Record 1 of 23
Author(s): Suhre K; Crassier V; Mari C; Rosset R; Johnson DW; Osborne S; Wood R; Andreae MO; Bandy B; Bates TS; Businger S; Gerbig C; Raes F; Rudolph J
Title: Chemistry and aerosols in the marine boundary layer: 1-D modelling of the three ACE-2 Lagrangian experiments
Source: ATMOSPHERIC ENVIRONMENT 2000, Vol 34, Iss 29-30, pp 5079-5094
Author Keywords: aerosol; marine boundary layer; Lagrangian
KeywordsPlus: CLOUDINESS; SIMULATION; MECHANISM
Abstract: Three Lagrangian experiments were conducted during IGAC's second aerosol characterization experiment (ACE-2) in the area between Portugal, Tenerife and Madeira in June/July 1997. During each Lagrangian experiment, a boundary layer air mass was followed for about 30 h, and the temporal evolution of its chemical and aerosol composition was documented by a series of vertical profiles and horizontal box pattern flown by the Meteorological Research Flight research aircraft Hercules C130. The wealth of observational data that has been collected during these three Lagrangian experiments is the basis for the development and testing of a one-dimensional Lagrangian boundary layer model with coupled gas, aqueous, and aerosol phase chemistry. The focus of this paper is on current model limitations and strengths. We show that the model is able to represent the dynamical and chemical evolution of the marine boundary layer, in some cases requiring adjustments of the subsidence velocity and of the surface heat fluxes. Entrainment of a layer rich in ozone and carbon monoxide from a residual continental boundary layer into the marine boundary layer as well as in-cloud oxidation of sulphur dioxide by hydrogen peroxide are simulated, and coherent results are obtained, concerning the evolution of the small, presumably sulphate-ammonia aerosol mode. (C) 2000 Elsevier Science Ltd. All rights reserved.
Source item page count: 16
IDS No.: 372XP
29-char source abbrev: ATMOS ENVIRON



Record 2 of 23
Author(s): Suhre K; Johnson DW; Mari C; Rosset R; Osborne S; Wood R; Bates TS; Raes F
Title: A continental outbreak of air during the Second Aerosol Characterization Experiment (ACE 2): A Lagrangian experiment
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2000, Vol 105, Iss D14, pp 17911-17924
KeywordsPlus: MARINE BOUNDARY-LAYER; MODEL; PARAMETERIZATION; CLOUDINESS; TURBULENCE; SIMULATION; MESOSCALE; TRANSPORT; OXIDATION; SYSTEM
Abstract: A mesoscale meteorological model is used to simulate the continental outbreak of air that occured over North Atlantic Ocean during the Second Aerosol Characterization Experiment (ACE 2). Comparison with Meteosat 6 visible images shows that the model is able to reproduce most of the observed cloud features in the entire modeling domain, including a frontal system, orographic clouds over the Pyrenees and the Iberian Peninsula, boundary layer clouds in the ACE 2 region, and cloud-free areas in the dry air outflow off the Portuguese coast. The model reproduces correctly the temperature, humidity, wind speed and direction, cloud water content, and light precipitation events observed by the aircraft during the Lagrangian experiment, while following a tagged boundary layer air parcel over a 28-hour long period. A passive tracer, introduced in the model at the time corresponding to the balloon launch, followed the balloon track with an error in position that is smaller than 1 degrees after 24-hours with about 20% higher speed. An estimate of the boundary layer entrainment velocity is obtained, based on observed boundary layer growth rates and modeled vertical wind speed. The average entrainment velocity of 1.28 cm/s for the 28-hour Lagrangian period agrees with experimentally derived entrainment velocities.
Source item page count: 14
Publication Date: JUL 27
IDS No.: 337NT
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 3 of 23
Author(s): Siems ST; Hess GD; Suhre K; Businger S; Draxler RR
Title: The impact of wind shear on observed and simulated trajectories during the ACE-1 Lagrangian experiments
Source: AUSTRALIAN METEOROLOGICAL MAGAZINE 2000, Vol 49, Iss 2, pp 109-120
KeywordsPlus: BOUNDARY-LAYER DYNAMICS; TEMPORAL RESOLUTION; METEOROLOGICAL DATA; SENSITIVITY; MODELS; ACCURACY; CLOUDINESS; TRANSPORT; SYSTEM; TRACER
Abstract: As part of the first Aerosol Characterization Experiment (ACE-I), two Lagrangian experiments were conducted with the intent of observing the evolution of boundary layer air over the course of 24 hours. Smart tetroons, which adjust their internal pressure to maintain a fixed elevation, were used to mark an ideal air mass. During both Lagrangians, however, the smart tetroons were observed to artificially lose elevation overnight; they dropped to near the ocean surface as a result of liquid-water loading: from condensation. First we use the tetroon trajectories to assess the accuracy of numerical trajectories based on the analysis of four global numerical weather prediction models. Comparable to other studies, the computed trajectory errors range from 12-34% of the travel distance in heterogeneous flow and 5-15% in homogeneous flow. The vertical motions, however, do not show a strong agreement. We then use numerical simulations to assess the sensitivity of the trajectories to the meteorology, Vertical wind shear was observed for both Lagrangians and had a major impact on the tetroon trajectories when coupled with the overnight decrease in altitude, We also find that the trajectories are more sensitive to the initial position in the first Lagrangian than in the second. This sensitivity is probably due to the presence of a nearby cold front. Finally, we assess the impact of the liquid-water loading on the tetroon trajectories through the use of composite numerical trajectories in which the altitude is prescribed hourly. The error over the entire time period was reduced to 15-23% if the trajectories were lowered to 100 m altitude overnight, and 5-15% if they were lowered to 10 m. This suggests that the tetroons interacted with the surface layer throughout the night. Budget and evolution studies of the ACE-I Lagrangians must take this into account.
Source item page count: 12
Publication Date: JUN
IDS No.: 333EA
29-char source abbrev: AUST METEOROL MAG



