bluuebunny/crossref_metadata_2025 huggingface dataset:
Land‐sea geometry and its effect on monsoon circulations
Authors: Dirmeyer Paul A.
Published: February 2004

The role of land‐sea geometry in determining the existence and character of monsoon circulations is examined using an atmospheric general circulation model with land surface properties represented by the simplified simple biosphere model. Idealized land‐sea distributions are used to examine the effects of the latitude of continental coastlines, the meridional and zonal extent of continents, the shape of continents, and the presence of orography on circulation in the tropics and subtropics. It is found that the latitude of the continent is critical to the establishment of a distinct seasonality of precipitation and a summer monsoon circulation. Low‐latitude positions of the continent lead to landlocked precipitation maxima, and poleward positions lead to a Mediterranean (winter monsoon) climate. In every case, the subsiding branch of the Hadley cell at continental longitudes locks over some part of the land. Variations in the meridional extent of land affect the strength of the Hadley cell and the degree of seasonality in the climate over land. The extension of a subtropical continent into the tropics is critical for establishing heavy convective rainfall over land in the summer. When tropical peninsulas are added to a subtropical continent, the distribution of moisture and rain over semi‐arid and arid regions of the original continent are affected. When a broad mountain of 1200 m maximum elevation is present on the idealized continent, there is a band of increased precipitation to the south and east of the mountain with a systematic decrease to the south, north, and west of the band.
Carbon cycling in the Kuparuk basin: Plant production, carbon storage, and sensitivity to future changes
Authors: Hobbie J. E. , Kwiatkowski B. L. , Rastetter E. B. , Walker D. A. , McKane R. B.
Published: February 2004

The Marine Biological Laboratory General Ecosystem Model was calibrated for an arctic tussock tundra system using data from long‐term observations and experiments at Toolik Lake, Alaska. These experiments include the effects of changes in temperature, light, CO2, and nutrients, so the model could be applied to five regions comprising the entire Kuparuk River basin. Net primary production, averaged for the entire basin, was 92 g C m−2 yr−1. A 150 year simulation of carbon storage under a doubling of CO2 (slow ramp‐up) and a temperature increase of 3.5°C gave an estimate of +400 g C m−2 when soil moisture increased and +500 g C m−2 when soil moisture decreased. Drier soils stimulated decomposition producing an increase in nitrogen availability; the increased N led to increased net primary production. If this result is applicable to other arctic ecosystems, then it is unlikely that warming will enhance carbon loss to the atmosphere to further enhance warming.
Long‐term trend of ozone column over the Indian region
Authors: Chakrabarty D. K. , Peshin S. K. , Pandya K. V. , Shah N. C.
Published: February 2004

Ozone observations taken during the past 23–45 years by Dobson spectrophotometer at six stations of India have been analyzed to examine its long‐term trend over this subcontinent. These stations are Kodaikanal (10°N, 77°E), Pune (18°N, 74°E), Mount Abu/Ahmedabad (24°N, 72°E), Varanasi (25°N, 82°E), New Delhi (28°N, 77°E), and Srinagar (34°N, 74°E). An increasing trend of this species over the years has been noticed at all the places, except at Varanasi, where a decreasing trend has been found. The Nimbus 7 total ozone mapping spectrometer data at all the six stations have been compared with the Dobson data. Good agreement is found at all the stations except at Kodaikanal and Ahmedabad. The cause of these trends could be attributed, partly, to the trends of ozone in the troposphere.
Atmospheric methane between 1000 A.D. and present: Evidence of anthropogenic emissions and climatic variability
Authors: Etheridge D. M. , Steele L. P. , Francey R. J. , Langenfelds R. L.
Published: February 2004

Atmospheric methane mixing ratios from 1000 A.D. to present are measured in three Antarctic ice cores, two Greenland ice cores, the Antarctic firn layer, and archived air from Tasmania, Australia. The record is unified by using the same measurement procedure and calibration scale for all samples and by ensuring high age resolution and accuracy of the ice core and firn air. In this way, methane mixing ratios, growth rates, and interpolar differences are accurately determined. From 1000 to 1800 A.D. the global mean methane mixing ratio averaged 695 ppb and varied about 40 ppb, contemporaneous with climatic variations. Interpolar (N‐S) differences varied between 24 and 58 ppb. The industrial period is marked by high methane growth rates from 1945 to 1990, peaking at about 17 ppb yr−1 in 1981 and decreasing significantly since. We calculate an average total methane source of 250 Tg yr−1 for 1000–1800 A.D., reaching near stabilization at about 560 Tg yr−1 in the 1980s and 1990s. The isotopic ratio, δ13CH4, measured in the archived air and firn air, increased since 1978 but the rate of increase slowed in the mid‐1980s. The combined CH4 and δ13CH4 trends support the stabilization of the total CH4 source.
Air‐surface exchange of nonmethane organic compounds at a grassland site: Seasonal variations and stressed emissions
Authors: Fukui Yoshiko , Doskey Paul V.
Published: February 2004

