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1.
Simulations of oxidized nitrogen performed withglobal transport tracer models systematicallyunderestimate the concentrations of total nitrate atremote marine locations in the Mid-Pacific. Higheremission rates in the models of nitrogen oxides(
) from continental sources or alarger influx from the stratosphere do not seem tobe able to account for the shortfall. We are led toconclude that there has to be a substantial sourcelocated in oceanic areas. We speculate that
-emission from electrical discharges overthe oceans could be the source we are looking for.Airborne observations of atmospheric concentrationsof oxidized nitrogen and ozone in the remoteatmosphere and observations of nitrate wetdeposition in remote sites are used as additionalconstraints to check the plausibility of thishypothesis. We find that a larger emission of
due to lightning activity over the oceansindeed results in a much improved simulation oftotal nitrate in the remote Pacific, particularly inthe Equatorial and Tropical South Pacific and thatsuch a scenario is generally consistent withavailable observations of nitrate wet deposition andatmospheric concentrations of oxidized nitrogen andozone. An alternative hypothesis is that there is ahitherto unknown in situ source of
over thePacific Ocean. 相似文献
2.
Effects of water vapour on the structure parameter of the refractive index for near-infrared radiation 总被引：2，自引：2，他引：0
A. F. Moene 《Boundary-Layer Meteorology》2003,107(3):635-653
The refractive index of air (n) mainly depends on temperature andwater vapour content. For near-infrared radiation, temperature isthe main determining factor. To determinethe structure parameter of temperature (
) fromthe structure parameter of the refractive index(
), the influence ofwater vapour content on n needs to be taken into account as acorrection. Three levels of approximation are presented. The firstinvolves the standard deviations of T and q (T andq) as well as the correlation coefficient betweenT and q (RTq). The second approximation involvesRTq and the Bowen ratio (), and the last uses only the Bowen ratio.The latter is the classical Bowen ratio correction.Evaluation of the validity of the assumptions used in the derivationreveals that a large error may be introduced (for situations withRTq < 0.8) by replacing T/qwith the Bowen ratio.Consequently, estimating
from
using the Bowen ratiocan contain errors of 5–40% for || < 1. Adding RTqas extra information reduces the errors only marginally. For || > 1,the correction is small, and all three approximations give errors of lessthan 1% in
. When
is used to compute the sensible heat flux,the influence of the quality of the correction forwater vapour fluctuations on the measured energy balance is small: forsmall ||, the correction is large, but the absolute value ofthe heat flux is small, whereas for large ||, the correctionis insignificant. 相似文献
3.
B. D. Katsoulis 《Theoretical and Applied Climatology》1991,44(3-4):181-186
Summary This paper attempts to test the applicability of existing correlation models to the estimation of diffuse radiation with respect to measured values at a station. There are two types of model: The first type depends on the fraction of monthly average daily diffuse radiation to total solar radiation,
, as a function of the clearness index,
. The second type expresses the fraction
or
as a function of the sunshine fraction
Therefore, it presents statistically based correlations between global radiation and its diffuse component on a horizontal surface and suggests two equations to determine the ratio of diffuse radiation to total radiation received on a horizontal surface. The results of these correlation equations are compared with other accepted equations.With 3 Figures 相似文献
4.
We have studied a neutrally-stratified flow over two-dimensional hills using a two-dimensional, non-hydrostatic version of the Regional Atmospheric Modeling System (RAMS). We have implemented three different turbulence closure models: the standardE- model, an Algebraic Reynolds Stress Model (ARSM) and a new
model. Model predictions for the mean and turbulence flows using different closure schemes are compared with the data of a wind tunnel experiment containing isolated two-dimensional hills of varying slope. From the comparison, it is concluded that all three models predict the mean flow velocities equally well while only the new
closure model accurately predicts the turbulence data statistics.The research reported in this paper was conducted while the first author held a National Research Council (NRC) Associateship. 相似文献
5.
