bluuebunny/crossref_metadata_2025 huggingface dataset:
Upper ocean thermohaline, oxygen, nutrient, and flow structure near the date line in the summer of 1993
Authors: Roden Gunnar I.
Published: February 2004

An overview is given of the upper ocean geopotential height, zonal flow, thermohaline, oxygen, and nutrient structures between the Bering Sea and Fiji islands, based on high‐resolution field measurements along 179°E. The geopotential topography is dominated by large‐amplitude (2–4 J kg−1) mesoscale perturbations in the subarctic and subtropical gyres and a smoother equatorial ridge‐trough system. The fastest midlatitude zonal flows (40 cm s−1) are associated with the Alaska Stream, the Subarctic Current, the Kuroshio Extension, and the North Equatorial Current. Prominent physical and chemical frontal zones are observed between 42°–45°N and 12°–15°N. A pronounced upwelling dome is found south of the Aleutians, which brings dense, nutrient rich waters within 125 m of the sea surface. Well‐defined upwelling domes also occur in the northern (5°10°N) and southern (3°–8°S) doldrums. El Niño conditions prevailed near the equator in August 1993, marked by surface temperatures of 30°C, low salinities, low nutrient concentrations, eastward surface flow (30 cm s−1), merging of the North Equatorial Countercurrent and Equatorial Undercurrent (50 cm s−1), absence of trade winds and abundant rainfall, and southward displacement of the South Equatorial Countercurrent (20 cm s−1). The South Equatorial Current (20 cm s−1) has a complex multicore structure and is accompanied by a major physical and chemical frontal zone between 13°–16°S. A fast coastal eastward jet is observed on the north slope of Vanua Levu island, Fiji.
Isoprene and monoterpene emissions from a eucalyptus plantation in Portugal
Authors: Street Rachel A. , Hewitt C. Nicholas , Mennicken Stefan
Published: February 2004

Measurements of isoprene and monoterpene emission rates were made from a mature and an immature Eucalyptus globulus tree in a commercial monoculture plantation in central Portugal in 1994 using a branch enclosure sampling system with analysis by gas chromatography/flame ionization and gas chromatography/mass selective methods. Isoprene was the dominant compound emitted and represented over 90% of the total assigned volatile organic compound plant emissions during the day. Other identified species were α‐pinene, sabinene, β‐pinene, myrcene, limonene, cineole, linalool, α‐terpineol, and, tentatatively, cis‐ and trans‐ocimine and an unidentified octatriene. When they were adjusted to standard conditions of temperature (30°C) and light (1000 μmol−2 ms−1) VOC emissions from a 1 year old sapling were 5 times higher (49 and 5.2 μg Cg−1 dry wt h−1 for isoprene and total monoterpenes, respectively) than those from a 7‐year‐old tree (15 and 0.7 μg C g−1 dry wt h−1 respectively). On a projected leaf area basis these differences were not so apparent (isoprene; 5 and 4 mg m−2 h−1, young and old trees, respectively; monoterpenes, 0.6 and 0.2 mg m−2 h−1, respectively). Emission rates from both trees were closely correlated with incident light flux and temperature, with daytime maxima, and with nighttime minima. Existing models describing emissions in terms of light, temperature, and empirical coefficients were found to adequately predict emissions from the young tree but to grossly overestimate emission rates from the mature tree. This finding has implications for the extrapolation of emission data obtained in the laboratory with immature trees to the canopy, regional, or global scales, although additional measurements are required to determine whether the results presented here can be generalized.
Measurements of spectral solar UV irradiance in tropical‐Australia
Authors: Bernhard G. , Mayer B. , Seckmeyer G. , Moise A.
Published: February 2004

