bluuebunny/crossref_metadata_2025 huggingface dataset:
Middle atmospheric ozone and temperature responses to solar irradiance variations over 27‐day periods
Authors: Chen Li , London Julius , Brasseur Guy
Published: February 2004

A one‐dimensional (1‐D), photochemical‐radiative, time‐dependent model with vertical diffusion is developed to investigate the response of ozone in the middle atmosphere to solar UV irradiance variations over 27‐day solar rotation periods. The model, based on equinoctial conditions at the equator, extends from 10 to 100 km with a vertical resolution of 0.5 km and employs an approximation based on photochemical families. The amplitudes of the wavelength‐dependent solar UV variation over 27‐day periods as observed by the Upper Atmosphere Research Satellite (UARS) are adopted in the model. The results of the 1‐D model show that at altitudes of 60–80 km, ozone decreases with increasing solar irradiance at Lyman α. The amplitude of the ozone variation is about 1% of its equilibrium value at about 70–75 km. Below 50 km an ozone increase is found due to increased photolysis of molecular oxygen by increased solar irradiance over the Herzberg continuum. The peak of this ozone increase (about 0.3%) is located at about 35 km. The peaks of the ozone oscillation in the upper stratosphere precede those of the solar oscillation as a result of the strong influence of the temperature feedback on the ozone response through the temperature dependent chemical reaction rates. A modified NCAR 2‐D model is also used to study the short‐term ozone response. Comparison of the 2‐D and 1‐D results shows that horizontal transport increases the phase lag of the temperature response. This large phase lag is essential to simulate the observed ozone response given by Nimbus 7 solar backscattered ultraviolet observations. The positive temperature response around 70 km observed by Nimbus 7 stratospheric and mesospheric sounder data is confirmed by the UARS microwave limb sounder temperature observation, but neither 1‐D nor 2‐D models are able to reproduce this observed temperature response at this level. The effects of the exothermic chemical heating and vertical diffusion coefficient on the mesospheric temperature and ozone responses are discussed. The relative response of ozone and temperature to normalized solar variations over different spectral regions and the roles of different photochemical families in the ozone response are presented. Finally, the seasonal and latitudinal (up to middle latitudes) variations in the ozone response are evaluated with the use of the 2‐D model.
Distribution and seasonality of selected hydrocarbons and halocarbons over the western Pacific basin during PEM‐West A and PEM‐West B
Authors: Blake Nicola J. , Blake Donald R. , Chen Tai‐Yih , Collins James E. , Sachse Glen W. , Anderson Bruce E. , Rowland F. Sherwood
Published: February 2004

Nonmethane hydrocarbons (NMHCs) and halocarbons were measured in the troposphere over the northwestern Pacific as part of the airborne component of NASA's Pacific Exploratory Mission‐West Phase B (PEM‐West B). This study took place in late winter of 1994, a period characterized by maximum outflow from the Asian continent. The results are compared to those from Pacific Exploratory Mission‐West Phase A (PEM‐West A), which was flown in the same region during late summer of 1991, when flow from the subtropical western Pacific dominated the lower troposphere. Mixing ratios of NMHCs, tetrachloroethene (C2Cl4), and methyl bromide (CH3Br) were significantly higher during PEM‐West B than during PEM‐West A, particularly at latitudes north of 25°N and altitudes lower than 6 km. The primary reasons for these higher ambient concentrations were the seasonal increase in the atmospheric lifetimes of trace gases controlled by HO radical reactions, and the more frequent input of continental air masses. During PEM‐West B, air masses of continental origin observed north of 25°N latitude were augmented with urban signature gases such as C2Cl4. By contrast, more southerly continental outflow had characteristics associated with combustion sources such as biomass burning, including wood fuel burning. During the summer PEM‐West A period, the spatial distribution of methyl iodide (CH3I) was consistent with effective oceanic sources at all latitudes, being especially strong in tropical and subtropical regions. At low latitudes, PEM‐West B CH3I mixing ratios in the lower troposphere were similar to PEM‐West A, but at latitudes greater than about 25°N PEM‐West B concentrations were significantly reduced. Equatorial regions exhibited enhanced CH3I mixing ratios extending into the upper tropical troposphere, consistent with fast vertical transport of air from the tropical marine boundary layer.
The Pacific Exploratory Mission‐West Phase B: February‐March, 1994
Authors: Hoell J. M. , Davis D. D. , Liu S. C. , Newell R. E. , Akimoto H. , McNeal R. J. , Bendura R. J.
Published: February 2004

