摘要:

I study the sensitivity of three‐dimensional Eulerian simulations of the evolution of 26 trace chemical species. The region simulated is 2,400 by 2,400 km horizontally and from the surface to about 15 km vertically. The uncertainty in simulated concentration is from perturbations or errors in input parameters and physical parameterizations: chemistry, emissions, meteorology, and initial and boundary conditions. I vary each input parameterpand calculate the root‐mean‐square (rms) change in concentration σ between the sensitivity run and the base run. The sensitivity parameter,S= ∂σ/∂p, is defined for each species and input parameter. For three scenarios I assign errors to each input parameter. For each species the total error in simulated concentration, σt, is the rms sum of the contributions by errors in each input parameter. I describe this error as the uncertainty,un= σt/cb, wherecbis the horizontal mean concentration in the base run, and as the normalized uncertainty,nu= σt/σb, where σbis the standard deviation of fluctuations horizontally aboutcb. The uncertainty suggests that O3is well simulated, but the normalized uncertainty shows it is poorly simulated. I prefernubecause it is more nearly constant for different species, butnuincreases with height, implying that the simulations are poorer aloft. If the input parameters have 25% errors, then, averaged for all species,un= 0.53 ± 0.43 andnu= 0.45 ± 0.24. Often, σtis largely from errors in meteorology and in initial and boundary conditions. Chemical errors dominate steady state species. Initial and boundary conditions must have errors less than 25% before the errors in emissions be

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02371

年代:1988

数据来源: WILEY

摘要:

On a spatial scale of up to 1,100 km and a temporal scale of up to 36 hours, we used Eulerian models to simulate the transport and diffusion of a passive tracer released from a point source near the surface. An Eulerian tracer model was driven by meteorological analysis of 6‐hour rawinsonde data supplemented by the simulations of an Eulerian mesoscale meteorological model. The tracer model simulations were compared with 6‐hour integrated samples collected at 86 surface stations during the Cross‐Appalachian Tracer Experiment (CAPTEX) for six different releases. We examined the effect of the parameterizations of vertical and horizontal sub‐grid scale turbulent transport and the finite difference advection scheme on the simulations of concentration and the trajectories of the center of mass of the tracer at the surface. We found that the simulated trajectory error was sensitive to the vertical eddy diffusivity but insensitive to the advection scheme and hence insensitive to (horizontal) numerical diffusion. Using 70‐km horizontal resolution, only the most sophisticated advection scheme tested here (Prather, 1986) simulated a tracer puff with a horizontal area that was not too large during the first 36 hours after a point source release. The other schemes tested (Russell and Lerner, 1981; a simplified version of Smolarkiewicz, 1983) had enough numerical diffusion that the simulated horizontal tracer puffs were larger than the observed puffs. There were considerable differences in the capability of the tracer models to simulate individual releases, particularly for quantitative comparisons of simulated and observed conce

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02389

年代:1988

数据来源: WILEY

摘要:

An analytical solution for the albedo to solar radiation of a broken cloud field over a black, nonreflecting ocean surface is presented. The clouds are assumed to be infinitely long, nontransmitting bars, with any top and side albedos. Cloud‐cloud shading and reflections are fully and analytically taken into account in the assessment of the contribution of the cloud sides to the cloud field albedo, while assuming, for this latter purpose only, the bi‐directional reflectivity of the sides to be isotropic. The model is an explicit function of cloud thickness, width, and intercloud spacing for all solar zenith and azimuth angles. Results are presented in the form of an effective cloudiness in azimuthally averaged form and as a function of azimuth angle for different solar elevation angles, aspect ratios, amounts of cloudiness, optical depth, and albedo for single scattering. In order to show the dominant effect of the geometry over the radiative transfer in this case, we simulated the [Harshvardhan and Thomas, 1984] model, adding only the explicit solution for the cloud‐cloud interaction. We then compared our results to theirs as well as to their Monte Carlo calculations, achieving a much better fit to the latter. The present model is neither more difficult to use than previous ones nor is it in need of refitting to data when more features are added or when optical properties of the cloud are changed. Tabular values of some necessary coefficients are given for independent use of the

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02405

年代:1988

数据来源: WILEY

摘要:

