bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical and chemical feedback in a two‐dimensional interactive model of the middle atmosphere
Authors: Huang Theresa Y. W. , Smith Anne K.
Published: February 2004

A two‐dimensional radiative‐dynamical‐chemical model is used to study the effect of dynamic and chemical feedback on the middle‐atmospheric response to perturbations. The role of these feedbacks is examined in controlled experiments by perturbing the external forcing fields (e.g., solar heating and wave driving). The effects of planetary and gravity wave feedbacks and chemical feedbacks are isolated by using certain fixed variables from the results of the control run. The model experiments suggest the importance of gravity wave feedback on various perturbations throughout the stratosphere and mesosphere, as a result of the large magnitude of gravity wave forcing, and the parameterized gravity waves forcing being extremely sensitive to changes in the mean zonal wind. Therefore a realistic description of gravity wave breaking process appears to be essential for an accurate portrayal of how the middle atmosphere responds to changes. Chemical feedback effects, particularly through ozone, are also shown to be quite effective in modifying the influence of perturbations on the middle atmosphere.
Deductions from a simple climate model: Factors governing surface temperature and atmospheric thermal structure
Authors: Weaver C. P. , Ramanathan V.
Published: February 2004

Radiative equilibrium solutions are the starting point in our attempt to understand how the atmospheric composition governs the surface and atmospheric temperatures, and the greenhouse effect. The Schwarzschild analytical grey gas model (SGM) was the workhorse of such attempts. However, the solutions suffered from serious deficiencies when applied to Earth's atmosphere and were abandoned about 3 decades ago in favor of more sophisticated computer models. Here we show that simple heuristic modifications to the SGM resolve these deficiencies, at least the catastrophic ones. The modifications include the addition of a spectral window, as well as allowing the scale height of optical depth to be different from that of the atmospheric pressure. The modified SGM reveals the fundamental factors that govern the radiative equilibrium thermal structure. (1) The presence of a spectral window allows the temperature jump between the surface and the immediately overlying atmosphere to become small, irrespective of the magnitude of the surface temperature. (2) In an optically thick atmosphere (such as Earth and Venus), the surface temperature and the runaway greenhouse effect depend inversely (as the one‐fourth power) on the Planck function‐weighted width of the window and are independent of the optical depth and other atmospheric parameters. The vertical variation of temperature within the atmosphere, however, is determined by the vertical variation of optical depth. (3) The degree of convective instability of the radiative equilibrium thermal structure γ is proportional to the ratio H/Hτ, where H is the atmospheric scale height and Hτ is the scale height of the vertical variation of optical depth. Here, γ is the ratio of the radiative equilibrium lapse rate and the neutral lapse rate for dry convection; γ > 1 indicates that the profile is unstable to free convection. Thus Hτ < H emerges as one of the fundamental criteria for convective instability. These factors lead to several corollaries regarding the specific details of atmospheric thermal structure on Earth and Venus. For example, according to the modified SGM, the radiative equilibrium temperature profile is strongly superadiabatic in Earth's lower atmosphere because Hτ is dominated by the water vapor's scale height being much less (2 compared with 8 km) than the atmospheric scale height. In the case of Venus, the pressure broadening of the CO2 rotational lines makes Hτ a factor of 2 smaller than H. Some of these results have been obtained using more detailed, multispectral radiative equilibrium models.
Marine boundary layer structure and fractional cloudiness
Authors: Albrecht Bruce A. , Jensen Michael P. , Syrett William J.
Published: February 2004

Radiosonde data collected during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE), 1987, the Atlantic Stratocumulus Transition Experiment (ASTEX), 1992, and the Tropical Instability and Waves Experiment (TIWE), 1990, were used to develop four composite thermodynamic soundings of the marine boundary layer for cloud conditions ranging from solid stratocumulus to trade cumulus and sea surface temperatures ranging from 16° to 27°C. Average cloud fraction and cloud base height for the composite soundings were estimated using laser ceilometers located at each of the four sites. The average fractional cloudiness varied from 0.83 off the coast of California at San Nicolas Island (33.4°N, 119.6°W) during FIRE to 0.26 over the central equatorial Pacific during TIWE (0°N, 140.0°W). During ASTEX, two sites in the vicinity of the Azores generally experienced cloud conditions characterized by cumulus clouds penetrating into a stratocumulus layer. At the more northerly site, the island of Santa Maria (37.0°N, 25.2°W), the average fractional cloudiness was 0.67 compared with 0.40, 1000 km downstream at the German R/V Valdivia (28.0°N, 24.0°W). The two composite soundings from ASTEX and the composite sounding from TIWE indicate decoupled boundary layer structures. These three soundings have a cloud layer that is conditionally unstable and show a systematic increase in relative humidity with increasing fractional cloudiness. The effect of cloud top entrainment on fractional cloudiness was evaluated. For the four composite soundings the fractional cloudiness decreases as the slope of the normalized w‐θ mixing line increases (greater instability), but this decrease is 4 times less than that from previous studies. Fractional cloudiness diagnosed from parameterizations using cloud layer relative humidity compares well with the observed mean cloudiness.
Ion chemistry relevant for chemical ionization detection of SO3
Authors: Arnold Susan T. , Morris Robert A. , Viggiano A. A. , Jayne John T.
Published: February 2004

