bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent mixing and the chemical breakdown of isoprene in the atmospheric boundary layer
Authors: Verver G. H. L. , van Dop H. , Holtslag A. A. M.
Published: September 2002

In this paper we study the effect of turbulence on the oxidation rate of isoprene and its reaction products in the atmospheric boundary layer. We use two models of different complexity: a simple model consisting of two well‐mixed layers and a one‐dimensional off‐line second‐order closure model. Both models include an extensive set of chemical reactions to describe the oxidation of isoprene. A 5‐day simulation is performed to compare the simple model output with data from the Amazon Boundary Layer Experiment (ABLE‐2A). The model is able to represent fairly the basic dynamics and chemistry during this experiment. Subsequently, the simple model provides boundary and initial conditions for a one‐dimensional second‐order closure model that is used to assess the impact of higher‐order chemistry terms on turbulent mixing and chemical transformations. We focus on covariances of NO with (peroxy‐) radicals and covariances of OH with stable intermediate products. We find only small effects on the effective reaction rates due to the OH covariances. A significant effect is found of the covariances of NO, inhibiting the effective reaction rates with the peroxy radicals by a maximum of 10% in the afternoon. The inclusion of covariance terms resulted in an increase of radical concentrations, but the NO concentration profiles remained unchanged. Higher‐order chemistry terms do have an effect on NO and NO2 fluxes, which change by 5 to 30% in the middle of the boundary layer. Therefore these terms have to be taken into account when flux‐gradient relationships or deposition velocities are derived from observations. The present results indicate that the incorporation of higher‐order chemistry terms is not essential for a correct representation of the mean profiles of most stable species involved.
Fractal properties and denoising of lidar signals from cirrus clouds
Authors: van den Heuvel J. C. , Driesenaar M. L. , Lerou R. J. L.
Published: September 2002

Airborne lidar signals of cirrus clouds are analyzed to determine the cloud structure. Climate modeling and numerical weather prediction benefit from accurate modeling of cirrus clouds. Airborne lidar measurements of the European Lidar in Space Technology Experiment (ELITE) campaign were analyzed by combining shots to obtain the backscatter at constant altitude. The signal at high altitude was analyzed for horizontal structure of cirrus clouds. The power spectrum and the structure function show straight lines on a double logarithmic plot. This behavior is characteristic for a Brownian fractal. Wavelet analysis using the Haar wavelet confirms the fractal aspects. It is shown that the horizontal structure of cirrus can be described by a fractal with a dimension of 1.8 over length scales that vary 4 orders of magnitude. We use the fractal properties in a new denoising method. Denoising is required for future lidar measurements from space that have a low signal to noise ratio. Our wavelet denoising is based on the Haar wavelet and uses the statistical fractal properties of cirrus clouds in a method based on the maximum a posteriori (MAP) probability. This denoising based on wavelets is tested on airborne lidar signals from ELITE using added Gaussian noise. Superior results with respect to averaging are obtained.
Carboxylic acids in gas and particulate phase above the Atlantic Ocean
Authors: Baboukas E. D. , Kanakidou M. , Mihalopoulos N.
Published: September 2002

Mixing ratios of acetic (CH3COOH), formic (HCOOH), pyruvic (CH3COCOOH), and oxalic ((COOH)2) acids were measured both in gas and particulate phase in the marine boundary layer, over the Atlantic Ocean from 63°N to 39°S on board of the R/V Polarstern in October/November 1996. The average mixing ratios for gas phase CH3COOH, HCOOH, CH3COCOOH, and (COOH)2 were 291.2±151.9, 448.7±182.1, 1.1±1.0, and 6.1±5.4 parts per trillion by volume (pptv), respectively. The partitioning of these acids in the aerosol phase and the size distribution of their particulate form was also investigated. In the fine mode the mean mixing ratios for acetate, formate, pyruvate, and oxalate were 69.7±47.5, 32.5±39.4, 1.0±1.0, and 5.1±3.7 pptv, respectively. Elevated levels of all organic acids were encountered in the southern hemisphere (springtime) compared to the northern hemisphere (autumn), indicating a possible seasonal variation in their source strength and/or enhanced photochemical production. The observed distributions of formic and acetic acids have been compared to the results of a global chemistry/transport three‐dimensional model. The model results show that acetic acid has mainly secondary photochemical sources (about 120 Tg CH3COOH/yr). On the opposite, the known chemical sources of HCOOH are quite weak (20 Tg HCOOH/yr) and insufficient to simulate the HCOOH levels observed in the marine atmosphere. A local marine source of HCOOH of about 50 Tg/yr on a global scale is required to reasonably simulate the observations in the marine atmosphere.
Atmospheric chemical transport based on high‐resolution model‐derived winds: A case study
Authors: Hannan John R. , Fuelberg Henry E. , Thompson Anne M. , Bieberbach George , Knabb Richard D. , Kondo Yutaka , Anderson Bruce E. , Browell Edward V. , Gregory Gerald L. , Sachse Glen W. , Singh Hanwant B.
Published: September 2002

