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- Author or Editor: William P. Elliott x
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Abstract
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Abstract
Hole closing by diffusion of water vapor and droplets is treated as a problem in classical diffusion theory with constant mixing coefficients. The results, for reasonable estimates of the variables involved, lead to closure times in the one-half to one hour range. However, the estimates of the appropriate diffusion coefficients are quite rough and it may be useful to employ cloud-dissipation techniques to estimate this variable.
Further calculations show that to maintain a given area free of clouds for the maximum time possible, a hole whose width is 75–80% of the distance between the smallest useful hole and the maximum possible hole should be opened.
Abstract
Hole closing by diffusion of water vapor and droplets is treated as a problem in classical diffusion theory with constant mixing coefficients. The results, for reasonable estimates of the variables involved, lead to closure times in the one-half to one hour range. However, the estimates of the appropriate diffusion coefficients are quite rough and it may be useful to employ cloud-dissipation techniques to estimate this variable.
Further calculations show that to maintain a given area free of clouds for the maximum time possible, a hole whose width is 75–80% of the distance between the smallest useful hole and the maximum possible hole should be opened.
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Abstract
An equation for the daytime lapse rate of temperature as a function of z/L is derived assuming the lapse rate varies as z−⅔ in very light winds. This variation is presumed to result from the geometry of buoyant plumes. The equation, which agrees very well with some data taken by Dyer, predicts a maximum value for the lapse rate at a fixed height and with given heat flux, at intermediate values of z/L. This variation suggests the concept of eddy viscosity as usually applied does not adequately describe the heat flux in unstable conditions.
Abstract
An equation for the daytime lapse rate of temperature as a function of z/L is derived assuming the lapse rate varies as z−⅔ in very light winds. This variation is presumed to result from the geometry of buoyant plumes. The equation, which agrees very well with some data taken by Dyer, predicts a maximum value for the lapse rate at a fixed height and with given heat flux, at intermediate values of z/L. This variation suggests the concept of eddy viscosity as usually applied does not adequately describe the heat flux in unstable conditions.
Abstract
Thermal, haline and total steric departures of sea level were calculated in a zone up to 165 n mi off Newport, Ore. The thermal and haline components were about equal in magnitudes and in phase, giving low steric sea levels nearshore and high sea levels offshore in summer and the reverse pattern in winter. These results are produced by local oceanographic conditions and reflect seasonal changes in upwelling and the position of the Columbia River plume.
In the region close to shore the combined effects of steric and atmospheric-pressure-caused departures do not fully account for the observed variations of sea level. Wind stress variations are likely to be the most important cause but other factors may well contribute.
Abstract
Thermal, haline and total steric departures of sea level were calculated in a zone up to 165 n mi off Newport, Ore. The thermal and haline components were about equal in magnitudes and in phase, giving low steric sea levels nearshore and high sea levels offshore in summer and the reverse pattern in winter. These results are produced by local oceanographic conditions and reflect seasonal changes in upwelling and the position of the Columbia River plume.
In the region close to shore the combined effects of steric and atmospheric-pressure-caused departures do not fully account for the observed variations of sea level. Wind stress variations are likely to be the most important cause but other factors may well contribute.
Abstract
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Abstract
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Abstract
Trends in tropospheric water vapor at Northern Hemisphere radiosonde stations are presented for two periods;1973–95 and 1958–95. Stations with incomplete or inhomogeneous temporal records were identified and excluded from the analysis. For the 1973–95 period, trends in surface–500-mb precipitable water and in specific humidity, dewpoint, and temperature at the 850-mb level are shown. At most stations in this analysis, precipitable water, specific humidity, and dewpoint temperature have increased along with temperature over the period. An exception is Europe, over which temperature increased but humidity slightly decreased. Water vapor increases are larger, more uniform, and more significant over North America than over Eurasia, and the differences in trend magnitude and sign between the two regions may be attributable to changes in the late 1970s that affected North America more than Eurasia.
Seasonal and annual correlations of surface–500-mb precipitable water with temperature, dewpoint temperature, and specific and relative humidity at the surface, 850, and 700 mb indicate a strong and relatively geographically invariant relationship between 850-mb specific humidity and surface–500-mb precipitable water. Specific humidity at 850 mb is then used as a surrogate for the surface–500-mb precipitable water over the 1958–95 period to avoid data quality problems in the pre-1973 precipitable water time series. Generally, 850-mb specific humidity trends at a small set of stations for 1958–95 show that only small increases occurred and that most of the overall increase probably occurred since 1973.