J.-P. LHOMME 《Boundary-Layer Meteorology》1997,82(2):179-191
The relationship between potential evaporation and arealevaporation is assessed using a closed-box model of the convectiveboundary layer (CBL). Potential evaporation is defined as theevaporation that would occur from a hypothetical saturated surface,with radiative properties similar to those of the whole area, and smallenough that the excess moisture flux does not modify thecharacteristics of the CBL. It is shown that the equilibrium rate ofpotential evaporation is given by Ep0=E0,where E0 is the equilibrium evaporation (radiative termof the Penman formula), and is a coefficient similar to thePriestley-Taylor coefficient. Its expression is
, where
is the areal surface resistance, ra is the localaerodynamic resistance, and is the dimensionless slope of thesaturation specific humidity at the temperature of the air. Itscalculated value is around 1 for any saturated surface surrounded bywater, about 1.3 for saturated grass surrounded by well-watered grassand can be greater than 3 over saturated forest surrounded by forest.The formulation obtained provides a theoretical basis to the overallmean value of 1.26, empirically found by Priestley and Taylor for thecoefficient . Examining, at the light of this formulation, thecomplementary relationship between potential and actual evaporation(as proposed by Bouchet and Morton), it appears that the sum ofthese two magnitudes is not a constant at equilibrium, but depends onthe value of the areal surface resistance. 相似文献
6.
In order to quantitatively investigate the role of leads and sea-ice in air-mass modification, aircraft observations were
conducted over the partially ice-covered Sea of Okhotsk. We investigated two cold-air outbreak events with different sea-ice
concentrations. In both cases, the difference between the temperatures of surface air and the sea surface (ΔT) dropped rapidly with the accumulated fetch-width of leads up to about 35-40 km, and then decreased very slowly. The surface
sensible heat flux originating from open water was about 300 W m−2 within a few kilometres from the coast and decreased with increasing accumulated fetch-width. The sensible heat flux was
about 100 W m−2 on average. These results indicate that the downwind air-mass modification depends mainly on the total (accumulated) extent
of open water. The total buoyancy flux
calculated by the joint frequency distribution method correlated very well with ice concentration. Such a relationship was
not clear in the case of the moisture flux
. The ratio between rising thermals
and cold downdrafts
differed significantly between upwind and downwind regions; that is, the buoyancy flux was dominated by
in the developing stage of the boundary layer, while
also became important after the development of the boundary layer. 相似文献
7.
In this study, profile functions for flux calculations during unstable conditions are proposed and examined. These functions are based on a direct interpolation for the dimensionless wind speed and temperature gradients between the standard Businger–Dyer formulae,
,
, and free convection forms,
,
being the Monin–Obukhov stability parameter. A previously presented interpolation between the corresponding profile relationships, in attempting to provide a general relationship for the whole unstable regime, leads to serious restrictions for the values of
in the free convection forms. These restrictions rendered available experimental data almost inapplicable, since the behaviour of the formulae in the near-neutral range controls the values of those parameters. The proposed interpolation provides functions that, firstly, fit the standard Businger–Dyer forms for near-neutral conditions and, secondly, satisfy the asymptotic behaviour as
, permitting wider ranges of possible
values. This step is very important, taking into account the large spread of the experimental data. Thus, as further and more accurate observations at strong instability become available, this approach could prove very efficient in fitting these data while retaining correct near-neutral behaviour. 相似文献
8.
Summary The efficiency of successive satellite-observed stages in the development of extratropical frontal cyclones for transporting eddy sensible heat at 850 mb on the Southern Hemisphere, is determined for the five winters (June through September) of 1973–1977. An inventory of cloud vortex data is allied with independent estimates of the zonally-averaged transient eddy heat flux,
, using a statistical technique known aspath analysis. Path analysis is an improvement over single equation linear regression models since it controls for the temporally continuous nature of cyclone evolution. The results indicate that different cloud vortex types are associated with characteristic regimes of
. The quite strong poleward flux of heat effected in the cyclogenetic stages weakens substantially by the onset of dissipation. These results are in general agreement with those for the summer and transition seasons derived using linear regression by Tucker (1979). However, a significant netequatorward flux of
is found to be connected with the short-lived mature (spiral) cloud vortex type. In association with a southward displacement of the maximum latitude of cyclogenesis and a reduced crosslatitude motion of systems in winter, this apparently results in the strong lower-level heat flux convergence characteristic of the circumpolar trough at that time. A systematic error, by year, in the statistical model specification of heat transport related to cloud vortex type is found to be associated with phase of the Southern Oscillation (SO). Incorporating this effect into the model greatly improves the goodness-of-fit of the heat flux estimates and indicates that the efficiency of the mcridional eddy heat transport by cyclones is greatest (least) when the SOI is low (high). The implications of these results in the context of other, related studies are discussed.With 7 Figures 相似文献
9.