Rate constants and products were measured for over 50 ion‐molecule reactions involving SO3 or ions formed from SO3. All negative ions studied reacted with SO3 at or near the collisional rate by a variety of processes including charge transfer, O− transfer, ligand exchange, and clustering. Ambient negative ions tended to form SO− 4 or SO− 4 core ions. A chemical ionization detection scheme for monitoring SO3 in the atmosphere is presented based on CO−3 (H2O)n = 0–1 or NO−3 (H2O)n = 0–1 as the primary ions. The proposed scheme can be used in conjunction with previous schemes for monitoring SO2 and H2SO4 concentrations to measure all three gases simultaneously. The measurements also confirm that the ion chemistry used in separate studies to monitor the reaction of SO3 with H2O is correct and rapid and that the reaction of SO3 with positive ion water clusters does not contribute to H2SO4 production in the atmosphere.
Relationships among aerosol constituents from Asia and the North Pacific during PEM‐West A
Authors: Arimoto R. , Duce R. A. , Savoie D. L. , Prospero J. M. , Talbot R. , Cullen J. D. , Tomza U. , Lewis N. F. , Ray B. J.
Published: February 2004

Aerosol particle samples collected from Asia and the North Pacific were analyzed to investigate the relationships among atmospheric sea salt, mineral aerosol, biogenic emissions (methanesulfonate (MSA)), and several anthropogenic substances (sulfate, nitrate, and various trace elements). These studies specifically focused on the sources for aerosol SO4= and on the long‐range transport of continental materials to the North Pacific. Ground‐based aerosol sampling was conducted at four coastal‐continental sites: Hong Kong, Taiwan, Okinawa, and Cheju; and at three remote Pacific islands, Shemya, Midway, and Oahu. Non‐sea‐salt (nss) SO4= and MSA were uncorrelated at the East Asian sites presumably because pollution sources overwhelm the biogenic emissions of nss SO4=. At the coastal‐continental sites, marine biogenic emissions accounted for only 10 to <5% of the total nss SO4=. In contrast, over the ocean the concentrations of nss SO4= and MSA were correlated (Midway r = 0.70; Oahu r = 0.59), and higher percentages of biogenic nss SO4= occurred, 55 and 70% at Oahu and Midway, respectively. The concentrations of nss SO4= and NO3− were correlated at Cheju, Hong Kong, Taiwan, Okinawa, Midway, and Oahu, indicating some similarities in their sources and the processes governing their transport; however, differences in the nss SO4=/NO3− ratios among sites suggest regional differences in the pollution component of the aerosol. At Shemya the concentrations of MSA during the summer (100 ng m−3 or more) are about 2 orders of magnitude higher than those in winter. The dimethylsulfide‐derived fraction of the nss SO4= is highest in the summer when the monthly median nss SO4=/MSA ratios range from 2.7 to 4.5, i.e., comparable to the ratios observed over Antarctica and other high‐latitude locations. However, the monthly median nss SO4=/MSA ratios increase, reaching 50 to 200 in the winter as productivity nearly ceases, and the biogenic fraction of nss SO4= at Shemya decreases dramatically; this suggests a strong seasonal pollution component to the sulfate aerosol. The meteorological conditions favoring the long‐range transport of Asian dust to the North Pacific also lead to transport of anthropogenic materials. At Oahu the correlation between NO3− and Al (dust) was highly significant (r = 0.75; p < 0.001), while the correlations between nitrate and Al at the continental sites were low. These differences indicate that the composition of the air sampled at the coastal‐continental stations may be quite different from the air transported to the remote ocean. This phenomenon also appeared to affect the relationship between nss SO4= and antimony. The correlations between nss SO4= and Sb were weak at the Asian sites but strong at the open ocean sites where the nss SO4=/Sb ratios were higher than those over the continent.
Preliminary study of spin‐up processes in land surface models with the first stage data of Project for Intercomparison of Land Surface Parameterization Schemes Phase 1(a)
Authors: Yang Z.‐L. , Dickinson R. E. , Henderson‐Sellers A. , Pitman A. J.
Published: February 2004

The spin‐up of a land surface model (LSM) is broadly defined as an adjustment process as the model approaches its equilibrium following initial anomalies in soil moisture content or after some abnormal environmental forcings (e.g., drought). The spin‐up timescale of LSMs has received little attention in the modeling community. This study uses results from Phase 1(a) of the Project for Intercomparison of Land Surface Parameterization Schemes, and finds that most land surface schemes require many years to come to thermal and hydrologic equilibrium with the forcing meteorology; the time needed depends on the total moisture holding capacity and the initialization of the moisture stores. The linear relationship established for bucket‐type models is just a special case of that found for the more sophisticated nonbucket‐type models, at least when the models start out with adequate soil moisture. When soil moisture begins at zero or when precipitation is set to zero, there is a nonlinear relationship. Sensitivity studies using the Biosphere‐Atmosphere Transfer Scheme confirm that precipitation intensity, solar radiation forcing, vegetation cover, and stomatal resistance also affect the length of spin‐up time. The results underline that the accurate calculation of precipitation and solar radiation incident at the Earth's surface is important for a realistic simulation of soil moisture content. Magnitudes of simulated heat fluxes at equilibrium are not related to the thickness of the soil layer below the rooting zone. For most LSMs, initial positive soil moisture anomalies are associated with initial positive evapotranspiration (E) anomalies, while initial negative anomalies of soil moisture are accompanied by the initial negative, but much stronger, E anomalies, as found in past studies performed with general circulation models. In addition, the implications of the spin‐up for numerical weather prediction and climate simulation are discussed.
Relationships between PAN and ozone at sites in eastern North America
Authors: Roberts J. M. , Tanner R. L. , Newman L. , Bowersox V. C. , Bottenheim J. W. , Anlauf K. G. , Brice K. A. , Parrish D. D. , Fehsenfeld F. C. , Buhr M. P. , Meagher J. F. , Bailey E. M.
Published: February 2004

