bluuebunny/crossref_metadata_2025 huggingface dataset:
Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) observations of tracer transport by inertially unstable circulations
Authors: Smith Anne K. , Riese Martin
Published: December 2003

The first mission of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument obtained 7 days of nearly continuous high‐resolution global data in the stratosphere and mesosphere during November 1994. During the later part of the mission, the temperature data near the equatorial stratopause have stacked perturbations with short (∼10 km) vertical scales. These type of structures have been identified in previous studies and are consistent with a low‐latitude circulation responding to inertial instability. The disturbances seen in CRISTA temperatures have, in common with previous measurements, paired perturbations of opposite sign near the equator and in the subtropics of the winter hemisphere, a horizontal location coincident with conditions of inertial instability, and the simultaneous extension of a planetary wave from midlatitudes into the equatorial region. The amplitude in the present case is smaller than previously documented. Concentrations of two trace species in the upper stratosphere (ozone and methane) show perturbations consistent with the predicted response to an inertially unstable circulation, either through transport (methane) or photochemical changes (ozone). A new finding is that the upper stratospheric dynamical features appear to be linked to a tropical Kelvin wave in the lower stratosphere. Motions associated with the Kelvin wave may affect or control the vertical scale of the unstable circulation cell that gives rise to the stacked temperature perturbations.
Seasonal and interannual variabilities in tropical tropospheric ozone
Authors: Ziemke J. R. , Chandra S.
Published: December 2003

This paper presents the first detailed characterization of seasonal and interannual variability in tropical tropospheric column ozone (TCO) to delineate the relative importance of biomass burning and large‐scale transport. TCO time series are derived from 20 years (1979–1998) of total ozone mapping spectrometer (TOMS) data using the convective cloud differential (CCD) method. Our study identifies three regions in the tropics with distinctly different characteristics related to seasonal and interannual variability. These three regions are the eastern Pacific, Atlantic, and western Pacific. TCO in the Atlantic region peaks at about the same time (September‐October) both north and south of the equator, while the annual‐cycle amplitude in TCO varies from about 3 to 6 Dobson units (DU) from north to south of the equator. In comparison, annual cycles in both the eastern and western Pacific are generally weak, with the largest TCO amount occurring around March‐April in the northern hemisphere and September‐November in the southern hemisphere. Interannual variabilities in these three regions are also very different. The Atlantic region indicates a predominant quasi‐biennial oscillation (QBO) in TCO which is out of phase with the QBO in stratospheric ozone. This behavior is consistent with a UV modulation of upper tropospheric photochemistry on a QBO timescale caused by the QBO in stratospheric ozone. However, photochemical models predict significantly smaller changes, and dynamical effects may be a critical factor. Interannual variability in TCO in the Atlantic also appears to have some influence from biomass burning, but our study indicates that it is of lesser significance. Interannual variability in the eastern and western Pacific is dominated by El Niño events. During an El Niño there is anomalously low TCO in the eastern Pacific and high values in the western Pacific. These signatures indicate combined effects of convectively driven transport and tropospheric ozone generated by intense biomass burning in the Indonesian region. Finally, a simplified tropospheric ozone residual (STOR) method which utilizes the small variability of TCO near the dateline is proposed in this study to derive high‐resolution maps and extended time series of TCO.
Rate constants for the reactions of OH radicals with CH3OCF2CHFCl, CHF2OCF2CHFCl, CHF2OCHClCF3, and CH3CH2OCF2CHF2
Authors: Tokuhashi Kazuaki , Takahashi Akifumi , Kaise Masahiro , Kondo Shigeo
Published: December 2003

The rate constants for reactions of OH radicals with CH3OCF2CHFCl, CHF2OCF2CHFCl, CHF2OCHClCF3, and CH3CH2OCF2CHF2 have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis, laser photolysis, and discharge flow methods, combined with the laser‐induced fluorescence technique to monitor the OH radical concentration. The influence of impurities contained in the samples has been examined by means of sample purification using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these four halogenated ethers when the purified samples were used in the kinetic measurements. The Arrhenius rate constants have been determined from the respective kinetic data as k(CH3OCF2CHFCl) = (2.59±0.51) × 10−12 exp [−(1260±60)/T], k(CHF2OCF2CHFCl) = (7.46±1.85) × 10−13 exp [−(1230±80)/T], k(CHF2OCHClCF3) = (1.12±0.18) × 10−12 exp [−(1280±50)/T], and k(CH3CH2OCF2CHF2) = (2.57±0.44) × 10−12 exp [−(730±50)/T] cm3 molecule−1 s−1.
Validation of Global Ozone Monitoring Experiment cloud fractions relevant for accurate ozone column retrieval
Authors: Koelemeijer R. B. A. , Stammes P.
Published: December 2003