Emissions of nonmethane organic compounds (NMOCs) were measured by a static enclosure technique at a grassland site in the midwestern United States during the growing seasons over a 2‐year period. A mixture of nonmethane hydrocarbons (NMHCs) and oxygenated hydrocarbons (OxHCs) was emitted from the surface at rates exhibiting large seasonal and year‐to‐year variations. The average emission rate (and standard error) of the total NMOCs around noontime on sunny days during the growing seasons for the 2‐year period was 1,300±170 μg m−2 h−1 (mass of the total NMOCs per area of enclosed soil surface per hour) or 5.5±0.9 μg g−1 h−1 (mass of the total NMOCs per mass of dry plant biomass in an enclosure per hour), with about 10% and 70% of the emissions being composed of tentatively identified NMHCs and OxHCs, respectively. Methanol was apparently derived from both the soil and vegetation and exhibited an average emission rate of 460±73 μg m−2 h−1 (1.4±0.2 μg g−1 h−1), which was the largest emission among the NMOCs. The year‐to‐year variation in the precipitation pattern greatly affected the NMOC emission rates. Emission rates normalized to biomass density exhibited a linear decrease as the growing season progressed. The emission rates of some NMOCs, particularly the OxHCs, from vegetation subjected to hypoxia, frost, and physical stresses were significantly greater than the average values observed at the site. Emissions of monoterpenes (α‐ and β−pinene, limonene, and myrcene) and cis‐3‐hexen‐l‐ol were accelerated during the flowering of the plants and were much greater than those predicted by algorithms that correlated emission rates with temperature. Herbaceous vegetation is estimated to contribute about 40% and 50% of the total NMOC and monoterpene emissions, respectively, in grasslands; the remaining contributions are from woody species within grasslands. Contributions of isoprene emissions from herbaceous vegetation in grasslands are negligible. Grasslands are estimated to contribute about 10% of the total biogenic NMOC emissions in the United States.
A one‐dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer: 3. Numerical methods and comparisons with exact solutions
Authors: Gelbard Fred , Fitzgerald James W. , Hoppel William A.
Published: February 2004

We present the theoretical framework and computational methods that were used by Fitzgerald et al. [this issue (a), (b)] describing a one‐dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer. The concepts and limitations of modeling spatially varying multicomponent aerosols are elucidated. New numerical sectional techniques are presented for simulating multicomponent aerosol growth, settling, and eddy transport, coupled to time‐dependent and spatially varying condensing vapor concentrations. Comparisons are presented with new exact solutions for settling and particle growth by simultaneous dynamic condensation of one vapor and by instantaneous equilibration with a spatially varying second vapor.
A one‐dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer: 2. Model application
Authors: Fitzgerald James W. , Marti James J. , Hoppel William A. , Frick Glendon M. , Gelbard Fred
Published: February 2004

The dynamics of aerosols in the marine boundary layer (MBL) are simulated with the marine boundary layer aerosol model (MARBLES), a one‐dimensional, multicomponent sectional aerosol model [Fitzgerald et al., this issue; Gelbard et al., this issue]. First, to illustrate how the various aerosol processes influence the particle size distribution, the model was run with one or two processes operating on the same initial size distribution. Because of current interest in the effects of cloud processing of aerosols and exchange of aerosols with the free troposphere (FT) on marine aerosol size distributions, these two processes are examined in considerable detail. The simulations show that the effect of cloud processing (characteristic double‐peaked size distribution) in the upper part of the MBL is manifested at the surface on a timescale that is much faster than changes due to exchange with the FT, assuming a typical exchange velocity of 0.6 cm s−1. The model predicts that the FT can be a significant source of particles for the MBL in the size range of the cloud‐processing minimum, between the unactivated interstitial particles and the cloud condensation nuclei (CCN) which have grown as a result of conversion of dissolved SO2 to sulfate in cloud droplets. The model was also used to simulate the evolution of the aerosol size distribution in an air mass advecting from the east coast of the United States out over the ocean for up to 10 days. The modification of a continental aerosol size distribution to one that is remote marine in character occurs on a timescale of 6–8 days. Nucleation was not observed in the base case 10‐day advection simulation which assumed rather typical meteorological conditions. However, significant nucleation was predicted under a more favorable (albeit, atypical) combination of conditions which included significant precipitation scavenging (5 mm h−1 of rain for 12 hours), colder temperatures by 10°C (283 K at the surface decreasing to 278 K at 1000 m) and a high DMS flux (40 μmol m−2 d−1). In a test of model self initialization, long‐term (8–10 days) predictions of marine aerosol size distributions were found to be essentially independent of initial conditions.
Interannual variability in the troposphere and stratosphere of the southern hemisphere winter
Authors: Kuroda Yuhji , Kodera Kunihiko
Published: February 2004

