bluuebunny/crossref_metadata_2025 huggingface dataset:
Urban and rural aerosol characterization of summer smog events during the PIPAPO field campaign in Milan, Italy
Authors: Baltensperger U. , Streit N. , Weingartner E. , Nyeki S. , Prévôt A. S. H. , Van Dingenen R. , Virkkula A. , Putaud J.‐P. , Even A. , ten Brink H. , Blatter A. , Neftel A. , Gäggeler H. W.
Published: November 2002

A comprehensive range of aerosol parameters was measured at an urban and a rural site in the Milan, Italy metropolitan region during summer smog events in summer 1998. Measurements were performed as part of the Pianura Padana Produzione di Ozono (PIPAPO) field campaign to determine the sensitivity of O3 production to NOX and volatile organic carbon concentrations at several ground stations. Primary aerosol parameters (i.e., direct emissions) such as aerosol black carbon showed a distinct diurnal variation with maxima at about 0000 and 0800 central European summer time (CEST), in contrast to secondary aerosol parameters such as sulfate and nitrate. Aerosol number size distributions were measured under ambient conditions as well as after conditioning with volatility and hygroscopicity systems. A mode at d = 20–30 nm in the number concentration was found at 0800 CEST and exhibited high volatility at 110°C (∼80% volume lost upon heating) but no hygroscopic behavior. Based on these measurements, small particles (d < 40 nm) are thought to consist mainly of hydrophobic particulate organic matter, rather than soot or H2SO4 aerosols. Two distinct hygroscopic modes with average growth factors d/d0 ∼ 1.02 and 1.21–1.28 were found for particles with dry (relative humidity of <30%) diameters d0 = 50–200 nm. Submicrometer aerosols exhibited lower volatility at the rural than at the urban site, which is attributed to additional particulate mass produced by secondary particle formation.
An overview of the SOLVE/THESEO 2000 campaign
Authors: Newman Paul A. , Harris Neil R. P. , Adriani Alberto , Amanatidis Georgios T. , Anderson James G. , Braathen Geir O. , Brune William H. , Carslaw Kenneth S. , Craig Michael S. , DeCola Philip L. , Guirlet Marielle , Hipskind R. Stephen , Kurylo Michael J. , Küllmann Harry , Larsen Niels , Mégie Gérard J. , Pommereau Jean‐Pierre , Poole Lamont R. , Schoeberl Mark R. , Stroh Fred , Toon Owen B. , Trepte Charles R. , Van Roozendael Michel
Published: November 2002

Between November 1999 and April 2000, two major field experiments, the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000), collaborated to form the largest field campaign yet mounted to study Arctic ozone loss. This international campaign involved more than 500 scientists from over 20 countries. These scientists made measurements across the high and middle latitudes of the Northern Hemisphere. The main scientific aims of SOLVE/THESEO 2000 were to study (1) the processes leading to ozone loss in the Arctic vortex and (2) the effect on ozone amounts over northern midlatitudes. The campaign included satellites, research balloons, six aircraft, ground stations, and scores of ozonesondes. Campaign activities were principally conducted in three intensive measurement phases centered on early December 1999, late January 2000, and early March 2000. Observations made during the campaign showed that temperatures were below normal in the polar lower stratosphere over the course of the 1999–2000 winter. Because of these low temperatures, extensive polar stratospheric clouds (PSC) formed across the Arctic. Large particles containing nitric acid trihydrate were observed for the first time, showing that denitrification can occur without the formation of ice particles. Heterogeneous chemical reactions on the surfaces of the PSC particles produced high levels of reactive chlorine within the polar vortex by early January. This reactive chlorine catalytically destroyed about 60% of the ozone in a layer near 20 km between late January and mid‐March 2000, with good agreement being found between a number of empirical and modeling studies. The measurements made during SOLVE/THESEO 2000 have improved our understanding of key photochemical parameters and the evolution of ozone‐destroying forms of chlorine.
Validation of the NOAH‐OSU land surface model using surface flux measurements in Oklahoma
Authors: Sridhar V. , Elliott Ronald L. , Chen Fei , Brotzge Jerald A.
Published: November 2002

Oklahoma Atmospheric Surface‐Layer Instrumentation System (OASIS) measurements of net radiation (Rn), latent heat flux (LH), sensible heat flux (SH), and ground heat flux (GH) were used to validate the NOAH‐Oregon State University Land Surface Model (NOAH‐OSU LSM). A 1‐year study period was used. Rn, LH, SH and GH data from seven sites were screened based on an energy balance closure criterion (daily/hourly sum of the flux components within the range of −10 to +10 W m−2). The vegetation fraction used in the model was computed using both the Gutman‐Ignatov (G‐I) and the Carlson‐Ripley (C‐R) schemes. The simulated net radiation and ground heat fluxes seem less sensitive to the choice of schemes for computing green vegetation fraction, while latent and sensible heat flux show more sensitivity particularly for soil dry‐down period. Therefore, the G‐I approach was used for the validation study, as it is widely used and linear in its form. The daily aggregated model outputs showed that the predicted Rn had a positive bias of 0.8 MJ m−2 d−1 and an RMSE of 1.6 MJ m−2 d−1 when averaged over all seven sites. The seven‐site average bias in LH was about 0.9 MJ m−2 d−1 with an RMSE of 2.5 MJ m−2 d−1. The bias in SH and GH was low and positive with an RMSE of about 2.2 MJ m−2 d−1 in SH estimation. The hourly average output showed similar results, with the exception that GH had a negative bias. The overall performance of the NOAH‐OSU LSM was good for a diverse set of Oklahoma conditions.
Evaluation of stratosphere–troposphere exchange and the hydroxyl radical distribution in three‐dimensional global atmospheric models using observations of cosmogenic 14CO
Authors: Jöckel Patrick , Brenninkmeijer Carl A. M. , Lawrence Mark G. , Jeuken Adriaan B. M. , van Velthoven Peter F. J.
Published: November 2002

