bluuebunny/crossref_metadata_2025 huggingface dataset:
Biogenic emissions in Europe: 2. Implications for ozone control strategies
Authors: Simpson David
Published: February 2004

As shown in a companion paper, uncertainties in the emissions of isoprene in Europe are significant, quite possibly of the order of 500%, and this uncertainty must be taken into account when assessing the effects of emission control measures in reducing ozone. The EMEP MSC‐W model has been used to estimate the effects of 50% reductions in man‐made NOx (nitrogen oxides = NO + NO2) and volatile organic compounds (VOCs) on rural ozone concentrations in different parts of Europe, under four different assumptions concerning biogenic emissions: (1) medium isoprene emissions, (2) high isoprene emissions, (3) zero isoprene emissions, and (4) zero soil NOx emissions. The model results suggest that uncertainties in isoprene emissions are not very important for the evaluation of long‐term (6 monthly) ozone scenarios in Europe, especially with regard to the relative merit of NOx versus VOC control. To explain these results, we have analyzed the sources and sinks of important radical species under different isoprene emission levels. It is shown that isoprene emissions are not sufficient to affect production or loss rates of key‐radical species significantly. The main effect of isoprene is to depress OH levels in isoprene‐rich areas, thereby reducing somewhat the share of ozone production possible from anthropogenic VOC. However, in such areas it is NOx emissions which are limiting as far as ozone production is concerned, so the policy advice from the model is quite robust against the isoprene uncertainties. The results obtained with respect to the effects of control measures on maximum ozone proved more sensitive to the assumed isoprene level. It is also shown that changes in isoprene emission level can alter the dates upon which ozone maxima occur, so predictions of the effects of man‐made control cannot rely upon a consideration of the chemistry occurring at the time of the base case maxima but rather require modeling over the summer period.
Hydration of black carbon
Authors: Chughtai A. R. , Brooks M. E. , Smith D. M.
Published: February 2004

Hydration studies of n‐hexane soot particles in the relative H2O pressure range 0.33–0.52 have revealed the nature of the processes between water molecules in the vapor phase and primary reaction sites at the particle surface. Initially, about 40% of the carbon‐oxygen functionalities (most likely the carboxylics) on freshly prepared soot reacts irreversibly with water vapor, while at P/Po ≥ 0.48, the adsorption follows the Dubinin‐Radushkevich equation. Determination of these parameters enables calculation of surface coverage at limiting adsorption and at the chemisorption limit for all materials studied. Limiting surface coverage of fresh soot is consistent with a 50% oxygen coverage determined earlier; it increases to about 100% for nitrated soot, which is the most extensively hydrated. Hydration has been shown to increase with soot aging, a phenomenon which has revealed an important role of physisorbed O2 in hydration. Trace‐metal incorporation at the 30–110 ppm level significantly increases particle hydration and demonstrates a role of metal centers in the process.
Implications of variations in the 15‐μm CO2 band cooling in the mesosphere and lower thermosphere associated with current climatologies of the atomic oxygen mixing ratio
Authors: Fomichev V. I. , Ward W. E. , McLandress C.
Published: February 2004

Higher values for the deactivation rate constant, kO, for collisions CO2(0110)‐O have gained acceptance recently. As a result, in the mesosphere and lower thermosphere, the latitude and height structure of the CO2 cooling is significantly modified, and the sensitivity of this cooling to variations in the atomic oxygen mixing ratio is increased. The magnitude of these effects depends on the value of kO chosen. Results are presented which illustrate the tendencies in the structure of the CO2 cooling as the rate constant is varied, so that its impact on atmospheric modeling may be discerned and possible constraints investigated. The latitudinal variability of the sensitivity of the cooling rate to variations in atomic oxygen is also examined. The latitudinal variation in heating rate for current climatological models of atomic oxygen, associated with the new rate constants, has a small but non negligible effect on the large‐scale circulation. Latitudinal variations in the oxygen mixing ratio result in changes in the residual circulation by about 20% relative to calculations with a single vertical profile of the atomic oxygen mixing ratio. Use of the larger rate constants does not result in significant changes to the latitudinal gradients in the temperature field and hence to the zonal winds. The sensitivity of the local heating rate to variations in the atomic oxygen mixing ratio shows a strong latitudinal variation. The sensitivity is greatest over the summer pole and least over the winter pole. The summer pole is the region most likely to exhibit the constituent‐driven convective processes mentioned by Ward and Fomichev (1993).
A multielement tracer technique for the determination of SO2 oxidation in clouds
Authors: Burkhard E. G. , Ghauri Badar M. , Dutkiewicz Vincent A. , Husain Liaquat
Published: February 2004

