bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of chemical and optical in situ measurements of polar stratospheric cloud particles
Authors: Larsen Niels , Mikkelsen Ib Steen , Knudsen Bjørn M. , Schreiner Jochen , Voigt Christiane , Mauersberger Konrad , Rosen James M. , Kjome Norman T.
Published: September 2002

The chemical composition of polar stratospheric cloud (PSC) particles has been measured in a balloon‐borne mass spectrometer experiment [Schreiner et al., 1999]. The cloud particles have simultaneously been observed by a backscatter sonde flown on the same gondola. Taken separately, the two data sets indicate that the PSC particles are composed of liquid supercooled ternary solutions (STS). The chemical analysis shows that the particles contain relatively low concentrations of nitric acid, indicating a not fully developed type 1b PSC. Assuming the particles to be composed of STS, it appears that the calculated particle volumes are too small to generate the large observed backscatter ratios. Possible explanations for the apparent discrepancy are discussed, based on STS equilibrium model and microphysical/optical model calculations and including a meteorological mesoscale analysis of the mountain lee wave situation during the flight. Assuming a relatively large value of the real part refractive index of STS particles around 1.50 at 940 nm wavelength would apparently bring the two data sets in agreement. However, this large value seems to be in conflict with previous laboratory measurements and theoretical predictions, although in better agreement with recent balloon‐borne observations. The limited observational data set does not allow us to assess if the particles could be composed of a metastable dilute solid solution or a higher nitric acid hydrate.
Determination of the amount of water vapor entering the stratosphere based on Halogen Occultation Experiment (HALOE) data
Authors: Dessler A. E. , Kim H.
Published: September 2002

Using version 19 Halogen Occultation Experiment (HALOE) data, we estimate the abundance of water vapor entering the stratosphere [H2O]e is 3.80±0.49 ppmv averaged over 1993–1997. The average of all of the recently published estimates of [H2O]e is 3.85 ppmv, which we believe is the best estimate of [H2O]e.
Seasonal variation of tropospheric ozone in Indonesia revealed by 5‐year ground‐based observations
Authors: Fujiwara Masatomo , Kita Kazuyuki , Ogawa Toshihiro , Kawakami Shuji , Sano Takuki , Komala Ninong , Saraspriya Slamet , Suripto Agus
Published: September 2002

Regular ozonesonde observation and total ozone observation with the Brewer spectrophotometer have been conducted at Watukosek (7.5°S, 112.6°E), Indonesia, since 1993. Three seasons are recognized for the vertical distribution of tropospheric ozone. (1) During the local wet season, between December and March, the ozone mixing ratio is nearly constant at 25 ppbv throughout the troposphere. (2) During the transition season from wet to dry, between April and July, the mixing ratio is often enhanced in the uppermost troposphere. (3) During the local dry season, between August and November, the concentration is enhanced in the planetary boundary layer, and extensive forest fires in Indonesia associated with the strong El Niño events of 1994 and of 1997 have enhanced the ozone mixing ratio in the middle troposphere, the integrated tropospheric ozone, and the total ozone at Watukosek.
Global warming potential assessment for CF3OCF = CF2
Authors: Li Zhuangjie , Tao Zhining , Naik Vaishali , Good David A. , Hansen Jaron C. , Jeong Gill‐Ran , Francisco Joseph S. , Jain Atul K. , Wuebbles Donald J.
Published: September 2002

We have examined CF3OCF = CF2 regarding its reactivity toward OH radical, its infrared spectroscopic properties, its atmospheric lifetime, and its radiative forcing. From these we then determined the Global Warming Potentials (GWPs) for CF3OCF = CF2. The examination is completed using a combination of discharge flow coupled with mass spectrometer and resonance fluorescence (DF/MS/RF), Fourier transform infrared (FTIR) spectroscopy, ab initio molecular orbital calculation, and atmospheric and radiative transfer modeling. Mass spectral evidence suggests that both HF and CF3OCFC(O)F are products from the reaction of CF3OCF = CF2 with OH. The Arrhenius expression for CF3OCF = CF2 + OH is determined to be k1 = (6.41±0.82)×10−11 exp[(−868±40)/T] cm3 molecule−1 s−1 in the temperature range of 253–348 K. The atmospheric lifetime of CF3OCF = CF2 is estimated to be less than 5 days due to the OH attack. The calculated vibrational frequencies using ab initio molecular orbital calculations are in good agreement with FTIR experimental observation for the CF3OCF = CF2 molecule. Both C‐O and C‐F stretching modes in the CF3OCF = CF2 contribute to prominent absorption in the atmospheric window region. The absolute adjusted radiative forcing at the tropopause due to an increase in the concentration of CF3OCF = CF2 by one part per billion by volume (ppbv) is calculated to be 0.041 W m−2 ppbv−1. The Global Warming Potential for CF3OCF = CF2 is evaluated to be 0.004 for 100‐year time horizon.
A process‐oriented model of N2O and NO emissions from forest soils: 2. Sensitivity analysis and validation
Authors: Stange Florian , Butterbach‐Bahl Klaus , Papen Hans , Zechmeister‐Boltenstern Sophie , Li Changsheng , Aber John
Published: September 2002

