Tropospheric Sources Research Articles

The Tropospheric and Stratospheric Effects in the Ionosphere

An overview of the concept of ionosphere coupling from below is presented. The D-region aeronomy, the winter anomaly of radio-wave absorption, the Es occurence and structure, the variations of atmospheric emissions, F-spread, the global morphology of F-region, wave disturbances and thermospheric wind regime should be considered in connection with tropospheric and stratospheric processes. There are regional and longitudinal effects in the morphology of thermospheric circulation, especially in the lower thermosphere. The response of prevailing and tidal thermospheric winds to the stratospheric warmings depends on the longitude. Some of experimental ionospheric data may be explained as being the result of upward propagation of broad spectrum of internal atmospheric waves (planetary waves, tides and gravity waves) from tropospheric sources. The transmissivity of the waves depends on the seasonal variations of the stratospheric and mesospheric circulations and intensity of the wave sources.

Middle Atmosphere Tides and Coupling between Atmospheric Regions

Atmospheric tides are discussed from the perspective of how these waves serve to dynamically couple different regions of the atmosphere from the ground to about 150km. Emphasis is placed on theoretical and modeling efforts which address new mechanisms, with a view towards providing some direction to future theory, modeling, experimental, and data analysis activities. A major area of recent and projected future research concerns the interactions between tides, gravity waves, and the mean tonal flow. Tidal wind oscillations between 70 and 100km modulate the transmissivity of gravity waves to the thermosphere, as well as the deposition of momentum within this height regime due to gravity waves propagating upwards from tropospheric sources. These modulated momentum fluxes in turn feed back to modify the tidal winds as well as the mean zonal flow; in addition, the tidal winds deposit net momentum and heat at the base of the thermosphere as they themselves undergo dissipation. Other promising areas of research include tide/tide and tide-planetary wave interactions, and the responses to transient tidal forcing. In addition, the mutual interactions between tidal dynamics and neutral and ionized constituent densities between 100 and 175km can now be addressed by newly-developed thermosphere-ionosphere general circulation models which include self-consistent interactions between the neutral and ionized species. Future spectral modeling of middle atmosphere tides would also benefit from new calculations of mean monthy thermotidal heating profiles that take into account new empirical prescriptions of seasonal-latitudinal and longitudinal variations of H2O and O3 densities derived from measurements by satellite sensors.

Evidence of individual solar proton events in Antarctic snow

The high-resolution nitrate analyses of a snow sequence in Antarctica reveals clear evidence that the snow contains a chemical record of ionization from charged particles incident upon the upper atmosphere of the Earth. The Antarctic continent acts as a cold trap that effectively freezes out this signal and retains it in the stratigraphy of the ice shelves and the continental ice sheet. The signal that we measure results from the ionization of nitrogen and oxygen, the two primary constituents of the Earth's atmosphere, which subsequently react to form oxides of nitrogen. A large portion of the nitrogen oxides produced are ultimately oxidized to nitric acid and incorporated in snow crystals together with nitrates from tropospheric sources that also contribute to the general background. The nitrate concentration in a firn core was measured in Antarctica by ultraviolet spectrophotometry under tightly controlled experimental procedures. Based on uninterrupted, high-resolution sampling, variations in nitrate concentration were found to average about 53% (one standard deviation) of the mean concentration for the entire core. Short pulses of high nitrate concentration were found to show a variance of up to 11 standard deviations above the mean. At the series mean, the precision of analysis is better than 2%.

Infrared aircraft measurements of stratospheric composition over Antarctica during September 1987

The Jet Propulsion Laboratory Mark IV interferometer recorded high‐resolution, infrared solar spectra from the NASA DC‐8 aircraft during flights over Antarctica in September 1987. The atmospheric absorption features in these spectra have been analyzed to determine the burdens of O3, NO, NO2, HNO3, ClNO3, HCl, HF, CO2, CH4, N2O, HCN, CO, H2O, CFCl3, and CF2Cl2. The results show a “collar” of high HNO3 and ClNO3 surrounding a “core” in which the burdens of these and of HCl and NO2 are very low. Clear increases in the burdens of HF and HNO3 were observed during the course of September in the vortex core. HCl and NO2 exhibited smaller, less significant increases. The burdens of the tropospheric source gases, N2O, CH4, HCN, CFCl3, CF2Cl2, CO, and H2O, were observed to be much smaller over Antarctica than at mid‐latitudes. This, together with the fact that HF over Antarctica was more than double its mid‐latitude value, suggests that downwelling had occurred.