A technique was developed in this laboratory which uses similarities in the physical and chemical properties of SO4 and Se aerosols to quantitatively resolve SO4 in cloud water derived from the gas and aqueous phase oxidation of SO2. We report here the extension of the technique to include As and Sb as tracers and present experimental data to verify assumptions in our earlier studies regarding the sampling of precloud aerosols. In situ SO4 production in clouds [(SO4in)] is given by [SO4in] = [(SO4/M) cw ‐ α/(β,δ,τ) (SO4/M)aa] (M)cw where M represents Se, As, or Sb; α,β, δ and τ are the scavenging efficiencies of SO4, Se, As, and Sb aerosols, respectively; and cw and aa represent cloud water and ambient precloud aerosols. Field data from three cloud systems are presented, which show that δ/β = 0.92 ± 0.12 and τ/β; = 0.95 ± 0.13. Therefore within experimental uncertainties, the scavenging efficiencies of As and Sb are determined to be equal to that of Se. Results of in‐cloud oxidation determined in three clouds using Se, As, and Sb are in excellent agreement. Regression analysis of SO4in by As and Se had a slope of 1.02 ± 0.05 (r=0.85). Similarly for Sb and Se the slope was 1.06 ± 0.05 (r=0.85).
Comparison of atmospheric correction models for thermal bands of the advanced very high resolution radiometer over FIFE
Authors: Kalluri S. N. V. , Dubayah R. O.
Published: February 2004

Using data from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), land surface temperature (LST) measurements from channels 4 and 5 of the advanced very high resolution radiometer (AVHRR) on NOAA 9 were corrected for atmospheric effects using five different algorithms on three days in 1987. The performances of three widely used algorithms were compared with two other correction schemes that use coincident radiosonde data. The radiosonde measurements were used (1) to derive local split window coefficients and (2) to derive linear coefficients for atmospheric correction. Each model's performance was assessed by comparing the corrected LSTs with ground measurements made using infrared thermometers. If the difference between the two measurements was within ±3°C, then the correction was considered satisfactory. The three general methods that did not use any radiosonde data failed to meet the ±3°C criterion on any of the days. Of the two techniques which used coincident radiosonde data, the split window method passed the ±3°C criterion on two days, while the linear method passed only on one day. All five techniques overestimated the LSTs in comparison with ground data. While the use of coincident radiosonde data did provide more accurate retrievals relative to the three generalized methods, the improvement is somewhat unconvincing when compared to uncorrected AVHRR channel 4 temperatures, which were much closer to ground truth than any of the algorithms on two of the three days. In addition, we performed a linear correction using the standard midlatitude summer water vapor and temperature profiles but scaled so that the total water vapor amount matched that derived from the radiosonde data. In this case, our results were significantly better with estimates on all three days within ±1.4°C. Although our results using the other methods are in reasonable agreement with ground truth, our failure to meet the accuracy criterion is perplexing, and while its ultimate causes are unknown, possible explanations are provided.
Sulfate, nitrate, methanesulfonate, chloride, ammonium, and sodium measurements from ship, island, and aircraft during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol Gas Exchange
Authors: Huebert Barry J. , Zhuang Liangzhong , Howell Steven , Noone Kevin , Noone Birgitta
Published: February 2004

We measured aerosol methanesulfonic acid (MSA), Cl−, NO3−, SO4=, Na+, and NH4+ concentrations and size distributions and gaseous ammonia and nitric acid concentrations from Santa Maria, Azores during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in June 1992. We also sampled some of these species in the free troposphere and marine boundary layer (MBL) from the National Center for Atmospheric Research's (NCAR's) Electra aircraft and at the surface from the R/V Oceanus. In relatively clean Atlantic marine air masses the mean (and standard error of the mean) observed MSA concentrations (27 ± 2 parts per trillion molar mixing ratio, ppt) were smaller than in continental polluted air masses (36 ± 6 ppt), reflecting either longer aerosol lifetimes in air with higher cloud condensation nuclei (CCN) concentrations or more active photochemical production in polluted air. Mean NH4+/non‐sea‐salt (nss) SO4= molar ratios in marine and continental air masses were 0.65 ± 0.05 and 1.3 ± 0.2, respectively, indicating that continental sulfate was neutralized by ammonia to a greater extent than marine sulfate was. Most of the NH4+ and nss SO4= was contained in submicrometer modes; Na+, Cl−, and NO3− were in supermicron modes; and MSA showed bimodal behavior, with major and minor peaks at 0.3–0.4 μm and 1.5 μm, respectively. The molar ratio NH4+/nss SO4= relative to size confirms that most ammonia vapor condensed on submicron nss SO4=. The average dry deposition fluxes for aerosol nss SO4=, MSA, NH4+ and NO3− during ASTEX/MAGE were 1.49, 0.09, 0.18, and 3.25 μmol m−2 d−1, respectively.
Source compositions of trace gases released during African savanna fires
Authors: Cofer Wesley R. , Levine Joel S. , Winstead Edward L. , Cahoon Donald R. , Sebacher Daniel I. , Pinto Joseph P. , Stocks Brian J.
Published: February 2004