Relative absorption cross sections for hydrogen peroxide vapor were measured over the temperature ranges 285–381 K for 230 nm ≤ λ ≤ 295 nm and 300–381 K for 193 nm ≤ λ ≤ 350 nm. The well‐established 298 K cross sections at 202.6 and 228.8 nm were used as an absolute calibration. A significant temperature dependence was observed at the important tropospheric photolysis wavelengths, λ>300 nm. Measured cross sections were extrapolated to lower temperatures, using a simple model which attributes the observed temperature dependence to enhanced absorption by molecules possessing one quantum of O–O stretch vibrational excitation. Upper tropospheric photodissociation rates calculated using the extrapolated cross sections are about 25% lower than those calculated using currently recommended 29

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02417

年代:1988

数据来源: WILEY

摘要:

The literature concerning the “greenhouse” warming potentials of Chlorofluorocarbons F‐11, F‐12, F‐22, F‐113, F‐114, F‐134a, and F‐142b is reviewed. Additionally, infrared intensities are reported for each of the fundamental absorption bands of F‐113 (CF2ClCFCl2) and F‐114 (CF2ClCF2Cl) in the region between 8 and 20 μm. The measurements were made with a Fourier transform infrared spectrometer operated at 0.04 cm−1apodized resolution. The total intensities measured for this region were 4905 cm−2atm−1for F‐113 and 6064 cm−2atm−1for F‐114, compared to a total intensity of 3404 cm−2atm−1for F‐12 (CF2Cl2) in the same region. On the basis of these infrared intensities and the atmospheric lifetimes of F‐113 and of F‐114 relative to F‐12, and on a per unit mass basis, F‐113 and F‐114 are about 0.8 and 1.9 times as effective, respective

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02423

年代:1988

数据来源: WILEY

摘要:

Measurements are presented of simultaneous horizontal and vertical electric fields from 42 lightning return strokes in 27 flashes at distances from 7 to 43 km. The data were obtained at the NASA Kennedy Space Center, Florida, using an elevated spherical antenna having a system bandwidth of 3 Hz to 4 MHz. The strokes studied occurred in a 6‐min interval from 1850 to 1856 UT on August 11, 1984. The 42 measured horizontal fields exhibited initial peaks having a mean half width of 0.52 μs. The ratio of the amplitude of the peak horizontal field to the associated vertical field peak had a mean value of 0.030, with a standard deviation of 0.007. The measured horizontal field wave shapes are compared with those obtained from calculations using the measured vertical fields and theory (the “wavetilt” formula) that models the fields as plane wave radiation over a homogeneous ground of uniform conductivity and permittivity. The local ground conductivity, measured as a function of depth using the Wenner four‐probe method, was found to increase with depth within the region relevant to this study, from the surface to a depth of a few meters: the conductivity was 8.2×10−3mho/m between the surface and a depth of 2.2 m, and 3.1×10−2mho/m below this layer to a depth of 11 m. If a ground conductivity equal to that of the top layer is used in the wavetilt formula, the calculated horizontal field peaks are found to be, on average, about 33% wider and larger than the measured field peaks. Errors and compensation procedures for tilt of the spherical antenna, for electronic system distortion, and for electric field distortion at the antenna due to proximity of the ground and of the antenna support structure

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02429

年代:1988

数据来源: WILEY

摘要:

Thermodynamic properties of solid phases containing H2O and HCl are examined for conditions expected over Antarctica in winter. It is shown that solid solutions with 0.02–0.035 mole fraction HCl in H2O ice will form in the stratosphere at temperatures between 193° and 190°K. Crystalline HNO3·H2O and/or HNO3·3H2O form in the same temperature range. Thus condensation of small quantities of H2O (<1 ppm) leads to nearly complete removal of both HCl and HNO3from the gas phase. Formation of ice‐HCl solid solutions provides a favorable setting for the heterogeneous reaction of HCl with ClNO3, initiating a rapid sequence of reactions that converts solid‐phase HCl into gaseous ClNO3or chlorine oxide radicals. Odd nitrogen species are simultaneously converted into solid‐phase nitrates. The cycle producing reactive chlorine gases is likely to be completed before particles grow large enough to fall from the stratosphere. Hence precipitation of particles from the polar stratospheric clouds is expected to remove odd nitrogen from the stratosphere efficiently, leaving chlorine gases behind. High concentrations of reactive chlorine oxide radicals are rapidly produced by heterogeneous reactions if the initial concentration of HCl exceeds a critical value, 0.5 times the concentration of NOxbefore onset of condensation. Production of unreactive ClNO3and HOCl is favored if HCl levels are lower than this value. The onset of Antarctic ozone depletion in the late 1970s may in part reflect growth of HCl levels beyond thi