Abstract
Trends in tropospheric water vapor at Northern Hemisphere radiosonde stations are presented for two periods;1973–95 and 1958–95. Stations with incomplete or inhomogeneous temporal records were identified and excluded from the analysis. For the 1973–95 period, trends in surface–500-mb precipitable water and in specific humidity, dewpoint, and temperature at the 850-mb level are shown. At most stations in this analysis, precipitable water, specific humidity, and dewpoint temperature have increased along with temperature over the period. An exception is Europe, over which temperature increased but humidity slightly decreased. Water vapor increases are larger, more uniform, and more significant over North America than over Eurasia, and the differences in trend magnitude and sign between the two regions may be attributable to changes in the late 1970s that affected North America more than Eurasia.
Seasonal and annual correlations of surface–500-mb precipitable water with temperature, dewpoint temperature, and specific and relative humidity at the surface, 850, and 700 mb indicate a strong and relatively geographically invariant relationship between 850-mb specific humidity and surface–500-mb precipitable water. Specific humidity at 850 mb is then used as a surrogate for the surface–500-mb precipitable water over the 1958–95 period to avoid data quality problems in the pre-1973 precipitable water time series. Generally, 850-mb specific humidity trends at a small set of stations for 1958–95 show that only small increases occurred and that most of the overall increase probably occurred since 1973.
Abstract
Shipboard measurements of CCN show the slope of the CCN spectra to be in agreement with other estimates in marine air from aircraft. Concentrations of CCN over the open ocean are quite low with estimates of a few tens per cubic entimeter. Only a few percent of the CCN were particles containing chlorides.
The Spectra of CCN in coastal waters exhibit slopes more like marine air but number concentrations more like continental air. The reason for this are not entirely clear.
Abstract
Shipboard measurements of CCN show the slope of the CCN spectra to be in agreement with other estimates in marine air from aircraft. Concentrations of CCN over the open ocean are quite low with estimates of a few tens per cubic entimeter. Only a few percent of the CCN were particles containing chlorides.
The Spectra of CCN in coastal waters exhibit slopes more like marine air but number concentrations more like continental air. The reason for this are not entirely clear.
Different nations use different algorithms or other techniques to convert temperatures and relative humidities from radiosonde observations to dewpoint depressions. Thus, it is possible for identical measured values to result in different reported dewpoints. On the basis of a sample of conversion methods, we calculate the possible differences among the national practices. In general, the discrepancies are not large and would often be lost in the usual round-off procedures associated with transmission over the Global Telecommunications System, but in cold, dry conditions dewpoints different by more than 1°C could be reported for identical conditions. Some of the methods have been changed over time, so there is also the possibility of inhomogeneities in climate records.
Different nations use different algorithms or other techniques to convert temperatures and relative humidities from radiosonde observations to dewpoint depressions. Thus, it is possible for identical measured values to result in different reported dewpoints. On the basis of a sample of conversion methods, we calculate the possible differences among the national practices. In general, the discrepancies are not large and would often be lost in the usual round-off procedures associated with transmission over the Global Telecommunications System, but in cold, dry conditions dewpoints different by more than 1°C could be reported for identical conditions. Some of the methods have been changed over time, so there is also the possibility of inhomogeneities in climate records.
This paper considers the use of upper-air data from radiosondes in long-term climate studies. The accuracy and precision of radiosonde humidity measurements, including temperature and pressure measurements used in calculating them, and their effects on the precision of reported and derived variables are estimated. Focusing on the U.S. radiosonde system, we outline the history of changes in instruments and reporting practices and attempt to assess the implications of such changes for studies of temporal variations in lower-tropospheric water vapor. Changes in biases in the data are highlighted, as these can lead to misinterpretation of climate change. We conclude that the upper-air data record for the United States is not homogeneous, especially before 1973. Because of problems with the humidity data in cold, dry conditions, the water vapor climatology in the upper troposphere, nominally above the 500-mb level, is not well known.
This paper considers the use of upper-air data from radiosondes in long-term climate studies. The accuracy and precision of radiosonde humidity measurements, including temperature and pressure measurements used in calculating them, and their effects on the precision of reported and derived variables are estimated. Focusing on the U.S. radiosonde system, we outline the history of changes in instruments and reporting practices and attempt to assess the implications of such changes for studies of temporal variations in lower-tropospheric water vapor. Changes in biases in the data are highlighted, as these can lead to misinterpretation of climate change. We conclude that the upper-air data record for the United States is not homogeneous, especially before 1973. Because of problems with the humidity data in cold, dry conditions, the water vapor climatology in the upper troposphere, nominally above the 500-mb level, is not well known.