A new method for the quantitative evaluation of global atmospheric transport and the hydroxyl radical (OH)‐based oxidation in three‐dimensional (3‐D) atmospheric chemistry transport models (CTMs) and general circulation models (GCMs) is developed. The method is based on a cosmogenic 14CO climatology that has been previously derived from a large number of 14CO observations. Using 14CO measurements to constrain model OH distributions and the simulated stratosphere–troposphere exchange (STE) provides a challenging test for 3‐D atmospheric models. Here, the evaluation method is applied to the CTMs MATCH and TM3. Whereas MATCH overestimates the STE in both hemispheres, TM3 does reproduce the STE in the Southern Hemisphere (SH) but underestimates it in the Northern Hemisphere (NH). The STE phase in MATCH is 1 month too early, whereas no significant phase shift for TM3 is revealed. These characteristic deficiencies in both models were consistently determined, i.e., with the same boundary conditions (OH distribution and 14CO source distribution). The robustness of the results is tested by various sensitivity studies, involving the 14CO source distribution and strength, the tropospheric OH distribution, the stratospheric OH abundance, and the applied numerical advection scheme. Consistency is further checked by comparison of the model simulated vertical 14CO profiles to 14CO observations from a number of aircraft campaigns. The 14CO simulations do not support an interhemispheric asymmetry in the OH abundance with an on average higher concentration in the SH.
A study of stratospheric GW fluctuations and sporadic E at midlatitudes with focus on possible orographic effect of Andes
Authors: Hocke Klemens , Tsuda Toshitaka , de la Torre Alejandro
Published: November 2002

Longitudinal dependences of stratospheric gravity wave (GW) fluctuations and lower ionospheric irregularities (sporadic E) at midlatitudes are studied by means of radio occultation data of the Global Positioning System/Meteorology Experiment (GPS/MET) satellite mission. The zonal average of temperature variance of GW fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes, but there is a significant interhemispheric difference in the longitudinal dependence of GW fluctuations. The GPS/MET data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height, resulting in a broad maximum of temperature variance located over the Atlantic and Eurasia. We only find in the wave distribution at h = 25 km some weak traces of possible orographic effects. On the other hand, the distribution of GW fluctuations at southern midlatitudes has a strong and sharp maximum over Andes, which is obviously due to orographic wave generation by the interaction of surface wind with the Andean mountain ridge. This observation of the new GPS radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders. The amplitude of the average wave field increases with height over Andes, while the amplitude maximum moves westward, against the prevailing wind. The temperature fluctuations have an apparent, dominant vertical wavelength of around 6 km. In situ measurements by a balloon‐borne rawinsonde at Ushuaia, Argentina (54.7°S, 68.1°W) are compared to a simultaneous GPS/MET temperature profile. The balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere. Wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation. Finally, the GPS/MET experiment indicates enhanced sporadic E in the lower ionosphere over Southern Andes. We assume that these plasma irregularities are generated by enhanced, upward wave flux due to the possible orographic effect of Andes.
Simulations with a radiation model and comparisons with LBA data sets
Authors: Franchito Sergio H. , Moraes E. C. , Rao V. Brahmananda
Published: November 2002

The Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia (LBA) data are used to estimate and validate infrared and solar radiation models calculations of Chou and Suarez [1994, 1999]. The models are tested for two contrasting vegetation regions. forest and grassland. Observed data of several days and different times of a day collected in the two sites are used to test the models. The results show that the model simulations in general agree well with the observations for both the forest and grassland cases. The mean errors are around the same order or lower than the instrument errors, except in the case of the reflected solar radiation. The radiation fluxes are strongly correlated with the observed data, significant at 99% confidence level, except in the case of the downward longwave radiation. The use of the Bonferrone technique confirmed the information given by the correlation coefficient calculations.
Accurate Measurements of Hydrocarbons in the Atmosphere (AMOHA): Three European intercomparisons
Authors: Slemr J. , Slemr F. , Partridge R. , D'Souza H. , Schmidbauer N.
Published: November 2002

