bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary organic aerosol 2. Thermodynamic model for gas/particle partitioning of molecular constituents
Authors: Pun Betty K. , Griffin Robert J. , Seigneur Christian , Seinfeld John H.
Published: October 2002

A model that predicts secondary organic aerosol (SOA) formation based on the thermodynamic equilibrium partitioning of secondary organic oxidation products has been developed for implementation into atmospheric models. Hydrophobic secondary products are assumed to partition to an absorbing organic aerosol consisting of primary organic aerosol (POA) and other secondary hydrophobic organics according to an equilibrium partitioning coefficient calculated iteratively for each secondary compound present. The hydrophobic module is evaluated by studying the partitioning of octadecanoic acid to surrogate POA species. As expected, the amount of octadecanoic acid predicted to be present in the aerosol phase increases as the total amount of absorbing material increases or as the total amount of acid present increases. Hydrophilic secondary compounds partition to an aqueous phase via Henry's law; the fraction of each compound's mass that partitions is determined by its Henry's law constant and its acid dissociation constant(s). The available liquid water content (LWC) of the aerosol is determined iteratively between an inorganic aerosol module and the hydrophilic module, which is evaluated by studying the partitioning of glyoxalic and malic acids. While glyoxalic acid tends to remain in the gas phase, malic acid partitions strongly to the aqueous phase, with ions being the dominant form in the aqueous phase. As expected, an increase in relative humidity increases the amount of water associated with the organics (ΔLWC), and a lower aerosol pH favors molecular solutes over ionized forms. Increasing pH results in higher effective Henry's law constants for the acids, yielding higher organic aerosol concentrations. Results also indicate that increasing ΔLWC induces additional partitioning of inorganics to the aqueous phase.
Electrochemical concentration cell (ECC) ozonesonde pump efficiency measurements and tests on the sensitivity to ozone of buffered and unbuffered ECC sensor cathode solutions
Authors: Johnson Bryan J. , Oltmans Samuel J. , Vömel Holger , Smit Herman G. J. , Deshler Terry , Kröger Chris
Published: October 2002

On the basis of extensive laboratory and field tests of electrochemical concentration cell (ECC) ozonesondes, a height‐dependent artifact in ozone profile measurements was found that is primarily due to side reactions of the phosphate buffers used in the “standard” 1% potassium iodide sensing solution. The influence of the buffers was revealed as a result of new, direct measurements of the ozonesonde pump flow rate efficiency made in an environmental chamber using an oil bubble flowmeter developed at National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL). The new flow rate measurements give pump efficiency correction factors that are 2 and 15% greater at 100 and 5 hPa, respectively, than those used in currently recommended procedures. Profile measurements using ozonesondes with differing ECC sensor solutions, on dual‐sonde balloons and experiments in a simulation chamber, show that the impact of the buffers is most pronounced above the ozone partial pressure maximum. The effect is about a 10–15% overmeasurement of ozone at an altitude of 30 km. Careful consideration must be given to the combination of the sensing solution composition and pump efficiency correction if representative ozone profiles are to be obtained from ozonesonde measurements.
PM2.5 carbonate concentrations at regionally representative Interagency Monitoring of Protected Visual Environment sites
Authors: Chow Judith C. , Watson John G.
Published: October 2002

This experiment shows that carbonate concentrations are negligible at most Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring sites. Even when present, carbonate does not cause significant biases in total carbon (TC), organic carbon (OC), and elemental carbon (EC) concentrations in the IMPROVE protocol. The analysis also shows that acidification to remove interferences from carbonates is not necessary when using a thermal evolution method in which the highest temperature is less than 800°C. Seventy‐seven samples with the highest calcium concentrations from 58 sites in the IMPROVE network were analyzed for carbonate by acidification. Measured carbonate carbon concentrations at most sites were <100 ng m−3, with many less than lower quantifiable limits; the highest carbonate carbon of 420 ng m−3 was measured at Guadalupe Mountains National Park in western Texas. Comparison of EC measured at 800°C with and without acidification showed no consistent biases for the nonacidified analysis, even when carbonate levels were high. Acidification may be advisable when sampling particle sizes larger than 2.5 μm, when samples are acquired at locations where carbonate carbon is expected to be high, or when >800°C temperatures are applied during thermal evolution carbon analysis.
Validation of version 5.20 ILAS HNO3, CH4, N2O, O3, and NO2 using ground‐based measurements at Arrival Heights and Kiruna
Authors: Wood S. W. , Bodeker G. E. , Boyd I. S. , Jones N. B. , Connor B. J. , Johnston P. V. , Matthews W. A. , Nichol S. E. , Murcray F. J. , Nakajima H. , Sasano Y.
Published: October 2002