The process‐oriented model PnET‐N‐DNDC describing biogeochemical cycling of C‐ and N and N‐trace gas fluxes (N2O and NO) in forest ecosystems was tested for its sensitivity to changes in environmental factors (e.g., temperature, precipitation, solar radiation, atmospheric N‐deposition, soil characteristics). Sensitivity analyses revealed that predicted N‐cycling and N‐trace gas emissions varied within measured ranges. For model validation, data sets of N‐trace gas emissions from seven different temperate forest ecosystems in the United States, Denmark, Austria, and Germany were used. Simulations of N2O emissions revealed that field observations and model predictions agreed well for both flux magnitude and its seasonal pattern. Differences between predicted and measured mean N2O fluxes were <27%. An exception to this was the N‐limited pine stand at Harvard Forest, where predictions of fluxes deviated by 380% from field measurements. This difference is most likely due to a missing mechanism in PnET‐N‐DNDC describing uptake of atmospheric N2O by soils. PnET‐N‐DNDC was also validated for its capability to predict NO emission from soils. Predicted and measured mean NO fluxes at three different field sites agreed within a range of ±13%. The correlation between modeled and predicted NO emissions from the spruce and beech stand at the Höglwald Forest was r2 = 0.24 (spruce) and r2 = 0.35 (beech), respectively. The results obtained from both sensitivity analyses and validations with field data sets from temperate forest soils indicate that PnET‐N‐DNDC can be successfully used to predict N2O and NO emissions from a broad range of temperate forest sites.
A comparison of single column model simulations of summertime midlatitude continental convection
Authors: Ghan Steven , Randall David , Xu Kuan‐Man , Cederwall Richard , Cripe Douglas , Hack James , Iacobellis Sam , Klein Stephen , Krueger Steven , Lohmann Ulrike , Pedretti John , Robock Alan , Rotstayn Leon , Somerville Richard , Stenchikov Georgiy , Sud Yogesh , Walker Gregory , Xie Shaocheng , Yio John , Zhang Minghua
Published: September 2002

Eleven different single‐column models (SCMs) and one cloud ensemble model (CEM) are driven by boundary conditions observed at the Atmospheric Radiation Measurement (ARM) program southern Great Plains site for a 17 day period during the summer of 1995. Comparison of the model simulations reveals common signatures identifiable as products of errors in the boundary conditions. Intermodel differences in the simulated temperature, humidity, cloud, precipitation, and radiative fluxes reflect differences in model resolution or physical parameterizations, although sensitive dependence on initial conditions can also contribute to intermodel differences. All models perform well at times but poorly at others. Although none of the SCM simulations stands out as superior to the others, the simulation by the CEM is in several respects in better agreement with the observations than the simulations by the SCMs. Nudging of the simulated temperature and humidity toward observations generally improves the simulated cloud and radiation fields as well as the simulated temperature and humidity but degrades the precipitation simulation for models with large temperature and humidity biases without nudging. Although some of the intermodel differences have not been explained, others have been identified as model problems that can be or have been corrected as a result of the comparison.
Isotopic signatures of sulfur in shallow Antarctic ice cores
Authors: Patris Nicolas , Delmas Robert J. , Jouzel Jean
Published: September 2002

Sulfur stable isotopes from Antarctic snow samples have been used to assess sources of sulfate. The novel experimental procedure presented here is suitable for the determination of sulfur isotopic composition at the micromolar level and has been adapted to polar ice samples. Measurements were carried out on three contiguous firn cores (PS6, PS7, and PS8) collected near Amundsen‐Scott Station (South Pole), covering the record of the Agung eruption (March 1963). Taking into account the minimum amount of sulfate required for the isotope analysis, it has been possible to delineate three time periods along the cores: pre‐1964 years (background sulfate level), 1964–1965 (volcanic deposition peak), and 1966–1968 (volcanic peak tail). A deeper part of another core (PS12) has been used to extend the background picture. Assuming the conservation of isotopic signatures during long‐range transport and deposition processes, results demonstrate the significant volcanic contribution to sulfate deposition on the central Antarctic ice cap a few months after a major low‐latitude eruption. They also confirm the marine biogenic origin of present background sulfate. Isotopic signatures (δ34S) of marine biogenic sulfate and volcanic sulfate from Mt. Agung have been found to be +18.6±0.9‰ and +2.7± .1‰, respectively.
Temporal variations of surface regional background ozone over Crete Island in the southeast Mediterranean
Authors: Kouvarakis G. , Tsigaridis K. , Kanakidou M. , Mihalopoulos N.
Published: September 2002

The first year‐round observations of seasonal and diurnal variations of background ozone at a coastal site on Crete Island in the southeast Mediterranean area are presented here. They point out (1) the existence of a well‐defined seasonal cycle with maximum during summer months, (2) the presence of elevated O3 levels (up to 80 ppbv) during daytime and over time periods of several days, and (3) the dependence of O3 mixing ratios on air mass origin. Comparison with three‐dimensional chemistry transport model results shows that during summer the measured O3 values exceed the calculated by 10–20 ppbv. Inclusion of biomass burning and biogenic volatile organic emissions in the model could partly offset the discrepancy between model results and observations.
Observations of NOy, CO, and SO2 and the origin of reactive nitrogen in the eastern United States
Authors: Stehr J. W. , Dickerson R. R. , Hallock‐Waters K. A. , Doddridge B. G. , Kirk D.
Published: September 2002

