bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of stratospheric HOCl: Concentration profiles, including diurnal variation
Authors: Chance K. V. , Johnson D. G. , Traub W. A.
Published: February 2008

We have made determinations of concentration profiles of HOCl in the Earth's stratosphere, including the diurnal variation. Measurements of the rotational Q2 branch at 99.5 cm−1 and of five RR(J3) transitions between 143 and 159 cm−1 were made using far infrared thermal emission spectroscopy. The spectra were obtained during a balloon flight of the FIRS 2 far infrared Fourier transform spectrometer and telescope from Palestine, Texas, on May 12–13, 1988. From these measurements, we obtain altitude profiles of HOCl from 23 to 42 km. We present daytime and nighttime average profiles of HOCl, as well as measurements on a 30‐min time scale through the sunset transition at a single (35 km) altitude. Our measured profiles are lower than the current predictions from several modeling groups by a factor of approximately 0.6.
Nitrous oxide as a dynamical tracer in the 1987 Airborne Antarctic Ozone Experiment
Authors: Loewenstein M. , Podolske J. R. , Chan K. R. , Strahan S. E.
Published: February 2008

In situ N2O measurements were made using an airborne tunable laser absorption spectrometer (ATLAS) on 12 flights into the Antarctic vortex, as well as on five transit flights outside the vortex region in August and September 1987, as part of the Airborne Antarctic Ozone Experiment. Vertical profiles of N2O were obtained within the vortex on most of these flights and were obtained outside the vortex on several occasions. Flights into the vortex region show N2O decreasing southward between 53° and 72°S latitude on constant potential temperature surfaces in the lower stratosphere. The data lead to two important conclusions about the vortex region: (1) The lower stratosphere in August/September 1987 was occupied by “old” air, which had subsided several kilometers during polar winter; (2) The N2O profile in the vortex was in an approximately steady state in August/September 1987, which indicates that the spring upwelling, suggested by several theories, did not occur.
A theoretical study of ozone measurements made with ground‐based microwave sensors
Authors: Brillet Jean
Published: February 2008

The amount of information which may be extracted from ozone measurements made with ground‐based microwave receivers is examined. After reviewing the observing procedures and the sources of experimental errors, a theoretical analysis shows that there are at most 10 independent pieces of information which may be determined. Four cases have been investigated. It is found that two experimental procedures commonly used are not strictly equivalent. The frequency‐switching mode appears to be slightly better than the load‐switching mode. Two methods involving transformations of the weighting function space have been examined. The first uses the differences between adjacent brightness temperatures, and the second a selection of the weighting functions. These transformations permit the application of the Chahine algorithm, but it is shown that they lead to an inherent loss of the retrieval accuracy even though the number of independent pieces of information is preserved. In the same way, a method based on a control of the information content is developed to define an optimal spectrometer. In the second part, an investigation with the Backus‐Gilbert inversion technique is used to quantify the relationship of the retrieval accuracy against the spatial resolving power. The qualitative results derived by the previous method are completely expressed by this inversion technique. The influence of the frequency resolution and the bandwidth of the spectrometer on these parameters is examined, and the scanning interval of the microwave technique is described in terms of altitude band‐pass filters. It is found that the retrieval accuracy increases when the altitude decreases and that the measurement capability vanishes rapidly above 65 km. The instrumental baseline is found to disturb the determination of the ozone concentration mainly at low altitudes. However, this effect may be regarded as a calibration term which does not affect the measurements of the ozone variability. Practical considerations lead to a preference for the load‐switching technique in spite of the small theoretical advantage yielded by the frequency‐switching mode. The results are presented for the 61–5 → 60–6 transition but can be easily transposed for the other ozone transitions. The theory and many qualitative results apply to the microwave measurements of the other minor atmospheric constituents.
Reactions of ozone with α‐pinene and β‐pinene in air: Yields of gaseous and particulate products
Authors: Hatakeyama Shiro , Izumi Katsuyuki , Fukuyama Tsutomu , Akimoto Hajime
Published: February 2008

Reactions of ozone with α‐pinene and β‐pinene were studied for the purpose of obtaining the quantitative yields of gaseous and particulate products. Major gaseous products from α‐pinene were CO, CO2, HCHO, and aldehydes mainly composed of pinonaldehyde and nor‐pinonaldehyde, while those from β‐pinene were CO2, HCHO, and 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one. Average molar yields from α‐pinene were CO; 9±1%, CO2; 30±2%, HCHO; 22±1%, and aldehydes; 51±6%. Average molar yields from β‐pinene were CO2; 27±2%, HCHO; 76±2%, and 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one; 40±2%. Particulate products were found to include pinonaldehyde, nor‐pinonaldehyde, pinonic acid, and nor‐pinonic acid from α‐pinene. The yields of the particulate aldehydes decreased with the reaction time, whereas the yields of the acids increased. This observation suggests the sequential oxidation of aldehydes to carboxylic acids. From β‐pinene, only 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one was identified as a particulate product. For α‐pinene, most of the products are explainable in terms of the reaction mechanism similar to that for the cyclohexene/ozone reaction, whereas for β‐pinene the principal reaction path is that of the doubly substituted Criegee intermediate. The total yields of organic aerosols from both α‐ and β‐pinene were measured with their concentrations at a lower ppb level. The yields were found almost constant in a pinene concentration range from 10 up to 100 ppb, being 18.3±1.1 and 13.8±0.8% for α‐ and β‐pinene, respectively, which are much lower than the previously reported values.
Carbon dioxide 4.3‐μm emission in the Earth's atmosphere: A comparison between Nimbus 7 SAMS measurements and non‐local thermodynamic equilibrium radiative transfer calculations
Authors: López‐Puertas M. , Taylor F. W.
Published: February 2008