Ground‐based measurements of O3 and NO2 columns at Kiruna (68°N) and Arrival Heights (78°S) were used to validate stratospheric profile measurements of the same species by the satellite‐based Improved Limb Atmospheric Spectrometer (ILAS) flown between November 1996 and June 1997. In addition, measurements of HNO3, CH4, and N2O made at Arrival Heights are compared with measurements of these species by ILAS. Even though there were no temporal coincidences in the latter comparison, the ground‐based data provide a climatological context for the ILAS measurements. ILAS profiles measured within 10° of longitude and 2° of latitude of each site were used. For the species with large tropospheric components (CH4 and N2O), ILAS profiles were integrated upward from 12 km and were compared with ground‐based retrievals of partial columns above 12 km. For O3, which is primarily stratospheric but has an appreciable tropospheric component, tropospheric columns (typically to 8–10 km altitude) calculated from ozonesonde climatologies were added to the integrated ILAS profiles to allow comparison with ground‐based total column ozone measurements. Tropospheric columns of HNO3 and NO2 were assumed to be sufficiently small so that ILAS profiles integrated above 8 km could be compared directly with ground‐based total column measurements.
Chemical characterization of the Saharan dust end‐member: Some biogeochemical implications for the western Mediterranean Sea
Authors: Guieu C. , Loÿe‐Pilot M.‐D. , Ridame C. , Thomas C.
Published: October 2002

Two types of samples were used to chemically characterize the Saharan end‐member: fine fractions of surface soil samples collected in Northern Africa and particulate phases of typical Saharan rains. Since the concentrations measured in the particulate phase of the Saharan rains were corrected from the dissolution losses in rainwater, these particles were considered to be representative of the transported Saharan dust before being blended into rainwater. Al, Fe, P, and Pb were analyzed: except for lead, the chemical composition of the transported Saharan dust was more homogeneous than the composition of individual soils. As confirmed by the air mass back trajectories, the higher level of homogeneity of the aerosol is partly due to the fact that a dust event affects a large area of the Saharan desert, and the composition of the particles reflects the average composition of the eroded areas. Pb concentration in the transported dust reflected an anthropogenic fraction. By using Pb/Al measurements from the soils it was shown that a typical Saharan rain event with no mixing with air masses from Europe appears to be very rare in the Mediterranean environment. The following values are proposed to characterize the Saharan dust end‐member: Al (%) = 7.09 ± 0.79; Fe (%) = 4.45 ± 0.49; P (%) = 0.082 ± 0.011; Pb (ppm) = 24 ± 9. This study suggests that the [element/Al or Fe)] ratio is also useful to characterize the Saharan end‐member as they are very homogeneous for the two sample types. Saharan dust represents a potential source of nutrients (P, Fe) for the Mediterranean water. Indeed, it accounts for ∼30–40% of the total atmospheric flux of phosphorus in the western Mediterranean, and it governs the biogeochemical cycle of iron being the main source of dissolved iron in the western Mediterranean waters.
Solar ultraviolet irradiance for clear sky days incident at Rosario, Argentina: Measurements and model calculations
Authors: Piacentini R. D. , Alfano O. M. , Albizzati E. D. , Luccini E. A. , Herman J. R.
Published: October 2002

Results of measurements are presented of clear‐sky day solar UV irradiance (295–385 nm) in the August 1995 to June 1999 period at the Observatorio Astronómico de Rosario, Argentina, a place typical of the most populated Humid Pampa region of the country. The data give a detailed description of UV variation as a function of time in a given day and for different days of the year. Model calculations for clear‐sky days at noon are done, employing the tropospheric ultraviolet visible radiation model (TUV) Madronich radiative transfer code, with the mean monthly ozone and aerosol content of the atmosphere and surface reflectivity provided by the Total Ozone Mapping Spectrometer (TOMS)/NASA instrument on board of the Earth Probe satellite. Two aerosol characteristics are tested in the model, rural‐urban and mean urban, with the mean urban giving best agreement with the measurements. A simple mathematical expression is proposed for the “mean” typical curve, which gives a good approximation to the clear sky UV noon data for Rosario. It can be used for extending the results to nearby places and for comparison with other regions of the world having similar atmospheric and albedo conditions.
A global assessment of the mosaic approach to modeling land surface heterogeneity
Authors: Molod Andrea , Salmun Haydee
Published: October 2002

Modeling the impact of small‐scale land surface heterogeneities on scales resolved by general circulation models (GCMs) has long been a challenging problem. We present here a global offline comparison between two approaches to account for the heterogeneities. These approaches are mosaic, which computes separate energy budgets for each surface type within a grid box, and dominant, which assumes that a grid box can be completely described by the dominant vegetation. The experiments are all conducted using the turbulence parameterization of the Goddard Earth Observing System (GEOS) GCM, coupled to the Koster‐Suarez Land Surface Model. The results show a large impact in the high‐ and middle‐latitude Northern Hemisphere climates. At high latitudes the warming of the surface after the spring snowmelt is more rapid for dominant. At midlatitudes, where the surface is potentially under moisture stress, the mosaic approach results in a drier, warmer climate. This impact is determined to a large extent by the influence of bare soil areas on the grid‐scale climate. The impact of the choice of approach is less important over more homogeneous terrains, such as deserts, as can be expected in the offline framework. These results support the need for a mosaic‐type approach to properly model the coupling at the land surface interface.
Mass balance of organic carbon fractions in atmospheric aerosols
Authors: Alves Célia , Carvalho Abel , Pio Casimiro
Published: October 2002