The Accurate Measurements of Hydrocarbons in the Atmosphere (AMOHA) project was proposed to evaluate and improve current gas chromatographic methods used across Europe to determine concentrations of C2–C9 nonmethane hydrocarbons (NMHCs) in ambient air. Four international intercomparisons of increasing complexity were carried out over a period of 4 years. These were designed to evaluate the analytical performance of a considerable number of European laboratories making frequent ambient NMHC measurements, to identify the major problems encountered in these analyses, and to recommend solutions for these problems. Calibration gas standards prepared gravimetrically and certified by the National Physical Laboratory (NPL) in the UK were used in all of the intercomparisons to eliminate the variability that would have been introduced by laboratories using their own calibration gas mixtures. The results presented here are for the first three of the AMOHA intercomparisons. A four‐component synthetic test gas mixture was used for the first intercomparison, a 30‐component synthetic test gas mixture for the second intercomparison, and both a pressurized ambient air sample and a 30‐component synthetic test gas mixture for the third intercomparison. The results of the 12–14 participating laboratories showed generally good agreement with the gravimetric concentrations of the synthetic NMHC mixtures, although some considerable differences also occurred. The analytical results on the pressurized air samples were similar, but with a greater scatter of values. Most importantly, there were distinct improvements in the measurement quality achieved in this project when compared to previous European intercomparisons. This emphasized the importance of using high‐quality NMHC multicomponent gas calibration standards when making accurate measurements of NMHCs in air. Despite the generally good results, some compounds, such as isobutene, butadiene, methyl pentanes, and trimethyl benzenes, gave considerable analytical problems in some laboratories. The most frequent causes of these problems were found to be interference by coelution with other compounds, breakthrough of C2 compounds during sample preconcentration, and adsorptive losses of C7–C9 compounds in the transfer lines before the analytical instrumentation. Calibration with multicomponent NMHC standards was demonstrated to provide significantly more accurate results than the frequently used method of calibration with just a single hydrocarbon species, such as n‐butane.
Statistics and characteristics of cloud‐to‐ground lightning with multiple ground contacts
Authors: Valine William C. , Krider E. Philip
Published: November 2002

During the summer of 1997, 386 cloud‐to‐ground (CG) lightning flashes were recorded on videotape near Tucson, Arizona. Within this sample, 136 flashes (35%) struck the ground in two or more places that were separated by tens of meters or more. Within this subset of 136, which we term “multiple channel flashes” (MCFs), 88 exhibited two or more separate and distinct channels between the cloud base and the ground, a type that we term a “new channel flash” (NCF); 37 forked or produced channels that struck the ground in two or more places and shared a common channel at higher altitudes, a type that we term an “altered channel flash” (ACF); and 11 exhibited both types of behavior. The ratio of NCFs to ACFs in Arizona was 99/48 or 2.1, a value that is consistent with measurements in Florida after allowing for differences in the cloud base heights. Altogether, the 386 CG flashes produced 558 different strike points; therefore, the average number of strike points per CG flash was 1.45. 67% of the new strike points were produced by the second stroke in the flash, and 72% of the changes in channel geometry occurred after there had been just one stroke in the previous channel. Ten of the 48 ACFs (21%) developed along a visible branch of the previous channel, and seven of the 136 MCFs (5%) contained strokes that reilluminated the first channel after a second channel had formed. The presence of a long, continuing luminosity during the initial three or more consecutive video frames appeared to lower the probability of forming either a new or altered channel on the second stroke (from 47% to 33%), but the statistics are limited, and our ability to identify individual strokes is biased by poor time resolution.
Seasonal and longer‐term variations in middle atmosphere temperature from HALOE on UARS
Authors: Remsberg Ellis E. , Bhatt Praful P. , Deaver Lance E.
Published: November 2002

The 9.5‐year temperature time series from the Halogen Occultation Experiment (HALOE) aboard the Upper Atmosphere Research Satellite (UARS) has been analyzed for 40°N, 30°N, 20°N, Tropics, 20°S, 30°S, and 40°S using multiple linear regression techniques at 12 pressure levels from 5 to 0.01 hPa. The HALOE sunset and sunrise temperature profiles have good vertical resolution and are representative of the variations of the zonal average state. Vertical profiles with latitude of the average sunset/sunrise differences agree qualitatively with that expected from the effects of tides. Periodic seasonal (annual and semiannual) terms are sampled well in the time series, and the seasonal cycle from HALOE at 40°N agrees well with the local variations reported from measurements with the ground‐based Rayleigh lidar instrument at 44°N, 6°E. Significant quasi‐biennial oscillation (QBO)‐like variations occur at most latitudes of the upper stratosphere in the HALOE data, and their phases are nearly symmetric about the equator. There is also a clear subbiennial (688‐day) cycle at Northern Hemisphere (NH) midlatitudes at those same pressure altitudes due to the interaction of the QBO and annual cycles. The solar cycle temperature term is in‐phase with the UV flux forcing in the upper stratosphere but lags it by a year or so in the upper mesosphere at NH midlatitudes. There is also a significant cooling trend for the HALOE time series that is of order 1.0 to 1.6 K per decade in the midmesosphere at 20°N and at 1 hPa in the tropics. The seasonal terms may be combined with the constant and autoregressive (AR) terms (or annual average distribution that we provided) in order to generate the monthly zonal average HALOE “climatology” of middle atmosphere temperature for the decade of the 1990s. Comparisons between the HALOE and CIRA climatologies for the upper stratosphere suggest a cooling of order 2.5 K per decade from the mid‐1970s to the mid‐1990s. HALOE/CIRA differences for the mesosphere change sign with altitude, an indication of bias errors in one or both.
Estimation of methane emissions in the St. Petersburg, Russia, region: An atmospheric nocturnal boundary layer budget approach
Authors: Zinchenko Alexander V. , Paramonova Nina N. , Privalov Vyacheslav I. , Reshetnikov Alexander I.
Published: November 2002