A detailed analysis of CO2 4.3‐μm limb radiances measured by the Stratospheric and Mesospheric Sounder on Nimbus 7 has been conducted using a non‐local thermodynamic equilibrium (non‐LTE) radiative transfer model. The data display diurnal, latitudinal, and seasonal variations which are shown, after the latitudinal variation of the instrument's response has been taken into account, to be caused by different conditions of solar illumination and variations in the kinetic temperature profile. A study of the sensitivity of the populations and limb radiances to spectral, atmospheric, and collisional interactions parameters has been undertaken, and a limited range of values for some of these quantities has been derived. Among other findings, we conclude that the rate at which energy is exchanged (as ν3 quanta) between N2 and CO2 may be approximately twice the initial model value, which was inferred from laboratory data, and that the CO2 volume mixing ratio above 80 km may be significantly less than that predicted by photochemical models.
Electric discharges between hydrometeors
Authors: Chauzy Serge , Kably Khalil
Published: February 2008

The phenomenon of the microdischarge between small conductors (simulating hydrometeors) is experimentally investigated. The study consists in directly measuring the electric current signature of the discharge under various initial conditions and for two different sets of conductors: sphere‐sphere and sphere‐needle. The second system produces an important initial streamer phase prior to the leader one. The characteristics of the current signatures are strongly dependent on gap length. The shorter the gap, the higher the current intensity and the narrower the pulse. Measurements made with real water drops provide comparable results. On the other hand, the radiated electric field generated by a microdischarge between two conducting spheres located within an intense electrostatic field has also been measured. The temporal characteristics of the field signatures obtained agree with those of the current pulses. Risetimes of the order of a few nanoseconds have been measured. The derived spectral content shows that the electromagnetic energy of this elementary phenomenon radiates within the VHF range. A numerical model based on the current dependence of the air conductivity contributes to the explanation of the mechanism.
Electric field changes and cloud electrical structure
Authors: Krider E. Philip
Published: February 2008

The NASA Kennedy Space Center and Cape Canaveral Air Force Station are currently operating a large network of electric field mills to detect lightning and electrified clouds that might present hazards to ground operations, launches, and landings. Here we summarize recent results of least squares analyses of multistation measurements of field changes that were produced by cloud‐to‐ground (Q model) and intracloud (P model) lightning. The values of the optimum parameters of 113 lightning events that occurred in one small storm on July 11, 1978, and a portion of a large storm on July 6, 1978, are tabulated and graphed. We note that, in both storms, there is considerable symmetry in the direction of P vectors around the Q region and that this pattern is consistent with the classic double‐dipole model of thundercloud charges. We note also that the vertical separation of the Q and P regions depends on the storm intensity.
Mesopause temperatures in polar summer
Authors: von Zahn U. , Meyer W.
Published: February 2008

Between June 10 and July 19, 1987, a total of 26 falling spheres have been successfully launched from the Andøya Rocket Range in Norway (69°N, 16°E). From precision radar tracking of the sphere trajectories, 26 temperature profiles were derived for the altitude range 50–90 km. A mean profile, calculated from all data obtained, shows the mesopause to be at an altitude of 88 km and at a temperature of 129±6 K. This mesopause temperature is considerably lower than predicted in some recently developed reference atmospheres. In the middle and upper mesosphere, each of the 26 profiles exhibits a lapse rate close to −6 K/km. These results are compared with parameters obtained previously in winter at the same site.
Nitrogen oxides from high‐altitude aircraft: An update of potential effects on ozone
Authors: Johnston Harold S. , Kinnison Douglas E. , Wuebbles Donald J.
Published: February 2008