Total suspended particulate matter was collected in two Portuguese urban areas (Lisbon and Aveiro) and in a Finnish forested site. Samples were sequentially extracted with dichloromethane and water. The solvent extract was separated by flash chromatography into aliphatics, aromatics, carbonyls, alcohols, and an acidic fraction, and analyzed by gas chromatography‐mass spectrometry. An organic/black carbon analyzer was used to evaluate the carbonaceous matter in filters, the water‐soluble fraction, solvent extractable material, and the content of different organic classes. Results showed that the common simple extraction with dichloromethane is able to dissolve less than 50% of the particulate organic material. The successive extraction with water removes an important quantity of the leftover organic polar compounds. The sum of both extractions recovers between 70% and 90% of the organic carbon present. The amount of oxygenated compounds is frequently more than 70% of the extracted material, with a large predominance of organic acids and alcohols, especially for particles with diameters less than 0.49 μm. The organic compounds identified in the extractable atmospheric particulate matter are represented by primary compounds with both anthropogenic and biogenic origin, which mainly derive from vegetation waxes and from petrogenic sources. Secondary products resulting from the oxidation of volatile organic compounds were also detected. The water‐soluble fraction contains essentially oxocarboxylic and dicarboxylic acids, and cellulosic constituents. In accordance with the anthropogenic characteristics of the sampling sites, nonpolar fractions constitute up to 24% of the extracted organic carbon in Lisbon and present high levels of petroleum markers, while in the forested station these compounds represent 8%. The oxygenated organic compounds account for 76–92% of the extracted carbon in samples from Aveiro and Finland. Owing to favorable photochemical conditions during the sampling campaign, secondary organic constituents present higher levels in Aveiro. The forested site is the one where the water‐soluble components show greater variability and concentrations.
Diagnosing black carbon trends in large urban areas using carbon monoxide measurements
Authors: Baumgardner Darrel , Raga G. , Peralta O. , Rosas I. , Castro T. , Kuhlbusch T. , John A. , Petzold A.
Published: October 2002

The relationship between black carbon (BC) and carbon monoxide (CO) has been analyzed using measurements from two sites in Mexico City and five urban areas in Germany. The correlation coefficient between BC and CO is greater than 0.90 for all sites. The average slope of the linear regression line for BC versus CO is 2.2 μg mg−1 for German sites and 1.1 μg mg−1 in Mexico City. The most important factors that affect the BC to CO relationship appear to be the ratio of diesel to gasoline usage and the combustion efficiency of vehicles in a particular area. The results of this analysis suggest that CO measurements in urban areas can be used to estimate BC mass when direct measurements are not available.
Seasonal soil fluxes of carbon monoxide in burned and unburned Brazilian savannas
Authors: Kisselle Keith W. , Zepp Richard G. , Burke Roger A. , de Siqueira Pinto Alexandre , Bustamante Mercedes M. C. , Opsahl Stephen , Varella Renato F. , Viana Laura T.
Published: October 2002

Soil‐atmosphere fluxes of carbon monoxide (CO) were measured from September 1999 through November 2000 in savanna areas in central Brazil (Cerrado) under different fire regimes using transparent and opaque static chambers. Studies focused on two vegetation types, cerrado stricto sensu (ss) (20–50% canopy cover) and campo sujo (open, scrubland), which were either burned every 2 years or protected from fire (for 26 years). CO emissions in transparent chambers varied seasonally, with highest fluxes during the late dry season and transition to wet season (August–October) and lowest fluxes late in the wet season (February–April). Daytime fluxes in the transparent chambers were always higher than in the opaque chambers. Similarly, a diurnal study showed negative fluxes for all nighttime measurements and positive measurements for all daytime measurements made with transparent chambers. Deposition velocities observed in the opaque chambers during the night fell in the 0.002–0.0014 cm s−1 range, which is at the lower end of the range that has been observed in tropical, temperate, and high‐latitude regions. No significant differences were found between the daytime annual average fluxes from unburned cerrado and unburned campo sujo (160 × 109 and 190 × 109 molecules cm−2 s−1, respectively). Fire increased soil surface CO emissions significantly in the burned cerrado plot. Measurements made 30 days after the fire showed daytime CO production over 10 times higher than that of the unburned cerrado ss (812.8 × 109 versus 76.8 × 109 molecules cm−2 s−1). Postfire CO emissions were greater than prefire emissions for both opaque and transparent chambers. However, the fire‐induced increase was greater in the transparent chambers. This suggests that the fire created both photochemically and thermally reactive precursors. Removal of litter and standing, dead plant material from plots in unburned campo sujo and a pasture was shown to dramatically decrease CO emissions. CO production in burned plots (using opaque chambers) was similar to previous measurements from Venezuelan and African savannas.
Comparison of ILAS and MkIV profiles of atmospheric trace gases measured above Alaska in May 1997
Authors: Toon Geoffrey , Sen Bhaswar , Blavier Jean‐Francois , Sasano Yasuhiro , Yokota Tatsuya , Kanzawa Hiroshi , Ogawa Toshihiro , Suzuki Makoto , Shibasaki Kazuo
Published: October 2002

