bluuebunny/crossref_metadata_2025 huggingface dataset:
Polar stratospheric cloud processed air and potential voracity in the northern hemisphere lower stratosphere at mid‐latitudes during winter
Authors: Tuck A. F. , Davies T. , Hovde S. J. , Noguer‐Alba M. , Fahey D. W. , Kawa S. R. , Kelly K. K. , Murphy D. M. , Proffitt M. H. , Margitan J. J. , Loewenstein M. , Podolske J. R. , Strahan S. E. , Chan K. R.
Published: February 2012

Small‐scale (<1000 km) features in ER‐2 measurements of ClO, O3, H2O, N2O, and NOy, outside the lower stratospheric Arctic vortex of 1988–1989 are compared with features on potential vorticity maps from the European Centre for Medium‐range Weather Forecasts (ECMWF). The potential vorticity maps are obtained from Tl06 analyses and forecasts. Some of the plots have been truncated to lower resolution (T63 or T42) which smooths out the finer‐scale structure. Comparison of these lower resolution plots shows how much detail is lost by excessive smoothing. It is also evident that the forecast plots lose fine‐scale structure due to dissipation in the model resulting mainly from horizontal diffusion. We conclude that blobs of air on the maps at latitudes between the vortex edge and 25°N having potential vorticities characteristic of the vortex, did indeed originate from the vortex, but that the real atmosphere is more sharply differentiated (inhomogeneous) than the meteorological analyses, implying that the potential vorticity maps underestimate the amount of peeled‐off material. Areal budgets of the ex‐vortex air are considered for ER‐2 flight days, and are performed for 24‐hour forecasts at T63, and analyses at T42, T63, and T106 resolution at θ = 475 K. Finally, it is concluded that the lower stratospheric Arctic vortex of 1988–1989 spread considerable amounts of air to mid‐latitudes which had been processed by polar stratospheric clouds, and that this mechanism is a realistic explanation for the wintertime loss of ozone observed over northern mid‐latitudes during the last decade.
Analysis of the ozone soundings made during the first quarter of 1989 in the Arctic
Authors: Kyrö Esko , Taalas Petteri , Jørgensen Torben S. , Knudsen Bjørn , Stordahl Frode , Braathen Geir , Dahlback Arne , Neuber Roland , Krüger Bernd C. , Dorokhov Valery , Yuskov V. A. , Rudakov V. V. , Torres Arnold
Published: February 2012

A total of 197 ozone profiles were obtained from the nine Arctic ozone sounding stations of Alert, Resolute, Ny Ålesund, Heiss Island, Bear Island, Ammassalik, Scoresbysund, Sodankylä, and Lerwick during January–March 1989. The sounding stations cover the latitude range from 60°N to 83°N and the longitude range from 95°W to 58°E. It was, for the first time, possible to get a detailed picture with a 150‐m resolution of the vertical distribution of ozone during winter and spring over extended areas of the north polar region. The fine structure of the Arctic ozone distribution shows considerable layering in profiles obtained outside and at the edge of the polar vortex, whereas little layering is found in profiles obtained well inside the vortex. The lowest temperatures were found at the edge of the vortex, e.g., at or below −90°C during January 30–31 at Lerwick and close to −90°C on January 24 at Bear Island at the altitudes of 20–25 km. Temperatures below −77°C, the condition for the formation of the type I polar stratospheric clouds (PSCs), were common during January and early February 1989 in the Arctic. Possibly as a consequence of the heterogeneous processes in the presence of PSCs, the ozone mixing ratios decreased, especially during late winter when the sun's irradiation intensifies in high latitudes. A trend of −0.1%/d around 80°N latitude was found in the altitude range of 420–600 K potential temperature during the period January 10 to February 13, 1989, increasing to −0.4%/d when the later period January 24 to February 13, 1989, is considered. If one were to take into account the downward diabatic motion (2.6 km/month) the negative trends would increase further by about −0.4%/d in magnitude.
Two years of regular ozone soundings in the European Arctic, Sodankylä
Authors: Taalas Petteri , Kyrö Esko
Published: February 2012

Data have been studied from 2 years (1989 and 1990) of weekly ozone soundings performed in Sodankylä (67.4°N, 26.6°E), northern Finland. Prior to 1989, no routine ozone sounding program had been carried out in northern Europe. General behavior of ozone, temperature, and potential temperature at various levels of the stratosphere and the troposphere is reported. The seasonal means, minima, maxima, and standard deviations have been calculated within 1000‐m layers from the surface to 35 km. Fairly high concentrations of ozone are found in the lower troposphere during spring and summer. The variation of stratospheric ozone in winter and spring may be explained by dynamical factors, although more chemical measurements are needed to explain the late winter‐early spring episodes.
Measurements and model simulations of the photostationary state during the Mauna Loa Observatory Photochemistry Experiment: Implications for radical concentrations and ozone production and loss rates
Authors: Ridley B. A. , Madronich S. , Chatfield R. B. , Walega J. G. , Shetter R. E. , Carroll M. A. , Montzka D. D.
Published: February 2012

