摘要:

The global daytime ozone was measured by the Solar Mesosphere Explorer satellite (SME) for 5 years. The measurements extend through the mesosphere, covering from 50 km to over 90 km. The ozone in the upper mesosphere varies annually by up to a factor of 3. The observed seasonal variations may be summarized in several different ways. From year to year there is a great deal of repeatability of these variations. This repeatability occurs in most of the upper mesosphere outside the tropics. Near 0.01 mbar (80 km) the mid‐ and high‐latitude mixing ratio peaks each year in mid‐April. A secondary maximum in the altitude profile of ozone density usually occurs near 85 km. Changes in this structure are directly related to the April maximum and other seasonal changes seen at 0.01 mbar. The changing seasonal structure produces a “bump” at the ozone mixing ratio minimum that is largest just after spring equinox. This perturbation to the mixing ratio profile seems to move upward during the first half of the year. The seasonal changes of ozone were analyzed in terms of annual and semiannual structure. The variations generally have both an annual and semiannual component depending on altitude and latitude. The phases of the variations change quickly with both altitude and latitude. The semiannual component peaks in April, over most of the upper m

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07395

年代:1990

数据来源: WILEY

摘要:

Currently archived ozone data from the Solar Backscatter Ultraviolet (SBUV) spectrometer experiment on the Nimbus 7 satellite has been reported to show large global decreases in the amount of atmospheric ozone, both total content and as a function of altitude, for the period from 1978 to 1987. Analysis of atmospheric albedo data leading to these reported trends was based on empirical models of the SBUV spectrometer and diffuser plate degradation with time. Their combined degradation can be obtained from apparent decreases in measured solar irradiance at wavelengths where little or no long‐term intensity changes are expected. The central problem in analyzing SBUV data is to separately specify the diffuser plate degradation [Husdon et al., 1988]. Ratios of radiance to solar irradiance used to obtain ozone amounts are proportional only to diffuser reflectivity and independent of any spectrometer degradation. Even observations of relatively short‐term solar irradiance changes with time must be based on a model of diffuser plate degradation, since the SBUV data provide no internal means to uniquely specify diffuser plate reflectivity changes at ail wavelengths. A new class of explicitly empirical models have been developed that produce a better fit to all of the SBUV solar flux data. The models have a single free parameter to separately specify the diffuser plate and spectrometer degradation. This parameter must be within a narrow range to bring the calculated ozone trend into approximate agreement with data from the Dobson network, Solar Mesospheric Explorer (SME) and Stratospheric Aerosol Gas Experiment (SAGE) satellites, or with the different trends reported from the Umkehr ground stations. It is shown that outside sources of ozone data must be used to obtain a unique solution from SBUV radiance data within the precision necessary to determine the existence of a global annual ozone decrease. A correction factor is given as a function of time and altitude that brings the SBUV data into approximate agreement with SAGE, SME, and Dobson ozone trends. The total ozone results also agree with a recently developed wavelength pair justification method of internal calibration for the SBUV instrument. In our opinion, the currently archived SBUV ozone data should be used with caution for periods of analysis exceeding 1 year, since it is likely that the yearly decreases contained in the archived data are too la

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07403

年代:1990

数据来源: WILEY

摘要:

Daily average solar proton flux data for the years 1963–1984 (two solar cycles) have been used in a proton energy degradation scheme to derive ion pair production rates and, subsequently, HOx(H, OH, HO2) and NOx(N, NO, NO2) production rates. These HOxand NOxproduction rates are computed in a form suitable for inclusion in an atmospheric two‐dimensional time‐dependent photochemical model. The HOxincreases, although large for certain solar proton events (SPEs), are relatively short‐lived because the HOxspecies have lifetimes of only hours in the middle atmosphere. For longer‐lived NOxspecies, increases are important for 2–4 months past the more intense SPEs but are generally negligible 6 months after the SPE. The only exception to this scenario was the gigantic August 1972 SPE, whose stratospheric effects lasted about a year past the event. Comparisons of model results with the ozone data from the Nimbus 4 backscattered ultraviolet (BUV) instrument indicate relatively good agreement in the time dependence and magnitude of the ozone depletion for the middle stratosphere between the model and measurements for the August 1972 SPE and for 2 months past the event. The model predictions for the August 1972 SPE indicate at most a 1% decrease in total ozone at the highest latitudes with a significant interhemispheric difference. The model predicts a larger middle latitude stratospheric ozone change in the southern than the northern hemisphere caused by the difference in seasons between the two hemispheres. The computed ozone decreases associated with the HOxand NOxincreases are substantial in the upper stratosphere at high latitudes for only a few SPEs in the 22 years studied. A mechanism is presented for transport of NOyfrom the stratosphere to the ground, which may be involved in the enhancements in nitrate fluxes noticed in Antarctic deposition data. Our computations, however, indicate that the SPE contributions to these nitrate fluxes (even for the August 1972 SPE) are pro