Vertical profiles of the gases O3, HNO3, NO2, N2O, H2O, and CH4, measured above Fairbanks, Alaska, during a May 1997 balloon flight of the JPL MkIV interferometer are compared with version 5.20 profiles measured by the ILAS instrument on board the ADEOS satellite. Both the ILAS and MkIV instruments employ the solar occultation technique, and for many of these gases, use the same absorption bands in their analyses. The results show good agreement for nearly all of these gases, after taking into account the slight differences in the potential vorticities of the sampled air masses and considering the error bars on the measurements.
Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities
Authors: Ammann C. , Meixner F.
Published: October 2002

The coefficient b of the relaxed eddy accumulation (REA) technique was investigated by simulation studies using extensive high‐resolution eddy correlation data sets of three different scalar quantities: the air temperature and the concentrations of CO2 and H2O. Measurements were performed in June–July 1995 over a senescent cereal field in the Rhineland‐Palatinate region of southwestern Germany. The wide range of stability conditions during the experiment made it possible to describe the coefficient b as a function of the dimensionless stability parameter z/L within the framework of the Monin‐Obukhov similarity theory. In good agreement with previous publications, a constant value of about 0.56 was obtained for unstable and near‐neutral conditions if no dead band applied. For stable conditions, however, a significant increase with stability was observed which could be well described by a logarithmic functional relationship between b and z/L. By additional dead‐band simulation studies the relationship was extended to variable dead‐band widths. The observed dependency on z/L is interpreted in relation to the bivariate joint frequency distribution of the vertical wind speed and the scalar quantity.
Three‐satellite comparison of polar mesospheric clouds: Evidence for long‐term change
Authors: Shettle E. P. , Thomas G. E. , Olivero J. J. , Evans W. F. J. , Debrestian D. J. , Chardon L.
Published: October 2002

Measurements of polar mesospheric clouds (PMCs) from three different satellite instruments are compared. These instruments are the Solar Mesospheric Explorer (SME), the Wind Imaging Interferometer (WINDII), and the Polar Ozone and Aerosol Measurement (POAM II). These measurements have been put on a common basis, correcting for differences in the wavelengths and measurement techniques used. This common basis is the probability distribution of the excess extinction ratio (EER) at a standard wavelength of 265 nm, where the EER is the ratio of the PMC extinction coefficient to the background molecular Rayleigh scattering coefficient. The results indicate that the POAM and WINDII measurements in the Southern Hemisphere had a higher probability of observing bright PMCs during the 1993–1996 time period than SME did a decade earlier in 1983–1986. Local time variations identified in WINDII data are interpreted in terms of a diurnal and semidiurnal component of average EER. These results are qualitatively similar to those found from lidar soundings of noctilucent cloud at sites in Norway and at the South Pole. Differences in interannual variability, local time of the measurements, assumed particle size distributions, and solar cycle effects are ruled out as possible explanations of the differences.
First sulfur isotope measurements in central Greenland ice cores along the preindustrial and industrial periods
Authors: Patris Nicolas , Delmas Robert , Legrand Michel , De Angelis Martine , Ferron Francisco A. , Stiévenard Michel , Jouzel Jean
Published: October 2002

Sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from Summit, central Greenland, covering the preindustrial (from the fourteenth to the eighteenth century) and industrial (from 1872 to 1969 A.D.) periods. Results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries. They indicate that the preindustrial background sulfate budget is slightly dominated on a year‐round average by marine biogenic emissions, amounting to close to half of the non‐sea‐salt sulfate (49%). The second contribution is provided by continental sources of secondary sulfate, including background volcanism and, to a lesser extent, continental biota (44% of the non‐sea‐salt sulfate). Sulfur emitted by relatively weak eruptions is found to be largely depleted in 34S compared to bulk volcanic S, suggesting an efficient washout of the heavier isotope during the tropospheric transport. The impact of human‐driven emissions on the sulfate deposited in central Greenland ice is visible in isotope data as early as 1870 A.D. The isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant (δ34S ≈ +3.0 ± 1.5‰), regardless of the changes of dominant source regions and emission processes. This signature is slightly but measurably lighter than the one reported for Arctic haze pollution events.
Infrared spectroscopic study of the low‐temperature phase behavior of ammonium sulfate
Authors: Fortin Tara J. , Shilling John E. , Tolbert Margaret A.
Published: October 2002

