bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic model studies of atmospheric droplet chemistry: 2. Homogeneous transition metal chemistry in raindrops
Authors: Graedel T. E. , Mandich M. L. , Weschler C. J.
Published: February 2008

Considerable evidence indicates that dissolved transition metal ions (TMI) are capable of catalyzing oxidations in atmospheric water droplets, at least in certain circumstances. Wide variations in the importance of TMI chemistry are expected in these systems because concentrations of transition metals in water droplets range over at least 4 orders of magnitude. In the present work we perform an extensive series of model calculations for TMI chemistry in raindrops. The specific TMI discussed are iron, manganese, and copper. The present treatment is restricted to homogeneous processes, that is, those involving dissolved molecules and ions. Results are presented for studies at pH 3 and pH 4, for both daytime and nighttime conditions. Among the results are the following: (1) At pH 3 and pH 4, Fe(III) is present largely as photosensitive hydroxide complexes. Our model results indicate that under atmospheric conditions the photolysis of these complexes is the primary daytime source of reactive free radicals within the droplets, even at quite low TMI concentrations. (2) TMI complex photolysis is not, of course, operative at night. At those times the presence of TMI continues to control the concentration of free radicals in raindrops through “Fenton type” reactions with hydrogen peroxide, for example, Fe(II) + H2O2 → Fe(III) + OH + OH−. (3) The oxidation of S(IV) to S(VI) by H2O2 is the most important daytime sulfite oxidation process in raindrops, but S(IV) oxidation catalyzed by Mn(II) can be significant under certain conditions, particularly at night or in the winter months. (4) Solution nitrogen chemistry is relatively unaffected by TMI. Its most important daytime chemical process is the (rather inefficient) photodissociation of the nitrate ion, a process which generates ozone (and hence HOx radicals). (5) Organic chemistry in atmospheric water droplets is very sensitive to the presence of hydroxyl radicals. Since OH· production is strongly influenced by catalysis involving iron complexes, the presence of soluble iron is a major stimulus for organic chemical processes (such as the conversion of alkyl aldehydes to carboxylic acids). (6) For cases where S(IV) concentrations exceed those of H2O2 the S(IV) effectively “titrates out” the H2O2. If the H2O2 concentration dominates, however, residual H2O2 remains to initiate a variety of solution oxidation chains, particularly those producing organic acids. The presence of H2O2 in the gas phase thus implies acid production in the aqueous phase, the form of the acid depending upon the particular oxidizable species available. (7) The chemical reactions and rate constants used in the calculations are relatively well determined, but our results are quite sensitive to the assumed concentrations of TMI and other species. Increased attention to measurement of species concentrations in fog, clouds, and rain is therefore indicated.
Atmospheric purging of El Chichon debris
Authors: Post Madison J.
Published: February 2008

A 3‐year program for sensing the vertical profiles of debris from El Chichon in the atmosphere over Boulder, Colorado has measured purging time constants of 208 and 60 days for the stratosphere and troposphere, respectively. No appreciable removal occurred from the atmosphere until the “cloud” descended to 6 km altitude 420 days after the eruptions. At a given altitude, data are lognormally distributed in time and, by assumption, in space. A simple theoretical model is offered in explanation.
The association of stratospheric warmings with tropospheric blocking
Authors: Quiroz Roderick S.
Published: February 2008

The discernment of an association between stratospheric warmings in winter and tropospheric blocking is made difficult by two factors: (1) the multiple occurrence of both features within a winter, complicating the determination of leads and lags, and (2) the choice of criteria for defining blocking and warmings. Criteria which take actual flow conditions into account, in distinction to the use of persistent height anomalies, were employed to monitor blocking in the Northern hemisphere since 1981. Major and minor warmings were identified with criteria consistent with the World Meteorological Organization definition. Broad and case‐by‐case comparisons were made of warming and blocking activity during November–March of 1981–1982 to 1984–1985. The broad comparison suggests a relation between the date of zonal flow reversal in major warmings and the number of blocking days in each winter. The detailed comparison, which included consideration of the thermal phase structure from 700 to 10 mbar, gave a demonstrable link between 500‐mbar blocking and 10‐mbar warming episodes in 85% of the cases examined, with blocks leading warmings by an average of 3.5 days. In the spectacular major warming of December–January 1984–1985 a tropospheric lead of 15 days was observed.
N2O5 photolysis: Quantum yields for NO3 and O(3P)
Authors: Ravishankara A. R. , Wine P. H. , Smith C. A. , Barbone P. E. , Torabi A.
Published: February 2008

The quantum yield for the production of NO3 in the N2O5 photolysis at 248 nm was measured to be unity. The concentration of NO3 produced upon photolysis was measured using 662‐nm laser absorption. The quantum yields for O(3P) production in the photolysis of N2O5 at 248 nm, 266 nm, 287 nm, and 289 nm were also measured using resonance fluorescence detection of O(3P). The quantum yield for O(3P) decreased from 0.7 at 248 nm to 0.15 at 289 nm. It is postulated that N2O5 photolysis at wavelengths less than 298 nm yields NO3 + NO + O(3P)in addition to NO3 + NO2.
Response of ozone to short‐term variations in the solar ultraviolet irradiance: 1. A theoretical model
Authors: Eckman Richard S.
Published: February 2008