Flight 10 of NASA's Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) extended southwest of Lajes, Azores. A variety of chemical signatures was encountered. These signatures are examined in detail, relating them to meteorological data from a high‐resolution numerical model having a horizontal grid spacing of 30 and 90 km with 26 vertical levels. The meteorological output at hourly intervals is used to create backward trajectories from the locations of the chemical signatures. Four major categories of chemical signatures are discussed: stratospheric, lightning, continental pollution, and a mixed chemical layer. The strong stratospheric signal is encountered just south of the Azores in a region of depressed tropopause height. Three chemical signatures at different altitudes in the upper troposphere are attributed to lightning. Backward trajectories from these signatures extend to locations of cloud‐to‐ground lightning. Specifically, results show that the trajectories pass over regions of lightning 1–2 days earlier over the eastern Gulf of Mexico and off the southeast coast of the United States. The lowest leg of the flight exhibits a chemical signature consistent with continental pollution. Trajectories from this signature are found to pass over the highly populated Northeast Corridor of the United States. Surface‐based pollution apparently is lofted to the altitudes of the trajectories by convective clouds along the East Coast that did not contain lightning. Finally, a mixed layer is described. Its chemical signature is intermediate to those of lightning and continental pollution. Backward trajectories from this layer pass between the trajectories of the lightning and pollution signatures. Thus they likely are impacted by both sources.
Chemical NOx budget in the upper troposphere over the tropical South Pacific
Authors: Schultz Martin G. , Jacob Daniel J. , Bradshaw John D. , Sandholm Scott T. , Dibb Jack E. , Talbot Robert W. , Singh Hanwant B.
Published: September 2002

The chemical NOx budget in the upper troposphere over the tropical South Pacific is analyzed using aircraft measurements made at 6–12 km altitude in September 1996 during the Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM) Tropics A campaign. Chemical loss and production rates of NOx along the aircraft flight tracks are calculated with a photochemical model constrained by observations. Calculations using a standard chemical mechanism show a large missing source for NOx; chemical loss exceeds chemical production by a factor of 2.4 on average. Similar or greater NOx budget imbalances have been reported in analyses of data from previous field studies. Ammonium aerosol concentrations in PEM‐Tropics A generally exceeded sulfate on a charge equivalent basis, and relative humidities were low (median 25% relative to ice). This implies that the aerosol could be dry in which case N2O5 hydrolysis would be suppressed as a sink for NOx. Suppression of NO2O5 hydrolysis and adoption of new measurements of the reaction rate constants for NO2 + OH + M and HNO3 + OH reduces the median chemical imbalance in the NOx budget for PEM‐Tropics A from 2.4 to 1.9. The remaining imbalance cannot be easily explained from known chemistry or long‐range transport of primary NOx and may imply a major gap in our understanding of the chemical cycling of NOx in the free troposphere.
A comparison of Global Positioning System retrieved precipitable water vapor with the numerical weather prediction analysis data over the Japanese Islands
Authors: Iwabuchi Tetsuya , Naito Isao , Mannoji Nobutaka
Published: September 2002

Behavior of precipitable water vapor (PWV) routinely retrieved from the nationwide array of the Global Positioning System (GPS) established by Geographical Survey Institute (GSI) of Japan are compared with the Japan area objective analysis data for numerical weather prediction (NWP) of the Japan Meteorological Agency (JMA). The array used here has a spatial resolution of about 50 km for monitoring crustal deformation. The 3‐hourly zenith tropospheric delay (ZTD) data obtained in GSI's routine analysis system are converted into PWV data by using the 12‐hourly NWP data. While a front accompanying with heavy rainfall moved eastward across the Japanese Islands from 0900 local standard time (LST) September 1 to 0900 LST September 3, 1996, the GPS array successfully detected the temporal anomalies of GPS PWV moving along with the front, in which the internal errors are estimated to be less than 3 mm. The results reveal that GSI's GPS array can work as an all weather giant array sensor of PWV over the Japanese Islands. It is found, however, that the GPS shows systematically fewer PWV than NWP data in mountainous areas reaching about 10 mm. This bias results mainly from the fact that most GPS sites located at bottom of valley in mountainous areas. After removing the topographical effects, there still remain significant differences amounting to 2–4 mm associated with errors of GPS observations and/or NWP objective analyses data.
Potential for downscaling soil moisture maps derived from spaceborne imaging radar data
Authors: Crow Wade T. , Wood Eric F. , Dubayah Ralph
Published: September 2002

The presence of nonlinear relationships between surface soil moisture and various hydrologic processes suggests that grid‐scale water and energy fluxes cannot be accurately modeled without subgrid‐scale soil moisture information. For land surface and energy balance models run over continental‐ to global‐scale domains, accurate fine‐scale soil moisture observations are nearly impossible to obtain on a consistent basis and will likely remain so through the next generation of soil moisture remote sensors. In the absence of such data sets, an alternative approach is to generalize the statistical behavior of soil moisture fields across the relevant range of spatial scales. Downscaling procedures offer the possibility that the fine‐scale statistical properties of soil moisture fields can be inferred from coarse‐scale data. Such an approach was used for a 29×200 km transect of 25 m active radar data acquired over Oklahoma by NASA's spaceborne imaging radar imaging (SIR‐C) mission on April 12, 1994. Using a soil dielectric inversion model, the radar data were processed to provide estimates of surface soil dielectric values, which can be equated to volumetric soil moisture content. The soil moisture field along each strip was analyzed for evidence of spatial scaling for scales ranging from 100 to 6400 m. Results suggest that a spatial scaling assumption may not always be an appropriate basis for a downscaling approach. Prospects for the development of a more robust downscaling procedure for soil moisture are discussed.
What controls tropospheric ozone?
Authors: Lelieveld Jos , Dentener Frank J.
Published: September 2002