Interannual variability in the tropospheric and stratospheric circulation of the southern‐hemisphere winter is studied over the 16‐year period from 1979 to 1994. In particular, the interannual mode of variability in the seasonal march from autumn to spring is investigated by means of a multiple empirical orthogonal function analysis. The extracted dominant mode of variability is characterized by the poleward and downward propagation of anomalous zonal‐mean zonal winds, accompanied by changes in wave activity. The overall features of the variability are similar to those found in the northern hemisphere except that the entire sequence of evolution is closely locked to the annual cycle and requires a longer period of 6 months. The time coefficients of this mode exhibit a very clear biennial oscillation and increasing trend. A similar spatial pattern of variability is also found in the simulated data of an atmospheric general circulation model with climalogical sea surface temperatures as the lower boundary conditions. The similarities in the time evolution of the spatial pattern suggest that this mode is essentially an internal mode of variability in the atmosphere, which is modulated by external conditions.
Physico‐chemical modeling of the First Aerosol Characterization Experiment (ACE 1) Lagrangian B: 2. DMS emission, transport and oxidation at the mesoscale
Authors: Mari Céline , Suhre Karsten , Bates Timothy S. , Johnson James E. , Rosset Robert , Bandy Alan R. , Eisele Fred L. , Lee Mauldin R. , Thornton Donald C.
Published: February 2004

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 R/V 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 (R2 = 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 R/V 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.
Sensitivity analysis of a mixed‐phase chemical mechanism using automatic differentiation
Authors: Zhang Yang , Bischof Christian H. , Easter Richard C. , Wu Po‐Ting
Published: February 2004

A sensitivity analysis of a comprehensive mixed‐phase chemical mechanism is conducted under a variety of atmospheric conditions. The local sensitivities of gas and aqueous phase species concentrations with respect to a variety of model parameters are calculated using the novel automatic differentiation ADIFOR tool. The main chemical reaction pathways in all phases, interfacial mass transfer processes, and ambient physical parameters that affect tropospheric O3 formation and O3‐precursor relations under all modeled conditions are identified and analyzed. The results show that the presence of clouds not only reduces many gas phase species concentrations and the total oxidizing capacity but alters O3‐precursor relations. Decreases in gas phase concentrations and photochemical formation rates of O3 can be up to 9% and 100%, respectively, depending on the preexisting atmospheric conditions. The decrease in O3 formation is primarily caused by the aqueous phase reactions of O2− with dissolved HO2 and O3 under most cloudy conditions.
Daytime and nighttime detection of mineral dust over desert using infrared spectral contrast
Authors: Wald A. E. , Kaufman Y. J. , Tanré D. , Gao B.‐C.
Published: February 2004

Desert dust has a potentially strong effect on climate and climate forcing as evident from satellite data, yet its detection close to its sources over deserts and semidesert regions is difficult. The lifted dust often has the same mineral composition as the surface sand left behind. The main consistent difference between airborne dust and surface sand is particle size. This difference is used here to develop a remote sensing technique for the detection of dust over desert. The technique uses two infrared channels that will be on the Earth Observing System (EOS) moderate resolution imaging spectroradiometer (MODIS). It is based on measurements and modeling of the thermal infrared spectrum of silicate and carbonate minerals that show strong differences between the thermal properties of the smaller dust particles (diameter of 2–5 μm) and the larger sand particles (diameter >70 μm). In particular, the emissivity of quartz increases with the particle size at 11 μm and decreases at 8.6 μm. This different behavior allows use of these two MODIS channels to distinguish between variations of the dust temperature and surface temperature from the variation in the loading of the smaller dust particles in the atmosphere. We report simulations of the technique for day and night remote sensing and apply it to high resolution infrared sounder (HIRS) data which is validated against ground‐based measurements by Sun photometers. The technique is found to be sensitive to the dust loading over sand surfaces and not very sensitive to the dust height.
Thermal band selection for the PRISM instrument: 3. Optimal band configurations
Authors: Caselles V. , Rubio E. , Coll C. , Valor E.
Published: February 2004

The European Space Agency (ESA) is presently supporting the Processes Research by Imaging Space Mission (PRISM), a project whose aim is the accurate retrieval of land surface temperature (LST) using a new thermal radiometer. Two previous papers have already addressed some aspects of the design and performance requirements for this thermal sensor: the analysis of different algorithms for emissivity‐temperature decoupling and the techniques for atmospheric and emissivity correction. This paper focuses on the selection of the most appropriate spectral channels for the PRISM thermal instrument. For this purpose, a theoretical argument was first used to obtain a preliminary selection of potential spectral channels in the 8.0–12.5 μm region. A simulation analysis, which contained a global database made up of 6120 surface‐atmosphere conditions, was subsequently performed to determine the LST retrieval error for each of the preliminary combinations of channels. Results indicate that channel configurations consisting of two separate bands in the 10.0–12.5 μm atmospheric window are the most suitable for LST retrieval. However, there is no single pair of optimal bands: there are 22 possible optimal band configurations which produce the minimum error in LST estimates (±0.9 K). Nevertheless, an alternative configuration was also found: the 8.5–9.0 μm band or the 8.6–9.1 μm band as channel 1 combined with the 8.0–8.5 μm band as channel 2 enable a LST retrieval with an error of ±1.1 K.
Ozone in the marine boundary layer over the tropical Indian Ocean
Authors: Lal S. , Naja M. , Jayaraman A.
Published: February 2004

