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1.
Weekly bulk aerosol samples collected at Funafuti, Tuvalu (8°30S, 179°12E), American Samoa (14°15S, 170°35W), and Rarotonga (21°15S, 159°45W), from 1983 through most of 1987 have been analyzed for nitrate and other constituents. The mean nitrate concentration is about 0.11 g m–3 at each of these stations: 0.107±0.011 g m–3 at Funafuti; 0.116±0.008 at American Samoa; and 0.117±0.010 at Rarotonga. Previous measurements of mineral aerosol and trace metal concentrations at American Samoa are among the lowest ever recorded for the near-surface troposphere and indicate that this region is minimally affected by transport of soil material and pollutants from the continents. Consequently, the nitrate concentration of 0.11 g m–3 can be regarded as the natural level for the remote marine boundary layer of the tropical South Pacific Ocean. In contrast, over the tropical North Pacific which is significantly impacted by the transport of material from Asia and North America, the mean nitrate concentrations are about three times higher, 0.29 and 0.36 g m–3 at Midway and Oahu, respectively. The major sources of the nitrate over the tropical South Pacific are still very uncertain. A very significant correlation between the nitrate concentrations at American Samoa and the concentrations of 210Pb suggests that transport from continental sources might be important. This continental source could be lightning, which occurs most frequently over the tropical continents. A near-zero correlation with 7Be indicates that the stratosphere and upper troposphere are probably not the major sources. A significant biogenic source would be consistent with the higher mean nitrate concentrations, 0.16 to 0.17 g m–3, found over the equatorial Pacific at Fanning Island (3°55N, 159°20W) and Nauru (0°32S, 166°57E). The lack of correlation between nitrate and nss sulfate at American Samoa does not necessarily preclude an important role for marine biogenic sources.  相似文献   

2.
Observations made with a monostatic sodar and from a 120 m instrumented tower have been used to study the variations in the atmospheric boundary layer at Tarapur (19° 50 N, 72° 41 E) during the solar eclipse of February 16, 1980. Atmospheric instability was reduced below normal values during the eclipse but the atmosphere at no time became stable.  相似文献   

3.
In early 1982 a station capable of sampling atmospheric trace gas constituents on a continuous basis was established at Palmer Station, Anvers Island, adjacent to the Antarctic Peninsula (64° 46S 64° 04W). Sampling operations began about 1 February 1982. This is an initial report on this station, its location, equipment and general research objectives along with some initial sampling results. The constituents being measured and recorded were: ozone, methane, carbon dioxide, carbon monoxide, CCl3F (fluorocarbon-11), CCl2F2 (fluorocarbon-12), carbontetrachloride, methylchloroform, nitrous oxide, and Aitken nuclei (CN). Data storage, data processing, and sampling system control is handled by a Hewlett-Packard 85 system. Preliminary analyses of about the first 20–22 months of data are presented and show not only the expected long-term trends but also shorter period concentration cycles that seem to be related to synoptic meteorology.  相似文献   

4.
A two-dimensional atmospheric boundary-layer model is applied to the Nanticoke region on the northern shore of Lake Erie (80 ° 03W and 42 ° 50N) to simulate numerically the observed wind and temperature profiles. In general, the profiles predicted by the model agree reasonably well with the observed profiles.  相似文献   

5.
The total ozone content in the atmosphere was determined from the multichannel photometer observations of direct solar radiation made in the urban environment at Pune (18° 32 N, 73° 51E, 559 m ASL) and Sinhagad hill station (18° 22N, 73° 45E, 1305 m ASL) during March 1980-February 1982. The total ozone content of the atmosphere was computed making use of the differential absorption of solar radiation due to ozone at 0.4 and 0.6 m wavelengths in the Chappuis band. The values of the ozone data obtained from the photometer observations at Pune and Sinhagad were compared with the corresponding ozone data obtained from the Dobson spectrophotometer located at Pune. Values of ozone obtained by the photometric method were found to be smaller by 8–18% than the Dobson values when Vigroux's absorption coefficients were used. Similarly, when the absorption coefficients of Inn and Tanaka (1953) were used, the ozone values obtained by the photometric method were smaller by 4–14% than the Dobson values. The ozone values at the hill station obtained from the photometric method were in better agreement (5%) with the Dobson values.  相似文献   