The NASA Pacific Exploratory Mission in the Western Pacific Ocean (PEM‐West) is a major component of the East Asia/North Pacific Regional Study (APARE), a project within the International Global Atmospheric Chemistry (IGAC) Program. The broad objectives of the PEM‐West/APARE initiative are to study chemical processes and long‐range transport of atmospheric trace species over the north‐west Pacific Ocean and to estimate the magnitude of the human impact on these species over this region. The first phase of PEM‐West (PEM‐West A) was conducted in September‐October 1991, a period characterized by minimum outflow from the Asian continent. The second phase of this mission, PEM‐West B, was conducted during February‐March 1994, a period characterized by enhanced outflow from the Asian continent. Both field campaigns of PEM‐West included intensive airborne measurements of trace gases and aerosols from the NASA DC‐8 aircraft coordinated with measurements at surface sites. This paper reports the experimental design for PEM‐West B and provides a brief summary of the salient results of the PEM‐West B campaign with particular emphases on the difference/similarities between phases A and B. Results from the two campaigns clearly quantify, from a trace gas perspective, the seasonal differences in the continental outflow that were qualitatively anticipated based upon meteorological considerations, and show the impact of major meteorological features within the region on the quality of tropospheric air over the North Pacific Ocean regions. The PEM‐West database provides a “baseline” tool by which future assessments of a continuing impact of Asian emissions on remote Pacific regions can be judged. [These data are currently available through the Global Troposhperic Experiment Data Archive at NASA's Langley Research Center (http://www‐gte.larc.nasa.gov) and the Langley Distributed Archive Center (http://eosdis.larc.nasa.gov)].
Interdependence of the tropical and extratropical QBO: Relationship to the solar cycle versus a biennial oscillation in the stratosphere
Authors: Salby Murry , Callaghan Patrick , Shea Dennis
Published: February 2004

Interannual variations in the tropical and polar stratosphere are investigated in monthly mean records of north polar temperature and equatorial zonal wind. The spectrum of polar temperature possesses discrete components associated with the tropical quasi‐biennial oscillation (QBO), as well as with a biennial oscillation (BO) that figures prominently in the record of north‐polar temperature. The BO, in fact, accounts for as much temperature variance as the QBO. The running correlation between equatorial zonal wind and polar temperature oscillates on a decadal timescale, resembling the 11‐year sunspot cycle [Kodera, 1993]. This oscillation is shown to follow from an interaction between the QBO and the BO. Interaction between the QBO and BO also figures in Labitzke and van Loon's [1988] evidence of the solar cycle, which results when data are stratified according to the QBO. Both apparent signatures of solar cycle influence therefore revolve about the interpretation of the BO.
Land surface processes and the potential for convective precipitation
Authors: De Ridder Koen
Published: February 2004

The impact of the land surface on the potential for precipitating convection is examined. To do so, an analytical expression that relates boundary layer equivalent potential temperature to the surface evaporative fraction is derived by means of the slab model of the convective boundary layer. Analysis of the resulting expression shows that the equivalent potential temperature increases with the evaporative fraction under most circumstances, except for very dry atmospheres, and that this increase is enhanced in the presence of a low‐level moist layer.
Use of correlations between long‐lived atmospheric species in assessment studies
Authors: Vohralik P. F. , Randeniya L. K. , Plumb I. C. , Ryan K. R.
Published: February 2004

The results of airborne measurement campaigns and two‐dimensional (2‐D) model calculations show compact relationships between certain pairs of long‐lived species. Such correlations have been used in the present study to reduce the number of transported species used in the Commonwealth Scientific and Industrial Research Organisation (CSIRO) two‐dimensional chemical transport model (2‐D CTM) when calculating ozone changes from proposed fleets of supersonic aircraft or changing halocarbon concentrations. Differences to both the composition of the background atmosphere and to the predicted ozone changes are examined. It is shown that the use of correlations has only a small effect on the predicted ozone changes. Larger differences are found for the changing halocarbon scenario than for the supersonic aircraft scenario. These differences are due to difficulties associated with correctly accounting for the time variation of the source gas mixing ratios. Further work is required to reduce this source of error. The results of these studies should be applicable to 3‐D CTMs, where large savings in computational time can be achieved through the reduction in the number of transported species.
Uncertainty analysis of indirect radiative forcing by anthropogenic sulfate aerosols
Authors: Pan Wenwei , Tatang Menner A. , McRae Gregory J. , Prinn Ronald G.
Published: February 2004

The effects of aerosols on the optical properties of water clouds (so‐called indirect aerosol effects) are a major current source of uncertainty in the radiative forcing of climate change. Uncertainty in the indirect radiative forcing by anthropogenic sulfate aerosols is analyzed for five different model structures with 20 input uncertain parameters using the probabilistic collocation method. The structural uncertainty, measuring the range of the mean responses in different models, is −1.2 to −1.7 W m−2; and the parametric uncertainty, induced by the uncertainties in the input model parameters, is −0.1 to −5.2 W m−2 with 95% confidence. This implies that refining the input parameters may be more important than improving models in order to minimize the uncertainty in the indirect radiative forcing by anthropogenic sulfate aerosols using these five models. The rankings of sensitivity to and variance contribution by the 20 uncertain parameters shows very different patterns. The variance analysis indicates that the parametric uncertainty comes mainly from aerosol size parameters and atmospheric transmittance, indicating the importance of developing size‐resolved global aerosol models. Although the conclusions reached here are subject to the choice of model structures and uncertain parameter distributions, this study introduces a useful framework for computing uncertainty in a critical climate issue.
The semiannual variation in the atmospheric hydrologic processes
Authors: Chen Jau‐Ming , Chen Tsing‐Chang
Published: February 2004

