bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrous acid formation in the urban atmosphere: Gradient measurements of NO2 and HONO over grass in Milan, Italy
Authors: Stutz Jochen , Alicke Björn , Neftel Albrecht
Published: November 2002

The source of nitrous acid, HONO, in the troposphere remains uncertain, even after two decades of research. It is currently believed that HONO is formed by heterogeneous conversion of NO2 on either the ground or the aerosol surface. While this conversion has been studied in the laboratory, few atmospheric studies have been reported. Here we present the first simultaneous determination of the vertical gradients and fluxes of HONO, its precursor NO2, and SO2 over a flat grass surface in the polluted atmosphere. The measurements were performed in Milan, Italy, during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono (LOOP/PIPAPO) study in summer 1998, using differential optical absorption spectroscopy. While deposition of NO2 onto the ground was frequently observed, heterogeneous HONO formation was much smaller than expected. We can explain our observation by a mechanism that consists of a combination of NO2 and HONO deposition, and a heterogeneous conversion of NO2 to HONO on the ground. The compensation point for deposition and formation of HONO is characterized by a HONO/NO2 ratio of ∼0.03, indicating that only one HONO molecule is released into the gas phase for every 33 NO2 molecules deposited. Our measurements also show that direct emission of HONO is an important source in strongly polluted areas.
Simulation of ozone depletion in spring 2000 with the Chemical Lagrangian Model of the Stratosphere (CLaMS)
Authors: Grooß J.‐U. , Günther G. , Konopka P. , Müller R. , McKenna D. S. , Stroh F. , Vogel B. , Engel A. , Müller M. , Hoppel K. , Bevilacqua R. , Richard E. , Webster C. R. , Elkins J. W. , Hurst D. F. , Romashkin P. A. , Baumgardner D. G.
Published: November 2002

Simulations of the development of the chemical composition of the Arctic stratosphere for spring 2000 are made with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations are performed for the entire Northern Hemisphere on four isentropic levels (400–475 K). The initialization in early February is based on observations made from satellite, balloon and ER‐2 aircraft platforms. Tracer‐tracer correlations from balloon‐borne cryosampler (Triple) and ER‐2 measurements, as well as tracer‐PV correlations, are used to derive a comprehensive hemispherical initialization of all relevant chemical trace species. Since significant denitrification has been observed on the ER‐2 flights, a parameterization of the denitrification is derived from NOy and N2O observations on board the ER‐2 aircraft and the temperature history of the air masses under consideration. Over the simulation period from 10 February to 20 March, a chemical ozone depletion of up to 60% was derived for 425–450 K potential temperature. Maximum vortex‐averaged chemical ozone loss rates of 50 ppb d−1 or 4 ppb per sunlight hour were simulated in early March 2000 at the 425 and 450 K potential temperature levels. We show comparisons between the measurements and the simulations for the location of the ER‐2 flight paths in late February and March and the location of the Triple balloon flight. The simulated tracer mixing ratios are in good agreement with the measurements. It was not possible to reproduce the exact details of the inorganic chlorine compounds. The simulation agrees with ClOx observations on the Triple balloon flight but overestimates for the ER‐2 flights. The simulated ozone depletion agrees with estimates from other observations in the 425 and 450 K levels, but is underestimated on the 475 K level.
Discriminating Types Ia and Ib polar stratospheric clouds in POAM satellite data
Authors: Strawa A. W. , Drdla K. , Fromm M. , Pueschel R. F. , Hoppel K. W. , Browell E. V. , Hamill P. , Dempsey David P.
Published: November 2002

A method for discriminating Types Ia and Ib Polar Stratospheric Clouds (PSCs) from Polar Ozone and Aerosol Measurement (POAM) satellite occultation measurements of aerosol extinction coefficient is described. The method has been validated by applying several statistical tests to the results and by using Differential Absorption Lidar (DIAL) and Ozone Lidar Experiment (OLEX) lidar observations made during Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone II (SOLVE/THESEO 2000). Type Ia PSCs are believed to be composed of large nitric‐acid‐containing particles that will sediment out of the stratosphere, causing denitrification and facilitating ozone depletion. Type Ib PSCs are believed to be much smaller and will not sediment out of the stratosphere. Discriminating between these two types of PSCs is significant because it will permit a better understanding of ozone depletion today and predict the fate and effect of PSCs using the more continuous temporal coverage and larger areal coverage that can be obtained from satellites. The method is made possible by the character of POAM observations when plotted as normalized extinction versus wavelength dependence. As the extinction increases, observations of Types Ia and Ib PSCs bifurcate. This behavior is also observed in idealized simulations of the formation of Supercooled Ternary Solutions (STS) and nitric acid trihydrate (NAT) particles, which are believed to make up Types Ib and Ia PSCs, respectively. Analysis of POAM observations from the 1999/2000 Arctic winter using the PSC discrimination algorithm revealed that the number of PSC observations peaked in January. In November, December, and January, the ratio of Type Ia to Ib PSCs was about 3. In February and March, this ratio was about 0.3. The average altitude of Type Ia PSCs descended more than the Type Ib, especially in the spring where the Type Ia observations were 2–3 km below the Type Ib observations. This is consistent with observations of denitrification during the 1999/2000 winter. The PSC discrimination algorithm is applicable to previous winters in both hemispheres and will work with SAGE III observations as well. This will permit a more extensive study of the statistical significance of some features of the PSCs observed during the 1999/2000 Arctic winter. It is our belief that the present method of analyzing satellite data to discriminate Type I PSCs will be of great utility in the study of PSCs and ozone depletion.
Dehydration in the Arctic stratosphere during the SOLVE/THESEO‐2000 campaigns
Authors: Schiller C. , Bauer R. , Cairo F. , Deshler T. , Dörnbrack A. , Elkins J. , Engel A. , Flentje H. , Larsen N. , Levin I. , Müller M. , Oltmans S. , Ovarlez H. , Ovarlez J. , Schreiner J. , Stroh F. , Voigt C. , Vömel H.
Published: November 2002