Surface measurements of ozone, aerosols (in 10 different size ranges), carbon monoxide, and methane are made during a ship cruise over the Indian Ocean from January 5 to February 3, 1996. These results have been used to study the variabilities in their distributions and mixing of the continental and pristine air masses over the tropical oceanic region. Concentrations of ozone, aerosols, and carbon monoxide show decreasing trends from coastal region to the open ocean region. During this cruise, influence of the continental polluted air from the South Asian region was observed, resulting in high levels of these species in the open ocean. Incidence of encountering extremely low levels of ozone has been observed near the equator. These low and high values of ozone, aerosols etc. are supported by the back trajectory analyses made using European Centre For Medium‐Range Weather Forecasts (ECMWF) meteorological parameters. These results confirm the transport of the continental air mass down to the equator over the Indian Ocean. A simple photochemical box model has been used to estimate the ozone production potential (OPP). The discrepancies in the observed and estimated ozone diurnal variation suggest a need for better understanding of the processes.
Factors affecting variation in CH4 emission from paddy soils grown with different rice cultivars: A pot experiment
Authors: Watanabe Akira , Kimura Makoto
Published: February 2004

The growth of rice plants greatly influences CH4 emission from paddy fields through the supply of organic materials such as root exudates and sloughed tissues, the release of oxygen to the root environment, and the transfer of CH4 from the rhizosphere into the atmosphere through the aerenchyma. In the present pot experiments, the effects of the release of water‐soluble organic substances from roots, the air space in roots, and the CH4‐oxidizing capacity of roots on intervarietal differences in CH4 emission were examined using three Japonica type cultivars (Norin 25, Nipponbare, and Aoinokaze), which differ in morphological properties. The CH4 emission rates varied among the cultivars from mid‐July (tillering stage) to the beginning of September (heading stage).Total CH4 emission throughout the rice growth period was largest for Norin 25, followed by Nipponbare, and Aoinokaze. In August, the rate of release of water‐soluble organic substances from roots was largest for Norin 25. The air space in roots was also largest in Norin 25 and least in Aoinokaze. The stable carbon isotopic ratios (δ13C) of CH4 in roots were 3–10‰ higher than those in soil in August. The difference in δ13C values of CH4 between roots and soil was largest for Aoinokaze and smallest for Norin 25. In September, the difference in δ13C values of CH4 between roots and soil became small (2–3‰). These findings suggest that the proportion of CH4 oxidation in the rhizosphere was largest in the cultivar which emitted the smallest amount of CH4 and that the proportion became smaller with continued plant growth.
Role of large scale moist dynamics in November 1–5, 1994, hazardous Mediterranean weather
Authors: Krichak S. O. , Alpert P.
Published: February 2004

Investigation of the role of moist dynamics in the atmospheric processes during the abnormally intensive stormy period of November 1–5, 1994, over the Mediterranean region is presented. Analysis focuses on the eastern Mediterranean area employing 96‐hour model predictions over the Mediterranean region with the Florida State University (FSU) global spectral model. Sensitivity simulations differ only by prescribing the initial moisture fields in the selected regions located in the Arabian Sea, Red Sea, and over large areas in the low and high latitudes. Both the tropospheric trajectories and the model tests suggest that the heavy rains over the eastern Mediterranean were associated with unusually intensive propagation of air masses from the Arabian Sea region, which took place before and during the first 24 hours of the period. Air masses from the Arabian Sea participated also in the intensive developments in Italy and southern France on November 5, 1994. According to the model simulations the convective processes over the equatorial Africa play a major role in the developments. Also, the intensification of the upper tropospheric westerly winds due to the convection over the equatorial Africa stimulates the northward extension of the Red Sea trough which consequently diminishes the moisture influx for the tropical convection and therefore seems to serve as a negative feedback.
A distributed thermal model for calculating soil temperature profiles and depth of thaw in permafrost regions
Authors: Hinzman Larry D. , Goering Douglas J. , Kane Douglas L.
Published: February 2004