The Global Ozone Monitoring Experiment (GOME), launched on board the ERS‐2 satellite of the European Space Agency, is a spectrometer measuring the Earth's reflectivity between 240 and 790 nm. The main geophysical product of GOME is the ozone vertical column density, also called ozone column. For accurate ozone column retrievals the presence of clouds should be taken into account. Therefore, as part of the operational ozone column retrieval algorithm, cloud fraction is derived by the initial cloud fitting algorithm (ICFA) from the spectral reflectivity between 758 and 778 nm, which encloses the O2 A band. In ICFA, cloud top pressure is assumed a priori, and is taken from the International Satellite Cloud Climatology Project (ISCCP) database. We validated the ICFA (version 2.3) cloud fraction product in two ways. First, a statistical approach was performed comparing monthly average ICFA cloud fractions with monthly average cloud fractions from ISCCP. Global cloud patterns in monthly average ICFA cloud fraction maps compare reasonably well with those from ISCCP. Second, a detailed comparison for individual pixels was performed between ICFA cloud fractions and cloud fractions derived from collocated Along Track Scanning Radiometer‐2 (ATSR‐2) data. We found that large differences exist between the (effective) cloud fractions from ATSR‐2 and ICFA. The mean difference between the cloud fractions of ATSR‐2 and ICFA is 0.18; the standard deviation of the difference is 0.23. It is argued that the errors in the ICFA cloud fractions are probably due to errors in the assumed cloud top pressure. A modified version of ICFA, which is less sensitive to the assumed cloud top pressure, is presented. This yields a much improved agreement with the ATSR‐2 cloud fractions. Effects of errors in cloud fraction and cloud top height on the vertical ozone column density retrieved from GOME are discussed.
A four‐dimensional variational chemistry data assimilation scheme for Eulerian chemistry transport modeling
Authors: Eibern Hendrik , Schmidt Hauke
Published: December 2003

The inverse problem of data assimilation of tropospheric trace gas observations into an Eulerian chemistry transport model has been solved by the four‐dimensional variational technique including chemical reactions, transport, and diffusion. The University of Cologne European Air Pollution Dispersion Chemistry Transport Model 2 with the Regional Acid Deposition Model 2 gas phase mechanism is taken as the basis for developing a full four‐dimensional variational data assimilation package, on the basis of the adjoint model version, which includes the adjoint operators of horizontal and vertical advection, implicit vertical diffusion, and the adjoint gas phase mechanism. To assess the potential and limitations of the technique without degrading the impact of nonperfect meteorological analyses and statistically not established error covariance estimates, artificial meteorological data and observations are used. The results are presented on the basis of a suite of experiments, where reduced records of artificial “observations” are provided to the assimilation procedure, while other “data” is retained for performance control of the analysis. The paper demonstrates that the four‐dimensional variational technique is applicable for a comprehensive chemistry transport model in terms of computational and storage requirements on advanced parallel platforms. It is further shown that observed species can generally be analyzed, even if the “measurements” have unbiased random errors. More challenging experiments are presented, aiming to tax the skill of the method (1) by restricting available observations mostly to surface ozone observations for a limited assimilation interval of 6 hours and (2) by starting with poorly chosen first guess values. In this first such application to a three‐dimensional chemistry transport model, success was also achieved in analyzing not only observed but also chemically closely related unobserved constituents.
Contrast between 1992 and 1997 high‐latitude spring Halogen Occultation Experiment observations of lower stratospheric HCl
Authors: Douglass A. R. , Kawa S. R.
Published: December 2003

HCl measurements from the Halogen Occultation Experiment (HALOE) in the northern hemisphere during mid‐May 1997 revealed vortex fragments in which the chlorine reservoir partitioning was strongly pushed toward HCl (∼90% HCl, ∼10% ClONO2), similar to partitioning previously observed in the Antarctic vortex region. In contrast, observations of ClONO2 and HCl in the northern polar spring, 1992, and in other years, show these species established the balance typical for gas phase photochemical reactions in this region (∼60% HCl, ∼40% ClONO2). Annually, chlorine reservoirs in the winter lower stratosphere polar vortex are converted to chlorine radicals via heterogeneous reactions on particle surfaces at very cold temperatures (less than about 200 K). As temperatures warm in spring, the heterogeneous processes become insignificant compared with gas phase reactions, and the chlorine reservoirs are reformed. Measurements through the northern winter/spring in 1992 show rapid formation of ClONO2, followed by steady loss of ClONO2 and increasing HCl. Although ClONO2 measurements are not available for 1997, the HCl increase in 1997 is observed to be much more rapid, and the eventual HCl mixing ratio is about 50% greater than that of 1992. The observations are examined through comparison with the Goddard three‐dimensional chemistry and transport model. This model utilizes winds and temperatures from the Goddard Earth Observing System Data Assimilation System and a complete integration scheme for stratospheric photochemistry. Analysis of the evolution of HCl and ClONO2 shows that the observed difference in the overall rate of HCl formation is explained by the sensitivity of the gas‐phase chemistry to the ozone mixing ratio and the temperature. The results show that the model accurately simulates HCl and ClONO2 evolution during these two winters. Model validity is further supported by comparisons with O3 and reactive nitrogen species NO and NO2. This analysis provides a sensitive test of the lower stratospheric chlorine photochemistry, particularly because the analysis considers constituent evolution at a time when the HCl and ClONO2 are far from a photochemical stationary state.
Non‐sea‐salt sulfate, methanesulfonate, and nitrate aerosol concentrations and size distributions at Cape Grim, Tasmania
Authors: Andreae Meinrat O. , Elbert Wolfgang , Cai Yong , Andreae Tracey W. , Gras John
Published: December 2003

