: 1) they are red-noise in character, 2) there is no systematic relationship between the shape of the spectrum and the local rate of earth's rotation, 3) there is a cut-down of spectral energy at low frequencies at 950 mb at some stations, 4) the shape of the spectrum is very much the same at levels in the mid and high troposphere, and 5) a spectral peak at some stations may correspond to the frequency of cyclone occurrence.
Abstract
The National Meteorological Center's tropical grid data together with sea surface temperature (SST) data at several Pacific stations wore used to test Bjerknes’ hypothesis that, through the mechanism of momentum transport, fluctuations of mean temperature in the tropical cast Pacific influence the sub-tropical and middle-latitude atmospheric circulations. Computed correlation coefficients indicate that the subtropical and equatorial upper tropospheric zonal wind anomalies in the eastern Pacific have a concurrent and tag (with ocean leading) relationship with SST anomalies at Puerto Chicama (in the El Niño area), but not with SST anomalies outside the El Niño area. There is also an indication of a relationship between fluctuations of the 250 mb zonal wind over the Indian monsoon area and fluctuations of SST in the El Niño area, with the former loading the latter, and a relationship between the 700 mb zonal winds in the western equatorial Pacific and SST in the El Niño area for both positive and negative lass. However, the lag-correlation coefficients between SST anomalies at Puerto Chicama and momentum transport in eastern Pacific are very small. The results of this study so far fail to confirm Bjerknes' hypothesis.
Abstract
The National Meteorological Center's tropical grid data together with sea surface temperature (SST) data at several Pacific stations wore used to test Bjerknes’ hypothesis that, through the mechanism of momentum transport, fluctuations of mean temperature in the tropical cast Pacific influence the sub-tropical and middle-latitude atmospheric circulations. Computed correlation coefficients indicate that the subtropical and equatorial upper tropospheric zonal wind anomalies in the eastern Pacific have a concurrent and tag (with ocean leading) relationship with SST anomalies at Puerto Chicama (in the El Niño area), but not with SST anomalies outside the El Niño area. There is also an indication of a relationship between fluctuations of the 250 mb zonal wind over the Indian monsoon area and fluctuations of SST in the El Niño area, with the former loading the latter, and a relationship between the 700 mb zonal winds in the western equatorial Pacific and SST in the El Niño area for both positive and negative lass. However, the lag-correlation coefficients between SST anomalies at Puerto Chicama and momentum transport in eastern Pacific are very small. The results of this study so far fail to confirm Bjerknes' hypothesis.
Abstract
The temperature variation at a fixed point in the free atmosphere or at a point which moves vertically with an isobaric surface is a result of the combined effect of radiation, horizontal advection of heat, vertical convection of heat, and other heat-exchange processes. A method is presented by which the 12-hr local temperature change that would have resulted from radiative processes alone may be estimated. This method and the conventional method of determining the 12-hr local temperature change due to the horizontal advective process lead to a way of estimating the relative importance of different heat-exchange processes.
Following these methods, the 12-hr local temperature changes in the lower stratosphere over a portion of the United States due to radiation, horizontal advection, and the vertical convective and eddy heat exchange processes combined are separately estimated from many years of radiosonde data and daily isobaric maps. The results of this study show that over the southeastern United States, at least, and probably over a much wider area, the horizontal advective process is more important than radiation in influencing the 12-hr local temperature change at the 200-mb and the l00-mb levels. These two processes are probably of equal importance near the 50-mb level. At the 200-mb and the 100-mb levels. These two processes are probably of exchange processes combined are estimated to be as important as, or even more important than, the radiative processes over the same area. These conclusions are probably true for both winter and summer, but especially for winter.
Abstract
The temperature variation at a fixed point in the free atmosphere or at a point which moves vertically with an isobaric surface is a result of the combined effect of radiation, horizontal advection of heat, vertical convection of heat, and other heat-exchange processes. A method is presented by which the 12-hr local temperature change that would have resulted from radiative processes alone may be estimated. This method and the conventional method of determining the 12-hr local temperature change due to the horizontal advective process lead to a way of estimating the relative importance of different heat-exchange processes.
Following these methods, the 12-hr local temperature changes in the lower stratosphere over a portion of the United States due to radiation, horizontal advection, and the vertical convective and eddy heat exchange processes combined are separately estimated from many years of radiosonde data and daily isobaric maps. The results of this study show that over the southeastern United States, at least, and probably over a much wider area, the horizontal advective process is more important than radiation in influencing the 12-hr local temperature change at the 200-mb and the l00-mb levels. These two processes are probably of equal importance near the 50-mb level. At the 200-mb and the 100-mb levels. These two processes are probably of exchange processes combined are estimated to be as important as, or even more important than, the radiative processes over the same area. These conclusions are probably true for both winter and summer, but especially for winter.
Abstract
Atmospheric wind data obtained from the Geophysical Fluid Dynamics Laboratory and from the National Meteorological Center together with sea surface temperature (SST) data at Puerto Chicama (7°42′S, 79°27′W) and Koko Head (21°18′N, 157°52′W) for the period May 1958 to September 1973 were used to test Bjerknes' hypothesis that, through the mechanism of momentum transport, fluctuations of SST in the equatorial eastern Pacific influence the subtropical and middle-latitude atmospheric circulations. Lag cross-correlation coefficients were calculated from the data and their statistical significance tested. The results, confirming earlier work, support the portion of his hypothesis regarding the influence of the equatorial eastern Pacific in the higher latitude atmospheric circulation, but do not support the portion of it suggesting that momentum transport is the agent transmitting the influence.
Abstract
Atmospheric wind data obtained from the Geophysical Fluid Dynamics Laboratory and from the National Meteorological Center together with sea surface temperature (SST) data at Puerto Chicama (7°42′S, 79°27′W) and Koko Head (21°18′N, 157°52′W) for the period May 1958 to September 1973 were used to test Bjerknes' hypothesis that, through the mechanism of momentum transport, fluctuations of SST in the equatorial eastern Pacific influence the subtropical and middle-latitude atmospheric circulations. Lag cross-correlation coefficients were calculated from the data and their statistical significance tested. The results, confirming earlier work, support the portion of his hypothesis regarding the influence of the equatorial eastern Pacific in the higher latitude atmospheric circulation, but do not support the portion of it suggesting that momentum transport is the agent transmitting the influence.
