摘要:

The tropical forests of the world are hypothesized to be an important source and/or sink for a number of atmospheric gas and aerosol species. As part of the National Aeronautics and Space Administration's Global Tropospheric Experiment, an aircraft flight (June 27, 1984) was conducted over the wet tropical forest of Guyana for purposes of characterizing the forest boundary layer. Instrumentation onboard the NASA Electra aircraft included measurement systems for a variety of chemical species, including ozone, carbon monoxide, dimethylsulfide, nonmethane hydrocarbons, and aerosols. The data reported represent the first comprehensive characterization of the wet tropical forest boundary layer from an aircraft platform. The data indicate that the boundary layer is a source of carbon monoxide, isoprene, and dimethylsulfide as well as being a sink for ozone. Reported aerosol data, including number density, mass concentration, and composition, indicate an increased aerosol presence in the boundary layer relative to the overriding troposphere. From an analysis of the aerosol composition this increase is the result of direct emissions from the forest as well as from various photochemical processes. The data are discussed in terms of their significance in the understanding of the wet tropical forest boundary layer as a source or sink for various species important to tropospheric chemistry.

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08603

年代:1986

数据来源: WILEY

摘要:

Turbulence data obtained from over 100 aircraft penetrations of isolated, nonprecipitating cumulus clouds are used to derive statistical parameters associated with the transport of ozone to and from the underlying boundary layer. The parameters are determined by the difference in ozone concentration between the cloud layer and boundary layer, ΔO3. The total cloud flux of ozone, defined as the transport across a horizontal plane within a cloud due to mean and turbulent cloud motions, is given by , whereis the cloud vertical velocity averaged over an observing period. Cloud turbulence contributes about 30% to the total cloud flux

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08613

年代:1986

数据来源: WILEY

摘要:

Aerosols from the marine boundary layer were collected during a cruise from the Peru/Ecuador shelf through the equatorial and tropical Pacific to the Hawaiian Islands. A variety of samplers of different design and independent analytical techniques were used to validate the results obtained. On large particles, little or no chloride deficiency relative to seawater composition was observed, while on submicrometer particles, as much as 40% of chloride had been lost. A silicate component with a composition similar to the crustal average was associated with sea‐salt particles as an internal mixture. Along the Peru coast, substantial concentrations of Cu, Zn, As, and Pb were found which must be related to large emissions from the metallurgical industry in that region. High levels of selenium in the remote equatorial region suggest a biological source of volatile selenium in this area of high productivity. The concentrations of excess sulfate were found to be consistent with the flux of dimethylsulfide determined on the same cruise. The presence of soot carbon, particulate organic carbon, and fine excess potassium showed evidence of long‐range transport of combustion‐derived aerosols to this remote region. Enhanced soot and crustal elements in the Intertropical Convergence Zone suggest downward mixing of materials transported in the upper troposphere in this region of active vertical exc

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08623

年代:1986

数据来源: WILEY

摘要:

Three time series of varves from the Eocene Green River Formation in Colorado, consisting of 1469, 1869, and 4158 annual thickness measurements, were analyzed by a variety of statistical techniques to characterize climate variations. The analyses reveal that the time series are lognormal after adjustment for a trend. Moreover, the analyses suggest that the time series are generally nonstationary and are noiselike in structure. Fourier spectra and maximum entropy spectra of the time series are “reddish,” indicating the importance of nonoscillatory changes in varve thickness at time scales ranging from tens to hundreds of years. There are no statistically significant peaks in Fourier spectra for the entire time series; however, one segment of one of the three time series displays statistically significant peaks corresponding to periods of 10.8 and 5.4 years. Overall, the time series are suggestive of a nonperiodic and weakly predictive climate during the time periods corresponding to deposition of the var

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08637

年代:1986

数据来源: WILEY

摘要:

This study introduces nonisothermal H2O emissivity (E) and absorptivity (A) formulations for the troposphere and the stratosphere. The nonisothermal effects arise from the wavelength integration of the Planck function, evaluated at the emitting level temperature (Te), with the monochromatic absorption evaluated at the temperature of the absorbing path (Tp). In general,TeandTpcan differ by as much as 20–50 K in the atmosphere. Most of the published emissivities are essentially isothermal emissivities. We formulate a nonisothermal emissivity that satisfies the constraints posed by the monochromatic form of the transfer equation for a nonisothermal atmosphere. The new formulations employ continuous analytical expressions forEandAthat retain the following H2O radiative properties: the asymptotic properties at small (≈0) and large (∞) pathlengths; temperature dependence of line parameters; nonisothermal effects; thee‐ andp‐type continuum in the 500–1200 cm−1region; and the overlap of thee‐type continuum with the H2O line absorption. TheEandAexpressions are derived from a set of reference 5 cm−1narrow‐band calculations for homogeneous atmospheres. When applied to the inhomogeneous atmosphere, including arctic, mid‐latitude, tropics, and antarctic atmospheres, the cooling rates from 0 to 40 km computed from the emissivity approach agree within 3% of those from the narrow‐band calculations; the surface downflux and the upflux at 50 km agree within 1.5%. A major fraction (>½) of these small errors are due to the strong‐line approximation employed in the emissivity model for the 0–800 cm−1and the 1200–2200 cm−1regions, and the emissivity approach itself introduces less than a 1% error in the fluxes. The excellent agreement with the narrow‐band calculations essentially verifies the nonisothermal emissivity approach proposed here. We also show that emissivities, fluxes, and cooling rates computed by narrow‐band models depend very strongly on the spectral resolution adopted in the model for computing transmittances. Thus the spectral resolution in the narrow‐band model is an arbitrary parameter. Furthermore, by comparing the narrow‐band model fluxes with line‐by‐line (LBL) calculations we conclude that the 5 cm−1resolution model underestimates atmospheric opacity due to inadequate treatment of the far wing opacity of lines. We employ a simple continuum‐type opacity in our emissivity scheme to bring the present nonisothermal emissivity scheme into excellent agreemen

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08649

年代:1986

数据来源: WILEY

摘要:

A maximum reduction of 20% of the ozone content in the altitude range 35–45 km is presently expected within the next 50 years. Early detection of trends is thus of particular importance to confirm such extrapolations. An active lidar system, which uses a powerful exciplex laser as the emitting source at 308 nm, has been operated at the Observatoire de Haute Provence to probe the upper stratospheric ozone distribution. A description of the lidar system and results of the measurements are given and compared with those obtained simultaneously by already proven techniques, such as Brewer‐Mast sondes and Umkehr spectroscopic measurements. A general agreement within the uncertainties of the various methods is found. The data are further analyzed to determine a total error budget and to extrapolate the potentiality of lidar systems, using up‐to‐date laser sources to reach a precison better than 3% in the considered altitud

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08667

年代:1986

数据来源: WILEY

摘要:

Five years of 160‐ to 400‐nm solar flux measurements by the Solar Backscattered Ultraviolet experiment on Nimbus 7 have been analyzed. The flux in the center of strong lines and at shorter wavelengths varies with periods that correspond to modulation by the rotation of active regions. The modulation is greater at the centers of strong lines and at shorter wavelengths, corresponding to radiation that originates at higher levels in the solar atmosphere. The ratio of the irradiance in the core of the Mg 280‐nm line to the irradiance at neighboring wavelengths is used as an index of solar variation. A scaling factor is derived by comparing rotational modulation at other wavelengths with the rotational modulation of the index. The scaled Mg II 280‐nm strength successfully represents both rotational and long‐term variations across the Al absorption edge near 210 nm. This ratio can therefore provide an empirical representation of long‐term ultraviolet solar variability. Scaling factors are derived and changes estimated at several ultraviolet wavelengths. At 204 nm, in the wavelength region that drives atmospheric photochemistry, the solar irradiance drops about 4% from its average level for 1979–1980 to late 1983. The total estimated range of variation of the 27‐day averaged (one rotation) 204‐nm irradiance is 6%, over the 5 years of measurements. A least squares fit shows that over the 5 years, 27‐day averages of 10.7‐cm radio flux and of the Mg II index follow a linear relation. The radio flux can therefore be used to estimate changes in the solar ultraviolet for times before t