A spatially distributed thermal model has been developed that simulates thermal processes at the surface of the tundra, within the active layer, and in the underlying permafrost. This model was developed and applied to simulate processes on the Kuparuk River watershed on the North Slope of Alaska. Gridded meteorological data came from seven stations. Meteorologic data to calculate the surface energy balance at each of the nodes were distributed across the watershed using kriging. The kriged air temperature was also adjusted to account for elevation differences using the dry or wet adiabatic lapse rate as appropriate, and incident shortwave radiation was adjusted to consider slope effects. The equations describing the thermal processes of the surface energy balance were solved simultaneously for the surface temperature. This calculated surface temperature was then used in the subsurface finite element formulation to calculate the temperature profile and depth of thaw in the soil. Thermal properties of the soil were estimated spatially on the basis of measurements collected in typical landform vegetation units and then distributed on the basis of a vegetation map. Performance of the model was judged on the basis of comparison to measurements of soil temperatures and thaw depths. The model performs quite well in areas where subsurface thermal properties are well known. The model explains greater than 80% of variance at the surface when comparing predicted subsurface temperatures versus measured soil temperatures, and it increases in performance at greater depths. The model explains 82% of variance when comparing predicted thaw depths versus thaw depths measured over 1 km2 grids.
Lifetimes and global warming potentials for dimethyl ether and for fluorinated ethers: CH3OCF3 (E143a), CHF2OCHF2 (E134), CHF2OCF3 (E125)
Authors: Good D. A. , Francisco J. S. , Jain A. K. , Wuebbles D. J.
Published: February 2004

Using recent kinetic data, two‐dimensional (2‐D) chemical‐transport modeling of the atmospheric lifetimes of dimethyl ether and fluorinated ethers CH3OCF3 (E143a), CHF2OCHF2 (E134), and CHF2OCF3 (E125) shows that E134 and E125 have substantially larger lifetimes than previously estimated. Dimethyl ether has a short atmospheric lifetime of 5.1 days and a relatively insignificant radiative forcing leading to a relatively low global warming potential. Increasing fluorination is accompanied by slower rates of reaction with hydroxyl radical and ultimately longer lifetimes. E143a, E134, and E125 were found to have lifetimes of 5.7, 29.7, and 165 years, respectively. In addition, our work uses ab initio methodology to determine IR absorption cross sections for each ether. Our study finds that E134 and E125 have significant infrared absorption and thus relatively high radiative forcing values. These two properties together yield global warming potentials for E134 and E125 of 5720 and 14,000, respectively, integrated over a 100 year period.
Optical properties of Saharan dust during ACE 2
Authors: Smirnov A. , Holben B. N. , Slutsker I. , Welton E. J. , Formenti P.
Published: February 2004

The Aerosol Robotic Network (AERONET) of automatic Sun/sky radiometers collected data on Tenerife, Canary Islands, in June‐July 1997 during the second Aerosol Characterization Experiment (ACE 2). Initially, two instruments were deployed at Izana observatory (2360 m above sea level) and one at a mountain station Teide (3570 m above sea level). Repeatability of the calibration constants (Langley method) for all instruments was less than 0.5%. Aerosol optical depths measured by colocated sunphotometers and column size distributions, retrieved from spectral sky radiance data, were in good agreement. Later, one of the instruments was relocated at sea level. On July 8,17, and 25, Saharan dust outbreaks were observed. Diurnal variations of spectral aerosol optical depth are presented. Relative diurnal stability of Saharan dust optical properties has been observed. Volume size distributions at various heights (sea level and 2360 m above sea level) show that the main portion of coarse particles is situated above 2360 m level. Measurements on July 25 showed how incoming dust has changed the magnitude and spectral dependence of aerosol optical depth and volume spectra of columnar aerosol. Mean optical depth and Angstrom parameter values for Saharan dust outbreaks during the ACE 2 experiment agree well with the Atlantic Ocean and Bermuda data obtained during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) in July 1996, as well as with previously reported Atlantic Ocean results. Also, there is a good agreement between ACE 2 data for Saharan air masses and data obtained on certain sites of the AERONET network.
Characterization of the Nashville urban plume on July 3 and July 18, 1995
Authors: Nunnermacker L. J. , Imre D. , Daum P. H. , Kleinman L. , Lee Y.‐N. , Lee J. H. , Springston S. R. , Newman L. , Weinstein‐Lloyd J. , Luke W. T. , Banta R. , Alvarez R. , Senff C. , Sillman S. , Holdren M. , Keigley G. W. , Zhou X.
Published: February 2004

This paper reports results from the Southern Oxidants Study field campaign designed to characterize the formation and distribution of ozone and related species in the Nashville urban region. Data from several airborne platforms as well as surface observations on July 3 and 18 are examined to gain insight into the factors that control O3 formation rates and concentrations in the regional plumes. On both days, well‐defined urban and power plant plumes were sampled. Utilizing both aircraft and surface data, a detailed kinetic analysis of the chemical evolution of the urban plume is performed to derive NOx lifetime, ozone production efficiency, OH concentration, HNO3 dry deposition rate, and the relative importance of natural and anthropogenic hydrocarbons to O3 production. Analysis of the urban plume data revealed a very active photochemical system (average [OH] ∼1.2×107 molecules cm−3) which consumed 50% of the NOx within approximately 2 hours, at an ozone production efficiency of 2.5 to 4 molecules for each molecule of NOx. Anthropogenic hydrocarbons provided approximately 44% of the fuel for ozone production by the urban plume. The dry deposition rate for HNO3 in the urban plume was estimated to be of the order of 5 to 7 cm s−1.
Modeling ambient air temperature time series using neural networks
Authors: Mihalakakou G. , Santamouris M. , Asimakopoulos D.
Published: February 2004