Balloon‐borne measurements of H2O, CH4, and H2 in January and March 2000 show clear evidence for dehydration inside the polar vortex. At 30–50 hPa, total hydrogen is reduced by approximately 0.5 ppmv. This phenomenon is apparent in all five in situ balloon observations of this period; therefore it is probable that dehydration occurred over extended regions and a long period of this winter which was characterized by a well‐confined vortex and low stratospheric temperatures. At altitudes below 50 hPa, where dehydration was strongest in previous Arctic observations and in the austral spring, total hydrogen values (2·CH4 + H2O + H2) were similar to those found in Arctic profiles from other years where there was no dehydration and to those found at midlatitudes. In some of the dehydrated air masses, small solid particles were found whose crystallization might be connected to the earlier formation of ice particles. Back trajectory calculations for the January observations indicate that the probed air masses had experienced temperatures below the ice frost point in a synoptic‐scale cold region several days before the observations. Most likely, the air was dehydrated there. In addition, temperatures in these air masses dropped below ice saturation several hours prior to the observations in the lee of the Scandinavian mountain ridge. For the March measurements, no ice saturation was apparent in the recent history of the air masses, again indicating that dehydration in the Arctic winter 1999/2000 was not a local phenomenon.
A vortex‐scale simulation of the growth and sedimentation of large nitric acid hydrate particles
Authors: Carslaw Kenneth S. , Kettleborough Jamie A. , Northway Megan J. , Davies Stewart , Gao Ru‐Shan , Fahey David W. , Baumgardner Darrel G. , Chipperfield Martyn P. , Kleinböhl Armin
Published: November 2002

Nitric acid–containing particles with diameters of 10–20 μm were detected inside the Arctic polar vortex in the period January to March 2000. We present the results of a unique three‐dimensional microphysical simulation of these large HNO3‐containing particles covering the entire Arctic vortex. The model describes the simultaneous growth, evaporation, sedimentation, and advection of several thousand individual nitric acid hydrate particles over their complete lifetime. We compare modeled and observed particle size distributions as a test of different particle nucleation mechanisms. The model is able to produce particles with sizes typical of those observed and broadly reproduces the change in particle characteristics through the winter assuming nitric acid trihydrate (NAT) particle growth. The possibility that the observed large nitric acid–containing particles were composed of nitric acid dihydrate (NAD) cannot be excluded within the uncertainty of the HNO3 field above the aircraft. The formation of nitric acid hydrate particles on synoptic ice clouds may be a source of some of the observed large nitric acid–containing particles. However, a direct, but highly selective, nucleation of NAT or NAD particles over wide regions appears to be necessary to explain the observations.
Reconstruction of three‐dimensional ozone fields using POAM III during SOLVE
Authors: Randall C. E. , Lumpe J. D. , Bevilacqua R. M. , Hoppel K. W. , Fromm M. D. , Salawitch R. J. , Swartz W. H. , Lloyd S. A. , Kyro E. , von der Gathen P. , Claude H. , Davies J. , DeBacker H. , Dier H. , Molyneux M. J. , Sancho J.
Published: November 2002

In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement (POAM) III data for providing semiglobal three‐dimensional ozone fields during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) winter. As a solar occultation instrument, POAM III measurements were limited to latitudes of 63°N to 68°N during the SOLVE campaign but covered a wide range of potential vorticity. Using established mapping techniques, we have used the relation between potential vorticity and ozone measured by POAM III to calculate three‐dimensional ozone mixing ratio fields throughout the Northern Hemisphere on a daily basis during the 1999/2000 winter. To validate the results, we have extensively compared profiles obtained from ozonesondes and the Halogen Occultation Experiment to the proxy O3 interpolated horizontally and vertically to the correlative measurement locations. On average, the proxy O3 agrees with the correlative observations to better than ∼5%, at potential temperatures below about 900 K and latitudes above about 30°N, demonstrating the reliability of the reconstructed O3 fields in these regions. We discuss the application of the POAM proxy ozone profiles for calculating photolysis rates along the ER‐2 and DC‐8 flight tracks during the SOLVE campaign, and we present a qualitative picture of the evolution of polar stratospheric ozone throughout the winter.
Quantification of the transport of chemical constituents from the polar vortex to midlatitudes in the lower stratosphere using the high‐resolution advection model MIMOSA and effective diffusivity
Authors: Hauchecorne Alain , Godin Sophie , Marchand Marion , Heese Birgit , Souprayen Claude
Published: November 2002

