bluuebunny/crossref_metadata_2025 huggingface dataset:
First simulations of cryoplane contrails
Authors: Ström Linda , Gierens Klaus
Published: October 2002

In this paper the first numerical simulations of condensation trails (contrails) from liquid hydrogen (LH2) fueled aircraft are presented. Such aircraft produces 2.6 times more exhaust water vapor than equivalent aircraft fueled by kerosene; however, combustion of LH2 produces no aerosol particles. LH2 ice crystals, which instead form on background aerosol, are consequently 1–2 orders of magnitude fewer than in a kerosene contrail. LH2 contrails are compared to kerosene contrails for two flight altitudes, which here is equivalent to two different background temperatures. The relative humidity with respect to ice was kept constant; a value of 110% was used. It is found that LH2 contrails are optically thinner than their kerosene counterparts owing to much lower number density of ice crystals in the LH2 contrails than in the kerosene contrails but similar amounts of ice mass. The latter is controlled by ambient humidity. However, the sedimentation in the LH2 contrails is not significantly stronger than the sedimentation in the kerosene contrails although the average crystal sizes in LH2 contrails are 4–6 times larger than in the corresponding kerosene contrail. Additionally, the sensitivity of the LH2 contrail properties to variations in the background aerosol distribution is investigated. We find that by increasing the aerosol density by 4, an order of magnitude difference in mean optical thickness results; the LH2 contrail will nevertheless be optically thinner than the corresponding kerosene contrail, as the number of ice crystals that form will be fewer.
Measurements of the kinetics of the OH‐initiated oxidation of isoprene
Authors: Chuong Bao , Stevens Philip S.
Published: October 2002

The mechanism of the OH‐initiated oxidation of isoprene has been studied at 300 K and 100 and 150 Torr total pressure using a turbulent flow technique coupled with laser‐induced fluorescence detection of the OH radical. The rate constant for the reaction of OH with isoprene was measured to be (10.8 ± 0.5) × 10−11 cm3 molecule−1 s−1 at 150 Torr total pressure and independent of pressure between 100 and 150 Torr, in excellent agreement with most previous absolute measurements. In the presence of O2 and NO, propagation of OH radicals and loss of OH through radical termination resulting from the formation of organic nitrates were measured at 150 Torr total pressure and compared to simulations of the kinetics of this reaction system. The results of these experiments are consistent with an overall rate constant of (1.1 ± 0.8) × 10−11 cm3 molecule−1 s−1 for the reaction of NO with isoprene‐based hydroxyalkyl peroxy radicals, with branching ratios of 0.85 ± 0.10 for the bimolecular channel (oxidation of NO to NO2) and 0.15 ± 0.10 for the termolecular channel (formation of organic nitrates). Although the organic nitrate yield reported here is the result of indirect measurements, it suggests that isoprene may be a more significant sink of NOx than previously estimated.
Studies of the aerosol indirect effect from sulfate and black carbon aerosols
Authors: Kristjánsson Jón Egill
Published: October 2002

The indirect effect of anthropogenic aerosols is investigated using the global climate model National Center for Atmospheric Research Community Climate Model Version 3 (NCAR CCM3). Two types of anthropogenic aerosols are considered, i.e., sulfate and black carbon aerosols. The concentrations and horizontal distributions of these aerosols were obtained from simulations with a life‐cycle model incorporated into the global climate model. They are then combined with size‐segregated background aerosols. The aerosol size distributions are subjected to condensation, coagulation, and humidity swelling. By making assumptions on supersaturation, we determine cloud droplet number concentrations in water clouds. Cloud droplet sizes and top of atmosphere (TOA) radiative fluxes are in good agreement with satellite observations. Both components of the indirect effect, i.e., the radius and lifetime effects, are computed as pure forcing terms. Using aerosol data for 2000 from the Intergovernmental Panel on Climate Change (IPCC), we find, globally averaged, a 5% decrease in cloud droplet radius and a 5% increase in cloud water path due to anthropogenic aerosols. The largest changes are found over SE Asia, followed by the North Atlantic, Europe, and the eastern United States. This is also the case for the radiative forcing (“indirect effect”), which has a global average of −1.8 W m−2. When the experiment is repeated using data for 2100 from the IPCC A2 scenario, an unchanged globally averaged radiative forcing is found, but the horizontal distribution has been shifted toward the tropics. Sensitivity experiments show that the radius effect is ∼3 times as important as the lifetime effect and that black carbon only contributes marginally to the overall indirect effect.
Aerosol formation during PARFORCE: Ternary nucleation of H2SO4, NH3, and H2O
Authors: Kulmala M. , Korhonen P. , Napari I. , Karlsson A. , Berresheim H. , O'Dowd C. D.
Published: October 2002