The response of atmospheric ozone and temperature to variations in the solar ultraviolet irradiance over time scales corresponding to the solar rotation period is examined using a one‐dimensional, time‐dependent radiative‐photochemical model of the upper stratosphere and lower mesosphere. The model uses temporally varying measurements of the solar irradiance in the 120‐ to 300‐nm range made by the Solar Mesospheric Explorer satellite. Calculations of the amplitude and phase of the ozone response due to solar UV oscillations made by the model show that the effects of the coupling of radiation and photochemistry in the region near the stratopause may not be neglected. At 0.85 mbar, the computed 27‐day 0.6 K temperature variation decreases the amplitude of the corresponding ozone response over the solar rotation period by 25%. The occurrence of small phase leads (up to 1.5 days) in the response of ozone with respect to the solar UV variations may also be explained in light of the radiative‐photochemical coupling.
Wind and temperature regime along the slope of Adelie Land, Antarctica
Authors: Kodama Yuji , Wendler Gerd
Published: February 2008

An analysis was made of data collected from automatic weather stations (AWS) on the slope of Adelie Land, Antarctica. The data were collected simultaneously at different stations on the ice‐covered slope of the continent, where no data have previously been obtained. The stations are classified into three groups according to their location (high plateau, intermediate plateau, or coastal region), each having distinct annual temperature and wind speed regimes. These classifications also correspond well to the stations' slopes. Change in surface air temperature along the slope with respect to height was smaller than −1°C/100 m between the high plateau and the intermediate plateau stations. The wind directions did not follow Ball's model, which suggests the importance of the gradient of surface potential air temperature along the slope on the wind regime. A scale analysis showed the condition in which the gradient of surface potential air temperature along the slope should not be considered negligible when considering the total pressure gradient force. This condition in turn indicates that the entrainment of momentum across the top of the katabatic wind layer is also important.
Elevated atmospheric sulfur levels off the Peruvian coast
Authors: Saltzman E. S. , Savoie D. L. , Prospero J. M. , Zika R. G. , Mosher B.
Published: February 2008

Elevated levels of non‐sea‐salt sulfate and SO2 in samples collected off the west coast of South America indicate that there is a major source of atmospheric sulfur in the region of southern Peru and northern Chile. During a 1983 cruise, observed concentrations of non‐sea‐salt sulfur, SO2, selenium, arsenic, and antimony were comparable to levels reported for moderately polluted urban air. In contrast, methanesulfonic acid levels were typical of coastal marine air. Clearly, the elevated atmospheric sulfur levels in this region cannot be ascribed to oceanic organosulfur emissions. The major inputs are tentatively attributed to the smelting of sulfide ores which is a major industry in this region. The transport of smelter derived aerosols to this region may have a number of consequences for the atmospheric and oceanic chemistry of the Peruvian upwelling area.
Some kinetic and thermochemical aspects of sodium in the stratosphere
Authors: Lamb John J. , Benson Sidney W.
Published: February 2008

Metallic species produced in the atmosphere by meteoroid ablation may play an important role in atmospheric chemistry, especially that related to ozone. Observations of sodium at 90 km yield estimated concentrations of 3 × 103 cm−3. We report here calculations on NaCl, which is formed by the reaction of NaOH with HCl. We show that while NaCl photolyzes rapidly in the upper stratosphere, in the 30–35 km region it rapidly polymerizes, producing (NaCl)m, where m ≤ 10,000. One effect of this polymerization is to reduce the concentration of NaCl to 30 cm−3 and subsequent polymers to even lower concentrations, where they can act as a permanent reservoir for sodium and chlorine and cease to affect ozone chemistry. These calculations represent upper limits for (NaCl)m, since other metallic salts may copolymerize with NaCl.
Evolution of lightning flash density and reflectivity structure in a multicell thunderstorm
Authors: Mazur Vladislav , Rust W. David , Gerlach John C.
Published: February 2008