The low‐temperature phase behavior of ammonium sulfate ((NH4)2SO4) films has been studied using Fourier transform infrared (FTIR) spectroscopy. While the deliquescence of ammonium sulfate aerosols is well characterized at temperatures above the eutectic of ice and anhydrous ammonium sulfate at 254 K, much less is known about the phase properties at lower temperatures. In the present study, experiments were performed over the temperature range from 166 to 235 K. The apparatus used for this work was a thin‐film, high‐vacuum apparatus in which the condensed phase is monitored via FTIR spectroscopy and water pressure is monitored with an MKS baratron. Results of experiments performed at low relative humidity (RH) confirm the presence of a ferroelectric phase of ammonium sulfate at temperatures less than 216 ± 8 K. Results of experiments performed as a function of increasing RH demonstrate that a phase transition from crystalline (NH4)2SO4 to a metastable aqueous solution (hereafter referred to as deliquescence) occurs at temperatures below the eutectic. Specifically, at temperatures >203 K we observed deliquescence near 88 ± 8% RH. These results are in satisfactory agreement with extrapolated results from experiments performed at temperatures above the eutectic, as well as theory. In experiments performed at temperatures between 166 and 203 K, we sometimes observed deliquescence and sometimes observed direct deposition of ice from the vapor phase, possibly indicating selective heterogeneous nucleation. Ice nucleation prevents the relative humidity from rising to the level needed for deliquescence, thus explaining the variability in our low‐temperature results. Possible implications of this work for cirrus cloud formation are also presented.
Formation of photochemical air pollution in central California 1. Development of a revised motor vehicle emission inventory
Authors: Marr Linsey C. , Black Douglas R. , Harley Robert A.
Published: October 2002

Photochemical air pollution problems have proved difficult to understand and control in central California. A major source of uncertainty is the rate of precursor volatile organic compounds and NOx emissions, especially from motor vehicles. We develop alternative emissions estimates for on‐road motor vehicles in 1990, using fuel sales data, emission factors measured in on‐road studies, and ambient pollutant ratios, for a region that includes the San Francisco Bay and San Joaquin Valley air basins and Sacramento County. Fuel‐based emissions estimates are compared with predictions of California's most recent motor vehicle emission factor model (EMFAC) and with an inventory that has been used in previous regional‐scale photochemical modeling studies. The fuel‐based inventory contains 10–50% less CO, 40–100% more nonmethane organic compounds, and 10–20% less NOx than estimated both by EMFAC and the photochemical modeling inventory. We also describe new temporal distributions of vehicle emissions by hour and day of week. Diesel trucks, a major source of NOx, have a broad midday peak in emissions on weekdays, in contrast to passenger vehicles, which show morning and afternoon commuter peaks. While passenger vehicle travel is similar on weekdays and weekends, diesel truck activity and emissions decrease by 70–80% on weekends. Vehicle emission rates and their temporal patterns are linked to a regional photochemical air pollution episode that spans a weekend in August 1990.
CRISTA observations of cirrus clouds around the tropopause
Authors: Spang Reinhold , Eidmann Gunnar , Riese Martin , Offermann Dirk , Preusse Peter , Pfister Leonhard , Wang Pi‐Huan
Published: October 2002

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument observed thin cirrus clouds at and above the tropopause during its two missions in November 1994 and August 1997. A simple cloud detection scheme was developed for extinctions greater than 2 × 10−3 km−1 through analysis of the measured infrared spectra in the 12‐μm range. Horizontal and vertical distributions of cloud occurrence frequencies are in good agreement with the Stratospheric Aerosol and Gas Experiment (SAGE) II subvisual cirrus cloud (SVC) climatology as well as SAGE measurements for the 1997 period. Seasonal variations, strong longitudinal variability, and indications of enhanced cloud occurrence frequencies in separated regions caused by El Niño events were detected in the CRISTA data set. A substantial day‐to‐day variability could be found throughout the tropics, and several regions with enhanced variability have been identified. In addition, a significant amount of cloud was found above the midlatitude tropopause. Backward trajectories in relation to outgoing longwave radiation (OLR) measurements and cloud observation in the troposphere by meteorological satellites suggest that about three fourths of the high clouds (>15 km) observed by CRISTA in the tropics stem from deep convection systems and the outflow of these systems. This would imply that on the order of at least one fourth of the observed cloud events are originated by other mechanisms, such as in situ formation due to cooling events on synoptic and/or gravity wave scales. For the convective generated cirrus clouds, a maximum lifetime of around 3–4 days was estimated over a wide range of latitudes. Such a long lifetime could be important for modeling the impact of cirrus clouds on radiation budget (climate) and heterogeneous chemical processes around the tropopause.
Water vapor at the tropopause during the CRISTA 2 mission
Authors: Offermann D. , Schaeler B. , Riese M. , Langfermann M. , Jarisch M. , Eidmann G. , Schiller C. , Smit H. G. J. , Read W. G.
Published: October 2002

Water vapor mixing ratios at the tropopause are derived as a new Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) data product from limb scan measurements of the second mission. Global maps are obtained on a daily basis. Data loss due to high clouds is found to be moderate. Good agreement with in situ airplane measurements (Fast In Situ Stratospheric Hygrometer (FISH)) is obtained for these Version 1 data. A number of different analyses are performed to show the research potential of the data product: the CRISTA data are compared to measurements of the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS). Version 4.9 climatology data and Version 5 coincident measurements are used. Good agreement of CRISTA and Version 4.9 data is obtained, whereas there are differences with respect to the Version 5.0 data. CRISTA finds vapor mixing ratios to be highly variable. Only a small part of this is instrumental. Variability is structured, and a scaling behavior is observed. Relation to convectively generated gravity waves is discussed. Relative humidity (RH) is determined on the basis of the CRISTA data. Suitability for supersaturation statistics is discussed and appears to be limited. CRISTA water vapor data are assimilated into a 3D transport model driven by UK Meteorological Office (UKMO) winds. Results are discussed in terms of meridional transports and atmospheric diffusivities. Diffusivities appear to be connected with the water vapor variances in a simple manner.
Submillimeter‐Wave Cloud Ice Radiometer: Simulations of retrieval algorithm performance
Authors: Evans K. Franklin , Walter Steven J. , Heymsfield Andrew J. , McFarquhar Greg M.
Published: October 2002