Simultaneous measurements of [NO2], [NO], [O3], and the NO2 photo‐dissociation rate coefficient, J2, were made during a one‐month field study in the spring of 1988 at Mauna Loa, Hawaii, and were used to evaluate the photostationary state ratio, ϕ = J2[NO2]/k1[NO][O3]. Over 5600 measurements were made for clear sky conditions, allowing a detailed comparison with photochemical theory. Values of ϕ determined from the observations were consistently higher than unity, approaching 2.0 for high sun, and indicated peroxy radical mixing ratios near 60 pptv. High sun values of ϕ were independent of NOx (NO + NO2), but correlated well with ozone and water vapor through the expression ϕ−1 = (0.11 ± 0.21) + (1.59 ± 0.64) × 10−3 × ([H2O]/[O3])½. A photochemical box model is shown to give good agreement with the values of ϕ, the peroxy radical concentrations, and the correlations with physical and chemical environmental variables determined from the observations. The rate of photochemical production of ozone was estimated from measurements of ϕ, and the rate of photochemical ozone destruction was estimated from the box model. For free tropospheric air samples characteristic of altitudes near 3.4 km, the 24‐hour average net ozone production rate is shown to be −0.5 ppbv/d (net ozone destruction), and is determined primarily by photolytic destruction.
Actinometer and Eppley radiometer measurements of the NO2 photolysis rate coefficient during the Mauna Loa Observatory photochemistry experiment
Authors: Shetter Richard E. , McDaniel Anthony H. , Cantrell Christopher A. , Madronich Sasha , Calvert Jack G.
Published: February 2012

Measurements of the apparent first‐order rate coefficient for NO2 photodissociation (jNO2) were made using a chemical actinometer during the month of May 1988 at the Mauna Loa Observatory, Hawaii. Simultaneous measurements of the ultraviolet irradiance (E), obtained with an Eppley radiometer, allowed extensive testing of the semi‐empirical relationships between E and jNO2 proposed by Madronich (1987a). More than 3700 simultaneous measurements of jNO2 and E were obtained for solar zenith angles ranging from 4–90 degrees, and for different sky conditions (including clear skies, partial cloud cover, arid valley clouds below the horizon). For overhead clear skies, the NO2 photodissociation rate coefficient derived from Eppley radiometer data, here denoted j′, was in good agreement with actinometric measurements, j′/jNO2=1.01±0.05(1σ). The actinometer‐radiometer relationship holds reasonably well even when low‐lying valley clouds are present. For the periods of overhead intermittent clouds, the j′values track jNO2 values well, but the observed ratio shows significantly more scatter and the average is somewhat less than unity: 0.93 ± 0.09 (1σ). Measurements taken with and without upward scattered and reflected radiation show that valley clouds can contribute to the jNO2 values for the conditions encountered during the Mauna Loa Observatory Photochemistry Experiment.
A source inventory for atmospheric methane in New Zealand and its global perspective
Authors: Lassey Keith R. , Lowe David C. , Manning Martin R. , Waghorn Garry C.
Published: February 2012

Methane is an important greenhouse constituent of the atmosphere. Its global source inventory is briefly reviewed, and the aggregated source in the range 270–760 Tg CH4/yr is compatible with independent measurement. The constraints imposed by isotopic information are also discussed. We then exploit this global data base to provide a first detailed estimate of New Zealand sources of methane and their uncertainties, placing these in global perspective. The aggregate New Zealand methane source is estimated to lie in the range 1.3 –2.2 Tg/yr. Nearly all of this emission is caused by human modification of the environment and is dominated ( ∼75%) by “enterically fermented” methane from farmed livestock, predominantly by sheep and lambs (58%) and by cattle (40%). At about 0.3% of global emissions, New Zealand is a disproportionately large methane source on either a per capita or land area basis, or when compared with the New Zealand share (0.13%) of global carbon dioxide emissions from industry and from fossil fuel consumption.
Airborne measurements of total reactive odd nitrogen (NOy)
Authors: Hübler G. , Fahey D. W. , Ridley B. A. , Gregory G. L. , Fehsenfeld F. C.
Published: February 2012

Airborne total reactive odd nitrogen measurements were made during August and September 1986 over the continental United States and off the west coast over the Pacific Ocean during NASAs Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation 2 program. The NOy instrument combined a catalytic surface converter which reduced NOy component species to NO on a heated Au surface with a NO/O3 chemiluminescence detector. Measurements were made in the marine and continental boundary layer and the free troposphere up to 6.1 km altitude. NOy mixing ratios between 24 pptv and more than 1 ppbv were found, with median values of 101 pptv in the marine boundary layer, 298 pptv in the marine free troposphere, and 288 pptv in the continental free troposphere, respectively. The marine troposphere exhibited layered structure which was also seen in the simultaneously measured ozone mixing ratio and dew point temperature. The averaged vertical NOy profile over the ocean does not show a distinct gradient. The NOy mixing ratio over the continent decreases with increasing altitude. The latter is consistent with our understanding that the continents are the major source region for these gases.
The DECAFE experiments: Overview and meteorology
Authors: Fontan Jacques , Druilhet Aimé , Benech Bruno , Lyra Roberto , Cros Bernard
Published: February 2012