A sensitivity study is carried out using the Lawrence Livermore National Laboratory one‐dimensional and two‐dimensional chemical‐radiative‐transport models of the global atmosphere to examine possible effects of future aircraft NOx emissions to stratospheric ozone. A broad range in magnitude, altitude, and latitude of the assumed NOx emissions is examined. Major findings of this initial study are as follows: (1) Nitrogen oxides from the exhaust gases of stratospheric aircraft can reduce stratospheric ozone on a global basis. These calculated ozone reductions depend strongly on NOx injection altitude and magnitude. (2) The altitude at which NOx emissions cause the largest reduction in the ozone column is about 25 km according to one‐dimensional model calculations and about 28 km according to the two‐dimensional model. (3) For a given altitude and magnitude Of NOx emissions, the two‐dimensional model finds that the reduction of global ozone depends on latitude of the injections, with maximum ozone reduction for tropical injection. For a given injection, the largest ozone column reductions occur in the polar regions. (4) For very large Clx mixing ratios, NOx emissions can increase the ozone column, partially counteracting the ozone reduction caused by Clx. This effect is found only in a highly Clx perturbed stratosphere where ozone is already greatly depleted. (5) Water vapor (without nitric oxide) in the exhaust gives a small ozone reduction; water vapor and nitric oxide together give an ozone reduction less than that calculated for NO alone by factors between 0.85 and 0.97. (6) Calculated global reductions of ozone due to NOx emissions are smaller in the two‐dimensional model than in the one‐dimensional model, by factors that range from 0.66 to 0.86 for injection altitudes between 20 to 34 km. (7) On the basis of an uncertain estimate of fuel consumption by future stratospheric aircraft, calculations for a fleet of 500 aircraft operating at 22 km with NOx emission properties of 1988 subsonic commercial aircraft engines give global ozone reductions of about 20%. There is reason to believe that such nitric oxide emissions may be lowered, perhaps by a factor of 10, by advanced emission reduction technology.
A comparison of the longitudinal distributions of polar stratospheric clouds and temperatures for the 1987 Antarctic spring
Authors: Watterson Ian G. , Tuck Adrian F.
Published: February 2008

The Stratospheric Aerosol Measurement (SAM) II stratospheric extinction coefficients have been analyzed to provide information on the geographical distribution of Antarctic stratospheric clouds in 1987. The peak extinction above 15 km was determined for each of the approximately 14 vertical profiles each day. A longitude by time graph of this extinction is presented, extending from early June to late October. Similar graphs for extinction at 17 km and for temperature at 17 km and 70 mbar geopotential height from the National Meteorological Center at the measurement locations are also shown. It is assumed that extinction is a measure of cloud density. Statistics of the fractional incidence of cloud and of temperature and pressure for five time periods and 24 longitudinal sectors are presented. Cloud incidences for latitudes which either cross or pass to the south of the Antarctic Peninsula are shown. In order to remove the effect of the latitudinal drift of the measurements the statistics are also shown for data binned by 70‐mbar geopotential height relative to the minimum within the vortex. In general, there is a good correlation between enhanced extinctions and cold temperatures. Both exhibit a planetary wave structure which tends to move eastward. However, the distribution of dense clouds is highly zonally asymmetric and unlike that of temperature. These clouds are very rare over East Antarctica even when temperatures are low there. After July, clouds are also rare close to the center of the vortex, as determined by the 70‐mbar geopotential height of the measurement locations. It is concluded that both cold temperature and the availability of condensable material are important in determining the location of cloud. The dehydration of the interior of the vortex through sedimentation restricts cloud formation as early as July 3. Cloud formation is closely associated with tropospheric weather systems which produce colder temperatures in the lower stratosphere through adiabatic expansion in the poleward flow to the east of the cyclonic region. In addition, moister air from farther out in the vortex can pass across the measurement locations because of the poleward flow. In August and September, clouds were periodically detected by SAM II in the 90° to 0°W sector between 75° and 78°S, well to the south of the northern edge of the chemically perturbed region of the ozone hole. The clouds occurred at temperatures and relative 70 mbar heights similar to those of locations over East Antarctica where low extinctions were usually measured. The difference in fractional incidence of cloud between the regions suggests that some resupply of condensable material by irreversible mixing occurred in the 90° to 0°W sector, to an altitude of at least 17 km and a potential temperature of at least 410 K.
Obtaining sub‐grid‐scale information from coarse‐resolution general circulation model output
Authors: Wigley T. M. L. , Jones P. D. , Briffa K. R. , Smith G.
Published: February 2008

The relationships between local temperature and precipitation and large‐scale climate are explored using regression analysis. The motivation for this study is the need of the impact analyst for small‐scale information given only coarser resolution General Circulation Model output. The predictor variables employed are area averages (over ∼2.5 × 106 km2) of temperature and precipitation and propinquitous grid point values of mean sea level pressure and 700 mbar height, together with the zonal and meridional gradients of these two variables. Regression analyses are performed using monthly‐mean data from Oregon, with separate analyses for each month. In independent verification, spatial‐mean explained variances range from 58 to 87% for temperature and from 39 to 76% for precipitation. Most of the variance explained arises from the area average of the variable which is the predictand: in other words, if the temperature, say, at point x is to be estimated, the best predictor is generally the area average temperature. There are large spatial differences in the amount of local climate variance that can be explained by large‐scale data. Examples are given which show how site‐specific changes can differ markedly from those at the grid point scale.
The beam filling error in the Nimbus 5 electronically scanning microwave radiometer observations of Global Atlantic Tropical Experiment rainfall
Authors: Short David A. , North Gerald R.
Published: February 2008

A comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer (ESMR 5) brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I shows that the beam filling error is the major source of discrepancy between the two. When averaged over a large scene (the GATE radar array, 400 km in diameter), the beam filling error is quite stable, being 50% of the observed rain rate. This suggests the simple procedure of multiplying retrieved rain rates by 2 (correction factor). A statistical model of the beam filling error is developed by envisioning an idealized instrument field‐of‐view that encompasses an entire gamma distribution of rain rates. A modeled correction factor near 2 is found for rain rate and temperature characteristics consistent with GATE conditions. The statistical model also suggests that (1) the correction factor varies from 1.5 to 2.5 for suppressed to enhanced tropical convective regimes and (2) decreases to 1.5 as the freezing level and average depth of the rain column decreases to 2.5 km.
Hydrogen peroxide and ozone over the northeastern United States in June 1987
Authors: Van Valin Charles C. , Luria Menachem , Ray John D. , Boatman Joe F.
Published: February 2008