The Submillimeter‐Wave Cloud Ice Radiometer (SWCIR), developed by the Jet Propulsion Laboratory to fly on the NASA DC‐8, has ten channels from four receivers at 183, 325, 448, and 643 GHz. The SWCIR is designed to retrieve upper tropospheric cloud ice water path (IWP) and median mass equivalent sphere diameter (Dme). This paper describes the retrieval algorithm developed for the SWCIR, results from retrieval simulations, and the rationale for choosing the SWCIR frequencies. The retrieval algorithm uses Bayes theorem to combine prior information about atmospheric properties with radiative transfer simulations. The algorithm uses a precalculated database of stochastic cirrus/atmospheric profiles and corresponding simulated SWCIR brightness temperatures. Statistics of cirrus microphysics are derived from in situ cloud probe data obtained during midlatitude winter and tropical field experiments, and include correlations between temperature, particle size, and ice water content. The Bayesian algorithm effectively interpolates between database cases that approximately match the observed SWCIR brightness temperatures. Retrieval experiments are performed for midlatitude winter ice clouds with the SWCIR viewing downward from 12 km and for tropical anvil cirrus with the SWCIR viewing upward from 10 km. Each experiment simulates SWCIR brightness temperatures (with 1 K added noise) from 10000 random cloud/atmosphere profiles. For clouds with IWP greater than 5 g/m2 (which contain 97% of the simulated total ice mass) the overall median retrieval error is about 30% for IWP and 15% for Dme. The effects of liquid clouds just below ice clouds and of nonspherical ice particle shapes are small.
Five years of observations of ozone profiles over Lauder, New Zealand
Authors: Brinksma E. J. , Ajtic J. , Bergwerff J. B. , Bodeker G. E. , Boyd I. S. , de Haan J. F. , Hogervorst W. , Hovenier J. W. , Swart D. P. J.
Published: October 2002

Altitude profiles of ozone (O3) over Lauder (45°S, 170°E) performed using a lidar, ozonesondes, and the satellite‐borne Stratospheric Aerosol and Gas Experiment (SAGE II) instrument are presented. These data form one of the few long‐term sets of O3 profiles at a Southern Hemisphere location. In the 5 years of data presented, the dominant variation is the annual cycle, the phase and amplitude of which differ below and above 27.5 km. Superposed are irregular episodic variations, caused by various processes. The first process studied is stratosphere‐troposphere exchange, characterized by dry and O3‐rich air residing in the troposphere, which was found in 21% of the measurements. The second relates to the positioning of the higher polar vortex over Lauder, often in combination with the exchange of air between midlatitude and subtropical stratospheric regions. We present examples of this which were observed over Lauder during the 1997 winter. This winter was selected for further study because of the record‐low O3 amounts measured. The third process is mixing of O3‐depleted vortex air with midlatitude air after the vortex breakup. We present one example, which shows that a filament originating from the depleted Antarctic vortex significantly lowers O3 amounts over Lauder around 27 November 1997. There is thus a connection between Antarctic O3 depletion and later decrease of O3 amounts at a Southern Hemisphere midlatitude location, namely Lauder.
Intraseasonal large‐scale circulations and mesoscale convective activity in tropical South America during the TRMM‐LBA campaign
Authors: Carvalho Leila M. V. , Jones Charles , Silva Dias Maria A. F.
Published: October 2002

An investigation linking the large‐scale intraseasonal variability in low‐level wind regimes and mesoscale convective activity in tropical South America (TSA) is presented. Observational evidence is gathered to support the hypothesis that periods of active and break phases in the South American Monsoon System (SAMS) are directly related to persistent westerly and easterly intraseasonal low‐level wind‐regime anomalies (10–70 days). The large‐scale circulation and tropical convection features are examined in this study with 19 austral summer seasons. The pattern of significant anomalies of the low‐level wind (850 hPa) and outgoing long‐wave radiation (10–70 days) evidenced the existence of an enhancement/suppression dipole of large‐scale features of convective activity over the northwest and southeast of TSA. Regional impacts upon the mesoscale activity during the Tropical Rainfall Measuring Mission (TRMM)/Large‐Scale Biosphere Atmosphere (LBA) Experiment campaign (23 January to 28 February 1999) are investigated. The mesoscale convective activity is described with the observation of the spatial and temporal characteristics of evolving convective systems in the infrared Geostationary Operational Environmental Satellite (GOES) images. The results indicated that the northwest TSA region was subjected to the most significant contrasts in the characteristics of convective systems as the wind regime changed. During easterly regimes (or break periods), the enhancement of convective systems in the northwest TSA and decrease in the southeast TSA resembled the autumn season. Properties such as number of convective systems, diurnal distribution, radius, fraction of cold tops, and fragmentation were modulated by wind anomalies in the southeast TSA as well.
Estimating the vertical variation of cloud droplet effective radius using multispectral near‐infrared satellite measurements
Authors: Chang Fu‐Lung , Li Zhanqing
Published: October 2002

