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Abstract
The 10.7-cm solar flux (S) is widely used for upper-atmosphere studies as an index of the solar extreme ultraviolet radiation (EUV), whose variations are responsible for major changes in properties above 200 km. A model was developed to calculate the density as a function of S for various local times and altitudes from 200 to 800 km. The accuracy was checked by comparison of calculated rates of satellite orbital decay with observed values for 7 satellites. This comparison revealed systematic differences between the calculated and observed decay values. From the analysis of these differences, it is concluded that the “semi-annual” effect is not a real effect in 1958 to 1961; rather this effect arises because S is not an accurate index for the total EUV. Evidently, the EUV has two variable components: one radiated from active (sunspot) areas, correlated with S, and the other radiated as a background emission rather uniformly distributed over the entire sun and not correlated with S.
A more accurate estimate of the relative variation of the EUV by months from 1958 to 1962 is presented in terms of a new parameter S′. While S appears to represent the year-to-year variation of the sun's EUV fairly well from 1958 to 1960, S′ averages much less than S in 1961 and 1962, indicating that S cannot be used to describe the long-term (solar cycle) variation of the EUV. Variations of the isothermal temperature above 400 km and the mean molecular weight from 400 to 800 km have been calculated for various S′ and local times with the generalized hydrostatic equation and constraints consistent with diffusive equilibrium. The average relative contribution of magnetic heating to the atmosphere is about 10 per cent of the total heating affecting the 100 to 200 km layer from July 1958 to September 1960.
Abstract
The 10.7-cm solar flux (S) is widely used for upper-atmosphere studies as an index of the solar extreme ultraviolet radiation (EUV), whose variations are responsible for major changes in properties above 200 km. A model was developed to calculate the density as a function of S for various local times and altitudes from 200 to 800 km. The accuracy was checked by comparison of calculated rates of satellite orbital decay with observed values for 7 satellites. This comparison revealed systematic differences between the calculated and observed decay values. From the analysis of these differences, it is concluded that the “semi-annual” effect is not a real effect in 1958 to 1961; rather this effect arises because S is not an accurate index for the total EUV. Evidently, the EUV has two variable components: one radiated from active (sunspot) areas, correlated with S, and the other radiated as a background emission rather uniformly distributed over the entire sun and not correlated with S.
A more accurate estimate of the relative variation of the EUV by months from 1958 to 1962 is presented in terms of a new parameter S′. While S appears to represent the year-to-year variation of the sun's EUV fairly well from 1958 to 1960, S′ averages much less than S in 1961 and 1962, indicating that S cannot be used to describe the long-term (solar cycle) variation of the EUV. Variations of the isothermal temperature above 400 km and the mean molecular weight from 400 to 800 km have been calculated for various S′ and local times with the generalized hydrostatic equation and constraints consistent with diffusive equilibrium. The average relative contribution of magnetic heating to the atmosphere is about 10 per cent of the total heating affecting the 100 to 200 km layer from July 1958 to September 1960.
Abstract
A simple atmospheric density model, based on satellite orbital decay data from four satellites, is derived by assuming that a direct proportionality applies between the 10.7-cm solar-radio-noise flux and the density. The model incorporates effects due to variations of solar activity and time of day in a single table of values from which the density and its variations, from altitudes of 200 to 800 km at low and middle latitudes, can be readily calculated as a function of the 10.7-cm solar flux. The accuracy with which the model represents the data from which it was derived is checked by comparing calculated rates of orbital decay with observed values.
As a result of these comparisons, it is concluded that the model has been able to represent the density derived from the four satellites with some degree of success. As the linear relationship between density and radio-noise flux is not likely on a physical basis, it is expected that a more complex relationship will have to be deduced ultimately in order to give good results near sunspot minimum.
This analysis demonstrates that great differences in air density exist between day and night in the upper thermosphere and lower exosphere, thus substantiating Jacchia generally. It strongly points up the need for satellite density measurements from the polar regions. The importance of 10.7-cm solar-radio-noise observations as a convenient index of solar ultraviolet radiation is evident, although its exact degree of representativeness over the range of a complete sunspot cycle is unknown.
Abstract
A simple atmospheric density model, based on satellite orbital decay data from four satellites, is derived by assuming that a direct proportionality applies between the 10.7-cm solar-radio-noise flux and the density. The model incorporates effects due to variations of solar activity and time of day in a single table of values from which the density and its variations, from altitudes of 200 to 800 km at low and middle latitudes, can be readily calculated as a function of the 10.7-cm solar flux. The accuracy with which the model represents the data from which it was derived is checked by comparing calculated rates of orbital decay with observed values.