The objective of the Dynamique et Chimie de l'Atmosphère en Forêt Equatoriale (DECAFE) program is to determine the influence of African tropics on atmospheric chemistry. Savannas and forests constitute the main ecosystems in this area. Because of the occurrence of biomass burning during the dry season, savannas of the northern and southern hemispheres are active sources of many constituents which are of interest to atmospheric chemistry. The rain forest, with its important biomass activity is also a source or sink for gases and aerosols. Man's impact on this ecosystem is important since the rate of deforestation is about 0.5% per year. Furthermore, a general air motion from savanna regions toward the tropical rain forest is observable in most parts of Africa, leading to important interactions between the respective emissions of these two ecosystems. The DECAFE experiments presented in this issue were located in the Mayombe forest (southern Congo) and in the forest of the northen Congo. A study of rain chemistry was undertaken in 1986 in the Mayombe forest, then continued in the northern forest. In February 1988 a coordinated experiment was held in the tropical rain forest of the north, near Impfondo. The paper presents an overview of the general meteorological and climatological situation in the African tropics, a study of the climatological features of the sites, and a short description of the Impfondo experiment, which is the subject of most of the contributions to this special issue. The local meteorological situation during the time of the experiment is analyzed.
Micrometeorological measurements of CH4 and CO2 exchange between the atmosphere and subarctic tundra
Authors: Fan S. M. , Wofsy S. C. , Bakwin P. S. , Jacob D. J. , Anderson S. M. , Kebabian P. L. , McManus J. B. , Kolb C. E. , Fitzjarrald D. R.
Published: February 2012

Exchanges of methane and carbon dioxide between the atmosphere and the Arctic tundra were measured continuously near Bethel, Alaska (61°05.41'N 162°00.92'W), for 5 weeks during July and August 1988. Fluxes were obtained directly using eddy correlation at 12‐m altitude, and concentrations were measured sequentially at eight altitudes between 0 and 12 m. A prototype differential infrared absorption methane instrument based on a Zeeman‐split HeNe laser was used for determination of methane and a flame ionization detector for total hydrocarbons (THC). Methane was found to account for nearly all the THC concentrations and fluxes. Methane fluxes at the tower site were apportioned to various methane‐producing habitats, using a satellite image to classify surface vegetation at 20 × 20 m resolution. The “footprint” of the tower was computed using a Gaussian plume model for dispersion in the surface layer. Grid cells classified as dry tundra (water level 5 cm below surface) emitted methane at an average rate of 11±3 (standard error) mgCH4/m2/d, and wet meadow tundra (water level near surface) emitted 29±3 mgCH4/m2/d. Fluxes from lakes depended on wind speed, averaging 57±6 mgCH4/m2/d at the site, where the mean wind speed was 5ms−1. The mean emission rate for tundra (including lakes) around the tower was 25±1 mgCH4/m2/d, notably smaller than adopted for boreal wetlands in recent inventories of global methane sources. Emissions from major habitats derived from the tower measurements were in reasonable agreement with data from chamber studies. Errors of a factor of ∼2 accrued in scaling up the chamber data, representing 1 m2 plots, to the footprint of the tower measurements (103 m), because the satellite could not fully resolve heterogeneous methane‐producing habitats. Fluxes obtained at the tower site were in harmony with fluxes from aircraft overflights. The aircraft data represent mainly afternoon periods with good flying weather, conditions associated with maximum CH4 fluxes in the tower time series. Mean fluxes from the aircraft are consequently ∼2 × higher than seasonal means from the region. Solar irradiance provided the primary control on the net ecosystem exchange (NEE) of carbon dioxide. The mean maximum uptake near the local solar noon was 1.4±0.2 gC/m2/d, and nocturnal respiration averaged 0.73±0.18 gC/m2/d. Net uptake of carbon dioxide averaged 0.30 gC/m2/d (0.1 tons C/hectare) during the period of the Arctic Boundary Layer Experiment (ABLE 3A). About 6% of the seasonal net uptake was returned to the atmosphere as methane.
On the evaluation of ozone depletion potentials
Authors: Solomon S. , Mills M. , Heidt L. E. , Pollock W. H. , Tuck A. F.
Published: February 2012

Observations of methane, CFC‐11, and ozone losses are used along with insights from models and observations regarding interrelationships between tracers to develop a semi‐empirical framework for evaluating global ozone depletion potentials. Direct measurements of some hydrochlorofluorocarbons including HCFC‐22 in the Arctic lower stratosphere are also used to evaluate the local ozone depletion potentials there. This approach assumes that all of the observed ozone destruction in the contemporary atmosphere is due to chlorine and that the depletion is proportional to the local relative chlorine release. It is shown that the global ozone depletion potentials for compounds with relatively long stratospheric lifetimes such as HCFC‐22 and HCFC‐142b are likely to be larger than those generally predicted by gas phase chemical models, due largely to the importance of lower stratospheric ozone losses that are not simulated in gas phase studies. The analysis presented suggests that the globally averaged efficiency for ozone depletion by HCFC‐22 is as much as a factor of 2 larger than some gas phase model estimates. For compounds with short stratospheric lifetimes such as (CCl4). and (CH3CCl3), on the other hand, gas phase models likely overestimate the ozone depletion potentials for the present‐day stratosphere. Observations of polar ozone loss and reactive halogen radical abundances also imply that the globally averaged ozone depletion potentials for brominated species for the contemporary stratosphere could be as much as 1.5–3 times greater than some gas phase model predictions, depending upon lower stratospheric loss processes.
The relationship between cloud droplet number concentrations and anthropogenic pollution: Observations and climatic implications
Authors: Leaitch W. R. , Isaac G. A. , Strapp J. W. , Banic C. M. , Wiebe H. A.
Published: February 2012