A new version of a ternary nucleation (sulphuric acid‐ammonia‐water) model based on classical nucleation theory, but with an improved ability to predict nucleation rates over a larger temperature range (258–303 K) compared with previous work, is presented. The modeled nucleation rates are given as a function of temperature and ambient acid and ammonia concentrations. For the first time the predicted ternary nucleation rates are compared to the observed particle production rates using measured ambient sulphuric acid and ammonia concentrations as input data. The ambient gas concentrations were measured simultaneously to aerosol formation rates during the 1999 New Particle Formation and Fate in the Coastal Environment (PARFORCE) coastal field campaign at Mace Head. According to the results, daytime ambient acid and ammonia concentrations were significantly higher than required by model calculations to induce the formation of new particles by homogeneous ternary nucleation. However, binary nucleation of sulphuric acid‐water molecules is not able to predict new particle formation since the binary nucleation rate is far too small. We conclude that all particle formation events observed at coastal sites can be initiated by ternary nucleation of sulphuric acid, ammonia, and water vapor. However, related studies illustrate that ambient sulphuric acid concentrations are, nevertheless, insufficient to explain observed rapid growth of particles from 1 to 3 nm sizes which can be detected by current instrumentation.
Determining the UV imaginary index of refraction of Saharan dust particles from Total Ozone Mapping Spectrometer data using a three‐dimensional model of dust transport
Authors: Colarco Peter R. , Toon Owen B. , Torres Omar , Rasch Philip J.
Published: October 2002

A three‐dimensional model has been developed for simulating Saharan dust emissions and transport over the tropical North Atlantic Ocean. The computed dust fields are constrained by data from ACE‐2, and we use a radiative transfer code to simulate the Total Ozone Mapping Spectrometer on the Earth Probe satellite (EP‐TOMS) aerosol index (AI). Using the observed relationship between AI and aerosol optical depth, we determine from our simulations the UV refractive index for dust particles at Dakar, Sal, and Tenerife. We find that the dust imaginary refractive index at Sal and Tenerife is approximately k = 0.0048 (0.0024–0.0060) at 331 nm and k = 0.004 (0.002–0.005) at 360 nm. At Dakar the dust imaginary refractive index is approximately k = 0.006 (0.0024–0.0207) at 331 nm and k = 0.005 (0.0020–0.0175) at 360 nm. These values are considerably less absorbing than the refractive index currently used in the TOMS retrievals of dust optical depth and single scatter albedo. Once the dust refractive index has been constrained, we calculate the single scatter albedo by integrating across the particle size distribution. We find that the particle single scatter albedo at 331 nm is ϖ0 = 0.81 (0.65–0.90) at Dakar, ϖ0 = 0.84 (0.82–0.91) at Sal, and ϖ0 = 0.86 (0.83–0.89) at Tenerife. The refractive index determined in this study should be useful for future retrievals using the TOMS data, as well as for energy balance studies that incorporate the radiative effects of mineral dust aerosols.
Two simultaneous charge structures in thunderstorm convection
Authors: Stolzenburg Maribeth , Marshall Thomas C. , Rust W. David , Bartels Diana L.
Published: October 2002

A pair of simultaneous, horizontally displaced, thunderstorm electric field soundings are used to investigate an existing conceptual model of thunderstorm charge structure. The soundings show that two different vertical charge structures, one in the updraft and one outside the updraft, can exist at the same time inside a storm, as depicted in the existing model. The data suggest that the two charge structures can be relatively close together, since the soundings are separated by only 3 to 8 km horizontally in the convective region of the storm. Horizontal extent of the charge structures is estimated to be at least 4 km × 4 km. The differences in the two charge structures are coincident with substantial differences over this same 3 to 8 km horizontal distance in the reflectivity structure, updraft speed, and lightning activity of the convection. The nonupdraft sounding was made through the intense reflectivity core found at middle levels in the convection. Additional electric field complexity and additional charge regions were found in the nonupdraft sounding, and the lightning‐related electric field changes tended to be larger in magnitude and more numerous in that sounding than in the updraft sounding.
NOy partitioning and budget and its correlation with N2O in the Arctic vortex and in summer midlatitudes in 1997
Authors: Wetzel G. , Oelhaf H. , Ruhnke R. , Friedl‐Vallon F. , Kleinert A. , Kouker W. , Maucher G. , Reddmann T. , Seefeldner M. , Stowasser M. , Trieschmann O. , von Clarmann T. , Fischer H.
Published: October 2002

Vertical profiles of the most important species of nocturnal total reactive nitrogen (NOy = NO2 + HNO3 + ClONO2 + 2 N2O5 + HO2NO2) together with its source gas N2O were retrieved from infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloon‐borne version (MIPAS‐B) instrument inside the late winter arctic vortex from Kiruna (Sweden, 68°N) on 24 March 1997 and in summer midlatitudes from Gap (France, 44°N) on 2 July 1997. The measured data were compared to calculations performed with the three‐dimensional chemistry transport model (CTM) Karlsruhe Simulation model of the Middle Atmosphere (KASIMA). The results show that in the late winter arctic vortex most of the available nitrogen and chlorine is in the form of HNO3 and ClONO2, respectively. An anomalous N2O‐NOy correlation observed in March 1997 appears to be caused to a large extent by quasi‐horizontal mixing of air masses across the vortex edge. However, near 20 km some denitrification of ∼1.5 to 2 ppbv NOy could be observed. The N2O profile measured in July 1997 indicates remnants of polar vortex air and is not reproduced by the CTM at the same location. However, the profile shapes of the individual compounds of the NOy family as well as the NOx/NOy ratio are reproduced fairly well by the model.
Observation of gamma‐ray dose increase associated with winter thunderstorm and lightning activity
Authors: Torii Tatsuo , Takeishi Minoru , Hosono Teruo
Published: October 2002