We have developed a technique to quantify better the relative significance of reactive nitrogen sources at a given site by measuring NOy, SO2, and CO. Measurements taken on Maryland's eastern shore of the Chesapeake Bay indicate that, on average, a minimum of 20% of the NOy is coming from coal‐fired point sources. Measurements in Shenandoah National Park, Virginia, and near Arendtsville, Pennsylvania, indicate that these minimum fractions are 34% and 32%, respectively. The remainder is coming predominantly from mobile sources, though there are some NOy sources whose influence cannot be determined with this technique. If the emissions inventories are taken to be correct, half the emitted NOy has been lost (probably deposited as nitrate) by the time it reaches the site. Analysis of air parcel back trajectories reveals that the likely source of elevated SO2 levels, and therefore point source emissions of NOy, is the industrialized Midwest of the United States.
A Global Morphology of Gravity Wave Activity in the Stratosphere Revealed by the GPS Occultation Data (GPS/MET)
Authors: Tsuda Toshitaka , Nishida Masahiro , Rocken Christian , Ware Randolph H.
Published: September 2002

Using temperature profiles obtained by the GPS/MET (GPS Meteorology) experiment from April 1995 to February 1997, we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km and background Brunt‐Väisälä frequency squared, N2. For each occultation event, we can evaluate a potential energy Ep which is assumed to be caused by atmospheric gravity waves. The monthly mean values of Ep at 15–20 km around Japan showed an annual variation with an enhancement in winter, which is consistent with the climatological behavior of the kinetic energy of gravity waves observed with the MU (middle and upper atmosphere) radar (34.9°N, 136.0°E) from 1985 to 1989. We have then derived the global distribution of Ep at 20–30 km during Northern Hemisphere winter (from November to February). Our analysis shows that the largest Ep values are generally centered around the equator between 25°N and 25°S with considerable longitude variations. Longitudinal variations of Ep at 20–30 km in a latitude range of 30°–60°N are also analyzed, resulting in larger Ep values over the continents than over the Pacific Ocean. Using GPS/MET data without antispoofing, latitudinal variations of Ep are determined in 15–45 km. Although large Ep values are concentrated near the equator at 20–30 km, Ep tends to become larger at midlatitudes at 30–40 km and higher‐altitude regions. At midlatitudes, Ep is found to be larger in winter months in both hemispheres. Height variations of Ep indicate a decrease at 25–30 km and a monotonic increase above 30 km.
Impact of aircraft emissions on reactive nitrogen over the North Atlantic Flight Corridor region
Authors: Koike M. , Kondo Y. , Ikeda H. , Gregory G. L. , Anderson B. E. , Sachse G. W. , Blake D. R. , Liu S. C. , Singh H. B. , Thompson A. M. , Kita K. , Zhao Y. , Sugita T. , Shetter R. E. , Toriyama N.
Published: September 2002

The impact of aircraft emissions on reactive nitrogen in the upper troposphere (UT) and lowermost stratosphere (LS) was estimated using the NOy‐O3 correlation obtained during the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) carried out over the U.S. continent and North Atlantic Flight Corridor (NAFC) region in October and November 1997. To evaluate the large‐scale impact, we made a reference NOy‐O3 relationship in air masses, upon which aircraft emissions were considered to have little impact. For this purpose, the integrated input of NOx from aircraft into an air mass along a 10‐day back trajectory (ΔNOy) was calculated based on the Abatement of Nuisance Caused by Air Traffic/European Commission (ANCAT/EC2) emission inventory. The excess NOy (dNOy) was calculated from the observed NOy and the reference NOy‐O3 relationship. As a result, a weak positive correlation was found between the dNOy and ΔNOy, and dNOy and NOx/NOy values, while no positive correlation between the dNOy and CO values was found, suggesting that dNOy values can be used as a measure of the NOx input from aircraft emissions. The excess NOy values calculated from another NOy‐O3 reference relationship made using in situ condensation nuclei data also agreed with these dNOy values, within the uncertainties. At the NAFC region (45°N–60°N) the median value of dNOy in the troposphere increased with altitude above 9 km and reached 70 parts per trillion by volume (pptv) (20% of NOy) at 11 km. The excess NOx was estimated to be about half of the dNOy values, corresponding to 30% of the observed NOx level. Higher dNOy values were generally found in air masses where O3 = 75–125 ppbv, suggesting a more pronounced effect around the tropopause. The median value of dNOy in the stratosphere at the NAFC region at 8.5–11.5 km was about 120 pptv. The higher dNOy values in the LS were probably due to the accumulated effect of aircraft emissions, given the long residence time of affected air in the LS. Similar dNOy values were also obtained in air masses sampled over the U.S. continent.
Analysis of ocean surface heat fluxes in a NOGAPS climate simulation: Influences from convection, clouds and dynamical processes
Authors: Waliser Duane E. , Hogan Timothy F.
Published: September 2002