Semiannual variations of several atmospheric hydrological processes are identified from two sets of data: (1) the monthly mean precipitation data generated by the Global Precipitation Climate Project (GPCP) and (2) the monthly mean upper air wind and moisture data generated by the Climate Data Assimilation System of National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis Project for the period 1986–1993. Three major findings of this study follow. First is that the existence of semiannual variations in precipitation and water vapor flux are revealed from (1) time series of area‐mean precipitation and divergence of water vapor flux over the Asian‐Australian (AA) monsoon (60°E‐120°W) and extra‐AA monsoon (120°W‐60°E) hemispheres and (2) the power spectra of that time series. Second is that the semiannual precipitation variation exhibits an east‐west seesaw oscillation. In January and July, positive precipitation anomalies concentrate in the AA monsoon hemisphere, while major negative precipitation anomalies exist in the extra‐AA monsoon hemisphere. Opposite spatial patterns occur in April and October. Third is that to maintain the semiannual variation of precipitation, water vapor diverges out of the extra‐AA (AA) monsoon hemisphere and converges toward the AA monsoon (extra‐AA monsoon) hemisphere in January and July (April and October).
Factors influencing the retention of hydrogen peroxide and molecular oxygen in rime ice
Authors: Snider Jefferson R. , Huang Jun
Published: February 2004

Vertical transport of many atmospheric trace gases is modulated by retention in solid (ice phase) precipitation during the impaction and freezing (i.e., riming) of supercooled cloud droplets. Here we report field measurements of the concentrations of both hydrogen peroxide (H2O2) and molecular oxygen (O2) in rime ice. Gas retention efficiencies, defined as the ratio of the observed concentration divided by the equilibrium concentration predicted by Henry's law, are presented. Rime ice collections were conducted in a wind tunnel using 3.2‐ and 9.5‐mm impaction cylinders. Velocities were varied between 9 and 20 m/s and ice substrate temperatures were colder than −3.5°C. Averaged values of the retention efficiencies for H2O2 and O2 were 0.05 and 0.32, respectively. Also discussed are direct measurements of H2O2 volatilization obtained by monitoring increases in gaseous H2O2 associated with droplet impingement and freezing on an impaction grid placed upstream of a gas sampling inlet. The observed relationships between retention and the time interval between droplet impaction suggest that H2O2 and O2 are volatilized subsequent to droplet freezing and prior to burial by continued riming. A comparison of the timescales that are expected to govern retention indicates that solute diffusivities in the solidified droplets are ∼10−12 m2 s−1.
The effects of sulfur emissions from HSCT aircraft: A 2‐D model intercomparison
Authors: Weisenstein Debra K. , Ko Malcolm K. W. , Dyominov Igor G. , Pitari Giovanni , Ricciardulli Lucrezia , Visconti Guido , Bekki Slimane
Published: February 2004

Four independently formulated two‐dimensional chemical transport models with sulfate aerosol microphysics are used to evaluate the possible effects of sulfur emissions from high‐speed civil transport (HSCT) aircraft operating in the stratosphere in 2015. Emission scenarios studied are those from Baughcum and Henderson [1995], while assumptions regarding the form of emitted sulfur are similar to those of Weisenstein et al. [1996]. All models show much larger increases in aerosol surface area when aircraft sulfur is assumed to be emitted as particles of 10 nm radius rather than as gas phase SO2. If we assume an emission index (EI) for SO2 of 0.4 gm (kg fuel burned)−1 in 2015, maximum increases in stratospheric sulfate aerosol surface area range from 0.1 μm2 cm−3 to 0.5 μm2 cm−3 with sulfur emitted as SO2 gas and from 1.0 μm2 cm−3 to 2.5 μm2 cm−3 with sulfur emitted as particles. Model differences in calculated surface area are deemed to be due mainly to differences in model transport. Calculated annual average ozone perturbations due to aircraft emissions with EI(NOx) = 5, EI(H2O) = 1230, and EI(SO2) = 0.4 range from −0.1% to −0.6% at 45°N for sulfur emission as SO2 gas and from −0.4% to −1.5% with sulfur emission as 100% particles. The effect of zonal and temporal inhomogeneities in temperature on heterogeneous reactions rates is accounted for in the Atmospheric and Environmental Research model and the Université degli Studi L'Aquila model and significantly increases the calculated ozone depletion due to HSCT, particularly for the cases with concurrent increases in aerosol surface area. Sensitivities to polar stratospheric clouds, background chlorine amount, additional heterogeneous reactions, and background aerosol loading are also explored.
High‐latitude stratospheric NO2 and HNO3 over Fairbanks (65°N) 1992–1994
Authors: Slusser J. , Liu X. , Stamnes K. , Shaw G. , Smith R. , Storvold R. , Murcray F. , Lee A. , Good P.
Published: February 2004

Column measurements of NO2 and HNO3 were made over Fairbanks, Alaska, between August 1992 and April 1994. The seasonal minimum of the NO2 column occurs in late December, while the minimum of the HNO3 column is in early August. The high HNO3 column amounts observed in February as opposed to the lower winter value predicted by gas phase two‐dimensional models suggest that the storage reservoir species N2O5 does not accumulate during the winter. Instead, it appears to be converted to HNO3 on sulfate aerosols. Three‐dimensional model calculations which include the heterogeneous reaction of N2O5 with aerosols simulate the anticorrelation relationship between NO2 and HNO3 well for the summer and predict the magnitude of the NO2 maximum but overestimate the HNO3 minimum.
Photodissociation and UV radiative transfer in a cloudy atmosphere: Modeling and measurements
Authors: Matthijsen J. , Suhre K. , Rosset R. , Eisele F. L. , Mauldin R. L. , Tanner D. J.
Published: February 2004