We collected weekly aerosol samples using high‐volume impactors over a period of 20 months (1988–1990) at the Cape Grim baseline station on the northwestern coast of Tasmania, Australia. The samples were analyzed for soluble ionic constituents, including sulfate, methanesulfonate (MS−), ammonium, nitrate, and the major sea‐salt ions. The sea‐salt component showed only a slight seasonal variation, whereas the non‐sea‐salt (nss) ions all had pronounced summer maxima. Significant interannual variability was seen between the nss ion concentrations measured during the two summers investigated. Nss sulfate and MS− were present both in the fine and coarse aerosol fractions, in the latter presumably associated with sea‐salt particles. During the winter period, there was more nss sulfate in the coarse fraction than in the fine fraction. These observations are consistent with an important role of liquid‐phase oxidation in haze and cloud droplets for the production of nss sulfate aerosol. The seasonal behavior of the sulfur and nitrogen species at Cape Grim and their mutual correlations suggest that DMS oxidation is the dominant sulfur source during summer, while nonbiogenic sulfur sources make significant contributions to nss sulfate outside of this season. Correlations of CN and CCN concentrations with nss sulfate, MS−, and wind speed suggest that DMS oxidation and, to a lesser extent, seaspray formation contributes to CN and CCN populations. The contrast between the weak seasonality of the sea‐salt component and the pronounced seasonal behavior in both sulfur species and CCN supports the central role of biogenic DMS emissions as precursors of CCN in this region, at least in the biologically productive season.
Photochemical and dynamical processes affecting gaseous H2O2 concentrations in the lower troposphere
Authors: Das Mita , Husain Liaquat
Published: December 2003

Measurements of gas phase H2O2, O3, and SO2 in ambient air, along with other meteorological parameters, were made at the Summit (1.5 km, above mean sea level, amsl) and at the Lodge (0.6 km, amsl) on Whiteface Mountain situated in the Adirondack region of northern New York state. These measurements were made during the summer of 1997 (July‐August) to study the dynamical and chemical processes that control the distribution of H2O2 at a pristine mountainous site. H2O2 and O3 exhibited considerable variability from day to day. Gas phase H2O2 ranged from 0.3 to 4.3 ppb with a mean of 1.2±0.6 at the Summit, whereas at the Lodge the range was 0.10 to 4.6 ppb with a mean of 1.1±0.8. H2O2 exhibited a weak reverse diurnal variation at the Summit, whereas a diurnal variation was observed in the H2O2 levels at the Lodge. The daytime H2O2 concentrations at the Lodge were significantly higher than those at the Summit, while the nighttime values were higher at the Summit. The observed diurnal variations at the Lodge have been explained in terms of photochemical production of H2O2 during the day and scavenging by aqueous aerosols during the nighttime under the influence of a stable nocturnal boundary layer (NBL). Ozone was observed to have a reverse diurnal variation at both sites though the concentrations at the Summit were higher than at the Lodge. Nocturnal maxima in H2O2 and O3 concentrations under certain meteorological conditions were observed at both sites and are believed to be due to transport of these pollutants above the NBL after they are mixed down in the presence of a weak NBL. Two case studies are presented to elucidate the influence of atmospheric chemical and dynamical processes on the ambient concentration of H2O2 and O3. Results of multivariate statistical analysis show that photochemical production is most important in regulating the formation of H2O2 at the Lodge, whereas at the Summit meteorological processes are most important.
Heterogeneous reactions of HOI on substrates of atmospheric importance
Authors: Allanic A. , Rossi M. J.
Published: December 2003

Experiments have been conducted in a Knudsen cell flow reactor in order to investigate the heterogeneous interaction of HOI on water ice and sulfuric acid at temperatures relevant to the lower stratosphere. They reveal a nonreactive uptake on ice whose rate is temperature independent in the range 180–200 K, whereas a negative temperature dependence has been observed in the range 195–250 K on liquid sulfuric acid. Two processes take place at the interface, namely, decomposition of HOI resulting in the formation of I2 and partial loss of HOI in the condensed phase without the apparent formation of a product. This latter fraction of HOI could not be retrieved by conversion to ICl or IBr upon addition of HCl or HBr. The heterogeneous reactions of HOI with alkali salts at ambient temperature have also been studied. HOI is found to interact reactively with KBr with an uptake coefficient γ = (6±2) × 10−2. I2 is observed as the main product, but IBr has also been detected at a branching ratio of approximately 6:1. Implications for atmospheric chemistry are briefly discussed.
Water content and morphology of sodium chloride aerosol particles
Authors: Weis David D. , Ewing George E.
Published: December 2003

