摘要:

For 46 multiple‐stroke flashes in which each stroke ground termination was located using a TV camera network and thunder ranging, 15 flashes (33%) had one or more subsequent return strokes whose initial electric field peak normalized to 100 km was greater than the first‐stroke field peak of the flash. In 9 of these 15 flashes the subsequent strokes with field peaks greater than the first stroke followed the same channel as the first stroke; in five flashes the subsequent strokes with the greater peaks followed a different channel to ground; and in one flash the subsequent strokes with the greater peaks occurred both in the first‐stroke channel and in a different channel. The interstroke intervals immediately preceding the 13 larger subsequent strokes that followed the first‐stroke channel had a geometric mean (GM) duration of 98 ms, 1.7 times greater than the GM of 57 ms for all 199 interstroke intervals (46 flashes) without any selection. Eight of the 13 larger subsequent strokes for which leader durations were measurable had a GM leader duration of 0.55 ms, 3.3 times smaller than the GM of 1.8 ms for 117 subsequent leaders with measurable duration in a previously formed channel of the 46 multiple‐stroke flashes. For the six larger subsequent strokes that created a new channel to ground, the preceding interstroke interval had a GM of 130 ms, and the leader duration had a GM of 15 ms. No subsequent stroke with peak field exceeding the first in any category had a preceding interstroke interval less than 35 ms. Analysis of direct current measurements from Switzerland shows that subsequent‐stroke currents exhibit many features similar to those of Florida subsequent‐stroke electric fields. In 22 Florida single‐stroke and multiple‐stroke ground flashes the distances between multiple channel terminations in a given flash (33 measurements) ranged from 0.3 km to 7.3 km, wi

ISSN:0148-0227    

DOI:10.1029/92JD00557

年代:1992

数据来源: WILEY

摘要:

A national inventory of soil nitric oxide (NO) emissions with county spatial resolution and monthly time resolution has been developed from empirical relationships that were derived from soil NO emissions data. The empirical relationships used to develop the inventory relate the emission of NO to soil temperature and a factor which is representative of an ecosystem or type of land use. Most of the ecosystem/land use factors were derived from analyses of NO emission data from seven different sites in the United States that are representative of three ecosystems and two agricultural land use types. Other agricultural (crop) land use factors were estimated from the two calculated factors based on differences in fertilization associated with the crops. This soil emission inventory exhibits three general features. First, croplands, especially where corn is grown, appear to be significant sources of NO. This has important implications because agricultural activities tend to be localized to certain regions in the United States (i.e., the Midwest) and are highest during the summer, when photochemistry is also most active. Second, undisturbed areas, such as grasslands, forests, and wetlands, do not appear to contribute substantially to atmospheric NO. Third, extensive areas in the western United States have not been included because soil NO emission data are lacking.

ISSN:0148-0227    

DOI:10.1029/92JD00412

年代:1992

数据来源: WILEY

摘要:

CH4emissions from rice paddies have been estimated to the year 2025. A model based on current rice production per capita values (1989) for the 94 major rice‐producing countries and United Nations population predictions was used to calculate future emission fluxes of CH4. Results show that CH4emissions from rice paddies are predicted to increase by an average of 1.1% yr−1from the 1990 level of 97 Tg yr−1to 145 Tg yr−1

ISSN:0148-0227    

DOI:10.1029/92JD00157

年代:1992

数据来源: WILEY

摘要:

Aircraft observations during the summer over the eastern Pacific Ocean, ≥400 km offshore, show that the free troposphere has a distinctly nonuniform, layered structure. Analysis of plots of ozone versus total water mixing ratio indicates that the layers typically consist of a mixture of air from several sources: (1) moist, ozone‐depleted boundary layer air, (2) very dry air with high ozone content, which probably originated in the middle or upper troposphere, and (3) air with relatively low ozone and moderate, varying moisture contents, which may represent residues of convective clouds that had formed over the ocean upstream of the research area. On two research days we also observed what we infer to be continental air. On one day in the usual research area we encountered air with elevated concentrations of aerosols whose trajectories, traced backward in time, indicated that it had passed over the Alaskan continent. On another day, when soundings were made about 100 km off the California coast, we observed a layer just above the marine inversion containing unusually high amounts of ozone, aerosols, and moisture. This layer probably represents a direct intrusion of polluted air from the coast, which could have been the result of baroclinic flow associated with boundary layer warming over land. Over the eastern Pacific Ocean in summer the subtropical high results in stably stratified, subsiding air, where discrete horizontal layers with differing flow velocities transport air over long distances with little vertical mixing. Here, localized large‐scale flows (such as tropospheric folding, deep convection, or baroclinic flow from coastal areas) “inject” air of different properties at various levels in the lower troposphere. This air is then subject to buoyancy sorting and differential advection. Because the lower troposphere is very stably stratified, the mixing eddies are small compared to the air mass size, and small‐scale turbulent diffusion is slow. Here, wind shear plays an important role through stretching and thinning the different air masses until small‐scale diffusion completes the m

ISSN:0148-0227    

DOI:10.1029/92JD00290

年代:1992

数据来源: WILEY

摘要:

The stable isotopic concentration (18O and2H) of water in phreatic aquifers in the Sahelo‐Sudanese zone of Africa is representative of the original mean rainfall contributing to ground water recharge. The isotopic decrease of18O in the rainwater and groundwater (−0.084 ‰ 100 km−1) showed an east‐west gradient. This suggests a supply of water vapor transported by the zonal flows East African Jet, Tropical Easterly Jet, and Easterly Waves, thus increasing the contribution from the evaporating surfaces of the Indian Ocean in relation to that of the Guinean monsoon. The gradient also indicates the importance of atmospheric recycling of continental water through evapotranspiration. A model of conservation of the isotopic masses is presented which takes into account the return of continental vapor toward the rain‐giving clouds. The remaining fraction of water vapor during the east‐west transit between Djibouti and Dakar is thus determined by evapo