The observed decrease of ozone in the northern midlatitude lower stratosphere is only partially reproduced by chemical models. The transport of ozone‐depleted air from the polar vortex is one of the proposed mechanisms to explain the discrepancy. Here we present a study on the quantification of the air mass transported from the polar vortex to midlatitude during the four winters 1996–1997 to 1999–2000, in relation with vortex filamentation and break up, using the high‐resolution advection model MIMOSA on isentropic surfaces. Sensitivity tests show that the advection model is able to predict the location of polar filaments with accuracy better than 100 km, limited by uncertainties in meteorological advecting wind fields. The effective diffusivity diagnostic is used to evaluate the intensity of the vortex edge barrier and to quantify the transport of air from the polar vortex to midlatitude. The intensity of the polar barrier is increasing with height from 400 to 550 K and is nearly constant above. During periods with a cold and undisturbed vortex, favorable to chlorine activation, the transport is very weak. This suggests that the midwinter vortex filamentation plays a minor role in the midlatitude ozone decline. In the opposite limit, during a stratospheric warming up to 30% of the polar vortex air is transported to midlatitudes. The cumulative transport from early January to end of April across the polar edge varies from almost 5% of the polar vortex air at 675 K in 1997 to 50% at 435 K in 1999.
Water‐soluble organic compounds in biomass burning aerosols over Amazonia 2. Apportionment of the chemical composition and importance of the polyacidic fraction
Authors: Mayol‐Bracero O. L. , Guyon P. , Graham B. , Roberts G. , Andreae M. O. , Decesari S. , Facchini M. C. , Fuzzi S. , Artaxo P.
Published: November 2002

Chemical characterization was performed on carbonaceous aerosols from Rondônia in the Brazilian Amazon region as part of the European contribution to the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA‐EUSTACH). The sampling period (October 1999) included the peak of the burning season as well as the dry‐to‐wet season transition. Characterization of the carbonaceous material was performed by using a thermal combustion method. This enabled determination of aerosol total carbon (TC), black carbon (BC), and organic carbon (OC). A significant fraction of the BC material (on average about 50%) seemed to be highly refractory organic material soluble in water. A more detailed analysis of the water‐soluble organic carbon (WSOC) fraction of the TC was undertaken, involving measurements of WSOC content, high‐performance liquid chromatography (HPLC) separation (with UV detection) of the water‐soluble components, and characterization of individual components by gas chromatography/mass spectrometry (GC/MS). The WSOC fraction accounted for 45−75% of the OC. This high WSOC fraction suggests an aerosol derived mainly from smoldering combustion. Using GC/MS, many different compounds, containing hydroxy, carboxylate, and carbonyl groups, were detected. The fraction of the WSOC identified by GC/MS was about 10%. Three classes of compounds were separated by HPLC/UV: neutral compounds (N), monocarboxylic and dicarboxylic acids (MDA), and polycarboxylic acids (PA). The sum of these three groups accounted for about 70% of the WSOC, with MDA and PA being most abundant (about 50%). Good correlations (r2between 0.84 and 0.99) of BCwater(BC after water extraction) and levoglucosan (both indicators of biomass combustion) with the water‐soluble species (i.e., WSOC, N, MDA, and PA), and their increase in concentrations during the burning period provided strong evidence that biomass burning is a major source of the WSOC. Particularly interesting is that PA and therefore, probably, humic‐like substances (due to their polyacidic nature) are generated in significant amounts during biomass burning. These substances, due to their water solubility and surface tension‐lowering effects, may play an important role in determining the overall cloud condensation nuclei activity of biomass burning aerosols and, consequently, could be important in cloud processes and climate forcing.
INDOEX aerosol: A comparison and summary of chemical, microphysical, and optical properties observed from land, ship, and aircraft
Authors: Clarke A. D. , Howell S. , Quinn P. K. , Bates T. S. , Ogren J. A. , Andrews E. , Jefferson A. , Massling A. , Mayol‐Bracero O. , Maring H. , Savoie D. , Cass G.
Published: November 2002