This study examines the simulation quality of the surface heat flux fields produced during a climate simulation of the Navy Operational Global Atmospheric Prediction System, version 3.4, with a reduced spectral truncation of T63 and 18 levels (herineafter referred to as NOGAPS‐CL). Comparisons are made between a 17‐year NOGAPS‐CL simulation using monthly sea surface temperatures as surface boundary conditions and a number of validating data sets consisting of ship, satellite, and/or reanalysis‐based surface heat fluxes, precipitation, top of the atmosphere radiation budget, water vapor, cloud frequency, surface wind stress, and tropospheric winds. In this extended, long‐range integration, NOGAPS‐CL underpredicts the net surface shortwave flux in much of the subtropical oceans and overpredicts the net shortwave flux in the western Pacific warm pool and the midlatitude oceans, when compared to several satellite‐derived climatological data sets. In addition, NOGAPS‐CL over predicts the latent heat flux in much of the subtropics and under predicts the latent heat flux over the northern ocean western boundary currents and under the storm track regions that extend eastward from them. These shortwave and evaporation biases combine to produce errors in the surface net heat flux, with too little heat entering the subtropical/tropical oceans and too much heat loss in the midlatitudes oceans. Examination of related quantities indicates that the tropical climate biases are coupled to shortcomings in the convective cloud and/or boundary layer parameterizations which leads to the premature release of moist instability from the boundary layer in regions just outside the deep convective zones. This leads to enhanced climatological cloudiness, rainfall, and surface evaporation, as well as to a reduction in the surface shortwave flux and outgoing longwave radiation (OLR), in the subtropical regions. Furthermore, because of this early release of the moist static energy, there is a reduction in clouds, rainfall and water vapor content, as well as enhanced surface shortwave flux and outgoing longwave radiation, in the deep convective zones. The reduction in rainfall and enhanced OLR reduces the strength of the tropical large‐scale circulation, which in turn reduces the strength of the subsidence in the subtropical regions which normally acts to suppress the convection processes in these regions. The implications of these results are discussed in terms of the relationship among the forecast model climatological surface fluxes, convection, clouds, and the dynamical processes, as well as their similarities to other climate models and their possible impact on the simulation of transient systems.
Impact of global warming on the Asian winter monsoon in a coupled GCM
Authors: Hu Zeng‐Zhen , Bengtsson Lennart , Arpe Klaus
Published: September 2002

The Asian winter monsoon (AWM) response to the global warming was investigated through a long‐term integration of the transient greenhouse warming with the ECHAM4/OPYC3 CGCM. The physics of the response was studied through analyses of the impact of the global warming on the variations of the ocean and land contrast near the ground in the Asian and western Pacific region and the east Asian trough and jet stream in the middle and upper troposphere. Forcing of transient eddy activity on the zonal circulation over the Asian and western Pacific region was also analyzed. It is found that in the global warming scenario the winter northeasterlies along the Pacific coast of the Eurasian continent weaken systematically and significantly, and intensity of the AWM reduces evidently, but the AWM variances on the interannual and interdecadal scales are not affected much by the global warming. It is suggested that the global warming makes the climate over the most part of Asia to be milder with enhanced moisture in winter. In the global warming scenario the contrasts of the sea level pressure and the near‐surface temperature between the Asian continent and the Pacific Ocean become significantly smaller, northward and eastward shifts and weakening of the east Asian trough and jet stream in the middle and upper troposphere are found. As a consequence, the cold air in the AWM originating from the east Asian trough and high latitudes is less powerful. In addition, feedback of the transient activity also makes a considerable contribution to the higher‐latitude shift of the jet stream over the North Pacific in the global warming scenario.
Chlorine activation during the early 1995–1996 Arctic winter
Authors: Massie Steven T. , Tie XueXi , Brasseur Guy P. , Bevilacqua Richard M. , Fromm Michael D. , Santee Michelle L.
Published: September 2002

The coupling of temperature, aerosol area density, and chlorine activation is studied by comparing values from a three‐dimensional chemical transport model with observed temperature, aerosol area density, and ClO data in the Arctic for the time period December 1, 1995, to January 9, 1996. The three‐dimensional model uses United Kingdom Meteorological Office (UKMO) winds and temperatures, run on pressure surfaces between 316 and 0.31 hPa, and the model results are examined at 100, 68, 46, 31, and 21 hPa. Radiosonde values are compared to individual UKMO temperature values to assess the impact of model temperature errors upon heterogeneous chemistry reaction probabilities. Polar Ozone and Aerosol Measurement (POAM II) aerosol extinction values are transformed into area density values and compared to model daily averaged time trends. The model is run with gas phase chemistry only, gas phase plus sulfate aerosol chemistry, and the case where gas phase, sulfate aerosol, and polar stratospheric cloud reactions are active. Results from these calculations are used to examine the sensitivity of chlorine activation to temperature biases, area density uncertainties, and the effects of the reaction paths OH + ClO → HCl + O2 (4% yield) and HO2 + ClO → HCl + O3 (4% yield). Sulfate aerosol is demonstrated to be very effective in activating chlorine in the Arctic polar vortex. Time trends of five‐day averages of model and Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) version 4 ClO over extended regions inside and outside the vortex at 21 and 46 hPa agree within the experimental error.
Variations in the free chlorine content of the stratosphere (1991–1997): Anthropogenic, volcanic, and methane influences
Authors: Froidevaux L. , Waters J. W. , Read W. G. , Connell P. S. , Kinnison D. E. , Russell J. M.
Published: September 2002

