bluuebunny/crossref_metadata_2025 huggingface dataset:
The sensitivity of subannual and intraseasonal tropical variability to model ocean mixed layer depth
Authors: Watterson I. G.
Published: October 2002

The influence of air‐sea interaction on subannual and intraseasonal tropical variability is explored through analysis of three long simulations of the Commonwealth Scientific and Industrial Research Organisation atmospheric general circulation model (GCM) with differing ocean specifications: a coupled ocean GCM, a simple 50‐m mixed layer model, or climatological sea surface temperatures (SST); together with 50‐year simulations with mixed layer depths of 10 m and 20 m. The analysis focuses initially on a signal similar to a Madden‐Julian Oscillation (MJO) contained in the first two empirical orthogonal functions (EOF) of monthly anomalies of tropical 807‐hPa winds in January in the coupled model. Time‐lag regression is used to demonstrate that these patterns propagate eastward, although at only half the speed of the MJO, and induce perturbations to the Australian monsoon. The specified SST model shows no such propagation. Similar results are then obtained using daily data filtered to retain subannual periods. The eastward propagation speed is faster in the shallower mixed layer cases, with the 10‐m case producing speeds close to observations. In the interactive models, surface energy fluxes force SST anomalies propagating ahead of the EOF convergence. These fluxes are largely consistent with evaporation perturbed by wind anomalies to the monsoon westerlies, augmented by solar radiation. The SST anomalies then further perturb the winds, as is confirmed by a separate SST perturbation experiment. From the examination of other seasons, it is seen that air‐sea interaction generally enhances the amplitude of the MJO‐like patterns. It also enhances their eastward propagation along westerly wind bands. Analysis of zonal wave number one winds confirms the strong sensitivity to mixed layer depth in the amplitude and period of the eastward propagating component, particularly during September through February. The results suggest that air‐sea interaction may be important to the MJO, provided that the SSTs are sufficiently responsive to the atmospheric patterns.
Snow megadunes in Antarctica: Sedimentary structure and genesis
Authors: Frezzotti M. , Gandolfi S. , Urbini S.
Published: October 2002

Megadune fields occupy large areas in the interior of the East Antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes. They therefore are important to surface mass balance and ice core interpretation. Field observations (GPS, GPR, and surface measurements) have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area, located 200 km east of Dome C. A combination of remote sensing analysis (using Landsat and satellite radar altimetry) and field measurements indicate that slope in the prevailing wind direction (SPWD) and climatic conditions play a crucial role in megadune genesis. The megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds. The megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation, ranging between 25% (leeward faces) to 120% (windward faces) of the accumulation in adjacent nonmegadune areas. Leeward faces are characterized by glazed, sastrugi‐free surfaces and extensive depth hoar formation. Windward faces are covered by large rough sastrugi up to 1.5 m in height.
Synoptic scale study of the Arctic polar vortex's influence on the middle atmosphere, 1, Observations
Authors: Gerrard Andrew J. , Kane Timothy J. , Thayer Jeffrey P. , Duck Thomas J. , Whiteway James A. , Fiedler Jens
Published: October 2002

We present nightly Rayleigh lidar temperature measurements of the high‐latitude middle atmosphere taken at three Arctic sites over similar time periods in midwinter. The four reported case studies depict changes in the thermal structure of the stratosphere and lower mesosphere over a period of days to weeks that can be attributed to movement and interaction of the polar vortex, the Aleutian High, and planetary waves as evidenced from the National Center for Environmental Prediction tropospheric and stratospheric analyses. In cases where substantial (i.e., large horizontal scale) movement of the vortex is observed, it is noted that regional middle atmospheric Arctic temperatures can change by tens of degrees. In other cases, we show that even very subtle (i.e., small horizontal scale) movement of the vortex system over similar timescales can result in notable temperature changes in the regional middle atmosphere. It appears that the observed events are dependant on the location, strength, and structure of the polar vortex and Aleutian High. All of these synoptic scale measurements indicate a change in the local dynamical structure of the middle atmosphere and are discussed in regards to this issue.
Determination of nucleation and growth rates from observation of a SO2 induced atmospheric nucleation event
Authors: Verheggen Bart , Mozurkewich Michael
Published: October 2002

A method to determine the particle nucleation rate directly from atmospheric measurements is presented. During the Southern Ontario Oxidant Study (SONTOS) field campaign in rural Ontario, Canada, particle size distributions and concentrations of a range of photochemical species were measured. On 25 August 1993, the size distribution showed a pronounced peak in the concentration of nucleation mode particles. This correlated with, but lagged behind, a peak in the SO2 concentration. The data imply that nucleation occurred aloft as an SO2 plume was entrained into the growing boundary layer. The particle growth rates were determined from the evolution of the measured particle size distributions, while accounting for coagulation and dilution. In principle, measurements of precursor species are not needed. However, in this case study, the ground‐based measurements did not reflect the aerosol concentrations in the plume aloft; as a result, extrapolation of the growth rate was necessary. This was accomplished by using a one‐dimensional model to calculate the gas phase sulfuric acid concentration. The particle growth rate due to condensation of H2SO4 was calculated and used to extrapolate the observed growth backward to obtain the time of formation. From the particle number in a certain size interval, suitably corrected for losses by coagulation and dilution, and the time interval in which they formed, the nucleation rate can be determined. We obtained nucleation rates of 5–40 cm−3 s−1 for sulfuric acid mixing ratios of 3–10 pptv. These nucleation rates are higher than predicted by classical binary nucleation theory for H2SO4 and H2O.
Atmosphere‐biosphere trace gas exchanges simulated with a single‐column model
Authors: Ganzeveld L. N. , Lelieveld J. , Dentener F. J. , Krol M. C. , Roelofs G.‐J.
Published: October 2002