A neural network approach is used in this study to analyze and model the ambient air temperature time series. The model's predictions can be very useful in Meteorology, atmospheric sciences, and in energy applications such as the control of conventional and passive cooling systems in order to achieve thermal comfort inside buildings. The future hourly values of ambient temperature for several years were predicted, using multiple‐layer backpropagation networks, by extracting knowledge from its past values. The results were tested using various sets of nontraining measurements, and it was found that predicted values correspond well to the actual values. Furthermore, “multilag” output predictions were performed using the predicted values to the input database in order to model future air temperature values with sufficient accuracy. The neural network model predictions were compared with the results of an autoregressive linear model. It was found that the neural network model makes significantly better predictions than the autoregressive model.
Spurious aerosol measurements when sampling from aircraft in the vicinity of clouds
Authors: Weber R. J. , Clarke A. D. , Litchy M. , Li J. , Kok G. , Schillawski R. D. , McMurry P. H.
Published: February 2004

Extensive airborne measurements of aerosol particles in a pristine marine region were made during the first Aerosol Characterization Experiment (ACE 1) from November 15 to December 14, 1995. During this study, high concentrations of condensation nuclei (CN) were frequently observed both near and within clouds. Near clouds, in the absence of liquid water, Clarke et al. [1998] have reported that high CN levels were from new particle formation by homogeneous nucleation. Here we show, however, that within clouds, elevated CN concentrations were not authentic, but instead a sampling artifact, likely related to fragmentation of cloud drops impacting the aerosol inlet. By themselves, these fragments were often indistinguishable from ambient particles. Spurious CN from fragmenting droplets were observed at temperatures down to roughly −20°C and spanned a broad size range, with diameters down to 3 nm. Comparison of two different sized isokinetic aerosol inlets showed that inlets with smaller openings produce higher droplet fragment concentrations. The mechanism for producing these particles is not completely understood. Although fragmentation appeared to be the primary mechanism, for one instrument, an additional spurious source, correlated with liquid water, was observed when ambient temperatures were below −5°C. These findings show that care must be taken when interpreting airborne aerosol measurements in regions of liquid water. This is particularly pertinent to studies of new particle formation by homogeneous nucleation in the vicinity of clouds.
Analysis of simulated advanced spaceborne thermal emission and reflection (ASTER) radiometer data of the Iron Hill, Colorado, study area for mapping lithologies
Authors: Rowan Lawrence C.
Published: February 2004

The advanced spaceborne thermal emission and reflection (ASTER) radiometer was designed to record reflected energy in nine channels with 15 or 30 m resolution, including stereoscopic images, and emitted energy in five channels with 90 m resolution from the NASA Earth Observing System AMI platform. A simulated ASTER data set was produced for the Iron Hill, Colorado, study area by resampling calibrated, registered airborne visible/infrared imaging spectrometer (AVIRIS) data, and thermal infrared multispectral scanner (TIMS) data to the appropriate spatial and spectral parameters. A digital elevation model was obtained to simulate ASTER‐derived topographic data. The main lithologic units in the area are granitic rocks and felsite into which a carbonatite stock and associated alkalic igneous rocks were intruded; these rocks are locally covered by Jurassic sandstone, Tertiary rhyolitic tuff, and colluvial deposits. Several methods were evaluated for mapping the main lithologic units, including the unsupervised classification and spectral curve‐matching techniques. In the five thermalinfrared (TIR) channels, comparison of the results of linear spectral unmixing and unsupervised classification with published geologic maps showed that the main lithologic units were mapped, but large areas with moderate to dense tree cover were not mapped in the TIR data. Compared to TIMS data, simulated ASTER data permitted slightly less discrimination in the mafic alkalic rock series, and carbonatite was not mapped in the TIMS nor in the simulated ASTER TIR data. In the nine visible and near‐infrared channels, unsupervised classification did not yield useful results, but both the spectral linear unmixing and the matched filter techniques produced useful results, including mapping calcitic and dolomitic carbonatite exposures, travertine in hot spring deposits, kaolinite in argillized sandstone and tuff, and muscovite in sericitized granite and felsite, as well as commonly occurring illite/muscovite. However, the distinction made in AVIRIS data between calcite and dolomite was not consistently feasible in the simulated ASTER data. Comparison of the lithologie information produced by spectral analysis of the simulated ASTER data to a photogeologic interpretation of a simulated ASTER color image illustrates the high potential of spectral analysis of ASTER data to geologic interpretation.
Global patterns of lake ice phenology and climate: Model simulations and observations
Authors: Walsh Sarah E. , Vavrus Stephen J. , Foley Jonathan A. , Fisher Veronica A. , Wynne Randolph H. , Lenters John D.
Published: February 2004