We present an analysis of UV radiative transfer under cloudy conditions in relation to the photochemistry of the hydroxyl radical (OH) by means of modeling and measurements. The measurements, which are part of the First Aerosol Characterization Experiment (ACE 1) campaign, consist of four different ascents/descents selected from research flight (RF) 12 and 28. The ascents/descents give vertical profiles of UV irradiances, microphysical properties, standard meteorological parameters, and OH concentration in the presence of one or more cloud layers. In order to assess the photochemical conditions for these (complex) cloudy cases we first compare the UV irradiance measurements with modeled profiles. We model the UV irradiances using cloud optical properties which we derive from the measured microphysical properties. Second, we use the simultaneously modeled actinic flux to calculate the rate constant of the photodissociation of ozone to the O(1D) radical (JO3). This reaction initiates the primary OH‐production. Finally, we compare the measured OH concentrations with those derived from the radiative transfer calculations. For single‐cloud layer cases we successfully simulated UV radiative transfer, JO3 and OH. For more complex multiple‐cloud layer cases the UV radiative transfer could only be explained allowing large variations of the cloud optical thickness (from zero to double the measurement derived values). The impact of such variations on the modeled radiation‐derived photochemical properties, JO3 and OH, was, with a variation of 25%, found to be relatively small. As a consequence, we were able to simulate the general profile of OH for these complex cloudy conditions.
Long‐term trends in ground level ozone over the contiguous United States, 1980–1995
Authors: Fiore Arlene M. , Jacob Daniel J. , Logan Jennifer A. , Yin Jeffrey H.
Published: February 2004

Long‐term trends of median and 90th percentile summer afternoon O3 concentrations were examined at 549 sites across the United States for the 1980–1995 period. Daily temperature data were used to account for the variability in O3 concentrations associated with temperature. Both before and after segregating the O3 data by temperature, trends were insignificant over most of the continental United States. No region of the United States experienced a significant increase in O3 concentrations during the 1980–1995 period. Decreasing trends were predominantly clustered in the three largest metropolitan areas: New York City, Los Angeles, and Chicago. In these areas, additional sites with trends were identified in the temperature‐segregated analysis. Correlation of trends with local anthropogenic emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOC) indicates a greater frequency of decreasing trends for urban sites with high emission. National emission inventories for the United States indicate that anthropogenic VOC emissions decreased by 12% over the 1980–1995 period while NOx emissions remained constant. The observed O3 trends are consistent with the view that summertime O3 production over the United States is NOx‐limited except in the largest metropolitan areas where it is partly VOC‐limited.
A dry deposition parameterization for sulfur oxides in a chemistry and general circulation model
Authors: Ganzeveld Laurens , Lelieveld Jos , Roelofs Geert‐Jan
Published: February 2004

A dry deposition scheme, originally developed to calculate the deposition velocities for the trace gases O3, NO2, NO, and HNO3 in the chemistry and general circulation European Centre Hamburg Model (ECHAM), is extended to sulfur dioxide (SO2) and sulfate (SO42−). In order to reduce some of the shortcomings of the previous model version a local surface roughness and a more realistic leaf area index (LAI), derived from a high‐resolution ecosystem database are introduced. The current model calculates the deposition velocities from the aerodynamic resistance, a quasi‐laminary boundary layer resistance and a surface resistance of the surface cover, e.g., snow/ice, bare soil, vegetation, wetted surfaces, and ocean. The SO2 deposition velocity over vegetated surfaces is calculated as a function of the vegetation activity, the canopy wetness, turbulent transport through the canopy to the soil, and uptake by the soil. The soil resistance is explicitly calculated from the relative humidity and the soil pH, derived from a high‐resolution global soil pH database. The snow/ice resistance of SO2 is a function of temperature. The SO2 deposition velocity over the oceans is controlled by turbulence. The sulfate deposition velocity is calculated considering diffusion, impaction, and sedimentation. Over sea surfaces the effect of bubble bursting, causing the breakdown of the quasi‐laminary boundary layer, scavenging of the sulfate aerosol by sea spray, and aerosol growth due to high local relative humidities are considered. An integrated sulfate deposition velocity is calculated, applying a unimodal mass size distribution over land and a bimodal mass size distribution over sea. The calculated sulfate deposition velocity is about an order of magnitude larger than that based on a monodisperse aerosol, which is often applied in chemistry‐transport models. Incorporation of the new dry deposition scheme in the ECHAM model yields significant relative differences (up to ∼50%) in mass flux densities and surface layer concentrations compared to those calculated with a simple, constant dry deposition scheme.
Impact of tropical heat sources on the South American tropospheric upper circulation and subsidence
Authors: Gandu Adilson W. , Silva Dias Pedro L.
Published: February 2004