Sodium chloride droplets with a median diameter of ∼0.4 μm were generated in the laboratory by atomizing an aqueous solution of NaCl under ambient conditions. Infrared extinction spectra of the aerosols under controlled relative humidity (RH) ranging from 15 to 95% were obtained. The extinction spectra contained both scattering and absorption components. In order to obtain an absorption spectrum of the condensed phase H2O associated with the particulates, it was necessary to subtract from the extinction spectra the absorption by H2O vapor and the scattering by the particulates. H2O vapor subtraction was accomplished by a standard technique. A procedure using Mie theory to subtract the scattering component of the extinction spectrum is described. The absorption spectra were used to determine the water content and structure of the particulates. Above ∼50% RH the aerosols contain aqueous droplets that have not reached equilibrium with the water vapor during the timescale of the experiments (∼10 s). There is a sharp transition in water content at around 50% RH which is consistent with other measures of the recrystallization point. Below 50% RH the NaCl particles contain an anomalously large amount of H2O. Several different particle models are considered to explain the H2O content. The model in which the NaCl particles contain pockets of aqueous NaCl solution was found to be most consistent with the spectroscopic observations. The relevance of salt particle morphology and water content to atmospheric aerosol chemistry is discussed.
A test of our understanding of the ozone chemistry in the Arctic polar vortex based on in situ measurements of ClO, BrO, and O3 in the 1994/1995 winter
Authors: Woyke Thomas , Müller Rolf , Stroh Fred , McKenna Daniel S. , Engel Andreas , Margitan James J. , Rex Markus , Carslaw Kenneth S.
Published: December 2003

We present an analysis of in situ measurements of ClO, BrO, O3, and long‐lived tracers obtained on a balloon flight in the Arctic polar vortex launched from Kiruna, Sweden, 68°N, on February 3, 1995. Using the method of tracer correlations, we deduce that the air masses sampled at an altitude of 21 km (480 K potential temperature), where a layer of enhanced ClO mixing ratios of up to 1150 parts per trillion by volume was observed, experienced a cumulative chemical ozone loss of 1.0±0.3 ppmv between late November 1994 and early February 1995. This estimate of chemical ozone loss can be confirmed using independent data sets and independent methods. Calculations using a trajectory box model show that the simulations underestimate the cumulative ozone loss by approximately a factor of 2, although observed ClO and BrO mixing ratios are well reproduced by the model. Employing additional simulations of ozone loss rates for idealized conditions, we conclude that the known chlorine and bromine catalytic cycles destroying odd oxygen with the known rate constants and absorption cross sections do not quantitatively account for the early winter ozone losses infered for air masses observed at 21 km.
In situ measurements of C2‐C10 volatile organic compounds above a Sierra Nevada ponderosa pine plantation
Authors: Lamanna Mark S. , Goldstein Allen H.
Published: December 2003

A fully automated gas chromatograph‐flame ionization detector system was designed and built to measure ambient concentrations of C2‐C10 volatile organic compounds, including many oxygenated compounds, without using liquid cryogen. It was deployed at Blodgett Forest Research Station in Georgetown, California, 38°53′42.9″N, 120°37′57.9″W, 1315 m elevation. More than 900 in situ measurements were made above a ponderosa pine canopy at 40‐min intervals, continuously from July 2 through August 1, 1997. Factor analysis and observed temporal patterns were used to categorize sources for measured compounds as biogenic or anthropogenic or both. Compounds that were clearly biogenic included methylbutenol, isoprene and its oxidation products (methacrolein and methyl vinyl ketone), and terpenes (α‐pinene, 3‐carene, d‐limonene). Other compounds were partially biogenic, including acetone, ethene, propene, hexanal, acetaldehyde, and methanol. Hydroxyl radical (OH) loss rates were dominated by the clearly biogenic compounds, accounting for 70% of the loss under mean midday conditions. The most important single compounds were isoprene (33%) and methylbutenol (21%). These two compounds were dominant under all conditions, including the coldest and most polluted days. Under the most polluted conditions, acetaldehyde became very important, accounting for 13% of the total. Total OH loss rates were highly correlated with temperature because emissions of biogenic compounds, which dominate OH loss, are strongly temperature dependent. Much of the research on biogenic volatile organic compounds has focused on isoprene and terpenes. Our results suggest that quantifying and understanding factors controlling biogenic emissions of other compounds such as methylbutenol, acetone, hexanal, methanol, and acetaldehyde are critical for improving our understanding of regional photochemistry.
Limitations of a diagnostic of stratospheric tracer lamination
Authors: Kettleborough J. A. , Holton J. R.
Published: December 2003

Tracer lamina are small‐scale features appearing in the vertical profiles of long‐lived tracers such as ozone and modified potential vorticity. Appenzeller and Holton [1997] diagnosed the production of tracer laminae from satellite data and assimilated fields using a quantity which they referred to as the tracer lamination rate (L). Subsequent studies with L have shown that this diagnostic must be treated with some caution. Two limitations of L calculated from low‐resolution horizontal data have been identified and are discussed here. First, L calculated from low‐resolution data does not refer to scales at which laminae are formed, and second, on the scales at which L is relevant there is a reversible contribution, due to the propagation of planetary waves. This reversible contribution is demonstrated using a simple model of a steady stationary Rossby wave. The magnitude of the reversible component is estimated from data and found to be a significant fraction of the L calculated from low‐resolution data.
Modeling the Canadian southern Atlantic region oxidants: A study of a Canadian EMEFS‐1 hyperintensive period
Authors: Gong Wanmin , Lin Xiude , Ménard Sylvain , Pellerin Pierre , Benoit Robert
Published: December 2003