Wind velocity and temperature measurements from a 200 m tower, locatedin a forest near Karlsruhe were used to investigatethe modified profile function of the wind velocity in theroughness sublayer.To avoid determination of the friction velocity we introduced analternative analysis with the expression
instead of
From the observed Fm* profiles we evaluated the profile function m*. The wind profiles observed under neutral conditions were well representedby a modified non-dimensional profile function with physically based boundary values at the top and at the bottom of theroughness sublayer.The results of our analysis can be used to take into consideration themomentum exchange between the atmosphere and a forest in mesoscaleatmospheric models in a refined way. 相似文献
10.
Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes (
,
and
) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri, the friction velocity (u
*) and the eddy diffusivities for heat (K
h
) and momentum (K
m
). The results show a big dependence of stability onK
m
,K
h
andu
*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K
h
/K
m
) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed. 相似文献
11.
J. E. Pinzón C. E. Puente M. B. Parlange W. Eichinger 《Boundary-Layer Meteorology》1995,76(4):323-347
Accurate and fast-response measurements of space-time observations of specific humidity were made above a drying land surface at the University of California at Davis, using the Los Alamos water Raman-lidar. In an attempt to quantify the space-time intermittency features of turbulent flows in the lower atmosphere, a multifractal analysis of these water vapour measurements was performed. The structure of the specific humidity, (x, t), was analyzed quantifying a scalar gradient measure
both in time and space, for all possible one-dimensional cuts, i.e.
and
. The results confirm the multifractal nature of this scalar gradient measure (a type of scalar dissipation rate) and show that humidity measurements at fixed times (x) are more intermittent (e.g. have less entropy dimension) than those at fixed locations in space (t). Similar multifractal behaviour of the spatial data, with and without a transformation from the observed wind velocities, supports the validity of Taylor's hypothesis for the studied fields. 相似文献
12.
To assess the realism of large-eddy simulation (LES) of the stratus-topped boundary layer and its predicted turbulent structure, we performed detailed data analyses on a LES (which has a 12.5 m grid size in all three directions), in a manner similar to those used by Nicholls (1989) on aircraft measurements. The first analysis retrieves the primary convective elements, i.e., the negatively buoyant downdrafts, which are driven mainly by cloud-top radiative cooling, through a conditional sampling technique. Comparison shows that the LES of this resolution reflects most of the observed downdraft features; most of the discrepancies that exist between the obervations and the LES can be explained by decoupling of the cloud layer from the underlying flow that exists in the former but not in the latter. The second analysis shows the vertical velocity spectrum and its agreement with the measurements. In the third analysis, showing the turbulent kinetic energy budgets, the discrepancy in the turbulent transport term (i.e., the divergence of the third-moment quantity
, the turbulent-kinetic-energy flux) between the LES and measurements exists even with such a fine resolution LES. This discrepancy is related mainly to the different behavior in
between the LES and observations, which may again be associated with decoupling.An advantage of LES over aircraft observations is that the former can provide three-dimensional flow structure at any instant. In this paper, we examined the instantaneous flow structure and observed closed cellular patterns near the cloud top in which updrafts occupy the broad centers and relatively strong downdrafts occur in the narrow edges. In the intersections of these cell boundaries, there exist weak downdrafts, consisting of relatively cold and dry air, that are the most likely origins of the strong downdrafts extending throughout the mixed layer.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
13.
A. Bongartz S. Schweighoefer C. Roose U. Schurath 《Journal of Atmospheric Chemistry》1995,20(1):35-58
The mass accommodation coefficient of ammonia gas on water has been determined by measuring the absorption rate of 50–200 ppm NH3 in one atm of air or helium into a liquid jet of 97 µm diameter as function of the exposed jet length, and comparing the results with numerical simulations which treat as the only free parameter. The model considers in detail transport of NH3 by molecular diffusion, penetration of the gas/water interface, hydrolysis in the acidified water, and transport of the solutes from the surface into the jet. A correction is applied for the time evolution of the jet surface speed, using literature data on the fluid mechanics of liquid jets. The result of nine sets of independent measurements is
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相似文献
14.
The present study investigated the chemical composition of wet atmospheric precipitation in India’s richest coal mining belt.