Measurements of biomass burn‐produced trace gases were made using low‐altitude helicopter penetrations of smoke plumes above burning African savanna during the Southern African Fire‐Atmosphere Research Initiative (SAFARI‐92). Smoke from two large prescribed fires conducted in the Kruger National Park, South Africa, on September 18 and 24, 1992, was sampled at altitudes ranging from 20 to 100 m above ground level during flaming and smoldering phases of combustion. Carbon dioxide (CO2) normalized emission ratios (dX/dCO2(vol/vol), whereXdenotes a trace gas) for carbon monoxide (CO), hydrogen (H2), methane (CH4), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N2O) were determined. The emission ratios were used in conjunction with fuel consumption estimates to calculate emission factors (grams of product per gram of fuel) for these gases. Emission factors for CO2, CO, CH4, and N2O of 1.61, 0.055, 0.003, and 1.6 × 10−4g/g fuel, respectively, were determined. The fires advanced rapidly through the savanna (primarily grass) fuels with minimal amounts of smoldering combustion. The relatively low emission ratios determined for these fires indicated excellent combustion efficiency. About 93% of the carbon released into the atmosphere as a result of these fires was in the form of CO2.
Formation and transport of 2‐nitrofluoranthene and 2‐nitropyrene of photochemical origin in the troposphere
Authors: Ciccioli Paolo , Cecinato Angelo , Brancaleoni Enzo , Frattoni Massimiliano , Zacchei Paolo , Miguel Antonio H. , de Castro Vasconcellos Perola
Published: February 2004

The occurrence of 2‐nitrofluoranthene and 2‐nitropyrene in particulate matter collected in urban, suburban, forest, and remote areas located in Europe, America, Asia, and Antarctica was investigated. The results obtained confirm the photochemical origin of these components by gas phase reactions with OH radicals and their ubiquitous occurrence in the troposphere. An important role in their formation and dispersion seems to be played by carbon particles.
Empirical orthogonal function analysis of humidity profiles over the Indian Ocean and an assessment of their retrievability using satellite microwave radiometry
Authors: Basu Sujit , Gairola R. M. , Kishtawal C. M. , Pandey P. C.
Published: February 2004

The paper examines the variability of vertical humidity profiles over the Indian oceanic region using a set of 1200 radiosonde observations spanning 10 years (1982–1991). The examination is based upon the method of empirical orthogonal function (EOF) analysis. The first EOF explains 61% of the total variance and the first three EOFs together account for 85% of the total variability. The first principal component is almost perfectly correlated with the total precipitable water (TPW) and the second one is well correlated with the ratio of boundary layer moisture and TPW. This fact and an inequality derived from the analysis of the variances of individual terms of the EOF expansion of specific humidity are utilised to establish an algorithm for retrieving humidity profile from satellite microwave measurement of TPW over the region of study. Power of the retrieval technique is demonstrated using 127 independent radiosonde measurements and by plotting the profiles of rms error and bias. The method is found to be distinctly superior compared to a power‐law retrieval. A few examples of profile retrieval from satellite measurements of TPW have been checked against colocated radiosonde measurements. Some examples of retrieval show that the method is uniquely able to capture the humidity variability in the boundary layer, particularly the high moisture loading in the monsoon season.
Doubled CO2 experiments with the Global Change Research Center two‐dimensional statistical dynamical climate model
Authors: MacKay R. M. , Khalil M. A. K.
Published: February 2004

The zonally averaged response of the Global Change Research Center two‐dimensional (2‐D) statistical dynamical climate model (GCRC 2‐D SDCM) to a doubling of atmospheric carbon dioxide (350 parts per million by volume (ppmv) to 700 ppmv) is reported. The model solves the two‐dimensional primitive equations in finite difference form (mass continuity, Newton's second law, and the first law of thermodynamics) for the prognostic variables: zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p=ρRT, and an assumed hydrostatic atmosphere, Delta;p=−ρgΔz, are used to diagnostically calculate the zonal mean pressure and vertical velocity for each grid node, and the moisture balance equation is used to estimate the precipitation rate. The model includes seasonal variations in solar intensity, including the effects of eccentricity, and has observed land and ocean fractions set for each zone. Seasonally varying values of cloud amounts, relative humidity profiles, ozone, and sea ice are all prescribed in the model. Equator to pole ocean heat transport is simulated in the model by turbulent diffusion. The change in global mean annual surface air temperature due to a doubling of atmospheric CO2 in the 2‐D model is 1.61 K, which is close to that simulated by the one‐dimensional (1‐D) radiative convective model (RCM) which is at the heart of the 2‐D model radiation code (1.67 K for the moist adiabatic lapse rate assumption in 1‐D RCM). We find that the change in temperature structure of the model atmosphere has many of the characteristics common to General Circulation Models, including amplified warming at the poles and the upper tropical troposphere, and stratospheric cooling. Because of the potential importance of atmospheric circulation feedbacks on climate change, we have also investigated the response of the zonal wind field to a doubling of CO2 and have found distinct patterns of change that are related to the change in temperature structure. In addition, we find that both the global mean kinetic energy and simulated Hadley circulation increase when CO2 is doubled. The increase in mean kinetic energy is a result of the increase in upper level meridional temperature gradients simulated by the model. It is stressed that changes in atmospheric dynamics associated with increased carbon dioxide may also be very important to the final steady state distribution of such greenhouse gases as ozone and water vapor. Hence further research in this regard is warranted.
Modeling of land surface evaporation by four schemes and comparison with FIFE observations
Authors: Chen Fei , Mitchell Kenneth , Schaake John , Xue Yongkang , Pan Hua‐Lu , Koren Victor , Duan Qing Yun , Ek Michael , Betts Alan
Published: February 2004