6.
Summary The seasonal and diurnal variations in the vertical component of the atmospheric electric field, air temperature, relative humidity and horizontal wind speed were studied using the surface data for the two periods (1936–40) and (1962–66) recorded at the tropical urban station, Colaba, Bombay (18°51N, 72°49E, 11 m ASL), located on the west coast of India.The atmospheric electric field during the latter period (1962–66) is significantly higher (up to 42.3%) than the earlier period (1936–40). This has been attributed to the enhanced particulate concentrations in the atmosphere. The increase noticed in the atmospheric electric field is a maximum during winter and minimum during the monsoon. The atmospheric electric field exhibited a marked semi-diurnal oscillation with peaks at 0900 LST and 2200 LST during winter, premonsoon and post-monsoon seasons of both the periods. During the monsoon season the double oscillation is not marked.The variations noticed in the surface air temperature and the relative humidity are in agreement with those observed in the atmospheric electric field. The horizontal wind speed showed a decrease which has been attributed to the surface roughness resulting from urbanization.With 7 Figures  相似文献   

7.
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within ±30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%.  相似文献   

8.
Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50S–77°31E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l-1 and from 1.4 to 11.3 nmol m-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 mol m-2 d-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 mol m-2 d-1, respectively.  相似文献   

9.
The nocturnal structure of the lower troposphere is studied using aerosol profile data (50–2800 m AGL) obtained with a bistatic, continuous wave, Argon ion lidar system during October 1986–September 1989 at Pune (18°32 N, 73°51 E, 559m AMSL), India. The top of the nocturnal groundbased inversion is taken as the height above ground where the negative vertical gradient in aerosol concentration first reaches a maximum. During the post-sunset period over this station, this height is as low as 160m and frequently lies around 550m. Greater heights are observed in pre-monsoon months and smaller ones during the southwest monsoon season. Positive vertical gradients in aerosol concentration, indicative of stable/elevated layers, appear frequently around 750m. Temporal variations of aerosol concentration gradients in two adjacent air layers, 920–1000m and 100–1100m, provide evidence that stability increases downward in the early night hours.  相似文献   

10.
Sublimation and melt disturb the environmental information obtained from ice core records in the Andes. In two case studies we demonstrate to what extent these post-depositional processes may remove major parts of the accumulated snow cover. Dark ash layers from the Tungurahua eruption changed the albedo of surface snow on Chimborazo glacier (6268 m, 1°30 S,78°36 W, Ecuador) between two ice core drilling campaigns and forced substantial melt. Re-distribution and washout of the chemical constituents shifted the concentration profiles obtained in December 1999 as compared to an equivalent core drilled in December 2000. The stable isotope records showed that approximately the water equivalent (weq) of an annual layer had melted, and that the percolating melt water penetrated within the firn layer to a depth of at least 16.5 m without refreezing. In the second example, from a site on the dry axis between the tropical and extra-tropical precipitation belts, significant loss of accumulated snow layers occurred by sublimation. A surface experiment at Cerro Tapado glacier (5536 m, 30°08 S,69°55 W, Chile) revealed that losses of 2 mm weq (5 mm snow) per day occurred during the dry period following the 1997/98 El Niño. This loss generally included the entire surface layer enriched in stable isotopes, and thus caused minimal disturbance of the isotopic signature (and hence climatic information) of the net accumulation, yet chemical constituents again experienced considerable changes in concentration. From annual layer counting and direct dating it is obvious that the major part of the accumulated ice on both glaciers is younger than 100 years; however, isotopic and chemical variations at least in the basal ice from Cerro Tapado clearly point to climate conditions different from the recent centuries. This evidence is supported by mass balance considerations derived from a glacier-climate model. The possibility of a third type of disturbance aside from sublimation and melting – in this case a significant hiatus in the environmental chronology – also deserves consideration for other icecore records from this region. Potential disruptions or discontinuities need to be carefully evaluated given the profound changes in climatic and glaciological conditions since the Last Glacial Maximum throughout Holocene times.  相似文献   