The Indian Ocean Experiment (INDOEX) measurements on land, sea, and in the air were designed to provide complementary assessment of chemical, physical, and optical properties of the haze aerosol over the Indian Ocean. Differences in platform requirements and objectives resulted in diverse techniques, measurements, and analyses being employed. In order to best interpret the properties of the INDOEX aerosol, comparisons of data by platform, air mass origin, and light scattering intensity were undertaken. These revealed significant variability in platform averages of aerosol extensive properties (e.g., mass, light scattering, and absorption) but less variability in intensive properties (e.g., mass scattering efficiency, single scattering albedo, backscatter fraction, and Ångström exponent) and the ratios of constituents. In general, ratios of chemical species were found to show greater variability than properties of the size distributions or aerosol optical properties. Even so, at higher haze concentrations with higher scattering values, various determinations of the mass scattering efficiency (MSE) at 33% relative humidity converged on values of about 3.8 ± 0.3 m2 g−1, providing a firm constraint upon the description and modeling of haze optical properties. MSE values trended lower with more dilute haze but became more variable in clean air or regions of low concentrations. This cross‐platform comparison resolved a number of measurement differences but also revealed that regional characterization from different platforms results in differences linked to variability in time and space. This emphasizes the need to combine such efforts with coordinated satellite and modeling studies able to characterize large‐scale regional structure and variability. These comparisons also indicate that “closure” between chemical, microphysical, and optical properties across platforms to better than about 20% will require significant improvements in techniques, calibration procedures, and comparison efforts.
Validation of ozone measurements from the Improved Limb Atmospheric Spectrometer
Authors: Sugita T. , Yokota T. , Nakajima H. , Kanzawa H. , Nakane H. , Gernandt H. , Yushkov V. , Shibasaki K. , Deshler T. , Kondo Y. , Godin S. , Goutail F. , Pommereau J.‐P. , Camy‐Peyret C. , Payan S. , Jeseck P. , Renard J.‐B. , Bösch H. , Fitzenberger R. , Pfeilsticker K. , von König M. , Bremer H. , Küllmann H. , Schlager H. , Margitan J. J. , Stachnik B. , Toon G. C. , Jucks K. , Traub W. A. , Johnson D. G. , Murata I. , Fukunishi H. , Sasano Y.
Published: November 2002

Vertical profiles of ozone concentration in the high latitudes were observed by the Improved Limb Atmospheric Spectrometer (ILAS) aboard the Advanced Earth Observing Satellite (ADEOS) from November 1996 to June 1997. The ozone data obtained by the version 5.20 ILAS retrieval algorithm are compared with those obtained by the version 19 Halogen Occultation Experiment (HALOE), the version 6 Stratospheric Aerosol and Gas Experiment (SAGE) II, and the version 6 Polar Ozone and Aerosol Measurement (POAM) II retrieval algorithms. The ILAS data are also compared with ozone data measured by ozonesondes, instruments on board balloons or an aircraft, and ground‐based instruments. The ILAS ozone data generally agree with its correlative data between 11 and 64 km with some exceptions. Quantitatively, the median value of the relative difference (absolute difference divided by its mean value) for these comparisons was within ±10%. Relative differences (18%) exceeding the combined measurement errors were found around 45–55 km altitude from comparisons with the HALOE and SAGE II data in January 1997 in the Southern Hemisphere (SH). Larger relative differences (around 50%) were also found below 15 km from comparisons with the HALOE and POAM II data in November 1996 in the SH, but these absolute differences were 0.10–0.16 ppmv as the median value. The ozone data processed by the version 5.20 were improved compared to the former version 3.10, which is available to the general public. The version 5.20 ozone data can be used for scientific analysis purposes based on the accuracy of the data in comparison with these other instruments.
Tangent height registration for the solar occultation satellite sensor ILAS: A new technique for Version 5.20 products
Authors: Nakajima H. , Suzuki M. , Yokota T. , Sugita T. , Itou Y. , Kaji M. , Araki N. , Waragai K. , Yamashita H. , Kanzawa H. , Sasano Y.
Published: November 2002

The Improved Limb Atmospheric Spectrometer (ILAS) was a solar occultation satellite sensor that was developed by the Environment Agency of Japan to monitor the stratospheric ozone layer. This paper describes methods of registering tangent heights for ILAS vertical profiles of gas mixing ratio and aerosol extinction coefficient. Accurate tangent height registration is crucial for the retrieval of accurate gas mixing ratios from atmospheric absorption spectra. Three methods for tangent height registration have been applied to retrieved ILAS data. The first method is the transmittance spectrum method (TS‐M), which uses absorption spectra of oxygen molecules at around 760 nm (O2A band) measured by the ILAS visible channel and compares the average transmittance with that calculated theoretically from temperature and pressure using meteorological data. A tangent height is derived from these data. Version 3.10 ILAS data products use the TS‐M. A second method is the Sun‐edge sensor method (SES‐M). This method for registering tangent heights was in mind when ILAS was originally designed. The SES‐M geometrically determines the direction of the instantaneous field‐of‐view (IFOV) of the spectrometer from the angular difference between the top edge of the Sun determined with the SES and the spectrometer's IFOV. Information on the satellite's orbital position and solar position relative to the center of the Earth is used to register the tangent height. Version 4.20 ILAS data products use SES‐M. The third method is a hybrid method (Hybrid‐M) that was developed to correct for seasonal differences in tangent heights computed by the SES‐M. The Hybrid‐M assumes that the TS‐M can correctly determine the tangent height at 30 km. Version 5.20 ILAS data products (the latest version) use Hybrid‐M. Random and systematic errors in the Hybrid‐M tangent height registration were estimated. The root‐sum‐square (RSS) total random error is 30 m, while the total systematic error is +300 ± 360 m in tangent height. Actual errors in tangent height registration in Version 5.20 algorithm are considered to be small judging from the results of comparisons with independent validation data sets. The Hybrid‐M gives good estimates of tangent heights in Version 5.20 of the ILAS data processing algorithms.
Chemical characterization of the organic fraction of atmospheric aerosol at two sites in Ontario, Canada
Authors: Blanchard P. , Brook J. R. , Brazal P.
Published: November 2002