Increases of environmental gamma‐ray dose which seem to originate from lightning activity were observed around a nuclear facility in Japan. Dose increases measured by thermoluminescent dosimeters (TLDs) exposed during a period including a lightning flash were up to about 0.1 mGy. Dose rates indicated by environmental radiation monitors around the facility also increased transiently at that time. From pulse‐height analysis of an NaI(Tl) scintillation detector, the photon energy spectrum evaluated by spectral unfolding is continuous with energy up to several MeV, consistent with bremsstrahlung emission from energetic electrons. Furthermore, energy spectra of bremsstrahlung photons emitted from high‐energy electrons are obtained by Monte Carlo calculation. These results are discussed in conjunction with observation.
Trace gas measurements along the Trans‐Siberian railroad: The TROICA 5 expedition
Authors: Oberlander Eva A. , Brenninkmeijer C. A. M. , Crutzen P. J. , Elansky N. F. , Golitsyn G. S. , Granberg I. G. , Scharffe D. H. , Hofmann R. , Belikov I. B. , Paretzke H. G. , van Velthoven P. F. J.
Published: October 2002

The chemical composition of the surface boundary layer over the Eurasian continent is still an area of high uncertainty. In the framework of the Trans‐Siberian Observations Into the Chemistry of the Atmosphere (TROICA) project, measurements of O3, NO, NO2, CO, CO2, CH4, 222Rn, J(NO2), and black carbon aerosol were carried out on the Trans‐Siberian railroad during June–July 1999. Boundary layer data over more than 16,000 km, from Kirov (∼58°N, 49°E; 972 km east of Moscow) to Khabarovsk (∼48°N, 135°E) and back to Moscow, were obtained without significant contamination, emphasizing the potential of using the Trans‐Siberian railroad system for atmospheric measurements. The 222Rn and CO2 concentrations were determined for the first time using our laboratory wagon. The diurnal variations of these gases and of CH4 due to micrometeorological conditions, as well as their dependence on various soil sources and vegetation types, were used to estimate ecosystem fluxes of CO2 and CH4. The highest soil flux of CH4 was 70 ± 35 μ mol m−2 h−1 for the wet habitats of the West Siberian lowlands, and the lowest CH4 flux was 3.2 ± 1.6 μ mol m−2 h−1 for drier habitats of eastern Siberia. Although the wet tundra emissions found between 67° and 77°N are higher than in comparable environments at much lower latitudes [Christensen et al., 1995], boreal wetlands in Siberia at 50°–60°N represent a very important player in the global methane budget. The CO2 density fluxes exhibited the opposite to CH4 fluxes tendency. Ozone mixing ratios varied from a few nmol/mol during nighttime inversions to more than 60 nmol/mol during the day. These values were generally higher than during the 1996 summer campaign (TROICA 2). CH4 and CO levels followed the pattern observed during TROICA 2; elevated levels of CH4 with a mean mixing ratio of 1.97 ± 0.009 μmol/mol were found over the West Siberian lowlands, decreasing to 1.88 ± 0.13 μmol/mol toward East Siberia. Conversely, while background CO levels of the West Siberian wetlands were generally below 140 nmol/mol, high CO concentrations, once even exceeding 2 μmol/mol, were registered east of Chita (∼52°N, 113°E), as a consequence of forest and other vegetation fires, which significantly affect the chemical composition of the air over parts of Russia.
Modeling approaches to assimilating L band passive microwave observations over land surfaces
Authors: Wigneron Jean‐Pierre , Chanzy André , Calvet Jean‐Christophe , Olioso Albert , Kerr Yann
Published: October 2002

L band passive microwave remotely sensed data have great potential for providing estimates of soil moisture with high temporal sampling and on a regional scale. Several studies have shown the possibility of assessing the hydrological conditions deep down in soil (in the top 1 or 2 m) from these repetitive estimates of surface soil moisture. Water availability for plants, which is related to soil moisture in the root zone, is a key variable for estimating the evapotranspiration fluxes over land surfaces. This estimation is an important issue for meteorological and hydrological modeling, since it is a basic term of land surface forcing in mesoscale atmospheric circulations. However, at the present time the assimilation approach of remotely sensed brightness temperature data for operational use in the fields of meteorology and hydrology is poorly defined and important issues remain to be addressed in order to develop an operational assimilation approach. Two important issues are to identify (1) how vegetation variables describing vegetation development can be accounted for and (2) how the attenuation effects of L band microwave radiation within the canopy layer can be computed on large spatial scales. On the basis of an exhaustive data set including multiangular and dual‐polarization passive microwave measurements acquired over a wheat crop during a 3‐month period in 1993, two main modeling approaches are tested in this study. The principle of both approaches was based on the use of dual‐polarization and multiangular observations to discriminate between the effects of soil and vegetation on the crop microwave signature. For the two approaches, both the initial soil water reservoir R2 (at the beginning of the crop development) and parameterizations of the crop development could be retrieved simultaneously from the assimilation of the passive microwave measurements. From these results, promising assimilation strategies can be expected from the multiangular Soil Moisture and Ocean Salinity (SMOS) observations made over the land surface.
High‐resolution Fourier transform measurement of the NO2 visible and near‐infrared absorption cross sections: Temperature and pressure effects
Authors: Vandaele A. C. , Hermans C. , Fally S. , Carleer M. , Colin R. , Mérienne M.‐F. , Jenouvrier A. , Coquart B.
Published: October 2002