Measurements of ozone and PAN (peroxyacetic nitric anhydride) were made at four sites in eastern North America; Bondville, Illinois, Egbert, Ontario, Scotia, Pennsylvania, and Whitetop Mountain, Virginia., in July and August of 1988 as part of a study of regional oxidant photochemistry. The concentrations of PAN ranged from <0.010 to 9.2 parts‐per‐billion by volume (ppbv) and those of O3 ranged from <2 to 139 ppbv. Diurnal concentration profiles showed PAN and O3 to be removed within nocturnal boundary layers, especially if nitric oxide was present, and that O3 was, for most sites, more rapidly removed than PAN. The only mountain top site at which PAN was measured showed distinctly different diurnal profiles in which O3 was actually higher at night, suggesting that convective flow driven by surface cooling served to transport air down from higher in the mixed layer at night. The afternoon production of PAN and O3 was also apparent and led to an overall linear correlation of O3 and PAN between the hours of 1300 and 1800. The comparison of this result with other measurements, estimates of PAN formation rates, and model calculations indicates that the production of PAN relative to ozone is far greater (x3) than can be accounted for by acetaldehyde reactions with OH, there is a wide disparity in model descriptions of PAN production, and confirms the non‐linear dependence of O3 production on NOx.
Volcanic sulfur dioxide measurements from the total ozone mapping spectrometer instruments
Authors: Krueger A. J. , Walter L. S. , Bhartia P. K. , Schnetzler C. C. , Krotkov N. A. , Sprod I. , Bluth G. J. S.
Published: February 2004

The total ozone mapping spectrometer (TOMS), first flown on the Nimbus 7 satellite, has delivered an unanticipated set of unique information about volcanic plumes because of its contiguous spatial mapping and use of UV wavelengths. The accuracies of TOMS sulfur dioxide retrievals, volcanic plume masses, and eruption totals under low‐latitude conditions are evaluated using radiative transfer simulations and error analysis. The retrieval algorithm is a simultaneous solution of the absorption optical depth equations including ozone and sulfur dioxide at the four shortest TOMS wavelengths and an empirical correction based on background condition residuals. The retrieval algorithm reproduces model stratospheric sulfur dioxide plume amounts within ±10% over most central scan angles and moderate solar zenith angles if no aerosols or ash are present. The errors grow to 30% under large solar zenith angle conditions. Volcanic ash and sulfate aerosols in the plume in moderate optical depths (0.3) produce an overestimation of the sulfur dioxide by 15–25% depending on particle size and composition. Retrievals of tropospheric volcanic plumes are affected by the reflectivity of the underlying surface or clouds. The precision of individual TOMS SO2soundings is limited by data quantization to ±6 Dobson units. The accuracy is independent of most instrument calibration errors but depends linearly on relative SO2absorption cross‐section errors at the TOMS wavelengths. Volcanic plume mass estimates are dependent on correction of background offsets integrated over the plume area. The errors vary with plume mass and area, thus are highly individual. In general, they are least for moderate size, compact plumes. Estimates of the total mass of explosively erupted sulfur dioxide depend on extrapolation of a series of daily plume masses backward to the time of the eruption. Errors of 15–30% are not unusual. Effusive eruption total mass estimates are more uncertain due to difficulties in separating new from old sulfur dioxide in daily observations.
Evidence of meridional motion in the summer lower stratosphere adjacent to monsoon regions
Authors: Dunkerton Timothy J.
Published: February 2004

Twenty‐one years of rawinsonde data were used together with 8 years of uninitialized European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses to describe the climatological structure of large‐scale circulations adjacent to monsoon regions in northern and southern hemisphere summers. In the upper troposphere and lower stratosphere, equatorward and poleward motions occur on the eastern and western sides of monsoon regions, respectively. It is shown that significant meridional velocities (>1 ms−1) penetrate the lower stratosphere up to a maximum height of 50–30 mbar. Largest meridional velocities are observed in connection with the Asian monsoon in northern summer. Although evanescent in height, these motions are relatively important for horizontal transport of constituents in the summer lower stratosphere, when planetary waves are otherwise small. Asian and Mexican monsoons in this season are displaced sufficiently far from the equator, in close proximity to the tropopause break, to have a significant role in stratosphere‐troposphere (S/T) exchange. The companion paper by Chen (1995) provides evidence of irreversible S/T exchange in the “upper middle world” during northern summer.
Luminosity characteristics of lightning M components
Authors: Jordan Douglas M. , Idone Vincent P. , Orville Richard E. , Rakov Vladimir A. , Uman Martin A.
Published: February 2004