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07417

年代:1990

数据来源: WILEY

摘要:

The polar twilight atmosphere is different from that at mid‐latitude in several ways which lead to significant changes in the wavelength‐dependent radiation field. Ozone depletion in the stratosphere leads to increased scattering below 340 nm. Polar stratospheric clouds produce changes in the radiation field which depend on cloud height and thickness. A surface albedo near unity produces a large increase in scattering. Multiple scattering becomes a larger percentage of the radiation field as solar zenith angle increases. These perturbations on the radiation field lead to enhanced ozone destruction in the stratosphere, increased surface irradiance, and a significant wavelength‐dependent increase in nadir rad

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07429

年代:1990

数据来源: WILEY

摘要:

Diurnal and nocturnal laser radar measurements of mesospheric sodium density at São José dos Campos, Brazil (23°S, 46°W), show strong oscillations with 12 and 24 hour periods. Data obtained in 1981 showed that atmospheric tides, mainly the vertical wind field, are the major causes of the density variations at a fixed height, thus making it possible to infer vertical wind parameters over a limited height range. In this work, 1984 and 1985 data are added to the earlier 1981 data and the 12‐ and 24‐hour components are determined for different seasons in order to study the seasonal variations of the tides. It is shown that the amplitudes of the oscillations in sodium density and consequently the vertical wind amplitudes, in general, are larger in winter than in other seasons. Above 97 km, the semidiurnal amplitude is larger than the diurnal in winter, of the same order of magnitude at the equinoxes and smaller in summer. The phases of the inferred semidiurnal vertical wind component, above 97 km, show regular propagating characteristics with little differences between winter and equinoxes, but a confused pattern in summer. Below 93 km the wavelengths decrease from winter to summer. In all seasons, the phase of the inferred diurnal vertical wind component stays at around 19–23 h below 85 km and above 93 km. The behavior of the phase of the diurnal oscillation in sodium density between 85 and 90 km is quite different in the three seasons. This is explained by seasonal differences in the relative phases of the oscillations in vertical wind an

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07435

年代:1990

数据来源: WILEY

摘要:

A rocket‐borne mass spectrometer has been developed for high‐time‐resolution and high‐accuracy measurements of the number densities of nitrogen,n(N2), and argon,n(Ar), in the altitude region from 90 to 130 km. Primary aims of the experiments are the determination of altitude profiles for the ration(Ar)/n(N2) and for small‐scale fluctuations ofn(N2). From the profiles we deduce the strength of eddy mixing, and from the fluctuations we deduce properties of instantaneous turbulence. We report on the results of four successful experiments, all performed during wintertime at polar latitudes. Near 100‐km altitude, eddy coefficients Kewere found to range from 102to>103m2/s, the spectral index ξ of the power spectral density ranged from −1.2 to −2.0, and the rates of dissipation of turbulent energy, ε, ranged f

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07443

年代:1990

数据来源: WILEY

摘要:

Extensive testing of the advective scheme, proposed by Prather (1986), has been carried out in support of the California Institute of Technology–Jet Propulsion Laboratory two‐dimensional model of the middle atmosphere. We generalize the original scheme to include higher‐order moments. In addition, we show how well the scheme works in the presence of chemistry as well as eddy diffusion. Six types of numerical experiments including simple clock motion and pure advection in two dimensions have been investigated in detail. By comparison with analytic solutions it is shown that the new algorithm can faithfully preserve concentration profiles, has essentially no numerical diffusion, and is superior to a typical fourth‐order finite difference