Lake ice phenology parameters (dates of ice onset and thaw) provide an integrative climatic description of autumn to springtime conditions. Interannual variations in lake ice duration and thickness allow estimates of local climatic variability. In addition, long‐term changes in lake ice phenology may provide a robust indication of climatic change. The relationship between lake ice and climate enables the use of process‐based models for predicting the dates of freeze‐up and thaw. LIMNOS (Lake Ice Model Numerical Operational Simulator) is one such model, which was originally designed to simulate the ice phenology of several lakes in southern Wisconsin. In this study, LIMNOS is modified to run globally on a 0.5° by 0.5° latitude‐longitude grid using average monthly climate data. We initially simulate the ice phenology for lakes of 5‐ and 20‐m mean depths across the northern hemisphere to demonstrate the effects of lake depth, latitude, and elevation on ice phenology. To evaluate the results of LIMNOS we also simulate the ice phenology of 30 lakes across the northern hemisphere which have long‐term ice records. LIMNOS reproduces the general geographic patterns of ice‐on and ice‐off dates, although ice‐off dates tend to occur later in the model. Lakes with extreme depths, surface areas, or precipitation are simulated less accurately than small, shallow lakes. This study reveals strengths and weaknesses of LIMNOS and suggests aspects which need improving. Future investigations should focus on the use of geographically extensive lake ice observations and modeling to elucidate patterns of climatic variability and/or climate change.
Single‐scattering albedo of smoke retrieved from the sky radiance and solar transmittance measured from ground
Authors: Dubovik O. , Holben B. N. , Kaufman Y. J. , Yamasoe M. , Smirnov A. , Tanré D. , Slutsker I.
Published: February 2004

A method of aerosol single‐scattering albedo retrieval from diffuse radiance measured in the solar almucantar and direct solar measurements is proposed. The aerosol scattering optical thickness is derived from the diffuse radiance by applying a radiative transfer model driven by aerosol microstructure parameters and Mie theory. To improve the accuracy of the scattering optical thickness, the inversion results are acceptable only if the radiance is measured across the total almucantar and is accurately fitted by a theoretical model. The aerosol is assumed as an external mixture of purely scattering particles and soot particles, with the soot approximated as a pure absorber. The criterion for the acceptance of fit is determined from the analysis of the effects of random and systematic errors on the single‐scattering albedo retrieval. The method was applied to measurements conducted during the Smoke, Clouds, and Radiation ‐ Brazil (SCAR‐B) campaign in August and September 1995. Aerosol radiance data were extensively collected by the Aerosol Robotic Network (AERONET) of ground‐based Sun/sky radiometers. The analysis focuses on the studies of the time variability of the biomass burning aerosol in the local Cuiabá area, supplemented by measurements collected in Cuiabá in 1993–1994. The results show reasonable ranges of the aerosol single‐scattering albedo variability (for example, single‐scattering albedo averages 0.87 ±0.08 at 670 nm). The spectral dependence of the single‐scattering albedo has both tendencies: decreasing and increasing with wavelength. The potential reasons causing different spectral behavior are analyzed theoretically.
Transport and production of NOX in electrified thunderstorms: Survey of previous studies and new observations at midlatitudes
Authors: Huntrieser H. , Schlager H. , Feigl C. , Höller H.
Published: February 2004

First airborne NOx (NO+NO2) measurements in anvils of active thunderstorms in Europe were performed in summer 1996 over southern Germany and Switzerland (47°‐49°N). This field experiment LINOX (lightning‐produced NOx) was designed to study the production of NOx by lightning discharges and the transport in convective storms. With the research aircraft Falcon of the Deutsches Zentrum für Luft‐ und Raumfahrt, about 20 anvil penetrations were performed including measurements of NO, NO2, CO2, O3, and meteorological parameters. In thunderstorm anvils, mean NOx mixing ratios between 0.8 and 2.2 ppbv were measured with peak values reaching up to 4 ppbv. A considerable part of these enhancements could be attributed to the transport of polluted air from the planetary boundary layer (PBL) using CO2 as tracer for PBL air. NOx produced by lightning can be obtained by subtracting the fraction of NOx transported from the PBL from total NOx measured in the anvil. The NOx/CO2 correlation in larger cumulus clouds without lightning was used as reference for the transport of PBL air in the anvils. In smaller LINOX thunderstorms the contribution from lightning, respectively, PBL transport to anvil NOx, was about equal. However, in medium and large LINOX thunderstorms the contribution from lightning dominated (60–75%). For these kind of thunderstorms it was estimated that ∼1.0±0.5 ppbv NOx resulted from lightning production. The observations were used to quantify the NOx production per thunderstorm and to give a rough estimate of the annual production of NOx. For the global lightning nitrogen budget the uncertainties were considerable (0.3–22 Tg(N) yr−1). The mean value for the global NOx production rate by lightning in the upper troposphere was estimated to 4 Tg(N) yr−1.
MOZART, a global chemical transport model for ozone and related chemical tracers: 2. Model results and evaluation
Authors: Hauglustaine D. A. , Brasseur G. P. , Walters S. , Rasch P. J. , Müller J.‐F. , Emmons L. K. , Carroll M. A.
Published: February 2004