A high‐speed streak photograph of a natural cloud‐to‐ground lightning return stroke followed by two M components is analyzed. As opposed to the return stroke light pulse whose amplitude and waveshape vary markedly with height, the amplitude and waveshape of one M component light pulse is essentially invariant with height between the cloud base (about 1 km) and ground, while the other M component has a relatively constant light waveshape and a light amplitude that varies somewhat with height. The two M component light pulses, both occurring within about 0.6 ms of the return stroke pulse, exhibit a more or less symmetrical waveshape with a risetime and falltime of the order of many tens of microseconds. For one of the two M components a downward direction of propagation and a corresponding speed of the order of 108 m/s are inferred.
Evaluation of current surface flux parameterization schemes in limited area and large‐scale models using FIFE and HAPEX‐Sahel measurements
Authors: Wai Mickey M.‐K. , Smith Eric A.
Published: February 2004

The performance of four popular surface closure schemes commonly used in limited area and large‐scale numerical models are evaluated using data obtained from the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) which took place in central Kansas during 1987–1989 and the Hydrologic Atmospheric Pilot Experiment in the Sahel (HAPEX‐Sahel) experiment which took place in Niger, West Africa, in 1992. The analysis uses the 21‐day FIFE data set from the 1989 IFC 5 intensive field campaign (July 23 to August 12) and golden day 283 (October 9) from the HAPEX‐Sahel intensive operational period. The surface heat flux closure schemes are based on (1) the bulk aerodynamic method of Laval et al. (1981), (2) the parametric bulk Richardson number scheme of Louis (1979), (3) the modified parametric Louis scheme of Louis et al. (1981), and (4) the level 2 closure scheme of Mellor and Yamada (1982). The analysis of surface flux RMS error statistics over the entire multistation, half hourly, 21‐day FIFE record indicates that all four schemes exhibit significant RMS errors, particularly for unstable conditions, although the day‐to‐day average RMS errors fluctuate considerably. The biases and histograms of RMS error distribution are examined in the context of the parameterization formulations, in order to identify specific weaknesses in the assumptions used in the closure schemes. In the composite diurnal cycle framework for unstable conditions in the FIFE analysis, large RMS errors exceeding 120 W m−2 are found for all four schemes during midday, with daytime fluxes always overestimated. However, when the schemes are tested on an individual day characterized by light wind, dry convection conditions from FIFE, the four schemes continue to overestimate fluxes but with considerably smaller RMS error. This result is corroborated with a similar case from HAPEX‐Sahel. The smaller errors for these cases are consistent with the idealized conditions under which the schemes are calibrated. Recalibration of the original bulk Richardson number closure scheme, based on the FIFE data, leads to a 40% RMS error improvement, suggesting there are alternate approaches that could be used to optimally calibrate the schemes. However, the recalibrated scheme has not been tested independently and thus should not be applied beyond a tallgrass prairie setting. The study concludes with explanations as to why the original calibrations would be expected to overestimate fluxes under unstable conditions given that meteorological conditions generally deviate from the idealized boundary layer situation.
Interactions of HBr, HCl, and HOBr with supercooled sulfuric acid solutions of stratospheric composition
Authors: Abbatt Jonathan P. D.
Published: February 2004

The time‐dependent uptakes of HBr and HCl by supercooled solutions of sulfuric acid have been studied using a low‐temperature flow tube coupled to a mass spectrometer. From these experiments, typical values for the quantity H*D1/2 (where H* is the effective Henry's law constant and D is the liquid phase diffusion coefficient) have been measured to be 1100 and 3.3 (M/atm)(cm2/s)1/2 for HBr and HCl, respectively, on 59.6 wt% sulfuric acid at 210 K. By estimating values for the liquid phase diffusion coefficient, these measurements indicate that HBr is over 2 orders of magnitude more soluble in atmospheric sulfate aerosols than HCl. Similarly, HD1/2 for HOBr on 69.8 wt% sulfuric acid at 228 K has been measured to be 20 (M/atm)(cm2/s)1/2, implying that HOBr, too, is highly soluble in sulfuric acid solutions. By exposing sulfuric acid films simultaneously to HOBr and either HCl or HBr, the liquid phase reactions HOBr + HCl → BrCl + H2O and HOBr + HBr → Br2 + H2O have been studied. The results indicate that the HOBr/HCl heterogeneous reaction may play an important role in the activation of stratospheric chlorine under volcanic aerosol conditions.
Measurements of hydrocarbons, oxygenated hydrocarbons, carbon monoxide, and nitrogen oxides in an urban basin in Colorado: Implications for emission inventories
Authors: Goldan P. D. , Trainer M. , Kuster W. C. , Parrish D. D. , Carpenter J. , Roberts J. M. , Yee J. E. , Fehsenfeld F. C.
Published: February 2004

