摘要:

Emissions of nitrous oxide, methane, and carbon dioxide were measured at diverse locations in tropical forests of Brazil, Ecuador, and Puerto Rico, using a static open chamber technique. Mean fluxes to the atmosphere were 1.7 × 1010, −0.7 × 1010, and 1.5 × 1014molecules cm−2s−1for N2O, CH4, and CO2, respectively. The data indicate that tropical forests contribute a significant fraction of the global source for atmospheric N2O, about 40% of the current source and possibly 75% of the preindustrial source. Methane is consumed by soils on average, but the sink is an insignificant part (<5%) of the atmospheric cycle for the gas. Emissions of CO2from forest soils are higher at equatorial sites than at middle or high latitudes, as expected from ecological considerations. Soils emit CO2at rates more than twice as large as the rate of carbon infall in litter; hence much of the emitted CO2must arise from root me

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11791

年代:1986

数据来源: WILEY

摘要:

CH4release rates from rice paddies were measured in Vercelli, Italy, in 1983 during a complete vegetation period, using a static box system. The rice paddies were found to be a source of atmospheric methane during the time of flooding. The CH4release rates range between a few milligrams of CH4per square meter per hour and 51 mg CH4m−2h−1and show a seasonal variation with maximum emission rates between tillering and flowering. Averaged over the complete vegetation period, the CH4release rate accounts for 16 mg m−2h−1. Significant differences in the CH4release rates of unfertilized field plots and plots fertilized with mineral fertilizer (CaCN2) were not observed. The CH4release rates show strong diurnal variations, with highest values in the late afternoon and lowest values in the early morning, which coincides with the temperature variation in the upper soil layer (1–10 cm). These variations must be taken into account in estimating reliable global CH4emission rates from rice paddies. CH4is almost exclusively emitted into the atmosphere by gas bubbles during the first 6 weeks after flooding the rice paddies, that is, on fields without vegetation. Afterwards, 80% of the observed CH4transport from the paddy soil into the atmosphere was due to diffusion through the stems of the rice plants. Transport by diffusion through the paddy water appeared to be of minor importance. The global annual CH4emission from rice paddies is estimated to be of the order of 39–94 Tg yr−1(Tg = 1012g) for 1940 conditions and 70–170 Tg yr−1for 1979 conditions, indicating a secular trend of the CH4emission by rice paddies of about 1.6% per year during

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11803

年代:1986

数据来源: WILEY

摘要:

The pulsed laser photolysis‐pulsed laser‐induced fluorescence technique has been employed to study the kinetics of the reaction, OH + CO→k1products, as a function of temperature and pressure in N2, air, and O2buffer gases. At pressures of 1 atm and below,k1is found to increase linearly with increasing pressure. Within experimental uncertainty, both the rate constant in the low‐pressure limit and the slope of thek1versus pressure dependence are found to be the same at 262 K as at 299 K. From our data we obtain the expressionk1= (1.47 ± 0.08) × 10−13[1 + (0.59 ± 0.10)P] independent of temperature, wherePis in units of atmospheres andk1is in units of cubic centimeters per molecule per second. Within experimental uncertainty, the pressure dependence ofk1at 299 K is the same in N2buffer gas as in O2buffer gas. In 700‐torr air at 299 K,k1is found to be independent of water vapor concentration over the range 0.01–20 torr. Our results will have little effect on current panel recommendations ofk1values for use in atmospheric models. However, uncertainties in the temperature dependence under atmospheric conditions, the third body efficiency of O2, and the effect of water vapor onk1are now

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11815

年代:1986

数据来源: WILEY

摘要:

During the fall of 1981 and the summer of 1982, airborne and ground‐level field studies were conducted in southern and central Ontario to investigate the processes leading to cloud water acidification. Aircraft measurements were made of aerosol particles, cloud droplets, and cloud liquid water content. Cloud water samples were collected in nonprecipitating cumulus and stratocumulus clouds and analyzed for the concentrations of SO4=, NO3−, Cl−, Na+, NH4+, Ca++, Mg++, and H+. Aerosol composition was studied at a rural location on the ground. The ground‐level aerosol composition was compared with the cloud water composition. Observations of the vertical variation of the aerosol particle size distribution were used to justify this procedure, but it was also assumed that the relative fraction of submicron aerosol SO4=did not vary between the ground and cloud base during individual flights. In this way the cloud water SO4=was explained by the nucleation of water droplets on sulphate aerosol particles in at least nine of 11 cases studied. In several of the cases the concentration of NO3−measured in cloud water samples was much higher than could be accounted for by the measurement of below‐cloud aerosol NO3−plus gaseous HNO3. Similarly, concentrations of Ca++found in the cloud water far exceeded concentrations measured i

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11821

年代:1986

数据来源: WILEY

摘要:

By comparing deposition of nitrate in successive hours of precipitation samples taken over a six year period at Brookhaven National Laboratory (BNL), Long Island, New York, we have estimated scavenging coefficients in air, λ, for nitrate under a variety of meteorological and seasonal conditions. The square root transformation of the scavenging coefficients λ½yields an approximately normal distribution; the mean value is 1.1 × 10−4s−1, in general agreement with previous experimental and theoretical estimates. An interesting property of the distribution of the scavenging coefficients is that the ratio of the mean value of λ½to its standard deviation varies little from 2.4 for various subsets of data; this property may limit the choice of stochastic models which describe the scavenging process. A trend analysis of the relationship between scavenging coefficients and rainfall rate indicates that the scavenging coefficient of nitrate does not increase for rainfall rates ≤3.2 mm h−1. The indicated increase at greater rainfall rates is qualitatively similar to model predictions but is based upon a small number of data points. The mean scavenging coefficient for winter rain events is greater