Atmospheric filter samples were collected during several field campaigns in 1998/1999 from two locations in and around the greater Toronto area. The objective of the campaigns was to investigate the difference in composition of the organic fraction of atmospheric aerosols at both an urban and rural site for different seasons. The composition of organic particulate matter, with an interest in organic carbon, elemental carbon, alkanoic acids, n‐alkanes, and polycyclic aromatic hydrocarbons (PAHs), was investigated using thermal desorption, solvent extraction, derivatization, and analysis by gas chromatography/mass spectroscopy. The concentrations measured were similar to other observations in urban and rural areas with seasonal differences observed at both sites. PM2.5 levels were larger in February at both urban and rural sites due to weather conditions favorable for buildup of particles. Organic carbon/elemental carbon ratios were typical of emission values except for the rural site where a greater potential for biogenic‐related particles, as well as secondary production, likely played a role. A comparison of the chemical species to the total organic carbon revealed that the acids, alkanes, and PAHs account for a very small portion of the mass, demonstrating the need for further analytical developments. Preliminary results of the tracer analyses indicated that at the urban site the distribution of alkanoic acids atmospheric concentrations was correlated to diesel emissions. The n‐alkanes distribution profile was representative of both anthropogenic sources for the urban site and biogenic sources for the rural site. At the rural site one sample exhibited a local source of atmospheric aerosol derived from vegetation.
Long‐range experimental hydrologic forecasting for the eastern United States
Authors: Wood Andrew W. , Maurer Edwin P. , Kumar Arun , Lettenmaier Dennis P.
Published: November 2002

We explore a strategy for long‐range hydrologic forecasting that uses ensemble climate model forecasts as input to a macroscale hydrologic model to produce runoff and streamflow forecasts at spatial and temporal scales appropriate for water management. Monthly ensemble climate model forecasts produced by the National Centers for Environmental Prediction/Climate Prediction Center global spectral model (GSM) are bias corrected, downscaled to 1/8° horizontal resolution, and disaggregated to a daily time step for input to the Variable Infiltration Capacity hydrologic model. Bias correction is effected by evaluating the GSM ensemble forecast variables as percentiles relative to the GSM model climatology and then extracting the percentiles' associated variable values instead from the observed climatology. The monthly meteorological forecasts are then interpolated to the finer hydrologic model scale, at which a daily signal that preserves the forecast anomaly is imposed through resampling of the historic record. With the resulting monthly runoff and streamflow forecasts for the East Coast and Ohio River basin, we evaluate the bias correction and resampling approaches during the southeastern United States drought from May to August 2000 and also for the El Niño conditions of December 1997 to February 1998. For the summer 2000 study period, persistence in anomalous initial hydrologic states predominates in determining the hydrologic forecasts. In contrast, the El Niño‐condition hydrologic forecasts derive direction both from the climate model forecast signal and the antecedent land surface state. From a qualitative standpoint the hydrologic forecasting strategy appears successful in translating climate forecast signals to hydrologic variables of interest for water management.
The CRISTA‐2 mission
Authors: Grossmann K. U. , Offermann D. , Gusev O. , Oberheide J. , Riese M. , Spang R.
Published: November 2002

The second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment took place in August 1997. The experiment was flown aboard the ASTROnomical Shuttle PAllet Satellite (ASTRO‐SPAS) free‐flying platform launched by the NASA space shuttle. CRISTA analyzes the infrared radiation emitted by trace gases from the Earth limb in the altitude regime from the upper troposphere to the lower thermosphere. The main aim of CRISTA is to detect small‐scale dynamically induced structures in the distribution of trace constituents in the middle atmosphere. The instrument is therefore equipped with three telescopes that simultaneously collect the infrared radiation from three different air volumes. The high spatial density of the measurement grid obtained during the first CRISTA mission in November 1994, as well as the latitudinal coverage, was considerably improved by making use of newly developed satellite pointing and maneuvering capabilities. The altitude coverage was extended to include the upper troposphere where water vapor distributions are analyzed. Dynamically induced features are observed in practically all trace gases and at various spatial scales. The smallest scales that could be analyzed on the basis of the CRISTA data set are well below 100 km. Compared to the first mission, much more emphasis was laid on measurements in the upper mesosphere and lower thermosphere—this was possible because of higher radiometric sensitivities in some channels. Atomic oxygen, carbon dioxide, and ozone densities are derived in the upper mesosphere and lower thermosphere. The mission conditions allowed the study of polar stratospheric clouds (PSC) over the Antarctic and of polar mesospheric clouds (PMC) at high northern latitudes. For the first time, summer high latitude mesopause temperatures were retrieved from CO2 15‐μm spectra using a nonlocal thermodynamic equilibrium model. The derived temperatures compare well with a temperature climatology based on rocket soundings.
Comparative measurements of carbon dioxide fluxes from two nearby towers in a central Amazonian rainforest: The Manaus LBA site
Authors: Araújo A. C. , Nobre A. D. , Kruijt B. , Elbers J. A. , Dallarosa R. , Stefani P. , von Randow C. , Manzi A. O. , Culf A. D. , Gash J. H. C. , Valentini R. , Kabat P.
Published: November 2002