Ground‐based infrared measurements of tropospheric source gases over Antarctica during the 1986 Austral Spring

Simultaneous measurements of the atmospheric burdens of CH4, N2O, CO2, CF2Cl2, and CO above McMurdo Station, Antarctica, have been derived from solar absorption spectra obtained by the Jet Propulsion Laboratory high‐resolution Fourier transform spectrometer. In all cases the burdens are smaller than mid‐latitude values. Furthermore, retrievals of N2O and CH4, for which we have information on the vertical distribution not only from the zenith angle dependence of the strength of their absorption, but also from the shapes of their spectral lines, indicate that the tropospheric mixing ratios were normal and that the depletion of the burdens can best be accounted for by a downward shift of the volume mixing ratio profiles by some 6–8 km. This rules out the possibility of large‐scale upwelling of ozone‐poor tropospheric air into the stratosphere being the cause of the Antarctic springtime ozone depletion.

Falling sphere observations of anisotropic gravity wave motions in the upper stratosphere over Australia

A study of inertial scale gravity wave motions in the region of the atmosphere between 30 and 60 km has been undertaken, using wind and temperature data derived from rocket-borne falling sphere density experiments performed over Woomera, Australia between 1962 nad 1976. The gross features of the wave field compare favorably with those found in similar northern hemispheric studies. Wave propagation is found to be both vertically and horizontally anisotropic. A rotary spectral analysis indicates predominately upgoing wave energy, suggesting that the majority of sources of these waves lie below 30 km. A detailed statistical investigation of the waves, made using the Stokes parameters technique, reveals that phase progression is also highly directional in the horizontal, with a significant zonal component in summer, but with a strong meridional component in winter. Propagation towards the southeast is inferred in summer, with the waves possibly emanating from tropospheric sources in equatorial regions to the north of Australia. The technique also shows that, on average, the waves appear to have mean ellipse eccentricities (=f/ω) around 0.4–0.45. Indirect estimates of a number of important wave parameters are made. In particular,v′ andw′ flux estimates are made over several height intervals. The vertical gradient of density weighted flux implies wave-induced mean flow accelerations of the order 0.1–1 ms−1day−1. This suggests that dissipating gravity waves are a significant source of the momentum residuals that are encountered in studies of satellite data from this region.

Simulated global distribution and deposition of reactive nitrogen emitted by fossil fuel combustion

We use the medium resolution (- 265 km horizontal grid) GFDL general circulation transport model to simulate the global spread and deposition of reactive nitrogen emitted by fossil fuel combustion. The nitrogen species are transported as a single tracer with no explicit chemistry. Chemical reactions are only present implicitly in the bulk coefficients for dry and wet removal. The observed wet deposition of nitrogen over North America is used to determine the global parameter for wet deposition, and constant bulk coefficients for dry deposition over land and sea are pre-calculated from measured concentrations and deposition velocities. The simulated yearly depositions in Western Europe and at regional export sites, as well as simulated yearly concentrations and their seasonal variation over the North Pacific, are compared with available observations. The agreement is generally quite good and almost always within a factor of 2. This model is then used to identify a number of important source regions and long-range transport mechanisms: (1) Asian emissions supply two-thirds of the soluble nitrogen compounds over the North Pacific. In the summer, North American emissions are important over the subtropical North Pacific. (2) Nitrogen emissions from Europe dominate the nitrogen component of Arctic haze in the lower troposphere, while North American and Asian emissions are only important locally. The model predicts a large gradient in the Arctic with average winter mixing ratios ranging from less than 0.1 ppbv over Alaska to more than 1 ppbv over eastern Russia. (3) Throughout the Southern Hemisphere, the emissions from fossil fuel combustion account for 10% or less of the observed soluble nitrogen at remote sites, an amount less than a previously simulated contribution from stratospheric injection. The long-range transport of PAN, NO, production by lightning and biomass burning, and some, as yet, unknown marine biogenic source may all supply part of this background soluble nitrogen. However, the similarity between the seasonal cycles observed at Samoa for soluble nitrogen and for 03. a species known to be supplied from the stratosphere, suggests a major r6le for either stratospheric injection or an upper tropospheric source.