Radars with wavelengths of 10 cm (S band) and 70 cm (UHF band) were used to acquire the vertical precipitation structure and lightning flash distribution, respectively, in a multicell thunderstorm near Wallops Island, Virginia, during about 1.5 hours of continuous observations. The storm contained six cells that appeared sequentially; two of them exhibited the features of cell merger. In all six cells, vertical growth was about 3 times faster than decay. Lightning flash density centers were determined from the number of flashes that occurred within the UHF‐band radar beam per minute for each kilometer along the beam. The lightning radar echo data were corrected for side lobe effects. A bimodal distribution of lightning flash density was observed in only one cell, and it occurred during the initial stage of storm development; both the lower and the upper centers had 32 flashes min−1 km−1, centered at 7 km and 13 km, respectively. The other cells had single (lower) centers of lightning activity, with maximum flash densities ranging from 12 to 40 flashes min−1 km−1. As others before have reported, we see a positive correlation in time between the maximum lightning density and the heights of both the 40‐ and 50‐dBZ reflectivity cores. In all six cells we observed the following repetitive patterns in reflectivity structure and lightning distribution: (1) during the initial rapid growth of a cell, lightning activity is concentrated within a region bordering on the leading edge of the 50‐dBZ core of the cell and between this cell and its dissipating neighboring cell, and (2) in the decaying stage of a cell, lightning activity spreads farther into the cell.
Infrared radiation models for atmospheric methane
Authors: Cess R. D. , Kratz D. P. , Kim S. J. , Caldwell J.
Published: February 2008

Mutually consistent line‐by‐line, narrow‐band and broad‐band infrared radiation models are presented for methane, a potentially important anthropogenic trace gas within the atmosphere. Comparisons of the modeled band absorptances with existing laboratory data produce the best agreement when, within the band models, spurious band intensities are used which are consistent with the respective laboratory data sets, but which are not consistent with current knowledge concerning the intensity of the infrared fundamental band of methane. This emphasizes the need for improved laboratory band absorptance measurements. Since, when applied to atmospheric radiation calculations, the line‐by‐line model does not require the use of scaling approximations, the mutual consistency of the band models provides a means of appraising the accuracy of scaling procedures. It is shown that Curtis‐Godson narrow‐band and Chan‐Tien broad‐band scaling provide accurate means of accounting for atmospheric temperature and pressure variations.
Approximate methods for finding CO2 15‐μm band transmission in planetary atmospheres
Authors: Crisp David , Fels Stephen B. , Schwarzkopf M. D.
Published: February 2008

The CO2 15‐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 CO2 15‐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 should therefore be used with caution.
210Pb and 137Cs in air and soils measure the rate and vertical profile of aerosol scavenging
Authors: Graustein William C. , Turekian Karl K.
Published: February 2008

We have determined the deposition rates of 210Pb and 137Cs from the atmosphere to the landscape of the eastern and mid‐western United States by measuring their inventories in core samples of undisturbed soils. The mean inventories in lowland sites are 27.7 dpm cm−2 for 210Pb and 21.8 dpm cm−2 for 137Cs as of January 1984. The mean annual concentration of 210Pb in surface air at the 9 sites of the SURE network decreases smoothly from about 0.060 dpm m−3 near the Mississippi River to about 0.030 near the Atlantic coast. The ratio of deposition rate to surface air concentration is 0.62 ± 0.03 cm s−1 for 210Pb and 1.36 ± 0.08 cm s−1 for 137Cs. Using the activity vs. altitude profiles of Moore, et al. [1973], for 210Pb and the fission product nuclide, 90Sr, we calculate tropospheric aerosol mean residence times for 210Pb and 137Cs, of 4.8 and 5.5 days, respectively. This near equality precludes a rapid decrease of the aerosol scavenging rate constant in the mid‐troposphere. The 137Cs/210Pb ratios in soils from elevations above 1000 m in the Appalachian Mountains are lower than those in adjacent lowland soils, indicating the preferential removal of aerosols from the lower layer of the troposphere, presumably by cloud droplet impaction or by seeder‐feeder clouds.
The sulfur cycle in the marine atmosphere
Authors: Toon Owen B. , Kasting James F. , Turco Richard P. , Liu May S.
Published: February 2008

A one‐dimensional photochemical model is used to simulate the sulfur cycle in the marine atmosphere. Reduced organic sulfur compounds, including carbon disulfide (CS2), hydrogen sulfide (H2S), carbonyl sulfide (OCS), and dimethyl sulfide (DMS), are released from the ocean surface to the atmosphere, where they are oxidized to SO2 and particulate sulfate. CS2 concentrations reported over the oceans are an order of magnitude higher than those expected on the basis of a 0.5 Tg S yr−1 source estimated from water column measurements; the discrepancy may reflect continental contamination. We require a sink for OCS of magnitude 1–4 Tg S yr−1 in order to balance its budget; known photochemical processes are inadequate, but uptake by land plants could be important. H2S concentrations are consistent with an oceanic source of 1–5 Tg S yr−1. Most of the SO2 in the marine atmosphere apparently derives from oxidation of DMS, which has an estimated source of about 40 Tg S yr−1. The main loss process for DMS is reaction with OH, but reaction with NO3 may also be important. SO2 concentrations increase with altitude in the marine troposphere, while sulfate concentrations decrease with altitude; this behavior may result from rapid heterogeneous removal of SO2 in the boundary layer or from altitude variations in the branching ratio for DMS oxidation rather than from the “tropical cloud pumping” mechanism, which has been proposed previously as the explanation. Measurements that could improve our understanding of the marine sulfur cycle are suggested.
Carbon monoxide measurements over the eastern Pacific during GTE/CITE 1
Authors: Condon Estelle P. , Danielsen Edwin F. , Sachse Glen W. , Hill Gerald F.
Published: February 2008