We tested four land surface parameterization schemes against long‐term (5 months) area‐averaged observations over the 15 km × 15 km First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) area. This approach proved to be very beneficial to understanding the performance and limitations of different land surface models. These four surface models, embodying different complexities of the evaporation/hydrology treatment, included the traditional simple bucket model, the simple water balance (SWB) model, the Oregon State University (OSU) model, and the simplified Simple Biosphere (SSiB) model. The bucket model overestimated the evaporation during wet periods, and this resulted in unrealistically large negative sensible heat fluxes. The SWB model, despite its simple evaporation formulation, simulated well the evaporation during wet periods, but it tended to underestimate the evaporation during dry periods. Overall, the OSU model ably simulated the observed seasonal and diurnal variation in evaporation, soil moisture, sensible heat flux, and surface skin temperature. The more complex SSiB model performed similarly to the OSU model. A range of sensitivity experiments showed that some complexity in the canopy resistance scheme is important in reducing both the overestimation of evaporation during wet periods and underestimation during dry periods. Properly parameterizing not only the effect of soil moisture stress but also other canopy resistance factors, such as the vapor pressure deficit stress, is critical for canopy resistance evaluation. An overly simple canopy resistance that includes only soil moisture stress is unable to simulate observed surface evaporation during dry periods. Given a modestly comprehensive time‐dependent canopy resistance treatment, a rather simple surface model such as the OSU model can provide good area‐averaged surface heat fluxes for mesoscale atmospheric models.
Black carbon formation by savanna fires: Measurements and implications for the global carbon cycle
Authors: Kuhlbusch T. A. J. , Andreae M. O. , Cachier H. , Goldammer J. G. , Lacaux J.‐P. , Shea R. , Crutzen P. J.
Published: February 2004

During a field study in southern Africa (Southern African Fire‐Atmosphere Research Initiative (SAFARI‐92)), black carbon formation was quantified in the residues of savanna fires. The volatilization ratios of C, H, N, and S were determined by measuring their contents in the fuel and residue loads on six experimental sites. The volatilization of sulfur (86 ± 8%) was significantly higher than previously reported. Volatilization of H, N, and S was significantly correlated with that of carbon, enabling us to estimate their volatilization during savanna fires by extrapolation from those of carbon. By partitioning the residues in various fractions (unburned, partially burned, and ash), a strong correlation between the H/C ratio in the residue and the formation of black carbon was obtained. The ratio of carbon contained in ash to carbon contained in the unburned and partially burned fraction is introduced as an indicator of the degree of charring. As nitrogen was enriched in the residue, especially in the ash fraction of >0.63 mm, this indicator may be useful for an assessment of nutrient cycling. We show that the formation of black carbon is dependent on the volatilization of carbon as well as the degree of charring. The ratio of black carbon produced to the carbon exposed to the fire in this field study (0.6–1.5%) was somewhat lower than in experimental fires under laboratory conditions (1.0–1.8%) which may be due to less complete combustion. The average ratio of black carbon in the residue to carbon emitted as CO2ranged from 0.7 to 2.0%. Using these ratios together with various estimates of carbon exposed or emitted by savanna fires, the worldwide black carbon formation was estimated to be 10–26 Tg C yr−1with more than 90% of the black carbon remaining on the ground. The formation of this black carbon is a net sink of biospheric carbon and thus of atmospheric CO2as well as a source of O2.
Retrieval of 91 and 150 GHz Earth surface emissivities
Authors: Felde Gerald W. , Pickle John D.
Published: February 2004

Surface emissivities at 91 and 150 GHz are retrieved using a microwave radiative transfer model and the atmospheric profiles and brightness temperatures (TBs) for the cloud‐free cases from a global data set of collocated SSM/T‐2 and radiosonde measurements. The retrieved emissivity values for various Earth surface types are consistent with those from other studies. The retrieval scheme displays limited sensitivity to uncertainty in the input data and the retrieved values are found to have good reproducibility for a given region. The possible use of special sensor microwave/imager (SSM/I) TB measurements for estimation of 91‐ and 150‐GHz emissivities is explored using a subset of the retrieved emissivity cases which was augmented with SSM/I data. It is demonstrated that SSM/I TBs are potentially useful for making accurate estimates of surface emissivities at 91 and 150 GHz. This should lead to improved SSM/T‐2 lower tropospheric water vapor profile retrievals.
Dry deposition parameterization in a chemistry general circulation model and its influence on the distribution of reactive trace gases
Authors: Ganzeveld Laurens , Lelieveld Jos
Published: February 2004