The nonlinear adjustment of the wind and mass fields to idealized tropical heat sources is studied with a simple nonlinear primitive equation model with emphasis on the upper level circulation over South America and neighboring oceanic regions during the austral summer. Numerical experiments are performed with (1) an idealized symmetrical heat source in the Amazon region, (2) the asymmetry induced in source (1) by the SACZ, (3) the effect of the Atlantic ITCZ off the Amazon mouth, (4) the African heat source, (5) the West Pacific source, and (6) the central Pacific source during the warm phase of ENSO. The linear response is obtained through the reduction of the heat source by a factor of 10 and subsequent multiplication of the results by the same factor. Two basic questions are discussed: (1) are localized heat sources important for the development of the observed cyclonic flow in the midequatorial Atlantic and (2) where is the compensating subsidence associated with the Amazon heat source located? The nonlinearity helps organizing a weak cyclonic curvature in the midequatorial Atlantic, with the inclusion of source (2). The basic state generated by the west Pacific source, and primarily by the central Pacific source, has a large impact on the cyclonic curvature on the equatorial Atlantic. The compensating subsidence associated with the Amazon source is concentrated on the southwest side of the source. The SACZ extension helps to enhance the subsidence over the northern Argentina, and the Atlantic ITCZ enhances the subsidence over northeast Brazil and central equatorial Atlantic. Nonlinearity weakens the subsidence at the 500 hPa level inducing a more barotropic structure in the dynamical response to the heating.
Role of the quasi‐biennial oscillation in the transport of aerosols from the tropical stratospheric reservoir to midlatitudes
Authors: Choi Wookap , Grant William B. , Park Jae H. , Lee Kwang‐Mog , Lee Hyunah , Russell James M.
Published: February 2004

The temporal evolution of the stratospheric aerosol distribution in the tropical stratospheric reservoir after the eruption of Mount Pinatubo was observed from 1992 to 1995 by the HALOE instrument on the UARS satellite. Since the spatial gradient of aerosol loading is large at the boundaries of the tropical stratospheric reservoir due to the volcanic aerosols, the effect of the meridional circulation on the distribution is seen clearly. The mechanism for dispersal of aerosol in the lower stratosphere from the tropics into midlatitudes strongly depends on the phase of the equatorial zonal wind. The time‐latitude crosssections of the normalized distribution of aerosol on isentropic surfaces are used to observe the equatorial variation as well as change in meridional dispersal during the quasibiennial period. Observed tropical stratospheric winds are used with a simple analytical dynamical model to examine transport processes of tracers from the tropics during several phases of the quasibiennial oscillation (QBO) from 1992 to 1995. The Lagrangian meridional circulation in the tropics is consistent with the vertical and meridional velocities correlated with the QBO in the zonal wind. We find that vertical motion plays a crucial role in vertical and subsequent meridional transport. The pattern of meridional divergence derived from the vertical velocity is closely related to the observed HALOE aerosol distributions and their temporal development in the equatorial region. The westerly (easterly) shear phase of the QBO is associated with sinking (rising) motions at the equator and subsequent poleward (equatorward) transport in the lower stratosphere.
On the indicator‐based approach to assess ozone sensitivities and emissions features
Authors: Lu Cheng‐Hsuan , Chang Julius S.
Published: February 2004

Previous model studies suggested that ambient measurements of key chemical species and ratios of species could be used to assess the sensitivities of ozone formation to reductions in precursor emissions. Threshold values of these indicator species and ratios, delineating the transition between VOG and NOx sensitivity, were proposed. Subsequently, measurement studies have assumed the universality of these threshold criteria and have compared local observed indicators with previously established criteria to assess ozone sensitivities. In this study the concept of indicator species is extended to combinations of observable species that are consistently associated with different site characteristics (e.g., ozone sensitivities and emissions features). The results of SARMAP Air Quality Model (SAQM) simulations in the San Joaquin Valley, California, are used to investigate the applicability of indicators to assess ozone sensitivities and emissions features. The use of three indicator ratios (O3/(NOy‐NOx), HCHO/NO2 and H2O2/HNO3) along with SAQM‐derived threshold criteria is found to be effective for identifying VOC‐ or NOx‐sensitive regimes. NOy and (NOy‐NOx)NOy are found to be useful in describing emission features and threshold criteria are derived by SAQM prediction. SAQM‐derived threshold criteria for assessing ozone sensitivities are found to differ from threshold criteria proposed by previous studies using different models and under different conditions. Such differences suggest that threshold criteria are likely to be dependent on locations and environmental conditions, including emission patterns and rates. Therefore local observed indicator species and ratios can be used to determine ozone sensitivities only if appropriate threshold criteria have been derived for the local conditions.
Lidar temperature measurements during the Tropical Ozone Transport Experiment (TOTE)/Vortex Ozone Transport Experiment (VOTE) mission
Authors: Burris J. , Heaps William , Gary B. , Hoegy W. , Lait L. , McGee T. , Gross M. , Singh U.
Published: February 2004