The exchange of oxidized nitrogen species (NOx) between the biosphere and atmosphere is controlled by complex interactions between emissions, dry deposition, (photochemical) chemical transformations, and turbulent exchanges, all varying with height within the canopy. We have developed a multilayer atmosphere‐biosphere trace gas exchange model to study the role of canopy interactions in the net atmosphere‐biosphere NOx exchange flux on a global scale. We evaluate this model, implemented in a single‐column chemistry and meteorological model, for a selection of ecosystems by comparison with observations. The modeled and observed ozone and oxidized nitrogen concentrations and fluxes are generally in reasonable agreement if we constrain our model with site‐specific surface and meteorological parameters. The sensitivity of atmosphere‐biosphere trace gas exchange to nocturnal turbulent exchange appears to be large. A comparison of the NOx fluxes calculated by the traditional big leaf approach and the atmosphere‐biosphere model is presented. For sites that are exposed to relatively large anthropogenic emission fluxes, the big‐leaf approach and biosphere model calculate similar NOx fluxes, which confirms the applicability of the big‐leaf approach for polluted regions. However, for relatively pristine sites, differences between the NOx fluxes of the biosphere model and the big leaf approach are significant. This underscores the importance of an explicit representation of the biosphere processes for those locations where the NO soil emissions flux is comparable to or exceeds the anthropogenic emissions.
Development and application of a mesoscale climate model for the tropics: Influence of sea surface temperature anomalies on the West African monsoon
Authors: Vizy Edward K. , Cook Kerry H.
Published: October 2002

A mesoscale climate model (MCM) is developed from the Pennsylvania State University/National Center for Atmospheric Research mesoscale model 5 to simulate the West African summer monsoon. Results from the MCM are compared to observations, a reanalysis, and global climate model (GCM) output to show that the MCM reasonably simulates the West African monsoon climate and its variability and improves on many shortcomings of the GCM simulations. The MCM's ability to capture correctly processes that cause interannual variability, and thereby allow us to improve our physical understanding of that variability, is investigated by examining the influence of Gulf of Guinea sea surface temperature anomalies (SSTAs) on the West African monsoon. Similar to observations, precipitation decreases over the Sahel and increases along the Guinean coast in response to warm SSTAs in the gulf. The increase in rainfall along the Guinean coast is associated with an increase in lower tropospheric water vapor content due to enhanced evaporation over the warm SSTAs and northward moisture advection in the monsoon flow. This stronger precipitation on the coast occurs despite a decrease in the land/sea temperature gradient, which is the fundamental driver of the monsoon. The decrease in rainfall over the southern Sahel is associated with lower tropospheric subsidence replacing rising vertical motions as the monsoon circulation is shifted equatorward. Dynamically, the subsidence over the southern Sahel is associated with shrinking of both planetary and relative vorticity. The former is related to the equatorward shift of the monsoon, which results in an expansion of the equatorward flow from the Sahel to the northern Guinean coast. The latter occurs because the equatorward flow over the southern Sahel occurs lower in the troposphere (i.e., 850 mbar) than in the control (i.e., 700 mbar), where the meridional relative vorticity gradient is opposite to the gradient at 700 mbar.
Formation of photochemical air pollution in central California 2. Impact of revised emissions on Eulerian model predictions
Authors: Marr Linsey C. , Noblet Gregory S. , Harley Robert A.
Published: October 2002

Attempts to characterize ozone formation as sensitive to either volatile organic compounds (VOC) or NOx within a region oversimplify a problem that shows spatial and temporal variation. California's Central Valley has some of the highest ozone levels in the country and a rapidly growing population, and air quality problems in this region can be influenced by interbasin transport of ozone and its precursors. An Eulerian photochemical airshed model is applied to the region for the period 3–6 August 1990. This episode spans a weekend, and the emission inventory incorporates revised motor vehicle emissions with day‐specific activity patterns. Compared with the baseline inventory, the revised inventory contains higher VOC and lower NOx emissions from motor vehicles and different temporal patterns of these emissions. Revised estimates of biogenic emissions are greatly reduced. The baseline emission inventory used in previous modeling efforts appears to contain compensating errors, with high biogenic emissions making up for low motor vehicle emissions of VOC. Results suggest that heavily urbanized areas around and downwind of the San Francisco Bay and Sacramento are VOC‐sensitive, while the more rural areas are NOx‐sensitive. Ozone formation in the San Joaquin Valley, where progress in reducing ambient ozone concentrations has been slow, exhibits sensitivity to emissions of both VOC and NOx, and is influenced by emissions from the San Francisco Bay Area during this modeling episode.
Monoterpene emissions from Scots pine (Pinus sylvestris): Field studies of emission rate variabilities
Authors: Komenda M. , Koppmann R.
Published: October 2002