High‐resolution NO2 absorption cross sections have been obtained in the near‐IR (NIR) and visible regions using a Fourier transform spectrometer coupled to a multiple reflection cell. Spectra were recorded at 0.05 cm−1 in the NIR region (10,800–15,100 cm−1) and at 0.1 cm−1 in the visible region (13,800–26,000 cm−1), under various pressure conditions (pure NO2 and NO2/air mixtures) and at three temperatures (220, 240, and 294 K). The effects of the temperature and the pressure on the NO2 cross sections have been investigated. As expected, an increase of temperature results in a decrease of the absorption at the maxima of the absorption bands and an increase at the minima. From the measurements performed with pure NO2 at different temperatures a linear regression of the cross section with temperature has been carried out. This enabled the cross sections to be reproduced within 2% at room temperature and 7% at the lower temperatures. The variation of the cross sections with the total pressure of NO2/air mixtures has also been investigated at high resolution.
Experimental determination of the phase function and degree of linear polarization of El Chichón and Pinatubo volcanic ashes
Authors: Muñoz O. , Volten H. , de Haan J. F. , Vassen W. , Hovenier J. W.
Published: October 2002

We present measurements of the phase function and degree of linear polarization for unpolarized incident light as a function of the scattering angle for El Chichón and Pinatubo volcanic ashes at 633 nm. The results are combined and compared with those for Pinatubo at 442 nm and Lokon volcanic ash at 442 and 633 nm [Volten et al., 2001]. The three samples of volcanic ashes consist of micron sized, irregularly shaped particles in random orientation. The results are presented in the form of figures and tables for all three samples. Similarities and differences between the results for the three samples are discussed. The measured phase functions and angular distributions of the polarization can be used to evaluate models used to calculate scattering properties of volcanic ash particles, to constrain scattering properties of volcanic ashes used in radiative transfer calculations, and to retrieve characteristics of (clouds of) volcanic ash particles in the atmosphere from remote sensing data.
Tropospheric ozone climatology over Peninsular Malaysia from 1992 to 1999
Authors: Yonemura Seiichiro , Tsuruta Haruo , Kawashima Shigeto , Sudo Shigeto , Peng Leong Chow , Fook Lim Sze , Johar Zubaidi , Hayashi Masayasu
Published: October 2002

We present the climatology of tropospheric ozone over Peninsular Malaysia in tropical Asia for the 8 years from 1992 through 1999 as measured by ozonesondes twice a month. The mean ozone concentrations in vertical profile were in the same range (30–40 ppbv) as those observed at Watukosek, Indonesia, and were lower than those at Natal, Brazil, South America, and at Brazzaville, Congo, Africa, indicating that air masses over Peninsular Malaysia are primarily influenced by the maritime environment and deep convection, as shown by the significant levels of water vapor in the middle troposphere throughout the year. Seasonally averaged ozone concentrations were highest in December, January, and February (DJF) from 6 to 7.5 km altitude and in March, April, and May (MAM) at all other heights and were lowest in June, July, and August (JJA) and September, October, and November (SON), excluding 1994 and 1997, at all heights. The ozone enhancements during DJF in the middle troposphere could be caused by depression of the deep convection because of the positive temperature anomaly and negative water vapor anomaly. The ozone enhancements above the middle troposphere (>5 km) in MAM, especially in 1997 and 1998, could be predominantly attributed to photochemical production from enhanced ozone precursor gases of Northern Hemisphere origin, especially biomass burning in continental Southeast Asia. Large ozone enhancements as high as 10–20 Dobson units observed during SON of 1994 and 1997 were associated with large‐scale biomass burnings in Indonesia.
Convective quasi‐equilibrium in midlatitude continental environment and its effect on convective parameterization
Authors: Zhang Guang J.
Published: October 2002

The quasi‐equilibrium assumption proposed by Arakawa and Schubert assumes that convection is controlled by the large‐scale forcing in a statistical sense, in such a way that the stabilization of the atmosphere by convection is in quasi‐equilibrium with the destabilization by the large‐scale forcing. The assumption was developed largely based on observations in the tropical maritime environment and has not been evaluated in midlatitudes. This study examines the quasi‐equilibrium assumption in midlatitude continental convection environment using summertime observations from the Southern Great Plains of the United States. Two complementary approaches are taken for this purpose. The first one compares the net time rate of change of convective available potential energy to that due to the large‐scale forcing. The second one examines the contributions to the net change of CAPE from the boundary layer air and the free tropospheric air above. Results from both the approaches indicate that the quasi‐equilibrium assumption is not well suited for midlatitude continental convection. It is shown that the net change of CAPE is comparable to and largely comes from that due to thermodynamic changes of the boundary layer air, while the contribution from the free troposphere above the boundary layer is negligible. The analysis also shows that the role of convective inhibition to suppress convection is the most pronounced when the large‐scale forcing in the free troposphere is weak. On the basis of these and other observations, a modification to the quasi‐equilibrium assumption is proposed. It assumes that convective and large‐scale processes in the free troposphere above the boundary layer are in balance, so that contribution from the free troposphere to changes in CAPE is negligible. This assumption is then tested using the single column model of the NCAR CCM3 by modifying the closure in the CCM3 convection scheme. Such a modification significantly improves the single column model simulation. The applicability of this new quasi‐equilibrium assumption to tropical convection environment is also discussed.
Atmospheric inorganic chlorine and bromine species in Arctic boundary layer of the winter/spring
Authors: Hara Keiichiro , Osada Kazuo , Matsunaga Katsuji , Iwasaka Yasunobu , Shibata Takashi , Furuya Keiichi
Published: October 2002