Continuous measurements of ozone (O3) and hydrogen peroxide (H2O2), and of other trace gases and meteorological parameters, were made using the NOAA King Air research aircraft. The atmosphere was sampled at various elevations from minimum altitude above ground level up to 4 km above sea level, over the northeastern United States between Columbus, Ohio, and Saranac Lake, New York, during June 1987. The average O3 concentrations, calculated for constant‐altitude flight segments, are in the range 50–110 ppbv; the H2O2 range for the same flight segments is 0.6–3.6 ppbv. Concentration profiles of O3 show little variation with altitude, with the exception of samples taken in polluted areas. The highest H2O2 concentrations are observed at the lowest altitudes in air from southern regions, i.e., in air containing the greatest water vapor density. The concentrations of both O3 and H2O2 show a clear decrease from lower (40°N) to higher (44°N) sampling latitudes.
BUGATTI experiments: Mass spectrometric studies of lower thermosphere eddy mixing and turbulence
Authors: von Zahn U. , Lübken F.‐J. , Pütz C.
Published: February 2008

A rocket‐borne mass spectrometer has been developed for high‐time‐resolution and high‐accuracy measurements of the number densities of nitrogen, n(N2), and argon, n(Ar), in the altitude region from 90 to 130 km. Primary aims of the experiments are the determination of altitude profiles for the ratio n(Ar)/n(N2) and for small‐scale fluctuations of n(N2). From the profiles we deduce the strength of eddy mixing, and from the fluctuations we deduce properties of instantaneous turbulence. We report on the results of four successful experiments, all performed during wintertime at polar latitudes. Near 100‐km altitude, eddy coefficients Ke were found to range from 102 to > 103 m2/s, the spectral index ξ of the power spectral density ranged from −1.2 to −2.0, and the rates of dissipation of turbulent energy, ε, ranged from 2 to 30 mW/kg.
A comparison of two major Earth radiation budget data sets
Authors: Kyle H. Lee , Mecherikunnel Ann , Ardanuy Philip , Penn Lanning , Groveman Brian , Campbell G. Garrett , Haar T. H. Vonder
Published: February 2008

The Earth radiation budget data obtained from the Nimbus 7 Earth Radiation Budget (ERB) and the Earth Radiation Budget Experiment (ERBE) spacecraft missions are compared for several overlapping months during the period November 1984 to January 1986. The Nimbus 7 ERB data set starts in November 1978 and extends through October 1987 (9 years). The ERBE data set starts in November 1984 with the ERBS satellite, which was supplemented by the NOAA 9 in January 1985 and the NOAA 10 in September 1986. Data from both the ERBS and the NOAA 9 are presently being released to the scientific community. The principal aim of the ERBE project is to obtain improved measurements of the diurnal variations in the Earth radiation budget in order to derive accurate radiation budget products. On the Nimbus 7 ERB, only the wide field of view sensors have been active since July 1980. During the comparison period, both the ERBS and NOAA 9 had active wide field of view, medium field of view, and narrow field of view (scanner) sensors. Top of the atmosphere, colocated wide field of view (WFOV) measurements are compared to estimate relative biases. Then all the time‐ and space‐averaged products are compared. Each WFOV instrument has a shortwave and a total spectral channel. The outgoing longwave radiation is taken as the difference between the total and shortwave readings. The Nimbus 7 WFOV shortwave sensor reads about 2.5% higher than the ERBS sensor, while the Nimbus 7 total channel reads about 1% below the ERBS channel near midnight and about 1% above it near noon. A comparative study of the time‐ and space‐averaged data products for April, July, and October 1985 and January 1986 shows that the Nimbus 7 ERB global averages agree in the mean with the combined ERBS/NOAA 9 scanner values to within 0.16% in the outgoing longwave radiation and 0.03% in the albedo. The agreement of the combined ERBS/NOAA 9 WFOV products to the ERBS/NOAA 9 scanner products is 0.17% in the outgoing longwave radiation and 3.55% in the albedo. Certain fortuitous approximations in the time‐ and space‐averaging algorithms appear to have helped the agreement in the final mean Nimbus 7 and ERBE products. Monthly and regional differences are somewhat larger than for the 4‐month mean global values.
Ozone profile measurements within, at the edge of, and outside the Antarctic polar vortex in the spring of 1988
Authors: Deshler T. , Hofmann D. J. , Hereford J. V.
Published: February 2008