Monoterpene emission rates from young and adult Scots pines (Pinus sylvestris), a typical central European conifer, were measured under ambient conditions using a dynamic enclosure chamber. We investigated diurnal and seasonal cycles of monoterpene emissions and branch‐to‐branch and plant‐to‐plant variabilities of emission rates. The four most abundant monoterpenes usually emitted from Pinus sylvestris were α‐pinene, 3‐carene, camphene, and β‐pinene. Emissions of individual monoterpenes were highly correlated to each other and increased exponentially with temperature. We obtained β coefficients for the temperature dependence of different monoterpenes between 0.08 and 0.13 K−1. The β coefficients varied with season by a factor of 2; the standard emission rates varied by more than 1 order of magnitude. Highest standard emission rates were found in April; lowest standard emission rates were found in July and October. In July and October the standard emission rates from two different branches of the same tree showed no significant differences; in September they differed by a factor of 2. Seasonal variations of a single branch and branch‐to‐branch variations in the spectrum of emitted monoterpenes were small. On the other hand, different individual Scots pines emitted a completely different spectrum of monoterpenes, indicating that the monoterpene emission spectrum is only typical for an individual plant but not for the whole plant species. The temperature normalized standard emission rates were found to be highly variable. Values for the sum of monoterpenes ranged between 0.06 and 3.7 μg g(dry weight)−1 h−1 (micrograms monoterpenes per gram dry weight (dw) of needles and hour). Temperature‐normalized monoterpene emission rates and temperature dependencies of the emissions were used to calculate monthly flux estimates of monoterpenes for the Hartheimer Wald.
Atmospheric expansion wave simulations of Popocatepetl explosions
Authors: Raga A. C. , Raga G. B. , Cantó J. , Alfonso L.
Published: October 2002

We present a compressible gasdynamic numerical model that utilizes a three‐dimensional adaptive grid to provide high spatial resolution of an expanding compression wave. We apply this model to recent explosions of Popocatepetl volcano in Mexico by incorporating both high resolution topography for a lower boundary and atmospheric stratification based upon climatological thermodynamic soundings. Explosions are simulated by the instantaneous release of an overpressure in a prescribed volume over the volcano's crater. The results show a compression wave that propagates as a supersonic shock close to the explosion, transforming into a sonic compression wave at larger distances. We validate the model predictions by comparing them to pressure‐time series measured by a microbarograph located 11 km away from the crater. With the model validation we estimate the equivalent initial internal energy of the explosions to range from 2 × 1013 J to 1.1 × 1015 J.
Atmospheric budget of acetone
Authors: Jacob Daniel J. , Field Brendan D. , Jin Emily M. , Bey Isabelle , Li Qinbin , Logan Jennifer A. , Yantosca Robert M. , Singh Hanwant B.
Published: October 2002

The atmospheric budget and distribution of acetone are investigated by using a priori estimates of sources and sinks to constrain a global three‐dimensional atmospheric model simulation and then using atmospheric observations from 14 surface sites and 5 aircraft missions to improve these estimates through an inversion analysis. Observations over the South Pacific imply a large photochemical marine source of acetone, either from the ocean or from marine organic aerosol. Low concentrations of acetone measured at European sites in winter‐spring and in the Arctic in summer suggest a large microbial ocean sink. The summer‐to‐fall decrease of concentrations observed in Europe argues against a large source from plant decay. Continental observations in the tropics and at northern midlatitudes in summer imply a large source from terrestrial vegetation. Observations in the Northern Hemisphere outside summer imply a large source from atmospheric oxidation of anthropogenic isoalkanes (propane, isobutane, isopentane). Model simulation of isoalkanes and comparison to observations yields best global emission estimates of 12 Tg C yr−1 for propane (including only 0.6 Tg C yr−1 from biomass burning), 3.6 Tg C yr−1 for isobutane, and 5.0 Tg C yr−1 for isopentane. Our best estimate of the global acetone source is 95 Tg yr−1. The mean tropospheric lifetime of acetone is estimated to be 15 days. Terrestrial vegetation and oceans are the principal sources of acetone in the tropopause region (0.1–0.7 ppbv) except in the extratropical Northern Hemisphere, where oxidation of isoalkanes is more important.
Ozone profile retrieval from recalibrated Global Ozone Monitoring Experiment data
Authors: van der A R. J. , van Oss R. F. , Piters A. J. M. , Fortuin J. P. F. , Meijer Y. J. , Kelder H. M.
Published: October 2002