Remote sensing of chlorine monoxide (ClO) by the Microwave Limb Sounder experiment aboard the Upper Atmosphere Research Satellite (UARS) has provided global measurements of variations in stratospheric free chlorine for 1991–1997. Linear trends were obtained from a multiple regression analysis of this data set at low latitudes and midlatitudes. ClO increases in the upper stratosphere (2 hPa) are significantly larger than expected from trends in chlorine source gases alone. Much of the upper stratospheric ClO variability can be explained by changes in CH4, as measured by the UARS Halogen Occultation Experiment. Decreasing ClO in the lower stratosphere is consistent with a relaxation from a chemically perturbed state attributed to the 1991 Mt. Pinatubo eruption.
Evaluating land surface parameters in the Biosphere‐Atmosphere Transfer Scheme using remotely sensed data sets
Authors: Oleson K. W. , Emery W. J. , Maslanik J. A.
Published: September 2002

Remotely sensed data sets were used to evaluate the spatial/temporal specification of albedo (α), roughness length (Z0), and green leaf area index (Lg) in the Biosphere‐Atmosphere Transfer Scheme (BATS). These parameters were evaluated for 1988 and 1993 in the Upper Mississippi River Basin (UMRB) using data from the International Satellite Land Surface Climatology Project Initiative 1 (ISLSCP 1) and by applying the ISLSCP 1 algorithms to high spatial resolution satellite data (Pathfinder advanced very high resolution radiometer (AVHRR) land (PAL)). ISLSCP 1 Lg was more variable spatially than BATS, particularly in midsummer months. ISLSCP 1 α was generally lower than BATS α. BATS and ISLSCP 1 generally showed small spatial variability in α for a given cover type. ISLSCP 1 Z0 were up to 100% larger than BATS. Spatial/temporal variability in ISLSCP 1 and BATS Z0 was primarily restricted to the spring. Comparisons between the ISLSCP 1 and PAL data indicated substantial differences in estimates of Lg and Z0 because of differences in the transformation of the vegetation index to Lg and grid cell heterogeneity. PAL Lg and Z0 were extremely variable spatially. Large differences between years in the PAL Lg were found, particularly in climate‐affected regions. The remotely sensed data indicate that improved parameterizations in BATS are needed to account for spatial variability in Lg and Z0, as well as interannual variability in Lg. However, the comparisons also demonstrate that assumptions inherent in remote sensing algorithms and the impact of these on parameter estimates must be carefully examined.
Interannual variations of snow accumulation on the Greenland Ice Sheet (1985–1996): new observations versus model predictions
Authors: McConnell Joseph R. , Mosley‐Thompson Ellen , Bromwich David H. , Bales Roger C. , Kyne Jay D.
Published: September 2002

Newly measured time series of net water‐equivalent accumulation from ice cores are reported for 11 sites located near the 2000‐m contour of the Greenland Ice Sheet. Many of these sites are located in regions where accumulation has not been previously measured. We compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range. Because ice core accumulation records include both regional and local accumulation components, we used adjacent ice core records at six multiple‐core sites to estimate the local component and extrapolated these results to the five single‐core sites. We investigated the impact of this short‐scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation. Although sealers were required to match the ∼12‐year mean modeled precipitation to the mean observed accumulation, a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations. The need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed. Although very encouraging, a more spatially distributed array of ice core accumulation measurements, spanning the same time period as the precipitation modeling, is necessary for continued model improvement and validation. In agreement with earlier studies, the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation.
A comparison of Arctic HNO3 profiles measured by the Improved Limb Atmospheric Spectrometer and balloon‐borne sensors
Authors: Koike M. , Kondo Y. , Irie H. , Murcray F. J. , Williams J. , Fogal P. , Blatherwick R. , Camy‐Peyret C. , Payan S. , Oelhaf H. , Wetzel G. , Traub W. , Johnson D. , Jucks K. , Toon G. C. , Sen B. , Blavier J.‐F. , Schlager H. , Ziereis H. , Toriyama N. , Danilin M. Y. , Rodriguez J. M. , Kanzawa H. , Sasano Y.
Published: September 2002

The Improved Limb Atmospheric Spectrometer (ILAS), a solar occultation infrared satellite sensor, was launched in August 1996. The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68°N, 21°E), in February and March 1997 and Fairbanks, Alaska (65°N, 148°W), in April and May 1997. During these campaigns, measurements of nitric acid (HNO3) were made using infrared emission spectrometers (Cold Atmospheric Emission Spectral Radiometer, Michelson Interferometer for Passive Atmospheric Sounding‐Balloon‐Borne version 2, and farinfrared spectrometer) and infrared solar occultation spectrometers (Limb Profile Monitor of the Atmosphere and Mark IV interferometer). An in situ experiment (Chemiluminescence Detector) measured total reactive nitrogen (NOy,), from which HNO3 mixing ratios in the lower stratosphere were calculated. In addition, an in situ NOy, measurement was also made at 12 km altitude from the Deutsche Luft‐und Raumfahrt Falcon aircraft in January 1997. The ILAS version 3.10 HNO3 mixing ratios obtained at the nearest location and averaged ILAS mixing ratios obtained within certain criteria were compared with the balloon data. The precision of the ILAS measurements was estimated from the random differences to be 0.8 parts per billion by volume (ppbv), corresponding to about 35% at 15 km and 10–15% at 20–35 km. While the absolute accuracy estimated from the systematic differences was as good as 0.5 ppbv (5%) at 20 km, the ILAS HNO3 mixing ratios were systematically lower than the balloon values by 1 ppbv (15–20%) at 25–30 km. The error in the altitude registration in the ILAS retrieval algorithm is a possible cause for the negative bias at higher altitudes.
Evidence of reflection of a long‐period gravity wave in observations of the nightglow over Arecibo on May 8–9, 1989
Authors: Walterscheid R. L. , Hecht J. H. , Djuth F. T. , Tepley C. A.
Published: September 2002