Atmospheric aerosol particles and inorganic acidic gases were simultaneously collected in Ny‐Ålesund (78°55'N, 11°56'E), Svalbard, during the winter/early‐spring seasons. Inorganic chlorine species were predominantly distributed in the particulate phase, which consisted of sea‐salt particles. Gaseous inorganic chlorine species probably arise via Cl− liberation from sea‐salt particles by acidic species such as sulfate. On the other hand, inorganic bromine species were mostly found in the gaseous phase. Moreover, the concentration of gaseous inorganic bromine species gradually increased from winter to early spring. The major particulate constituent was Br−, whose concentration exceeded to sea‐salt Br− concentration, whereas bromate (BrO3−) was also found as a minor particulate bromine constituent. Thus, inorganic bromine species were suggested to be accumulated in the boundary layer during the winter/early‐spring. Halogen liberation from sea‐salt particles was often observed in analyses of individual aerosol particles and size fractionation of aerosol constituents. Chlorine liberation mostly occurred in the fine particle mode (0.2 – 2.0 μm), while Br− liberation occurred in both coarse particle (>2.0 μm) and fine modes. Non‐sea‐salt Br− was predominantly distributed in fine and backup modes and internally mixed with fine sulfate particles.
Retrieval of polar stratospheric cloud microphysical properties from lidar measurements: Dependence on particle shape assumptions
Authors: Reichardt J. , Reichardt S. , Yang P. , McGee T. J.
Published: October 2002

Computational simulations have been performed to deduce the dependence of the microphysical analysis of polar stratospheric cloud (PSC) optical data measured with lidar on the assumptions made about particle shape. In a forward model, PSCs are modeled as crystalline and liquid particles in order to generate synthetic optical properties. The parameterization scheme of the PSC microphysical properties allows for coexistence of up to three different particle types with size‐dependent shapes; optical properties of individual crystals, specifically hexagonal and asymmetric polyhedral crystals, are determined using the finite difference time domain (FDTD) method. The set of calculated PSC optical properties is selected based on the wavelengths and measurement capabilities of lidar instruments that are typically used to monitor stratospheric aerosols, such as the Airborne Raman Ozone and Temperature Lidar (AROTEL) and the NASA Langley Differential Absorption Lidar (DIAL) onboard the NASA DC‐8 during the Stratospheric Aerosol and Gas Experiment (SAGE) Ozone Loss Validation Experiment (SOLVE) campaign in winter 1999/2000. The retrieval process then inverts these synthetic measurement data using a model approach in which the PSC particles are represented purely by an ensemble of spheroids, and the differences between initial and retrieved microphysical properties are examined. The model simulations show that under the assumption of spheroidal particle shapes, surface area density and volume density of leewave PSCs are systematically smaller by, respectively, ∼10–30% and ∼5–25% than the values found for mixtures of droplets, asymmetric polyhedra, and hexagons.
In situ observations of HO2 and OH obtained on the NASA ER‐2 in the high‐ClO conditions of the 1999/2000 Arctic polar vortex
Authors: Hanisco T. F. , Smith J. B. , Stimpfle R. M. , Wilmouth D. M. , Anderson J. G. , Richard E. C. , Bui T. P.
Published: October 2002

Extensive observations of OH and HO2 obtained aboard the NASA ER‐2 inside the Arctic polar vortex during the SAGE III Ozone loss and Validation Experiment (SOLVE) provide the opportunity to identify and test interferences during the measurement of HO2 in the presence of high concentrations of ClO. In‐flight calibrations are consistent with small interferences from CH3O2 (8%) and from ClO (3%) to the total signal on average inside the vortex. Measurements of HO2, OH, ClO, and O3 are used with rate constants derived from laboratory measurements to test the consistency of the reactions that control HO2/OH. Inside the vortex the calculated HO2/OH under predicts the observed HO2/OH by 7% with the JPL‐00 rate constants and over‐predicts the observations by 23% when recent laboratory rates are used. Measurements of HO2 and ClO are used to calculate ozone loss rates and concentrations of HOCl with uncertainties determined from the analysis of HO2/OH. The calculated concentration of HOCl is 52−28+50 pptv, or 0.07 × ClO on average in the vortex. The ozone loss rate from the two cycles controlled by HO2 + ClO is ∼1.5−0.5+1.2 ppbv d−1 in early March.
Temperature profile determination from microwave oxygen emissions in limb sounding geometry
Authors: von Engeln Axel , Bühler Stefan
Published: October 2002