Ozone and temperature were measured during 38 balloon soundings at McMurdo Station, Antarctica (78° S), in the spring of 1988. Because of the motion of the Antarctic polar vortex, measurements were obtained within, at the edge of, and outside the vortex. Although the polar vortex did not remain over McMurdo as it did in 1986 and 1987, it was overhead long enough to establish that ozone depletion was less extensive and ended earlier than in either 1986 or 1987. In the vortex the ozone mixing ratio at 18 km decayed with an exponential half‐life of 29 days compared to 25 and 12 days in 1986 and 1987. While ozone partial pressure in the 16–18 km layer decayed to values as low as 10 nbar in 1986 and 3 nbar in 1987, ozone partial pressure dropped to only 60–70 nbar in 1988 in the depleted region, a reduction of 30 to 50%. Even with these differences in degree of ozone depletion there were similarities to previous measurements. Ozone depletion was caused by a sink between 12 and 20 km, and primary depletion was episodic, occurring in periods of <10 days. Measurements at the edge of the vortex displayed the ozone layering observed in 1986 and 1987 and suggest the exchange of ozone rich and poor air across the vortex wall in the 12–20 km layer. Outside the vortex, vertical profiles displayed a region of high ozone and constant temperature above 20 km.
An intercomparison of airborne nitric oxide measurements: A second opportunity
Authors: Gregory Gerald L. , Hoell James M. , Torres Arnold L. , Carroll Mary Anne , Ridley Brian A. , Rodgers Michael O. , Bradshaw John , Sandholm Scott , Davis Douglas D.
Published: February 2008

Results from an airborne intercomparison of techniques to measure tropospheric levels of NO are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a two‐photon laser‐induced fluorescence system and two NO/O3 chemiluminescence detectors. These three instruments also participated in the NO intercomparisons conducted during the Chemical Instrumentation Test and Evaluation (CITE) 1 mission in 1983–1984, and therefore the current results are a revisit to the question of how well NO can be measured from an aircraft in remote tropospheric environments. The intercomparisons were weighed to mixing ratios less than 20 pptv. Results from CITE 2 were similar to those of CITE 1. The most noteworthy observation common to both campaigns is that at these low mixing ratios, agreement among the three instruments is almost always within about 15 or 20 pptv for sampling periods of 1–6 min. Analyses of multipoint data sets suggest that on the average the difference between data from any pair of the instruments at the low mixing ratios is about 5–7 pptv. Since this agreement was obtained among instruments using fundamentally different detection principles (chemiluminescent and laser) and the data suggested that all provided equally valid measurements of NO, the observed level of agreement perhaps represents the uncertainity in the current measurement of low mixing ratio ambient NO. The major question which must be addressed by the scientific community is the influence of, for example, a 5‐pptv uncertainty in NO at 10 pptv in photochemistry studies, nitrogen budget studies, and so on, in the “clean” remote troposphere.
Comparison of cloud forcing derived from the Earth Radiation Budget Experiment with that simulated by the NCAR community climate model
Authors: Kiehl J. T. , Ramanathan V.
Published: February 2008

A comprehensive comparison of top of atmosphere radiative quantities from the Earth Radiation Budget Experiment (ERBE) with the same quantities from the latest version of the National Center for Atmospheric Research Community Climate Model (CCM) is presented. The ERBE data set offers a unique collection of top of atmosphere radiation fields for it includes clear‐sky radiation fields that have in the past not been available for such comparisons. Comparison between ERBE clear‐sky longwave fluxes and CCMl indicates larger outgoing flux in the model than measured by ERBE. This overestimation is ascribed to the prevalent dryness of the model. Comparison of clear sky albedo indicates good agreement over oceans and land. Total outgoing longwave flux also reflects the moisture deficiency of the model, but differences due to an underprediction of “effective” high cloud are also apparent. The clear‐sky and total fluxes are combined to form the cloud radiative forcing from the ERBE data and the CCM. Comparison of shortwave cloud radiative forcing indicates deficiencies in the model where marine stratus clouds are absent. Large longwave cloud forcing over the tropical deep convective regions in Indonesia and South America are present in the model but are underestimated compared with the ERBE results. Three regions, located over Indonesia, the equatorial Pacific, and the North Atlantic, are considered in detail. For the Indonesian region where deep convection is present, we consider the statistical correlation between the longwave cloud forcing and the shortwave cloud forcing from the ERBE data and CCM. Results indicate a near cancellation between the SWCF and LWCF for these regions, whereas the model predicts a net cooling. Another major area of discrepancy is over the North Atlantic and Pacific oceans where ERBE shows that clouds significantly reduce the solar heating of the oceans. While the model simulates this cooling, the magnitude is underpredicted by more than a factor of 2.
Parameterization of subgrid scale vertical tracer transport in a global two‐dimensional model of the troposphere
Authors: Langner J. , Rodhe H. , Olofsson M.
Published: February 2008

A two‐dimensional (latitude‐height) tropospheric tracer model has been used to simulate the global distributions of CO2, 85Kr, 222Rn, and SO2. A nondiffusive parameterization has been developed describing subgrid scale vertical transport, including transport in convective clouds and frontal zones of midlatitude cyclones. The parameters governing this transport have been estimated using the seasonal variation of CO2. For long‐lived tracers such as CO2 and 85Kr the parameterization yields results that are similar to those obtained with the subgrid scale vertical transport described as an eddy diffusion process only. For short‐lived tracers, with lifetimes of a few days to weeks, the nondiffusive parameterization results in vertical concentration profiles that are much steeper and probably more realistic than those obtained with a diffusive parameterization.
Volatility of aerosol at Mace Head, on the west coast of Ireland
Authors: Jennings S. G. , O'Dowd C. D.
Published: February 2008