Concentrations of a wide variety of volatile organic compounds (VOCs) in the C3 to C10 range, CO, NOy (total reactive oxidized nitrogen), SO2, and meteorological parameters were measured concurrently at a site on the western perimeter of Boulder, Colorado, during February 1991. The measurement site, located some 150 m above the Boulder urban basin, receives air masses typifying averaged local sources. The highest hydrocarbon concentrations observed showed little effects of photochemical loss processes and reflect the pattern of the local emission sources. The observed ratios of CO and the VOCs to NOy are compared to those predicted by the 1985 National Acid Precipitation Assessment Program (NAPAP) inventory.These comparisons indicate (1) good agreement for CO/NOY, (2) significant overpredictions by the NAPAP inventory for many of the hydrocarbon to NOY ratios, (3) much more benzene from mobile sources (and less from area sources) than predicted by the NAPAP inventory, and (4) large underpredictions of the light alcohols and carbonyls by the NAPAP inventory. These first two results are in marked contrast to the conclusions of the recent tunnel study reported by Ingalls in 1989. Source profile reconciliation implies substantial input from both a local propane source and gasoline headspace venting.
Nonmethane hydrocarbon and halocarbon distributions during Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange, June 1992
Authors: Blake Donald R. , Blake Nicola J. , Smith Tyrrel W. , Wingenter Oliver W. , Rowland F. Sherwood
Published: February 2004

Aircraft measurements of selected nonmethane hydrocarbon and halocarbon species were made in the lower troposphere of the NE Atlantic near the Azores, Portugal, during June 1992 as part of the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange. In this paper, the impact of continental outflow from both Europe and North America on the study region were assessed. Four main air mass types were characterized from trajectories and trace gas concentrations: clean marine from the Atlantic, and continental air from the Iberian Peninsula, the British Isles and Northern Europe, and North America. Each classification exhibited trace gas concentrations that had been modified en route by photochemical processes and mixing. Comparison with the clean marine boundary layer (MBL) shows that the boundary layer of the predominantly continental air masses were enhanced in hydrocarbons and halocarbons by factors of approximately 2 for ethane, 5 for propane, 2–6 for ethyne and benzene, and 2–3 for C2Cl4. The same air masses also exhibited large ozone enhancements, with 2 to 3 times higher mixing ratios in the continental boundary layer air compared to the clean MBL. This indicates a primarily anthropogenic photochemical source for a significant fraction of the lower tropospheric ozone in this region. Methyl bromide exhibited on average 10–20% higher concentrations in the boundary layer affected by continental outflow than in the clean MBL, and was seen to be enhanced in individual plumes of air of continental origin. This is consistent with significant anthropogenic sources for methyl bromide. In addition, median MBL concentrations of ethene and methyl iodide showed enhancements of approximately a factor of 2 above free tropospheric values, suggesting primarily coastal/oceanic sources for these species.
Upper tropospheric water vapor and cirrus: Comparison of DC‐8 observations, preliminary UARS microwave limb sounder measurements and meteorological analyses
Authors: Newell Reginald E. , Zhu Yong , Browell Edward V. , Ismail Syed , Read William G. , Waters Joe W. , Kelly Kenneth K. , Liu Shaw C.
Published: February 2004

Upper tropospheric water vapor in the tropical West Pacific has been examined by three approaches that were operational during the NASA Pacific Exploratory Mission‐West A (PEM‐West A) in September–October 1991: direct measurement with a Lyman‐α fluorescence instrument on the NASA DC‐8; remote sensing by the microwave limb sounder (MLS) on the Upper Atmosphere Research Satellite (UARS); and deduction of cirrus clouds by differential absorption lidar (DIAL) flown on the DC‐8 together with environmental conditions derived from meteorological analyses made by the European Centre for Medium‐Range Weather Forecasts (ECMWF). Comparison between the DC‐8 direct measurement and the preliminary MLS (12 cases) estimates showed fair agreement with a tendency for MLS to show an overestimate at low mixing ratio values (≤∼200 parts per million by volume). The comparison between the DIAL and the ECMWF analyses (13 cases) showed that cirrus occurred in regions where there was rising motion and relative humidity near 100%. The DIAL observations are from much smaller spatial regions than can be resolved from the ECMWF analyses. The cirrus tops occurred below the tropopause as measured by the vertical ozone gradient in the DIAL data; no cases of tropopause penetration were observed during this season. In most cases the cirrus formed in air of low potential voracity and relatively low ozone. At 150 and 200 hPa the center of the rising motion, as shown by the maximum in the velocity potential pattern based on the ECMWF analysis, is at about 18°N, 145°E in close correspondence to the MLS water vapor mixing ratio maximum deduced for 147 and 215 hPa.
Compositional variations of sea‐salt‐mode aerosol particles from the North Atlantic
Authors: Pósfai Mihály , Anderson James R. , Buseck Peter R. , Sievering Herman
Published: February 2004