As part of the Global Tropospheric Experiment's Chemical Instrumentation Test and Evaluation (GTE/CITE 1) intercomparison, carbon monoxide (CO) measurements were made from the NASA CV‐990 aircraft during the fall of 1983 and again in the spring of 1984. The experimental measurements for CO obtained during those flight series over the eastern and mid‐Pacific are presented here. Data were acquired from 10° to 20°N latitude over the mid‐Pacific and from 30° to 37°N latitude over the eastern Pacific off the coast of California. A seasonal variation of approximately 34 parts per billion by volume was measured over the altitudes and latitudes sampled, and a small latitudinal variation was also noted. The data are discussed in terms of the meteorological context in which they were collected.
An assessment of averaging strategies associated with day/night sampling of dry‐deposition fluxes of SO2 and O3
Authors: Meyers T. P. , Yuen T. S.
Published: February 2008

The uncertainties associated with daily, weekly, and day/night sampling of dry‐deposition fluxes of SO2 and O3 are addressed, using a multiple‐resistance deposition velocity model. Several day/night sampling protocols for both daily and weekly periods are investigated. Inferred fluxes from the various protocols are compared with the average of hourly fluxes computed as the product of the hourly concentration and deposition velocity Vd. For the daily period, day/night sampling gave better estimates of the daily average hourly flux of O3 than the product of the daily average Vd and concentration, but for SO2 the gain in accuracy with greater time resolution was negligible. For the weekly period, day/night sampling for O3 again gave improved estimates over the product of the weekly averaged Vd and concentration. However, fractional errors were on the order of 40%, because Vd and [O3] are positively correlated over weekly periods when the leaf area index is large enough to dominate Vd. For SO2, day/night sampling provided no improvement over the excellent estimates given by the product of the weekly average Vd and [SO2].
Visible spectroscopy at McMurdo Station, Antarctica: 3. Observations of NO3
Authors: Sanders R. W. , Solomon S. , Mount G. H. , Bates M. W. , Schmeltekopf A. L.
Published: February 2008

The total column abundance of NO3 was measured in Antarctica during the nights of September 17–19, 1986, by visible absorption, using the moon as the light source. The variation of the observed abundance with lunar zenith angle suggests that the bulk of the layer is located in the stratosphere. In agreement with theoretical model calculations, the total column was about 2.0×1013 molecule cm−2 and increased systematically with time during the night.
Aerosol and graphitic carbon content of snow
Authors: Chýlek Petr , Srivastava Vandana , Cahenzli Lynn , Pinnick R. G. , Dod R. L. , Novakov T. , Cook Terri L. , Hinds B. D.
Published: February 2008

Snow samples from southern New Mexico, west Texas, Antarctica, and Greenland were analyzed for aerosol and graphitic carbon. Graphitic carbon contents were found to be between 2.2 and 25 μg L−1 of snow meltwater; water‐insoluble aerosol content varied between 0.62 and 8.5 mg L−1. For comparison, two samples of Camp Century, Greenland, ice core, having approximate ages of 4,000 and 6,000 years, were also analyzed. Ice core graphitic carbon contents were found to be 2.5 and 1.1 μg L−1.
A transformed Eulerian model to study possible effects of the El Chichón eruption on the stratospheric circulation
Authors: Pitari Giovanni , Verdecchia Marco , Visconti Guido
Published: February 2008

A zonally averaged model using the residual circulation formalism has been built to study the possible dynamical effects of the El Chichón dust cloud in the middle atmosphere. A time dependent calculation of the residual mean velocities is performed, using as data the temperature field and the ozone distribution from a run of an updated version of the Massachusetts Institute of Technology‐Georgia Institute of Technology stratospheric general circulation model (GCM). Eddy fluxes are parameterized using the technique described by Tung (1983) input data are the time dependent fields of stream function and vertical velocity from the same run of the stratospheric GCM. Dust effects are included through a perturbation in the diabatic advection calculated as a function of net heating rates introduced by the presence of dust. A perturbative approach is used to solve the thermodynamic, continuity, thermal wind, and momentum balance equations, along with the explicit calculation of heating rates produced by the interaction of both long‐wave and solar radiation with dust. Heating rates due to absorption of scattered radiation by the aerosol cloud are also included. The numerical experiment starts about 3 months after the eruption, using lidar data by McCormick et al. (1984) as an initial condition for the aerosols, and is continued for about 1 year. Results are shown for heating rates, temperature, residual velocities, and aerosol distribution following the time evolution of the El Chichón dust cloud. It is shown that the perturbation in the heating rates is readily balanced by the radiative relaxation processes, so that the effects on the residual circulation are negligible.
The 40‐ to 50‐day oscillation in a perpetual january simulation with a general circulation model
Authors: Pitcher Eric J. , Geisler John E.
Published: February 2008