ISSN:0148-0227    

DOI:10.1029/92JD00288

年代:1992

数据来源: WILEY

摘要:

Aerosol samples were collected to study the variabilities of marine aerosols at different times and in different ocean areas. The samples were collected during the first three cruises (December 12, 1985, to February 21, 1986; November 11, 1986, to March 1, 1987; September 27 to November 4, 1987) operated by the cooperative program between the United States and the People's Republic of China. The concentrations of crustal and pollution elements in aerosols were high over the ocean area close to the China coast and decreased very rapidly with increasing distance from land. For the third cruise, in the ocean area northeast of the Philippines, the concentrations of crustal and pollution elements in aerosols were high, especially Fe, whose values reached 3.15 × 10−5g m−3. For all three cruises, the mass size distributions of crustal elements and pollution elements in aerosols showed more large particles. The morphology and elemental composition of aerosol particles showed that sea‐salt particles may conglomerate with small crustal and pollution particles from land to form large particles. The size distributions of suspended particles (d>0.3 μm) in surface seawater approximately fitted the Junge size distribution. The concentration of suspended particles in surface seawater decreased with increasing distance from land except at the equator, where particle concentrations were high. In addition, results from rain chemistry show that the relative importance between wet deposition and dry deposition varies with trace e

ISSN:0148-0227    

DOI:10.1029/92JD00507

年代:1992

数据来源: WILEY

摘要:

The extent to which H2O2dissolved in cloud droplets is trapped in rime ice affects the composition of precipitation and the rate of H2O2removal from the atmosphere. Measurements were conducted in winter stratiform clouds at a remote mountain‐top site in southeastern Wyoming, thus avoiding the difficulties of preparing laboratory clouds whose chemical and physical properties are similar to natural clouds. Quantities directly observed were H2O2concentrations in cloud water collected as rime, air temperature, gaseous H2O2, O3, and SO2, and cloud liquid water concentration. Values of the retention coefficient, Γ, defined as the ratio of the H2O2concentration in the melted rime sample divided by the equilibrium concentration in the supercooled droplets, were always less than unity(Γ¯=0.24±0.07). Corrections to account for the rapid reaction between dissolved H2O2and sulfur(IV) increase the average value of the retention coefficient to only 0.30. An observed correlation between Γ and riming rate suggests that H2O2is released to the gas phase during riming. These field measurements do not agree with laboratory determination

ISSN:0148-0227    

DOI:10.1029/92JD00237

年代:1992

数据来源: WILEY

摘要:

Precision Measurements of UVB global irradiance in 5‐nm‐wide spectral bands centered from 290 to 320 nm were made continuously from September 1975 through December 1990. The spectral radiometer was calibrated at roughly monthly intervals. Annual maximum monthly means for total daily radiation, radiation at solar noon, and clear sky radiation at small secants all were observed to be significantly higher during the period from 1983 through 1989. The maximum monthly mean of integrated 295–320 nm total daily radiation in 1986 was 29% above the long‐term mean, 47% above the maximum in 1982, and 54% above the mean maxima for 1979–1982. These interannual changes were largest for the shorter wavelengths but were significant for all spectral bands. Interannual variations in clear sky radiation were largest at small secants. For maximum monthly means of integrated 295–320 nm flux, the secant 1.2 maximum in 1989 was 19% above the long‐term mean and the average of the maxima during 1983–1989 was 13% above the

ISSN:0148-0227    

DOI:10.1029/92JD00478

年代:1992

数据来源: WILEY

摘要:

Isaksen's algorithm of the photolysis rate calculation in Luther's modification (I‐L method) is analyzed. The interpretations suggested by Thompson [1984] and Madronich [1982]are also considered. The accuracy of the I‐L method is tested by (1) evaluation of the transmittance and reflectance coefficients for a single homogeneous Rayleigh scattering layer against delta Eddington and discrete ordinate results and (2) comparison of I‐L and delta Eddington photolysis rates. These tests show that if the I‐L method is applied for calculation of twilight UV photolysis rates, its inaccuracy can exceed 50% (compare 10% according to the earlier estimations). The possible effect of such inaccuracy on model predictions is illustrated by comparing the results obtained by the same one‐dimensional PCM successively employing I‐L and delta Eddington radi

ISSN:0148-0227    

DOI:10.1029/91JD02861

年代:1992

数据来源: WILEY

摘要:

Motivated by the desire for a more flexible and general solar radiation calculation in the NCAR community climate model (CCM), the δ‐Eddington approximation has been employed in the CCM version 2 (CCM2). Eighteen spectral intervals span the solar spectrum from 0.2 to 5.0 μm. Absorption parameterizations for H2O, O3, CO2, and O2were developed by making use of the latest theoretical calculations. Water droplet scattering and absorption are parameterized as shown by Slingo (1989). An accurate and efficient convolution of the H2O vapor spectrum with water droplet clouds is presented that yields good agreement with available line‐by‐line (LBL) calculations for single‐layer clouds. A simple and efficient method to simulate partial cloud cover and cloud overlap is included. The simulated albedo‐solar zenith angle dependence agrees very well with adding/doubling scattering calculations. The CCM2 δ‐Eddington method will make possible many interesting applications of CCM2 in the

ISSN:0148-0227    

DOI:10.1029/92JD00291

年代:1992

数据来源: WILEY