The aim of the study is quantitative estimation of methane emissions in the area of St. Petersburg and its suburbs based on observations at the Voeikovo station. The approach is based on formulation and regularized solution of an inverse problem. The effect of methane accumulation in the nocturnal boundary layer is used by the formulation of the problem. The emission field is not homogeneous. The mean flux density on the urban territory is 1 ± 0.3 g km−2 s−1. The total methane flux from the urban territory and its suburbs is estimated to be 60 kT year−1. These emissions estimates refer to nighttime conditions in summer; they do not include emissions through tall chimneys. The proposed technique of data processing allows, in principal, for locating unknown sources of emissions. It is the first experience in getting emission estimates from the large industrial region in Russia on the basis of atmospheric measurements. This work shows that national statistical self‐assessments of methane emissions can be verified using independent atmospheric measurements.
Control of fossil‐fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming
Authors: Jacobson Mark Z.
Published: November 2002

Under the 1997 Kyoto Protocol, no control of black carbon (BC) was considered. Here, it is found, through simulations in which 12 identifiable effects of aerosol particles on climate are treated, that any emission reduction of fossil‐fuel (f.f.) particulate BC plus associated organic matter (OM) may slow global warming more than may any emission reduction of CO2 or CH4 for a specific period. When all f.f. BC + OM and anthropogenic CO2 and CH4 emissions are eliminated together, the period is 25–100 years. It is also estimated that historical net global warming can be attributed roughly to greenhouse gas plus f.f. BC + OM warming minus substantial cooling by other particles. Eliminating all f.f. BC + OM could eliminate 20–45% of net warming (8–18% of total warming before cooling is subtracted out) within 3–5 years if no other change occurred. Reducing CO2 emissions by a third would have the same effect, but after 50–200 years. Finally, diesel cars emitting continuously under the most recent U.S. and E.U. particulate standards (0.08 g/mi; 0.05 g/km) may warm climate per distance driven over the next 100+ years more than equivalent gasoline cars. Thus, fuel and carbon tax laws that favor diesel appear to promote global warming. Toughening vehicle particulate emission standards by a factor of 8 (0.01 g/mi; 0.006 g/km) does not change this conclusion, although it shortens the period over which diesel cars warm to 13–54 years. Although control of BC + OM can slow warming, control of greenhouse gases is necessary to stop warming. Reducing BC + OM will not only slow global warming but also improve human health.
Global distribution and climate forcing of carbonaceous aerosols
Authors: Chung Serena H. , Seinfeld John H.
Published: November 2002

The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute for Space Studies General Circulation Model II‐prime (GISS GCM II‐prime). Prognostic tracers include black carbon (BC), primary organic aerosol (POA), five groups of biogenic volatile organic compounds (BVOCs), and 14 semivolatile products of BVOC oxidation by O3, OH, and NO3, which condense to form secondary organic aerosols (SOA) based on an equilibrium partitioning model and experimental observations. Estimated global burdens of BC, organic carbon (OC), and SOA are 0.22, 1.2, and 0.19 Tg with lifetimes of 6.4, 5.3, and 6.2 days, respectively. The predicted global production of SOA is 11.2 Tg yr−1, with 91% due to O3 and OH oxidation. Globally averaged, top of the atmosphere (TOA) radiative forcing by anthropogenic BC is predicted as +0.51 to +0.8 W m−2, the former being for BC in an external mixture and the latter for BC in an internal mixture of sulfate, OC, and BC. Globally averaged, anthropogenic BC, OC, and sulfate are predicted to exert a TOA radiative forcing of −0.39 to −0.78 W m−2, depending on the exact assumptions of aerosol mixing and water uptake by OC. Forcing estimates are compared with those published previously.
Fast‐response airborne in situ measurements of HNO3 during the Texas 2000 Air Quality Study
Authors: Neuman J. A. , Huey L. G. , Dissly R. W. , Fehsenfeld F. C. , Flocke F. , Holecek J. C. , Holloway J. S. , Hübler G. , Jakoubek R. , Nicks D. K. , Parrish D. D. , Ryerson T. B. , Sueper D. T. , Weinheimer A. J.
Published: November 2002

Nitric acid (HNO3) was measured from an aircraft in the planetary boundary layer and free troposphere up to 7 km on 14 flights during the Texas Air Quality Study in August and September 2000. HNO3 mixing ratios were measured at 1 Hz using a fast‐response chemical ionization mass spectrometer with SiF5− reagent ions. HNO3 measurement using this highly selective ion chemistry is insensitive to water vapor and is not degraded by interferences from other species. Rapid time response (1 s) was achieved using a heated Teflon inlet. In‐flight standard addition calibrations from a HNO3 permeation source were used to determine the instrument sensitivity of 1.1 ± 0.1 ion counts pptv−1 s−1 over the duration of the study. Contributions to the HNO3 signal from instrument artifacts were accounted for by regularly performing in‐flight instrument background checks, where HNO3 was removed from the ambient air sample by diverting the sampled air though a nylon wool scrubber. Measurement inaccuracy, which is determined from uncertainties in the standard addition calibrations, was ±10%. Measurement precision at low HNO3 levels was ±25 pptv (1σ) for the 1 Hz data and ±9 pptv for 10 s averages of the 1 s measurements. Coincident in situ measurements of other reactive nitrogen species are used to examine NOy partitioning and HNO3 formation during this month long measurement campaign. The sum of the individually measured reactive nitrogen species is shown to be in agreement with the measured NOy. HNO3 formation in plumes from electric utility power plants, urban areas, and petrochemical facilities was studied. The observed differences in the fractional contribution of HNO3 to NOy in plumes from different anthropogenic source types are discussed.
An observation of a fast external atmospheric acoustic‐gravity wave
Authors: Hecht J. H. , Walterscheid R. L. , Hickey M. P. , Rudy R. J. , Liu A. Z.
Published: November 2002