We have applied a global three‐dimensional chemistry‐transport model to quantify the photochemistry of tropospheric O3 and compare the main source categories. We simulated a 15 year period (1979–1993) on the basis of the European Centre for Medium‐Range Weather Forecasts meteorological reanalyses and a time‐varying emission data set. We calculate that stratosphere‐troposphere exchange (STE) strongly contributes to O3 in regions where the photochemistry is quiescent. Since such regions play a minor role in radiative and chemical processes, we argue that STE‐derived O3 is much less important than is suggested by its column abundance. By distinguishing between photochemical pathways in the model we calculate that tropospheric O3 in the extratropical Northern Hemisphere is strongly affected by industrial and fossil fuel‐related emissions. In the tropics and Southern Hemisphere, natural emissions still play a major role. Our model results indicate a less important role for man‐made biomass burning emissions than previous analyses. Further, the results show that tropospheric O3 trends are strongly influenced by transports of pollution and by meteorological variability. Scenario calculations for the year 2025 suggest that man‐made emissions at low northern latitudes, in particular in southern and eastern Asia, will become a very strong tropospheric O3 source in the next decades. This will influence O3 levels on a hemispheric scale so that despite pollution regulations in Europe and North America, surface O3 will continue to grow.
Partitioning of reactive nitrogen in the midlatitude lower stratosphere
Authors: Kondo Y. , Sugita T. , Koike M. , Kawa S. R. , Danilin M. Y. , Rodriguez J. M. , Spreng S. , Golinger K. , Arnold F.
Published: September 2002

Balloon‐borne in situ measurements of total reactive nitrogen (NOy), nitric oxide (NO), nitric acid (HNO3), ozone (O3), and aerosols were conducted over Aire sur l'Adour, France (44°N), between October 11 and 12, 1994. NOy and NO were measured by chemiluminescence NO detectors combined with a gold catalytic converter, and HNO3 was measured by ion mass spectrometry. Two independent box models (Goddard Space Flight Center and Atmospheric and Environment Inc.) run on isentropic trajectories were used to interpret the observed partitioning of reactive nitrogen. The NOy partitioning calculated by the two models agreed within 10% of each other. The model‐calculated NO/NOy ratios increase by ∼25% when the updated reaction rates of NO2 + OH, HNO3 + OH, and NO2 + O [Portmann et al., 1999] were used instead of those given by DeMore et al. [1997], leading to a better agreement with the observations by the same amount. At 21–25 km the calculated NO/NOy ratios depended sensitively on the estimate of aerosol surface area. Within the uncertainty of the estimate of aerosol surface area the NO/NOy and HNO3/NOy ratios calculated by the models reproduced those observed within 20%. The same trajectory models also reproduced the NO/NOy ratios measured below 25 km under high aerosol loading in October and November 1992 within ±20%, which is the accuracy level of the measurements.
A case study of transport of tropical marine boundary layer and lower tropospheric air masses to the northern midlatitude upper troposphere
Authors: Grant William B. , Browell Edward V. , Butler Carolyn F. , Fenn Marta A. , Clayton Marian B. , Hannan John R. , Fuelberg Henry E. , Blake Donald R. , Blake Nicola J. , Gregory Gerald L. , Heikes Brian G. , Sachse Glen W. , Singh Hanwant B. , Snow Julie , Talbot Robert W.
Published: September 2002

Low‐ozone (<20 ppbv) air masses were observed in the upper troposphere in northern midlatitudes over the eastern United States and the North Atlantic Ocean on several occasions in October 1997 during the NASA Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission. Three cases of low‐ozone air masses were shown to have originated in the tropical Pacific marine boundary layer or lower troposphere and advected poleward along a warm conveyor belt during a synoptic‐scale disturbance. The tropopause was elevated in the region with the low‐ozone air mass. Stratospheric intrusions accompanied the disturbances. On the basis of storm track and stratospheric intrusion climatologies, such events appear to be more frequent from September through March than the rest of the year.
Mesoscale numerical investigations of air traffic emissions over the North Atlantic during SONEX flight 8: A case study
Authors: Bieberbach George , Fuelberg Henry E. , Thompson Anne M. , Schmitt Alfons , Hannan John R. , Gregory G. L. , Kondo Yutaka , Knabb Richard D. , Sachse G. W. , Talbot R. W.
Published: September 2002

Chemical data from flight 8 of NASA's Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) exhibited signatures consistent with aircraft emissions, stratospheric air, and surface‐based pollution. These signatures are examined in detail, focusing on the broad aircraft emission signatures that are several hundred kilometers in length. A mesoscale meteorological model provides high‐resolution wind data that are used to calculate backward trajectories arriving at locations along the flight track. These trajectories are compared to aircraft locations in the North Atlantic Flight Corridor (NAFC) over a 27–33 hour period. Time series of flight level NO and the number of trajectory/aircraft encounters within the NAFC show excellent agreement. Trajectories arriving within the stratospheric and surface‐based pollution regions are found to experience very few aircraft encounters. Conversely, there are many trajectory/aircraft encounters within the two chemical signatures corresponding to aircraft emissions. Even many detailed fluctuations of NO within the two aircraft signature regions correspond to similar fluctuations in aircraft encountered. These NO spikes are due to the superposition of 14 to 25 aircraft plumes transported to the DC‐8 flight track during the previous 33 hours. Results confirm that aircraft emissions were responsible for two chemical signatures observed during SONEX flight 8. They also indicate that high‐resolution meteorological modeling, when coupled with detailed aircraft location data, is useful for understanding chemical signatures from aircraft emissions at scales of several hundred kilometers.
Model calculations of the impact of NOx from air traffic, lightning, and surface emissions, compared with measurements
Authors: Meijer E. W. , van Velthoven P. F. J. , Thompson A. M. , Pfister L. , Schlager H. , Schulte P. , Kelder H.
Published: September 2002