Total 418 samples were collected on event basis at six sites from July to October in 2003 and May to October in 2004 and analysed
for pH, EC, F−, Cl−, , , Ca2+, Mg2+, Na+, K+ and . The average pH value (5.7) of the rainwater of the investigated area is alkaline in nature. However, the temporal pH variation
showed the alkaline nature during the early phase of monsoonal rainfall but it trends towards acidic during the late and high
rainfall periods. The rainwater chemistry of the region showed high contribution of Ca2+ (47%) and (21%) in cations and (55%) and Cl− (23%) in anionic abundance. The high non seas salt fraction (nss) of Ca2+ (99%) and Mg2+ (96%) suggests crustal source of the ions, while the high nss (96%) and high ratio signifying the impact of anthropogenic sources and the source of the acidity. The ratio of varies from 0.03 to 3.23 with the average value of 0.84 suggesting that Ca2+ and play a major role in neutralization processes. The assessment of the wet ionic deposition rates shows no any specific trend,
however Ca2+ deposition rate was highest followed by and
. 相似文献
15.
Zusammenfassung An zahlreichen über das ganze Stadtgebiet von Wien verteilten Beobachtungsstellen wurden vom September 1956 bis September 1957 an je vier Wochen lang ausgesetzten, mit einem Absorptionsmittel getränkten Baumwollappen SO2-Ablagerungen gesammelt. Die gefundenen SO2-Mengen zeigen eine stark unterschiedliche Verteilung im Stadtbereich und einen deutlichen Jahresgang mit einem Maximum im Winter und einem Minimum im Juli. Der Einfluß meteorologischer Faktoren auf den SO2-Gehalt der Luft und seine Änderungen wird unter besonderer Berücksichtigung der orographischen Verhältnisse und örtlicher SO2-Quellen eingehend diskutiert. Abschließend wird auch über eine Analyse von Schneeproben auf
berichtet.
Summary During the period September 1956 to September 1957 the amount of SO2 deposited from the atmosphere was observed at numerous locations in the town of Vienna. The observations were made by means of cotton rags, soaked with an absorbing chemical, and each rag was exposed for four weeks. The amounts of SO2 show great differences within the area, and a pronounced annual variation, with a maximum in winter and a minimum in July. The influence on the SO2 content of the air of meteorological factors is discussed in detail, with special regard to variations by orographic conditions and local SO2 sources. Additional determinations on snow samples are reported. Résumé Des prélèvements de SO2 par absorption sur des bandes de coton imprégné, laissées sur place pendant quatre semaines, ont été faits en de nombreux endroits de l'agglomération viennoise de septembre 1956 à septembre 1957. Les quantités de SO2 varient beaucoup selon les endroits et la saison; elles sont maximum en hiver et minimum en juillet. Etude des facteurs météorologiques agissant sur la répartition du gaz en tenant compte en particulier du relief et des sources locales d'anhydride sulfureux. On a également déterminé la teneur de d'échantillons de neige. Mit 4 Textabbildungen 相似文献 16.
The precipitation events (n = 91), collected for 3 years (2000–2002) during the period of SW-monsoon (Jun–Aug) from an urban
site (Ahmedabad, 23.0°N, 72.6°E) of a semi-arid region in western India, are found to exhibit characteristic differences in
terms of their solute contents. The low solute (<700 μeq L−1) events are either marked by heavy precipitation amount or successive events collected during an extended rain spell; whereas
light precipitation events occurring after antecedent dry period are characterized by high solutes (>700 μeq L−1). The ionic composition of low solute events show large variability due to varying contribution of anthropogenic species
(: 1%–74%; : 1%–25%; and : 8%–68%) to the respective ion balance. In high solute events, ionic abundances are dominated by mineral dust (Ca2+ and ) and sea-salts (Na+ and Cl−). These differences are also reflected in the pH of low solute events (range: 5.2–7.4, VWM: 6.4) and high solute events (range:
6.6–8.2, VWM: 7.3). The comparison of Ca2+/Na+ and nss- ratios (on equivalent basis) in rain and aerosols suggests that the ionic composition of high solute events is influenced
by below-cloud scavenging; whereas evidence for in-cloud scavenging is significantly reflected in low solute events. The annual
wet-deposition fluxes of and are 330 and 480 mg m−2 y−1, respectively, in contrast to their corresponding dry-deposition fluxes (14 and 160 mg m−2 y−1); whereas wet and dry removal of Ca2+, Mg2+ and are comparable. 相似文献
17.