In November 1999 a new near‐IR airglow imaging system was deployed at the Starfire Optical Range outside of Albuquerque, New Mexico. This system allowed wide angle images of the airglow to be collected, with high signal to noise, every 3 seconds with a one second integration time. At approximately 1000 UT on November 17, 1999, a fast wavelike disturbance was seen propagating through the OH Meinel airglow layer. This wave had an observed period of ≈215 seconds, an observed phase velocity of ≈160 m/s and a horizontal wavelength of ≈35 km. This phase velocity is among the fastest yet reported using an imager viewing the OH Meinel bands, while the wave period is among the shortest. Simultaneous Na lidar wind and temperature data from 80 to nearly 110 km altitude allow the intrinsic properties of the wave to be calculated. The Einaudi and Hines [1970] WKB approximation for the acoustic‐gravity wave dispersion relation was used to calculate the wave's intrinsic properties. Using this approach indicates that the observed disturbance was an external acoustic wave in the 90 to 107 km altitude region and an external gravity wave at other altitudes between 80 and 90 km. Using model atmospheric data for altitudes below and above this altitude regime indicates that the wave is essentially external everywhere except perhaps in narrow regions around 80 and 105–110 km. This is confirmed using a more exact full‐wave model analysis. The observations and model results suggest that this wave was not generated in the troposphere and propagated up to the mesosphere, but rather near 100 km altitude where it was possibly generated by a Leonids meteor.
Characteristics and performance of the Improved Limb Atmospheric Spectrometer (ILAS) in orbit
Authors: Nakajima H. , Suzuki M. , Matsuzaki A. , Ishigaki T. , Waragai K. , Mogi Y. , Kimura N. , Araki N. , Yokota T. , Kanzawa H. , Sugita T. , Sasano Y.
Published: November 2002

The Improved Limb Atmospheric Spectrometer (ILAS) was a satellite‐based solar occultation sensor that was developed by the Environment Agency of Japan (EA) to monitor and study the stratospheric ozone layer. This paper describes the characteristics of the ILAS instrument and its performance in orbit. ILAS measured the vertical distribution of ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, water vapor, temperature, pressure, and aerosol extinction coefficients at 1.6‐km vertical resolution. ILAS was equipped with two spectrometers: an infrared (IR) spectrometer with an uncooled pyroelectric linear array detector to sense between 6.21 and 11.76 μm and a visible spectrometer to monitor 753–784 nm. In addition, a Sun‐edge sensor (SES) assigned the tangent height of the instantaneous field‐of‐view (IFOV). A two‐axis gimbals control system on ILAS used two Sun position sensors to track the center of brightness of the Sun during occultation measurements. Before launch onboard the Advanced Earth Observing Satellite (ADEOS), the performance of ILAS was checked on the ground using several methods, including gas‐cell measurements, time response measurements, Sun‐tracking tests, and hollow‐cathode lamp measurements. After the launch of ADEOS on 17 August 1996, ILAS functioned successfully for 8 months of routine operation, from 30 October 1996 to 30 June 1997, collecting more than 6700 solar occultation measurements, after which time the satellite failed due to a failure in a solar paddle. The time delay response of the IR channel was characterized using stepwise IR input. Instrument functions of the ILAS IR and visible spectrometers were determined by combining theoretical optical calculations, experimental measurements using a gas‐cell before launch, and in‐orbit data. The signal‐to‐noise ratio (SNR) of each element in the IR channel was estimated to be 400–1200. In the visible channel, it was 1600–1800 for a 100% direct Sun signal. At sunset occultation, ILAS was able to track the Sun below a tangent height of 10 km in some cases. The method of determining the solar edges from the SES data worked correctly, giving adequate tangent height information for observations. Output signal levels of the SES, visible channel, and IR channel showed slight degradation during the period that ILAS was operational, which is attributed to space‐borne contaminants. However, changes in absolute signal levels do not affect data retrieval, because the solar occultation technique was self‐calibrating. Overall, ILAS worked as designed during its operation in orbit and gathered valuable data for ozone layer studies.
A climatology of stratospheric polar vortices and anticyclones
Authors: Harvey V. Lynn , Pierce R. Bradley , Fairlie T. Duncan , Hitchman Matthew H.
Published: November 2002