Volatile properties of maritime and modified maritime aerosol were measured at the remote site at Mace Head (53°19′N, 9°54′W) on the west coast of Ireland, located on the eastern edge of the North Atlantic Ocean. The volatility measurements were made with a light‐scattering counter equipped with a temperature‐controlled heated inlet. The work extends the temperature range from 300°C to 850°C for the first time for aerosol volatility studies. Representative measurements made over the period of about a year show that the submicrometer particles with radius <0.2 μm are highly volatile for the maritime aerosol and show temperature fractionation features of ammonium sulfate (or ammonium bisulfate). It is estimated that 85–95% of this size fraction (by volume) is composed of these sulfates. For the higher temperatures, temperature‐fractionation characteristics of sodium chloride are shown for the supermicron and also the submicron maritime particles. About 80% of the particle size interval of 0.3–1.5 μm radius is composed of sodium chloride. The temperature profile curves for the modified maritime aerosol, which has made a partial traverse overland, do not display definitive features characteristic of known atmospheric constituents such as ammonium sulfate or sodium chloride, but rather properties indicative of mixtures of these species with other unknown constituents. For both airmasses, between about 5% and 30% (by volume) of the aerosol particles remain involatile at least up to a temperature of 850°C.
The effects of biogenic hydrocarbons on the transformation of nitrogen oxides in the troposphere
Authors: Atherton Cynthia S. , Penner Joyce E.
Published: February 2008

The reactive odd nitrogen chemistry is examined for environments both typical of the urban troposphere and in which biogenic hydrocarbon emissions are appreciable. Results are presented in terms of a nitrogen shortfall, X/NOy, the fraction of reactive nitrogen present as species other than NO, NO2, HNO3, NO3−, and peroxyacetyl nitrate. In urban environments, the calculated nitrogen shortfall is 0.02–0.33. Both higher initial hydrocarbon concentrations and higher initial hydrocarbon‐to‐NOx ratios lead to greater shortfalls, with the latter effect being more important. Products of biogenic hydrocarbon emissions greatly increase the nitrogen shortfall in urban air that has aged for 48 hours. The nitrogen shortfall increases from 0.25 for a simulation with background isoprene and pinene emissions to 0.45 for a scenario with high pinene emissions. In addition, two sensitivity studies which examine the stability of nitrate species formed from the biogenic hydrocarbons are also presented. These show that for our scenarios, the stability of ISON, a species formed during isoprene oxidation can change the calculated nitrogen shortfall by 0.15. However, the stability of nitrates from the reactions of isoprene and pinene with NO3 changes the calculated nitrogen shortfall by only 0.05.
Spectroscopic observations of atmospheric trace gases over Kitt Peak: 2. Nitrous oxide and carbon monoxide from 1979 to 1985
Authors: Wallace L. , Livingston W.
Published: February 2008

We have analyzed solar spectra obtained with the 1‐m Fourier transform spectrometer on Kitt Peak for absorption by N2O and CO. During the period 1979–1985 we find that N2O shows no detectable seasonal variation or trend and can place an upper limit on the growth rate of 1. ppb per year. This is consistent with results of ground level gas sampling. For CO we see a large seasonal variation, but because of inadequate sampling we cannot detect a trend. Combined with other Spectroscopic studies, our mean CO level suggests a northern hemisphere tropospheric scale height for CO of ∼3.5 km.
Gaseous oxygenated hydrocarbons in the remote marine troposphere
Authors: Arlander D. W. , Cronn D. R. , Farmer J. C. , Menzia F. A. , Westberg H. H.
Published: February 2008

Measurement of the background levels and study of the chemistry of trace organic carbon species in the remote marine troposphere occurred during an April–July 1987 SAGA II cruise in remote regions of the Pacific and Indian Oceans. Measured compounds included carboxylic acids, formaldehyde, light hydrocarbons (C2–C4), and ozone. The results show seasonal, diel, and spatial dependencies for the organic acids. Distinct latitudinal gradients are seen for most sampled compounds. Formic acid is well correlated with suspected precursors, formaldehyde and light hydrocarbons. Acetic acid follows a similar pattern as formic acid, although its precursors are as yet undefined. Diel patterns of low amplitude for the organic acids in the remote marine troposphere suggest a natural contribution to tropospheric photochemistry, and to the global carbon cycle as well. For the northern hemisphere Pacific Ocean, the mean formic acid mixing ratio was 0.80±0.30 ppbv, the mean acetic acid value was 0.78±0.32 ppbv. For the southern hemisphere Pacific Ocean, formic acid averaged 0.22±0.13 ppbv, for acetic acid, the mean was 0.28±0.18 ppbv. For the northern hemisphere Indian Ocean, the mean formic acid mixing ratio was 0.75±0.24 ppbv, and the mean acetic acid value was 0.69±0.27 ppbv. For the southern hemisphere Indian Ocean, the mean formic acid value was 0.19±0.17 ppbv, and the mean acetic acid value was 0.29±0.16 ppbv. Highest levels of organic acids were encountered near known anthropogenic source regions, in air masses of continental origin, or near regions of naturally produced alkenes (C2, C3). The ozone‐alkene oxidation scheme appears to play a major role in gas phase organic acid production in the remote marine troposphere. Nighttime gas phase deposition of the organic acids onto the ocean surface appears to be a major sink.
Synthesis of nitric oxide during the formation of an artificially ionized level in the atmosphere
Authors: Milikh G. M.
Published: February 2008