A dry deposition scheme has been developed for the chemistry general circulation model to improve the description of the removal of chemically reactive trace gases at the earth's surface. The chemistry scheme simulates background CH4‐CO‐NOx‐ HOx photochemistry and calculates concentrations of, for example, HNO3, NOx, and O3. A resistance analog is used to parameterize the dry deposition velocity for these gases. The aerodynamic resistance is calculated from the model boundary layer stability, wind speed, and surface roughness, and a quasi‐laminar boundary layer resistance is incorporated. The stomatal resistance is explicitly calculated and combined with representative cuticle and mesophyll resistances for each trace gas. The new scheme contributes to internal consistency in the model, in particular with respect to diurnal and seasonal cycles in both the chemistry and the planetary boundary layer processes and surface characteristics that control dry deposition. Evaluation of the model indicates satisfactory agreement between calculated and observed deposition velocities. Comparison of the results with model simulations in which the deposition velocity was kept constant indicates significant relative differences in deposition fluxes and surface layer trace gas concentrations up to about ±35%. Shortcomings are discussed, for example, violation of the constant flux approach for the surface layer, the lacking canopy description, and effects of surface water layers.
The 1991 PEACAMPOT aircraft observation of ozone, NOx, and SO2 over the East China Sea, the Yellow Sea, and the Sea of Japan
Authors: Hatakeyama Shiro , Murano Kentaro , Bandow Hiroshi , Sakamaki Fumio , Yamato Masahiko , Tanaka Shigeru , Akimoto Hajime
Published: February 2004

Atmospheric pollutants over northwest Pacific Rim region (the East China Sea, the Yellow Sea, and the Sea of Japan) were observed from an airplane from October 5 to October 11, 1991, as one of the first intensive field studies of the International Global Atmospheric Chemistry/East Asian North Pacific Regional Experiment (IGAC/APARE). Ozone, NOx, Aerosols, SO2, hydrocarbons, CO, and aldehydes were measured. In this paper, the results of this experiment for ozone, NOx and SO2 measurements are described. Ozone and NOx were negatively correlated, which is contrary to the normal correlation observed in background areas. We believe that this is due to the large contribution of the upper atmosphere in most cases. The vertical distribution of SO2 concentrations indicates the impact of the Asian continental air mass.
Enhanced formation and development of sulfate particles due to marine boundary layer circulation
Authors: Kerminen Veli‐Matti , Wexler Anthony S.
Published: February 2004

Production and the subsequent development of sulfur‐derived particles in the marine boundary layer have been of great interest due to their potential role in modifying the radiative properties of marine stratiform clouds. In this work these phenomena were studied using a dynamic air parcel model, with the emphasis placed on examining how the boundary layer dynamics affects the system. Our simulations suggest that a homogeneous or steady boundary layer assumption may lead to a considerable underestimation of the number of nuclei formed. Further, we showed that if the observed particle size distributions and nonsea‐salt fraction of cloud condensation nuclei (CCN) production are to be explained by in situ particle production and growth, the sulfuric acid accommodation coefficient onto nuclei must be greater than 0.1 under conditions typical for clean marine areas. These high values require either a sulfuric acid vapor source in addition to SO2(g) oxidation or a H2SO4(g) accommodation coefficient onto more aged particles which is less than that onto nuclei. Both these options were tested and can be considered viable based on our present understanding of the marine environment. Finally, we showed that a nighttime interaction of the boundary layer air with clouds does not significantly affect nuclei formation or growth, but may lead to significant scavenging of fresh nuclei if their sulfuric acid accommodation coefficient is small. Cloud interactions during photochemically active periods may completely inhibit new particle production, and the growth of preexisting nuclei is likely to be significantly decelerated.
Linkage of scaling and thermodynamic parameters of rainfall: Results from midlatitude mesoscale convective systems
Authors: Perica S. , Foufoula‐Georgiou E.
Published: February 2004

In this paper we explore the possibility of establishing predictive relationships between statistical characteristics of rainfall at the mesoscale (approximately 102 to 104 km2) and representative meteorological parameters of the storm environment. To increase the usefulness of these relationships and, in particular, to explore their use in subgrid‐scale rainfall parameterization, special attention is given to statistical characteristics of rainfall that are scale invariant, i.e., are constant at least within a significant range of scales. The main contributions of this paper are the following: (1) we establish the presence of statistical (simple) scaling in “standardized rainfall fluctuations” (derived from rainfall intensities via an orthogonal wavelet transform and normalization by local means) and (2) we establish empirical connections between statistical and physical storm characteristics by quantifying relations between the scaling parameters and kinematic and thermodynamic indices of the prestorm environment. The data used for this analysis are rainfall events and corresponding soundings observed during the PRE‐STORM experiment (May and June 1985) over Oklahoma and Kansas. The developed relationships are applicable to midlatitude mesoscale convective systems, which are the major rainfall producers over most of the Global Energy and Water Cycle Experiment (GEWEX) Continental International Project (GCIP) region, and are envisioned to play a key role in disaggregating rainfall (predicted by mesoscale numerical models) to subgrid scales for runoff prediction and other hydrologic applications.
Black carbon measurements using an integrating sphere
Authors: Hitzenberger R. , Dusek U. , Berner A.
Published: February 2004

An integrating sphere was used to determine the black carbon (BC) content of aerosol filter samples dissolved in chloroform (method originally described by Heintzenberg [1982]). The specific absorption coefficient Ba (equal to absorption per mass) of the samples was also measured using the sphere as an integrating detector for transmitted light. Comparing the Ba of ambient samples taken in Vienna, Austria, to the BC concentrations measured on the dissolved filters, a value of approximately 6 m2/g was found to be a reasonable value for the Ba of the black carbon found at the site. The size dependence of Ba of a nebulized suspension of soot was measured using a rotating impactor, and a reasonable agreement between measured and calculated values was found.
Horizontal and vertical structure of observed tropospheric equatorial Rossby waves
Authors: Kiladis George N. , Wheeler Matthew
Published: February 2004