We present a theoretical investigation of the temperature profile retrieval capabilities of oxygen emission lines in the microwave. The main focus is on two strong lines, both allowing temperature retrieval throughout the mesosphere. One is within the oxygen cluster at 61.15 GHz, the other one is isolated at 118.75 GHz. A thorough comparison of these two lines is presented. Several instrumental parameters such as system noise temperature, antenna beam width, filter width, and coverage of the line are assessed, as well as the possible impact of an error in the spectroscopic parameters. The instrumental setup follows roughly the specifications for the Millimeter Wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER) instrument, serving as a basis for a modern passive microwave instrument. The instrumental parameters have also been varied in order to allow comparisons with two instruments that use the 118.75‐GHz line for temperature profile determination, the Odin submillimeter radiameter (SMR) and the EOS microwave limb sounder (MLS). Simultaneous retrieval of temperature and pointing bias is performed with the Optimal Estimation Method. We find temperature retrieval errors of <5 K in the mesosphere, and at sub‐Kelvin level in the lower stratosphere. Good knowledge of spectroscopic parameters is required for accurate retrievals. The simultaneous retrieval of a pointing bias can reduce the impact of spectroscopic parameter errors on the temperature retrieval.
Improvement in thin cirrus retrievals using an emissivity‐adjusted CO2 slicing algorithm
Authors: Zhang Hong , Menzel W. Paul
Published: October 2002

CO2 slicing has been generally accepted as a useful algorithm for determining cloud top pressure (CTP) and effective cloud amount (ECA) for tropospheric clouds above 600 hPa. To date, the technique has assumed that the surface emissivity is that of a blackbody in the long‐wavelength infrared radiances and that the cloud emissivities in spectrally close bands are approximately equal. The modified CO2 slicing algorithm considers adjustments of both surface emissivity and cloud emissivity ratio. Surface emissivity is adjusted according to the surface types. The ratio of cloud emissivities in spectrally close bands is adjusted away from unity according to radiative transfer calculations. The new CO2 slicing algorithm is examined with Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator (MAS) CO2 band radiance measurements over thin clouds and validated against Cloud Lidar System (CLS) measurements of the same clouds; it is also applied to Geostationary Operational Environmental Satellite (GOES) Sounder data to study the overall impact on cloud property determinations. For high thin clouds an improved product emerges, while for thick and opaque clouds there is little change. For very thin clouds, the CTP increases by about 10–20 hPa and RMS (root mean square bias) difference is approximately 50 hPa; for thin clouds, the CTP increase is about 10 hPa bias and RMS difference is approximately 30 hPa. The new CO2 slicing algorithm places the clouds lower in the troposphere.
Distribution and influence of convection in the tropical tropopause region
Authors: Gettelman A. , Salby M. L. , Sassi F.
Published: October 2002

A global analysis of convective cloud in the tropical tropopause region (12–17 km) is presented. The analysis is based on high‐resolution global imagery of cloud brightness temperatures from satellites and from contemporaneous reanalysis temperatures. The coverage by deep convection decreases nearly exponentially with increasing altitude in the tropopause region. Convection is found at temperatures colder than the tropical cold point tropopause over ∼0.5% (±0.25%) of the tropics. Convection rarely penetrates more than 1.5 km above the tropopause. Large‐scale relationships between cold tropopause temperatures and deep convection indicate that where the tropopause is coldest convection penetrates most frequently. Small‐scale relationships show that the coldest diurnal tropopause temperatures occur after the diurnal peak in deep convection at tropopause levels over land. The coverage by deep convection is used to estimate the mass exchange or turnover time due to convection in the tropopause region. This turnover time is of the order of weeks at 12 km but increases to longer than a year at 18 km, with significant uncertainties in the tropopause region.
Particle growth in the plumes of coal‐fired power plants
Authors: Brock Charles A. , Washenfelder Rebecca A. , Trainer Michael , Ryerson Thomas B. , Wilson J. Charles , Reeves J. Michael , Huey L. Gregory , Holloway John S. , Parrish David D. , Hübler Gerhard , Fehsenfeld Fred C.
Published: October 2002

Submicron particle‐size distributions were measured with 10‐s resolution aboard the National Oceanic and Atmospheric Administration WP‐3D Orion research aircraft in the plumes downwind of coal‐fired power generation plants in the eastern United States and the urban areas of Nashville, Tennessee, and Atlanta, Georgia. Recently formed particles were present at the edges of some power plant plumes within 2 hours of emission, coinciding with OH maxima predicted by a numerical plume photochemistry model. Clearly detectable increases in particle volume (mass) concentration with increasing plume age, indicating gas‐to‐particle conversion, were found in only those plumes from sources that emit substantial quantities of SO2. The observed growth in particulate volume could be explained by the calculated oxidation of SO2 by OH. However, the amount of volume growth varied substantially from day to day, even in the plume of the same power plant. In the only case in which a quantitative growth law analysis could be performed, the observed growth of particle size with increasing plume age was consistent with condensation and inconsistent with aqueous oxidation. The advected particle volume flux in SO2‐rich power plant plumes substantially exceeded that measured in the urban plumes downwind of Nashville and Atlanta.
Evidence for a persistent and extensive greening trend in Eurasia inferred from satellite vegetation index data
Authors: Bogaert J. , Zhou L. , Tucker C. J. , Myneni R. B. , Ceulemans R.
Published: October 2002