The satellite instrument Global Ozone Monitoring Experiment (GOME), on board the ERS‐2 mission of the European Space Agency, is measuring backscattered sunlight from the atmosphere in the range from 240 to 790 nm. This spectrum is used for deriving global, height‐resolved information on the ozone distribution in the atmosphere. Contrary to total ozone column retrieval, the retrieval algorithm for ozone profiles requires absolutely calibrated reflectivity spectra. However, the in‐flight calibration of the GOME reflectivity spectra needs to be corrected before the spectra can be used for profile retrieval. A general method for this calibration correction of satellite data and the profile retrieval method are described in this paper. The retrieved profiles from the recalibrated reflectivity spectra of GOME differ in the stratosphere by up to 50% from retrieved profiles without the correction. With the calibration correction, improved ozone profiles are retrieved for the complete range of 0–50 km. The GOME ozone profiles have been validated with ground and satellite measurements at a representative urban midlatitude and a rural tropical ground station.
Ozone production from Canadian wildfires during June and July of 1995
Authors: McKeen S. A. , Wotawa G. , Parrish D. D. , Holloway J. S. , Buhr M. P. , Hübler G. , Fehsenfeld F. C. , Meagher J. F.
Published: October 2002

During the summer of 1995, especially between June and mid July, extensive wildfires occurred throughout Canada, primarily north of 55°N latitude. A previous report used aircraft and surface observations and tracer simulations to show these fires strongly influenced CO concentrations as far south as 35°N in the central and eastern United States [Wotawa and Trainer, 2000]. This study extends those results by incorporating wildfire emissions estimates for CO, NOx, and nonmethane hydrocarbons into a three‐dimensional photochemical transport model specifically designed to simulate ozone photochemistry in the continental United States. The results of the model are compared to observations from four measurement platforms deployed during the time period of interest: National Oceanic and Atmospheric Administration WP‐3 aircraft observations collected during the 1995 Southern Oxidants Study (SOS‐95) field campaign; 12 eastern U.S. surface stations that measured ozone, CO, and NOy; rural ozone measurements from the Aerometric Information Retrieval System network collected by the U.S. Environmental Protection Agency; and daily ozonesondes obtained near Nashville, Tennessee, during SOS‐95. Model performance, as determined by correlation and bias with observations from these four platforms, is significantly improved for both O3and CO when the Canadian fires are considered. Both observations and model results show enhanced O3from air transported from the Northwest Territory. The model results imply that during the period of strongest fire influence 10 to 30 ppbv enhancement of O3throughout a large region of the central and eastern United States was due to these fires. Modeled O3increases are sensitive to the NOx/CO emission ratio assumed for the fires, which is highly uncertain and variable. A molar NOx/CO ratio of 0.007 yields model comparisons that are most consistent for O3and ΔO3/ΔCO observations within aged fire plumes during SOS‐95, and is also consistent with previously observed NOx/CO ratios from boreal fires. For this NOx/CO emission ratio, and considering the entire eastern United States, most of the O3increase is associated with the NOxemitted directly by the fires and the photochemical O3formation that occurs before the plumes actually reach the United States. However, the in situ oxidation of CO from the Canadian fires with NOxemitted locally leads to significantly higher O3increases for high‐NOx‐emitting regions that are limited by hydrocarbon availability. Thus O3in urban areas, or any other region modified by nearby NOxsources, is more sensitive to long‐range fires compared to less populated or polluted regions.
Space‐based measurements of stratospheric mountain waves by CRISTA 1. Sensitivity, analysis method, and a case study
Authors: Preusse Peter , Dörnbrack Andreas , Eckermann Stephen D. , Riese Martin , Schaeler Bernd , Bacmeister Julio T. , Broutman Dave , Grossmann Klaus U.
Published: October 2002

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured stratospheric temperatures and trace species concentrations with high precision and spatial resolution during two missions. The measuring technique is infrared limb‐sounding of optically thin emissions. In a general approach, we investigate the applicability of the technique to measure gravity waves (GWs) in the retrieved temperature data. It is shown that GWs with wavelengths of the order of 100–200 km horizontally can be detected. The results are applicable to any instrument using the same technique. We discuss additional constraints inherent to the CRISTA instrument. The vertical field of view and the influence of the sampling and retrieval imply that waves with vertical wavelengths ∼3–5 km or larger can be retrieved. Global distributions of GW fluctuations were extracted from temperature data measured by CRISTA using Maximum Entropy Method (MEM) and Harmonic Analysis (HA), yielding height profiles of vertical wavelength and peak amplitude for fluctuations in each scanned profile. The method is discussed and compared to Fourier transform analyses and standard deviations. Analysis of data from the first mission reveals large GW amplitudes in the stratosphere over southernmost South America. These waves obey the dispersion relation for linear two‐dimensional mountain waves (MWs). The horizontal structure on 6 November 1994 is compared to temperature fields calculated by the Pennsylvania State University (PSU)/National Center for Atmospheric Research (NCAR) mesoscale model (MM5). It is demonstrated that precise knowledge of the instrument's sensitivity is essential. Particularly good agreement is found at the southern tip of South America where the MM5 accurately reproduces the amplitudes and phases of a large‐scale wave with 400 km horizontal wavelength. Targeted ray‐tracing simulations allow us to interpret some of the observed wave features. A companion paper will discuss MWs on a global scale and estimates the fraction that MWs contribute to the total GW energy (Preusse et al., in preparation, 2002).
Evaluation of aerosol measurements from SAGE II, HALOE, and balloonborne optical particle counters
Authors: Hervig Mark , Deshler Terry
Published: October 2002