The artificially ionized layers in the atmosphere caused by microwave pulses are actively studied for possible application to communication services. The possible negative influences of this project on the environment will be considered. They are connected with the synthesis of nitric oxide, which is aggressive to the ozone layer. The mechanism of nitric oxide synthesis in the ionized region is based on the chemical reactions of molecules and atoms in the metastable electronic states excited by electron impact. These reactions are effective under conditions which are optimum for the formation of an artificially ionized layer. The concentration of nitrogen oxide produced in the ionized region is estimated for a variety of parameters of microwave pulses which can be used for breakdown of the atmosphere. The spatial shape of the artificial NOx cloud formed by the atmospheric wind and diffusion is studied. Artificially ionized layers are considered as the anthropogenic source of NOx on an annual global basis and compared to the existing natural sources. It is shown that the worldwide net of these layers does not appear to be sufficient to be of environmental concern.
Passive microwave remote sensing of cloud liquid water over land regions
Authors: Jones Andrew S. , Vonder Haar Thomas H.
Published: February 2008

Techniques for cloud liquid water retrieval over land are developed using data from the Special Sensor Microwave/Imager 85.5 GHz (3.5 mm) channels. To minimize the effect of surface emittance variability on the calculations, the surface emittance was estimated with the aid of surface skin temperature retrievals from the Visible Infrared Spin Scan Radiometer in geosynchronous orbit. The high sensitivity of the 85.5 GHz channels to cloud liquid water allows for the estimation of integrated cloud liquid water based on the microwave brightness temperature depression caused by attenuation and emission of microwave radiation at the colder ambient temperature of the cloud. The method assumes nonscattering radiative processes are dominant, therefore only nonprecipitating cloud liquid water is considered. Integrated cloud liquid water retrievals show good qualitative agreement with other available data sources. Numerical error sensitivity analysis show integrated cloud liquid water error estimates of 0.05–0.50 kg m−2 depending on the contrast of cloud over background.
Mechanisms of nocturnal exchange between the rain forest and the atmosphere
Authors: Fitzjarrald David R. , Moore Kathleen E.
Published: February 2008

We have observed a number of events that lead to nocturnal turbulent mixing between the Amazon rain forest and the atmosphere. Two mechanisms that weaken the stable nocturnal thermal inversion at canopy top are identified with nocturnal release of carbon dioxide and concurrent heat flux into and moisture flux out of the Amazon forest canopy. In the first mechanism, abrupt onset of cloudiness interrupts nocturnal radiative cooling, leading to a period with lowered Richardson number and enhanced heat, moisture, and carbon dioxide fluxes. Significant exchange between the forest canopy and the atmosphere can also occur even on totally clear nights. On these nights, occasional nocturnal increases in the wind speed above the canopy stimulate vertical oscillations in the canopy layer that are both amplitude and frequency modulated during the event. A simple model is presented to support the postulate that these oscillations result from a resonant interaction, hypothesized to be a consequence of a vertically fluctuating pressure gradient force operating on a deepening stable layer near canopy top. Turbulent diffusion associated with increased winds deepens and weakens the stable layer at canopy top, lowering the buoyancy frequency in the canopy. Eventually, periods of resonance occur. Model results indicate that the recovery of the layer takes approximately twice as long as the period of enhanced wind that produced the event.
Ozone and aerosol distributions over the Amazon Basin during the wet season
Authors: Browell E. V. , Gregory G. L. , Harriss R. C. , Kirchhoff V. W. J. H.
Published: February 2008

Measurements of ozone (O3) and aerosols were made over the tropical rain forest of Brazil during the wet season in April–May 1987 as part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer. Remote and in situ measurements of O3 and aerosols were made from aircraft on flights over Brazil in the vicinity of Manaus and between Manaus and Belem. Ozonesonde data were also obtained near Manaus. Ozone mixing ratios of <12 ppbv were found in the mixed layer during the wet season with no significant evidence of O3 produced from biomass burning or photochemistry. These values are lower than those found during the 1985 dry season by 6–8 ppbv. These low O3 mixing ratios indicate a strong removal process near the surface during the wet season. The region from the mixed layer top to 3 km in altitude had a slowly increasing O3 profile from 12 to 20 ppbv. On long‐range flights between Manaus and Belem, no significant difference was found in the distribution of O3 above the mixed layer between the inland tropical rain forest and the marine conditions near the coast. Within the mixed layer, there was a definite trend to lower O3 levels above the forest compared to over the ocean. This reflects the marked difference in the sinks for O3 over these two regions. The rate of growth of the mixed layer over the rain forest in the wet season was found to be ∼9 cm s−1, which is within the 7–10 cm s−1 range found for the dry season. There was no evidence of the trade wind inversion that was seen during the dry season, and due to frequent precipitation, the background aerosol loading was lower in the wet season than in the dry season.
Rainfall and surface kinematic conditions over central Amazonia during ABLE 2B
Authors: Greco Steven , Swap Robert , Garstang Michael , Ulanski Stanley , Shipham Mark , Harriss R. C. , Talbot R. , Andreae M. O. , Artaxo P.
Published: February 2008