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11833

年代:1986

数据来源: WILEY

摘要:

The vertical distributions of tritium content in glacier ice were determined at two different heights of the Yala Glacier in the Langtang Region, Nepal Himalayas. In the vertical profile of tritium content at the upper point (about 5,400 m high) there exists a clear peak, which shows the injection of artificial tritium due to nuclear weapon test series. The average accumulation rate from 1963 to 1982 at this point is estimated to be 0.85 m of water equivalent per year. At the lower point (about 5,200 m high) the tritium content is relatively low throughout the ice core, decreasing with depth. Precipitation nourishes the glacier in the accumulation area, and, after a long time, it appears in the ablation area with the movement of the ice body, resulting in the different profiles of the tritium content between the two points. From the viewpoint of tritium content, the precipitation in the Yala Glacier is more similar to that in New Delhi, India, than that in Karizimir, Afghanistan. Generally speaking, the tritium content in the precipitation is lower in the coastal area than in the continental area. The precipitation in the Yala Glacier belongs to the coastal type. There possibly exists a great difference in tritium content between the glaciers nourished by water vapor coming directly from the sea and by that coming over the continent.

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11841

年代:1986

数据来源: WILEY

摘要:

Trends in atmospheric temperatures from 850 to 30 mbar are estimated, using radiosonde data from 1957 through 1979. These estimated trends are not significantly different from zero, but they do show a “greenhouse” type profile. Trends calculated with 1968 through 1979 data are compared with model estimates for the period 1971 through 1981. The major differences are that the data show more cooling between 200 and 100 mbar than the model predicts and less warming at 850 mbar than the model predi

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11845

年代:1986

数据来源: WILEY

摘要:

The CO215‐μm band provides an important source of thermal opacity in the atmospheres of Venus, Earth, and Mars. Efficient and accurate methods for finding the transmission in this band are therefore needed before complete, self‐consistent physical models of these atmospheres can be developed. In this paper we describe a hierarchy of such methods. The most versatile and accurate of these is an “exact” line‐by‐line model (Fels and Schwarzkopf, 1981). Other methods described here employ simplifying assumptions about the structure of the 15‐μm band which significantly improve their efficiency. Because such approximations can reduce the accuracy of a model, as well as its computational expense, we established the range of validity of these simpler models by comparing their results to those generated by the line‐by‐line model. Pressures and absorber amounts like those encountered in the atmospheres of Venus, Earth, and Mars were used in these tests. Physical band models based on the Goody (1952) random model compose the first class of approximate methods. These narrow‐band models include a general random model and other more efficient techniques that employ the Malkmus (1967) line‐strength distribution. Two simple strategies for including Voigt and Doppler line‐shape effects are tested. We show that the accuracy of these models at low pressures is very sensitive to the line‐strength distribution as well as the line shape. The second class of approximate methods is represented by an exponential wideband model. This physical band model is much more efficient than those described above, since it can be used to find transmission functions for broad sections of the CO215‐μm band in a single step. When combined with a simple Voigt parameterization, this method produces results almost as accurate as those obtained from the more expensive narrow ‐ band random models. The final class of approximate methods tested here includes the empirical logarithmic wideband models that have been used extensively in climate‐modeling studies (Kiehl and Ramanathan, 1983; Pollack et al., 1981). These methods are very efficient, but their range of validity is more limited than that of the other methods tested here. These methods sho

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11851

年代:1986

数据来源: WILEY

摘要:

Virtually all previous work on the subject of atmospheric normal modes has concentrated on the relatively long‐period Rossby modes, such as the familiar “5‐day” and “16‐day” waves. However, theory does predict the existence of shorter‐period Rossby‐gravity, Kelvin, and gravity modes. In the present investigation, long time series of hourly and 3‐hourly barometric observations from several tropical stations were employed in a search for these high‐frequency modes. Evidence was found for several spectral peaks that can be identified with various Rossby‐gravity, Kelvin, and gravity wave normal modes. Particularly prominent is the zonal wave number 1 Kelvin normal mode with a period of about 33 hours. This mode was found to undergo systematic seasonal and interannual variations. The theory of short‐period normal modes in the Martian atmosphere is also briefly examined. Such modes might be detectable in the surface pressure time series obtained in th

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11867

年代:1986

数据来源: WILEY

摘要:

Two 60‐day simulations of the global atmospheric circulation produced by the Canadian Climate Centre general circulation model were analyzed to determine the solar diurnal and semidiurnal variations in the wind, pressure, and precipitation fields. In these simulations the radiative transfer calculations were performed every hour in order to resolve adequately the diurnal cycle. One simulation was for boreal summer, and the other was for winter conditions. The diurnal and semidiurnal surface pressure variations in the model were found to be quite realistic, although somewhat smaller than actually observed. Even some fairly subtle details of the geographical and seasonal variability of the solar tidal pressure oscillation were well simulated. The daily cycle of the wind in the model also appears to be reasonably consistent with the limited observations available. By contrast, the diurnal and semidiurnal variations of precipitation were not successfully simulated by the model. Linear tidal theory calculations were performed with thermal forcings, vertical resolution, and boundary conditions similar to those in the full general circulation model. These calculations allowed an evaluation of the effects of the different numerical approximations in the general circulation model on the simulated tide. One striking result of these linear computations was the indication of a tendency for the effects of the “rigid‐lid” upper boundary condition to compensate for the omission of the thermal tidal forcing above the top level of th

ISSN:0148-0227    

DOI:10.1029/JD091iD11p11877

年代:1986

数据来源: WILEY