11.
Springtime measurements of NOx, ozone, PAN,J(NO2), and other compounds were made near Ny-Ålesund,Svalbard (78°54N, 11°53E), in 1994 and Poker Flat,Alaska (65°08N, 147°29W), in 1995. At Svalbard medianmixing ratios for PAN and NOx of 237 and 23.7 pptv,respectively, were observed. The median mixing ratios at Poker Flat for PANand NOx were 79.5 and 85.9 pptv, respectively. These data areused to estimate thermal PAN decomposition using several differentapproaches. At Svalbard PAN decomposition was very small, while at PokerFlat up to 30 pptv/h PAN decomposed. At both sites the NOx/PANratio increased with temperature between –10 and 20°C implyingthat PAN decomposition is an important NOx source. In-situozone production was calculated from the measured NO, NO2,O3, J(NO2), and temperature data, using thesteady state assumption Median ozone production was 605 pptv/h at PokerFlat, and one order of magnitude smaller at Svalbard during the daytime.Only at Poker Flat could a direct influence on the diurnal ozone cycle beobserved from in-situ production. These results imply that PAN decompositionis a major source of NOx in the high latitude troposphere, andthat this contributes to the observed spring maximum in surface ozone.  相似文献   

12.
Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO2, CO and C2H2 or CH4 have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R 2=0.92,n=25) and COS and C2H2 (R 2=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO2 emission factors (COS/CO2) during field experiments ranged from 1.2 to 61×10–6 (11.4×10–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO2 emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.  相似文献   

13.
Summary During an expedition to the high Andes of Southern Peru in June–July 1977, measurements of direct solar radiation in four spectral bands (0.270–0.530–0.630–0.695–2.900 ) were conducted at six sites in elevations ranging from sea level to 5645 m. These measurements were evaluated in Langley plots to determine total optical depths () and irradiances at the top of the atmosphere. In addition, water vapor optical depths (wv) were calculated from the mean radiosounding over Lima during the expedition, and Rayleigh (ray) and ozone (oz) optical depths were obtained from published tabulations. Subtracting ray, oz, and wv from yielded estimates of aerosol optical depth aer. The components ray and oz decrease from the shorter towards the longer wavelength bands and from the lower towards the higher elevation sites; aer also decreases towards the higher elevations. Particularly pronounced is the decrease of aer and from the lowlands of the Pacific coast to the highlands of the interior, reflecting the effect of a persistent lower-tropospheric inversion and the contrast from the marine boundary layer to the clear atmosphere of the high Andes.With 4 Figures  相似文献   

14.
Summary A time series and extreme value analysis of maximum precipitation for distinct time intervals from 10 minutes to 1 day have been deduced for the observatory Zagreb-Gri ( = 45°49 and = 15°59,H s = 157 m) for the period between 1908 and 1985. The Spearman rank correlation test revealed that the short-term precipitation maxima series for the time intervals of 10 to 30 minutes and 8 to 24 hours indicate no significant trend for the 95 percent probability level. The 40-minute to 4-hour precipitation maxima exhibited an increaese in recent time. Annual maximumt-minute precipitation was estimated using the Gumbel distribution for sets of data gradually prolonged with 10-year steps towards the past. The ratios (q) of maximum precipitation estimates for the shorter periods and of estimates for the reference period (1908–1985) have been calculated. Their positions according to the confidence interval on the reference estimates were determined. Confident extreme value estimates could be obtained using at least the 50–60 year data series.With 3 Figures  相似文献   