Individual sea‐salt‐mode aerosol particles collected during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in June 1992 were studied using transmission electron microscopy in both imaging and analysis modes. The set of eight samples provided an opportunity to compare “clean,” “intermediate,” and “dirty” oceanic aerosols. In the clean samples, major species include NaCl, mixed‐cation (Na, Mg, K, and Ca) sulfates, and in some particles, NaNO3. The same compounds also occur in intermediate samples, but compositional groups can be distinguished that are characterized by low‐ and high‐Cl losses from sea salt. In these samples, most Cl loss is compensated by NaNO3 formation. Several compositional groups occur in the dirty samples; these include, in addition to the particle types in clean and intermediate samples, Na2SO4 (with minor Mg, K, and Ca), (NH4)2SO4, and silicates. The uniform compositions of sea‐salt‐mode particles in the clean samples suggest that the same process was acting on all particles. Their excess sulfate and nitrate probably formed through the oxidation of SO2 in the sea‐salt aerosol water and by reactions between NOx and NaCl. On the other hand, distinct compositional groups in the dirty samples reveal that long‐range transport of continental air masses resulted in the mixing of aerosols that were exposed to different conditions. In addition to O3 oxidation, cloud processing may have contributed to the formation of excess sulfate in these samples.
O3, NOy, and NOx/NOy in the upper troposphere of the equatorial Pacific
Authors: Folkins I. A. , Weinheimer A. J. , Ridley B. A. , Walega J. G. , Anderson B. , Collins J. E. , Sachse G. , Pueschel R. F. , Blake D. R.
Published: February 2004

Two of the DC‐8 flights during the 1991–1992 second Airborne Arctic Stratospheric Expedition (AASE 2) were between California and Tahiti. Extremely abrupt changes in O3 and NOy were observed on both flights as the aircraft crossed the subtropical jet. They indicate that the width of the transition from midlatitude to tropical air in the troposphere can be as short as 1 km. The NOy/O3 ratio was remarkably stable across the transition. We discuss some of the dynamical features associated with the transitions and speculate on the reasons for their abruptness. They occurred south of the subtropical frontal zone and were accompanied by changes in humidity, NOx/NOy, and modest changes in CO, CH4, and CO2. In addition, a chemical model constrained by measurements of the long‐lived species is used to simulate the variation of NOx/NOy along the two flight tracks. Although this model is quite successful at simulating observed NOx/NOy in midlatitude air, it drastically overestimates NOx/NOy in tropical air. The rate at which the model converts NOx to HNO3 via the NO2 + OH reaction is very slow in the upper tropical troposphere because the low O3 concentrations and cold temperatures force most of the NOx to be in the form of NO during the day. We argue that there is an important NO to NO2 pathway in this region not presently included in models, that much of the NOy is in a stable (possibly aerosol) form that is not readily converted to NOx, or that there has been insufficient time since convection for NOx to be released from other more stable forms of NOy. It is important to resolve this discrepancy because present models which have the correct O3 and NOy may overestimate O3 production rates and OH concentrations in the upper tropical troposphere.
Error reduction in NOAA satellite monitoring of the land surface vegetation during FIFE
Authors: Ba Mamoudou B. , Deschamps Pierre‐Yves , Frouin Robert
Published: February 2004

A model of the top‐of‐atmosphere reflectance in the visible and near infrared is presented. The reflectance is parameterized as the product of a constant and normalized bidirectional and temporal functions. Bidirectional and temporal effects are thus separated. The bidirectional function includes isotropic, nonazimuthally dependent, and azimuthally dependent, yet symmetric, components. The temporal function is a development in modified Fourier series. An iterative scheme is used to determine the constants of the model. Applying the scheme to AVHRR data acquired in 1987 over the Konza Prairie during FIFE, 98 and 95% of the variance is explained in the visible and near‐infrared channels, respectively. The remaining variance exhibits no apparent dependence with water vapor and aerosol contents.
Measurements of NO, NOy, CO and O3 and estimation of the ozone production rate at Oki Island, Japan, during PEM‐West
Authors: Jaffe Daniel A. , Honrath Richard E. , Zhang Lizhen , Akimoto Hajime , Shimizu Akira , Mukai Hitoshi , Murano Kentaro , Hatakeyama Shiro , Merrill John
Published: February 2004

Measurements of NO, NOy, CO, and O3 were conducted at Oki Island, 65 km west of the Japanese mainland during September–October 1991. The results show that the Oki Island site is relatively clean with mean (and median) CO and NOy concentrations of 137 (130) ppbv and 713 (505) pptv, respectively. These relatively low concentrations reflect the frequent occurrence of windsfrom the less populated regions to the north during this campaign. During several periods, elevated CO, NOy, and O3 concentrations were associated with transport of pollutants from Japan and Korea. CO and NOy are significantly correlated in the entire data set, reflecting the overall influence of anthropogenic emissions. Mean CO and NOy concentrations show small diurnal cycles with a maximum in the morning and early evening hours. Hourly mean O3 concentrations exhibit a diurnal cycle of amplitude 3.5 parts per billion by volume, with a maximum in the early afternoon attributed to photochemical O3 production. The source of this afternoon O3 enhancement is analyzed using regression analysis of O3 and NOy and of O3 and CO. Both NOy and CO are significantly correlated with O3 during the daytime but are poorly or insignificantly correlated with O3 at night, indicating that upwind photochemistry operating within the previous ∼1 day was responsible for the observed afternoon O3 enhancement. The NOy‐O3 regression analysis indicates formation of ∼9 O3 molecules per NOy molecule reaching Oki Island. The mean and median midday NO concentrations of 55 and 23 parts per trillion by volume, respectively, were sufficient to support net production of O3. Using the results of these measurements and prior modeling studies (Lin et al., 1988), we estimate a “lifetime‐averaged” O3 production efficiency of 10 molecules O3 per NOx molecule. Combined with estimated East Asian NOx emissions for 1987, this indicates an annual O3 production of 1.0 × 1014 g O from photochemistry which is approximately 2 times the annual stratospheric flux in this region. This value must be considered as a rough estimate but is probably accurate to within a factor of 2.
Dynamics of the mesosphere and lower thermosphere as seen by MF radars and by the high‐resolution Doppler imager/UARS
Authors: Khattatov B. V. , Geller M. A. , Yudin V. A. , Hays P. B. , Skinner W. R. , Burrage M. D. , Franke S. J. , Fritts D. C. , Isler J. R. , Manson A. H. , Meek C. E. , McMurray R. , Singer W. , Hoffmann P. , Vincent R. A.
Published: February 2004