Record 4 of 23
Author(s): Johnson DW; Osborne S; Wood R; Suhre K; Johnson R; Businger S; Quinn PK; Wiedensohler A; Durkee PA; Russell LM; Andreae MO; O'Dowd C; Noone KJ; Bandy B; Rudolph J; Rapsomanikis S
Title: An overview of the Lagrangian experiments undertaken during the North Atlantic regional Aerosol Characterisation Experiment (ACE-2)
Source: TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 2000, Vol 52, Iss 2, pp 290-320
KeywordsPlus: MARINE BOUNDARY-LAYER; STRATOCUMULUS TRANSITION EXPERIMENT; SEA-SALT; 3-DIMENSIONAL MODEL; PARTICLE-PRODUCTION; WARM STRATOCUMULUS; SULFATE AEROSOLS; CUMULUS CLOUDS; SULFUR; CLIMATE
Abstract: One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic.
Source item page count: 31
Publication Date: APR
IDS No.: 316BR
29-char source abbrev: TELLUS B-CHEM PHYS METEOROL



Record 5 of 23
Author(s): Johnson DW; Osborne S; Wood R; Suhre K; Quinn PK; Bates T; Andreae MO; Noone KJ; Glantz P; Bandy B; Rudolph J; O'Dowd C
Title: Observations of the evolution of the aerosol, cloud and boundary-layer characteristics during the 1st ACE-2 Lagrangian experiment
Source: TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 2000, Vol 52, Iss 2, pp 348-374
KeywordsPlus: STRATOCUMULUS TRANSITION EXPERIMENT; SEA-SALT; ATMOSPHERIC AEROSOLS; PARTICLE-PRODUCTION; MARINE; ATLANTIC; ASTEX
Abstract: During the Ist Lagrangian experiment of the North Atlantic Regional Aerosol Characterisation Experiment (ACE-2), a parcel of air was tagged by releasing a smart, constant level balloon into it from the Research Vessel Vodyanitskiy. The Meteorological Research Flight's C-130 aircraft then followed this parcel over a period of 30 h characterising the marine boundary layer (MBL), the cloud and the physical and chemical aerosol evolution. The air mass had originated over the northern North Atlantic and thus was clean and had low aerosol concentrations. At the beginning of the experiment the MBL was over 1500 m deep and made up of a surface mixed layer (SML) underlying a layer containing cloud beneath a subsidence inversion. Subsidence in the free troposphere caused the depth of the MBL to almost halve during the experiment and, after 26 h, the MBL became well mixed throughout its whole depth. Salt particle mass in the MBL increased as the surface wind speed increased from 8 m s(-1) to 16 m s(-1) and the accumulation mode (0.1 mu m to 3.0 mu m) aerosol concentrations quadrupled from 50 cm(-3) to 200 cm(-3). However, at the same time the total condensation nuclei (> 3 nm) decreased from over 1000 cm(-3) to 750 cm(-3). The changes in the accumulation mode aerosol concentrations had a significant effect on the observed cloud microphysics. Observational evidence suggests that the important processes in controlling the Aitken mode concentration which, dominated the total CN concentration, included, scavenging of interstitial aerosol by cloud droplets, enhanced coagulation of Aitken mode aerosol and accumulation mode aerosol due to the increased sea salt aerosol surface area, and dilution of the MBL by free tropospheric air.
Source item page count: 27
Publication Date: APR
IDS No.: 316BR
29-char source abbrev: TELLUS B-CHEM PHYS METEOROL



Record 6 of 23
Author(s): Wood R; Johnson D; Osborne S; Andreae MO; Bandy B; Bates TS; O'Dowd C; Glantz P; Noone K; Quinn PK; Rudolph J; Suhre K
Title: Boundary layer and aerosol evolution during the 3rd Lagrangian experiment of ACE-2
Source: TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 2000, Vol 52, Iss 2, pp 401-422
KeywordsPlus: SPECTROMETER PROBE; ENTRAINMENT; PARAMETERIZATION; INSTABILITY; PARTICLES; DYNAMICS; SURFACE; NUMBER; MODEL
Abstract: Aircraft measurements are presented of the Lagrangian evolution of a marine boundary layer over a 30-h period during the ACE-2 field campaign. At the start of the observational period, a 500-m deep polluted marine internal boundary layer (MIBL) was overlain by the remnants of a polluted continental boundary layer extending to around 2 km below a clean, dry free troposphere. The MIBL grew rapidly to a thickness of 900-1000 m in response to increasing sea surface temperatures. No significant aerosol spectral evolution was observed in the boundary layer. Low concentrations of SO2 were observed in the MIBL suggesting that the air mass contained relatively aged aerosol. Aerosol spectra show a broad mode with a modal diameter of around 0.1 mu m. The polluted layer between the MIBL and the unpolluted free troposphere was only weakly and intermittently turbulent which prevented significant entrainment of clean air into the polluted layer from aloft. The polluted layer depth was thus controlled mainly by subsidence which as a result becomes shallower, decreasing from over 2000 m to around 1200 m during the observational period. The aerosol characteristics of the polluted layer were similar to those in the MIBL and so although the MIBL entrained considerable amounts of air from above the MIBL the aerosol characteristics underwent no significant change. This has important implications for the rate at which a polluted continental air mass is converted to a clean marine one. The dataset should prove useful in the validation of the modelling of continental pollution outbreaks.
Source item page count: 22
Publication Date: APR
IDS No.: 316BR
29-char source abbrev: TELLUS B-CHEM PHYS METEOROL