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02442

年代:1988

数据来源: WILEY

摘要:

On September 19–20 and October 4, 1985, in situ measurements of nitric oxide and ozone were carried out on board balloons launched from Aire sur l'Adour (44°N, 0°W) in France as a part of the Middle Atmosphere Program Global Budget of Stratospheric Trace Constituents NOxcampaign. On September 19 a daytime NO profile from 6 to 33 km and the variation of NO in the afternoon at a float altitude of about 32 km were measured precisely. In the afternoon, when the solar zenith angle was between 48° and 70°, NO concentration was fairly stable, probably to within 10%. The slow decrease of NO near sunset at solar zenith angles larger than 80° was observed. A calculation assuming photochemical equilibrium between NO and NO2has shown that the decay of NO toward sunset can be explained mainly by the decrease of the photodissociation rate of NO2at large solar zenith angles. On October 4 the variation of NO at an altitude of about 33 km was measured for 2.5 hours after sunrise. Following the rapid buildup, which takes place for 30 min after visible sunrise, NO increases at a rate of approximately 1.2 parts per billion by volume (ppbv) per hour. From the rate of increase in NO in the morning, the N2O5mixing ratio at sunrise at 33 km has been estimated to be 3.9±1

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02451

年代:1988

数据来源: WILEY

摘要:

A numerical model for the brightness of polar mesospheric clouds (PMC) is described, and is compared with measurements from the Solar mesosphere Explorer (SME) satellite. These clouds occur during the summer months at polar latitudes where temperatures are known to fall below 140 K. We calculate the optical properties of a cloud by simulating the growth and sedimentation of ice particles at the cold supersaturated mesopause. Time‐dependent trajectories of ice particles are calculated from their origin at the temperature minimum region to their demise at the cloud base through evaporation. We consider the effects of the removal of atmospheric water vapor by the growing particles and its restoration by ice evaporation at the cloud base. This “freeze‐drying” effect is crucial in limiting the maximum size of the particles and therefore the maximum brightness of the cloud. Assuming spherical particles, Mie‐scattering calculations of the directional albedo of a cloud are performed using a range of possible values for the atmospheric variables (water vapor mixing ratio, temperature, upward wind speed, atmospheric pressure, and eddy diffusion coefficient). We find that for a nominal atmospheric case the model predicts a moderately weak cloud at 265 nm, the wavelength of the SME measurements. An extreme model (cold and moist with high vertical wind and eddy transport) is needed to account for the brightest cloud observed. We estimate an upper limit for the water vapor to be of the order of 5 parts per million by volume. Higher values would imply the existence of clouds which exceed in brightness every cloud observed by the satellite over the time period 1981–1986. SME observations of greater cloud height in the northern hemisphere, despite their greater brightness, possibly imply an excess (by a factor of 2) of northern hemisphere water vapor. This holds if the other atmospheric variables (and cloud particle numbers) are the same in both north and south. Dependence of model cloud brightness on atmospheric pressure (∼P4.4), water vapor mixing ratio (∼w2.8), thickness of the cloud saturation region (∼d4) and advective wind speed (∼υ) are determined. These scalings are shown to result from a calculated proportionality of the cloud brightness toR6(Ris the maximum particle radius), and from simple considerations of ice layer growth, particle sedimentation, and the mass budget of water. Mie scattering calculations for a wavelength of 550 nm show that SME and OGO‐6 data on PMC brigh

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02461

年代:1988

数据来源: WILEY

摘要:

Since February 1985, the 2‐MHz narrow beam radar near Adelaide, Australia, has been used to measure the short‐term root‐mean‐square fluctuating velocities of radio wave scatterers in the altitude range 80–100 km. Data have been recorded about every 2 to 3 hours. This is in addition to the routine measurement of winds in the region between 60 and 100 km altitude. Under certain assumptions, these fluctuating velocities can then be converted to turbulent energy dissipation rates and eddy diffusion coefficients. These measurements are presented, and their interpretation as turbulence is discussed. The possibility of contamination from high frequency, short wavelength gravity waves is considered and a correction procedure to allow for such contamination is developed. It is concluded that the corrected measurements represent a good indication of turbulence activity. Between 84 and 92 km, the turbulence intensities were approximately constant with increasing height, but between 80 and 84 km turbulence was relatively weak. Seasonal variations are discussed, and important interannual differences between 1985 and 1986

ISSN:0148-0227    

DOI:10.1029/JD093iD03p02475

年代:1988

数据来源: WILEY