Stratospheric aerosol measurements from the University of Wyoming balloonborne optical particle counters (OPCs), the Stratospheric Aerosol and Gas Experiment (SAGE) II, and the Halogen Occultation Experiment (HALOE) were compared in the period 1982–2000, when measurements were available. The OPCs measure aerosol size distributions, and HALOE multiwavelength (2.45–5.26 μm) extinction measurements can be used to retrieve aerosol size distributions. Aerosol extinctions at the SAGE II wavelengths (0.386–1.02 μm) were computed from these size distributions and compared to SAGE II measurements. In addition, surface areas derived from all three experiments were compared. While the overall impression from these results is encouraging, the agreement can change with latitude, altitude, time, and parameter. In the broadest sense, these comparisons fall into two categories: high aerosol loading (volcanic periods) and low aerosol loading (background periods and altitudes above 25 km). When the aerosol amount was low, SAGE II and HALOE extinctions were higher than the OPC estimates, while the SAGE II surface areas were lower than HALOE and the OPCs. Under high loading conditions all three instruments mutually agree to within 50%.
Atmospheric correction for satellite‐based volcanic ash mapping and retrievals using “split window” IR data from GOES and AVHRR
Authors: Yu Tianxu , Rose William I. , Prata A. J.
Published: October 2002

Volcanic ash in volcanic clouds can be mapped in two dimensions using two‐band thermal infrared data available from meteorological satellites. Wen and Rose [1994] developed an algorithm that allows retrieval of the effective particle size, the optical depth of the volcanic cloud, and the mass of fine ash in the cloud. Both the mapping and the retrieval scheme are less accurate in the humid tropical atmosphere. In this study we devised and tested a scheme for atmospheric correction of volcanic ash mapping and retrievals. The scheme utilizes infrared (IR) brightness temperature (BT) information in two infrared channels (both between 10 and 12.5 μm) and the brightness temperature differences (BTD) to estimate the amount of BTD shift caused by lower tropospheric water vapor. It is supported by the moderate resolution transmission (MODTRAN) analysis. The discrimination of volcanic clouds in the new scheme also uses both BT and BTD data but corrects for the effects of the water vapor. The new scheme is demonstrated and compared with the old scheme using two well‐documented examples: (1) the 18 August 1992 volcanic cloud of Crater Peak, Mount Spurr, Alaska, and (2) the 26 December 1997 volcanic cloud from Soufriere Hills, Montserrat. The Spurr example represents a relatively “dry” subarctic atmospheric condition. The new scheme sees a volcanic cloud that is about 50% larger than the old. The mean optical depth and effective radii of cloud particles are lower by 22% and 9%, and the fine ash mass in the cloud is 14% higher. The Montserrat cloud is much smaller than Spurr and is more sensitive to atmospheric moisture. It also was located in a moist tropical atmosphere. For the Montserrat example the new scheme shows larger differences, with the area of the volcanic cloud being about 5.5 times larger, the optical depth and effective radii of particles lower by 56% and 28%, and the total fine particle mass in the cloud increased by 53%. The new scheme can be automated and can contribute to more accurate remote volcanic ash detection. More tests are needed to find the best way to estimate the water vapor effects in real time.
Balloon‐borne observations of water vapor and ozone in the tropical upper troposphere and lower stratosphere
Authors: Vömel H. , Oltmans S. J. , Johnson B. J. , Hasebe F. , Shiotani M. , Fujiwara M. , Nishi N. , Agama M. , Cornejo J. , Paredes F. , Enriquez H.
Published: October 2002

Balloon‐borne observations of frost‐point temperature and ozone in the equatorial western, central and eastern Pacific as well as over equatorial eastern Brazil provide a highly accurate data set of water vapor across the tropical tropopause. Data were obtained at San Cristóbal, Galapagos, Ecuador (0.9°S, 89.6°W), during the late northern winter and the late northern summer in 1998 and 1999 and at Juazeiro do Norte, Brazil (7.2°S, 39.3°W), in February and November 1997. Earlier data in the western Pacific region in March 1993 were reanalyzed to extend the scope of the observations. The data show three different circumstances in which saturation or supersaturation occurs and imply different mechanisms for dehydration at the tropical tropopause: (1) convective dehydration, (2) slow‐ascent dehydration, and (3) large‐scale wave‐driven dehydration. Furthermore, air that crosses the tropical tropopause in the late northern summer may be dehydrated further during late northern fall, as the average tropical tropopause rises and cools. Not all soundings show dehydration, and there are clear differences in the frequency and depth of saturation in different regions and seasons. The tropopause transition region can be identified in accurate measurements of relative humidity, even under conditions where ozone observations are ambiguous. Deep convection plays an important role in setting up this transition region, which is then subject to large‐scale wave activity and wave breaking at the tropopause or midlatitude intrusions. High relative humidities over regions of strong subsidence show that descending motion in the troposphere is limited to levels below the transition region.
Isotopic ratios of water vapor and methane in the stratosphere: Comparison between ATMOS measurements and a one‐dimensional model
Authors: Ridal Martin
Published: October 2002