Record 7 of 23
Author(s): Cohard JM; Pinty JP; Suhre K
Title: On the parameterization of activation spectra from cloud condensation nuclei microphysical properties
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2000, Vol 105, Iss D9, pp 11753-11766
KeywordsPlus: SIZE DISTRIBUTIONS; MODEL; AEROSOLS; PARTICLES; ALBEDO; DELIQUESCENCE; PREDICTION; DROPLETS; GROWTH; NUMBER
Abstract: A simple parametric relationship is established between factors describing the shape of cloud condensation nuclei (CCN) activation spectra and observable properties of the aerosol population they grow on (size distribution and solubility). This is done independently for maritime and continental aerosol types because of their very different characteristics. The data used for the multiple statistical adjustments in the procedure described in this paper are generated by running a numerical model of aerosol growth coupled to a simple cloud droplet activation scheme. Each aerosol population (maritime and continental) is assumed to be of homogeneous chemical composition, lognormally distributed and with variable solubility. The parameterization is then evaluated using a large set of aerosol populations with randomized properties. Finally, the study presents a preliminary analysis of the most important aerosol properties that influence the shape of the CCN spectra. An idealized scenario of a clean maritime boundary layer cloud perturbed by anthropogenic emissions (such as the ship track problem) illustrates the capability of the parameterization to selectively increase the cloud droplet concentration in a partially polluted cloud. The calibration results presented in this paper are not meant to be the definitive activation spectra produced by any lognormally distributed aerosols. These results are indeed a step toward an objective initialization of CCN spectra and hence toward the computation of cloud droplet concentrations based on measurable multimodal aerosol features, as required by three-dimensional numerical models with a coupled interactive aerosol module.
Source item page count: 14
Publication Date: MAY 16
IDS No.: 315RA
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 8 of 23
Author(s): Crassier V; Suhre K; Tulet P; Rosset R
Title: Development of a reduced chemical scheme for use in mesoscale meteorological models
Source: ATMOSPHERIC ENVIRONMENT 2000, Vol 34, Iss 16, pp 2633-2644
Author Keywords: reactivity weighting; mesoscale modelling; photochemical mechanism; RACM
KeywordsPlus: ACID DEPOSITION MODEL; MECHANISM; TRANSPORT; OZONE
Abstract: A new Regional Lumped Atmospheric Chemical Scheme (ReLACS) is introduced. This mechanism is intended to be valid for clean to polluted conditions. ReLACS is derived from a new reactivity weighting approach which may be applied to any atmospheric chemical scheme. In this work, ReLACS is based upon the reduction of the regional atmospheric chemistry mechanism (RACM) (Stockwell ct al., 1997. Journal of Geophysical Research D22, 25847-25849) on a given moderately polluted emission scenario. However, sensitivity tests around this scenario show that ReLACS compares favorably with RACM, not only for ozone but also for other important atmospheric oxidants. The gain obtained from this lumping in the number of species allows ReLACS to be suitable to perform, otherwise costly, three dimensional pollution studies when coupled with mesoscale meteorological models. (C) 2000 Elsevier Science Ltd. All rights reserved.
Source item page count: 12
IDS No.: 308EL
29-char source abbrev: ATMOS ENVIRON