Comments on “Relative contributions of tropospheric and stratospheric sources to nitrate in Antarctic snow” by M. R. Legrand and R. J. Delmas

Comments on “Relative contributions of tropospheric and stratospheric sources to nitrate in Antarctic snow” by M. R. Legrand and R. J. Delmas

Sources and sinks of acetone in the troposphere: Behavior of reactive hydrocarbons and a stable product

Acetone, a relatively unreactive carbonyl compound in the atmosphere, has been detected in concentrations of ≃500 parts per trillion in surface air over the central Atlantic and several hundred ppt (volume) near the tropopause. This represents a substantially higher mixing ratio than anticipated from previous descriptions of its sources which are primarily much more reactive hydrocarbon emissions and skinks. We assimilate new information about the tropospheric sources and sinks of this substance into a numerical model of its chemistry, cloud transport, and removal. Simulations relevant to the tropical and the mid‐latitude atmosphere are presented. Photolysis provides a rather slow sink, giving a first‐order decay time scale of 40 days (near the surface) to 10 days (at 200 mbar). Attack by HO radicals is of comparable importance, with a time scale of about 20 days (near the surface) to a hundred days (at 200 mbar). A significant amount of carbon, approximately 70 Tg (C) yr−1, appears to be cycled as acetone. Many of the sources of acetone involve the oxidation of higher molecular weight hydrocarbons, but the relative contribution of primary, nonanthropogenic, sources, e.g., biogenic and oceanic, may be significant. Acetone, like CO, is a useful tracer recording previous photochemical activity in an air parcel, a tracer that might be used to describe the photochemical production of compounds like ozone. The mid‐latitude simulations required some adaptation of the Chatfield (1982) transport model. The activity of vertical transport was constrained to reproduce available 222Rn data. Simulations of these data suggest that mid‐latitude vertical transport is less active than tropical, but rather more active than Kz parameterizations suggest.

Rainout lifetimes of highly soluble aerosols and gases as inferred from simulations with a general circulation model

The rainout‐determined lifetimes of highly soluble particulate and gaseous atmospheric compounds are investigated using general circulation model simulations in which removal is explicitly calculated in terms of the local, model‐produced precipitation rates. Our calculations indicate that because of the episodic and asymmetric nature of rainout, species' lifetimes depend not only on the amount of precipitation but also on the characteristics of the precipitation regime (such as duration and frequency of the precipitation events) and on the direction of the tracer main flow (determined by the species' average mixing ratio gradient). For this reason, averaged rainout lifetimes of tracers flowing downward from the stratosphere are found to differ substantially from those of tracers of surface origin flowing upward or tracers of a more ubiquitous tropospheric source. These results imply that the use of a first‐order parameterization to simulate rainout in a photochemical model that does not explicitly calculate precipitation can be inadequate in representing this process. A computationally efficient parameterization that includes the effects of intermittence and asymmetry of rainout is proposed, and it is shown how this parameterization can be used to estimate rainout‐determined tropospheric residence times from observational data sets. A review of published estimates of submicron aerosol tropospheric residence times based on observations shows that these are consistent with our model results.

Relative contributions of tropospheric and stratospheric sources to nitrate in Antarctic snow

The nitrate contents of nearly 500 firn samples collected at various sites on the Antarctic ice sheet are reported. Additional chemical measurements of all major ions, in particular protons, have also been performed so that new conclusions regarding the most probable form and origin of nitrate in the Antarctic can now be drawn. It is shown that nitrate is deposited as gaseous HNO 3 and that tropospheric sources dominate in this remote region. Continental and anthropogenic nitrates are not significant contributors. It is suggested that lightning at tropical and/or mid latitudes is the most likely source of Antarctic nitrate. The formation of HNO 3 (or its precursors) in the stratosphere is discussed and the possible evidence for this contribution in several profiles is carefully investigated. The absence of a convincing correlation between solar factors and nitrate concentrations in snow confirms that past solar activity fluctuations cannot be reconstructed from polar ice cores. The spatial and temporal variations observed in this study are, however, not fully explained. Finally, emphasis is placed on the necessity of undertaking HNO 3 measurements in the Antarctic atmosphere in order to elucidate the deposition mechanism of this major component of atmospheric chemistry. DOI: 10.1111/j.1600-0889.1986.tb00190.x

Climatology of Sr-90 in Surface Air: A Simple Model using Diffusion and Scavenging

Abstract The evolution of Sr-90 distribution following an instantaneous stratospheric or tropospheric source in an annulus defined by latitude walls is investigated by means of a very simple model that uses 12 stratospheric and 12 tropospheric annular boxes and which assumes diffusional transport between boxes and wet and dry scavenging from tropospheric boxes. Coefficients for interbox transport are expressed in terms of half-residence times, and these are adjusted to be consistent with reasonable eddy diffusivities and/or variable local stratospheric residence times suggested by previous studies. Precipitation scavenging is proportional to precipitation rate, for which a sinusoidal variation was assumed, with annual mean, amplitude of oscillation and phase all determined by climatology. The spring peak and fall minimum in tropospheric air are obtained at all latitudes. At middle and high latitudes, these extremes result primarily from annual oscillation of mixing downward from the stratosphere, while at...