Forests around Manaus have staged the oldest and the longest forest‐atmosphere CO2 exchange studies made anywhere in the Amazon. Since July 1999 the exchange of CO2, water, and energy, as well as weather variables, have been measured almost continuously over two forests, 11 km apart, in the Cuieiras reserve near Manaus, Brazil. This paper presents the sites and climatology of the region based upon the new data sets. The landscape consists of plateaus dissected by often waterlogged valleys, and the two sites differ in terms of the relative areas of those two landscape components represented in the tower footprints. The radiation and wind climate was similar to both towers. Generally, both the long‐wave and short‐wave radiation input was less in the wet than in the dry season. The energy balance closure was imperfect (on average 80%) in both towers, with little variation in energy partitioning between the wet and dry seasons; likely a result of anomalously high rainfall in the 1999 dry season. Fluxes of CO2 also showed little seasonal variation except for a slightly shorter daytime uptake duration and somewhat lower respiratory fluxes in the dry season. The net effect is one of lower daily net ecosystem exchange (NEE) in the dry season. The tower, which has less waterlogged valley areas in its footprint, measured a higher overall CO2 uptake rate. We found that on first sight, NEE is underestimated during calm nights, as was observed in many other tower sites before. However, a closer inspection of the diurnal variation of CO2 storage fluxes and NEE suggests that at least part of the nighttime deficits is recovered from either lateral influx of CO2 from valleys or outgassing of soil storage. Therefore there is a high uncertainty in the magnitude of nocturnal NEE, and consequently preliminary estimates of annual carbon uptake reflecting this range from 1 to 8 T ha−1 y−1, with an even higher upper range for the less waterlogged area. The high uptake rates are clearly unsustainable and call for further investigations into the integral carbon balance of Amazon landscapes.
Dynamics of the middle atmosphere during CRISTA‐2 as simulated by the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model
Authors: Hagan M. E. , Roble R. G. , Hartsough C. , Oberheide J. , Jarisch M.
Published: November 2002

The National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME GCM) was run to study middle and upper atmospheric dynamics during the second flight of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument on 7–16 August 1997. Strong quasi‐stationary zonal wave number 1 and 2 signatures characterize the TIME GCM middle and high‐latitude dynamics in the Southern Hemisphere. There is a migrating diurnal tide and a westward propagating wave number 2 nonmigrating diurnal tide at equatorial and low latitudes in both hemispheres. A westward propagating zonal wave number 1 quasi 5‐day wave and a migrating semidiurnal tide are also evident in the TIME GCM mesopause region. We subsequently sample the TIME GCM results along the CRISTA orbital trajectory and process this subset of model data using the techniques invoked for the CRISTA data analyses. We compare these results with the full model analysis and find that the quasi‐stationary wave 1 and wave 2 estimates are slightly affected by unresolved signatures of the semidiurnal tide and propagating planetary wave(s) in the middle and high‐latitude Southern Hemisphere. The satellite sampling also results in a convolved migrating and nonmigrating diurnal tidal signature at low latitudes. We compare the TIME GCM sampled results with the CRISTA observations and find that the modeled stationary planetary waves are more confined to stratospheric high latitudes than the observed waves are, but there is more favorable model measurement agreement aloft. TIME GCM underestimates the diurnal tide that CRISTA observed throughout the middle atmosphere at equatorial and low middle latitudes.
Meteorological conditions of the stratosphere for the CRISTA 2 campaign, August 1997
Authors: Günther G. , McKenna D. S. , Spang R.
Published: November 2002

During the CRISTA 2 campaign in August 1997 the Antarctic polar vortex according to UK Met Office (UKMO) data was strong but temporarily disturbed by planetary waves. This winter was in general warmer than the five previous winters; nevertheless, temperatures cold enough to allow the formation of nitric acid trihydrate (NAT) and ice particles occurred throughout the period from mid‐June to the end of August. The cold vortex core developed in the potential temperature range from 400 to 700 K at the beginning of the winter, initially centered at 600 K but slowly progressing downward to 450 K in the subsequent months. The vortex disturbances showed a clear zonal wave number 1 and 2 pattern. This planetary wave activity caused a strong day‐to‐day fluctuation of the vortex shape. During August when the second Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA 2) mission took place the vortex was elongated toward the southern Atlantic Ocean, processing slowly eastward. The perturbation of the vortex was associated with air masses transported from middle and low latitudes into the polar region in small‐scale streamers. Similarly, tongues of vortex air peeled off the vortex edge and moved equatorward, enhancing the exchange between polar regions and the tropics. In addition, the disturbance of the vortex led to the generation of filaments at the inner side of the vortex edge, thus covering the vortex interior with small‐scale structures. A comparison between CRISTA observations and potential vorticity derived from UKMO data shows discrepancies concerning small‐scale structures. High‐resolution potential vorticity fields calculated from reverse domain filling trajectory simulations on isentropic surfaces based on horizontal winds from UKMO analyses and vertical motion from diabatic calculations are much more consistent with the measurements. Both observation and reverse domain filling (RDF) simulations show the strong atmospheric variability of this period of unusual enhanced planetary wave activity in the Southern Hemisphere.
The vertical and horizontal distribution of CO2 densities in the upper mesosphere and lower thermosphere as measured by CRISTA
Authors: Kaufmann M. , Gusev O. A. , Grossmann K. U. , Roble R. G. , Hagan M. E. , Hartsough C. , Kutepov A. A.
Published: November 2002