During the Arecibo Initiative in Dynamics of the Atmosphere (AIDA) campaign there were several unusual observations of the O2 Atmospheric (0,1) and OH Meinel (6,2) brightness fluctuations being nearly 180° out of phase. In this paper we discuss data from May 8–9, 1989, during which meteor radar and airglow instrumentations were operating and thus wind data were available. We show that the nearly out‐of‐phase result on this night is due to the fact that the OH Meinel brightness and temperature are out of phase while the O2 atmospheric temperature and brightness are nearly in phase. The characteristics of the wave causing the out of phase fluctuations are derived and comparisons are made between results obtained by the Aerospace nightglow camera and those obtained by the York University airglow camera [Zhang et al., 1993]. Although there are differences between them, both of the instrumental data sets are consistent with the presence of a wave with a horizontal wavelength ≥600 km and a period of several hours. An analysis of these data shows that the out‐of‐phase relationship is most likely due to strong wave reflection in the lower thermosphere caused by thermal gradients and wind shears.
Dependence of the OH concentration on solar UV
Authors: Ehhalt Dieter H. , Rohrer Franz
Published: September 2002

OH and the major parameters determining its concentration were measured during a field campaign in August 1994 at Mankmoos, a rural, relatively unpolluted site in northeastern Germany. The measured OH concentrations were previously shown to depend mainly on the intensity of solar UV and on the mixing ratio of NO2. In this paper we develop a simple parameterization of the dependence on solar UV and on NO2. The photolysis of O3 to O1D, of NO2 to NO, and of HCHO to HCO and H, all contribute significantly to the total dependence of OH on solar UV. We demonstrate that the photolysis frequency of O3, JO1D, is a suitable measure for that dependence which is slightly less than linear. The highly nonlinear dependence of OH on NOx is approximated by a Padé function. The parameterization provides a tool for a future quantitative intercomparison of the measured and modeled dependences of OH on UV and NO2. It also allows the removal of the variation in the measured OH induced by the dependences on the variables, UV and NO2, and thus enables a search for dependences on other, less influential parameters.
Observations of particulates within the North Atlantic Flight Corridor: POLINAT 2, September‐October 1997
Authors: Paladino J. D. , Hagen D. E. , Whitefield P. D. , Hopkins A. R. , Schmid O. , Wilson M. R. , Schlager H. , Schulte P.
Published: September 2002

This paper discusses participate concentration and size distribution data gathered using the University of Missouri‐Rolla Mobile Aerosol Sampling System (UMR‐MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on “the corridor effect,” or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions immediately adjacent to the corridor, were performed. The profiles showed a time‐dependent enhancement of particulates within the corridor, and a nonvolatile (with respect to thermal volatilization at 300°C) aerosol enhancement at corridor altitudes by a factor of 3.6. The southern extent of the North Atlantic Flight Corridor was established from a four flight average of the particulate data and yielded a boundary near 42.5°N during the study period. A size distribution analysis of the nonvolatile particulates revealed an enhancement in the <40 nm particulates for size distributions recorded within the flight corridor.
Interpolation of surface radiative temperature measured from polar orbiting satellites to a diurnal cycle: 2. Cloudy‐pixel treatment
Authors: Jin Menglin
Published: September 2002

Global skin temperature is very important for the understanding of surface climate and for evaluating climate models. However, when the surface is obscured by clouds, this variable cannot be measured directly by using satellite thermal infrared channels. Methods for calculating skin temperature for a satellite cloudy pixel are important, yet little research on their relative merits has been done. The “cloudy‐pixel treatment” presented here is a hybrid technique of “neighboring‐pixel” and “surface air temperature” approaches. The neighboring‐pixel approach (NP) for calculating skin temperature for a satellite cloudy pixel is described and tested against field experiments and climate model CCM3/BATS simulations. This approach is based on the surface energy balance with the soil heat flux being treated by a conventional force‐restore method for bare soil and short vegetated surfaces, where ground heat flux is important. For other surfaces where soil heat flux is less important, for example, the fully vegetated forests in temperate and tropical regions, observed empirical relationships between solar radiative energy and skin temperature (i.e., ΔSn/ΔTs) are used. In addition, a “surface air temperature (Ta) adjustment” is developed from the Monin‐Obukhov similarity theory to infer skin temperature from 2‐m air temperature using a knowledge of wind speed, pressure, boundary layer stability, and other surface properties. This adjustment is useful wherever surface air temperatures are available to insure the skin temperature consistency during daytime and nighttime. Error analyses show that this cloudy‐pixel treatment has an accuracy of 1°–2° K at monthly mean pixel level resolution. This accuracy varies with season and vegetation type. Despite the uncertainty in this algorithm, this work can be practically used to calculate skin temperature for a cloudy pixel.
Evidence for a link between climate and northern wetland methane emissions
Authors: Worthy Douglas E. J. , Levin Ingeborg , Hopper Fred , Ernst Michele K. , Trivett Neil B. A.
Published: September 2002