Temperature profiles were acquired on the Tropical Ozone Transport Experiment (TOTE) and Vortex Ozone Transport Experiment (VOTE) flights by the Goddard Airborne Raman Lidar. The objective was to compare the temperature product from this new instrument with those generated by the Jet Propulsion Laboratory's Microwave Temperature Profiler and Goddard Space Flight Center's ground‐based Stratospheric Ozone Lidar. Simultaneous measurements were made between the Airborne Raman Lidar and O3 lidar on three dates; average temperatures differences varied from ∼0.5 K‐5 K over the 16–24 km altitude region. Comparisons between the Microwave Temperature Profiler and Airborne Raman Lidar for all flights (17) during TOTE/VOTE were performed over the same altitude region. The average temperature difference, Airborne Raman Lidar minus Microwave Temperature Profiler, was +2.3 K. In comparing temperatures between the Airborne Raman Lidar and Goddard's Data Assimilation Model, the ARL showed small scale structures not evident in those of the model for altitudes between ∼16 and 43 km.
Export of reactive nitrogen from North America during summertime: Sensitivity to hydrocarbon chemistry
Authors: Horowitz Larry W. , Liang Jinyou , Gardner Geraldine M. , Jacob Daniel J.
Published: February 2004

The global influence on tropospheric chemistry of nitrogen oxides (NOx = NO + NO2) emitted by fossil fuel combustion may be strongly modulated by nonmethane hydrocarbon (NMHC) chemistry taking place in the continental boundary layer. This effect is investigated using a three‐dimensional, continental‐scale model of tropospheric O3‐NOx‐NMHC chemistry over North America in summer. The model includes detailed representation of NMHC chemistry including in particular isoprene. Model results are evaluated with observations for ozone, reactive nitrogen species, and photochemical tracers at a number of sites in North America. Sensitivity analyses are conducted to explore the effects of assumptions regarding the aerosol chemistry of peroxy radicals and the fate of hydroxy organic nitrates produced from the oxidation of isoprene. A budget analysis for the United States in the model indicates that 9% Of NOx. emitted from fossil fuel combustion is exported out of the continental boundary layer as NOx, 3.5% is exported as peroxyacetyl nitrate (PAN), and 3.7% is exported as other organic nitrates. Isoprene is the principal NMHC responsible for the formation and export of organic nitrates, which eventually decompose to provide a source of NOx in the remote troposphere. Export of NOx. and organic nitrates from the U.S. boundary layer is found to be a major source of NOx. on the scale of the northern hemisphere troposphere and on the scale of the upper troposphere at northern midlatitudes. Proper representation of isoprene chemistry in the continental boundary layer is important for simulation Of NOx in global tropospheric chemistry models.
Micrometeorological measurements of methane and nitrous oxide exchange above a boreal aspen forest
Authors: Simpson I. J. , Edwards G. C. , Thurtell G. W. , den Hartog G. , Neumann H. H. , Staebler R. M.
Published: February 2004

This paper presents tower‐based measurements of methane (CH4) and nitrous oxide (N2O) exchange between a boreal aspen stand and the atmosphere. Boreal ecosystems are a priority trace gas research area, and the work was conducted as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). Methane and nitrous oxide fluxes were measured continuously between April 16 and September 16, 1994, in the Prince Albert National Park, Saskatchewan. The fluxes were determined using a high‐resolution tunable diode laser Trace Gas Analysis System (TGAS) together with micrometeorological techniques. Both the CH4 and the N2O fluxes were small and required long averaging times to be resolved. Over the full experiment, small emissions of both CH4 and N2O were measured above the aspen stand. The mean flux of N2O was 1.4±0.7 ng m−2 s−1, or 1.9–2.5 ng m−2 s−1 when an enhancement factor to compensate for the breakdown of similarity theory just above forest canopies is included. Low rates of nitrification and denitrification throughout the growing season may explain the consistently small N2O fluxes. The CH4 flux averaged 15.7±2.8 ng m−2 s−1, or 21–28 ng m−2 s−1, including the similarity theory enhancement factor. The CH4 emissions were highest between late July and mid‐September, and there was a strong correlation between the CH4 flux and the soil temperature. Whereas CH4 emission was measured from the above‐canopy footprint, uptake was recorded close to the tower base. Overall, it appears that CH4 emissions from anoxic wet patches located throughout the above‐canopy footprint overwhelmed uptake from drier areas to produce a net emission of CH4 from the aspen site.
Total ozone/UVB monitoring and forecasting: Impact of clouds and the horizontal resolution of satellite retrievals
Authors: Ziemke J. R. , Herman J. R. , Stanford J. L. , Bhartia P. K.
Published: February 2004