Measurements of the concentrations of sulfate and nitrate in approximately 400 cloud water samples collected during four field studies carried out since 1982 are used with coincident measurements of cloud droplet number concentrations (CDNC) and liquid water content (LWC) to examine the relationship between CDNC and anthropogenic pollution, where sulfate concentration is used as the measure of the latter. The number of samples is compressed to 92 by averaging duplicates and multiple samples at similar altitudes during any particular flight, with 85 including CDNC measurements. Positive linear regressions between log (CDNC) and log (cloud water sulfate concentration) are determined for both stratiform and cumuliform cloud. Because of the number of factors affecting the CDNC, the coefficients of determination are only 0.30 and 0.49 for the respective cloud types. The LWC is relatively invariant with the cloud water sulfate concentration. The observed range of CDNC for the study region is 20–600 cm−3 (median of 59 observations is 210 cm−3) for stratiform clouds and 170–1100 cm−3 (median of 26 observations is 400 cm−3) for cumuliform clouds. The median CDNC for all sampled clouds is 250 cm−3. CDNC are also determined for “clean‐air” conditions. The latter is defined as cases for which the concentrations of both cloud water sulfate and cloud water nitrate are comparable to aerosol sulfate concentrations and aerosol nitrate plus HNO3 concentrations, respectively, as reported for remote regions of the globe. For the clean‐air clouds the observed range of CDNC for the study region is 20–250 cm−3 (median of 12 observations is 120 cm−3) for stratiform clouds and 170–370 cm−3 (median of four observations is 240 cm−3) for cumuliform clouds. The median CDNC for all clean‐air clouds is 160 cm−3. The median CDNC for the complete population is 56% greater than the clean‐air CDNC; the hypothesis that the clean‐air CDNC is not different from the median CDNC is rejected at a confidence level of >99.5%. The present‐day climatic forcing due to cloud albedo change arising from increased CDNC is estimated from a rudimentary model at between −2 W m−2 and −3 W m−2 for eastern North America.
A re‐evaluation of the Stokes drift in the polar summer mesosphere
Authors: Hall Timothy M. , Cho John Y. N. , Kelley Michael C. , Hocking Wayne K.
Published: February 2012

The Stokes drift argument put forth by Coy et al. (1986) to explain the monthly mean downward vertical velocities observed in the summer polar mesosphere by radars is critically re‐examined. The size of the effect is quite sensitive to the choice of gravity wave wavenumber and phase speed. We reproduce the Coy et al. (1986) result for a monochromatic gravity wave and then generalize to a Garrett‐Munk type spectrum. This allows us to easily incorporate experimentally determined wave field parameters in order to predict a Stokes drift magnitude. The Stokes drift we calculate for mesospheric spectra reported in the literature is less than 4 cm/s. This is nearly a factor of 10 smaller than the mean June and July downward vertical velocities we have verified from 4‐year averaging of the Poker Flat, Alaska, radar data base. In this extended analysis we also find that the upward winter mean vertical velocity is smaller than previously reported but still in apparent conflict with the mesospheric winter circulation theory. We suggest, as an alternative to the Stokes drift idea, that the observed summer velocity might be the terminal velocity of charged aerosols. Such an explanation would have the advantage of relating the mean velocity observations to the large VHF radar cross section exhibited by the polar summer Mesosphere. This possible connection is discussed further in a companion paper.
Stratospheric HNO3 measurements from 0.002‐cm−1 resolution solar occultation spectra and improved spectroscopic line parameters in the 5.8‐μm region
Authors: Goldman A. , Murcray F. J. , Blatherwick R. D. , Kosters J. J. , Murcray D. G. , Rinsland C. P. , Flaud J.‐M. , Camy‐Peyret C.
Published: February 2012

Measurements of stratospheric HNO3 are presented based on new very high resolution (0.002‐cm−1 full width at half maximum (FWHM)) solar occultation spectra recorded at 32°N latitude with a balloon‐borne interferometer in the region of the HNO3 v2 band at 5.8 μm and improved spectroscopic line parameters generated for this HNO3 band and the interfering bands of O3 and H2O. The line parameters for HNO3, computed from the spectroscopic constants reported by Maki, are a significant improvement in that the calculated positions are more accurate than previous data and the line list now includes higher J and Ka transitions needed to account for weaker HNO3 absorption features observable in the stratospheric spectra. Verifications of the new line parameters based on the stratospheric spectra and a 0.002‐cm−1 resolution HNO3 laboratory spectrum are presented along with comparisons generated with the parameters from the 1986 HITRAN compilation. Significant improvements are apparent for all the updated bands. Finally, the stratospheric HNO3 profile retrieved from the stratospheric solar spectra using a nonlinear least squares fitting algorithm and the new line parameters is reported and compared with previously reported measurements.
Aircraft studies of size‐dependent aerosol sampling through inlets
Authors: Porter J. N. , Clarke A. D. , Ferry G. , Pueschel R. F.
Published: February 2012