The impact of NOx from aircraft emissions, lightning, and surface contributions on atmospheric nitrogen oxides and ozone in the North Atlantic flight corridor has been investigated with the three‐dimensional global chemistry transport model TM3 by partitioning the nitrogen oxides and ozone according to source category. The results have been compared with Pollution from Aircraft Emissions in the North Atlantic flight corridor (POLINAT 2) and Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) airborne measurements in the North Atlantic flight corridor in 1997. Various cases have been investigated: measurements during a stagnant anticyclone and an almost cutoff low, both with expected high aircraft contributions, a southward bound flight with an expected strong flight corridor gradient and lightning contributions in the south, and a transatlantic flight with expected boundary layer pollution near the U.S. coast. The agreement between modeled results and measurements is reasonably good for NO and ozone. Also, the calculated impact of the three defined sources was consistent with the estimated exposure of the sampled air to these sources, obtained by specialized back trajectory model products. Model calculations indicate that aircraft contributes 55% to the mean NOx concentration and 10% to the O3 concentration in the North Atlantic flight corridor in October 1997, whereas lightning and surface emissions add 15% and 25% to the NOx concentration and 20% and 30% to the O3 concentration.
Measurements of stratospheric plume dispersion by imagery of solid rocket motor exhaust
Authors: Beiting Edward J.
Published: September 2002

Plume expansion from nine space shuttle and Titan IV vehicles was measured at altitudes of 18, 24, and 30 km in the stratosphere. The plume diameters, inferred from electronic images of polarized, near‐infrared solar radiation scattered from the exhaust particles, increased linearly with time. The expansion rate was measured for as long as 50 min. Observations made simultaneously at multiple altitudes showed that the expansion rate increased with increasing altitude for six measurements made at Cape Canaveral but decreased between 24 and 30 km for the one measurement made at Vandenberg Air Force Base. The average expansion rates for all measurements are 4.3±1.0 m s−1 at 18 km, 6.8±1.9 m s−1 at 24 km, and 8.7±2.4 m s−1 at 30 km. Expansion rates varied from launch to launch by as much as a factor of 1.6 at 18 km, 2.2 at 24 km, and 2.6 at 30 km. No correlation between the expansion rate and wind speed or wind shear was evident. These data are compared with several models for diffusivity and are used to update a comprehensive particle model of solid rocket motor exhaust in the stratosphere. The expansion rates are required by models to calculate the spatial extent and temporal persistence of the local stratospheric ozone depletion cause by solid rocket exhaust.
Simulation of mineral dust effects on UV radiation levels
Authors: Díaz Juan P. , Expósito Francisco J. , Torres Carlos J. , Carreño Virgilio , Redondas A.
Published: September 2002

The role played by aerosols on UV radiative transfer in the atmosphere is very uncertain. This is especially true regarding mineral dust. To determine the sensitivity of the UV levels to the presence of this atmospheric specie, we have simulated the UV irradiance with different vertical distributions of mineral dust. We have used a discrete ordinates radiative transfer model to obtain the UV levels both at sea level and at 3000 m. We have computed the aerosol single‐scattering albedo, the phase function, and the asymmetry factor by Mie scattering theory. The background aerosol profiles were taken from WCRP [1986] models, whereas the radiative properties of mineral dust have been calculated from the aerosol size distribution obtained during Saharan dust invasions at Tenerife island (28.5°N, 16.3°W). The values for aerosol optical depth assumed as input for the model calculations are 0.2 (at 550 nm) for clean background aerosols and 0.3 (at 550 nm) for the mineral dust component. From the results we can conclude that the dust vertical size distribution can affect the irradiance ratio F (with Saharan dust)/F (no Saharan dust) by 2–4%. In addition, we observe that to the same total optical depth the diffuse UV levels depend not only on the vertical dust distribution but also on the background aerosol vertical distribution. We have computed differences for the diffuse radiation fluxes of about 5% between a maritime and a continental model to the same mineral dust vertical distribution.
Some observational and modeling evidence of long‐range transport of air pollutants from Europe toward the Israeli coast
Authors: Wanger Aryeh , Peleg Mordechai , Sharf Geula , Mahrer Yitzhak , Dayan Uri , Kallos George , Kotroni Vassiliki , Lagouvardos Konstantinos , Varinou Maria , Papadopoulos Anastasios , Luria Menachem
Published: September 2002