Wetlands are an important source of atmospheric methane (CH4), but the strength of this source and its sensitivity to potential changes in climate are still uncertain. In this study, continuous measurements from 1990 to 1998 of atmospheric CH4 from the Canadian observational sites at Fraserdale (49°53′N 81°34′W) and Alert (82°27′N 62°31′W) are used to estimate CH4 emissions from the Hudson Bay Lowland (HBL), a 320,000 km2 semicontinuous wetland region in central Canada. The HBL comprises ∼10% of the total area of northern wetlands. A conceptually simple approach was used to calculate the methane emission flux using the CH4 concentration difference between Alert and Fraserdale, the residence time of the air mass over the HBL, and the mixing height of the convective boundary layer. Emission rates estimated using this approach for 1990 compare well with empirical aircraft and tower flux measurements made within the HBL during the same time period, thus indicating that the methodology used is reasonable. Annual CH4 emission rates range from 0.23 to 0.50 Tg CH4 yr−1 and are much lower than many empirical flux measurements observed at other northern wetland sites. A seasonal temperature sensitivity with a Q10 of about 4 was found. Moreover, the observed interannual variations in emissions are well correlated to variations in annual air temperatures corresponding to a sensitivity of Q10 ≈ 7. That is, a 10°C change in annual temperature would result in a sevenfold change in wetland emissions which is much larger than Q10 values used in current global CH4 models (typically Q10 ≈ 1.5). Our findings suggest that northern wetland emissions are probably overestimated to date but may increase significantly due to predicted global warming.
Interannual and longer‐term variability of upper air circulation in the northeast Brazil‐tropical Atlantic sector
Authors: Hastenrath Stefan
Published: September 2002

The NCEP‐NCAR 1958–1997 upper air data set along with surface ship observations have been analyzed for the March‐April extremum of the annual cycle in the tropical Atlantic sector and core of the Northeast Brazil (Nordeste) rainy season. (1) In the long‐term mean, the Intertropical Convergence Zone (ITCZ) overlies a band of warmest surface waters and is accompanied by ascending motion and upper tropospheric divergent outflow directed mainly into a band of upper tropospheric convergence and subsidence over the tropical North Atlantic. (2) During years of extreme drought in the Nordeste the band of warmest surface waters is displaced northward, and concomitant with this is a northward shift of the strongest lower tropospheric convergence, ascending motion, and upper tropospheric divergent outflow. (3) During the low/warm as compared to the high/cold (SO) phase the bands of warmest surface waters, most intense convection, and largest lower tropospheric convergence, ascending motion, and upper tropospheric outflow are all shifted northward, similar to the pattern characteristic of the Nordeste drought years. (4) Long‐term trends are documented by a southward displacement of the bands of most intense convection, largest lower tropospheric convergence, ascending motion, and upper tropospheric divergence, and increasing cloudiness over the equatorial Atlantic. The study thus substantiates the upper air processes instrumental for the interannual and decadal‐scale variability in the surface climate of the region.
Structure and spectral features of the stratospheric aerosol extinction profiles in the UV‐visible range derived from SAGE II data
Authors: Bingen Christine , Fussen Didier
Published: September 2002

We discuss a climatological model named Extinction Coefficient for Stratospheric Aerosols (ECSTRA), describing the vertical and spectral dependence of the stratospheric aerosol extinction in the UV‐visible range. The basic variables used for the analytical formulation of the model are the wavelength, a reduced altitude referenced from the tropopause level, the latitude, and a parameter that describes the volcanic status of the atmosphere. The evolution of the spectral and vertical features of the extinction profile is discussed with respect to the different basic variables. The behavior of the spectral coefficients is qualitatively interpreted as a function of volcanism. The volcanism dependence of the parameters characterizing the Junge layer is also investigated: the peak position shows variations of several kilometers, with a minimum value reached between 0 and 2 km above the tropopause, while the peak width presents a weak volcanism dependence. The most important discrepancies between the model and the SAGE II input data set are found to be related to dynamical effects, and particularly to the influence of the quasi‐biennial oscillation.
A 1500 year record of accumulation at Amundsenisen western Dronning Maud Land, Antarctica, derived from electrical and radioactive measurements on a 120 m ice core
Authors: Karlöf L. , Winther J.‐G. , Isaksson E. , Kohler J. , Pinglot J. F. , Wilhelms F. , Hansson M. , Holmlund P. , Nyman M. , Pettersson R. , Stenberg M. , Thomassen M. P. A. , van der Veen C. , van de Wal R. S. W.
Published: September 2002