Tropospheric sources of NOx: Lightning and biology

Laboratory experiments to quantify the global production of NO x ( NO + NO 2) in the troposphere due to atmospheric lightning and biogenic activity in soil are presented. These laboratory experiments, as well as other studies, suggest that the global production of NO x by lightning probably ranges between 2 and 20 MT(N)y − of NO and is strongly dependent on the total energy deposited by lightning, a quantity not well-known. In our laboratory experiments, nitrifying micro-organisms in soil were found to be a significant source of both NO and nitrous oxide (N 2O). The measured production ratio of NO to N 2O averaged 2–3 for oxygen partial pressures of 0.5–10%. Extrapolating these laboratory measurements to the global scale, which is somewhat risky, suggests that nitrifying micro-organisms in soil may account for as much as 10 MT(N)y −1 of NO. Additional experiments with denitrifying micro-organisms gave an NO to N 2O production ratio ranging from 2 to 4 for an oxygen partial pressure of 0.5% and a ratio of less than unity for oxygen partial pressures ranging from 1 to 20%. The production of NO and N 2O, normalized with respect to micro-organism number indicates that the production of both NO and N 2O by denitrifying microorganisms is at least an order of magnitude less than production by nitrifying micro-organisms for the microorganisms studied.

On the relationship between the greenhouse effect, atmospheric photochemistry, and species distribution

A radiative‐convective‐photochemical model that extends from 0 to 53 km is used to examine the effect on atmospheric constituents and thermal structure of changes in the atmospheric levels of CO2, CFM's, CO, N2O, and combinations of these species. Calculations were carried out for two reference atmospheres, one with high (HINOX) and one with low (LONOX) levels of NOx. The HINOX atmosphere has a vertical distribution of NOx similar to that resulting from recently published measurements. Such a distribution requires an unrealistically large value for the integrated tropospheric source of NOx. This suggests that the HINOX profile, and the measurements from which it was drawn, are more characteristic of contaminated, rather than clean, air masses. The HINOX troposphere provides a net photochemical source of O3 and is not greatly sensitive to downward transport of O3 from the stratosphere. The LONOX troposphere is a photochemical sink for O3 and, as a result, is sensitive to such variations in downward transport. Results of this study suggest that (1) infrared opacity changes due to CO2 and CFM increases can cause significant changes in tropospheric O3, OH, CH4, CO, and other species through changes in tropospheric water vapor; (2) perturbation or sensitivity studies conducted with tropospheric photochemical models may be subject to significant errors due to the absence of modulating effects provided by the stratosphere; (3) the response to given perturbations is significantly dependent upon the tropospheric NOx distribution present in the model; (4) CO2 growth rates must be included in the calculation of CFM‐O3 time scenarios and must account for surface temperature changes, especially in the steady state; and (5) that thermal or chemical perturbations introduce a variety of coupling or interactive mechanisms which are significant and which may provide compensating effects.

Acetonitrile in the lower troposphere

Measurements of air samples taken near the ground at different locations in urban as well as in rural areas show the presence of acetonitrile (CH3CN) in concentrations up to 7 ppbv. The measurements of this compound were carried out by a gas chromatographic method with an electron capture detector and by a mass spectrometric method with a GC‐MS quadrupol mass filter system. The present results support tropospheric sources for acetonitrile recently found in stratospheric ion‐clusters.

An advective model for two‐dimensional transport of stratospheric trace species

A parameterization of two‐dimensional transport is developed for application to photochemical models of stratospheric trace species. It is shown that in a first approximation tracer transport in the meridional plane may be treated as an advective, rather than a diffusive, process. The mean meridional motion used in this advective model is a modified Eulerian mean which is a good approximation to the Lagrangian mean motion. The potential of the proposed parameterization is demonstrated by a simple numerical experiment in which the equilibrium distribution is computed for a tracer with a uniform tropospheric source and a stratospheric sink proportional to the local mixing ratio. The resulting distribution is qualitatively in accord with the oberved stratospheric distribution of trace species whose sources are in the troposphere, e.g., N2O.