Record 9 of 23
Author(s): Mari C; Suhre K; Rosset R; Bates TS; Huebert BJ; Bandy AR; Thornton DC; Businger S
Title: One-dimensional modeling of sulfur species during the First Aerosol Characterization Experiment (ACE 1) Lagrangian B
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1999, Vol 104, Iss D17, pp 21733-21749
KeywordsPlus: MARINE BOUNDARY-LAYER; SEA-SALT AEROSOL; ATMOSPHERIC CHEMISTRY; DIMETHYL-SULFIDE; SENSITIVITY ANALYSIS; 3-DIMENSIONAL MODEL; OZONE OXIDATION; GAS-EXCHANGE; PARTICLES; MECHANISM
Abstract: A one-dimensional Lagrangian model is used to simulate vertical profiles and temporal evolution of dimethylsulfide (DMS), sulfur dioxide (SO2), aerosol methane sulfonate, and non-sea-salt sulfate (nss sulfate) that were measured during the three flights of the second First Aerosol Characterization Experiment (ACE 1) Lagrangian (Lagrangian B) experiment. Entrainment rate, mixing heights, and cloud occurrence are calculated prognostically in this type of model. The model is forced by geostrophic winds and large scale subsidence from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and sea surface temperature measured on board Research Weasel Discoverer. Gas phase oxidation and heterogeneous oxidation of SO2 to nss sulfate in clouds and sea-salt particles are considered. The evolution of dynamical variables in the column is found to be well reproduced by the model. The model captures 82% of the variance of observed DMS assuming OH is the only oxidant and a DMS flux term calculated from Liss and Merlivat [1986] parameterization and seawater DMS concentrations measured aboard RN Discoverer. However, uncertainties in DMS oxidation rates and regional seawater concentrations are too great to identify a best fit wind speed-transfer velocity relationship. SO2 mixing ratios are correctly represented in the model (least squares correlation coefficient r(2) = 75%) using a DMS to SO2 conversion efficiency of about 70%. Oxidation of SO2 in sea-salt particle appears to be a dominant process and controls SO2 lifetime during the Lagrangian B at least in the well mixed lower layer. Removing heterogeneous loss of SO2 in sea salt significantly deteriorates the simulation (r(2) = 50%). Under cloudy conditions, heterogeneous loss in cloud droplets and in sea-salt particles are competitive (relative rates are 35% and 41%, respectively, during flight 26). Model-generated aerosol methane sulfonate mixing ratios agree with the observations (r(2) = 62.5%) when high branching ratio for an addition oxidation pathway is used. The model estimates nss sulfate mixing ratios with little bias (median simulated-to-observed concentration ratio 1.03 and slope of the regression line 0.7) but captures only one third of the observed variance of nss sulfate. Part of the discrepancy could be due to the assumption of a decrease of nss sulfate mixing ratios with altitude in the model, whereas observations revealed high concentrations at 4500 m during the last two flights suggesting that horizontal transport could be more important than vertical mixing in this region. Nss sulfate is found to be produced photochemically under non cloudy, low wind speed conditions encountered during the first flight. During the last two flights, nss sulfate is produced mainly by oxidation in cloud droplets (48% during flight 25 and 69% during flight 26) and sea-salt particles (50% during flight 25 and 22% during flight 26).
Source item page count: 17
Publication Date: SEP 20
IDS No.: 238BC
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 10 of 23
Author(s): Wang Q; Suhre K; Krummel P; Siems S; Pan LL; Bates TS; Johnson JE; Lenschow DH; Heubert BJ; Kok GL; Schillawski RD; Prevot ASH; Businger S
Title: Characteristics of marine boundary layers during two Lagrangian measurement periods 1. General conditions and mean characteristics
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1999, Vol 104, Iss D17, pp 21751-21765
KeywordsPlus: CHARACTERIZATION EXPERIMENT ACE-1; STRATOCUMULUS; AEROSOL; TRANSITION; DYNAMICS; ASTEX
Abstract: Two sets of Lagrangian measurements were made during the southern Aerosol Characterization Experiment (ACE1) South of Tasmania, Australia, in December 1995. This paper intends to provide an overview of the general conditions encountered during the two intensive observational periods. The measurements by the NCAR C-130 provide the main data set for this study. We also use the sea surface temperature obtained from the R/V Discoverer and the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses field for the large-scale divergence field. Emphases of the paper are on the atmospheric and oceanic environment and the: boundary layer mean structure during the six flights in the two Lagrangian measurement periods. The large scale features, such as variations of sea surface temperature, synoptic conditions, and large-scale velocity fields, are discussed. These large-scale environments had significant influences on boundary layer turbulence and the inversion structure. The boundary layer mean structure and its evolution along the Lagrangian trajectory are also studied using two-dimensional cross-section plots of vertical and horizontal (along the flight track) variation of potential temperature, water vapor, wind components, and ozone concentration. The most prominent feature of the boundary layer is the two-layered structure observed throughout Lagrangian B and during the last flight of Lagrangian A. The two layers have detectable differences in potential temperature, water vapor, and, to a lesser extent, ozone concentration. These differences make it necessary to study the exchange between the two layers. Low-level cloud structure and cloud microphysics are also discussed. We emphasize, though, that the results on cloud fractions should be used with caution due to the variable nature of the cloud bands observed during ACE1.
Source item page count: 15
Publication Date: SEP 20
IDS No.: 238BC
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 11 of 23
Author(s): Wang Q; Lenschow DH; Pan LL; Schillawski RD; Kok GL; Prevot ASH; Laursen K; Russell LM; Bandy AR; Thornton DC; Suhre K
Title: Characteristics of the marine boundary layers during two Lagrangian measurement periods 2. Turbulence structure
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1999, Vol 104, Iss D17, pp 21767-21784
KeywordsPlus: ENTRAINMENT; MECHANISM; CLOUDS
Abstract: Characteristics of turbulence mixing in remote marine boundary layers are analyzed using aircraft measurements from six flights during the two intensive Lagrangian measurement periods of ACE1 (the southern hemisphere Aerosol Characterization Experiment). The six cases studied here represent a variety of boundary layer conditions in the region south of Tasmania, Australia. Our study indicated that (1) Lagrangian A (LA) had stronger turbulence mixing and entrainment compared to Lagrangian B (LB) due to greater shear generation of turbulence kinetic energy (TKE), (2) strong mesoscale variation in boundary layer turbulence and thus turbulence mixing existed in the ACE1 region during LB due to variations in sea surface temperature (SST), (3) stable thermal stratification in the boundary layer was found during the last flight of each Lagrangian, consequently, TKE decreased rapidly with height resulting in small or near-zero entrainment rate in spite of strong shear forcing at the surface and in the boundary layer; and (4) the buffer layer, which lies above the boundary layer and below the main inversion, had weak and intermittent turbulence mostly associated with cloud bands and cumulus. Evidence of entrainment was found in the buffer layer. However, it is difficult to quantify by flux measurements due to the weak and intermittent nature of the turbulence field.
Source item page count: 18
Publication Date: SEP 20
IDS No.: 238BC
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 12 of 23
Author(s): Cammas JP; Jacoby-Koaly S; Suhre K; Rosset R; Marenco A
Title: Atlantic subtropical potential vorticity barrier as seen by Measurements of Ozone by Airbus In-Service Aircraft (MOZAIC) flights
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1998, Vol 103, Iss D19, pp 25681-25693
KeywordsPlus: 500-MB HEIGHT FLUCTUATIONS; SHORT-TIME SCALES; TROPOPAUSE FOLDS; STRATOSPHERE; TROPOSPHERE; EXCHANGE; WAVES; INTERMEDIATE; DYNAMICS; MODEL
Abstract: The existence and the seasonal variability of the Atlantic subtropical potential vorticity barrier controlling the stratosphere-troposphere exchanges between the lowermost extratropical stratosphere and the upper equatorial troposphere are investigated using Measurements of Ozone by Airbus In-Service Aircraft (MOZAIC). The methodology is based on the relationship between strong gradients of potential vorticity and of ozone mixing ratio situated on the cyclonic-shear side of the subtropical jet stream. Episodes of high ozone mixing ratio sampled along MOZAIC flight tracks over the subtropical Atlantic with mixing ratio exceeding 100 ppbv on length scales larger than 200 km on flight levels between 11 and 12 km are studied. A total of 154 high ozone episodes is extracted from the MOZAIC database over the period August 1994 to April 1997. All these high ozone episodes are observed north of 15 degrees N and have lengths ranging from subsynoptic to synoptic scales. It is shown that this barrier effect at 15 degrees N over the central/eastern Atlantic fits with the southernmost latitude of the subtropical jet stream during the period of interest. South of the subtropical jet stream within the latitude band where the Intertropical Convergence Zone oscillates, tens of ozone-rich transients (high-ozone episodes with length scales smaller than 80 km) are sampled within the upper equatorial Atlantic troposphere (9 to 12 km). At present, the origin of these tropical ozone-rich transients is still not clear, Some outlooks are given to investigate the possibility that some of the ozone-rich transients may be interpreted as the final result of tropopause foldings and small scale mixing processes. The seasonal variability of the subtropical barrier is captured when determining the subtropical tropopause break (STB) point for each flight, that is, the southernmost latitude of the southernmost high-ozone episode of a flight, and classifying STB points on a monthly basis. A sinusoidal evolution of STB points appears, reflecting the northernmost (southernmost) position of the dynamical barrier in summer (winter) boreal months. This seasonal variability clearly agrees with that of the position of the subtropical jet stream as derived from mean isotach analysis.
Source item page count: 13
Publication Date: OCT 20
IDS No.: 129XW
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 13 of 23