Measurements of global spectral irradiance in the UV and visible range were carried out during December 1995 and January 1996 in Townsville, Australia (19.33°S, 146.76°E, 30 m above sea level (asl)) using the mobile spectroradiometer of the Fraunhofer Institute for Atmospheric Environmental Research, Germany. These are, to our knowledge, the first reported spectral UV measurements in the tropics of Australia. For cloudless days, the spectral measurements are consistent with results of a radiative transfer model. In the UVA, measurement and model agree within ±10% for solar elevations above 10°. In the UVB, the differences are larger (≈15% at 300 nm), which can be explained by uncertainties in the model input parameters of total ozone column and ozone absorption cross section. The variation of the daily erythemal irradiation was found to be ±24% (±1 σ) for the period of the campaign. The variation of the total ozone column contributes less than ±3% to this variability; the main part is introduced by clouds. These attenuate UV irradiation less than total irradiation (300 nm – 3000 nm); the daily total irradiation averaged over the period of the campaign was reduced by a factor of 0.71 owing to cloudiness compared to the clear‐sky case while the erythemal irradiation was only diminished by a factor of 0.78. Using long‐term records of total irradiation and ozone column, the parameters influencing UV radiation on Earth were found to be typical for the period and site of the campaign. The maximum erythemally weighted irradiance measured during the campaign was 429 mW/m2, and the average daily erythemal irradiation for this period was 6.06 kJ/m2. These high radiation levels were found to exceed the corresponding values for Garmisch‐Partenkirchen (47.5°N, 11.0°E, 730 m asl), Germany, by between 55 and 70%. This pronounced difference in the radiation environment between Australia and Germany is explained by the higher solar elevation and the lower ozone column in the tropics.
NO2 absorption cross section and its temperature dependence
Authors: Kirmse B. , Delon A. , Jost R.
Published: February 2004

Presented in this text is a compilation of existing absorption cross sections of NO2, mainly at room temperature but also at lower and higher temperatures, with a quantitative comparison of their cross sections and wavelength calibrations. From this, we concatenate three selected cross sections (slightly corrected) in order to cover the widest possible spectral range from 300 to 708 nm, at a resolution of 0.05 nm. At longer wavelengths, λ>708 nm, the (much weaker) cross section exists only at low‐resolution (≅1 nm), giving a low‐resolution cross section from 300 to 908 nm. We show that the cross‐section temperature dependence (data exist from 200 to 673 K) can be decomposed into two parts, a bell‐shaped envelope and superimposed spectral fluctuations. The envelope broaden slightly with increasing temperature, while the amplitude of the fluctuations decreases (increases) with increasing (decreasing) temperature. Finally, we sketch the “reflection” model, which allows us to get the cross‐section envelope from the shapes of the ground state vibrational wave function and of the potential energy surface of the first excited state.
Sulfur Chemistry in the Antarctic Troposphere Experiment: An overview of project SCATE
Authors: Berresheim H. , Eisele F. L.
Published: February 2004

In January and February 1994 the Sulfur Chemistry in the Antarctic Troposphere Experiment (SCATE), a multi‐institutional field research project, was conducted at Palmer Station (64°46'S, 64°03'W), Antarctica. In this paper we describe the scientific background and major objectives of SCATE and present an overview of the field measurement program, the study site, and meteorological conditions prevailing during the experiment. A specific goal of the SCATE study was to improve the current understanding of the chemistry of dimethylsulfide (DMS) in the remote marine atmosphere and its relation to the climate of Antarctica. The SCATE campaign included for the first time measurements of hydroxyl radical (OH), gas phase sulfuric acid (H2SO4), methanesulfonic acid (MSA), and nitric oxide (NO) concentrations over Antarctica. Because of the high time resolution and sensitivity of the corresponding measurement techniques it was possible to distinguish between meteorological and chemical processes contributing to the distribution of DMS oxidation products at the study site. Strong vertical exchange processes and long‐range transport of marine air masses frequently dominated the observed concentrations. These processes were governed by intensive low‐pressure cells passing through the Drake Passage and circling around the Antarctic coastline.
Energy balance and canopy conductance of a boreal aspen forest: Partitioning overstory and understory components
Authors: Blanken P. D. , Black T. A. , Yang P. C. , Neumann H. H. , Nesic Z. , Staebler R. , den Hartog G. , Novak M. D. , Lee X.
Published: February 2004