The present paper reports results of a study that attempted to elucidate the factors causing relatively high levels of particulate sulfate that have frequently been observed over central Israel. Aircraft research flights were performed some 70 km west of and parallel to the Israeli coastline during September 1993 and June 1994. Comparison between the two measurement periods revealed a distinctive difference between the two different sampled air masses. While both air masses were nearly homogeneous throughout the measurement period and along the 180 km flight path, the air mass sampled in September 1993 was much “cleaner” than the air mass sampled during June 1994. The concentrations of the air pollutants measured during the 1993 campaign averaged 0.7±0.4 parts per billion by volume (ppbv) SO2, 1.0±0.6 ppbv NOy, 39±7 ppbv O3 and 38±7 nmol/m3 particulate sulfate, whereas in the second period the levels averaged 3.0±1.0, 3.9±1.8, 48±9, and 10 ±63, respectively. These results suggest that the two air masses traveled different paths before reaching the eastern Mediterranean region. Further examination of the air mass sources and transport were performed using the Regional Atmospheric Modeling System for meteorological simulations and the Hybrid Particle and Concentration Transport Package for dispersion modeling. The model simulation showed that during the 1993 measurement period, the pollution sources in southern Europe and the Balkans did not effect the eastern coasts of the Mediterranean, while the synoptic conditions and simulation results for the June 1994 period indicated that the winds over the eastern Mediterranean tended to be northwesterly and thus forcing the polluted air masses toward the coast of Israel.
Absorption of solar radiation by the atmosphere as determined using satellite, aircraft, and surface data during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE)
Authors: Valero Francisco P. J. , Minnis Patrick , Pope Shelly K. , Bucholtz Anthony , Bush Brett C. , Doelling David R. , Smith William L. , Dong Xiquan
Published: September 2002

Data sets acquired during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE) using simultaneous measurements from five independent platforms (GOES 8 geostationary satellite, ER‐2, Egrett and Twin Otter aircraft, and surface) are analyzed and compared. A consistent data set can be built for selected days during ARESE on the basis of the observations from these platforms. The GOES 8 albedos agree with the ER 2, Egrett, and Twin Otter measured instantaneous albedos within 0.013±0.016, 0.018±0.032, and 0.006±0.011, respectively. It is found that for heavy overcast conditions the aircraft measurements yield an absorptance of 0.32±0.03 for the layer between the aircraft (0.5–13 km), while the GOES 8 albedo versus surface transmittance analysis gives an absorptance of 0.33±0.04 for the total atmosphere (surface to top). The absorptance of solar radiation estimated by model calculations for overcast conditions varies between 0.16 and 0.24, depending on the model used and on cloud and aerosol implementation. These results are in general agreement with recent findings for cloudy skies, but here a data set that brings together independent simultaneous observations (satellite, surface, and aircraft) is used. Previous ARESE results are reexamined in light of the new findings, and it is concluded that the overcast absorptance in the 0.224–0.68 μm spectral region ranges between 0.04±0.06 and 0.08±0.06, depending on the particular case analyzed. No evidence of excess clear‐sky absorption beyond model and experimental errors is found.
Modeling the chemistry of the marine boundary layer: Sulphate formation and the role of sea‐salt aerosol particles
Authors: van den Berg Ad , Dentener Frank , Lelieveld Jos
Published: September 2002

A one‐dimensional model is presented that interactively simulates the dynamics and the gas‐aqueous phase chemistry of the cloud‐topped marine boundary layer. The model is described and tested using observations from the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) measurement campaign. The comparison generally indicates satisfactory agreement for dynamical properties and chemical species, except for SO2. We present several explanations for this discrepancy. However, a conclusive account is dependent on quantitative information about free tropospheric SO2 and H2O2 that is not available. Furthermore, a series of sensitivity runs is presented to explain the large quantities of non‐sea‐salt sulphate associated with sea‐salt particles, as observed during ASTEX/MAGE. The main conclusions are that most sulphate associated with sea‐salt particles is formed in cloud droplets that subsequently evaporate and that only a small amount is formed in deliquesced aerosol particles. The model results are sensitive to changes in the assumed sea‐salt emission rate and the overall aerosol size distribution. The latter indicates that a shift in the sea‐salt aerosol distribution toward the smaller particle sizes might explain the observed amount of sulphate associated with sea‐salt particles.
Lagrangian approach for Stratospheric Aerosol and Gas Experiment (SAGE) II profile intercomparisons
Authors: Lu Cheng‐Hsuan , Yue Glenn K. , Manney Gloria L. , Jäger Horst , Mohnen Volker A.
Published: September 2002

Trajectory calculations are employed to identify Stratospheric Aerosol and Gas Experiment (SAGE) II flights sampling the same air mass as is observed by a ground‐based aerosol lidar at Garmisch‐Partenkirchen, Germany (47.5°N, 11.1°E, 735 m above sea level), during the periods of January–April 1993 and January–December 1998. Intercomparisons between lidar‐observed and SAGE II‐derived backscatters at 532 nm are conducted. Percentage differences between trajectory‐tracked SAGE II profiles and ground‐based lidar observations with respect to aerosol lidar are generally within 20–40%, though localized discrepancies >50% are found for some cases. In addition, aerosol extinction, aerosol to molecular extinction ratio, and ozone mixing ratio profiles obtained from the SAGE II flights overpassing the vicinity of Garmisch‐Partenkirchen during the January–April 1993 period are compared with profiles obtained from corresponding trajectory‐tracked SAGE II flights. Percentage discrepancies between SAGE II ozone profiles are generally within 10–20% above the Junge layer. Data comparisons for aerosol profiles show mixed results. While some cases agree within the error bars, there are several cases where percentage discrepancies exceed 50%.
Radar observations of longitudinal variability of tidal/planetary waves and mean motions in the tropical mesosphere
Authors: Zhou Q. H. , Monroy H. , Fritts D. C. , Ierkic H. M. , Isham B. , Isler J. R. , Palo S. E.
Published: September 2002