This study compares the horizontal resolution of solar backscatter ultraviolet 2 (SBUV2) total ozone (Ω) fields with those from the new NASA earth probe (EP) and Advanced Earth Observing Satellite (ADEOS) total ozone mapping spectrometer (TOMS) side‐scanning photometers. The latter instruments provide high resolution, easily resolving the medium‐scale waves (4–7 wavelengths around the Earth at a fixed latitude) that dominate day‐to‐day midlatitude Ω fluctuations. In contrast, SBUV2 instruments do not, since these devices measure only at nadir (straight downward), yielding ∼14 measurements daily at a given latitude. This method has consequences not only for global monitoring of Ω and ultraviolet B (UVB, 290–320 nm), but also for short‐timescale Ω and UVB predictions in summer because timescales of a few days are coupled to medium horizontal scales (several thousand kilometers) by baroclinic waves that typically force the observed Ω variations. We use a simple Ω prediction model to test the use of Ω fields from TOMS and SBUV instruments and show that the higher zonal resolution from side‐scanning TOMS instruments results in sizeable reductions in Ω prediction errors, whereas predictions using SBUV2 Ω are no better than persistence (where tomorrow's Ω is taken to be today's) in the biologically important summer months. Daily variabilities (equivalent to errors in 24‐hour persistence forecasting of Ω) in high‐resolution TOMS midlatitude ozone during summer are shown to sometimes exceed 50 Dobson units, producing daily changes of 20% or greater in computed ground‐level clear‐sky UV index. This study demonstrates that even these large daily changes in measured or predicted clear‐sky UV are usually smaller than daily UV changes associated with transient clouds. While surface UVB variability is dominated by local cloudiness variations, Ω forecasts can enhance UVB prediction in relatively cloud free regions such as the U.S. desert southwest and in stagnant high‐pressure regimes that can persist for 1–2 weeks in summer. Furthermore, as weather forecast models increase in accuracy of forecasted cloudiness, accurate predictions will allow more accurate UVB forecasts for cloud free regions, the locations where they are most needed. Results from the present paper show, however, that high‐resolution TOMS‐like side‐scanning Ω measurements are required for ozone and UVB monitoring and prediction, rather than SBUV‐type nadir observations.
Atmospheric near‐surface nitrate at coastal Antarctic sites
Authors: Wagenbach D. , Legrand M. , Fischer H. , Pichlmayer F. , Wolff E. W.
Published: February 2004

Records of atmospheric nitrate were obtained by year‐round aerosol sampling at Neumayer and Dumont D'Urville stations, located in the Atlantic and Pacific sector of coastal Antarctica, respectively. Where possible, evaluation of the nitrate records is mainly based on concurrently measured radioisotopes (10Be, 7Be, 210Pb) as well as δ15N in nitrate nitrogen. Observations made at these (and two other coastal Antarctic sites [Savoie et al., 1993]) reveal a uniform nitrate background near 10 ng m−3 persisting throughout coastal Antarctica between approximately April and June. The dominant seasonal nitrate maximum, which occurred between spring and midsummer and ranged from 20 to 70 ng m−3, tended to increase with latitude. An estimate based on Neumayer mineral dust concentrations suggests that an average of less than 5% of the observed atmospheric nitrate load may be associated with continental tropospheric sources, while a separate estimate based on 210Pb records implies a much higher proportion of up to 60%. Stratospheric nitrate influx rates seen at coastal sites, deduced from Neumayer 10Be/7Be records for stratospheric air mass intrusions and from tritium for the sedimentation of polar stratospheric clouds (PSC), exceed the theoretical stratospheric odd nitrogen production rate from N2O oxidation by almost a factor of 5 and are found to be in close agreement with the observed surface nitrate flux, implying again that the continental source contribution is relatively unimportant. Consideration of nitrate reemission from near‐surface snow layers reveals a minor effect of this flux on the global Antarctic troposphere but possibly a substantial influence on the nitrate load of a persistent surface inversion layer. Evaluation of the mean seasonal nitrate pattern, based on concurrent 10Be, 210Pb, and δ15N records at Neumayer and on tritium in precipitation at Halley, suggests that the period of significant enhancement above the background mainly reflects inputs of stratospheric nitrate with secondary peaks in winter and late summer most likely dominated by PSC sedimentation and stratospheric air mass intrusions, respectively.
Characteristics of the sporadic Na layers observed during the Airborne Lidar and Observations of Hawaiian Airglow/Airborne Noctilucent Cloud (ALOHA/ANLC‐93) campaigns
Authors: Qian Jun , Gu Yiyun , Gardner Chester S.
Published: February 2004

We summarize the characteristics of the 43 sporadic Na (Nas) layers observed by the airborne Na density and the Haleakala Na wind/temperature lidars during the Airborne Lidar and Observations of Hawaiian Airglow/Airborne Noctilucent Cloud (ALOHA/ANLC‐93) campaigns. Nas layers are clearly not a local phenomenon since the horizontal extents varied from approximately 25 to almost 1600 km with a mean of 440 km. For the majority of the Nas layers observed above Haleakala, the temperatures were significantly warmer than the mean. The average enhancement was 12.9°K or about 6%. The temperature variations typically led the Nas density variations in time and on average reached their maximum values approximately 0.7 km below and 23 min before the Nas maxima. However, the maximum temperatures and Nas densities were only weakly correlated. Strong vertical shears in the horizontal winds were observed during the majority of the Nas events. The average maximum total shear was approximately equal to the shear instability limit of 42 m s−1 km−1. The maximum shears were located on average about 0.5 km below the Nas layer. In most cases the meridional shears were significantly stronger than the zonal shears. The maximum total shears were generally directed to the N‐NE and to the south. The strong temperature and wind perturbations observed during the majority of the events suggest that gravity waves play an important role in Nas formation, although the exact nature of that role remains unclear.
Influence of small‐scale structure on radiative transfer and photosynthesis in vegetation canopies
Authors: Knyazikhin Yuri , Kranigk Jörn , Myneni Ranga B. , Panfyorov Oleg , Gravenhorst Gode
Published: February 2004