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured the global distribution of CO2 4.3 μm infrared emissions in the mesosphere and lower thermosphere during two Space Shuttle missions in November 1994 and August 1997. The daytime radiances have been inverted to CO2 number densities in the 60–130 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved CO2 number densities was carried out. The O(1D) excitation mechanism and model parameters constitute the most important uncertainties of retrieved CO2, typically 10–20%. The inaccuracy due to uncertainties in other atmospheric parameters is usually less than 10%. The CO2 volume mixing ratio (VMR) deviates from being well mixed between 70 and 80 km, which is significantly lower than indicated by previous rocket‐borne mass spectrometer data and model calculations but is in good agreement with the data obtained by other 4.3 μm emission and absorption experiments. The global distribution of CRISTA‐2 CO2 density shows significant longitudinal and latitudinal structures. The zonal mean CO2 densities are increasing toward polar summer latitudes below 90 km and above 115 km. Between 90 and 115 km, the latitudinal gradient is reversed. At 100 km, the gradient is mostly pronounced, reaching up to 50% difference between low and high latitudes. These variations are compared with results obtained by the Thermosphere/Ionosphere/Mesosphere Electrodynamics General Circulation Model (TIME‐GCM), showing very good agreement for the latitudinal distribution. Below 110 km, this variation is mostly due to the change in total density rather than to the CO2 VMR.
The local and global effects of Amazon deforestation
Authors: Werth David , Avissar Roni
Published: November 2002

To quantify the effects of land cover changes in the Amazon on local and global climate, numerical simulation experiments using the Goddard Institute for Space Studies Model II global climate model are conducted. An ensemble approach is adopted, in which a group of six control simulations is compared with a group of six deforested simulations. The deforestation effect in the Amazon is strong, with reductions in precipitation, evapotranspiration, and cloudiness. We also detect a noticeable impact in several other regions of the world, several of which show a reduction in rainy season precipitation that exhibits a high signal‐to‐noise ratio (determined by the t statistic). To determine the significance of the deforestation signal, we create several “false” ensembles, combining control and deforested members randomly, for comparison with the actual “true” ensemble. Such an analysis has not been used previously in deforestation studies and is useful for verifying the significance of a purported effect. The globally averaged precipitation deficits for the true ensemble are generally high in comparison with the false ensembles. Furthermore, changes in the Amazon due to the deforestation correlate significantly with remote changes in several areas. This suggests that the Amazon deforestation is producing a detectable signal throughout the Earth, and this finding underscores the importance of human activity in that region.
Stratospheric variability of temperature and ozone as inferred from the second CRISTA mission: Zonal means and local structures
Authors: Eidmann Gunnar , Offermann Dirk , Schaeler Bernd , Jarisch Michael , Schmidlin Francis J.
Published: November 2002

During the second Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) orbital mission from 8 to 16 August 1997, temperature, potential temperature, and ozone data have been derived with unprecedented spatial and temporal resolution on a global scale. The variability of these quantities is analyzed by statistical means. This “fluctuation analysis” determines the variability of the quantity under investigation within well‐defined “regions” with horizontal dimensions of about 20 by 20 degrees. Spatial variability is expressed in terms of standard deviations of differences of observed quantities with about 250, 500, 750, or 1000 km horizontal separation. The variances of temperature and therefore potential temperature for pressure levels between about 100 and 0.45 hPa and ozone between about 50 and 0.45 hPa depend greatly on geographical location and altitude. Practically all latitudes and altitudes exhibit strong zonal asymmetries. In contrast to the temperature variability distribution, that of potential temperature appears to focus more strongly on adiabatic processes, i.e., mainly on gravity and planetary wave activity depending upon geographical location and altitude. From the variances in a given “region” an autocorrelation function depending on horizontal scale can be derived. This correlation function suggests frequent wavelike structures with horizontal scales around 1000 km.
Winter N2O emission rate and its production rate in soil underlying the snowpack in a subboreal region, Japan
Authors: Kim Yongwon , Tanaka Noriyuki
Published: November 2002

Concentrations of N2O and 222Rn were observed in the snowpack and the soil from the subboreal region of Japan during the winter of 1996 to 1997. These observations were made to validate 222Rn as a proxy for temporal variation of N2O diffusivity within a snowpack having many ice lenses in order to estimate N2O emission through the snowpack to the atmosphere, to make a better evaluation of soil N2O production rate underlying the snowpack using 222Rn mixing rate in soil, and to clarify the factors influencing N2O flux and the production rate in subboreal ecosystems. Using a one‐dimensional vertical diffusion model under a nonsteady state condition, N2O flux markedly increased from 0.0034 to 18 μg N/m2/d with snow depth of an average of 4.1 ± 4.4 μg N/m2/d (1σ). The wide range of low N2O flux results from the surface soil freezing in early winter and the existence of multilayered ice lenses within the snowpack throughout the winter. When the 222Rn mixing rate varied from 4.0 cm/d to 16 cm/d, the soil N2O production rate underlying the snowpack significantly increased −3.4 to 48 mg N/m3/h with an average of 22 ± 15 mg N/m3/h (1σ). The soil temperature had a remarkably positive correlation with snow depth (R = 0.85). Therefore it can be concluded that the deeper snow cover does not prevent but does promote the production of N2O in soil and its emission to the atmosphere in the subboreal region of Japan. Although we estimated some N2O flux through the snowpack during the winter, based on the results presented here and published elsewhere, the winter regional N2O emission rate through the snowpack is estimated to be 0.07 Tg N/season, which corresponds to 30% of the annual N2O emission in the boreal ecosystem in the Northern Hemisphere. This unambiguously suggests that further data on the winter N2O fluxes are needed to assess the contribution of natural soils to the regional N2O budget and to evaluate impacts of the seasonality of the N2O emission rate on tropospheric N2O distribution.
Annual carbon flux from woody debris for a boreal black spruce fire chronosequence
Authors: Bond‐Lamberty B. , Wang C. , Gower S. T.
Published: November 2002