The roles and mechanisms of transport and chemical transformation affecting surface ozone in the Canadian southern Atlantic region (SAR) are investigated using a three‐dimensional Eulerian comprehensive modeling system. The investigation is focused a regional ozone episode over the eastern North America during the first week of August 1988. The model performance is evaluated with available observations during this period. The model is shown to reproduce the general features of this regional episode, with better performance for the sites with clear local photochemical activities than for those strongly influenced by complex coastal flow. It is shown from the reconstructed time history of various processes along the backward trajectories originating from a site in Nova Scotia that the elevated ground‐level ozone in the SAR during the study period was associated with transport at low levels, under a strong southwesterly flow. The high ozone brought to the site was mostly produced within the stable marine boundary layer from precursors picked up earlier over the emission area on the east coast of the United States. A second transport situation was also simulated and shown to be associated with transport aloft that was never mixed to the surface. This study also shows that differential advection, due to stable stratification and vertical shear of horizontal wind, can deform surface‐based plumes to produce elevated layers of pollutants over the Gulf of Maine.
A 3‐year continuous record of nitrogen trace gas fluxes from untreated and limed soil of a N‐saturated spruce and beech forest ecosystem in Germany: 2. NO and NO2 fluxes
Authors: Gasche Rainer , Papen Hans
Published: December 2003

For 3 years we followed the complete annual cycles of NO and NO2 flux rates from soil of a spruce control site, a limed spruce site, and a beech site at the Höglwald Forest, Bavaria, Germany, with high temporal resolution in order to gain detailed information about (1) the impacts of forest type, liming, and atmospheric N input by wet deposition on the magnitude of NO and NO2 flux rates and (2) the microbial processes involved in NO production and emission. In addition to identification of seasonal variations of flux rates the huge database allowed calculation of annual mean NO and NO2 fluxes with high accuracy and identification of interannual variations of fluxes. The long‐term annual mean NOx emission was 61.7 μg NOx N m−2 h−1 for the spruce control site, 17.3 μg NOx N m−2 h−1 for the limed spruce site, and 4.0 μg NOx N m−2 h−1 for the beech site. These extremely high soil NOx emissions from a temperate forest most likely reflect the status of N saturation of the Höglwald Forest as a consequence of year‐long heavy atmospheric N input. Multiple regression analyses revealed the following sequence of importance of environmental factors on NO flux: soil temperature to water‐filled pore space to soil NO3− concentrations to soil NH4+ concentrations. Nitrification was the dominating biotic modulator of NO emission at all sites: >60% of the variation of NO emission rates were associated with variations of net nitrification rates. There was a strong positive correlation between amount of in situ N input by wet deposition and magnitude of in situ NO flux rates. Approximately 15% and 7% of the actual N input was lost as NO from the soil stocked with spruce and beech, respectively. Liming resulted in 49% reduction of NO emissions as compared to an unlimed spruce control site. The results indicate that the reduction in NO emission was due to an increase in NO consumption within the limed soil. In contrast to NO flux, NO2 flux was modulated by physico‐chemical rather than biological factors. Using the data of this study, we estimate that the contribution of N‐affected temperate coniferous and deciduous forests to the global NOx release is 0.3 Tg NOx N yr−1.
Arctic winter climate and its interannual variations simulated by a regional climate model
Authors: Rinke Annette , Dethloff Klaus , Christensen Jens H.
Published: December 2003

The mean Arctic January climatology and its interannual variation have been examined by simulations with a regional climate model of the Arctic atmosphere. To this end, an ensemble of monthlong simulations (January of the 11 years 1985–1995) has been investigated in which the ensemble is large enough to represent a broad range of climatic conditions. The model produces credible simulations of the meteorological patterns. Only small deviations occur between simulations and European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses; that is, over most of the model area these differences in sea level pressure, 850 hPa temperature, and 500 hPa height are below 3 hPa, 1 K, and 5 m, respectively. Larger deviations (up to 5 hPa in the sea level pressure and 20 m in the 500 hPa height) are found over parts of the Arctic Ocean, which seems to be related to the crude sea ice representation at the lower model boundary and deficiencies in the planetary boundary layer parameterization. It is shown that the dynamical aspects of the interannual variability can be adequately captured by the model simulations; that is, the maximum of the model bias of the dynamical variables is significantly smaller than the interannual variability throughout the entire domain. To gain more insight into the spatial and temporal structures of the model's variability, an empirical orthogonal function (EOF) analysis has been applied to determine the most significant structures in the fluctuations of the monthly mean dynamical fields. EOF 1 of the 500 hPa height field describes a regime with well‐pronounced polar vortex and corresponds to the “Arctic Oscillation”, whereas EOFs 2 and 3 show wave structures. A pronounced interannual variability is noticed in the time series of the amplitudes of the EOFs.
Observations and interpretation of column OClO seasonal cycles at two polar sites
Authors: Miller Henry L. , Sanders Ryan W. , Solomon Susan
Published: December 2003