Ground-based measurements of atmospheric NO2 by differential optical absorption

Nitrogen dioxide is important to stratospheric ozone chemistry1. The few observations of vertical distribution of the gas are reviewed elsewhere2. Most available data relate to ground-based measurements of the total amount in the vertical column. Such observations are ideally made from a high altitude site to avoid local tropospheric sources. Noxon3 observed a mean value of 5 × 1015 molecules cm–2 from Fritz Peak Observatory. Pommereau and Hauchecorne4 obtained much higher values, of a few ×1017 molecules cm–2, at Haute-Provence Observatory. Noxon et al. have reported latitudinal gradients5,6 and response to stratospheric warmings7, reporting stratospheric column values in the range 1–5 × 1015 molecules cm–2. During the past year, several series of observations have been made from a low altitude rural site in the UK. Values obtained for the vertical column were in the range 0.8–5.6 × 1016 molecules cm–2. In view of the tropospheric contribution expected at this site8, these values represent an upper limit to the stratospheric NO2 column and we show here that the values reported by Pommereau and Hauchecorne were anomalously high.

Circumpolar measurements of ozone, particles, and carbon monoxide from a commercial airliner

Trace constituent data are presented from the unique flight of an airliner around the world over both poles. Relatively high resolution and simultaneous measurements of ozone, carbon monoxide, light‐scattering particles, condensation nuclei, and meteorological parameters were obtained. The mutual variations of the data in the polar stratospheres, and in the tropical upper troposphere, are discussed in their meteorological setting. The data from the Arctic lower stratosphere are consistent with a tropospheric source of condensation nuclei, but not of carbon monoxide. Carbon monoxide mixing ratios in the Antarctic stratosphere averaged 44 ppbv. In the tropical troposphere they averaged 66 ppbv over the Pacific versus 89 ppbv over Africa. A local area of higher concentration (115 ppbv) was encountered over tropical Africa; its possible relation to carbon monoxide production by vegetation and deep convection is discussed. Evidence was found in the tropical upper troposphere of distinct boundaries between air masses of different temperature, ozone content, and particle content.

Determination of stratospheric ozone at ground level using 7Be/ozone ratios

The 7Be and O3 concentrations were measured and the 7Be/O3 ratios calculated for air particulates collected on several flights of two specially equipped commercial B747 jetliners between altitudes of 10 and 12 km and latitudes of 21° to 55° N. Upper tropospheric 7Be concentrations averaged about 520 pCi/10³m³, whereas the stratospheric average was about 4,700 pCi/10³m³. The 7Be/O3 ratio at 35° ‐ 42° N was determined to be 10.78 pCi/10³m³/ppbv for April‐June 1978. Concentrations of 7Be and O3 were also measured daily during June and July 1977 at Whiteface Mountain, New York. Daily variations in 7Be data indicated the arrival of a stratospheric air mass on June 15‐16. Comparison of 7Be concentrations show approximately a tenfold dilution of the stratospheric air during tropospheric descent. The 7Be/O3 ratio on June 15‐16 was 9.8 pCi/10³m³/ppbv within experimental error of the stratospheric value. This suggests that at least at times, stratospheric air, although diluted, reaches ground level without significant relative fractionation of 7Be and O3. Assuming this to be true on days when 7Be concentration is > 200 pCi/10³m³ (or ≥ 5% of the stratospheric value), we have determined the stratospheric ozone concentration at Whiteface Mountain to vary between 19 and 47 ppbv for summer months. Thus at a remote location such as Whiteface Mountain both stratospheric and the tropospheric sources play an important role.

Some aspects of break and active monsoon over southern Asia during summer

North of 10° N, at least three synoptic phases of the summer monsoon can be identified. Two of these phases—the break and active monsoon—are extremes. Patterns of cloudiness and rainfall for these two phases differ substantially. These indicate differences in the geographic location and intensity of tropospheric energy sources. Tropospheric circulations over the equatorial Indian Ocean during break and active monsoon also differ. A break is often accompanied by the development of a trough in the lower troposphere northeast of Gan; this appears to enhance rainfall over southeast India. Although cause and effect are difficult to separate using scanty aerological data, synoptic variation over the equatorial Indian Ocean east of 60°–65° E may influence rainfall over western and southern India. DOI: 10.1111/j.2153-3490.1977.tb00743.x