As a result of these comparisons, it is concluded that the model has been able to represent the density derived from the four satellites with some degree of success. As the linear relationship between density and radio-noise flux is not likely on a physical basis, it is expected that a more complex relationship will have to be deduced ultimately in order to give good results near sunspot minimum.
This analysis demonstrates that great differences in air density exist between day and night in the upper thermosphere and lower exosphere, thus substantiating Jacchia generally. It strongly points up the need for satellite density measurements from the polar regions. The importance of 10.7-cm solar-radio-noise observations as a convenient index of solar ultraviolet radiation is evident, although its exact degree of representativeness over the range of a complete sunspot cycle is unknown.
Abstract
A nonintrusive remote sensing method to measure water level is examined. It relies on the fact that water is a good reflector of radio frequency energy, thus, on a satellite-to-ground path when the satellite is near the horizon, a readily detectable interference pattern is formed as the satellite moves through its orbit. Provided that the elevation angles from the ground-based receiver to the satellite are small enough for good reflection but not so small that atmospheric refractive effects contribute, the shape of this interference pattern is strongly related to the geometry of propagation. Results from interferometric observations of Global Positioning System (GPS) satellite signals are presented for two sets of measurements where the receiving antenna varied from 7 to 10 m above the nominal water surface. These results, compared to in situ or nearby tide gauges, show that water level is measured to an accuracy of about 12 cm. A GPS receiver, a laptop computer, and a clear over-water path to the horizon are all that is needed to provide an affordable means for tracking water levels or ocean tides.
Abstract
A nonintrusive remote sensing method to measure water level is examined. It relies on the fact that water is a good reflector of radio frequency energy, thus, on a satellite-to-ground path when the satellite is near the horizon, a readily detectable interference pattern is formed as the satellite moves through its orbit. Provided that the elevation angles from the ground-based receiver to the satellite are small enough for good reflection but not so small that atmospheric refractive effects contribute, the shape of this interference pattern is strongly related to the geometry of propagation. Results from interferometric observations of Global Positioning System (GPS) satellite signals are presented for two sets of measurements where the receiving antenna varied from 7 to 10 m above the nominal water surface. These results, compared to in situ or nearby tide gauges, show that water level is measured to an accuracy of about 12 cm. A GPS receiver, a laptop computer, and a clear over-water path to the horizon are all that is needed to provide an affordable means for tracking water levels or ocean tides.
Abstract
Current fallout-computation methods do not account for the early-time dynamics of the fallout process. Therefore, the present theory was originated in the attempt to explain the mechanics of fallout more completely. This theory is checked by developing from it a mathematical fallout model for land-surface bursts (the D model) and then by using this model to predict fallout properties for nuclear tests. From a comparison of the predictions with observed test data, it is concluded that the new theory, despite certain idealizations, is useful for fallout computation.
Abstract
Current fallout-computation methods do not account for the early-time dynamics of the fallout process. Therefore, the present theory was originated in the attempt to explain the mechanics of fallout more completely. This theory is checked by developing from it a mathematical fallout model for land-surface bursts (the D model) and then by using this model to predict fallout properties for nuclear tests. From a comparison of the predictions with observed test data, it is concluded that the new theory, despite certain idealizations, is useful for fallout computation.
Abstract
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Abstract
Eighteen hundred seventy-seven layers of turbulence, measured between 3000-18,300 m at four widely separated locations during all seasons by a parachuted telemetering instrument, have been analyzed by reducing the data to punched cards with the corresponding meteorological data. The altitude distribution of the layers exhibited three relative maxima (7400, 11,000, and 14,400 m), and three relative minima (6200, 9500, and 12,800 m). The first maximum, due to fronts, is the strongest. The other two are associated with the jet stream and probably represent clear-air turbulence. The trend is for turbulence to increase from 3000 to 7400 m, then to decrease slightly to 14,400 m, and then to decrease rapidly to 18,300 m. The average thickness of the layers was 239 m ; 87 per cent were less than 400 m thick. Most of this turbulence was indicated to be fairly persistent and moderate to heavy, having horizontal dimensions of at least 10 to 20 mi. This turbulence is below normal at the lowest freezing level. It is above normal at the base and top of well-marked tropospheric inversions, most of which are thought to be frontal inversions. No correlation was found with the base and top of the tropopause.
Correlations have been found between this turbulence and ranges of the following parameters: Richardson's number, vertical wind shear, lapse rate, wind speed and direction, temperature, and relative humidity. A theory of free-air turbulence, derived by analysis of the above-normal turbulence ranges for these parameters, has the following elements: 1. transitions occur in free-air turbulence flow, similar to transitions occurring in incompressible fluid flow; 2. transitions occur at certain values of Richardson's number R; 3. the vertical wind shear term is the most important parameter in R governing the turbulent flow. From the theory, it follows that the critical value of R can be taken to be unity, which means that the coefficients of turbulent diffusion for heat and momentum are equal in the free air.