OClO and NO2 slant column abundances have been measured by ground‐based spectrographs in both the Arctic (Kangerlussuaq, Greenland, at 67.0°N, 51.0°W) and the Antarctic (McMurdo Station, Antarctica, at 77.8°S, 166.6°E). A key process for stratospheric ozone depletion is the activation of chlorine by heterogeneous reactions. Sunlight is also an essential ingredient in the catalytic cycles that destroy ozone. This data set illustrates the seasonal timing of autumnal chlorine activation and the springtime disappearance of active chlorine at two polar sites. As such, the data provide constraints for model calculations. In the Northern Hemisphere during the winters of 1994–1995 and 1995–1996, the OClO data show the seasonal onset of stratospheric chlorine activation in mid‐December and seasonal disappearance of active chlorine in mid‐March. The data also show the seasonal decline and recovery (in mid‐March) of nitrogen dioxide levels. In the Southern Hemisphere during the winters of 1991, 1993, and 1996, similar chemical processing occurs during late April to early May and late September to early October. The role of several factors in determining the seasonal cycles of column OClO are probed through model studies. Observed cold temperatures and reactions on liquid sulfate aerosols appear to play a key role in producing the timing of the observed OClO seasonal cycle in the Northern Hemisphere.
A simple snow‐atmosphere‐soil transfer model
Authors: Sun Shufen , Jin Jiming , Xue Yongkang
Published: December 2003

This paper presents a simple snow model for climate studies. There are three prognostic variables in the model: specific enthalpy, snow water equivalent, and snow depth. This model is developed on the basis of up‐to‐date comprehensive and complex snow schemes but with substantial simplification and improvement. The effects of vapor on snow processes have been analyzed in the paper. On the basis of the analysis, vapor's contribution in the mass equation is eliminated, and an effective conductivity coefficient, which includes a simple parameterization for vapor diffusion effect, is used to describe its contribution in the energy equation to simplify the computation. Specific enthalpy is used in the energy balance equation. Using enthalpy rather than temperature greatly simplifies the computational procedure for the phase change calculation in the snow process. This approach, along with a one‐step test scheme that avoids iterations, saves computational time, which is important for general circulation model (GCM) simulations. The layering scheme is a critical part in the model. After many tests, it is found that three layers with an appropriate layering scheme are adequate for most cases. Preliminary testing using Russian and French snow data shows that the three‐layer model is able to produce reasonable and consistent results.
Surface UV radiation over Australia, 1979–1992: Effects of ozone and cloud cover changes on variations of UV radiation
Authors: Udelhofen Petra M. , Gies Peter , Roy Colin , Randel William J.
Published: December 2003

Time series of daily erythemal ultraviolet radiation (UVR) exposure, ozone, and cloud cover were analyzed over the Australian continent using data sets from the NASA Total Ozone Mapping Spectrometer (TOMS) from 1979–1992. The TOMS UVR exposures showed good agreement with data from surface observations. Using a relationship derived from comparisons of the TOMS partial cloud reflectivities with surface cloud cover observations, the TOMS reflectivities were converted into estimates of cloud cover for several Australian regions. It was shown that the deseasonalized time series of UVR exposures can be statistically described as a linear function of ozone and cloud cover anomalies. Results of a trend analysis indicated statistically significant increases in UVR exposures of 10% decade−1 in the summer months in the tropics. These were associated with a simultaneous depletion of ozone and a decrease in cloud cover. Midlatitudinal regions showed no significant trends of UVR. It was found that variations of ozone and UVR over Australia were significantly influenced by the quasi‐biennial oscillation (QBO). An increase in zonal wind strength of 20 m s−1 was correlative with reductions of ozone of 1.7% and enhancements of UVR exposures of 2.2%. An increase in solar radio flux of 100×10−22 W m−2 (Hz)−1 was associated with significant reductions of UVR of 5–10% in the tropical and subtropical regions in summer. The results suggested that enhancements in summer UVR exposures of about 10–20% above the climatological average might be expected in years in which the QBO is in its westerly phase and the solar cycle is at its minimum.
Analyses of Atmospheric Radiation Measurement (ARM) program's Enhanced Shortwave Experiment (ARESE) multiple data sets for studying cloud absorption
Authors: Li Z. , Trishchenko A. P. , Barker H. W. , Stephens G. L. , Partain P.
Published: December 2003

Following the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE), some studies reported a cloud absorption anomaly (CAA) of unprecedented magnitude. The largest discrepancy was found on a heavy overcast day (October 30, 1995) when cloud absorptance inferred from aircraft observations was 37% of the incoming solar irradiance, almost twice that of model calculations. The essential measurements supporting the finding were made with an airborne total solar broadband radiometer (TSBR). A thorough analysis is performed here, employing a variety of observations from more sources including aircraft, spacecraft, and ground‐based instruments. It is found that albedos measured with the TSBR are systematically less than those inferred from other instruments. The difference in mean albedo between TSBR and that inferred from the scanning spectral polarimeter (SSP) on board the same aircraft amounts to 0.15, which is comparable to the reported CAA. SSP data were validated by (1) comparing them to data from the total direct diffuse radiometer (TDDR) spectral radiometer, (2) comparing the SSP's albedo‐transmittance slope with that derived from ScaRaB satellite data, and (3) comparing SSP‐derived albedos with those inferred from cloud optical parameters estimated from ground‐based passive and active observations. All these comparisons show that SSP data are consistent with other measurements within the data uncertainties whose accumulated upper limit is <0.06. A reasonable doubt is thus cast on the claim of a very strong cloud absorption anomaly found using TSBR data on October 30.
Aircraft‐borne measurements of peroxy radicals by chemical conversion/ion molecule reaction mass spectrometry: Calibration, diagnostics, and results
Authors: Reiner Thomas , Hanke Markus , Arnold Frank , Ziereis Helmut , Schlager Hans , Junkermann Wolfgang
Published: December 2003