During the summer of 1995, two MF radars located at Hawaii and Puerto Rico were in operation to measure mesospheric motions. We use the data obtained at the two sites to study the longitudinal variability of mean winds, planetary waves, and tides. On average the winds at Puerto Rico were more westward and equatorward than those at Hawaii. Quasi 2‐day planetary wave activity was evident most of the time from June 28 to July 25. The quasi 2‐day wave had a zonal wave number (m) of 3 during one occasion and 4 during another, and the periods of the two planetary waves were 56 and 48 hours, respectively. The diurnal tide at Puerto Rico was stronger than that at Hawaii above 86 km, and the semidiurnal tide at Hawaii was strongly damped in the altitude range of 90–98 km. Both the semidiurnal and the diurnal tides were apparently modulated by longer‐period waves, which was perhaps the most important factor in accounting for their large spatial and temporal variability. The phase difference at the two sites deviates considerably from the expectation of purely migrating tides.
Space‐time rainfall organization and its role in validating quantitative precipitation forecasts
Authors: Zepeda‐Arce Jesus , Foufoula‐Georgiou Efi , Droegemeier Kelvin K.
Published: September 2002

The scope of this paper is to introduce a suite of new multiscale statistical measures which can be used, in addition to traditional measures, to compare observed and model‐predicted patterns for model validation. Recent research on analysis of observed precipitation patterns at a multitude of scales has revealed interesting spatial and spatiotemporal organizations which have often been related to physical properties of the storm environment. By testing whether this multiscale statistical organization is also reproduced in the model‐predicted patterns or whether there are significant biases and disagreements in such comparisons is conjectured to hold promise for understanding model performance and guiding future model improvements. Results from application of the developed methodologies to the May 7–8, 1995, multisquall line storm over central Oklahoma are presented and discussed in light of the additional information gained by the new validation measures as compared to traditional measures.
Remote sensing of cloud properties using MODIS airborne simulator imagery during SUCCESS: 3. Cloud Overlap
Authors: Baum Bryan A. , Spinhirne James D.
Published: September 2002

The vertical distribution of cloud layers has a significant effect on atmospheric radiative heating/cooling distributions. While multiple cloud layers are often observed to occur simultaneously by surface observers, satellite cloud retrieval methodology typically assumes that any individual imager pixel contains a single cloud layer. The purpose of this paper is to demonstrate a bispectral method that detects imager pixels containing possible cloud overlap when an optically thin cirrus cloud overlies a low‐level water cloud, with at least a 2‐km separation between layers. The method is developed from a scatterplot of the near‐infrared 1.63‐μm band reflectances and the 11‐μm brightness temperatures using data from the MODIS (Moderate‐Resolution Imaging Spectroradiometer) airborne simulator (MAS). The bispectral method is applied to a scene recorded by the MAS scanning spectrometer that was flown on the NASA ER‐2 during the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) field campaign during April and May 1996. For a scene recorded on April 21, 1996, at 2000 UTC, the complex vertical cloud structure was captured by lidar backscatter measurements from the Cloud Lidar System (CLS). The bispectral method appears to have a promising facility for identifying areas containing potential cloud overlap.
Non‐LTE effects on retrieval of temperature from the CO2 laser bands using CIRRIS 1A data
Authors: Miller Steven M. , Winick Jeremy , Snell Hilary E.
Published: September 2002

It is well known that in the upper stratosphere and lower mesosphere, the CO2 laser band (00011–10001) transitions are populated by both local thermodynamic equilibrium (LTE) and non‐LTE mechanisms. Examination of infrared (IR) limb emission measurements from the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS 1A) experiment clearly illustrates this effect. The presence of non‐LTE emissions, if left unaccounted for, will severely degrade the retrieval of kinetic temperature profiles. We have applied a non‐LTE compensation technique whereby the non‐LTE component is modeled and the resulting non‐LTE radiance is subtracted from the measured radiances. The kinetic temperature profile is then retrieved utilizing the modified data. As a means of validating this approach, we have compared the resulting temperature profiles to ones retrieved using the 792 cm−1 Q branch of CO2, the (11101–10002) transition, which is not significantly affected by non‐LTE excitation.
An overview of the Stratospheric‐Tropospheric Experiment: Radiation, Aerosols, and Ozone (STERAO)‐Deep Convection experiment with results for the July 10, 1996 storm
Authors: Dye J. E. , Ridley B. A. , Skamarock W. , Barth M. , Venticinque M. , Defer E. , Blanchet P. , Thery C. , Laroche P. , Baumann K. , Hubler G. , Parrish D. D. , Ryerson T. , Trainer M. , Frost G. , Holloway J. S. , Matejka T. , Bartels D. , Fehsenfeld F. C. , Tuck A. , Rutledge S. A. , Lang T. , Stith J. , Zerr R.
Published: September 2002