Equatorial Rossby (ER) waves are identified in an 8‐year data set of National Meteorological Center operational analyses. The westward moving waves have symmetric circulations about the equator and eastward energy dispersion, with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10°–15° off the equator. They have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones. The circulations thus possess many of the features of the equatorially trapped n = 1 Rossby modes derived by Matsuno [1966]. They are generally around zonal planetary wavenumber 6 scale and have a deep, nearly equivalent barotropic structure up to 100 mbar. This is in contrast with the Madden‐Julian Oscillation and mixed Rossby gravity waves, which generally have a first baroclinic mode vertical structure. During the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) and in other years, westward propagating ER disturbances along the equator are observed by using 6‐ to 30‐day filtered circulation data at 850 mbar. Zonal wind anomalies at 850 mbar are preferentially associated with like‐signed anomalies in a deep layer at this frequency, as was observed during COARE. The ER waves are most common during northern winter in the central Pacific, although they can be detected sporadically over the other ocean basins and in other seasons as well. One source for the equatorial Rossby waves appears to be upper level extratropical Rossby wave activity propagating into the eastern Pacific, although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent. We cite evidence that propagation of ER wave activity from the central into the western Pacific is related to occurrences of westerly wind bursts.
Application of a macroscale hydrologic model to estimate the water balance of the Arkansas‐Red River Basin
Authors: Abdulla Fayez A. , Lettenmaier Dennis P. , Wood Eric F. , Smith James A.
Published: February 2004

An approach for estimation of the parameters of a macroscale land surface hydrology model is illustrated for the Global and Water Cycle Experiment (GEWEX) Continental Scale International Project (GCIP) large‐scale area southwest (LSA‐SW) which essentially comprises the Arkansas‐Red River basin. The macroscale land surface hydrology model parameters were estimated for 44 catchments within LSA‐SW with areas ranging from 180 to 7100 km2 using an automated search procedure. The catchment parameters were then linearly interpolated and overlaid on a one degree grid, which was used to represent the drainage network. The macroscale grid network model was run off‐line at a daily time step, forced by gridded station precipitation and potential evapotranspiration. The model‐generated long‐term mean streamflows were compared with observations (corrected for management effects such as reservoir storage and diversions) and were found to agree to within one percent for the Arkansas River and about two percent for the Red River. For both rivers, the model underestimates the seasonal peak streamflow in late spring, and overestimates the late summer and early fall minimum. Model‐derived evapotranspiration, spatially averaged over the entire Arkansas‐Red basin, was compared to evapotranspiration derived from an atmospheric moisture budget of the Arkansas‐Red River basin. On an average annual basis, for the period 1973–1986, the two agree to within one percent. The mean seasonal cycles for the two estimates agree quite closely from late winter to midsummer. However, the hydrologic model estimates less evapotranspiration in the fall, and more in midwinter, than the atmospheric budget.
The boreal forest and the polar front
Authors: Pielke Roger A. , Vidale Pier Luigi
Published: February 2004

The analysis presented in this paper suggests that the larger heating over the boreal forest in the spring and summer, as contrasted with weaker heating over the adjacent tundra, results in a preferred position of the polar front along the northern edge of the boreal forest. This positioning is well documented in the literature (see, for example, Bryson, 1966; Barry and Hare, 1974; Kreps and Barry, 1970). This heating results from the lower albedo of the boreal forest which is not compensated by an increase in transpiration, even with the larger leaf area index of the forest. The warmer temperatures are mixed upward by the deep boundary layer over the forest and mesoscale circulations which result from the patchiness of heating associated with the heterogeneous landscapes of the forest. Thus in contrast to previous assumptions in which the arctic front position in the summer determines the northern limit of the boreal tree line, our study suggests the boreal forest itself significantly influences the preferred position of the front. This conclusion reinforces the findings of Bonan et al. (1992) and Foley et al. (1994) on the important role of boreal forest‐tundra interactions with climate.
Hydrocarbon and halocarbon measurements as photochemical and dynamical indicators of atmospheric hydroxyl, atomic chlorine, and vertical mixing obtained during Lagrangian flights
Authors: Wingenter Oliver W. , Kubo Michael K. , Blake Nicola J. , Smith Tyrrel W. , Blake Donald R. , Rowland F. Sherwood
Published: February 2004