Accurate measurement of atmospheric aerosol from aircraft platforms is of importance to a variety of research interests. Representative measurement of aerosol from aircraft‐aspirated systems requires special efforts in order to (1) maintain near isokinetic sampling conditions, (2) estimate aerosol losses in the sample system, and (3) obtain a measurement of sufficient duration to be statistically significant for all sizes of interest. This last point is especially critical for aircraft measurements which typically require fast response times while sampling in clean remote regions. Here we present size‐resolved tests, intercomparisons, and analysis of aerosol inlet performance as determined by a custom laser optical particle counter. Measurements discussed here took place during the Global Backscatter Experiment (1988–1989) and the Central Pacific Atmospheric Chemistry Experiment (1988). System configurations are discussed including (1) nozzle design and performance, (2) system transmission efficiency, (3) nonadiabatic effects in the sample line and its effect on sample line relative humidity, and (4) the use and calibration of a virtual impactor.
Seasonal variations of mesospheric hydrogen and ozone concentrations derived from ground‐based airglow and lidar observations
Authors: Takahashi H. , Clemesha B. R. , Sahai Y. , Batista P. P. , Simonich D. M.
Published: February 2012

Upper atmospheric airglow emissions in the mesopause region, OI557.7 nm, NaD at 589.3 nm and OH(9,4) band at 774.6 nm have been observed since 1977 at Cachoeira Paulista (22.7°S, 45.0°W), Brazil. The seasonal dependence of the intensity variations of these emissions was studied using the data from a total of 560 nights, during the period June 1977 to November 1986. Strong semiannual variations in the NaD and OI557.7 nm emissions were observed with maxima at the equinoxes, in contrast to the OH(9,4) emission, which showed a much smaller seasonal variation. Hydrogen and ozone concentrations at around 87–89 km were calculated using the observed NaD and OH(9,4) band intensities and the sodium concentration observed by lidar at a nearby station. The obtained seasonal variations of the two species, opposite in phase with each other, are in good agreement with current atmospheric dynamics models, which show a seasonal variation of the vertical transport of atomic oxygen and hydrogen.
Comparisons of surface flux measurement systems used in FIFE 1989
Authors: Fritschen L. J. , Qian P. , Kanemasu E. T. , Nie D. , Smith E. A. , Stewart J. B. , Verma S. B. , Wesely M. L.
Published: February 2012

Several types of Bowen ratio energy balance and eddy correlation systems were used to estimate sensible and latent heat fluxes during FIFE. To provide information on the ability of these systems to make representative measurements of sensible and latent heat fluxes at individual sites, several systems were compared by operating them side by side. The different Bowen ratio systems produced estimates that were usually in close agreement; most of the discrepancies were minor and were due to differing estimates of Rn and G. Comparisons between results of Bowen ratio systems and eddy correlation systems at sites 906 (2133‐ECA) and 926 (8739‐ECB), however, were less satisfactory. The discrepancies were occasionally large and seemed to vary in complex terrain with local conditions such as wind direction, upwind slope aspect, and solar zenith angle.
Momentum, water vapor, and carbon dioxide exchange at a centrally located prairie site during FIFE
Authors: Verma Shashi B. , Kim Joon , Clement Robert J.
Published: February 2012

Eddy correlation measurements were made of fluxes of momentum, sensible heat, water vapor, and carbon dioxide at a centrally located plateau site in the FIFE study area during the period from May to October 1987. About 82% of the vegetation at the site was comprised of several C4 grass species (big bluestem, Indian grass, switchgrass, tall dropseed, little bluestem, and blue grama), with the remainder being C3 grasses, sedges, forbs, and woody plants. The prairie was burned in mid‐April and was not grazed. Precipitation during the study period was about normal, except for a 3‐week dry period in late July to early August, which caused moisture stress conditions. The drag coefficient (
, where u* is the friction velocity and ū is the mean wind speed at 2.25 m above the ground) of the prairie vegetation ranged from 0.0087 to 0.0099. The average d/zc and z0/zc (where d is the zero plane displacement, z0 is the roughness parameter, and zc is the canopy height) were estimated to be about 0.71 and 0.028, respectively. Information was developed on the aerodynamic conductance (ga) in terms of mean wind speed (measured at a reference height) for different periods in the growing season. During the early and peak growth stages, with favorable soil moisture, the daily evapotranspiration (ET) rates ranged from 3.9 to 6.6 mm d−1. The ET rate during the dry period was between 2.9 and 3.8 mm d−1. The value of the Priestley‐Taylor coefficient (α), calculated as the ratio of the measured ET to the equilibrium ET, averaged around 1.26 when the canopy stomatal resistance (rc) was less than 100 s m−1. When rc increased above 100 s m−1, α decreased rapidly. The atmospheric CO2 flux data (eddy correlation) were used, in conjunction with estimated soil CO2 flux, to evaluate canopy photosynthesis (Pc). The dependence of Pc on photosynthetically active radiation (KPAR), vapor pressure deficit, and soil moisture was examined. Under nonlimiting soil moisture conditions, Pc was primarily controlled by KPAR through a rectangular hyperbolic relationship. Our data did not indicate light saturation of the canopy up to KPAR levels of 2100 μEi m−2 s−1. Midday values of Pc reached a seasonal peak of 1.4–1.5 mg m−2 (ground area) s−1 during late June and early July. During the dry period (late July to early August), midday Pc declined to a minimum of almost zero. Examination of data on Pc, λE/Rn (the proportion of net radiation consumed in latent heat flux), extractable soil water, and the predawn leaf water potential indicated a remarkable similarity in overall patterns throughout the season. The photosynthetic efficiency was 1.5–2% during midday through most of the growing season (except during the dry period). The midday value of the prairie water use efficiency during the peak growth stage was 8–12 × 10−3 g CO2/g H2O.
Global inventory of sulfur emissions with 1°×1° resolution
Authors: Spiro Peter A. , Jacob Daniel J. , Logan Jennifer A.
Published: February 2012