The northern latitudes have warmed by ∼0.8°C since the early 1970s, but not all areas have warmed equally. Eurasia shows an overall warming trend, while North America exhibits warming at a lower rate and even a slight cooling trend during the last 50 years in the eastern United States. We analyzed a recently developed satellite normalized difference vegetation index (NDVI) data set (July 1981 to December 1999) to assess vegetation response to these temperature changes. An index of persistence of the NDVI trend was used to generate patches of different levels of persistence. The persistence data were analyzed for patch area, patch perimeter, patch number, patch coherence, largest patch size, patch fragmentation, pixel contiguity, pixel clustering, and conditional probability of pixel adjacency. We address two questions: (1) Is there a difference in the spatial pattern of long‐term NDVI increase in comparison to short‐term increase? and (2) Are there differences in the spatial patterns of patches between Eurasia and North America? The results indicate a persistent and spatially extensive and connected greening trend in Eurasia, relative to North America. The regions showing short‐term greening in Eurasia show a scattered pattern of spatially remote small patches. In North America the long‐term greening pattern is spatially fragmented, and a mixture of short‐ and long‐term NDVI increase is found, unlike in Eurasia. Therefore we conclude that the greening trend in Eurasia is more persistent and spatially extensive than in North America, which is qualitatively consistent with near‐surface air temperature observations.
Electric fields near triggered lightning channels measured with Pockels sensors
Authors: Miki Megumu , Rakov Vladimir A. , Rambo Keith J. , Schnetzer George H. , Uman Martin A.
Published: October 2002

Electric field waveforms at horizontal distances from the triggered lightning channel attachment point ranging from 0.1 to 1.6 m have been measured with Pockels sensors at the International Center for Lightning Research and Testing at Camp Blanding, Florida. The measuring system had a dynamic range from 20 kV/m to 5 MV/m and a bandwidth from 50 Hz to 1 MHz. The corresponding currents at the channel base and electric fields at 5, 15, and 30 m from the lightning channel were also measured using a current viewing resistor and flat‐plate antennas, respectively. Very close vertical electric fields for 36 strokes in nine triggered lightning flashes were obtained using Pockels sensors. For 8 out of the 36 strokes, horizontal electric fields were also measured using Pockels sensors. Electric field waveforms appear as pulses, with the leading edge of the pulse being due to the leader and the trailing edge due to the return stroke. Of the 36 vertical electric field waveforms, six were more or less V‐shaped, while 30 exhibited a considerably slower variation during the return‐stroke stage than during the leader stage. Vertical electric field pulse peaks are in the range from 176 kV/m to 1.5 MV/m (the median is 577 kV/m), and horizontal electric field pulse peaks are in the range from 495 kV/m to 1.2 MV/m (the median is 821 kV/m). On‐site calibration results show that these electric fields measured using Pockels sensors may be underestimated by 40% or so due to the insufficient upper frequency response of 1 MHz of the measuring system. Additionally, vertical electric fields due to M components were measured and compared to electric fields produced by leader/return stroke sequences. For 8 out of 10 M components having channel‐base peak currents greater than 500 A, vertical electric fields at 0.1 to 1.6 m were below 20 kV/m, the lower measurement limit. For the remaining 2 of 10 M components, whose current peaks were between 2.3 and 3.2 kA, vertical electric field peaks were about 100 and 48 kV/m at a distance of 0.1 m from the attachment point, apparently unaffected by the upper frequency response of the measuring system. The vertical electric field measured very close to the lightning channel tends to increase with an increase in the previous no‐current interval, that is, in the time elapsed from the cessation of current of the preceding stroke (or of the initial‐stage current).
Gas/aerosol partitioning 2. Global modeling results
Authors: Metzger Swen , Dentener Frank , Krol Maarten , Jeuken Ad , Lelieveld Jos
Published: October 2002

We present gas/aerosol partitioning calculations of multicomponent aerosols and aerosol associated water on a global scale. We have coupled a computationally efficient gas‐aerosol scheme (EQSAM) to a global atmospheric chemistry‐transport model (TM3). Our results show that gas/aerosol partitioning strongly affects the gas‐phase concentrations at relatively low temperatures. During winter and at night during all seasons the calculated aerosol load, including water, is considerably higher than without accounting for gas/aerosol partitioning. The reason is that gaseous nitric acid near the surface is often neutralized by ammonia and therefore partitions almost completely into the aerosol phase to yield ammonium nitrate (NH4NO3). The aerosol NH4NO3 has a longer atmospheric residence time compared to the corresponding precursor gases (NH3 and HNO3) and can therefore be transported over larger distances, for instance from India to Africa and Europe. These modeling results are intriguing; however, verification requires in situ measurements. A comparison with a limited set of ground‐based measurements indicates that our model yields realistic results for the ammonium‐sulfate‐nitrate‐water aerosol system in relatively polluted locations where ammonium nitrate is important. For remote locations for which we underestimate the total aerosol load, however, it will be necessary to also account for other aerosol species such as sea salt, mineral dust and organic compounds. We further show that assumptions on turbulent mixing and model resolution have a much stronger effect on aerosol calculations than the uncertainties resulting from the simplifications made in EQSAM.
European pollution outbreaks during ACE 2: Optical particle properties inferred from multiwavelength lidar and star‐Sun photometry
Authors: Ansmann Albert , Wagner Frank , Müller Detlef , Althausen Dietrich , Herber Andreas , von Hoyningen‐Huene Wolfgang , Wandinger Ulla
Published: October 2002