United Kingdom Meteorological Office global analyses from 1991 to 2001 are used to create a global climatology of stratospheric polar vortices and anticyclones. New methodologies are developed that identify vortices in terms of evolving three‐dimensional (3‐D) air masses. A case study illustrates the performance of the identification schemes during February and March of 1999 when a merger of anticyclones led to a stratospheric warming that split the Arctic polar vortex. The 3‐D structure and temporal evolution of the Arctic vortex and identified anticyclones demonstrates the algorithm's ability to capture complicated phenomena. The mean geographical distribution of polar vortex and anticyclone frequency is shown for each season. The frequency distributions illustrate the climatological location and persistence of polar vortices and anticyclones. A counterpart to the Aleutian High is documented in the Southern Hemisphere: the “Australian High.” The temporal evolution of the area occupied by polar vortices and anticyclones in each hemisphere is shown as a function of potential temperature. Large polar vortex area leads to an increase in anticyclone area, which in turn results in a decrease in the size of the polar vortex. During Northern winter and Southern spring, 9 years of daily anticyclone movement are shown on the 1200 K (36 km, 4 hPa) isentropic surface. Preferred locations of anticyclogenesis are related to cross‐equatorial flow and weak inertial stability. Regimes of traveling and stationary anticyclones are discussed.
Validation of POAM III NO2 measurements
Authors: Randall C. E. , Lumpe J. D. , Bevilacqua R. M. , Hoppel K. W. , Shettle E. P. , Rusch D. W. , Gordley L. L. , Kreher K. , Pfeilsticker K. , Boesch H. , Toon G. , Goutail F. , Pommereau J.‐P.
Published: November 2002

We describe the Polar Ozone and Aerosol Measurement (POAM) III NO2 measurements and associated errors and compare the POAM III data to correlative measurements obtained from satellite‐, balloon‐, and ground‐based instruments. POAM III NO2 densities are retrieved from 20 to 45 km, with a vertical resolution of about 1.5–2.5 km at altitudes below 40 km and increasing to more than 7 km at an altitude of 45 km. Predicted random errors are on the order of 5% in this altitude range. Sunspots and high aerosol extinction can cause errors in the NO2 retrievals but generally affect only about 10% of the data or less, depending on the altitude. The agreement between POAM III NO2 data and correlative observations is excellent, demonstrating that the POAM III measurements are reasonable in terms of their magnitude, profile structure, and temporal variations. The largest number of comparisons was made with the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite. On average, POAM and HALOE agree to within about 0.2 ppbv from 20 to 33 km or within about 6% at most of these altitudes, with no systematic bias. Differences increase to about 0.7 ppbv (17%, POAM higher than HALOE) by 40 km. This difference decreases to about 12% after accounting for a recently discovered error in the HALOE retrievals. Differences decrease above 40 km and are slightly negative (0.1–0.2 ppbv on average) at 45 km, the top edge of the valid POAM III NO2 altitude range. We conclude that the POAM III NO2 profiles from 20 to 45 km are appropriate for scientific analysis and for the validation of NO2 measurements from other instruments.
An assessment of the quality of Halogen Occultation Experiment temperature profiles in the mesosphere based on comparisons with Rayleigh backscatter lidar and inflatable falling sphere measurements
Authors: Remsberg E. , Deaver L. , Wells J. , Lingenfelser G. , Bhatt P. , Gordley L. , Thompson R. , McHugh M. , Russell J. M. , Keckhut P. , Schmidlin F.
Published: November 2002

Bias errors for retrieved temperature profiles T(p) from the Halogen Occultation Experiment (HALOE) are evaluated by pairing with nearby soundings from ground‐based Rayleigh lidar and from inflatable falling spheres. Findings for the mesosphere must be based on large sets of pairings because an individual HALOE T(p) measurement is somewhat noisy and may not view the same atmospheric structure. Simulated estimates of total bias errors for the HALOE profiles are of the order of 2% (or 5 K). The average biases with the lidar profiles at 44°N, 6°E are within 3 K from 33 to 66 km and 4 K to 74 km, at least when zonal easterlies (and reduced wave activity) prevail. Tidal effects can account for most of that difference. Comparisons with shipboard lidar soundings that begin near 100 km indicate no significant bias even in the 77 to 85 km range. Similar comparisons with falling sphere profiles at Cape Canaveral and Wallops Island indicate no significant bias from 40 to 66 km and 71 to 85 km. HALOE profiles are warmer than sphere values from 67 to 70 km, but this is also the altitude region where the sphere profile has greater uncertainties. For those months when the lidar soundings indicate inversion layers the sets of profiles paired with lidar indicate that the HALOE T(p) is somewhat colder in the upper mesosphere, in part owing to the effects of limb path averaging of horizontal structure by HALOE and its inability to completely resolve the inversion layer maximum. On the basis of the combined sets of findings it is concluded that most of the error in a single HALOE T(p) is random, except where there is a sharp inversion. Daily zonal averages of the HALOE profiles are accurate and useful for defining the seasonal and longer‐term variations of T(p) in the mesosphere.
An efficient method to increase vertical resolution of actinic flux calculations in clouds
Authors: Kay Merlinde J. , Box Michael A. , Trautmann Thomas
Published: November 2002

The errors associated with using different vertical resolutions for broadband actinic flux calculations have been investigated for the case of a boundary layer cloud. Results are presented for 10, 20, and 40 layers in the lowest kilometer of the atmosphere, with comparisons made against a benchmark of 100 layers. A more accurate picture of actinic flux profiles is obtained by increasing the number of vertical layers. We also derive an expression for the average value of actinic flux within a computational layer. This result, when used to quadratically interpolate the coarser layerings, improved the accuracy in the 10‐layer case by a factor of five, when compared with a simple linear interpolation between the original data points.
Quantification of aerosol signal in GOES 8 visible imagery over the United States
Authors: Knapp Kenneth R.
Published: November 2002