The Stratospheric‐Tropospheric Experiment: Radiation, Aerosols and Ozone (STERAO)‐Deep Convection Field Project with closely coordinated chemical, dynamical, electrical, and microphysical observations was conducted in northeastern Colorado during June and July of 1996 to investigate the production of NOx by lightning, the transport and redistribution of chemical species in the troposphere by thunderstorms, and the temporal evolution of intracloud and cloud‐to‐ground lightning for evolving storms on the Colorado high plains. Major observations were airborne chemical measurements in the boundary layer, middle and upper troposphere, and thunderstorm anvils; airborne and ground‐based Doppler radar measurements; measurement of both intracloud (IC) and cloud‐to‐ground (CG) lightning flash rates and locations; and multiparameter radar and in situ observations of microphysical structure. Cloud and mesoscale models are being used to synthesize and extend the observations. Herein we present an overview of the project and selected results for an isolated, severe storm that occurred on July 10. Time histories of reflectivity structure, IC and CG lightning flash rates, and chemical measurements in the boundary layer and in the anvil are presented showing large spatial and temporal variations. The observations for one period of time suggest that limited mixing of environmental air into the updraft core occurred during transport from cloud base to the anvil adjacent to the storm core. We deduce that the most likely contribution of lightning to the total NOx observed in the anvil is 60–90% with a minimum of 45%. For the July 10 storm the NOx produced by lightning was almost exclusively from IC flashes with a ratio of IC to total flashes >0.95 throughout most of the storm's lifetime. It is argued that in this storm and probably others, IC flashes can be major contributors to NOx production. Superposition of VHF lightning source locations on Doppler retrieved air motion fields for one 5 min time period shows that lightning activity occurred primarily in moderate updrafts and weak downdrafts with little excursion into the main downdraft. This may have important implications for the vertical redistribution of NOx resulting from lightning production, if found to be true at other times and in other storms.
Wintertime precipitation behavior in the western Canadian Arctic region
Authors: Asuma Yoshio , Inoue Yusuke , Kikuchi Katsuhiro , Kajikawa Masahiro , Sato Noboru , Hayasaka Tadahiro
Published: September 2002

To investigate the precipitation formation process in the two major types of weather systems (“Pacific origin” and “storm track” types) in the western Canadian Arctic region, an X‐band vertical pointing Doppler radar, microwave radiometer were installed at Inuvik, Northwest Territories, Canada, during the midwinter of 1995/1996. Precise precipitation observations specially for ice crystals with replicator, microscope, and close‐up photos were also conducted at the same place. Precipitation formation mechanisms were quite different between these two major weather systems. For the Pacific‐origin‐type disturbance, warm and moist air was advected from the Pacific Ocean between 1.5 and 3.5 km msl. Convective echo patterns appeared by radar, and a large amount of precipitable water vapor and liquid water path were estimated by a microwave radiometer. As the air temperature was below the freezing point, the liquid water was identified as being in the supercooled state. Densely rimed dendrites and graupel particles were observed predominantly on the ground. Collision and coalescence processes of supercooled cloud droplets were dominant. On the contrary, for the storm track disturbance the moisture came from the Arctic Ocean, and strong winds were observed on the ground. The air mass was colder than −20°C throughout the layer. Stratiform echo patterns were observed by radar, a smaller amount of precipitable water vapor, and only a small liquid water path were observed by a microwave radiometer. It was suggested that the condensation growth was predominant. Snow crystal shapes of plates, columns, and bullet rosettes were observed predominantly on the ground.
Consistent sets of atmospheric lifetimes and radiative forcings on climate for CFC replacements: HCFCs and HFCs
Authors: Naik Vaishali , Jain Atul K. , Patten Kenneth O. , Wuebbles Donald J.
Published: September 2002

Recognition of deleterious effects of chlorine and bromine on ozone and climate over the last several decades has resulted in international accords to halt the production of chlorine‐containing chlorofluorocarbons (CFCs) and bromine‐containing halons. It is well recognized, however, that these chemicals have had important uses to society, particularly as refrigerants, as solvents, as plastic blowing agents, as fire retardants and as aerosol propellants. This has led to an extensive search for substitute chemicals with appropriate properties to be used in place of the CFCs and halons. The purpose of this study is to evaluate in a consistent manner the atmospheric lifetime and radiative forcing on climate for a number of replacement compounds. The unique aspect of this study is its attempt to resolve inconsistencies in previous evaluations of atmospheric lifetimes and radiative forcings for these compounds by adopting a uniform approach. Using the latest version of our two‐dimensional chemical‐radiative‐transport model of the global atmosphere, we have determined the atmospheric lifetimes of 28 hydrohalocarbons (HCFCs and HFCs). Through the comparison of the model‐calculated lifetimes with lifetimes derived using a simple scaling method, our study adds to earlier findings that consideration of stratospheric losses is important in determining the lifetimes of gases. Discrepancies were found in the reported lifetimes of several replacement compounds reported in the international assessment of stratospheric ozone published by the World Meteorological Organization [Granier et al., 1999] and have been resolved. We have also derived the adjusted and instantaneous radiative forcings for CFC‐11 and 20 other halocarbons using our radiative transfer model. The sensitivity of radiative forcings to the vertical distribution of these gases is investigated in this study and is shown to be significant. The difference in the global radiative forcing arising from the assumption of a constant vertical profile for these gases is found to range from 0 to 36%, with higher difference for short‐lived gases. Global Warming Potentials (GWPs) for the compounds are determined using the lifetimes and radiative forcings evaluated in this study and are found to differ from values reported by Granier et al. [1999] owing to the differences in our calculated radiative forcings and lifetimes.
Human‐activity‐enhanced formation of organic aerosols by biogenic hydrocarbon oxidation
Authors: Kanakidou Maria , Tsigaridis Kostas , Dentener Frank J. , Crutzen Paul J.
Published: September 2002