We describe a novel instrument for aircraft‐borne measurements of peroxy radicals developed and built at the Max‐Planck‐Institut für Kernphysik in Heidelberg. The instrument measures peroxy radicals using the chemical conversion of peroxy radicals to sulfuric acid and the detection of sulfuric acid by ion molecule reaction mass spectrometry. The peroxy radical measurement system was calibrated at the ground using the UV photolysis of H2O and was further characterized by laboratory and in‐flight diagnostic measurements. Particular attention was paid to the effects of wall losses in the flow reactor and sampling system and the measurement efficiency for organic peroxy radicals. The conversion efficiency of methyl peroxy radicals to sulfuric acid was investigated by detailed laboratory studies and was found to be >80% for the conditions of our experiment. The instrument was employed for aircraft‐borne measurements of peroxy radicals in the free troposphere over south Germany in combination with measurements of O3, NO, H2O, and J(O1D). Peroxy radical mixing ratios between 10 and 40 pptv were measured at altitudes between 3.8 and 7.8 km. A comparison of the measured peroxy radical concentrations with the results of a simple steady state estimate is presented.
Polar vortex dynamics during spring and fall diagnosed using trace gas observations from the Atmospheric Trace Molecule Spectroscopy instrument
Authors: Manney G. L. , Michelsen H. A. , Santee M. L. , Gunson M. R. , Irion F. W. , Roche A. E. , Livesey N. J.
Published: December 2003

Trace gases measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during three Atmospheric Laboratory for Applications and Science (ATLAS) space‐shuttle missions, in March/April 1992 (AT‐1), April 1993 (AT‐2), and November 1994 (AT‐3) have been mapped into equivalent latitude/potential temperature (EqL/θ) coordinates. The asymmetry of the spring vortices results in coverage of subtropical to polar EqLs. EqL/θ fields of long‐lived tracers in spring in both hemispheres show the net effects of descent at high EqL throughout the winter, reflecting strong descent in the upper stratosphere, decreasing descent at lower altitudes, and evidence of greater descent at the edge of the lower stratospheric vortex than in the vortex center; these results are consistent with trajectory calculations examining the history of the air measured by ATMOS in the month prior to each mission. EqL/θ tracer fields, the derived fields CH4‐CH4* (CH4* is the expected CH4 calculated from a prescribed relationship with N2O for fall) and NOy−NOy* (analogous to CH4*), and parcel histories all indicate regions of strong mixing in the 1994 Southern Hemisphere (SH) spring vortex above 500 K, with the strongest mixing confined to the vortex edge region between 500 and 700 K, and mixing throughout the Northern Hemisphere (NH) spring vortex in 1993 below about 850 K. Parcel histories indicate mixing of extravortex air with air near the vortex edge below 500 K in the SH but not with air in the vortex core; they show extravortex air mixing well into the vortex above ∼450 K in the NH and into the vortex edge region below. The effects of severe denitrification are apparent in EqL/θ HNO3 in the SH lower stratospheric spring vortex. The morphology of HNO3 in the Arctic spring lower stratospheric vortex is consistent with the effects of descent. EqL/θ fields of ATMOS NOy−NOy* show decreases consistent with the effects of mixing throughout the NH lower stratospheric vortex. The EqL/θ‐mapped ATMOS data thus indicate no significant denitrification during the 1992–1993 NH winter. Examination of H2O+2CH4 shows that dehydration in SH spring 1994 extended up to ∼600 K; it also suggests the possibility of a small amount of dehydration in the NH 1993 spring vortex below ∼465 K. Ozone depletion is evident in the spring vortices in both hemispheres. Differences in autumn EqL/θ tracer fields between the missions reflect the fact that each succeeding mission took place ∼2 weeks later in the season, when the vortex had developed further. There was greater average descent and greater isolation of air in the developing vortex during each succeeding mission, consistent with progressively larger downward excursions of long‐lived tracer contours observed in the upper stratosphere at high EqL.
Particle size distributions in an expanding plume undergoing simultaneous coagulation and condensation
Authors: Turco Richard P. , Yu Fangqun
Published: December 2003

In previous work [Turco and Yu, 1997, 1998], analytical solutions of the equations describing aerosol coagulation in an expanding plume were derived. Those solutions were shown to depend on a single dimensionless time‐dependent number, NT, which is related to the particle coagulation kernel and the plume volume. Here these results are extended to the case in which a vapor, either primary or secondary, is also condensing on the aerosol. We show that for several important regimes of condensation encountered in the atmosphere, relatively simple empirical relations can be deduced that accurately describe the evolving particle size distribution, again in terms of NT. In addition, the effects on the plume aerosol of entrained background particles and gases are explicitly treated. These new analytical solutions offer insights into the physics governing the evolution of aerosol plumes under atmospheric conditions, lead to a simple methodology for carrying out sensitivity studies, allow objective testing and validation of numerical codes and provide a useful means of extrapolating from plume scales to the scales appropriate for regional and global modeling.
Importance of the Indian Ocean for simulating rainfall anomalies over eastern and southern Africa
Authors: Goddard Lisa , Graham Nicholas E.
Published: December 2003