This paper presents a satellite‐based retrieval method for inferring the vertical variation of cloud droplet effective radius (DER) by utilizing multispectral near‐infrared (NIR) measurements at 1.25, 1.65, 2.15, and 3.75 μm, available from the Moderate Resolution Imaging Spectrometer (MODIS) satellite observations. The method is based on the principle that these multispectral NIR measurements convey DER information from different heights within a cloud, which is sufficient to allow for the retrieval of a linear DER vertical profile. The method is applicable to low‐level, nonprecipitating, stratiform clouds as their DER often increases monotonically from cloud bottom to cloud top. As such, an optimum linear DER profile can be derived by comparing multispectral NIR measurements to corresponding model values generated for a large set of linear DER profiles. The retrieval method was evaluated and compared to the conventional 3.7‐μm retrieval method by applying both methods to some marine stratocumulus clouds with in situ observations of microphysical profiles. Capable of capturing the DER variation trend, the retrieved linear DER profiles showed large improvement over the conventional 3.75‐μm retrievals. Mean differences between the linear DER retrievals and observed profiles were generally small for both cloud top and bottom (<1.0 μm), whereas the conventional retrievals are prone to systematic overestimation near cloud bottom. The sensitivities of the linear DER retrieval to various parameters, as well as the error analyses, were also investigated extensively.
First interactive simulations of cirrus clouds formed by homogeneous freezing in the ECHAM general circulation model
Authors: Lohmann U. , Kärcher B.
Published: October 2002

A physically based parameterization for the nucleation and initial growth of ice crystals in cirrus clouds at low (<238 K) temperatures prevailing in the upper troposphere and in the tropopause region is implemented in the ECHAM general circulation model (GCM). With this model we performed the first interactive simulations of cirrus clouds in a global climate model. As homogeneous ice crystal nucleation requires relative humidities with respect to ice of 140–170% at these temperatures, we abandoned the saturation adjustment scheme previously used to compute the properties of cirrus clouds in GCMs. The comparison with relative humidity data taken on commercial aircraft showed that ECHAM reproduces the frequency distribution of supersaturation with respect to ice in cloud‐free regions well especially if high values of the subgrid‐scale vertical velocity are assumed. On the other hand, the higher frequency of occurrence of high supersaturations in the model may point to heterogeneous freezing as the missing mechanism for ice formation. We found that homogeneous freezing may be limited by the number of hygroscopic aerosols present. However, as the ice water content remains the same for the natural and present‐day aerosol scenarios the longwave radiation does not change. Thus anthropogenic aerosol and precursor emissions have only a small effect on cirrus formed by homogeneous freezing. Aircraft emissions of sulfate aerosols are not likely to be important for cirrus formation. Aircraft soot emissions may be important if the soot particles nucleate ice more efficiently than by homogeneous freezing.
A thermal dissociation laser‐induced fluorescence instrument for in situ detection of NO2, peroxy nitrates, alkyl nitrates, and HNO3
Authors: Day D. A. , Wooldridge P. J. , Dillon M. B. , Thornton J. A. , Cohen R. C.
Published: October 2002

This paper describes a new instrument that uses a combination of thermal dissociation and laser‐induced fluorescence detection of NO2for in situ detection of the sum total peroxy nitrates, the sum total of alkyl nitrates and hydroxyalkyl nitrates, and HNO3. The instrument is capable of routine, continuous in situ measurements of these three classes of compounds that are accurate (15%) with a low detection limit (90 parts per trillion (ppt) 10 s−1, S/N ratio = 2 on a background of 1 ppb NO2and 30 ppt 10 s−1on a background of 100 ppt NO2). Theoretical analysis of potential interferences combined with laboratory experiments that test for interferences show that rapidly cooling the gas and dropping the pressure after the thermal dissociation reduces interferences to the order of 1–5%. Observations in ambient air at the University of California Blodgett Forest Research Station demonstrate the capabilities of this instrument under field conditions. These field observations are compared with independent total NOyobservations.
Atmospheric remote sensing using a combined extinctive and refractive stellar occultation technique 2. Inversion method for extinction measurements
Authors: DeMajistre Robert , Yee Jeng‐Hwa
Published: October 2002