Author(s): Suhre K; Mari C; Bates TS; Johnson JE; Rosset R; Wang Q; Bandy AR; Blake DR; Businger S; Eisele FL; Huebert BJ; Kok GL; Mauldin RL; Prevot ASH; Schillawski RD; Tanner DJ; Thornton DC
Title: Physico-chemical modeling of the First Aerosol Characterization Experiment (ACE 1) Lagrangian B - 1. A moving column approach
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1998, Vol 103, Iss D13, pp 16433-16455
KeywordsPlus: MARINE BOUNDARY-LAYER; EQUATORIAL PACIFIC; DIMETHYL SULFIDE; OZONE; PHOTODISSOCIATION; ATMOSPHERE; SIMULATION; CLOUDS; GAS; MICROPHYSICS
Abstract: During Lagrangian experiment B (LB in the following) of the First Aerosol Characterization Experiment (ACE 1): a clean maritime air mass was followed over a period of 28 hours. During that time span, the vertical distribution of aerosols and their gas phase precursors were characterized by a total of nine aircraft soundings which were performed during three research flights that followed the trajectory of a set of marked tetroons. The objective of this paper is to study the time evolution of gas phase photochemistry in this Lagrangian framework. A box model approach to the wind shear driven and vertically stratified boundary layer is questionable, since its basic assumption of instantaneous turbulent mixing of the entire air column is not satisfied here. To overcome this obstacle, a one-dimensional Lagrangian boundary layer meteorological model with coupled gas phase photochemistry is used. To our knowledge, this is the first time that such a model is applied to a Lagrangian experiment and that enough measurements are available to fully constrain the simulations. A major part of this paper is devoted to the question of to what degree our model is able to reproduce the time evolution and the vertical distribution of the observed species. Comparison with observations of O-3, OH, H2O2, CH3OOH, DMS, and CH3I, made on the nine Lagrangian aircraft soundings shows that this is in general the case, although the dynamical simulation started to deviate from the observations on the last Lagrangian flight. In agreement with experimental findings reported by Q.Wang et al. (unpublished manuscript, 1998b), generation of turbulence in the model appears to be most sensitive to the imposed sea surface temperature. Concerning the different modeled and observed chemical species, a number of conclusions are drawn: (1) Ozone, having a relatively long photochemical lifetime in the clean marine boundary layer, is found to be controlled by vertical transport processes, in particular synoptic-scale subsidence or ascent. (2) Starting with initally constant vertical profiles, the model is able to "create'' qualitatively the vertical structure of the observed peroxides. (3) OH concentrations are in agreement with observations, both on cloudy and noncloudy days. On the first flight, a layer of dry ozone rich air topped the boundary layer. The model predicts a minimum in OH and peroxides at that altitude consistent with observations. (4) Atmospheric DMS concentrations are modeled correctly only when using the Liss and Merlivat [1986] flux parameterization, the Wanninkhof [1992] flux parameterization giving values twice those observed. To arrive at this conclusion, OH is assumed to be the major DMS oxidant, but no assumptions about mixing heights or entrainment rates are necessary in this type of model. DMS seawater concentrations are constrained by observations.
Source item page count: 23
Publication Date: JUL 20
IDS No.: 100RB
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 14 of 23
Author(s): Mari C; Suhre K; Bates TS; Johnson JE; Rosset R; Bandy AR; Eisele FL; Mauldin RL; Thornton DC
Title: Physico-chemical modeling of the First Aerosol Characterization Experiment (ACE 1) Lagrangian B - 2. DMS emission, transport and oxidation at the mesoscale
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1998, Vol 103, Iss D13, pp 16457-16473
KeywordsPlus: MARINE BOUNDARY-LAYER; BIOGEOCHEMICAL SULFUR CYCLE; SHORT-TERM VARIABILITY; DIMETHYL SULFIDE; BIOGENIC SULFUR; 3-DIMENSIONAL MODEL; PACIFIC-OCEAN; GAS-EXCHANGE; ATMOSPHERE; FLUX
Abstract: A three-dimensional mesoscale meteorological model was used to study the interplay between the dynamical (turbulent mixing and advection) and physico-chemical (sea-air flux and photochemical sink by OH) processes that control dimethylsulfide DMS concentrations and their distribution in the marine boundary layer (MBL) during the First Aerosol Characterization Experiment ACE 1, Atmospheric DMS concentrations were constrained using observed seawater DMS concentrations and box model derived OH concentrations. Lateral boundary values of dynamical parameters were derived from the 6-hourly meteorological analysis of the European Centre for Medium-Range Weather Forecasts. Calculated DMS concentrations, wind speed and direction, and cloud cover were compared with measurements made aboard the RN Discoverer and on the three NCAR/C130 aircraft flights during the LagB experiment. Model-generated atmospheric DMS concentrations agreed with the DMS observations from the NCAR/C130 aircraft flights during the LagB experiment (R-2 = 0.69) assuming OH is the only oxidant and DMS flux parameterization based on Liss and Merlivat [1986], Comparison with Eulerian measurements made aboard the RN Discoverer showed that the model simulated the range of observed values but not the hour-to-hour variation observed in the atmospheric DMS concentrations. Part of the discrepancy was attributed to uncertainties in DMS sea-to-air transfer velocity, small scale features of seawater DMS that are beyond the model resolution, and uncertainties in the venting of the boundary layer by shallow clouds. A quantitative budget at the ship location revealed a strong impact of advection processes in determining DMS levels and temporal evolution. The three-dimensional mesoscale meteorological model was also used to estimate the effect of the low spatial resolution used in global models on seawater DMS concentrations and atmospheric OH concentrations.
Source item page count: 17
Publication Date: JUL 20
IDS No.: 100RB
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 15 of 23
Author(s): Matthijsen J; Suhre K; Rosset R; Eisele FL; Mauldin RL; Tanner DJ
Title: Photodissociation and UV radiative transfer in a cloudy atmosphere: Modeling and measurements
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1998, Vol 103, Iss D13, pp 16665-16676
KeywordsPlus: OBSERVATORY PHOTOCHEMISTRY EXPERIMENT; ACTINIC FLUX; PHOTOLYSIS RATES; WATER CLOUDS; OZONE; NO2; PARAMETERIZATION; TROPOSPHERE; MARINE
Abstract: We present an analysis of UV radiative transfer under cloudy conditions in relation to the photochemistry of the hydroxyl radical (OH) by means of modeling and measurements. The measurements, which are part of the First Aerosol Characterization Experiment (ACE 1) campaign, consist of four different ascents/descents selected from research flight (RF) 12 and 28. The ascents/descents give vertical profiles of UV irradiances, microphysical properties, standard meteorological parameters, and OH concentration in the presence of one or more cloud layers, In order to assess the photochemical conditions for these (complex) cloudy cases we first comp.are the UV irradiance measurements with modeled profiles. We model the UV irradiances using cloud optical properties which we derive from the measured microphysical properties. Second, we use the simultaneously modeled actinic flux to calculate the rate constant of the photodissociation of ozone to the O(D-1) radical (J(O3)) This reaction initiates the primary OH-production. Finally, we compare the measured OH concentrations with those derived from the radiative transfer calculations. For single-cloud layer cases we successfully simulated UV radiative transfer, J(O3) and OH. For more complex multiple-cloud layer cases the UV radiative transfer could only be explained allowing large variations of the cloud optical thickness (from zero to double the measurement derived values). The impact of such variations on the modeled radiation-derived photochemical properties, J(O3) and OH, was, with a variation of 25%, found to be relatively small. As a consequence, we were able to simulate the general profile of OH for these complex cloudy conditions.
Source item page count: 12
Publication Date: JUL 20
IDS No.: 100RB
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 16 of 23
Author(s): Matthijsen J; Suhre K; Bechtold P; Rosset R
Title: The effect of fractional cloudiness on the oxidation of SO2
Source: TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 1997, Vol 49, Iss 4, pp 343-356
KeywordsPlus: MARINE BOUNDARY-LAYER; TROPOSPHERIC OZONE; AMBIENT SULFATE; ACID DEPOSITION; CLOUDS; MODEL; SULFUR; WATER; OH; PARAMETERIZATION
Abstract: We have investigated the effect of fractional cloudiness on the oxidation of SO2 in the marine boundary layer. We address the question to which extent the budget of SO2 is affected by the way cloudwater content and cloudcover are resolved in mesoscale meteorological models. In these models, the cloudwater and cloud cover are calculated simply from the grid-cell average temperature and total water content (all-or-nothing), or, mostly, a subgrid parameterization (fractional cloudiness) is used. Such a subgrid parameterization is considered much more realistic, but does not allow for a direct implementation of cloud chemistry. For both approaches, we have simulated the SO2 concentration with a two-layer model, which contains the basic production and loss mechanism of SO2 in a cloudy marine boundary layer. We found that the SO2 concentration calculated using the subgrid parameterization to calculate the cloud parameters may deviate up to a factor of two as compared to that calculated using an air-or-nothing cloud parameterization. Calculations performed in a similar way for 5 observed cases of fractional cloudiness show maximum deviations between -85% and +33%. These observed cases have been selected from the GATE, Puerto Rico '72, ASTEX, FIRE and Semamphore measurement campaigns. Meteorological chemical mesoscale models which can take fractional cloudiness into account in the simulation of cloud chemistry are expected to give an important improvement of the quantification of the sulfur budget. Consequently, the results of meteorological mesoscale models which treat SO, aqueous phase chemistry with ah-or-nothing cloud parameters should be treated with care. Moreover, we conclude that fractional cloudiness can have a major effect on the oxidation of SO2 in the MBL even for a relatively small cloud cover. Parameters critical to the effect are the over-all lifetime of SO2 in the cloud and the rate of exchange between cloudy and non-cloudy air.
Source item page count: 14
Publication Date: SEP
IDS No.: XW205
29-char source abbrev: TELLUS B-CHEM PHYS METEOROL