A 1200‐day record from a perpetual‐January simulation with a general circulation model is analyzed for the presence of an oscillation resembling the 40‐ to 50‐day oscillation observed in the atmosphere. Representation of the global velocity potential at 200 mbar by empirical orthogonal functions (EOFs) reveals an eastward propagating disturbance having a principally zonal wave number 1 character. It is determined from power spectra of the velocity potential at points around the equator that the period of the oscillation is in the range of 28–31 days. Time series of the coefficients of the first two EOFs are used to define epochs for the compositing in equatorial latitudes of anomalies in zonal winds, in 500‐mbar convective heating, and in precipitation. Time‐longitude diagrams of the zonal wind anomalies indicate the presence of an eastward propagating disturbance characterized by two longitudinal scales. The principal anomalies in convective heating and precipitation appear as two stationary oscillations, one situated in a zone extending from 120°E to the dateline and the other in a relatively narrow zone near 60°W.
Heavy ozone distribution in the stratosphere from far‐infrared observations
Authors: Abbas M. M. , Guo J. , Carli B. , Mencaraglia F. , Carlotti M. , Nolt I. G.
Published: February 2008

The distribution of isotopically heavy ozone in the stratosphere has been obtained from an analysis of balloon‐based high‐resolution thermal emission spectra in the far infrared. The mixing ratio profiles of 16O16O18O and 16O18O 16O retrieved from inversion of several limb sequences of a number of spectral lines in the 39–76 cm−1 region, indicate enhancements over the expected values in the 25‐ to 37‐km altitude range. The ratio of total heavy isotopic ozone 50O3 to normal 48O3 shows enhancements of ∼45% at 37 km, decreasing to a minimum of ∼13% at ∼29 km, and increasing to ∼18% at 25 km. The results from this work are compared with Mauersberger's (1987) in situ mass spectrometer measurements.
Detecting changes in global climate induced by greenhouse gases
Authors: Barnett Tim P. , Schlesinger Michael E.
Published: February 2008

A quantitative search for a theoretically predicted CO2 signal in surface air temperature data extending back to 1899 was marginally successful in a statistical sense. However, the nature of the signal strength time series suggested that this result is an artifact of large‐scale decadal variations at the beginning and end of the record. Application of the “fingerprint” strategy to three different global fields of climate variables over the last 25–35 years showed no significant CO2 signal. The analysis pointed up the need to use: (1) model signal‐to‐noise ratios in selecting fields for subsequent analysis and (2) multiple fields in the detection process. Most importantly, we found the primary pattern of natural air temperature variability to be very similar to the expected CO2 signal, thus suggesting that the air temperature field is not the best place to attempt early detection of the CO2 signal. By contrast, the primary pattern of natural variability and the expected CO2 signal in the ocean's surface temperature are substantially different; this suggests the oceans as a low‐noise environment in which to attempt early detection.
Impact of El Niño on the delineation of tropospheric cooling due to volcanic eruptions
Authors: Angell J. K.
Published: February 2008

It is well known that there has been a close relation between sea surface temperature (SST) variations in the eastern equatorial Pacific (El Niño region) and tropospheric temperature variations in the tropics, with the amplitude of the SST variations averaging about twice that of the tropospheric temperature variations. In particular, it is shown in this paper that during 1960–1986 there was a correlation of 0.66 (significant at the 1% level) between SST in the region 0°–10°S, 180°–80°W and zonally averaged 850‐ to 300‐mbar temperature in the equatorial zone one season later. In the north and south subtropics the maximum correlations between this SST and 850‐ to 300‐mbar temperature were 0.48 and 0.52 (significant at the 5% level) at a lag of two seasons. In temperate and polar latitudes the correlations were a maximum (though nonsignificant except in the south polar zone) at lags of two to three seasons. There is the implication of a tropospheric thermal pulse originating at the equator and spreading poleward, decaying as it does so. On the basis of the magnitude of these lagged correlations in the tropics it appears that the reason tropospheric temperatures cooled following the Agung eruption in 1963 but warmed following the El Chichón eruption in 1982 is the occurrence of a very strong El Niño after El Chichón but only a relatively weak El Niño after Agung. When tropical tropospheric temperatures are adjusted by “subtracting out” the usual relation with equatorial SST (by displacing the tropospheric temperatures two seasons earlier with respect to SST and dividing the SST deviations from the mean by 2 before subtraction from the tropospheric temperature deviations), the magnitude of the tropical tropospheric cooling following El Chichón becomes similar to that following Agung (about 0.5°C) but is of shorter duration. When a similar adjustment procedure is applied to the five major volcanic episodes since 1880, the eruptions of the tropical volcanoes of El Chichón, Agung, Santa Maria‐Pelée‐Soufrière, and Krakatau are all indicated to have brought about a decrease in northern hemisphere continental surface temperatures of about 0.3°C, whereas the eruption of Katmai in Alaska is indicated to have decreased this temperature by only about 0.1°C. It is proposed that the reason the evidence for volcanically induced cooling of the Earth's surface has been so uncertain and controversial in the past is that such cooling may or may not be observed depending on the extent of sea surface warming in the eastern equatorial Pacific after the volcanic eruption.
Effect of computed horizontal diffusion coefficients on two‐dimensional N2O model distributions
Authors: Jackman Charles H. , Newman Paul A. , Guthrie Paul D. , Schoeberl Mark R.
Published: February 2008