A global inventory of gaseous sulfur emissions with 1°×1° resolution is described. Emissions from fuel combustion and industrial activities are estimated for countries where no detailed inventories are available by using economic data for individual sulfur‐emitting activities, sulfur emission factors, and information on sulfur recovery. Fuel sulfur contents are specified as a function of fuel type and country of origin and are conserved during international trading. This procedure for estimating emissions reproduces well existing inventories for countries in Europe and North America, suggesting that it can be applied with some confidence to other countries. Emissions from biomass burning, volcanoes, and oceans are derived from existing data bases and are distributed with fine spatial resolution. Emissions from terrestrial vegetation are computed as a function of leaf area index, temperature, and solar radiation. The global emission of sulfur gases in 1980 is estimated to be 102 Tg S yr−1, apportioned among fuel combustion and industrial activities (76%), marine biosphere (12%), volcanoes (9%), biomass burning (2%), and terrestrial biosphere (1%). Detailed breakdowns of anthropogenic and natural sources are given for individual countries and regions. Anthropogenic sources account for 84% of total sulfur emissions in the northern hemisphere and for 50% in the southern hemisphere. Biomass burning dominates emissions in central Africa during the dry season but is of minor importance elsewhere. Smelters dominate anthropogenic emissions in the Arctic and in the southern hemisphere. Volcanoes are significant contributors to the sulfur budget in Central America, the East Indies, and some subarctic regions.
The annual variation of the height of the atmospheric sodium layer at 23°S: possible evidence for convective transport
Authors: Clemesha B. R. , Simonich D. M. , Takahashi H. , Batista P. P. , Sahai Y.
Published: February 2012

On the basis of a long series of lidar measurements made at São José dos Campos, it is found that the centroid height of the atmospheric sodium layer is about 1 km lower in November than during the rest of the year. Photometric measurements of the OH(9,4) and OI 557.7 nm airglow intensities, observed at a nearby location, show that these emissions have maximum values at this time of the year. The hydroxyl emission shows a sharp increase in intensity by about 20% in November, and the atomic oxygen emission has a broader peak in October, November, and December. There is a strong inverse correlation between the seasonal variations in sodium layer centroid height and the OH intensity, with a correlation coefficient of 0.86 and a regression coefficient of −89±16 Rayleighs km−1. It is suggested that the anticorrelated variations in sodium layer height and airglow intensity could be the result of seasonal changes in convective transport in the lower thermosphere.
Revision of 20 years of Dobson total ozone data at Uccle (Belgium): Fictitious Dobson total ozone trends induced by sulfur dioxide trends
Authors: De Muer D. , De Backer H.
Published: February 2012

Since July 1971, total ozone measurements have been performed at Uccle (50°48′N, 4°21′E) with the Dobson spectrophotometer 40. All the individual measurements were reevaluated after a careful homogenization, using the detailed calibration history of the instrument. Special care was taken to assure the consistency between direct Sun (DS) and zenith sky (ZS) measurements. The monthly mean values of percentage differences between the quasi‐simultaneous direct Sun and zenith sky measurements show a weak modulation, probably induced by long‐term changes in the mean vertical ozone distribution. The overall standard deviation of the percentage differences between the two types of observations amounts to 1.72%. From a detailed comparison of our revised data over the period 1971–1986 with the results of an approximate revision on a month‐by‐month basis (used in the Report of the International Ozone Trends Panel), it is concluded that the latter method of revision is not reliable. The trend of the reduced thickness of the SO2 amount in the lower troposphere, as measured with the Brewer instrument 16 located at the same site as the Dobson spectrophotometer, is in agreement with the trend of the SO2 density near the ground which has been measured in the urban area of Brussels since 1968. From these two SO2 data sets the variation of the reduced SO2 amount since 1968 and the corresponding correction of the Dobson instrument data of Uccle were calculated on a month‐by‐month basis. Without the SO2 correction the revised Dobson data for the period from August 1971 through July 1991 show a statistically significant downward trend (± standard deviation) that amounts to −1.38 ± 0.50% per decade, while after the SO2 correction a nonsignificant trend of 0.31 ± 0.51% per decade is found. This means that the decrease of SO2 over the last two decades at Uccle has induced a fictitious Dobson total ozone trend of −1.69% per decade. At the subperiod for which reprocessed total ozone mapping spectrometer (TOMS) data are available (November 1978 to May 1990) our corrected Dobson data show a statistically significant downward trend (± standard deviation) of −2.93 ± 1.17% per decade which is consistent with the results from TOMS; this proves that analysis of total ozone data over time periods as short as one solar cycle does not allow to make conclusive statements about long‐term trends. The spectacular decrease of SO2 densities is not a regional phenomenon but has been generally ascertained in European and North American urban areas; therefore it should not be neglected in any study about global ozone trends derived from Dobson data.
Budget analysis of the boundary layer grid flights during FIFE 1987
Authors: Betts A. K. , Desjardins R. L. , MacPherson J. I.
Published: February 2012