Tropospheric aerosol can affect climate and the chemistry of the atmosphere. Organic particulates form a significant fraction of the atmospheric suspended matter over forested areas and may originate to a large extent from the oxidation of natural hydrocarbons. A three‐dimensional global model of the troposphere is used to evaluate the contribution to the global organic aerosol (OA) source of the secondary organic aerosol (SOA) derived from the ozonolysis of biogenic volatile organic compounds (BVOC) and its evolution since preindustrial times. BVOC have been represented by a mixture of α‐ and β‐pinenes, and their aerosol‐forming parameters and chemical reactivities versus O3, OH, and NO3 have been estimated using laboratory information. An important factor in SOA formation is the deposition of condensable aerosol oxidation products onto preexisting organic aerosol, and this has been taken into account. The thus‐calculated source of SOA is evaluated to have increased from 17–28 Tg/yr in preindustrial times to 61–79 Tg/yr at present. This threefold to fourfold enhancement of the formation of organic aerosol from natural BVOC is attributed to an increase in ozone and organic aerosol from anthropogenic sources. The main uncertainties involved in our calculations are related to the composition of BVOC emissions and the details of their aerosol formation capabilities.
Carbon monoxide, hydrogen, and methane uptake by soils in a temperate arable field and a forest
Authors: Yonemura S. , Kawashima S. , Tsuruta H.
Published: September 2002

CO, H2, and CH4 uptake by the soil of an arable field and a forest soil (360 m apart) was measured by a closed‐chamber method in temperate Japan for about 1 year. CO production observed was exponentially dependent on top soil temperature. CO production was greater in the forest soil than in the soil of the arable field at the same soil temperature. (Gross) CO, H2, and CH4 deposition velocities ranged from 0 to 7×10−2, from 0 to 9×10−2, and from 0.05 to 0.1×10−2 cm s−1 in the arable field and from 1.5 to 4.5×10−2, 5 to 8×10−2, and from 0.3 to 0.6×10−2 cm s−1 in the forest, respectively. Variations in the deposition velocities were smaller in the forest than in the arable field and corresponded to variations in soil moisture in the top soil. Seasonal trends caused by the variation in temperature were observed only for CH4 deposition, reflecting the clear dependence on soil temperature. Application of dead plant material to the arable field led to acceleration of CO and H2 deposition onto the soil. The deposition velocities of CO and H2 were positively correlated (n =36, R2* = 0.881, p<0.0001; R2* is the coefficient of determination adjusted by degrees of freedom) in the arable field and (n = 37, R2* = 0.408, p<0.0001) in the forest, suggesting diffusion control on their deposition velocities.
Columnar physical and radiative properties of atmospheric aerosols in north central Spain
Authors: Cachorro Victoria E. , Durán Plinio , Vergaz Ricardo , de Frutos Angel M.
Published: September 2002

Direct solar irradiance spectra under clear skies have been measured in a rural station in the region of Castilla y León in north central Spain from March to November 1995 to determine the physical and radiative characteristics of atmospheric aerosols. About 300 spectra were measured with a LI‐COR Model LI‐1800 spectroradiometer, with a spectral resolution (full width at half maximum) of 6 nm from 300 nm to 1100 nm. This moderately high spectral resolution permitted the retrieval of the spectral aerosol optical depth (AOD) using a method based on spectral windows in nonabsorbing regions and modelling by the Ångström formula in the spectral range 370–1000 nm. These modelled Ångström AOD spectra were used to determine the columnar particle size distribution of atmospheric aerosols using Mie theory and a pseudo‐inversion method. We assumed a monomodal lognormal function with a fixed standard deviation, σ = 2.5, and two particle refractive indices (absorbing and nonabsorbing aerosols) based on climatological characteristics of the continental area of study. Physical parameters, such as the effective radius, the total vertical volume, and mass loading, have been derived. The effective radius ranged from 0.015 to 1 μm, and the values of the vertical aerosol volume, from 0.01 to 0.3 μm. Aerosol mass loading varied from 0.03 to 0.53 g m−2. Radiative properties represented by the asymmetry parameter g, the single‐scattering albedo ωo, and the phase function P were also evaluated for each of the retrieved particle size distributions as a function of wavelength. Because the radiative parameters show low wavelength dependence from 300 to 1000nm, we present their behavior at 500 nm. The parameter g varies from 0.45 to 0.75 (the average value is 0.6), and ωo varies from 0.75 to 0.94. Relationships of the effective radius and the asymmetry parameter with the Ångström turbidity parameter α have been found, which is of interest for the parametrization of aerosol properties. Finally, the phase function at 500nm, 120° (where it has a minimum) has also been evaluated and correlated with the α parameter, thus providing information about the size of aerosol particles. The uncertainties of all of these parameters are also estimated and discussed.