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08672

年代:1986

数据来源: WILEY

摘要:

Metallic species produced in the atmosphere by meteoroid ablation may play an important role in atmospheric chemistry, especially that related to ozone. Observations of sodium at 90 km yield estimated concentrations of 3 × 103cm−3. We report here calculations on NaCl, which is formed by the reaction of NaOH with HCl. We show that while NaCl photolyzes rapidly in the upper stratosphere, in the 30–35 km region it rapidly polymerizes, producing (NaCl)m, where m ≤ 10,000. One effect of this polymerization is to reduce the concentration of NaCl to 30 cm−3and subsequent polymers to even lower concentrations, where they can act as a permanent reservoir for sodium and chlorine and cease to affect ozone chemistry. These calculations represent upper limits for (NaCl)m, since other metallic salts may copolymerize w

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08683

年代:1986

数据来源: WILEY

摘要:

Radars with wavelengths of 10 cm (S band) and 70 cm (UHF band) were used to acquire the vertical precipitation structure and lightning flash distribution, respectively, in a multicell thunderstorm near Wallops Island, Virginia, during about 1.5 hours of continuous observations. The storm contained six cells that appeared sequentially; two of them exhibited the features of cell merger. In all six cells, vertical growth was about 3 times faster than decay. Lightning flash density centers were determined from the number of flashes that occurred within the UHF‐band radar beam per minute for each kilometer along the beam. The lightning radar echo data were corrected for side lobe effects. A bimodal distribution of lightning flash density was observed in only one cell, and it occurred during the initial stage of storm development; both the lower and the upper centers had 32 flashes min−1km−1, centered at 7 km and 13 km, respectively. The other cells had single (lower) centers of lightning activity, with maximum flash densities ranging from 12 to 40 flashes min−1km−1. As others before have reported, we see a positive correlation in time between the maximum lightning density and the heights of both the 40‐ and 50‐dBZ reflectivity cores. In all six cells we observed the following repetitive patterns in reflectivity structure and lightning distribution: (1) during the initial rapid growth of a cell, lightning activity is concentrated within a region bordering on the leading edge of the 50‐dBZ core of the cell and between this cell and its dissipating neighboring cell, and (2) in the decaying stage of a cell, lightning activity spreads farthe

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08690

年代:1986

数据来源: WILEY

摘要:

On the basis of data from 3 days in 1978 this paper investigates the relation between thunderstorm dimensions and electrical activity to determine the relative importance of thunderstorm size and thunderstorm environment on the sferics rate. Sferics were recorded continuously by a wide‐band (100 ± 50 kHz) crossed‐loop radio direction finder located at the radar site; precipitation data during the corresponding period came from the radar volume scan. The number of sferics associated with specific storms and recorded in 5‐min intervals varied from a few tens to a few thousands, depending on the dimensions of the source storm and on its distance from the sferics receiver. For four thunderstorm situations this variation was reduced to a small scatter, with standard deviations corresponding to factors of 1.17–1.47, by fitting the data with the empirical relation:S∝Ax× 10yH× 10−zr, whereSis the observed number of sferics per 5 min,Athe cross‐sectional area,Hthe height, andrthe range of the storm. For three of the four sets of data analyzed,xwas just over unity, giving a nearly linear relation between the sferics rate and the storm's area; for a supercell storm the relation was higher than linear. For thunderstorms between 50 and 300 km distant the number of recorded sferics decreased exponentially, by a factor of about 2 every 45 km, or withz= 0.0068 ± 0.0011 per km. Thunderstorm height appeared the dominant parameter determining the rate of electrical activity; values ofyfor the 3 days were between 0.13 and 0.28 per km, the greater effect of thunderstorm height was found associated with a stronger wind shear in the 7.

ISSN:0148-0227    

DOI:10.1029/JD091iD08p08701

年代:1986

数据来源: WILEY