The energy balance components were measured throughout most of 1994 in and above a southern boreal aspen (Populus tremuloides Michx.) forest (53.629°N 106.200°W) with a hazelnut (Corylus cornuta Marsh.) understory as part of the Boreal Ecosystem‐Atmosphere Study. The turbulent fluxes were measured at both levels using the eddy‐covariance technique. After rejection of suspect data due to instationarity or inhomogeneity, occasional erratic behavior in turbulent fluxes and lack of energy balance closure led to a recalculation of the fluxes of sensible and latent heat using their ratio and the available energy. The seasonal development in leaf area was reflected in a strong seasonal pattern of the energy balance. Leaf growth began during the third week of May with a maximum forest leaf area index of 5.6 m2 m−2 reached by mid‐July. During the full‐leaf period, aspen and hazelnut accounted for approximately 40 and 60% of the forest leaf area, respectively. Sensible heat was the dominant consumer of forest net radiation during the preleaf period, while latent heat accounted for the majority of forest net radiation during the leafed period. Hazelnut transpiration accounted for 25% of the forest transpiration during the summer months. During the full‐leaf period (June 1 to September 7) daytime dry‐canopy mean aspen and hazelnut canopy conductances were 330 mmol m−2 s−1 (8.4 mm s−1) (70% of the total forest conductance) and 113 mmol m−2 s−1 (2.9 mm s−1) (24% of the total forest conductance), respectively. Maximum aspen and hazelnut canopy conductances were 1200 mmol m−2 s−1 (30 mm s−1) and 910 mmol m−2 s−1 (23 mm s−1 ), respectively, and maximum stomatal conductances were 490 mmol m−2 s−1 (12.5 mm s−1) and 280 mmol m−2 s−1 (7 m s−1), aspen and hazelnut, respectively. Both species showed a decrease in canopy conductance as the saturation deficit increased and both showed an increase in canopy conductance as the photosynthetic active radiation increased. There was a linear relationship between forest leaf area index and forest canopy conductance. The timing, duration, and maximum leaf area of this deciduous boreal forest was found to be an important control on transpiration at both levels of the canopy. The full‐leaf hazelnut daytime mean Priestley and Taylor [1972] α coefficient of 1.22 indicated transpiration was largely energy controlled and the quantity of energy received at the hazelnut surface was a function of aspen leaf area. The full‐leaf aspen daytime mean α of 0.91 indicated some stomatal control on transpiration, with a directly proportional relationship between forest leaf area and forest canopy conductance, varying α during much of the season through a range very sensitive to regional scale transpiration and surface‐convective boundary layer feedbacks.
Atmospheric correction of visible to middle‐infrared EOS‐MODIS data over land surfaces: Background, operational algorithm and validation
Authors: Vermote E. F. , El Saleous N. , Justice C. O. , Kaufman Y. J. , Privette J. L. , Remer L. , Roger J. C. , Tanré D.
Published: February 2004

The NASA moderate resolution imaging spectroradiometer (MODIS) instrument will provide a global and improved source of information for the study of land surfaces with a spatial resolution of up to 250 m. Prior to the derivation of various biophysical parameters based on surface reflectances, the top of the atmosphere signals need to be radiometrically calibrated and corrected for atmospheric effects. The present paper describes in detail the state of the art techniques that will be used for atmospheric correction of MODIS bands 1 through 7, centered at 648, 858, 470, 555, 1240, 1640, and 2130 nm, respectively. Previous operational correction schemes have assumed a standard atmosphere with zero or constant aerosol loading and a uniform, Lambertian surface. The MODIS operational atmospheric correction algorithm, reported here, uses aerosol and water vapor information derived from the MODIS data, corrects for adjacency effects and takes into account the directional properties of the observed surface. This paper also describes the operational implementation of these techniques and its optimization. The techniques are applied to remote sensing data from the Landsat Thematic Mapper (TM), the NOAA advanced very high resolution radiometer (AVHRR), and the MODIS airborne simulator (MAS) and validated against ground‐based measurements from the Aerosol Robotic Network (AERONET).
Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated‐k model for the longwave
Authors: Mlawer Eli J. , Taubman Steven J. , Brown Patrick D. , Iacono Michael J. , Clough Shepard A.
Published: February 2004

A rapid and accurate radiative transfer model (RRTM) for climate applications has been developed and the results extensively evaluated. The current version of RRTM calculates fluxes and cooling rates for the longwave spectral region (10–3000 cm−1) for an arbitrary clear atmosphere. The molecular species treated in the model are water vapor, carbon dioxide, ozone, methane, nitrous oxide, and the common halocarbons. The radiative transfer in RRTM is performed using the correlated‐k method: the k distributions are attained directly from the LBLRTM line‐by‐line model, which connects the absorption coefficients used by RRTM to high‐resolution radiance validations done with observations. Refined methods have been developed for treating bands containing gases with overlapping absorption, for the determination of values of the Planck function appropriate for use in the correlated‐k approach, and for the inclusion of minor absorbing species in a band. The flux and cooling rate results of RRTM are linked to measurement through the use of LBLRTM, which has been substantially validated with observations. Validations of RRTM using LBLRTM have been performed for the midlatitude summer, tropical, midlatitude winter, subarctic winter, and four atmospheres from the Spectral Radiance Experiment campaign. On the basis of these validations the longwave accuracy of RRTM for any atmosphere is as follows: 0.6 W m−2 (relative to LBLRTM) for net flux in each band at all altitudes, with a total (10–3000 cm−1) error of less than 1.0 W m−2 at any altitude; 0.07 K d−1 for total cooling rate error in the troposphere and lower stratosphere, and 0.75 K d−1 in the upper stratosphere and above. Other comparisons have been performed on RRTM using LBLRTM to gauge its sensitivity to changes in the abundance of specific species, including the halocarbons and carbon dioxide. The radiative forcing due to doubling the concentration of carbon dioxide is attained with an accuracy of 0.24 W m−2, an error of less than 5%. The speed of execution of RRTM compares favorably with that of other rapid radiation models, indicating that the model is suitable for use in general circulation models.
Scaling up flux measurements for the boreal forest using aircraft‐tower combinations
Authors: Desjardins R. L. , MacPherson J. I. , Mahrt L. , Schuepp P. , Pattey E. , Neumann H. , Baldocchi D. , Wofsy S. , Fitzjarrald D. , McCaughey H. , Joiner D. W.
Published: February 2004