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07467

年代:1990

数据来源: WILEY

摘要:

Results of recent International Ultraviolet Explorer (IUE) observations of Venus made on January 20, 1987, and April 2 and 3, 1988, along with a reanalysis of the 1979 observations (Conway et al., 1979) are presented. The observations indicate that the amount of sulfur dioxide at the cloud tops of Venus declined by a factor of 8±4 from 380±70 ppb in 1979 to 50±20 ppb in 1987 and 1988. These values are consistent with the Pioneer Venus results (L. W. Esposito, A recalibration of the solar flux for Pioneer Venus results and a comparison of existing SO2measurements on Venus, unpublished manuscript, 1989). We identify absorption features of sulfur monoxide for the first time, and estimate the SO mixing ratio above the cloud level is 20±10 ppb for 1979. This is consistent with photochemical models by Winick and Stewart (1980) and Yung and DeMore (1982) and with the upper limit from Wilson et al. (19

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07485

年代:1990

数据来源: WILEY

摘要:

Measurements of nonmethane hydrocarbons (NMHCs) from urban plumes have previously been used to deduce average OH concentrations by monitoring the decay of the NMHCs from initial values and comparing their time rates of decay to the decay rate of a relatively inert tracer emitted from the same source. Under the assumption of no interaction between photochemistry and transport, these observationally derived indirect OH concentrations are lower for NMHCs with successively higher reactivities toward OH. In this study, analytical solutions to simple flow situations and a three‐dimensional mesoscale model are used to test this assumption. When turbulent transport is parameterized in terms of diffusion coefficients, the models yield results that are consistent with the observations and suggest that the assumption is not generally valid. Daytime vertical mixing within the planetary boundary layer (PBL) and horizontal diffusion are two transport processes that cannot be assumed to be separable from species reactivity. The net effect is that under most daytime conditions the OH concentrations can be underpredicted by more than a factor of 2 when highly reactive NMHCs are used to derive OH concentrations in the usual manner. However, these results only apply when the species used to derive OH concentrations are emitted from a continuous source. The assumption of separability between photochemistry and transport is valid when only instantaneous or puff emissions are considered. An explanation of these effects is presented within the context of the analytical results to some simple flow systems. Results from the three‐dimensional model are used to illustrate the interaction of species reactivity and transport for more realistic parameterizations of atmospheric transport. The results of this study have important implications for experiments designed to indirectly determine OH concentrations and also for the treatment of turbulent transport in Lagrangian and Eulerian photochemical mod

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07493

年代:1990

数据来源: WILEY

摘要:

Experiments were conducted to examine the chemical properties of dew (and guttation) that affect the dry deposition of SO2to prairie grasses of tall stature and mixed broadleaf plants of short stature. For 2–3 hours after sunrise, liquid samples were extracted directly from the upper of the plant canopies and from surrogate surfaces, concurrently with selected atmospheric observations. Chemical analyses showed that aqueous concentrations of S(IV), SO42‐, and several other ions in the leaf wetness were often high compared to values typically found in rain, while NH4+was not very abundant. Guttation produced substantial amounts of liquid, which mainly contributed Cl−to the leaf wetness. The dry deposition of S(IV) to leaf wetness was not always apparently limited by aqueous oxidation by O3, especially when aerodynamic resistances limited the maximum potential deposition velocity to less than 0.5 cm/s at a height of 8 m. A more effective oxidant than atmospheric O3or NO2could have been present and could have lessened the inferred substantial contributions of particle deposition to leaf wetness SO42‐. Foliar uptake of NO3‐and SO42‐was significant after sunrise. ThepH of the leaf wetness in the broadleaf vegetation seemed to have a lower limit of about 5.3, possibly because of neutralization by substances leached from leaves, while thepH of the grasses reached values as low as 4.5 when the amount of leaf wetness was small. The potassium ion concentration in leaf wetness appeared to be an effective marker for le

ISSN:0148-0227    

DOI:10.1029/JD095iD06p07501

年代:1990

数据来源: WILEY