The sensitivity of the N2O distribution in our two‐dimensional photochemical model to horizontal diffusion coefficients (both Kyy and Kyz values) has been explored. The residual circulation was computed using temperature data from the National Meteorological Center (NMC) and heating rates from Rosenfield et al. (1987). The Kyy and Kyz values were computed from these same data using quasigeostrophic potential vorticity. For comparison we also computed self‐consistent Kyy values from our residual circulation. The use of either set of these diffusion coefficients produced substantial changes in the N2O distribution, especially in the middle to upper stratosphere and at high latitudes in the winter. In general, the changes lead to an enhanced transport of N2O to higher latitudes with the set of self‐consistent Kyy values transporting the greatest amount of N2O. The enhanced transport increases the lifetime of N2O because the photochemical lifetime is larger at high latitudes.
Climatic response to large atmospheric smoke injections: Sensitivity studies with a tropospheric general circulation model
Authors: Ghan Steven J. , MacCracken Michael C. , Walton John J.
Published: February 2008

A tropospheric general circulation model is coupled with a Lagrangian trace species transport and removal model to determine the climatic response to continental‐scale smoke injections arising from fires generated following a hypothetical nuclear war. The hydrological response is found to be particularly sensitive, with significant reductions in precipitation over land areas occurring for smoke injections that yield only modest cooling. This sensitivity is traced to the suppression of surface evaporation caused by a smoke‐induced reduction in the convective mixing of boundary layer and upper tropospheric air. A variety of sensitivity experiments is considered, including the sensitivity to smoke injection mass, location, day, season, duration and altitude of injection, and smoke composition and size distribution. For modest injections the land surface cooling in the first few weeks is found to be proportional to the smoke loading, while for larger injections the amount of smoke affects only the duration of the surface cooling. After several weeks the northern hemisphere land surface cooling for an April injection is found to be comparable to that for a July injection. A protracted smoke injection, which produces a more homogeneous horizontal distribution of smoke than an instantaneous injection, yields a greater surface cooling. The assumed initial aerosol size distribution of the injection is found to play a particularly important role in determining the climatic response, with injections composed primarily of submicron spherical particles producing a larger and longer surface cooling than an injection composed primarily of supermicron spherical aerosols. The importance of various feedback processes is also discussed. Smoke lofting associated with solar absorption by the aerosols enhances the aerosol residence time in the atmosphere by an order of magnitude, compared to aerosol lifetimes in the control atmosphere. The ground hydrology feedback in the tropics is found to amplify the sensitivity of precipitation over land areas and to enhance surface warming after several weeks. The treatment of a stability dependent rather than neutral boundary layer enhances the surface cooling in the first few weeks by about 30%.
North Pacific marine background aerosol: Average ammonium to sulfate molar ratio equals 1
Authors: Covert David S.
Published: February 2008

Measurements of the chemical composition of marine aerosol were made at a location on the north‐west coast of the continental United States. The average concentration of sulfate ion in submicrometric aerosol particles was 0.4 μg m−3. The average ammonium ion to sulfate ion molar ratio was 1.0 and was nearly the same as the ratio of 1.1 for concurrently collected rain samples. There was a large variability in these parameters on the 3‐hour basis of the measurement method.
Airborne measurement of atmospheric aerosol particles in the lower troposphere over the central United States
Authors: Kim Young J. , Sievering H. , Boatman J. F.
Published: February 2008