Changes in the top‐of‐the‐atmosphere reflectance due to variations in the aerosol optical depth (τ) make retrieving τ from satellite possible. This aerosol signal is greatest for non‐absorbing aerosol over dark surfaces and is least (often less than zero) for absorbing aerosols over bright surfaces. In general, previous aerosol retrieval research has been in regions where the signal is known to be large, for example, aerosol over ocean or biomass burning over heavily vegetated land. This study, however, looks at the aerosol signal and its variation over North America to determine when and where τ retrieval is possible. The results show that the aerosol signal is sufficiently large for τ retrieval over most of the sites studied; exceptions are located in the southwestern United States where the surface reflectance is large. Further, this aerosol signal closely corresponds with radiative transfer simulations, which suggests that aerosol optical depth retrieval over North America and the adjoining oceans is possible from geostationary orbit. The implication is that timely (e.g., 30 min intervals) observations of aerosol are possible. Such observations could aid research efforts in pollutant transport, air quality forecasting, and wildfire monitoring.
Trajectory hunting as an effective technique to validate multiplatform measurements: Analysis of the MLS, HALOE, SAGE‐II, ILAS, and POAM‐II data in October–November 1996
Authors: Danilin M. Y. , Ko M. K. W. , Froidevaux L. , Santee M. L. , Lyjak L. V. , Bevilacqua R. M. , Zawodny J. M. , Sasano Y. , Irie H. , Kondo Y. , Russell J. M. , Scott C. J. , Read W. G.
Published: November 2002

The goal of this study is to show that trajectory hunting is an effective technique for comparison of multiplatform measurements. In order to achieve this goal, we (1) describe in detail the trajectory hunting technique (THT), (2) perform several consistency tests for THT (self‐hunting and reversibility), (3) estimate uncertainties of this technique, and (4) validate THT results against those obtained by the traditional correlative analysis (TCA). THT launches backward and forward trajectories from the locations of measurements and finds air parcels sampled at least twice within a prescribed match criterion during the course of several days. TCA finds matched profiles for a chosen match criterion, averages them for each instrument separately, and compares the averaged profiles. As an example, we consider the 22 October to 30 November 1996 period in the Southern Hemisphere and compare the latest versions of relevant measurements made by the following five instruments: Microwave Limb Sounder (MLS, version 5 (v.5)), Halogen Occultation Experiment (HALOE, v.19), Polar Ozone and Aerosol Measurement II (POAM‐II, v.6), Stratospheric Aerosol and Gas Experiment II (SAGE‐II, v.6.1), and Improved Limb Atmospheric Spectrometer (ILAS, v.5.20). We present results for O3, H2O, CH4, HNO3, and NO2, which show that (1) ozone measurements from all five instruments agree to better than 0.4 (0.2) ppmv below (above) 30 km; (2) water vapor measurements agree within ±5–10% above 22 km; (3) methane measurements by HALOE and ILAS agree to better than 10% above 30 km with a possible positive offset of up to 10–15% by ILAS in the lower stratosphere; (4) MLS HNO3 data corrected to account for some excited vibrational lines omitted in the v.5 HNO3 retrieval agree with ILAS HNO3 measurements to within ∼0.5 ppbv (∼10–20%) over the range ∼450–750 K; (5) ILAS sunset NO2 measurements are larger than both POAM‐II and SAGE‐II values by up to 10–15% below 30 km. The self‐hunting tests show that the THT RMS noise is of the order of 1–2% for O3, CH4, and H2O and 4% for NO2 and HNO3 measurements in the stratosphere. Total THT‐related uncertainties may be 3–5% for O3 measurements when photochemical effects and sensitivities of the results to duration of trajectories and match criteria are taken into account. Good agreement is found between the THT and TCA results for each of these products and for each possible pair of instruments, with considerably better statistics (typically by at least an order of magnitude) in the THT case. This agreement validates the THT results.
On nonstationarity and antipersistency in global temperature series
Authors: Kärner O.
Published: November 2002

Statistical analysis is carried out for satellite‐based global daily tropospheric and stratospheric temperature anomaly and solar irradiance data sets. Behavior of the series appears to be nonstationary with stationary daily increments. Estimating long‐range dependence between the increments reveals a remarkable difference between the two temperature series. Global average tropospheric temperature anomaly behaves similarly to the solar irradiance anomaly. Their daily increments show antipersistency for scales longer than 2 months. The property points at a cumulative negative feedback in the Earth climate system governing the tropospheric variability during the last 22 years. The result emphasizes a dominating role of the solar irradiance variability in variations of the tropospheric temperature and gives no support to the theory of anthropogenic climate change. The global average stratospheric temperature anomaly proceeds like a 1‐dim random walk at least up to 11 years, allowing good presentation by means of the autoregressive integrated moving average (ARIMA) models for monthly series.
Quantum yields of O(1D) formation in the photolysis of ozone between 230 and 308 nm
Authors: Takahashi Kenshi , Hayashi Shinsuke , Matsumi Yutaka , Taniguchi Nori , Hayashida Sachiko
Published: November 2002