An aircraft grid pattern was flown by the Canadian Twin Otter to map the low‐level fluxes and structure over the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) research area in 1987. The time dependence and horizontal advection of heat and moisture were extracted from these flights, combined with surface flux measurements and boundary layer top measurements from radiosondes, to analyze the boundary layer budget using a mixed layer model. The results confirm the suggestion of an earlier study that the boundary layer top entrainment (when parameterized using the buoyancy flux) is nearly double the value used by many modeling studies. Both surface and aircraft data have been revised, and it now appears that the direct measurements of the sensible and latent heat fluxes by the aircraft underestimated these fluxes by about 20%, because of filtering and undersampling of long wavelength contributions.
Methane emissions from Alaska Arctic tundra: An assessment of local spatial variability
Authors: Morrissey L. A. , Livingston G. P.
Published: February 2012

Methane flux was measured in situ in the Alaska Arctic tundra to assess the magnitude and controls on spatial variability of emissions. A total of 122 measurements were made at 57 spatially independent sites across the Alaska North Slope during the summer of 1987. Variability in rates of emissions was similar in magnitude on local and regional scales, ranging from 0 to 286.5 mg CH4 m−2 d−1 overall and often varying across two orders of magnitude within 0.5‐m distances. Primary control on rates of emissions was determined by the substrate and the position of the water table relative to the surface. Secondary controls were defined by the substrate temperature and the type and quantity of vegetation participating in the plant‐mediated release of CH4 to the atmosphere. Emission rates in the Arctic Foothills ranged from 0.2 mg CH4 m−2 d−1 for tussock tundra to 55.3 mg CH4 m−2 d−1 over wet meadows. Within the Arctic Coastal Plain, rates of emissions were highest on inundated terrestrial sites (72.2 mg CH4 m−2 d−1), decreasing nearly 12 fold on comparable sites where the water table was 5 cm or more below the surface (6.1 mg CH4 m−2 d−1). Emission rates increased linearly with substrate temperatures at 10‐cm depth, increasing nearly ninefold over the 6°C temperature range observed. Plant mediated release of CH4 to the atmosphere was directly proportional to green leaf area and represented 92–98% of the total emission rates over vegetated sites. Comparisons between boreal studies reflect similarities in environmental controls on emissions at local‐to‐regional scales and demonstrate the sensitivity of regional to global estimates to sampling bias. These results suggest that current published emissions rates may have overestimated the contribution of boreal ecosystems to the global CH4 budget by several fold.
Variations of stratospheric ozone concentrations above Spitsbergen in summer 1989
Authors: Laurila Tuomas , Hakola Hannele , Junila Päivi , Joffre Sylvain M.
Published: February 2012

We report on the meteorological analysis and interpretation of ozone profiles carried out by electro chemical concentration cell sondes in July 1989 from the station of Ny Ålesund, Spitsbergen (79°N, 12°E). The soundings have been compared to other summertime ozone observations in the Arctic area. The data reveal strong day‐to‐day variations in ozone concentrations, especially near the 23 km level, where the minimum, mean, and maximum ozone concentration values were 2.5, 3.25, and 3.75 ppmv, respectively. The possible roles of horizontal and vertical advection and photochemistry in creating these variations were analyzed. The very small vertical movements do not explain these deviations. The gradually decreasing average ozone concentrations seem to be a balance between vertical and horizontal advection and chemical net loss. Trajectory analysis demonstrated the existence of two distinct circulation modes explaining the observed variations of ozone concentrations. During calm periods or southeastward advection the ozone concentrations decreased, starting from higher levels, whereas ozone concentrations increased rapidly when large‐scale circulation systems advected ozone‐rich air from the south.
An intracloud lightning parameterization scheme for a storm electrification model
Authors: Helsdon John H. , Wu Gang , Farley Richard D.
Published: February 2012

The parameterization of an intracloud lightning discharge has been implemented in our Storm Electrification Model. The initiation, propagation direction, and termination of the discharge are computed using the magnitude and direction of the electric field vector as the determining criteria. The charge redistribution due to the lightning is approximated assuming the channel to be an isolated conductor with zero net charge over its entire length. Various simulations involving differing amounts of charge transferred and distribution of charges have been done. Values of charge transfer, dipole moment change, and electrical energy dissipation computed in the model are consistent with observations. The effects of the lightning‐produced ions on the hydrometeor charges and electric field components depend strongly on the amount of charge transferred. A comparison between the measured electric field change of an actual intracloud flash and the field change due to the simulated discharge shows favorable agreement. Limitations of the parameterization scheme are discussed.
The effect of atmospheric carbon dioxide concentration on continental glaciation of the northern hemisphere
Authors: Verbitsky Mikhail Ya. , Oglesby Robert J.
Published: February 2012