A series of airborne measurements of atmospheric aerosols were made in four seasonal field periods over the central United States as a part of Central U.S. RADM Test and Assessment Intensives (CURTAIN). The primary objective of the CURTAIN aerosol measurements was to provide a data base for evaluation of the Regional Acid Deposition Model (RADM). Aerosol size distributions were measured at two altitudes of about 1450 and 2450 m above sea level (asl) over the size range 0.1–16 μm, using two Particle Measuring Systems, Inc., probes, an active scattering aerosol spectrometer probe and a forward scattering spectrometer probe, mounted on the National Oceanic and Atmospheric Administration King Air research aircraft. Aerosol samples were also collected by a 2.5‐cm filter pack system for subsequent elemental analysis by X ray fluorescence (XRF). The average aerosol number concentration reached a maximum in summer at both low and high altitudes. The average aerosol number concentration was minimized during fall at low altitude and during winter at high altitude. The coarse particle mode of the aerosol volume distributions displayed a drastic seasonal change, with a winter volume geometric median diameter (VGMD) of 4.34 μm and a summer VGMD of 9.21 μm. The summer peak in the coarse‐mode VGMD and volume concentration is attributed to increased windblown dust particles and the presence of liquid water as part of the aerosol volume under high relative humidity conditions. No significant latitudinal dependence was found in the CURTAIN aerosol data at low and high‐altitude, during the day or night, or from season to season. The CURTAIN aerosol data are influenced differently by the mixed layer from season to season. In winter, high‐altitude aerosol data were collected above the top of the mixed layer. Therefore the vertical profile of aerosol concentration shows a general decrease above the base of the mixed layer temperature inversion. In summer, high‐altitude aerosol data were collected within the mixed layer. The vertical distribution of aerosol number concentration was rather constant during summer. XRF elemental analysis performed on the collected aerosol samples shows that fine‐fraction Fe and K are fairly strongly correlated with accumulation mode mass during summer. This indicates that soil and agricultural fertilizer aerosol sources are important contributors. Correlations for fine and coarse masses with various atmospheric parameters are calculated. Positive correlations with temperature and relative humidity are found. Low wind speed and east winds are correlated with higher fine mass.
Ozone calculations with large nitrous oxide and chlorine changes
Authors: Kinnison Douglas , Johnston Harold , Wuebbles Donald
Published: February 2008

The purpose of this study is broadly to reinvestigate NOx‐Clx interactions relative to ozone control in the stratosphere, using the long‐established Lawrence Livermore National Laboratory one‐dimensional model. To obtain perspective on reasonably expected atmospheric perturbations, this study includes unrealistic conditions in the calculations, and several interesting or unexpected features are found. (1) By varying both NOx and Clx over wide ranges, regions are found where ozone column reduction is linear and nonlinear in added chlorine or in added nitrogen oxides. (2) If the stratosphere had much less NOx than the natural amount, small chlorine increases would cause large reductions of ozone. (3) At high Clx, a region of NOx‐Clx space is found where added NOx (at constant Clx) increases the ozone column, but no region was found where added chlorine (at constant nitrous oxide boundary condition) increases the ozone column. (4) The solar self‐healing effect in response to ozone reduction by increasing Clx is much greater than that associated with ozone reduction by increasing nitrous oxide. (5) For any fixed amount of Clx, the amount of chlorine nitrate in the stratosphere is decreased by added NOx, and an explanation for this effect is presented. (6) Any increase of stratospheric Clx shrinks the rate profile of ozone destruction by NOx, and any increase of nitrous oxide shrinks the rate profile of ozone destruction by Clx. (7) Total ozone changes linearly with Clx until the rate of ClO + O exceeds that of NO2 + O below about 30 km, and then it becomes nonlinear with downward curvature. (8) Removal of all Clx and all HOx from the stratosphere has only a slight effect on the magnitude and shape of the altitude profile of the rate of ozone destruction by NOx. (9) The NOx and HOx families almost completely suppress the effect of 1 parts per billion by volume (ppbv) chlorine on ozone; but in the absence of NOx and HOx, even 1 ppbv chlorine is a powerful ozone‐destroying catalyst from the bottom to the top of the stratosphere. (10) In its altitude flexibility, Clx destruction of ozone is qualitatively different from NOx and HOx destruction of ozone.
Analytic solution of the box diffusion model for a global ocean
Authors: Lebedeff Sergej A.
Published: February 2008

An analytic solution for the temperature of the mixed layer for a box diffusion model of a global ocean is derived. It is shown that the analytic solution for the temperature of the mixed layer is expressed in terms of error functions. Arguments of the error functions are, in general, complex. It is shown that the exact solution approaches the appropriate limits of a mixed layer ocean model and of a diffusive ocean without a mixed layer on top. The effect of random noise on the temperature response is considered. Scaling transformations are used to derive the analytic solution for the box diffusion model which, in the case of the doubled CO2 experiment, depends on only one parameter. This dependence on one parameter permits derivation of a simple expression for the e‐folding time and formulation of a quantitative sensitivity analysis for the response of the temperature of the mixed layer to changes of the parameters of the global ocean‐atmosphere model. The sensitivity analysis is extended to include forcing functions which are integer powers of time.
The 1986 drought in the southeastern United States: How rare an event was it?
Authors: Cook Edward R. , Kablack Mark A. , Jacoby Gordon C.
Published: February 2008

The recent drought in the southeastern United States is the most severe episode of moisture deficiency to strike that area in the past 111 years, based on meteorological records. Using those records, the recurrence interval of this event has been estimated to be of the order of 100–200 years. We develop a much longer history of drought occurrence for this region, using tree‐ring series of old‐age trees growing in the southern Appalachian Mountains. This record, which extends back to 1700, indicates that the 1986 drought was unprecedented in its severity as a single‐year event. On this basis we conclude that the 1986 drought is a very rare event, with a probable recurrence interval of at least 287 years.
NO and NO2 in the troposphere: Technique and measurements in regions of a folded tropopause
Authors: Ridley Brian A. , Carroll Mary Anne , Gregory Gerald L. , Sachse Glen W.
Published: February 2008