Nonmethane hydrocarbons and halocarbons were measured during two Lagrangian experiments conducted in the lower troposphere of the North Atlantic as part of the June 1992, Atlantic Stratosphere Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) expedition. The first experiment was performed in very clean marine air. Meteorological observations indicate that the height of the marine boundary layer rose rapidly, entraining free tropospheric air. However, the free tropospheric and marine boundary layer halocarbon concentrations were too similar to allow this entrainment to be quantified by these measurements. The second Lagrangian experiment took place along the concentration gradient of an aged continental air mass advecting from Europe. The trace gas measurements confirm that the National Center for Atmospheric Research (NCAR) Electra aircraft successfully intercepted the same air mass on consecutive days. Two layers, a surface layer and a mixed layer with chemically distinct compositions, were present within the marine boundary layer. The composition of the free troposphere was very different from that of the mixed layer, making entrainment from the free troposphere evident. Concentrations of the nonmethane hydrocarbons in the Lagrangian surface layer were observed to become depleted relative to the longer‐lived tetrachloroethene. A best fit to the observations was calculated using various combinations of the three parameters, loss by reaction with hydroxyl, loss by reaction with chlorine, and/or dilution from the mixed layer. These calculations provided estimated average concentrations in the surface layer for a 5‐hour period from dawn to 11 UT of 0.3 ± 0.5 × 106 molecules cm−3 for HO, and 3.3 ± 1.1 × 104 molecules cm−3 for Cl. Noontime concentration estimates were 2.6 ± 0.7 × 106 molecules cm−3 for HO and 6.5 ± 1.4 × 104 molecules cm−3 for Cl.
Hydrocarbon measurements in the southeastern United States: The Rural Oxidants in the Southern Environment (ROSE) Program 1990
Authors: Goldan Paul D. , Kuster William C. , Fehsenfeld Fred C. , Montzka Stephen A.
Published: February 2004

An automated gas Chromatographic system was employed at a rural site in western central Alabama to measure atmospheric hydrocarbons and oxygenated hydrocarbons (oxy‐hydrocarbons) on an hourly basis from June 8 to July 19, 1990. The location, which was a designated site for the Southern Oxidant Study (SOS), was instrumented for a wide variety of measurements allowing the hydrocarbon and oxy‐hydrocarbon measurements to be interpreted both in terms of meteorological data and as part of a large suite of gas phase measurements. Although the site is situated in a Loblolly pine plantation, isoprene was observed to be the dominant hydrocarbon during the daytime with afternoon maxima of about 7 parts per billion by volume (ppbv). Decrease of isoprene after sunset was too rapid to be accounted for solely on the basis of gas phase chemistry. During the nighttime, α‐pinene and β‐pinene were the dominant hydrocarbons of natural origin. The ratio of α‐pinene to β‐pinene showed a well‐defined diurnal pattern, decreasing by more than 30% during the night; a decrease that could be understood on the basis of local gas phase chemistry. Oxy‐hydrocarbons, dominated by methanol and acetone, were the most abundant compounds observed. On a carbon atom basis, the oxy‐hydrocarbons contributed about 46% of the measured atmospheric burden during the daytime and about 40% at night. The similarity of the observed diurnal methanol variation to that of isoprene and subsequent measurements [McDonald and Fall, 1993] indicate that much of the observed methanol was of local biogenic origin. Correlation of acetone with methanol suggests that it, also, has a significant biogenic source. In spite of the site's rural location, anthropogenic hydrocarbons constituted, on a carbon atom basis, about 21% of the hydrocarbon burden measured during the daytime and about 55% at night. Significant diurnal variations of the anthropogenic hydrocarbons, with increases at night, appeared to be driven by the frequent formation of a shallow nocturnal boundary layer.
A comparison of Sun photometer derivations of total column water vapor and ozone to standard measures of same at the Southern Great Plains Atmospheric Radiation Measurement site
Authors: Michalsky J. J. , Liljegren J. C. , Harrison L. C.
Published: February 2004

Total column water vapor measurements made over a 1‐year period by collocated instruments at the Southern Great Plains Atmospheric Radiation Measurement program site in northern Oklahoma are compared. Microwave radiometer measurements were validated in an earlier program with extensive comparisons to balloon sonde measurements. Sun photometry, using the multifilter rotating shadowband radiometer (MFRSR), was the second technique used to derive water vapor using the 940‐nm water band when no clouds were between the radiometer and the sun. Bruegge et al.'s implementation of Reagan et al.'s modified Langley technique was applied in this case. This approach is noteworthy in that it does not rely on a comparison to a standard for calibration. The comparison of 101 one‐half‐hour to two‐hour averages produced a root‐mean‐square difference of 0.18 cm compared to a mean value of 1.49 cm, or about 12%, with the MFRSR showing an overall bias of +0.03 cm relative to the microwave radiometer data. This is a somewhat higher rms error than other results using the modified Langley technique, but the comparison was made over the entire range of water vapor columns experienced in a year of observations. As a by‐product of the water vapor derivation procedure for the MFRSR, ozone column abundance was estimated. Seasonally averaged, these data compare favorably with Dobson measurements from Nashville, Tennessee, which is near the same latitude. A more definitive conclusion regarding the Sun photometer ozone derivation technique requires colocated ozone measurements using an accepted standard approach, however, the technique appears to provide a useful ozone estimate for correcting aerosol optical depth derivations.
Ratios of reactive nitrogen species over the Pacific during PEM‐West A
Authors: Koike M. , Kondo Y. , Kawakami S. , Singh H. B. , Ziereis H. , Merrill J. T.
Published: February 2004