A one‐dimensional model simulating the transport and chemistry of methane and water vapor including their isotopic ratios in the tropical stratosphere is compared to measurements by the Atmospheric Trace Molecule Spectroscopy experiment (ATMOS) instrument. The model and measurements show good agreement in the isotopic ratio profiles. The δD depletion for water vapor is −600‰ to −500‰ at the tropopause with a small increase up to ∼10 hPa. Above this altitude the modeled isotopic ratio shows a strong increase due to methane oxidation. The measured profiles are rather noisy above 10 hPa but give an indication of a stronger increase in the isotopic ratio than modeled. If the isotopic ratio of water vapor is allowed to vary at the tropopause simulating an annual cycle in the input values, a wave pattern that is transported upwards arises on the vertical profile. This is a similar effect as the “tape recorder” for water vapor. A wave pattern can also be detected in the tropical δD profiles from ATMOS. The methane isotopic ratio shows behavior similar to that of water vapor but without the wave pattern. The increase in methane δD above 10 hPa is very strong. The measured profiles are again rather noisy above this altitude, but measurements from inside the polar vortex show that the methane isotopic ratio in the upper stratosphere is very high. The δD values are in the range of +300‰ to +500‰ at altitudes as low as 40 hPa (∼25 km) in the polar vortex.
Model structure and land parameter identification: An inverse problem approach
Authors: Tsuang Ben‐Jei , Tu Chia‐Ying
Published: October 2002

Model structures for the parameterization of energy and water exchanges between the atmosphere and the land are explored, and the parameters are identified. Minimizing the root‐mean‐square error (RMSE) of the calculated air temperature is used as the objective function. Eight parameters are determined within 14 iterations over two urban sites in a subtropical island. The identified values of these parameters can be compared with those listed in the literature. The results show that (1) a proper choice of canopy resistance is important in determining the mean temperature; (2) using a scheme to calculate stomatal resistance from vegetated areas shows improvements in simulating the diurnal variations of the temperature, decreasing the RMSE by 0.4 K; (3) using a scheme to accommodate the effect of evaporation from skin reservoirs during rain events shows improvements in determining the temperature immediately after the rain, decreasing the RMSE by 0.1 K; (4) while incorporating a soil‐moisture availability function does not show improvement in the model performance unless an extra water table variable is added, which decreases the RMSE by 0.03 K. Incorporating all of the above model structures, the calculated hourly air temperature has a correlation coefficient of as high as 0.97 with a RMSE of 1.4 K.
Mesoscale model cloud scheme assessment using satellite observations
Authors: Chaboureau Jean‐Pierre , Cammas Jean‐Pierre , Mascart Patrick J. , Pinty Jean‐Pierre , Lafore Jean‐Philippe
Published: October 2002

An exploratory evaluation of the explicit cloud scheme of the mesoscale nonhydrostatic (Meso‐NH) model has been conducted by comparing synthetic METEOSAT brightness temperatures (BT) to the observed ones. Three different meteorological situations are examined to illustrate the expected degree of accuracy in simulating realistic synthetic BTs in the midlatitude and in the subtropics, with a horizontal grid length ranging from 75 to 12 km. It is shown that the model to satellite approach, which combines the output from a bulk explicit cloud scheme routinely used in mesoscale simulations with a detailed radiative transfer code, offers the possibility of tuning a critical parameter. For instance, tests made with three different values of an ice to snow autoconversion threshold reveal a profound impact on the synthetic BT maps which results in unbiased differences with satellite observations when the appropriate value is selected. The main discrepancies that remain are partly due to errors in the vertical or horizontal placement of the cloud layer or in the amount of condensates, but also due to the lack of subgrid‐scale cloudiness in the model. A similar test conducted on the ice water and the liquid water paths confirms the fairly good agreement with retrievals from microwave observations. The paper concludes by discussing the need not only to extend the model to satellite approach to other well‐documented cases but also to derive diagnostics from deep convection scheme characteristics in order to include the radiative effect of the convective towers in the generation of synthetic BT maps.
Product analysis of the OH oxidation of isoprene and 1,3‐butadiene in the presence of NO
Authors: Sprengnether Michele , Demerjian Kenneth L. , Donahue Neil M. , Anderson James G.
Published: October 2002

The oxidation mechanisms of isoprene and butadiene initiated by OH in the presence of NO have been explored under “wall‐less” flowing conditions, with products observed a few seconds after reaction by infrared spectroscopy. Since only ∼1% of alkene is reacted, any secondary chemistry is negligible. The use of reaction modulation spectroscopy permits the accurate measurement of a percent change in high alkene concentration and of 1013 molecules/cm3 concentrations for products. Measured carbonyl species agree with previous studies, while alkyl nitrate yields are consistent with upper values reported in the literature. NO sensitivity studies performed exclude the possibility of competing chemistry. Isoprene is not observed to form 3‐methyl furan, indicating that this is not a prompt oxidation product. However, butadiene does form furan. In an auxiliary experiment, peroxy radicals in the second stage of butadiene oxidation are fully converted to peroxynitrates. Average cross sections for integrated peroxynitrate bands are determined from this experiment.
Decadal change in carbon monoxide to nitrogen oxide ratio in U.S. vehicular emissions
Authors: Parrish D. D. , Trainer M. , Hereid D. , Williams E. J. , Olszyna K. J. , Harley R. A. , Meagher J. F. , Fehsenfeld F. C.
Published: October 2002