This paper presents comparisons between wind measurements in the mesosphere and lower thermosphere by medium‐frequency (MF) radars and by the high‐resolution Doppler imager onboard the Upper Atmosphere Research Satellite (UARS). Because of distinctive observational patterns, time and space averaging, and data processing algorithms, satellites and radars observe the atmosphere from their own perspectives. Because thermal tides are an important part of dynamics in these regions of the atmosphere, tidal determinations from both techniques were given particular attention. Differences and similarities of the two methods are discussed and analyzed.
Validation of hydrogen fluoride measurements made by the Halogen Occultation Experiment from the UARS platform
Authors: Russell James M. , Deaver Lance E. , Luo Mingzhao , Cicerone Ralph J. , Park Jae H. , Gordley Larry L. , Toon Geoffrey C. , Gunson Michael R. , Traub Wesley A. , Johnson David G. , Jucks Kenneth W. , Zander Rudolph , Nolt Ira G.
Published: February 2004

The hydrogen fluoride (HF) molecule is important as a tracer and for study of chlorine input to the stratosphere due to CFC's. This paper describes the characteristics of and data from the Halogen Occultation Experiment (HALOE) HF channel, including steps taken to validate the results. The on‐orbit precision of the HF measurements is shown to be better than 0.04 parts per billion by volume (ppbv) to 0.06 ppbv throughout the stratosphere. The estimated accuracy is 14% to 27% depending on altitude. The internal consistency of the HF measurements is excellent as judged by sunrise/sunset differences and comparison with HALOE CH4 distributions. The mean difference between HALOE HF and correlative balloon underflight measurements is <7% from 5 mbar to 50 mbar. Comparisons with the shuttle ATLAS 1 Atmospheric Trace Molecules Observed by Spectroscopy (ATMOS) data are not as good and there is a systematic difference between HALOE (smaller) and ATMOS (larger) ranging from 10% to 20% at altitudes above the 10‐mbar pressure level. Differences with ATMOS reach as much as 40% or more below the 10‐mbar level. The larger differences in this region are believed to be due to dynamical influences on HF coupled with wide separations in space and time between HALOE and ATMOS measurements. Analysis of HALOE HF pressure versus longitude cross sections shows that obtaining close space and time coincidence can be very important in comparing tracer distributions. Typical characteristics of a pressure versus latitude cross section and polar orthographic projection are also discussed. Comparisons with latitudinal distributions of tracer measurements from previous experiments show similar features like the tropical double minimum due to the semiannual oscillation. All comparisons and analyses conducted provide good confidence in the validity of the HALOE HF results.
Validation of temperature measurements from the improved stratospheric and mesospheric sounder
Authors: Dudhia Anu , Livesey Nathaniel
Published: February 2004

Atmospheric temperature measurements from the improved stratospheric and mesospheric sounder (ISAMS) are evaluated. Flown on the Upper Atmosphere Research Satellite (UARS), ISAMS obtained 180 days of science data between September 26, 1991 and July 29, 1992. Typically, over 2600 temperature profiles/day were retrieved, spaced every 200 km along the limb‐viewing track and nominally extending from 100 to 0.01 mbar (15–80 km). The latitude coverage ranged from 80°S to 80°N, depending on the particular ISAMS/UARS viewing geometry on any day. UARS is in a near‐Sun‐synchronous orbit, so that while the 15 orbits/d are spaced approximately every 24° longitude around the equator, the sampled local solar time actually changes by 20 min/d. The ISAMS temperature retrieval process is outlined and the various products are described. A detailed error budget for the retrieval is presented and comparisons are made with temperature measurements from other sources. Finally, a table is provided summarizing the best estimates of ISAMS temperature bias and precision. The results suggest a general cold bias of around 1 K in the stratospheric temperatures, with a superimposed 2–3 K warm bias associated with the densest part of the Pinatubo aerosol cloud. The precision of individual profiles is ±2 K throughout the stratosphere but falls off in the mesosphere to about ±10 K at 80 km. The error bars produced by the retrieval appear to be reasonable (although slightly pessimistic) estimates of the precision.
Possible sources and preferred pathways for biogenic and non‐sea‐salt sulfur for the high Arctic
Authors: Hopke P. K. , Barrie L. A. , Li S.‐M. , Cheng M.‐D. , Li C. , Xie Y.
Published: February 2004