Record 17 of 23
Author(s): Suhre K; Cammas JP; Nedelec P; Rosset R; Marenco A; Smit HGJ
Title: Ozone-rich transients in the upper equatorial Atlantic troposphere
Source: NATURE 1997, Vol 388, Iss 6643, pp 661-663
KeywordsPlus: DEHYDRATION MECHANISM; STRATOSPHERE; EXCHANGE
Abstract: High concentrations of ozone are found in the Earth's stratosphere, but strong stratification suppresses efficient exchange of this ozone-rich air with the underlying troposphere. Upward transport of tropospheric trace constituents occurs mainly through equatorial deep convective systems. In contrast, significant downward transport of ozone-rich stratospheric air is thought to take place only outside the tropics by exchange processes in upper-level fronts associated with strong distortions of the tropopause(1). Ozone within the tropical troposphere is assumed to originate predominantly from ground-based emissions of ozone precursors, particularly from biomass burning(2), rather than from a stratospheric source. Recent measurements of ozone in the upper troposphere in convective regions over the Pacific Ocean(3) indeed reveal near-zero concentrations. Here we present sharply contrasting observations: ozone-rich (100-500 parts per billion by volume) transients were frequently encountered by specially equipped commercial aircraft at a cruising altitude of 10-12 km (in the upper troposphere) in the vicinity of strong convective activity over the equatorial Atlantic Ocean. This strongly suggests that the input of stratospheric ozone into the troposphere can take place in the tropics. We suggest that this transport occurs either by direct downward movement of air masses or by quasi-isentropic transport from the extratropical stratosphere.
Source item page count: 3
Publication Date: AUG 14
IDS No.: XQ863
29-char source abbrev: NATURE