During the Nordic EPICA pre‐site survey in Dronning Maud Land in 1997/1998 a 120 m long ice core was retrieved (76°00′S 08°03′W, 2400 m above sea level). The whole core has been measured using the electric conductivity measurement (ECM) and dielectric profiling (DEP) techniques, and the core chronology has been established by detecting major volcanic eruptions. In a nearby shallow core radioactive traces from nuclear tests conducted during the 1950s and 1960s have been identified. Altogether, 13 ECM and DEP peaks in the long core are identified as originating from specific volcanic eruptions. In addition two peaks of increased total β activity are identified in the short core. Accumulation is calculated as averages over the time periods between these dated events. Accumulation rate is 62 millimetres (w. eq./yr) for the last 181 years (1816 A.D. to present) and 61 mm w. eq./yr for the last 1457 years (540 A.D. to present). Our record shows an 8% decrease in accumulation between 1452 and 1641 A.D. (i.e. part of the Little Ice Age), compared to the long‐term mean.
Influence of convection and biomass burning outflow on tropospheric chemistry over the tropical Pacific
Authors: Wang Yuhang , Liu Shaw C. , Yu Hongbin , Sandholm Scott T. , Chen Tai‐Yih , Blake Donald R.
Published: September 2002

Observations over the tropics from the Pacific Exploratory Mission‐Tropics A Experiment are analyzed using a one‐dimensional model with an explicit formulation for convective transport. Adopting tropical convective mass fluxes from a general circulation model (GCM) yields a large discrepancy between observed and simulated CH3I concentrations. Observations of CH3I imply the convective mass outflux to be more evenly distributed with altitude over the tropical ocean than suggested by the GCM. We find that using a uniform convective turnover lifetime of 20 days in the upper and middle troposphere enables the model to reproduce CH3I observations. The model reproduces observed concentrations of H2O2 and CH3OOH. Convective transport of CH3OOH from the lower troposphere is estimated to account for 40–80% of CH3OOH concentrations in the upper troposphere. Photolysis of CH3OOH transported by convection more than doubles the primary HOx source and increases OH concentrations and O3 production by 10–50% and 0.4 ppbv d−1, respectively, above 11 km. Its effect on the OH concentration and O3 production integrated over the tropospheric column is, however, small. The effects of pollutant import from biomass burning regions are much more dominant. Using C2H2 as a tracer, we estimate that biomass burning outflow enhances O3 concentrations, O3 production, and concentrations of NOx and OH by 60%, 45%, 75%, and 7%, respectively. The model overestimates HNO3 concentrations by about a factor of 2 above 4 km for the upper one‐third quantile of C2H2 data while it generally reproduces HNO3 concentrations for the lower and middle one‐third quantiles of C2H2 data.
Time evolution of tropospheric ozone and its radiative forcing
Authors: Berntsen Terje K. , Myhre Gunnar , Stordal Frode , Isaksen Ivar S. A.
Published: September 2002

Emission trends of ozone precursors have been estimated on the basis of CO2 emissions from use of fossil fuels and cement production (with regional emission indices), biomass burning estimates, use of fertilizers, and aircraft emissions. “Timeslice” calculations of changes in tropospheric ozone for 1850, 1900, 1950, 1960, 1970, 1980, and 1990 have been performed with the University of Oslo global three‐dimensional chemistry transport model (OsloCTM‐1). For surface ozone the regions of maximum growth are found to have shifted during the period. Up to 1950 the largest increase is found over central United States (+25–30 ppbv), while for the 1950–1970 period it occurs over southeastern Europe and northeastern Asia (+15–20 ppbv). For the last period (1970 to 1990) most of the growth is found over Asia (over the Persian Gulf, India, and northern China) reaching 15 to 20 ppbv. During the period up to 1970 the changes in the tropospheric ozone column are found to be most profound at northern high and midlatitudes (about 80% of the increase before 1970), while the increase at lower latitudes is found to accelerate in the 1970s and 1980s (60% of the increase before 1970). Radiative transfer models for thermal infrared radiation and shortwave radiation are used to calculate the time evolution of the radiative forcing. In 1950 the radiative forcing due to increase in tropospheric ozone since preindustrial times was about 1/3 of the present radiative forcing due tropospheric ozone. The present radiative forcing due to increase in tropospheric ozone since preindustrial times is estimated to 0.34 W m−2. Significant regional differences in the evolution of the radiative forcing is found due to the differences in ozone trends. The tropospheric ozone results are available at http://www.geofysikk.uio.no/data/ozone/trend.
Effect of canopy structure and the presence of snow on the albedo of boreal conifer forests
Authors: Ni Wenge , Woodcock Curtis E.
Published: September 2002

A Geometric‐Optical and Radiative Transfer (GORT) approach for modeling the radiation regime within plant canopies is capable of predicting temporal variation in the albedo of boreal conifer forests. Model predictions of daily surface albedo patterns and reflected solar radiation during the winter and summer seasons were validated using field measurements from two forest stands in the northern study area of BOReal Ecosystem‐Atmosphere Study (BOREAS) in 1995. The model is able to predict the “W” shape for the daily albedo over the sparse old jack pine forest stand during the snow season and the “bowl” shape of daily albedo during clear days in the summer. Results immediately following new snow and at the end of the snowmelt season indicate the sensitivity of overall forest albedos to the albedo of snow. Incorporation of time‐varying values for snow albedo may improve future efforts to estimate forest albedos in the winter.

Forest albedos are a complicated function of the canopy structure, the presence or absence of snow on the ground and the angular distribution of irradiance. These effects differ for the visible, near‐infrared and midinfrared portions of the solar spectrum. Forest albedos vary dramatically as a function of canopy cover when snow covers the ground, but very little when snow is not present. It is found that for tree cover over about 70%, the presence of snow has little effect on albedo.