Abstract
Eighteen hundred seventy-seven layers of turbulence, measured between 3000-18,300 m at four widely separated locations during all seasons by a parachuted telemetering instrument, have been analyzed by reducing the data to punched cards with the corresponding meteorological data. The altitude distribution of the layers exhibited three relative maxima (7400, 11,000, and 14,400 m), and three relative minima (6200, 9500, and 12,800 m). The first maximum, due to fronts, is the strongest. The other two are associated with the jet stream and probably represent clear-air turbulence. The trend is for turbulence to increase from 3000 to 7400 m, then to decrease slightly to 14,400 m, and then to decrease rapidly to 18,300 m. The average thickness of the layers was 239 m ; 87 per cent were less than 400 m thick. Most of this turbulence was indicated to be fairly persistent and moderate to heavy, having horizontal dimensions of at least 10 to 20 mi. This turbulence is below normal at the lowest freezing level. It is above normal at the base and top of well-marked tropospheric inversions, most of which are thought to be frontal inversions. No correlation was found with the base and top of the tropopause.
Correlations have been found between this turbulence and ranges of the following parameters: Richardson's number, vertical wind shear, lapse rate, wind speed and direction, temperature, and relative humidity. A theory of free-air turbulence, derived by analysis of the above-normal turbulence ranges for these parameters, has the following elements: 1. transitions occur in free-air turbulence flow, similar to transitions occurring in incompressible fluid flow; 2. transitions occur at certain values of Richardson's number R; 3. the vertical wind shear term is the most important parameter in R governing the turbulent flow. From the theory, it follows that the critical value of R can be taken to be unity, which means that the coefficients of turbulent diffusion for heat and momentum are equal in the free air.
Abstract
No Abstract Available.
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No Abstract Available.
Abstract
A semi-theoretical model of the upper atmosphere has been constructed to allow the calculation of neutral properties from 100 to 10,000 km as a function of local time and solar activity. The calculations are based on empirical density profiles obtained from a density (satelite-drag) model. Assuming diffusive equilibrium above 110 km and an isothermal region above 200 to 400 km, the remaining properties (pressure, temperature, molecular weight and constituent concentrations) are computed from a least squares procedure that, together with the hydrostatic equation and equation of state, determines individual particle concentrations.
Some justification should be made for the introduction of a new model. The model greatly extends the altitude range covered by most models. In order to do this, it accounts for the variation in the rate of escape of hydrogen from the exosphere over a solar cycle. In addition, the model represents the diurnal variation of hydrogen in the exosphere, a factor previously neglected. The maximum variation in the atomic hydrogen concentration from 6000 to 10,000 km, due to both the solar activity and diurnal effects, is about a factor of four. The total variation in atomic helium is much greater; it varies by about five orders of magnitude.
Finally, the diurnal and solar activity effects are enumerated in a consistent way from 100 to 200 km. Nine tables present the neutral atmospheric properties versus altitude fox sunspot maximum, average, and minimum conditions and for local times of 5 hr, 14 hr, and 21 hr (or 8 hr). These tables provide a simple format for the diurnal and solar activity variation of the properties, especially their profiles, for comparison with other models and with measurements made from rockets and satellites.
Abstract
A semi-theoretical model of the upper atmosphere has been constructed to allow the calculation of neutral properties from 100 to 10,000 km as a function of local time and solar activity. The calculations are based on empirical density profiles obtained from a density (satelite-drag) model. Assuming diffusive equilibrium above 110 km and an isothermal region above 200 to 400 km, the remaining properties (pressure, temperature, molecular weight and constituent concentrations) are computed from a least squares procedure that, together with the hydrostatic equation and equation of state, determines individual particle concentrations.
Some justification should be made for the introduction of a new model. The model greatly extends the altitude range covered by most models. In order to do this, it accounts for the variation in the rate of escape of hydrogen from the exosphere over a solar cycle. In addition, the model represents the diurnal variation of hydrogen in the exosphere, a factor previously neglected. The maximum variation in the atomic hydrogen concentration from 6000 to 10,000 km, due to both the solar activity and diurnal effects, is about a factor of four. The total variation in atomic helium is much greater; it varies by about five orders of magnitude.
Finally, the diurnal and solar activity effects are enumerated in a consistent way from 100 to 200 km. Nine tables present the neutral atmospheric properties versus altitude fox sunspot maximum, average, and minimum conditions and for local times of 5 hr, 14 hr, and 21 hr (or 8 hr). These tables provide a simple format for the diurnal and solar activity variation of the properties, especially their profiles, for comparison with other models and with measurements made from rockets and satellites.
Abstract
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