The relative contributions of the Indian Ocean and Pacific Ocean sea surface temperatures (SSTs) to the rainfall variability over eastern central, and southern Africa during the austral spring‐summer are examined. The variability of African rainfall is statistically related to both oceans, but the variability in the two oceans is also related. To separate the effects of the Indian and Pacific Oceans, a suite of numerical model simulations is presented: GOGA, the atmosphere is forced by observed SSTs globally; IOGA, the atmosphere is forced by observed SSTs only in the Indian Ocean basin; and POGA, the atmosphere is forced by observed SSTs only in the tropical Pacific basin. While the SST variability of the tropical Pacific exerts some influence over the African region, it is the atmospheric response to the Indian Ocean variability that is essential for simulating the correct rainfall response over eastern, central, and southern Africa. Analyses of the dynamical response(s) seen in the numerical experiments and in the observations indicate that the Pacific and Indian Oceans have a competing influence over the Indian Ocean/African region. This competition is related to the influence of the two oceans on the Walker circulation and the consequences of that variability on low‐level fluxes of moisture over central and southern Africa. Finally, given the high correlation found between SST variability in the Indian and Pacific Oceans with the Pacific leading by ∼3 months, we speculate on an approach to long‐lead dynamical climate prediction over central‐east and southern Africa.
On the lidar‐observed sandwich structure of polar stratospheric clouds (PSCs): 2. Numerical simulations of externally mixed PSC particles
Authors: Shibata Takashi
Published: December 2003

Polar stratospheric clouds (PSCs) were simulated via a mixture of (1) liquid‐ternary‐solution particles consisting of H2SO4, HNO3, and H2O, and (2) solid nitric acid trihydrate (NAT) particles in a microphysical box model. The simulations indicated that the scattering ratio increases as the temperature decreases to near the frost point of ice without a concomitant increase in the depolarization. When the decrease in temperature was halted a few degrees above the frost point, the time‐dependent depolarization was subsequently observed to increase. This response was found when the total number of solid particles was in the finite range, 0.001–0.01/cm3. This number range agrees well with the (large size) particle number concentration observed via an optical particle counter.
On the lidar‐observed sandwich structure of polar stratospheric clouds (PSCs): 1. Implications for the mixing state of the PSC particles
Authors: Shibata Takashi , Shiraishi Kouichi , Adachi Hiroshi , Iwasaka Yasunobu , Fujiwara Motowo
Published: December 2003

A vertical sandwich structure of (type I) polar stratospheric clouds (PSCs), in which layers of relative depolarization are above and below a scattering layer has frequently been observed by lidar at Ny‐Ålesund, Svalbard, when the stratospheric temperature decreases to near the frost point of ice. Using lidar observations and backward trajectory analysis, we studied the time evolution of this structure and its temperature history. The main difference between the temperature history of PSCs in the scattering layer and those in the depolarization layer was the temperature at which the structure is observed. The small increase in the scattering ratio over time at the altitude of the depolarization maximum implies a slow nucleation of solid particles. These lidar observations including temperature histories suggest that the sandwich structure arises from the external mixing of two different types of particles. A large fraction of liquid particles, grown at low temperature, constitutes the scattering layer, while at higher temperatures, a very small fraction of solid particles is responsible for the depolarization layer.
Effects of nonmethane hydrocarbons on lower stratospheric and upper tropospheric chemical climatology in a two‐dimensional zonal average model
Authors: Kotamarthi V. R. , Wuebbles D. J. , Reck R. A.
Published: December 2003

The effect on the modeled chemical climatology of the upper troposphere and lower stratosphere of including a limited set of nonmethane hydrocarbons in a two‐dimensional (2‐D) zonal average model is presented. Recent measurements of nitrogenated and oxygenated hydrocarbons in the upper troposphere and lower stratosphere have revealed the possibility of significant perturbation of this region. A zonally averaged 2‐D chemical transport model enhanced to represent tropospheric processes was used to explore the extent of this perturbation on global and regional spatial scales and on seasonal and annual average timescales. Acetone was shown to cause a significant increase in the HOx budgets of the upper troposphere in the midlatitude Northern Hemisphere during the winter and early spring months, with acetone photolysis providing the most significant source of HOx radicals. The tropical upper troposphere has a uniform increase in HOx of up to 20% throughout the year because of acetone photolysis. Including the hydrocarbons caused a net increase in ozone of 5 ppbv in the lower and middle troposphere and 5–10 ppbv in the upper troposphere for global and annual averages. The effect of including the hydrocarbons on the calculated model ozone response for the case of doubled surface mixing ratios of atmospheric CH4 is also discussed. It is shown that including hydrocarbons in the model has a significant effect on the modeled ozone response to the methane increase.