Engineering topics

Heath, D. F.

Publications and source records attributed to Heath, D. F..

At least 37 records · Page 2

NASA NTRS1984

Feasibility of determining cloud-top heights using the backscattered ultraviolet satellite observation technique

A technique for determining cloud-top height by means of backscattered ultraviolet (BUV) solar radiation is presented. Cloud-top heights can be inferred using this technique of both the BUV radiance and its degree of polarization are measured by a spacecraft and compared with theoretical values. The cases of satellites with high-inclination orbits and geosynchronous satellites are discussed here. Based on calculations of radiance and polarization, the resolutions of cloud-top height determinations are roughly estimated in both cases. The estimates show that inference is possible as long as the angle between the direction of the sun and the satellite from the point of interest in the atmosphere is larger than about 10 deg. The estimates also indicate that the cloud-top-height resolution depends on solar zenith angle theta(0) in the case of nadir observation by satellites in nonequatorial orbits: The resolution is about 0.5 km for theta(0) = 30 and about 0.3 km for larger theta(0). On the other hand, when observations are made by geosynchronous satellites, the resolution depends strongly on the latitude of the point of interest, alpha(1); a resolution within 0.4 km can be achieved for alpha(1) less than or equal to 65 deg (0.2 km resolution can be obtained for middle latitudes). Resolution becomes rapidly worse with increasing latitude, and alpha(1) = about 70 deg seems to be the limit of observations with this technique.

Aruga, T.↗

NASA NTRS1983

Differences in the temporal variations of solar UV flux, 10.7-cm solar radio flux, sunspot number, and Ca-K plage data caused by solar rotation and active region evolution

Attention is given to two types of temporal variations in the solar UV spectral irradiance caused by solar rotation and active region evolution. It is noted that the first type of dissimilar temporal behavior occurs when concentrations of solar active regions evolve at solar longitudes nearly 180 deg apart. Both the UV observations and modeled UV fluxes based on Ca-K plage data then exhibit pronounced 13-day periodicity, whereas the 10.7-cm solar radio flux and sunspot number exhibit quite dissimilar temporal variations. This type of dissimilarity is related to the modeled UV flux and has a dependence on the solar central meridian distance that is narrower than that for the 10.7-cm radio flux or for sunspot numbers. A second case of marked dissimilarity is seen when major new solar active regions arise and dominate the full-disk fluxes for several rotations. It is found that the strongest peaks in 10.7 cm and sunspot numbers tend to occur on their first rotation, for example, during major dips in the total solar irradiance, whereas the Ca-K plages and UV enhancements peak on the next rotation and then decay more slowly on subsequent rotations.

Donnelly, R. F.↗

NASA NTRS1983

User's guide for the Solar Backscattered Ultraviolet (SBUV) and the Total Ozone Mapping Spectrometer (TOMS) RUT-S and RUT-T data sets: October 31, 1978 to November 1, 1980

Raw data from the Solar Backscattered Ultrviolet/Total Ozone Mapping Spectrometer (SBUV/TOMS) Nimbus 7 operation are available on computer tape. These data are contained on two separate sets of RUTs (Raw Units Tapes) for SBUV and TOMS, labelled RUT-S and RUT-T respectively. The RUT-S and RUT-T tapes contain uncalibrated radiance and irradiance data, housekeeping data, wavelength and electronic calibration data, instrument field-of-view location and solar ephemeris information. These tapes also contain colocated cloud, terrain pressure and snow/ice thickness data, each derived from an independent source. The "RUT User's Guide" describes the SBUV and TOMS experiments, the instrument calibration and performance, operating schedules, and data coverage, and provides an assessment of RUT-S and -T data quality. It also provides detailed information on the data available on the computer tapes.