Ozone molecules are photolyzed in the strong photoabsorption band of the Hartley band at 230–308 nm, and the O(3Pj) photofragments produced by the photolysis are detected directly by a technique of laser‐induced fluorescence around 130 nm. The quantum yield values for O(1D) formation in the photolysis of ozone at 297 ± 2 K are determined as a function of the photolysis wavelength, using the O(1D) quantum yield value of 0.79 at 308 nm as a reference. The O(1D) quantum yield values obtained are found to be almost independent of the photolysis wavelength over the Hartley band (∼0.91). The results are compared with the values measured previously using various experimental techniques and also with the recommendation values for use in atmospheric modeling. The effects of the present yield data on the O(1D) production rates from ozone photolysis in the stratosphere are evaluated. Impact of our new O(1D) quantum yield values on the stratospheric chemistry has also been explored using a one‐dimensional photochemical model. The smaller O(1D) production rates as compared to the latest NASA/JPL recommendation values are followed by changes in the efficiency of the chemical chain reactions involving HOx, NOx, and ClOx and result in the higher O3 concentrations throughout the stratosphere.
Cooling of lava flows on Venus: The coupling of radiative and convective heat transfer
Authors: Snyder Don
Published: November 2002

A lava flow extruded on the surface of Venus cools by radiating heat and by advecting heat upward by thermal convection. Unlike on other planetary bodies, these processes are intimately coupled on Venus because the dense CO2‐rich atmosphere has strong absorption bands in the infrared. Relative to a transparent atmosphere, absorption (and emission) of radiation within short distances above a lava reduces the radiant heat loss and substantially diminishes the vigor of convection by dampening the thermal gradients within the boundary layer. For these reasons, lavas on Venus cool significantly more slowly (30–40%) than they would if the atmosphere were transparent in the infrared, as assumed in previous calculations. Considering these effects indicates that lavas on Venus cool more slowly than their equivalents on Earth rather than more rapidly as previously estimated. The reduction in cooling rate due to the suppression of convection by radiation extends our understanding of how some lavas on Venus reach extraordinary lengths, on the order of a thousand kilometers, before solidifying.
A preliminary semiempirical thermosphere model of Mars: DTM‐Mars
Authors: Bruinsma Sean , Lemoine Frank G.
Published: November 2002

A semiempirical thermosphere model of Mars has been constructed based on the DTM algorithm that was developed for the terrestrial thermosphere. DTM‐Mars reproduces the observed densities with a 1‐σ model uncertainty of approximately 35% outside dust season. During dust storms the uncertainty increases by approximately a factor two. The data used in this study have been derived from the Mars Global Surveyor accelerometer observations as well as from analysis of precise orbit determination results. The temperature modeling is based on the Mars‐GRAM 2000 [Justus and James, 2000] and the MTGCM [Bougher et al., 2000] models, while the CO2, O, and He constituent modeling has been achieved through the adjustment of model coefficients to density data. DTM‐Mars is preliminary because the geographical and solar activity coverage of the assimilated density data currently available is not representative of all atmospheric conditions. For example, the effect of dust storms on the thermospheric density is only represented by a temperature increase on a planetary scale, because the data did not allow the determination of a semidiurnal variation caused by local effects in the lower atmosphere. The model accuracy will be improved in the future by assimilating density data taken under different atmospheric conditions, for example, from the Mars Odyssey mission, once these become available.
Scaling of hypervelocity impact craters in ice with impact angle
Authors: Grey Ivan D. S. , Burchell Mark J. , Shrine Nick R. G.
Published: November 2002

Hypervelocity oblique impacts using spherical 1 mm diameter aluminum projectiles at velocities of (5.2 ± 0.2) km s−1 were incident at angles ranging from normal (0° to the vertical) to grazing incidence (80°) onto thick polycrystalline H2O ice targets at 253 K. Data were obtained to distinguish changes in crater size and shape. The resultant craters had a deep central pit surrounded by a shallower terrace. Results on crater size showed that volume and crater depth had varying levels of dependence on obliquity for the full angular range, and terrace depth had a dependence only at angles > 45°. Length and width measurements held a strong dependence on obliquity only at angles > 50° from the normal. These results for ice show that it is hard to determine angle of impact from crater morphology. Although crater depth and volume do change with angle, it would be hard to separate this effect from the influence of an impact of a projectile of different speed, density, etc., which might also affect crater depth or crater depth/diameter ratios. Only at extreme angles > 70° do real differences in shape emerge for ice.
Chemical studies of H chondrites 11. Cosmogenic radionuclides in falls
Authors: Ferko T. E. , Wang M.‐S. , Lipschutz M. E.
Published: November 2002

We measured the long‐lived cosmogenic radionuclides 10Be, 26Al, and 36Cl in 47 H chondrite falls: 13 “Cluster 1” members, 9 “Cluster 5” members, and 25 random falls. From the date and time of fall, Clusters 1 and 5 were previously identified as possible coorbital meteoroid streams with distinctive thermal histories being confirmed by contents of volatile trace elements. Here, we use model data, including a three‐radionuclide plot (10Bebulk/26Albulk versus 36Clmetal/26Albulk) and the multivariate statistical techniques of logistic regression and linear discriminant analysis to compare radionuclide levels and their utility to differentiate specific suites from other H chondrites. From our radionuclide results and from noble gas data from other workers, we identified 35 falls with simple irradiation histories and cosmic ray exposure ages >4 Ma. Eight others exhibit evidence for shorter (≤4 Ma) exposure, three of which had complex exposure histories (two having been reported by others previously); three others may have had such a history. In any event, the small proportion of H chondrite falls with complex exposure histories supports recent suggestions that they are not commonly encountered, as earlier workers suggested. Although cosmogenic radionuclides do not differentiate between Cluster 1 and a random set of H chondrites, H chondrites that lost 3He from solar heating are distinguishable from those with normal 3He levels.