The use of Beer's law to describe the radiation regime in plant canopies is valid for a sufficiently large volume filled densely with phytoelements. This set a limit to the scale at which models, based on Beer's law, can account for structural features of vegetation canopies and provide an adequate prediction of the radiation regime. The aim of our paper is to analyze radiation interaction in vegetation canopies and consequent photosynthetic rates at a scale at which Beer's law loses its validity. We use fractals to simulate the structure of vegetation canopies at this scale. It is shown that both the radiation regime and the photosynthesis depend on the fractal dimension of the plant stand. The development of radiative transfer models in fractal‐like media as well as measurements and modeling of fractal characteristics of trees and tree communities are essential for better understanding and scaling of radiative transfer and photosynthetic processes from an individual leaf to the canopy.
Large‐scale coupling between the tropical greenhouse effect and latent heat flux via atmospheric dynamics
Authors: Gershunov Alexander , Michaelsen Joel , Gautier Catherine
Published: February 2004

The clear‐sky greenhouse effect (GE) is determined primarily by the amount and vertical distribution of water vapor in the atmospheric column. GE hampers surface radiative cooling and is maintained through surface evaporative cooling. This paper examines the intimate space‐time relationships between the patterns of radiative heating of the atmosphere and surface evaporative cooling. We use data derived from satellite and in situ observations to show that tropical maritime GE is decoupled in space and time from latent heat flux (LHF), its source of water vapor. Large scale transport of atmospheric water vapor responsible for the observed relationships between GE and LHF is discussed. The spatial patterns of average GE and LHF are imbedded in the Walker and Hadley circulations and reinforce these circulations with strong evaporative cooling in the subtropical highs and greenhouse warming in the equatorial trough zones. Throughout tropical areas characterized by strong seasonality, the seasonal cycles of GE and LHF are out of phase. Much of the moisture that feeds GE in these off‐equatorial regions is advected by the Hadley circulation from tropical moisture source regions of the opposite hemisphere. An out‐of‐phase relationship between GE and LHF also turns up on El Niño ‐ Southern Oscillation timescales, most notably in the central tropical Pacific. The “super” greenhouse effect (SGE), a situation when GE absorption increases more than colocated surface longwave emission, is a seasonal feature of extensive tropical off‐equatorial areas where it is maintained by moisture convergence and convection. On interannual timescales, the same dynamical processes appear to assert the SGE in the central equatorial Pacific. GE and LHF regimes are also described for the equatorial cold tongue and warm pool regions.
Electrical structure in thunderstorm convective regions: 3. Synthesis
Authors: Stolzenburg Maribeth , Rust W. David , Marshall Thomas C.
Published: February 2004

In this paper, results from nearly 50 electric field soundings through convective regions of mesoscale convective systems (MCSs), isolated supercells, and isolated New Mexican mountain storms are compared and synthesized. These three types of thunderstorm convection are found to have a common, basic electrical structure. Within convective updrafts the basic charge structure has four charge regions, alternating in polarity, and the lowest is positive. Outside updrafts of convection there are typically at least six charge regions, alternating in polarity, and the lowest is again positive. Among the three storm types, there are differences in the heights and temperatures at which the basic four charge regions are found in updrafts. The height (temperature) of the center of the main negative charge region averages 6.93 km (−16°C) in MCS convective region updrafts, 9.12 km (−22°C) in supercell updrafts, and 6.05 km (−7°C) in New Mexican mountain storm updrafts. In updraft soundings through all three storm types, the center height of the main negative charge region increases with increasing average balloon ascent rate and updraft speed at a rate of about 0.3 km per 1 m s−1, with a correlation coefficient of 0.94. A schematic illustrates the basic four‐ and six‐charge structure for thunderstorm convective regions, and it is offered as an improved model for thunderstorm charge structure.
Parameterizations for sulfuric acid/water nucleation rates
Authors: Kulmala Markka , Laaksonen Ari , Pirjola Liisa
Published: February 2004

We present parameterized equations for calculation of sulfuric acid/water critical nucleus compositions and homogeneous nucleation rates. The parameterizations are in agreement with the thermodynamically consistent version of classical binary homogeneous nucleation theory [Wilemski, 1984] incorporating the hydration effect. The new parameterizations produce nucleation rates that differ by several orders of magnitude from the rates predicted by other parameterizations available in the literature. Model simulations of atmospheric aerosol formation show that the use of the new parameterizations may in some cases result in simulated nucleation mode particle number densities that are by a factor of 1000 lower than those obtained using the old parameterizations.
A parameterization of aerosol activation: 1. Single aerosol type
Authors: Abdul‐Razzak Hayder , Ghan Steven J. , Rivera‐Carpio Carlos
Published: February 2004

This paper presents a parameterization of the fraction of aerosol particles activated to form cloud droplets in a parcel of air rising adiabatically. The study applies to aerosols of a single lognormal size distribution with uniform chemical composition and capable of serving as cloud condensation nuclei. The parameterization is based on analysis of the rate equations for the parcel supersaturation and aerosol activation process. The analysis leads to the identification of only four dimensionless parameters on which the fraction of activation strongly depends. Using results of detailed numerical simulations by a size‐resolving Lagrangian parcel model, errors due to simplifying assumptions used in the analysis were largely eliminated by employing adjustment coefficients. For a wide range of governing parameters (e.g., particle radius, standard deviation, updraft velocity, etc.), differences between the parametric equations and the numerical model results are less than 10% for most conditions and less than 25% for some extreme but realistic conditions. This new parameterization is significantly more accurate and successful in representing the fraction of activation in terms of governing parameters than any known parameterization.