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- Author or Editor: Philip Clapp x
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Abstract
Due to the opposing albedo and greenhouse effects of clouds, the possibility exists that the net radiation at the top of the earth-atmosphere system is, in the mean, insensitive to changes in cloud amount. If so, this would have important implications for climate studies. This question is examined with the use of data on the components of the radiation budget at the top of the atmosphere obtained from the processing of 45 months of scanning radiometer observations of the NOAA satellites. Year-to-year changes in monthly mean values of outgoing longwave radiation and albedo are analysed at a sample of geographic and climatic areas of the earth. By using the albedo changes as a measure of changes in cloud amount, it is possible to determined the sensitivity of the outgoing longwave radiation and the net radiation to changes in cloud amount. For each geographic/climatic area, the results indicate that the net radiation at the top of the atmosphere is sensitive to cloud amount changes and the sensitivity is such that the albedo effect of the clouds predominates over their greenhouse effect. Thus, for the earth as a whole the net radiation at the top of the atmosphere is sensitive to changes in cloud amount. Estimates of the numerical values of the global mean sensitivity of net radiation and outgoing longwave radiation to changes in cloud amount are presented and compared with previous findings.
Abstract
Due to the opposing albedo and greenhouse effects of clouds, the possibility exists that the net radiation at the top of the earth-atmosphere system is, in the mean, insensitive to changes in cloud amount. If so, this would have important implications for climate studies. This question is examined with the use of data on the components of the radiation budget at the top of the atmosphere obtained from the processing of 45 months of scanning radiometer observations of the NOAA satellites. Year-to-year changes in monthly mean values of outgoing longwave radiation and albedo are analysed at a sample of geographic and climatic areas of the earth. By using the albedo changes as a measure of changes in cloud amount, it is possible to determined the sensitivity of the outgoing longwave radiation and the net radiation to changes in cloud amount. For each geographic/climatic area, the results indicate that the net radiation at the top of the atmosphere is sensitive to cloud amount changes and the sensitivity is such that the albedo effect of the clouds predominates over their greenhouse effect. Thus, for the earth as a whole the net radiation at the top of the atmosphere is sensitive to changes in cloud amount. Estimates of the numerical values of the global mean sensitivity of net radiation and outgoing longwave radiation to changes in cloud amount are presented and compared with previous findings.
Abstract
Basic problems encountered in the preparation of medium- and long-range forecasts by numerical methods are revealed through the use of time-averaged charts.
It is found that forecasts up to five days in advance may be prepared by use of the vorticity-tendency equation, provided certain broad-scale sources and sinks of vorticity are taken into account. Since these appear in the final prognosis as locally time-averaged values, it is probable that they may be sufficiently well represented by crude approximations.
It is not possible to forecast for a month or more in advance by integrating the tendency equation, because of approximate balance between the terms not containing time derivatives. A modified conservation equation is suggested as the solution to this problem.
Finally, it is suggested that the eddy transfer of meteorological properties will not be a major problem in long-range forecasting, since this transfer can probably be expressed in terms of the large-scale circulation.
Abstract
Basic problems encountered in the preparation of medium- and long-range forecasts by numerical methods are revealed through the use of time-averaged charts.
It is found that forecasts up to five days in advance may be prepared by use of the vorticity-tendency equation, provided certain broad-scale sources and sinks of vorticity are taken into account. Since these appear in the final prognosis as locally time-averaged values, it is probable that they may be sufficiently well represented by crude approximations.
It is not possible to forecast for a month or more in advance by integrating the tendency equation, because of approximate balance between the terms not containing time derivatives. A modified conservation equation is suggested as the solution to this problem.
Finally, it is suggested that the eddy transfer of meteorological properties will not be a major problem in long-range forecasting, since this transfer can probably be expressed in terms of the large-scale circulation.
Abstract
Recent work on mean-motion models of the general circulation has led to renewed interest in the parameterization (i.e., expression in terms of model-generated average variables) of the horizontal flux of heat in the atmosphere by transient eddies on the scale of cyclones.
A brief review is made of previous work on this subject and some new computations are presented, leading to confirmation of the usual assumption that the cross-isotherm flux of heat can be expressed using the well-known “Austausch coefficient” method. This empirical finding appears to agree with what is expected from the theory of cyclone development.
When considering heat flow over the globe it is necessary to account for the transient flux component parallel, as well as perpendicular, to the mean isotherms. Apparently, no empirical work has yet been done on this subject.
The geographical fields of the parallel component for different seasons of several years were examined in the light of a theoretical study of Welander, which suggests that, in a rotating fluid, there must be a component of heat flux parallel to the thermal wind and proportional to the mean temperature gradient. Appartently, Welander's conclusion (obtained for the case of small-scale turbulence) does not appear to be applicable to macroscale heat transfer on the scale of traveling wave cyclones. Nevertheless, some variants of this concept may lead to a useful parameterization of the parallel flux.
Abstract
Recent work on mean-motion models of the general circulation has led to renewed interest in the parameterization (i.e., expression in terms of model-generated average variables) of the horizontal flux of heat in the atmosphere by transient eddies on the scale of cyclones.
A brief review is made of previous work on this subject and some new computations are presented, leading to confirmation of the usual assumption that the cross-isotherm flux of heat can be expressed using the well-known “Austausch coefficient” method. This empirical finding appears to agree with what is expected from the theory of cyclone development.
When considering heat flow over the globe it is necessary to account for the transient flux component parallel, as well as perpendicular, to the mean isotherms. Apparently, no empirical work has yet been done on this subject.