Accurate emission inventories and their temporal trends must be incorporated into pollutant inventories to allow for reliable modeling of the country's past, present, and future air quality. Measured carbon monoxide (CO) and nitrogen oxide (NOx) concentrations from two urban areas show that the CO/NOx vehicular emission ratio has decreased at an average rate of 7–9% per year from 1987 to 1999. This amounts to a factor of nearly 3 over the 12 years. The current U.S. Environmental Protection Agency tabulations of estimated pollutant emission trends indicate a rate of decrease smaller by a factor of 2–3. The trend in maximum ambient CO levels in U.S. cities suggests a 5.2 ± 0.8% per year average annual decrease in CO vehicular emissions, which implies a 2–3% annual increase in NOx emissions from vehicles. Thus over the decade of the 1990s, annual U.S. CO emissions from vehicles have decreased from ∼65 to ∼38 Tg, representing approximate decreases of 6 and 3% in the annual global fuel‐use CO emissions and in total global anthropogenic CO emissions, respectively. It is expected that the volatile organic compound (VOC)/NOx vehicular exhaust emission ratio has decreased similarly, implying that the character of atmospheric photochemistry in U.S. urban areas has changed significantly over the decade.
Are CH2O measurements in the marine boundary layer suitable for testing the current understanding of CH4 photooxidation?: A model study
Authors: Wagner V. , von Glasow R. , Fischer H. , Crutzen P. J.
Published: October 2002

On the basis of a data set collected during the Indian Ocean Experiment (INDOEX) campaign 1999, we investigated the formaldehyde (CH2O) budget in the southern Indian Ocean (SIO). With a photochemical box model we simulated the contribution of methane and nonmethane volatile organic compounds to the CH2O budget. To identify the reactions and model constraints that introduce the largest uncertainties in the modeled CH2O concentration, we carried out a local sensitivity analysis. Furthermore, a Monte Carlo method was used to assess the global error of the model predictions. According to this analysis the 2σ uncertainty in the modeled CH2O concentration is 49%. The deviation between observed (200 ± 70 parts per trillion by volume (pptv) (2σ)) and modeled (224 ± 110 pptv (2σ)) daily mean CH2O concentration is 12%. However, the combined errors of model and measurement are such that deviations as large as 65% are not significant at the 2σ level. Beyond the “standard” photochemistry we analyzed the impact of halogen and aerosol chemistry on the CH2O concentration and investigated the vertical distribution of CH2O in the marine boundary layer (MBL). Calculations with the Model of Chemistry Considering Aerosols indicate that, based on the current understanding, halogen chemistry and aerosol chemistry have no significant impact on the CH2O concentration under conditions encountered in the SIO. However, a detailed investigation including meteorological effects such as precipitation scavenging and convection reveals an uncertainty in state‐of‐the‐art model predictions for CH2O in the MBL that is too large for a meaningful test of the current understanding of CH4 photooxidation.
Emission characteristics of CO, NOx, SO2and indications of biomass burning observed at a rural site in eastern China
Authors: Wang T. , Cheung T. F. , Li Y. S. , Yu X. M. , Blake D. R.
Published: October 2002

Atmospheric O3, CO, SO2, and NOy* (NOy* ≈ NO + NO2+ PAN + organic nitrates + HNO3+ N2O5+ ⋯) were measured in 1999–2000 at a rural/agricultural site in the Yangtze Delta of China. In this paper we analyze the measurement results to show the emission characteristics of the measured gases and to infer relevant emission ratios. Positive correlations were found between CO and NOy* with a slope (Δ[CO]/Δ[NOy*]) of 36 (ppbv/ppbv) for the winter and nighttime measurements. The ratio is considerably larger than that (≈10 ppbv/ppbv) observed in the industrialized countries. The highest CO/NOy* ratio (30–40 ppbv/ppbv) occurred in September–December 1999 and June 2000. The good correlation between CO and the biomass burning tracer CH3Cl and the lack of correlation with the industrial tracer C2Cl4suggests that the burning of biofuels and crop residues is a major source for the elevated CO and possibly for other trace gases as well. The average SO2to NOy* ratio was 1.37 ppbv/ppbv, resulting from the use of relatively high‐sulfur coals in China. The measured SO2/NOy* and ΔCO/ΔNOy* were compared with the respective ratios from the current emission inventories for the study region, which indicated a comparable SO2/NOxemission ratio but a large discrepancy for CO/NOx. The observed CO to NOy* ratio was more than 3 times the emission ratio derived from the inventories, indicating the need for further improvement of emission estimates for the rural/agricultural regions in China. Additional research will be needed to study the implications of rural emissions to atmospheric chemistry and climate on both regional and global scales.
Air mass classification during the INDOEX R/V Ronald Brown cruise using measurements of nonmethane hydrocarbons, CH4, CO2, CO, 14CO, and δ18O(CO)
Authors: Mühle, Jens , Zahn, Andreas , Brenninkmeijer, Carl A. M. , Gros, Valérie , Crutzen Paul J.
Published: October 2002