During the 1984 spring program of the NASA Global Tropospheric Experiment, measurements of NO, NO2, O3, and CO were made during two aircraft flights that encountered tropopause fold events. The technique used to measure NOx (NO + NO2) is described. In the neighborhood of both tropopause fold events, CO and O3 were strongly anticorrelated [Danielsen et al., 1987; Hipskind et al., 1987]. In one fold, encountered over the eastern Pacific Ocean at night, NOx was positively correlated with O3, negatively correlated with the dew point, and negatively correlated with CO, consistent with the stratospheric origin of the air mass. In this fold at altitudes between 5.5 and 6.0 km, NOx reached mixing ratios near 150 parts per trillion by volume (pptv), considerably larger than the levels of 10–50 pptv in the air external to the fold. In contrast, in a daytime encounter with a fold over the southwestern United States at altitudes of 6.7–8.8 km, NOx did not correlate well with CO, O3, or dew point, but remained roughly constant at levels of 100–200 pptv. Outside of the fold, in a region of strong convective activity, NOx peaked to just over 500 pptv. It appears that mixing of tropospheric air containing elevated NOx weakened the expected trends for the fold over the continent compared to the fold over the ocean, and therefore NOx may not always be a good tracer of air of recent stratospheric origin. However, the observations emphasize that the stratospheric source of NOx acts to introduce NOx over a short period and through a large vertical region of the troposphere, not just near the tropopause, as is assumed in many tropospheric models.
Electrical structure in two thunderstorm anvil clouds
Authors: Marshall Thomas C. , Rust W. David , Winn William P. , Gilbert Kenneth E.
Published: February 2008

Two electric field soundings through thunderstorm anvil clouds show similar charge structures: negatively charged screening layers on the top and bottom surfaces, a layer of positive charge in the interior, and one or two layers of zero charge. Both anvil clouds were strongly electrified: the peak magnitudes of the electric field in the two storms were 70 and 90 kV/m, respectively. The nonzero layers had charge densities comparable to those found in the cores of thunderstorms, ranging in magnitude from 0.4 to 2.7 nC/m3. Layers varied in thickness from 300 to 2000 m. The positive charge probably originated in the main positive charge region normally found at high altitudes in the core of thunderclouds. Transporting positive charge from the storm core to the anvil may influence the ratio of intracloud to cloud‐to‐ground lightning flashes and the rate of generation of charge in the core. The negatively charged layers probably were screening layers, resulting from the discontinuity in the electrical conductivity at the cloud boundaries. The lower negative screening layer appeared to be carried toward the storm core by winds below and at the lower anvil boundary.
Latitudinal distribution of the sources and sinks of atmospheric carbon dioxide derived from surface observations and an atmospheric transport model
Authors: Tans Pieter P. , Conway Thomas J. , Nakazawa Takakiyo
Published: February 2008

Determination of the present global budget of atmospheric carbon dioxide (CO2) from the small and persistent concentration gradients that exist in the atmosphere is discussed. The CO2 concentration at any site results from a combination of two factors: local sources or sinks and long‐range transport. To separate these two effects, an atmospheric transport model is needed. The extensive sets of global CO2 measurements of the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Monitoring for Climatic Change (GMCC) division and of the Upper Atmosphere and Space Research Laboratory of Tohoku University are combined with a two‐dimensional transport model to derive, in an “inverse” calculation, the latitudinal and seasonal distributions of sources and sinks of CO2 necessary to reproduce the observed concentrations. The model transport parameters were previously derived from a three‐dimensional general circulation model. It is found that the southern oceans are a sink of carbon of 0.8–1.5 Gt yr−1 (1 Gt equals 1015g) and that the equatorial areas are a source to the atmosphere of 1.4–2.8 Gt yr−1. Tropical deforestation as a major source of CO2 must be smaller than that because the oceans account for a significant part of the equatorial flux. There seems to be significant seasonality in the sources and sinks of CO2, both in the tropics and in the southern oceans. The seasonal net ecosystem production north of 25°N is found to be 6.2–8.2 Gt of carbon, but these estimates are probably somewhat too low. The source deduction problem is difficult to solve, especially for the middle and high latitudes in the northern hemisphere. This is due to a lack of observations over the continents, which occupy more than half of the global area at these latitudes and are the regions where the sources and sinks are most intense. Evidence is found in the results obtained for the GMCC and Tohoku data that the longitudinal variability of the data is large enough, even in equatorial and southern latitudes, to prevent a two‐dimensional model from calculating a fully credible source/sink field. The longitudinal variations in the observations have to be accounted for with a three‐dimensional transport model.