Measurements of total reactive odd nitrogen (NOy) and known individual odd nitrogen species were made over the Pacific Ocean in September and October 1991 during the NASA Global Tropospheric Experiment, Pacific Exploratory Mission‐West A (GTE/PEM‐West A). The ratios between NOx (NO + NO2) calculated from observed NO assuming photochemical equilibrium ((NOx)mc), peroxyacetyl nitrate (PAN), and NOy have been investigated for these data. The mixing ratios of (NOx)mc, PAN, and NOy in the lower and middle troposphere generally decreased with the air mass age, which has been defined by the propane/ethane ratio (C3H8/C2H6). The (NOx)mc/NOy ratios in the continental air showed a C‐shaped vertical profile and median values were 0.27, 0.11, and 0.20 in the lower, middle, and upper troposphere, respectively. In the maritime and tropical air the (NOx)mc/NOy ratios generally increased with altitude and were about 0.1 and 0.15 in the lower and upper troposphere, respectively. In the middle troposphere the (NOx)mc/NOy ratios were similar in continental, maritime, and tropical air. These results are consistent with the fact that the (NOx)mc/NOy ratio did not decrease with the air mass age in the middle troposphere, suggesting the existence of NOx sources in the free troposphere. The PAN/NOy ratios in the continental air were about 0.3 at all altitudes. In maritime and tropical air the PAN/NOy ratio increased sharply at altitudes between 3 and 5 km with values of about 0.03 below 3 km and between 0.1 and 0.2 in the middle and upper troposphere. The PAN/NOy ratio generally decreased with the air mass age in the middle troposphere. In spite of a longer photochemical lifetime of PAN than NOx the PAN/(NOx)mc ratio also generally decreased with air mass age. These observations indicate that the reactive nitrogen ratios in the continental air mass are influenced by anthropogenic emissions at all altitudes, although relative contributions from various NOx sources in the upper troposphere are still poorly understood. Some influence from the continental air can be seen in the anthropogenic origin species in the maritime air mass when compared with the tropical air mass (Kondo et al., this issue). Similar (NOx)mc/NOy ratios, however, were generally found between the maritime and tropical air masses and a difference was only seen in the slightly higher PAN/NOy ratios in the maritime middle tropospheric air. The high‐latitude air is characterized by low (NOx)mc/NOy ratios and high PAN/(NOx)mc ratios, probably due to the low atmospheric temperatures.
Properties of M components from currents measured at triggered lightning channel base
Authors: Thottappillil Rajeev , Goldberg Jon D. , Rakov Vladimir A. , Uman Martin A. , Fisher Richard J. , Schnetzer George H.
Published: February 2004

Channel base currents from triggered lightning were measured at the NASA Kennedy Space Center, Florida, during summer 1990 and at Fort McClellan, Alabama, during summer 1991. An analysis of the return stroke data and overall continuing current data has been published by Fisher et al. [1993]. Here an analysis is given of the impulsive processes, called M components, that occur during the continuing current following return strokes. The 14 flashes analyzed contain 37 leader‐return stroke sequences and 158 M components, both processes lowering negative charge from cloud to ground. Statistics are presented for the following M current pulse parameters: magnitude, rise time, duration, half‐peak width, preceding continuing current level, M interval, elapsed time since the return stroke, and charge transferred by the M current pulse. A typical M component in triggered lightning is characterized by a more or less symmetrical current pulse having an amplitude of 100–200 A (2 orders of magnitude lower than that for a typical return stroke [Fisher et al., 1993]), a 10–90% rise time of 300–500 μs (3 orders of magnitude larger than that for a typical return stroke [Fisher et al., 1993]), and a charge transfer to ground of the order of 0.1 to 0.2 C (1 order of magnitude smaller than that for a typical subsequent return stroke pulse [Berger et al., 1975]). About one third of M components transferred charge greater than the minimum charge reported by Berger et al. [1975] for subsequent leader‐return stroke sequences. No correlation was found between either the M charge or the magnitude of the M component current (the two are moderately correlated) and any other parameter considered. M current pulses occurring soon after the return stroke tend to have shorter rise times, shorter durations, and shorter M intervals than those which occur later. M current pulses were observed to be superimposed on continuing currents greater than 30 A or so, with one exception out of 140 cases, wherein the continuing current level was measured to be about 20 A. The first M component virtually always (one exception out of 34 cases) occurred within 4 ms of the return stroke. This relatively short separation time between return stroke and the first M component, coupled with the observation of Fisher et al. [1993] that continuing currents lasting longer than 10 ms never occur without M current pulses, implies that the M component is a necessary feature of the continuing current mode of charge transfer to ground.
PEM‐West A: Meteorological overview
Authors: Bachmeier A. Scott , Newell Reginald E. , Shipham Mark C. , Zhu Yong , Blake Donald R. , Browell Edward V.
Published: February 2004

Phase A of the NASA Pacific Exploratory Mission in the western North Pacific (PEM‐West A) region was conducted during September–October 1991. The background meteorology of eastern Asia and the western North Pacific region during the PEM‐West A study is described. Mean large‐scale flow patterns are discussed along with transient synoptic scale features (e.g., midlatitude cyclones, anticyclones, and frontal systems) responsible for long‐range transport of trace species over the study region. Synoptic summaries are given for each of the 18 data flights, together with selected examples of meteorological processes that gave rise to some of the changes observed in the measured trace gases. Examples of large‐scale ozone features observed above and below the DC‐8 flight altitude by an onboard lidar system are also related to meteorological processes such as stratospheric‐tropospheric exchange and upward transport of air from the boundary layer.