Sulfate is a major constituent observed in Arctic haze. Sulfur sources include anthropogenic, biogenic, and other natural sources. Previous studies have examined the concentrations and temporal variability of the concentrations of methanesulfonic acid (MSA) and sulfate (SO4=) at Alert, Northwest Territories, Canada. A receptor modeling method called the potential source contribution function (PSCF) combines the concentration data for these species measured in 7‐day samples continuously collected between 1980 and 1991 with meteorological information in the form of air parcel back trajectories into conditional probability maps indicating the possible source areas and/or the preferred pathways that give rise to the observed high‐concentration samples. After examination of the time series for MSA and SO4=, the data were segregated into time periods representing the spring, summer, and winter months and the PSCF analyses performed based on criterion values of the annual average species concentration. The potential source contribution method has been found to be effective in identifying possible source locations and the preferred pathways of MSA and SO4= in samples collected at Alert. Two concentration peaks are typically observed in the time series for MSA. The time series for SO4= is quite different from the series for MSA. The SO4= series only has peaks in the winter caused primarily by anthropogenic emissions. It was found that different regions of the North Atlantic Ocean contribute to the observed MSA concentrations during these different periods in agreement with prior hypotheses. Sources areas for sulfate during the summer and MSA during the winter can only be observed by changing the criterion value to the average during the period.
Validation of measurements of carbon monoxide from the improved stratospheric and mesospheric sounder
Authors: López‐Valverde M. A. , López‐Puertas M. , Remedios J. J. , Rodgers C. D. , Taylor F. W. , Zipf E. C. , Erdman P. W.
Published: February 2004

Carbon monoxide abundances in the middle atmosphere are retrieved from infrared measurements of the emission of this molecule at 4.6 μm taken by the improved stratospheric and mesospheric sounder (ISAMS) onboard the Upper Atmosphere Research Satellite. In addition to a limited signal‐to‐noise ratio, the measured radiances include significant contamination by other compounds in the stratosphere and show clear non‐local thermodynamic equilibrium effects in the mesosphere which also affect the stratospheric limb views. The application of the ISAMS retrieval method to these measurements and the particular method followed to deal with these difficulties are described. The actions carried out to understand and validate the obtained CO abundances are detailed. They include analysis of the radiances, sensitivity studies of the product to retrieval parameters, evaluation of the main sources of systematic and random errors, and comparisons with theoretical model predictions and with the few correlative measurements available. The gross features observed in the CO distribution present good agreement with dynamical‐chemical models of the middle atmosphere. The aspects of the retrieval that need further improvement are identified, and the global quality of the database and the expectations for its scientific use are discussed.
An intercomparison of wet precipitation scavenging schemes and the emission rates of 222Rn for the simulation of global transport and deposition of 210Pb
Authors: Lee H. N. , Feichter J.
Published: February 2004

We simulated the transport of 222Rn and its progeny 210Pb using a global three‐dimensional atmospheric tracer transport model. The purpose of this study was to understand the effects of wet deposition scavenging processes and the emission rate of 222Rn on the global transport and deposition of 210Pb. We examined the deposition of 210Pb aerosols due to wet scavenging in stratiform and convective precipitation. Four schemes for wet precipitation scavenging removal, and two assumed distributions of the emission rate of 222Rn, were studied and tested. One was assumed to have a global constant rate and in the other the constant rate was assumed to have changed with latitude. The results of the model simulations were compared with archived radionuclide data measurements from the Environmental Measurements Laboratory's global network of sampling stations. The model‐calculated global distributions of the yearly mean of the surface air concentrations of 222Rn and 210Pb, and the yearly mean total deposition of 210Pb for 1986 data for each wet precipitation scavenging scheme studied are presented. For each scheme, we have also compared yearly mean total deposition and monthly averages of the surface air concentrations and the vertical distributions of 210Pb with the measurements. We found that the Walton et al. (1988) scheme produces the best results of the four schemes studied. Although this scheme, when utilizing a constant emission rate, gives satisfactory results, use of an emission rate that changes with latitudes improves the bias of this scheme, particularly at high northern latitude sites. The model comparisons with the measurements helped us to validate and improve the model. This atmospheric tracer transport model can be used for the simulation of other radionuclide and nonradionuclide tracers for future studies related to global climate change.
Balancing the atmospheric hydrologic budget
Authors: Chen Shyh‐Chin , Norris Charles L. , Roads John O.
Published: February 2004

The atmospheric hydrologic budget in an idealized general circulation model is difficult to balance, especially if samples are too infrequent, mainly because of an inaccurately determined moisture flux divergence. Although the climatology can be reasonably derived by considering longer time averages, the aliased anomalous moisture divergences due to insufficient sampling are intrinsic and cannot be removed; the effect is noticeable and detrimental out to seasonal timescales. Increased temporal resolution or even continuous accumulations are really required. Lack of temporal resolution also affects forecast skill as well as the perceived importance of the precipitable water tendency. Current atmospheric hydrologic analyses of moisture fluxes and even satellite precipitation observations may have similar sampling problems. We recommend that modern analyses should provide more frequently sampled or even continuously accumulated hydrologic quantities, just as precipitation is currently provided.