Using an ice sheet model that is asynchronously coupled to an atmospheric general circulation model (GCM), we have computed the volume and areal extent of northern hemisphere ice sheets as a function of atmospheric carbon dioxide concentration. The ice sheet model includes an asthenosphere component for computing isostatic adjustment. Our basic strategy involves determining the net rate of snow accumulation in the GCM as a function of CO2 by seeding all northern hemisphere land points initially with 10 m of (water equivalent) snow and determining the resultant net snow balance over the course of a year. The net snow accumulations were then used as input to the ice sheet model, which in turn was used to compute the resultant ice sheet height and extent after 25 kyr. In order to judge model uncertainty, two different but reasonable snowmelt formulations were used in the GCM. The basic results of the simulations are: (1) The ice sheet volume is strongly a function of CO2 concentration, with a more or less monotonic increase in volume as CO2 is decreased. (2) The computed ice sheet volumes are an order of magnitude less than those of (reconstructed) Pleistocene ice sheets. These results suggest that CO2 changes are an important but not dominant factor in accounting for the Pleistocene ice ages, though considerable future work is required to clarify this more fully. (3) While the choice of snowmelt formulation strongly affected the total volume of ice, the rate of change dV/d[CO2] appears to be basically unaffected. (4) Through use of a computed “glaciation sensitivity” index we show that Greenland is by far the most likely to have an ice sheet; Tibet and Siberia were more likely to have an ice sheet than Canada or Fenno‐Scandinavia; and Alaska and North Africa were least likely to have ice sheets (though each did occur for at least one CO2 value). These results represent the first step in the process of asynchronous coupling of a GCM and ice sheet model. These simulations do not account for such effects as the elevational feedback of the ice sheets on the overall climate or orbital insolation changes; only albedo effects are accounted for. In a future study we plan to continue the runs iteratively by using the GCM to determine new net snow accumulations consistent with the ice sheets computed in this present study and to investigate the possible effects of orbital insolation changes.
Arctic ice surface temperature retrieval from AVHRR thermal channels
Authors: Key J. , Haefliger M.
Published: February 2012

The relationship between AVHRR thermal radiances and the surface (skin) temperature of Arctic snow‐covered sea ice is examined through forward calculations of the radiative transfer equation, providing an ice/snow surface temperature retrieval algorithm for the central Arctic Basin. Temperature and humidity profiles with cloud observations collected on an ice island during 1986–1987 are used. Coefficients that correct for atmospheric attenuation are given for three Arctic clear sky “seasons”, as defined through statistical analysis of the daily profiles, for the NOAA 7, 9, and 11 satellites. Modeled directional snow emissivities, different in the two split‐window (11 and 12 μm) channels, are used. While the sensor scan angle is included explicitly in the correction equation, its effect in the dry Arctic atmosphere is small, generally less than 0.1 K. Using the split‐window channels and scan angle, the rms error in the estimated ice surface temperature (IST) is less than 0.1 K in all seasons. Inclusion of channel 3 (3.7 μm) during the winter decreases the rms error by less than 0.003 K. The seasonal dependence of the coefficients is important, with errors in the range of 0.1 – 0.6 K when coefficients from one season are used with data from another. Similarly, mixing coefficients and data from different satellites results in average errors from 0.1 to 1.0 K. Overall, employing the IST coefficients results in increased accuracy of up to 0.6 K over SST coefficients developed for the North Atlantic and the Greenland Sea areas.
Absorption cross sections for gaseous ClNO2 and Cl2 at 298 K: Potential organic oxidant source in the marine troposphere
Authors: Ganske J. A. , Berko H. N. , Finlayson‐Pitts B. J.
Published: February 2012

The absorption cross sections for gaseous ClNO2 in the 200–370 nm region and for Cl2 in the 270–400 nm region have been determined at 298 K. The cross sections for Cl2 are in excellent agreement with the literature. At λ < 300 nm the absorption cross sections for ClNO2 are in good agreement with those of lilies and Takacs (1976/1977) and Nelson and Johnston (1981) but are higher than those of Martin and Gareis (1956) from 220 to 240 nm. In the tropospherically important region beyond 290 nm our results, which have been corrected for impurity Cl2 using a combination of mass spectrometry and UV absorption, fall between those of Martin and Gareis (1956) and lilies and Takacs (1976/1977) and are in excellent agreement with the values of Nelson and Johnston (1981). Estimates of the photolysis rate constants and photolytic lifetimes for ClNO2 for various solar zenith angles at the Earth's surface are reported. It is shown that atomic chlorine from ClNO2 photolysis may be a significant initiator of organic photooxidation in both moderately polluted and remote marine atmospheres.
Electricity in dying thunderstorms
Authors: Marshall Thomas C. , Lin Bu
Published: February 2012

We made one balloon sounding of the electric field in each of two dying thunderstorms. Both balloons were launched 20 min after the storm's last lightning flash. Each sounding revealed substantial residual electrification. The peak magnitudes of electric field in the two dying storms were 35 and 71 kV/m. The charge structure in both storms appeared to consist of one internal negative charge region with positive screening layers at the upper and lower cloud boundaries. One or two negative charge regions were found below cloud base. The main charge regions had inferred charge densities of about 1 nC/m3 and were hundreds of meters thick.