On the basis of multiwavelength backscatter and 532‐nm extinction profiling with lidar at Sagres (37°N, 9°W), southern Portugal, and optical depth observations with a star photometer at the lidar site and a Sun photometer atop a nearby mountain, several European pollution outbreaks were characterized during the Second Aerosol Characterization Experiment (ACE 2) in the summer of 1997. A sophisticated analysis scheme applied to the lidar‐photometer data set is described. The observations are mainly presented in terms of profiles of the 532‐nm extinction‐to‐backscatter ratio (lidar ratio) and of Ångström exponents calculated for the wavelength ranges 400–532 nm and 532–800 nm. The lidar ratio indicates the aerosol type (marine, soil, pollution) whereas the Ångström exponents are sensitive to changes in the particle size distribution (accumulation mode, coarse mode). Results of an extensive correlation analysis considering all determined optical parameters, relative humidity, and measurement height are discussed. Finally, the spectrally resolved optical depth and the column Ångström exponents for the lofted outbreak plumes determined from the lidar profiles are compared with respective values derived from the star and Sun photometer measurements.
Effect of volcanoes on the vertical temperature profile in radiosonde data
Authors: Free Melissa , Angell James K.
Published: October 2002

Comparison of the responses of radiosonde temperatures to aerosol forcing from the Agung, El Chichon, and Pinatubo volcanic eruptions shows the expected stratospheric warming, with a maximum at 50 mbar in the tropics, and a predominantly cooling effect in the troposphere with a maximum in the middle or upper troposphere. The tropospheric cooling is greater after the Pinatubo eruption, with a significant effect on the temperature difference between the upper and lower tropical troposphere. The tropospheric coolings after El Chichon and Agung are more vertically uniform. The size of the difference between the Pinatubo and El Chichon responses is somewhat sensitive to the choice of data subset and the index used to account for the effects of El Niño‐Southern Oscillation. Differential effects of volcanic eruptions on the upper and lower tropical troposphere should be considered as possible causes of differential temperature trends at those levels.
Cloud‐to‐ground lightning characteristics over Houston, Texas: 1989–2000
Authors: Steiger Scott M. , Orville Richard E. , Huffines Gary
Published: October 2002

Cloud‐to‐ground (CG) lightning detected by the National Lightning Detection Network (NLDN) indicates a relatively high flash density over Houston, Texas, for the 12‐year period 1989–2000. A significant enhancement of 45% in the flash density is observed compared to the nearby surrounding areas. The strength of the enhancement varies on the basis of season and time of day, with the greatest increases occurring during the summer (58%) and during the 0900–1800 LT time periods in each season. Observations indicate that large lightning events (defined as days with >100 flashes in a geographic region that includes Houston and nearby rural areas) were responsible for the climatological lightning anomaly and that increased thunderstorm initiation was not the most significant cause of the enhancement. A decrease (−12%) in the percentage of positive flashes is observed over the city. Higher negative median peak currents along the coast and well into the Gulf of Mexico were also discovered. Several explanations for our observations are suggested. The urban heat island and increased cloud condensation nuclei concentrations, especially from industrial pollution, are speculated to be significant factors in creating lightning enhancement. Pollution effects are speculated to cause a change in a thunderstorm's charge distribution, which can affect the polarity of CG flashes. The potential effect of the nearby coastal Gulf salt water on the calculated peak current is examined. Variations in multiplicity values across the region are observed but not explained.
Multiyear infrared solar spectroscopic measurements of HCN, CO, C2H6, and C2H2tropospheric columns above Lauder, New Zealand (45°S latitude)
Authors: Rinsland Curtis P. , Jones Nicholas B. , Connor Brian J. , Wood Stephen W. , Goldman Aaron , Stephen Thomas M. , Murcray Frank J. , Chiou Linda S. , Zander Rodolphe , Mahieu Emmanuel
Published: October 2002

Near‐simultaneous, 0.0035 or 0.007 cm−1resolution infrared solar absorption spectra of tropospheric HCN, C2H2, CO, and C2H6have been recorded from the Network for the Detection of Stratospheric Change station in Lauder, New Zealand (45.04°S, 169.68°E, 0.37 km altitude). All four molecules were measured on over 350 days with HCN and C2H2reported for the first time based on a new analysis procedure that significantly increases the effective signal‐to‐noise of weak tropospheric absorption features in the measured spectra. The CO measurements extend by 2.5 years a database of measurements begun in January 1994 for CO with improved sensitivity in the lower and middle troposphere. The C2H6measurements lengthen a time series begun in July 1993 with peak sensitivity in the upper troposphere. Retrievals of all four molecules were obtained with an algorithm based on the semiempirical application of the Rodgers optimal estimation technique. Columns are reported for the 0.37‐ to 12‐km‐altitude region, approximately the troposphere above the station. The seasonal cycles of all four molecules are asymmetric, with minima in March–June and sharp peaks and increased variability during August–November, which corresponds to the period of maximum biomass burning near the end of the Southern Hemisphere tropical dry season. Except for a possible HCN column decrease, no evidence was found for a statistically significant long‐term trend.