Fleig, A. J.↗

NASA NTRS1983

Asymmetries of the upper stratospheric ozone distribution between two hemispheres

In connection with the eccentricity of the earth's orbit, conditions of solar radiation are not strictly symmetrical for the two hemispheres. The intensity of solar irradiation is approximately 6.6 percent higher near perihelion than near aphelion. As the ozone densities in the upper stratosphere and mesosphere are mainly controlled by photochemical processes, the asymmetry of irradiation conditions for both hemispheres could result in corresponding asymmetries regarding the ozone content. The present investigation is concerned with this possibility. The investigation takes into account Nimbus-7 and Nimbus-4 satellite data. It is found that the hemispheric asymmetries of the ozone distribution in the summer mesosphere and upper stratosphere are fully ascribable to the hemispheric temperature differences due to the combined effects of the earth's orbital ellipticity and its tilted spin axis from the ecliptic plane. The wintertime hemispheric asymmetries imply the presence of additional effects.

Maeda, K.↗

NASA NTRS1983

Observation of El Chichon volcanic aerosols by the solar backscattered ultraviolet (SBUV) experiment

The Solar Backscatter Ultraviolet Experiment (SBUV) aboard the Nimbus-7 satellite identified large amounts of SO2 in the tropical stratosphere on April 15, 1982, 11 days after major eruption of the El Chichon volcano in southern Mexico. It is shown in the present study that the backscattered ultraviolet radiances measured by the SBUV experiment have been strongly affected by the presence of stratospheric volcanic cloud from the El Chichon eruptions. Both SO2 and aerosol amounts present in the volcanic cloud have been mapped on the basis of an analysis of the radiances measured by the SBUV and TOMS (Total Ozone Mapping Spectrometer) experiments. It is estimated that a volcanic cloud of optical depths as small as 0.03 can be detected using SBUV, provided the cloud reaches the middle atmosphere. Lower-altitude clouds have progressively smaller effects on the radiances as well as on the ozone profile derived from them and are therefore harder to detect.

Bhartia, P. K.↗

NASA NTRS1982

Ozone climatology series. Volume 1: Atlas of total ozone, April 1970 - December 1976

Contours and gridded values are given for seven years of monthly mean total ozone data derived from observations with the Backscattered Ultraviolet instrument on Nimbus-4 for the Northern and Southern Hemispheres. The instrument, algorithm, uncertainties in derived ozone and systematic changes in the bias with respect to the international groundbased ozone network of Dobson instruments, are discussed.

Heath, D. F.↗

NASA NTRS1982

A three-component model of the variability of the solar ultraviolet flux 145-200 nM

The variability of the ultraviolet flux between 145 and 200 nm over both the eleven-year cycle and the 27-day solar rotation period is examined in terms of chromospheric activity, as determined from ground-based observations of the CaII K chromosphere. A three-component model of the solar UV flux is developed which includes the contributions to the full disk flux from both plage and active network emission. Solar cycle and solar rotation variations derived from the model are compared with the results of satellite and rocket experiments and with the two-component model of Cook et al (1980). Finally, possible ways of improving the model are discussed.

Lean, J. L.↗

NASA NTRS1982

Active-region evolution and solar rotation variations in solar UV irradiance, total solar irradiance, and soft X rays

Variations in the total solar irradiance, solar UV spectral irradiance, and solar soft X-ray emission caused by active region evolution and solar rotation are analyzed by using concurrent measurements from the NIMBUS 7 and GOES satellites. The observations are interpreted by using simple empirical models that relate ground-based observations of the size and location of sunspots and plages to the full-disk temporal variations. It is found that the major dips in the photospheric total solar irradiance S, which are evident in both satellite measurements and model predictions, are usually not accompanied by outstanding enhancements in the chromospheric and upper photospheric UV spectral irradiance or coronal X rays. The main cause of this difference between the variability of S and of the UV flux is that the total chromospheric plage enhancements are not outstanding at those times when the total sunspot are outstanding. X rays are even more variable because of a much wider CMD sensitivity.

Donnelly, R. F.↗

NASA NTRS1982

On the adequacy of the fixed locations of the surface-based international network for inferring interannual ozone variability

The influence of the geographical distribution and the number of the surface stations in the ozone detecting network on changes in global ozone inferred from the surface measurements is investigated by comparison with information obtained from satellite backscattered UV observations on the Nimbus 4 with nearly complete global coverage for the period 1970-1972. Results show that the geographical distribution of the stations does not properly represent different latitudes. While the number of stations in the north temperate zone appears adequate to represent monthly ozone averages to within 0.5% except during the early phase of the Northern Hemisphere spring maximum, the resultant error in the derived change in north temperature zone ozone between 1970-1972 is 0.5%. In the tropical and south temperate zones the smaller number of stations reduces precision, and the ozone averages for use in deriving seasonal variability and trends are uncertain by about 1%. However, in the south temperature zone, the average from the sample may differ as much as 5% in some months from the averages derived from the full set. It is concluded that the resulting uncertainty in the global averages is comparable in size to typical yearly changes.