This study examined the distribution and respiration dynamics of woody debris (WD) in a black spruce‐dominated fire chronosequence in northern Manitoba, Canada. The chronosequence included seven stands that burned between 1870 and 1998; each stand contained separate well‐drained and poorly drained areas. The objectives of this study were to (1) quantify the distribution of WD, by diameter and decay class, in well‐drained and poorly drained stands across the chronosequence, (2) measure the evolution of CO2 from WD samples and model the effects of moisture, size and decay on respiration, and (3) model annual WD respiration and compute decay constants for each site. Coarse woody debris biomass ranged from 1.4 Mg ha−1 to 177.6 Mg ha−1, generally declining in the older stands of the chronosequence. More decayed WD had significantly (α = 0.05) higher moisture, lower density, and higher respiration rates than less decayed WD. Moisture and decay class were significant predictors of respiration when moisture was below 43%. Above this level, moisture was not significant, but stand soil drainage was significant, with drier sites having higher WD respiration. Year of burn was not significant in the respiration models. Modeled annual carbon emissions from WD ranged from 0.11 to 1.92 Mg C ha−1 yr−1. Modeled annual decay rates, between k = 0.01 and k = 0.06, changed across the age sequence. Thus a single‐exponential decay model may not be appropriate for the age sequence. Calculating k directly from wood respiration measurements, as done here, may be useful in allowing examination of year‐to‐year changes in k.
Global direct radiative forcing by process‐parameterized aerosol optical properties
Authors: Kirkevåg Alf , Iversen Trond
Published: November 2002

A parameterization of aerosol optical parameters is developed and implemented in an extended version of the community climate model version 3.2 (CCM3) of the U.S. National Center for Atmospheric Research. Direct radiative forcing (DRF) by monthly averaged calculated concentrations of non‐sea‐salt sulfate and black carbon (BC) is estimated. Inputs are production‐specific BC and sulfate from Iversen and Seland [2002] and background aerosol size distribution and composition. The scheme interpolates between tabulated values to obtain the aerosol single scattering albedo, asymmetry factor, extinction coefficient, and specific extinction coefficient. The tables are constructed by full calculations of optical properties for an array of aerosol input values, for which size‐distributed aerosol properties are estimated from theory for condensation and Brownian coagulation, assumed distribution of cloud‐droplet residuals from aqueous phase oxidation, and prescribed properties of the background aerosols. Humidity swelling is estimated from the Köhler equation, and Mie calculations finally yield spectrally resolved aerosol optical parameters for 13 solar bands. The scheme is shown to give excellent agreement with nonparameterized DRF calculations for a wide range of situations. Using IPCC emission scenarios for the years 2000 and 2100, calculations with an atmospheric global cliamte model (AFCM) yield a global net anthropogenic DRF of −0.11 and 0.11 W m−2, respectively, when 90% of BC from biomass burning is assumed anthropogenic. In the 2000 scenario, the individual DRF due to sulfate and BC has separately been estimated to −0.29 and 0.19 W m−2, respectively. Our estimates of DRF by BC per BC mass burden are lower than earlier published estimates. Some sensitivity tests are included to investigate to what extent uncertain assumptions may influence these results.
Direct measurement of the deep soil respiration accompanying seasonal thawing of a boreal forest soil
Authors: Hirsch Adam I. , Trumbore Susan E. , Goulden Michael L.
Published: November 2002

This paper presents data collected by an automated system designed to measure the seasonal cycle of both the quantity and isotopic composition of soil respiration. The results support the hypothesis that deep soil respiration at the BOREAS Northern Old Black Spruce site is sensitive to soil thaw and that much of this CO2 represents decomposition of old organic matter, rather than simply root respiration. This is the first study to use a completely automated soil gas sampling system in the field to measure the soil CO2 profile and collect samples of soil air for subsequent isotopic analysis. During the summer of 1999, deep soil respiration varied linearly with 50 cm temperature, with a slope of 0.2 kg C ha−1 d−1 °C−1. Late in the season, this respiration was dominated by decomposition of old soil organic matter (fixed from the atmosphere centuries ago). This study has taken an important step toward clarifying the temperature sensitivity of deep soil CO2 production in black spruce ecosystems through direct measurements within the soil and to quantify the seasonal variation of the relative contributions of recently fixed versus old carbon in deep soil respiration.