Record 18 of 23
Author(s): FassiFihri A; Suhre K; Rosset R
Title: Internal and external mixing in atmospheric aerosols by coagulation: Impact on the optical and hygroscopic properties of the sulphate-soot system
Source: ATMOSPHERIC ENVIRONMENT 1997, Vol 31, Iss 10, pp 1393-1402
Author Keywords: aerosol modelling; sectional model; aerosol mixing; radiative forcing; soot-sulphate aerosols
KeywordsPlus: PARTICLES; CONDENSATION; SIMULATION; SIZE
Abstract: A sectional aerosol model is used to study the impact of internal/external aerosol mixing on the optical and hygroscopic properties of two-component aerosol populations. Time evolution of the aerosol spectrum due to mixing by coagulation of two initially different particle populations is simulated. The impact of the state of mixing is determined through comparison of model results assuming either internal mixture (IM) only or both internal and external mixture (IEM). The model is first validated using the analytic solution for an idealized IEM problem and secondly against experimental data in an urban plume.

Then, a preliminary application is made which consists in a scenario of mixing between a plume containing soot particles and its environment mainly loaded with accumulation-mode sulphate particles. Emphasis is put on the evolving state of mixing of the aerosols thus formed. Evolution of the optical properties is computed using Mie theory for both homogeneous and concentric spheres (coated aerosols). For this particular scenario, the IEM model is more light-diffusive and less light-absorbant than the IM model. The extinction coefficient is practically insensitive to the way of modelling of the state of mixing. Hygroscopic properties are also derived, based on empirical growth laws, showing more activation in the IEM than in the IM model. However, further such studies are necessary to determine more fully the variability range in the optical and hygroscopic properties of aerosols at different degrees of mixing. (C) 1997 Elsevier Science Ltd.

Source item page count: 10
Publication Date: MAY
IDS No.: WR160
29-char source abbrev: ATMOS ENVIRON