The geographical fields of the parallel component for different seasons of several years were examined in the light of a theoretical study of Welander, which suggests that, in a rotating fluid, there must be a component of heat flux parallel to the thermal wind and proportional to the mean temperature gradient. Appartently, Welander's conclusion (obtained for the case of small-scale turbulence) does not appear to be applicable to macroscale heat transfer on the scale of traveling wave cyclones. Nevertheless, some variants of this concept may lead to a useful parameterization of the parallel flux.
Abstract
The most likely number of days with snow on the ground during an individual month is expressed empirically as a function of the mean temperature and total precipitation for that month, as well as the presence or absence of a snow cover at the end of the preceding month. Although this study is of some value in the field of synoptic climatology, it was designed primarily to serve as a useful method for generating snow cover within numerical weather-prediction models which do not contain water- or snow-budget formulas.
Abstract
The most likely number of days with snow on the ground during an individual month is expressed empirically as a function of the mean temperature and total precipitation for that month, as well as the presence or absence of a snow cover at the end of the preceding month. Although this study is of some value in the field of synoptic climatology, it was designed primarily to serve as a useful method for generating snow cover within numerical weather-prediction models which do not contain water- or snow-budget formulas.
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Abstract
TIROS nephanalyses are used to obtain global maps and latitudinal profiles of average cloud amount for the four seasons for the year March 1962 through February 1963. It is found that the gross patterns and season-to-season variations of these cloud distributions bear a striking resemblance to corresponding features of normal cloudiness, although there are some differences which call for further study. In many cases anomalies in cloudiness can be related to corresponding anomalies of the general circulation.
In considering the magnitude as distinct from the pattern of cloudiness, there is some suggestion that during the chosen period the TIROS nephanalyses gave too much cloudiness for large cloud amount, and too little for small cloud amount.
Abstract
TIROS nephanalyses are used to obtain global maps and latitudinal profiles of average cloud amount for the four seasons for the year March 1962 through February 1963. It is found that the gross patterns and season-to-season variations of these cloud distributions bear a striking resemblance to corresponding features of normal cloudiness, although there are some differences which call for further study. In many cases anomalies in cloudiness can be related to corresponding anomalies of the general circulation.
In considering the magnitude as distinct from the pattern of cloudiness, there is some suggestion that during the chosen period the TIROS nephanalyses gave too much cloudiness for large cloud amount, and too little for small cloud amount.
Abstract
A synthesis is made of several published studies of the normal heat budget of the lower troposphere over the Northern Hemisphere in winter. Charts of heat sources and sinks are presented, based on two independent methods, one using the thermodynamic energy equation and the other a heat-balance procedure. Although there are differences in important details, both methods indicate that the horizontal scale of heating is the same as that of the normal lower-tropospheric temperature field, but that the field of heating is almost 90° out of phase with that of temperature.
This result has an important bearing on the energy budget of the circulation. It is concluded that the heat-balance method is correct in indicating that there is a positive correlation between the normal temperature and heating fields. According to the energy transformation equations, this means that there is a positive transformation from heating to potential energy at the scale of the climatological long waves. This energy is directly available for maintaining these waves against friction.
It is hoped that this study will be of some use in the design of numerical general circulation experiments, and as a basis of comparison with data from meteorological satellites.
Abstract
A synthesis is made of several published studies of the normal heat budget of the lower troposphere over the Northern Hemisphere in winter. Charts of heat sources and sinks are presented, based on two independent methods, one using the thermodynamic energy equation and the other a heat-balance procedure. Although there are differences in important details, both methods indicate that the horizontal scale of heating is the same as that of the normal lower-tropospheric temperature field, but that the field of heating is almost 90° out of phase with that of temperature.
This result has an important bearing on the energy budget of the circulation. It is concluded that the heat-balance method is correct in indicating that there is a positive correlation between the normal temperature and heating fields. According to the energy transformation equations, this means that there is a positive transformation from heating to potential energy at the scale of the climatological long waves. This energy is directly available for maintaining these waves against friction.
It is hoped that this study will be of some use in the design of numerical general circulation experiments, and as a basis of comparison with data from meteorological satellites.
Abstract
Ship weather and sea-temperature observations were used to obtain averaged values of sea and air temperature, dewpoint, windspeed and the transfer of real and latent heat from the sea-surface for a large number of 10-day and 5-day periods from the hurricane seasons of several years; and for an area comprising the Atlantic south of 35H, the Gulf of Mexico and the Caribbean Sea. These parameters were studied with regard to the possibility of forecasting hurricane and tropical storm genesis and paths for several days in advance.
Although none of the parameters provided a definite indication in each case of storm formation and track, the energy-transfer parameter showed some skill when averaged for several storms, in the sense that storms appear to form downstream from geographical centers of maximum heat transfer. The sea-temperature anomaly (studied for only part of the above data) seems especially consistent in indicating the subsequent track of the storms, which tend to be along axes of maximum positive anomaly.
Abstract
Ship weather and sea-temperature observations were used to obtain averaged values of sea and air temperature, dewpoint, windspeed and the transfer of real and latent heat from the sea-surface for a large number of 10-day and 5-day periods from the hurricane seasons of several years; and for an area comprising the Atlantic south of 35H, the Gulf of Mexico and the Caribbean Sea. These parameters were studied with regard to the possibility of forecasting hurricane and tropical storm genesis and paths for several days in advance.
Although none of the parameters provided a definite indication in each case of storm formation and track, the energy-transfer parameter showed some skill when averaged for several storms, in the sense that storms appear to form downstream from geographical centers of maximum heat transfer. The sea-temperature anomaly (studied for only part of the above data) seems especially consistent in indicating the subsequent track of the storms, which tend to be along axes of maximum positive anomaly.