15.
This paper presents a new reconstruction of the mean annual temperature obtained from a high altitude pollen sequence in equatorial Africa (3°28S, 29°34E, 2240 m). It has been achieved with an extended modern African reference data set by adding spectra from 228 new sites and using another selection for pollen taxa. The purpose of this paper is to test how the obtained temperature value depends upon the availability of modern analogues. The results are in good agreement with those previously published, reinforcing the validity of the method. The mean standard error is reduced by 0.3°C. The mean temperature for the Holocene appears + 1.4°C warmer than the present and the last glacial maximum (25-18 kyrs BP) cooling is better specified at – 3 ± 1.9° C, a conservative value, more consistent with reconstructed sea surface temperature in the equatorial ocean.Contribution to Clima Locarno - Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program  相似文献   

16.
Further laboratory studies of emission by O(1 S) and by O2 A 3 u + ,A3 u andc 1 u – in the oxygen afterglow lead to the conclusion that Barth's mechanism for the excitation of the auroral green line O 2 * +O(3P=O2+O(1S)–(1) is correct and that levelsv=6 and 7 of O2 A 3 u + are Barth precursors. The value ofk 1=7×10–11 cm3 s–1 deduced for these levels is shown to be in fair agreement with atmospheric measurements.  相似文献   

17.
Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO2 concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO2, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO2. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= cw for CO2, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux c w. Thus, when the net flux of CO2 is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., c w = – c w. Corrections for the mean convective flux are particularly significant for CO2 because cw and c w are often of similar magnitude. The correct measurement of the net CO2 flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.  相似文献   

18.
Summary The Balkan Peninsula is situated in the impact zone of Saharan dust storms. The case of Saharan dust transport to Belgrade in the period of 14–17 April 1994 is analyzed using the Eta model for synoptic and meso scale processes. Air back trajectories are calculated at six model levels from 434 up to 5129m with horizontal grid resolutions of 1°×1° and 10×10. Following cyclonic circulation the dust was picked up from North Africa, and transported over Mediterranean. Simultaneously, according to the analysis of the three lowest trajectories, transport of trace metals from Macedonia and southern Serbia by the Koshava wind might be dominant in the observed episode. Turbulent flow enhanced the coagulation process of initially clean dust particles with particles containing Pb and Cd. The coagulation and scavenging processes below and in clouds increased deposition rates of Pb and Cd in Belgrade in the course of wet removal, and consequently trough resuspension processes. Dry deposition samples contained characteristic particles up to 30µm in diameter with Fe content of 11 to 15 atomic% and significant ratio Si/Fe of 3 to 5, determined for selected single particles by the SEM/EDX method. Following dry and wet deposition of Cd and Pb, a residual effect of dustfall is noticed throughout the vegetational period.  相似文献   

19.
Wind characteristics in the lowest 340 m (agl) of the atmospheric boundary layer at Pune (18°32N, 73°51E, 559 m ASL) have been investigated using the pilot balloon wind observations obtained during the summer monsoon seasons of 1976, 1979 and 1980. Variations in the zonal and meridional components of wind at the surface, 40, 150 and 340 m (agl) have been described. Frequency distribution of the zonal component showed an unimodal character at the surface, which gradually approached a multimodal character at 340 m. The distribution pattern of the wind components was, by and large, normal. Spectral analysis of the wind components showed that the spectral energy was predominantly shared by 5–7 and 2–3 day periods.  相似文献   

20.
Flow distortion by supporting structures   总被引：3，自引：0，他引：3  
During the 1976 International Turbulence Comparison Experiment, a number of participants found significant values of upflow over the horizontal support arm of the sensor used. For example, the Japanese sonic anemometer reported an average upflow of 2.4 °. By means of model experiments and fitting to a potential flow solution, it is predicted that the horizontal support would introduce an upflow of 0.5 °. Further model experiments with a full sonic anemometer model plus associated structures predicted an upflow of 2.2 °, in reasonable agreement with the observed result. The need for extreme care in the exposure of turbulence sensors is emphasized. The theory is capable of predicting the error incurred in the various turbulence parameters, such as uw, and these error equations bear a close similarity to those normally used in applying a tilt correction.  相似文献   

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