In this second of two companion papers, we present results from a new global three‐dimensional chemical transport model, called MOZART (model for ozone and related chemical tracers). MOZART is developed in the framework of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) and includes a detailed representation of tropospheric chemistry. The model provides the distribution of 56 chemical species at a spatial resolution of 2.8° in both latitude and longitude, with 25 levels in the vertical (from the surface to level of 3 mbar) and a time step of 20 min. The meteorological information is supplied from a 2‐year run of the NCAR Community Climate Model. The simulated distributions of ozone (O3) and its precursors are evaluated by comparison with observational data. The distribution of methane, nonmethane hydrocarbons (NMHCs), and CO are generally well simulated by the model. The model evaluation in the tropics stresses the need for a better representation of biomass burning emissions in order to evaluate the budget of carbon monoxide, nitrogen species, and ozone with more accuracy in these regions, MOZART reproduces the NO observations in most parts of the troposphere. Nitric acid, however, is overestimated over the Pacific by up to a factor of 10 and over continental regions by a factor of 2–3. Discrepancies are also found in the simulation of PAN in the upper troposphere and in biomass burning regions. These results highlight shortcomings in our understanding of the nitrogen budget in the troposphere. The seasonal cycle of ozone in the troposphere is generally well reproduced by the model in comparison with ozone soundings. MOZART tends, however, to underestimate O3 at higher latitudes, and specifically above 300 mbar. The global photochemical production and destruction of ozone in the troposphere are 3018 Tg/yr and 2511 Tg/yr, respectively (net ozone production of 507 Tg/yr). The stratospheric influx of O3 is estimated to be 391 Tg/yr and the surface dry deposition 898 Tg/yr. The calculated global lifetime of methane is 9.9 years in the annual average.
Diel variation in methane emission from a midlatitude prairie wetland: Significance of convective throughflow in Phragmites australis
Authors: Kim J. , Verma S. B. , Billesbach D. P. , Clement R. J.
Published: February 2004

Methane flux was measured at a Phragmites‐dominated marsh in the Sandhills of north‐central Nebraska from late July to September 1993. The eddy covariance technique employing a tunable diode laser spectrometer was used to measure spatially integrated fluxes of methane. Rates of methane emission increased rapidly after sunrise and peaked (at up to 50 mg CH4 m−2 h−1) between midmorning and noon. The emission rates during midday hours were 2 to 5 times higher than the relatively constant rates observed at night. This marked diel variation was attributed to plant‐mediated transport of methane by convective throughflow which typically accounted for about 60% of the total methane emission during the daylight hours. Our analysis suggests that the enhanced rate of plant‐mediated methane emission during daytime is significantly correlated with changes in photosynthetically active radiation and the temperature difference between the canopy and the ambient air. Data on windy nights showed enhanced methane emission with increasing wind speeds, perhaps indicating an occurrence of Venturi‐induced convection and/or enhanced ebullition. When averaged over the study period of 65 days, the methane flux was 25 mg CH4 m−2 h−1 during daytime and 8 mg CH4 m−2 h−1 during nighttime. Changes in the daily averaged methane flux were strongly correlated with sediment temperatures at 0–0.25 m depth.
Estimating vegetation structural effects on carbon uptake using satellite data fusion and inverse modeling
Authors: Asner Gregory P. , Bateson C. Ann , Privette Jeffrey L. , El Saleous Nazmi , Wessman Carol A.
Published: February 2004

Regional analyses of biogeochemical processes can benefit significantly from observational information on land cover, vegetation structure (e.g., leaf area index), and biophysical properties such as fractional PAR absorption. Few remote sensing efforts have provided a suite of plant attributes needed to link vegetation structure to ecosystem function at high spatial resolution. In arid and semiarid ecosystems (e.g., savannas), high spatial heterogeneity of land cover results in significant functional interaction between dominant vegetation types, requiring new approaches to resolve their structural characteristics for regional‐scale biogeochemical research. We developed and tested a satellite data fusion and radiative transfer inverse modeling approach to deliver estimates of vegetation structure in a savanna region of Texas. Spectral mixture analysis of Landsat data provided verifiable estimates of woody plant, herbaceous, bare soil, and shade fractions at 28.5 m resolution. Using these subpixel cover fractions, a geometric‐optical model was inverted to estimate overstory stand density and crown dimensions with reasonable accuracy. The Landsat cover estimates were then used to spectrally unmix the contribution of woody plant and herbaceous canopies to AVHRR multiangle reflectance data. These angular reflectances were used with radiative transfer model inversions to estimate canopy leaf area index (LAI). The suite of estimated canopy and landscape variables indicated distinct patterns in land cover and structural attributes related to land use. These variables were used to calculate diurnal PAR absorption and carbon uptake by woody and herbaceous canopies in contrasting land cover and land use types. We found that both LAI and the spatial distribution of vegetation structural types exert strong control on carbon fluxes and that intercanopy shading is an important factor controlling functional processes in spatially heterogeneous environments.