Meteorological and chemical data collected during the wet season Amazon Boundary Layer Experiment near Manaus, Brazil, are used to investigate the rainfall, rainfall systems, and surface kinematics of the central Amazon basin wet season. Analysis of the Geostationary Operational Environmental Satellite (GOES‐West) imagery indicates that, based on location of initial development, there are three main types of convective systems which influence a mesoscale network near Manaus. Coastal Occurring Systems (COS) are mesoscale to synoptic scale sized systems of generally linear orientation which form along the northern coast of Brazil and propagate across the Amazon basin. The Basin Occurring Systems (BOS) form in the basin east and north of Manaus and also propagate toward the network. Locally Occurring Systems (LOS) form in and around the mesoscale network and rarely are larger than 1000 km2. Composites of hourly rainfall totals and satellite‐derived cloud cover show that rainfall and cloudiness associated with COS occurred in the network between 1400 and 1800 UT, while BOS rainfall was most common between 1000 and 1400 UT. Little rain or cloud cover was seen before 1600 UT during days influenced by LOS. Chemical analysis of the rainwater delivered by these systems also shows significant differences in the concentrations of formate, acetate, pyruvate, sulfate, and hydrogen ion. In addition, aerosol concentrations measured near Manaus indicate large influxes of aerosols (sodium, chlorine, and silicon) into central Amazonia after the passage of BOS and COS. The satellite‐based classification indicates a definite intraseasonal variation in regard to the dominant rain‐producing system. During April 11–20, BOS occurred on 8 days and produced 98% of the rainfall. Eight COS occurred during April 21 to May 3 and accounted for 89% of the rainfall. The final part of the experiment, May 4–14, was influenced solely by LOS. Harmonic analysis of surface divergence during this period exhibits a peak at 24 hours. This peak, representing the diurnal heating cycle, does not exist earlier in the experiment when BOS and COS are more frequent.
Cloud draft structure and trace gas transport
Authors: Scala John R. , Garstang Michael , Tao Wei‐kuo , Pickering Kenneth E. , Thompson Anne M. , Simpson Joanne , Kirchhoff Volker W. J. H. , Browell Edward V. , Sachse Glen W. , Torres Arnold L. , Gregory Gerald L. , Rasmussen R. A. , Khalil M. A. K.
Published: February 2008

Field observations obtained during the second NASA Amazon Boundary Layer Experiment (ABLE 2B), and two‐dimensional moist cloud model simulations are used to determine the dominant transport pathways within a continental tropical squall line. A surface‐based network triangle provided the focus for a multi‐instrumental sampling of the May 6, 1987, squall line which propagated through the central Amazon basin at a rate of 40–50 km h−1. Extensive use is made of the vertical distribution of specific trace gases that are representative of the prestorm and poststorm environment. One‐dimensional photochemical model results suggest the observed poststorm changes in ozone concentration can be attributed to convective transports rather than photochemical production. Two‐dimensional cloud model results detail the dynamic and thermodynamic attributes of the simulated squall convection. The well‐mixed moist troposphere in which the observed squall system developed may have hindered strong downdraft development. Parcel trajectory analyses are conducted to investigate the flow patterns of convective transports. A significant proportion (> 50%) of the air transported to the anvil region originated at or above 6 km, not from the boundary layer via undilute cores. The presence of a midlevel inflow and a strong melting layer at 5.5 km reduced the vertical development of the core updraft and aided in the maintenance of a rotor circulation. The predicted absence of more than one active cell in the model cloud field, the lack of a well‐organized downdraft in the presence of model estimated net upward mass flux, and the initial wind profile suggest the May 6 squall line was unicell in character.
Cloud characteristics over central Amazonia during GTE/ABLE 2B derived from multispectral visible and infrared spin scan radiometer atmospheric sounder observations
Authors: Menzel W. P. , Schmit T. J. , Wylie D. P.
Published: February 2008

Multispectral GOES/Visible and Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) observations in the carbon dioxide absorption band at 15 μm have been used to calculate diurnal cloud statistics over central Amazonia region for 4 days during the Global Tropospheric Experiment/Amazon Boundary Layer Experiment (GTE/ABLE IIB). The CO2 technique calculates both cloud top pressure and effective emissivity from radiative transfer principles. Transmissive clouds that are partially transparent to terrestrial radiation have been reliably separated from opaque clouds in the statistics of cloud cover. A high incidence of transmissive clouds (about 47%) was found on the average. Diurnal characteristics of cloud cover over Amazonia have been linked to convective activity over this region. On days with afternoon convection, an increase in low‐altitude opaque clouds was followed by a subsequent increase in high‐altitude transmissive clouds.