Heath, D. F.↗

NASA NTRS1982

Backscattered UV radiation - Effects of multiple scattering and the lower boundary of the atmosphere

A method is proposed for the calculation of a multiple-scattering correction to the single-scattering calculation of the radiance of the terrestrial atmosphere resulting from backscattered ultraviolet solar radiation in the spectral region used in the ozone profile inversion. This method uses jointly the usual analytical and Monte Carlo methods. Effects of the lower boundary of the atmosphere, cloud tops, and ground surface are investigated both qualitatively and quantitatively. The ratio of multiple to single scattering is determined, and its importance in ozone profile inversion of backscattered UV solar radiation from the terrestrial atmosphere is evaluated. The polarization of the atmospheric radiance is treated briefly.

Aruga, T.↗

NASA NTRS1982

Determination of vertical ozone distributions by spacecraft measurements using a limb-scan technique

The principle of a new inversion technique which uses multiple wavelength-solar UV radiation satellite measurements for determining vertical ozone profiles is described, and examples of computer simulations for 280, 300, 320, and 340 nm are discussed. Weighting functions corresponding to the sensitivity of the limb radiance to the relative ozone density at each altitude are the basis for the inversion equation, which is then solved by an iteration technique. The use of multiple wavelengths can provide more information of higher accuracy over a wider height range than those profiles recovered at a single wavelength. It is indicated that an effective range of altitude of approximately 20-70 km with a vertical resolution of 1-2 km is feasible for determining ozone profiles with an inferred profile error about three to four times larger than the measurement error within that altitude region. Ozone profile accuracy of the highest altitude region may be improved using wavelengths down to 260 nm, and inferred ozone profiles above 70 km are possible, but with a larger error.

Aruga, T.↗

NASA NTRS1982

Total ozone variations 1970-74 using Backscattered Ultraviolet /BUV/ and ground-based observations

The most long-lived satellite set of ozone observations, to date, is that derived from the Backscatter Ultraviolet (BUV) ozone sensor on Nimbus 4 and extends from April 1970 through 1976. Unfortunately, this experiment suffered spacecraft power limitations which limited the spatial and temporal coverage and also appears to have suffered from long-term drifts which may be associated with changes in the instrument characteristics or the incident solar flux. Techniques have been developed to account for these problems, and this paper presents results of the BUV total ozone variations and compares them with those from ground-based observations, specifically the computations of Angell and Korshover (1978). After adjustments for the spatial gaps and comparison with concurrent Dobson ground-based observations, no significant trend was found in the BUV data over the years 1970-74. This finding is in contrast to a general decrease of about 2% during the same period appearing in the data of Angell and Korshover. The difference in these results is discussed in terms of the geographic sampling and the methods of hemispheric integration.

Miller, A. J.↗

NASA NTRS1981

A mechanism for solar ultraviolet flux variability

Following an examination of solar UV emission observed by a filter photometer on Nimbus IV from 1969 to 1973 in an attempt to understand the 27-day and secular variability, two models are proposed to account for the variations: (1) a calcium plage model and (2) a chromospheric network faculae and spicule structure model. An association between UV brightenings and the large scale magnetic field has been found to be consistent with the network model. An increase in the UV emittance can be achieved by raising the effective chromospheric temperature closer to a photospheric level. If the sun's luminosity is constant on these time intervals, the enhanced UV radiation could be partially offset by an overall decrease in photospheric temperature such as that measured by Livingston (1978) in visible photospheric profiles.