During the Indian Ocean Experiment (INDOEX) in February‐March 1999 the impact of continental outflow to the Indian Ocean was analyzed. On board the R/V Ronald Brown altogether 93 air samples were taken for analysis of nonmethane hydrocarbons (NMHC), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and the 14C/12C and 18O/16O isotope ratios of CO. Five types of air masses differing in origin, degree of pollution, and chemical age were identified based on back trajectory analyses and the trace gas data, supported by continuous CO and ozone (O3) observations from other investigators. The Indian Ocean was found to be frequently affected by nearby emissions from the Indian subcontinent and Indochina, but the strongest pollution event (characterized inter alia by high mixing ratios of medium‐ and long‐lived NMHC) was due to long‐range advection from the extratropical northern hemisphere. Carbon monoxide 14 showing a distinct meridional profile unequivocally confirms this remote impact. The ratio acetylene/CO was found to be often inadequate as a measure for atmospheric processing, the integrated influence of OH chemistry and mixing. Our data suggest that the influence from fresh continental pollution was less pronounced along the INDOEX R/V Ronald Brown cruise compared to observations made during other tropical campaigns, such as the Pacific Exploratory Mission‐West B in the Pacific Ocean.
Trace gases and air mass origin at Kaashidhoo, Indian Ocean
Authors: Lobert Jürgen M. , Harris Joyce M.
Published: October 2002

Carbon monoxide (CO) was measured at the Kaashidhoo Climate Observatory (KCO, Republic of Maldives) between February 1998 and March 2000 to assess the regional pollution of the remote atmosphere in the northern Indian Ocean. CO showed a distinct annual cycle with maximum daily mixing ratios of around 240 parts per billion (ppb), a seasonal difference of about 200 ppb, and high variability during the dry seasons. Detailed air mass trajectory analysis for 1998, 1999, and 2000 was used to identify source regions and to associate them with various levels of pollution encountered at KCO. We conclude that most significant changes in local pollution throughout the year are caused by changes in air masses. Air at KCO generally originated from three main regions with decreasing pollution: India and southeast Asia, the Arabian Sea, and the Southern Hemisphere. We show that isentropic air mass trajectories can be used to predict CO pollution levels at KCO to a certain extent and vice versa. Nitrous oxide, CFC‐11, CFC‐12, CCI4, and SF6 were measured during the Indian Ocean Experiment (February to March 1999) to support pollution analysis and to confirm that India is the main source for heavy pollution measured at KCO. Correlations between CO and other gases and aerosol properties measured at the surface illustrate that CO may also be used as a proxy for aerosol loading and general pollution at the surface.
Long‐term simulations of discharge and floods in the Amazon Basin
Authors: Coe Michael T. , Costa Marcos Heil , Botta Aurélie , Birkett Charon
Published: October 2002

A terrestrial ecosystem model (integrated biosphere simulator (IBIS)) and a hydrological routing algorithm (HYDRA) are used in conjunction with long time series climate data to simulate the river discharge and flooded area of the Amazon/Tocantins River basin over the last 60 years. Evaluating the results of this modeling exercise over the entire basin yields three major results: (1) Observations at 121 stations throughout the basin show that discharge is well simulated for most tributaries originating in Brazil. However, the discharge is consistently underestimated, by greater than 20%, for tributaries draining regions outside of Brazil and the main stem of the Amazon. The discharge underestimation is most likely a result of underestimated precipitation in the data set used as model input. (2) A new flooding algorithm within HYDRA captures the magnitude and timing of the river height and flooded area in relatively good agreement with observations, particularly downstream of the confluence of the Negro and Solimões Rivers. (3) Climatic variability strongly impacts the hydrology of the basin. Specifically, we find that short (∼3–4 years) and long (∼28 years) modes of precipitation variability drive spatial and temporal variability in river discharge and flooded area throughout the Amazon/Tocantins River basins.
Retrieval for physical parameters of aerosols in an urban area by ground‐based FTIR measurement
Authors: Shimota Akiro , Kobayashi Hirokazu , Wada Koji
Published: October 2002

An IR Fourier‐transformed spectrometer for use in field observation, named the tropospheric infrared interferometric sounder (TIIS), was developed by the Central Research Institute of Electric Power Industry (CRIEPI). Downwelling atmospheric infrared emission spectra were measured by ground‐based operation of the TIIS in the Tokyo area. From the measured spectra, the aerosol extinction coefficient spectra in the lowest layer (0–2 km) were retrieved, and then using the retrieved aerosol extinction coefficient spectra we carried out the retrieval of the volume density of each aerosol component, in which aerosols in the lowest layer of the urban area were assumed to consist of three components, namely, water‐soluble, soot, and dust‐like components. The results were evaluated by means of comparisons with backscattering intensity profiles and the size‐selective particle number density, which were measured from synchronized operations of a lidar and a laser particle counter, respectively. The retrieved values of water‐soluble and dust‐like aerosol components were found to correspond with results from the lidar measurement and the laser particle counter. Regarding the soot component, we were unable to make a direct comparison using data measured by the lidar and the laser particle counter. However, the spectrum calculated by FASCODE3 applying the retrieved aerosol parameters corresponded closely to the spectrum measured by TIIS. Therefore, the retrieved soot aerosol parameters were considered to be reliable.