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Preliminary Concepts
Published in Hillel Rubin, Joseph Atkinson, Environmental Fluid Mechanics, 2001
One further modification is obtained by using virtual temperatures, Tv, rather than the actual temperatures. The virtual temperature is defined as the temperature of dry air having the same density as the actual moist air. This provides a more realistic driving force for the convection. The virtual temperature is related to actual temperature by
A proposed new model for the prediction of latitude-dependent atmospheric pressures at altitude
Published in Science and Technology for the Built Environment, 2021
The NCEP/NCAR Reanalysis 1 project (Kalnay et al. 1996) uses a state-of-the-art analysis/forecast system to perform data assimilation using past data from 1948 to the present. It is a continually updated (1948–present) globally gridded dataset that represents the state of the earth's atmosphere, incorporating observations and numerical weather prediction (NWP) model output from 1948 to present. It is a joint product from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR). The global archived weather data can be accessed and downloaded through the NOAA Physical Sciences Laboratory website (NOAA 1996). The program will calculate annual and seasonal means based on the monthly range, latitude, and longitude entered and the pressure selected by the user. The spatial coverage can be user selected, ranging from a 2.5° latitude by 2.5° longitude single grid point to an entire zone such as 0° to 360° latitude coverage. The pressure levels are preset with the following values: 1000 mb, 925 mb, 850 mb, 700 mb, 600 mb, 500 mb, 400 mb, and 300 mb. At 60° latitude and above, at lower elevations near sea level there is a noticeable influence on the air temperature, presumably due to the albedo effect. Consequently, the dry air lapse rate is not constant. At higher elevations of 925 mb and above, the change in dry air temperature with altitude assumes nearly linear behavior and the lapse rate can be assumed to be constant. Due to nonlinear behavior near sea level, only the following pressure levels were considered when computing the lapse rate, sea-level temperature, and sea-level pressure: 925 mb, 850 mb, 700 mb, 600 mb, and 500 mb. At 45° latitude, this corresponds to an elevation range from 777 m to 4231 m. This pressure and elevation range is that of general interest for this study and a range of engineering applications. By omitting the data corresponding to 1000 mb near sea level, the accuracy of the atmospheric pressure prediction is greatly increased at 60° latitude and above. At mid-latitudes there is no noticeable difference, but for consistency reasons the 1000 mb data were omitted here too. In most of the southern hemisphere, a similar behavior can be observed. However, the southern tip of Chile is at −55° latitude and this study does not cover any geographical areas further south than −60°. Near the equator the lapse rate shows a similar but less pronounced behavior of nonlinearity near sea level. Figure 5 shows an example of the nonlinear behavior for select latitudes. The air temperature used in Figure 5 is based on a calculated “virtual air temperature” and not the actual humid air temperature. In this case, the virtual temperature is defined as the temperature of an air parcel with the dry air pressure and density being equal to the air pressure and density of humid air. To obey the conditions set forth for the derivation of Equation 18 the lapse rate must show a linear behavior. A linear regression was used for the computation of the lapse rate and the mean sea-level temperature.