Schatten, K. H.↗

NASA NTRS1981

Comparisons of global ozone trends inferred from the BUV experiment on Nimbus 4 and the ground-based network

Preliminary comparisons between global ozone burdens derived from the backscattered ultraviolet (BUV) experiment on Nimbus 4 and those inferred from an analysis of ground-based network data seem to indicate significant differences in the inter-annual variability of ozone. Some of the observed differences may be due to improper weighting of the ground-based network data, slowly changing planetary wave structure over the fixed station, of small inter-annual changes in meridional transport parameters. There is also some evidence which indicates that the polar stratosphere at high latitudes may represent an important ozone storage resevoir which tends to compensate for large scale changes observed in the regions outside of the polar stratosphere. Possible consequences of this are that the global trends derived from ground based ozone measurements may not be valid and furthermore that the current satellite techniques by themselves may be sufficient. An ozone monitoring system which includes observations from satellites, ground-based stations, balloons and rockets may be necessary.

Heath, D. F.↗

NASA NTRS1981

Effects of the August 1972 solar particle events on stratospheric ozone

High-energy proton data obtained by polar-orbiting satellite and several balloon flights are used to derive the spatial extent and ionization profiles of regions irradiated by the intense solar particle events (SPE) of August 1972. Backscattered ultraviolet ozone sensors on the Nimbus 4 satellite identified and tracked the polar ozone cavity created by particle ionization during the intense, ten-hour period of August 4, which persisted and rotated as a semirigid mass in an east-to-west direction during 53 days of continuous tracking. Time-dependent chemistry calculations have been performed to show the cause, magnitude, and temporal features of the ozone reduction. Attempts to verify the predicted temperature changes have been unsuccessful due to limitations in the temperature measurement techniques used.

Reagan, J. B.↗

NASA NTRS1981

Stratospheric ozone response to a solar proton event - Hemispheric asymmetries

Large-scale stratospheric ozone reduction due to precipitating energetic solar protons is examined, based on the backscattered ultraviolet experiment on the Nimbus 4 satellite during the 1972 solar flare. Some chemical equations for the processes are outlined. Distinct asymmetries in the columnar ozone content, the amount of ozone depression, and their temporal variation above 4 mb level (about 38 km) were observed between the two hemispheres. These asymmetries are ascribed to the differences mainly in dynamics and partly in the solar illumination and the vertical temperature structure between the summer and the winter polar atmospheres.

Maeda, K.↗

NASA NTRS1981

Results and analyses of ground-based and satellite ozone observations A review

The ground-based network that has been in existence for several decades is described. Attention is given to two basic questions, namely the way in which monthly satellite analyses compare with those from the ground-based network and the way in which the trends from the satellite and ground-based data compare. Synoptic analyses of total ozone for December 1970 are compared with a subjective analysis of the ground-based network and an objective backscatter ultraviolet (BUV) analysis. It is found that the BUV analysis is the more consistent of the two. Considering monthly analyses for September 1970, satellite and ground-based data are found to agree quite well. In considering the question of trend determination by the ground-based versus the satellite systems, attention is given to the sources of error in the satellite system. The principal sources of error in BUV analysis are thought to be calibration drift with time and the fact that, over the lifetime of the satellite spacecraft, power limitations result in a decrease in the number of data points per month, possibly with significant gaps in the coverage.

Miller, A. J.↗

NASA NTRS1981

Seasonal variations of total ozone revealed by the Nimbus-4 BUV data set

Backscattered ultraviolet (BUV) data from the Nimbus-4 spacecraft for the period 1970-1977 have been processed to a refined level. The seasonal and interannual variations of total ozone are examined on a global scale, using daily zonal means of 10 deg latitude bands and a time-latitude cross section. A harmonic analysis was performed on the daily zonal means and the amplitude, days of peak ozone values, and percentage of variance were computed for the annual, semiannual and higer harmonics for several years and each year. A clear quasi-biennial oscillation (QBO) was revealed from the tropics to midlatitudes after removing the mean annual wave. Asymmetries in the annual wave in the two hemispheres found earlier for the period 1970-1972 persist through the entire observation period. Interannual variations appear to be the result of the QBO of ozone from low to midlatitudes. Asymmetries in the QBO amplitude phase, and period were also detected in the two hemispheres.

Hilsenrath, E.↗