Role of atmospheric ammonia in the formation of inorganic secondary particulate matter: A study at Kanpur,India 总被引：1，自引：0，他引：1
Mukesh Sharma Shyam Kishore S. N. Tripathi S. N. Behera 《Journal of Atmospheric Chemistry》2007,57(1):1-17
Levels of fine Particulate Matter (PMfine), SO2 and NOx are interlinked through atmospheric reactions to a large extent. NOx, NH3, SO2, temperature and humidity are the important atmospheric constituents/conditions governing formation of fine particulate sulfates
and nitrates. To understand the formation of inorganic secondary particles (nitrates and sulfates) in the atmosphere, a study
was undertaken in Kanpur, India. Specifically, the study was designed to measure the atmospheric levels of covering winter and summer seasons and day and night samplings to capture the diurnal variations. Results showed are found to be significantly high in winter season compared to the summer season. In winter, the molar ratio of to was found to be greater than 2:1. This higher molar ratio suggests that in addition to (NH4)2SO4, NH4NO3 will be formed because of excess quantity of present. In summer, the molar ratio was less than 2:1 indicating deficit of to produce NH4NO3. The nitrogen conversion ratio (NO2 to NO3) was found to be nearly 50% in the study area that suggested quick conversion of NO2 into nitric acid. As an overall conclusion, this study finds that NH3 plays a vital role in the formation of fine inorganic secondary particles particularly so in winter months and there is a
need to identify and assess sources of ammonia emissions in India. 相似文献
18.
Diana Rodriguez Ana Rodriguez Amparo Soto Alfonso Aranda Yolanda Diaz-de-Mera Alberto Notario 《Journal of Atmospheric Chemistry》2008,59(3):187-197
The reactions of three structurally similar unsaturated alcohols, 2-buten-1-ol (crotyl alcohol), 2-methyl-2-propen-1-ol (MPO221)
and 3-methyl-2-buten-1-ol (MBO321) with Cl atoms, have been investigated for the first time, using a 400 l Teflon reaction
chamber coupled with gas chromatograph-coupled with flame-ionization detection (GC-FID). The experiments were performed at
atmospheric pressure and at temperatures between 255 and 298 K, in air or nitrogen as the bath gas. The obtained kinetic data
were used to derive the Arrhenius expressions , , (in units of cm3 molecule−1 s−1). Finally, atmospheric lifetimes of those unsaturated alcohols with respect to OH, NO3, O3 and Cl have been calculated. 相似文献
19.
THORSTEN HOFFMANN JAY R. ODUM FRANK BOWMAN DONALD COLLINS DIETER KLOCKOW RICHARD C. FLAGAN JOHN H. SEINFELD 《Journal of Atmospheric Chemistry》1997,26(2):189-222
Measurements of aerosol formation during thephotooxidation of -pinene, -pinene,d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, andtrans-caryophyllene were conducted in anoutdoor smog chamber. Daylight experiments in thepresence of
and dark experiments withelevated ozone concentrations were performed. Theevolution of the aerosol was simulated by theapplication of a gas/particle absorption model inconnection with a chemical reaction mechanism. Thefractional aerosol yield is shown to be a function ofthe organic aerosol mass concentration andtemperature. Ozone and, for selected hydrocarbons, theNO3 reaction of the compounds were found torepresent efficient routes to the formation ofcondensable products. For initial hydrocarbon mixingratios of about 100 ppb, the fractional aerosol yieldsfrom daylight runs have been estimated to be 5%for open-chain hydrocarbons, such as ocimene andlinalool, 5–25% for monounsaturated cyclicmonoterpenes, such as -pinene, d-3-carene, orterpinene-4-ol, and 40% for a cyclic monoterpenewith two double bonds like d-limonene. For the onlysesquiterpene investigated, trans-caryophyllene, afractional aerosol yield of close to 100% wasobserved. The majority of the compounds studied showedan even higher aerosol yield during dark experimentsin the presence of ozone. 相似文献
20.
Summary The paper presents a detailed investigation of magnitudes and properties pertaining to the large population of rainfall events recorded during 49 years at the Fabra Observatory in Barcelona. The study includes a statistical analysis of event durationT and rainfall quantityQ together with the statistical rainfall rate parameters:
,
2(R) and maximum Rm within an event. The decorrelation time is also analysed. It is found thatQ, T, and can be well modelled by a lognormal distribution, but
,
2 and Rm are only so for a limited range of precipitation ratesR. The regression analysis between pairs of logarithms of the magnitudes investigated is generally good and a regression coefficient is often better than 0.9. Comparison with published work is also carried out. An attempt is made to discriminate between heavy and non-heavy rainfall rates, and the 50 mm/h threshold is used for the study. The twelve-monthly running average indicates that the rainfall amount has a small increasing trend over the fifty year period. However, this trend is reversed when considering heavy rains. Finally, the return period in years to exceeding a thresholdR within an event is also investigated and the distribution of the population of annual extremes is found to be Gumbel II.With 6 Figures 相似文献
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