Record 19 of 23
Author(s): Martin D; Tsivou M; Bonsang B; Abonnel C; Carsey T; SpringerYoung M; Pszenny A; Suhre K
Title: Hydrogen peroxide in the marine atmospheric boundary layer during the Atlantic Stratocumulus Transition Experiment Marine Aerosol and Gas Exchange Experiment in the eastern subtropical North Atlantic
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1997, Vol 102, Iss D5, pp 6003-6015
KeywordsPlus: ASTEX LAGRANGIAN EXPERIMENTS; NORTHEASTERN UNITED-STATES; TROPOSPHERIC CHEMISTRY; AIRCRAFT MEASUREMENTS; ACID GENERATION; H2O2; OZONE; PHASE; CLOUD; AIR
Abstract: Gas phase H2O2 was measured in surface air on the NOAA ship Malcolm Baldrige from June 8 to 27, 1992 (Julian days 160-179), during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic region. Average H2O2 mixing ratios observed were 0.63 +/- 0.28 ppbv, ranging between detection limit and 1.5 ppbv. For the entire experiment, only weak or no correlation was found between H2O2 mixing ratio and meteorological parameters (pressure, temperature, humidity, or UV radiation flux) as well as with tracers of continental air masses (CO, black carbon, radon), The average daily H2O2 cycle for the entire period exhibits a maximum of 0.8 +/- 0.3 ppbv near sunset and a minimum of 0.4 +/- 0.2 ppbv 4-5 hours after sunrise, Several clear H2O2 diurnal variations have been observed, from which a first-order removal rate of about 1 x 10(-5) s(-1) for H2O2 can be inferred from nighttime measurements, This rate compares well with those deduced from measurements taken at Cape Grim (Tasmania, 41 degrees S) and during the Soviet-American Gas and Aerosol III experiment (equatorial Pacific Ocean).
Source item page count: 13
Publication Date: MAR 20
IDS No.: WQ021
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 20 of 23
Author(s): Bedos C; Suhre K; Rosset R
Title: Adaptation of a cloud activation scheme to a spectral-chemical aerosol model
Source: ATMOSPHERIC RESEARCH 1996, Vol 41, Iss 3-4, pp 267-279
KeywordsPlus: ATMOSPHERIC AEROSOLS; SULFATE
Abstract: Development and preliminary tests of a cloud activation scheme adapted to a spectral-chemical aerosol model are presented. After some sensitivity studies bearing on changes in ambient relative humidity and various sulfate formation rates, the model is used to calculate cloud droplet nucleation for an ascending air parcel. Using the spectrum obtained with the aerosol model initialized with experimentally determined chemical concentrations, the critical radius thus obtained appears quite realistic. Sensitivity studies on the vertical velocity and on the aerosol mass concentrations display good agreement with previous published results.
Source item page count: 13
Publication Date: SEP
IDS No.: VQ092
29-char source abbrev: ATMOS RES



Record 21 of 23
Author(s): SUHRE K; ANDREAE MO; ROSSET R
Title: BIOGENIC SULFUR EMISSIONS AND AEROSOLS OVER THE TROPICAL SOUTH-ATLANTIC .2. ONE-DIMENSIONAL SIMULATION OF SULFUR CHEMISTRY IN THE MARINE BOUNDARY-LAYER
Source: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1995, Vol 100, Iss D6, pp 11323-11334
KeywordsPlus: SEA-SALT; VERTICAL-DISTRIBUTION; OXIDATION; DIMETHYLSULFIDE; ATMOSPHERE; CONVERSION; MECHANISM; KINETICS; DIOXIDE; PACIFIC
Abstract: Based on experimental data collected during cruise 15/3 of R/V Meteor in the tropical South Atlantic (19 degrees S), the marine sulfur cycle has been simulated with a one-dimensional coupled meteorological-chemical model. The potential of sea-spray aerosols to act as a sink for SO2 produced from dimethylsulfide (DMS) oxidation has been examined by using a simple humidity and height dependent parameterization for sea salt aerosol distribution. Simulations show significant reduction of total SO2 concentrations to 27-82% of the values found in the absence of this heterogenous process. The sulfur species concentrations calculated using a zero-dimensional box model agree with excess sulfate measurements in aerosol samples. The DMS, SO2, K2SO4 (sulfates formed by SO2 oxidation in the gas phase), and XSO(4) (sulfates formed by SO2 oxidation in sea-spray aerosols) vertical profiles, their diurnal cycles, and turbulent fluxes have been calculated with a one-dimensional model, based solely on shipboard chemical measurements and meteorological radiosonde soundings. Sensitivity analysis of the sea salt aerosol parameterization shows strong dependence on the assumed aerosol distribution, thus calling for a more comprehensive approach using a coupled aerosol-meteorological model.
Source item page count: 12
Publication Date: JUN 20
IDS No.: RF051
29-char source abbrev: J GEOPHYS RES-ATMOS



Record 22 of 23
Author(s): SUHRE K; ROSSET R
Title: DMS OXIDATION AND TURBULENT TRANSPORT IN THE MARINE BOUNDARY-LAYER - A NUMERICAL STUDY
Source: JOURNAL OF ATMOSPHERIC CHEMISTRY 1994, Vol 18, Iss 4, pp 379-395
Author Keywords: DIMETHYL SULFIDE; COUPLED MODEL; MESOSCALE; MODELING; TURBULENT TRANSPORT
KeywordsPlus: ATMOSPHERIC SULFUR; DIMETHYL SULFIDE; OCEAN; MODEL; SIMULATION; CLOUDS; CYCLE; RAIN
Abstract: DMS oxidation in the marine boundary layer has been simulated with a mesoscale meteorological model including detailed physical parameterizations. The impact of vertical turbulent transport on the DMS and SO2 diurnal cycles with and without in-cloud SO2 oxidation has been studied in a one-dimensional version of the model and compared to results obtained with a zero-dimensional box model. Initialisation has been done using balanced values issued from the imposed sea-air fluxes, dry deposition fluxes and chemical source/sink terms. Particular emphasis has been put on the important role played by evolving vertical mixing in the marine boundary layer.
Source item page count: 17
Publication Date: MAY
IDS No.: PH931
29-char source abbrev: J ATMOS CHEM



Record 23 of 23
Author(s): SUHRE K; ROSSET R
Title: MODIFICATION OF A LINEARIZED SEMIIMPLICIT SCHEME FOR CHEMICAL-REACTIONS USING A STEADY-STATE APPROXIMATION
Source: ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES 1994, Vol 12, Iss 4, pp 359-361
KeywordsPlus: MODEL
Abstract: A modification of a semi-implicit scheme for solving stiff chemical differential equations in atmospheric chemistry is proposed to include a steady-state-approximation implicitly into the scheme. The linearized version of the method has similar characteristics as the method SIS, but allows for larger time-steps by suppressing numerical oscillations in the rapidly reacting species.
Source item page count: 3
Publication Date: MAY
IDS No.: NP653
29-char source abbrev: ANN GEOPHYS-ATMOS HYDROS SPAC



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