In this paper, an inversion algorithm for the retrieval of ozone and other constituent profiles in the Earth's lower atmosphere from spectroscopic stellar occultation measurements is developed and evaluated through simulated retrievals. In addition to extinction by absorption and scattering, the effects of refractive bending, refractive attenuation, scintillation, and spatial variations in the extinction cross sections along the line of sight introduced by temperature dependence in absorption cross sections or variations in aerosol properties are considered. For computational efficiency, the inversion is conducted in two stages. The transmission spectra are first fitted to obtain the line‐of‐sight column quantities, followed by a spatial inversion to retrieve the vertical profiles. The use of smoothness constraints and a priori information are investigated. Retrieval simulations conducted for reasonable instrument parameters and measurement “noise” (described within) demonstrate that ozone profiles can be retrieved between 15 and 50 km with statistical uncertainties better than 5% (2% at the ozone peak) and systematic bias better than 0.5%. Although these accuracies depend upon the particular measurement scenario (i.e., stellar type and magnitude, instrument noise, etc.), they are representative of the results expected for a properly optimized stellar occultation experiment.
Lidar observations of Asian dust over Hefei, China, in spring 2000
Authors: Zhou Jun , Yu Guming , Jin Chuanjia , Qi Fudi , Liu Dong , Hu Huanling , Gong Zhiben , Shi Guangyu , Nakajima Teruyuki , Takamura Tamio
Published: October 2002

A Mie lidar was used to make observations of Asian dust over Hefei (31.90°N, 117.16°E) in spring 2000. This paper presents main features of vertical distribution and temporal variation of Asian dust extinction coefficient at 532‐nm wavelength. It was found that the Asian dust events contributed significantly to very large aerosol extinction coefficients in the boundary layer or middle troposphere. Extinction coefficient value as large as 0.7 km−1 at 3 km above ground level (AGL) has been observed. The Asian dust extinction coefficient profiles showed very big changes from early morning to evening and also appeared substantial amount of temporal variation during the nighttime. For the severe Asian dust days the depth of boundary layer rose up to around 4 km AGL, but only 1∼2 km AGL for normal days. The seasonal average aerosol extinction coefficient profiles also showed that larger aerosol extinction coefficients from 1‐ to 10‐km altitude range were observed in the springtime rather than in any other season. Meanwhile, solar extinction and radiation measurements indicated that the Asian dust particles were composed of larger size particles and they produced significantly perturbation in solar radiation on the Earth surface.
Measurements and parameterizations of small aerosol deposition velocities to grassland, arable crops, and forest: Influence of surface roughness length on deposition
Authors: Gallagher M. W. , Nemitz E. , Dorsey J. R. , Fowler D. , Sutton M. A. , Flynn M. , Duyzer J.
Published: October 2002

New micrometeorological measurements of small (0.1–0.2 μm diameter) aerosol particle fluxes using the eddy correlation technique are presented for moorland and also for grassland vegetation, the latter measurements being made both before and after cutting of the grassland to observe the resultant change in particle deposition velocity. These data are considered together with previously reported and reanalyzed micrometeorological measurements, again using the eddy correlation technique, for a number of different surface types, including arable crops and forest. Differences in observed surface deposition velocities, vds, due to the different surface roughnesses are highlighted. It was found that the various data sets showed a wholly consistent behavior when ensemble averages over the typical range of atmospheric stability ranges are considered in order to reduce the scatter inherent in these types of measurements. A working parameterization of surface deposition velocity in terms of the surface's roughness length, zo, is presented. This is then extended for different atmospheric stabilities, using the parameterization suggested by Lamaud et al. [1994c], to yield vds/u* = k1 + k2 (−300 z/L)2/3, where k1 = k1 = 0.001222 log(zo) + 0.003906, k2 = 0.0009, where z is the measurement height, L is the Obukhov stability length, and u* is the local friction speed. The new data are finally compared to current analytical model descriptions of the deposition process, highlighting deficiencies in our understanding of the surface collection efficiency even for these small particles.
Late Cretaceous ocean: Coupled simulations with the National Center for Atmospheric Research Climate System Model
Authors: Otto‐Bliesner Bette L. , Brady Esther C. , Shields Christine
Published: October 2002

Deep‐ocean circulation may be a significant factor in determining climate. Here, we describe two long, fully coupled atmosphere‐ocean simulations with the National Center for Atmospheric Research Climate System Model for the Late Cretaceous (80 Ma). Our results suggest that higher levels of atmospheric CO2 and the altered paleogeography of the Late Cretaceous resulted in a surface ocean state, temperature, salinity, and circulation, significantly different than at present. This, in turn, resulted in deepwater features that, although formed by mechanisms similar to the present, were quite different from the present. The simulations exhibit large overturning cells in both hemispheres extending from the surface to the ocean bottom and with intensity comparable to the present‐day North Atlantic simulated overturning. In the Northern Hemisphere the sinking takes place in the Pacific due to cooling of the much warmer and saltier waters compared to the present day. In the Southern Hemisphere the sinking occurs primarily in the southern Atlantic and Indian Oceans. For a simulation with atmospheric CO2reduced from 6 times to 4 times preindustrial concentrations, the southern branch is reduced by 35%percnt; due to less poleward transport of salty waters in the South Atlantic Ocean. Warm waters inferred from proxy data in deep‐sea cores can be explained by the high‐latitude sites of overturning. These results contradict the traditional hypothesis that warm Cretaceous ocean bottom waters must have formed by sinking in shallow low‐latitude seas.