Fluxes of carbon dioxide, water vapor, sensible heat, and momentum obtained over the boreal forest from the Twin Otter aircraft and six tower‐based systems are compared. These measurements were collected as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS) during three intensive field campaigns between May 25 and September 17, 1994. The representativeness of the tower‐based measurements collected during BOREAS is discussed. Even though the net radiation from aircraft‐ and tower‐based systems agreed well, in general, the aircraft tended to observe larger latent heat and smaller sensible heat fluxes than the towers. The CO2 fluxes from the aircraft were substantially less than from the tower, while the differences were relatively small for the momentum fluxes. The relationships between aircraft and tower‐based flux measurements obtained by making repeated runs past various towers are used to scale up tower‐based fluxes to a 16×16 km2 area near Prince Albert, Saskatchewan. It is demonstrated that except for a couple of cases primarily due to rapidly changing radiation conditions, this combination of measurements provides regional flux estimates of momentum, CO2, and sensible and latent heat similar to those obtained by flying a grid pattern over the area.
Thermal band selection for the PRISM instrument: 1. Analysis of emissivity‐temperature separation algorithms
Authors: Caselles Vicente , Valor Enric , Coll César , Rubio Eva
Published: February 2004

One of the missions being planned by the European Space Agency (ESA) within the framework of its Earth Observation Programme is the Processes Research by Imaging Space Mission (PRISM). The PRISM instrument consists of a thermal sensor whose main objective is to retrieve accurate land surface temperatures (LST) and whose band positions are 3.5–4.1 μm, 8.1–9.5 μm, 10.3–11.3 μm, and 11.5–12.5 μm. We have studied the optimal design of this instrument to retrieve accurate LSTs. First, we have analyzed several emissivity‐temperature separation methods (part 1) and atmospheric and emissivity correction algorithms (part 2). Finally, we have identified the optimal band configuration (part 3). This paper is the first of a series of three and addresses the question of the emissivity‐temperature separability. Among all the existing algorithms, we have studied the “absolute methods,” which are able to estimate the absolute value of emissivity at satellite scale and can yield better results in the emissivity estimate. These methods are the algorithm based on the temperature‐independent thermal infrared spectral index (TISI), the alpha coefficients method, and the algorithms which use visible, near‐infrared, and shortwave infrared data to estimate the thermal emissivity (vegetation cover method (VCM)). The study consisted of an analysis of both random and systematic errors of each method. The results indicate that emissivity can be obtained with an error of ±1.7–5% using the alpha coefficients, ±1.7–3% using the TISIs, and ±0.5–1.4% using the VCM, depending on the spectral region. In all cases the error decreases with wavelength, and the lowest errors are achieved in the 10–12 μm spectral region, due to small variability of emissivity. It is necessary that the two first methods use radiosondes simultaneous with the satellite overpass to perform the atmospheric corrections on the thermal data; in addition, they show important sources of systematic errors, which will increase the uncertainty in the emissivity estimate (even in the best possible case). The VCM does not use radiosondes and does not present important sources of systematic error. It appears to be the procedure with the most favorable error propagation characteristics. Thus the VCM could be the most adequate method for retrieving the land surface emissivity (LSE), within the framework of this work.
Lidar observations of polar stratospheric clouds at the South Pole: 2. Stratospheric perturbed conditions, 1992 and 1993
Authors: Cacciani Marco , Colagrande Paola , di Sarra Alcide , Fuà Daniele , Di Girolamo Paolo , Fiocco Giorgio
Published: February 2004

Observations of polar stratospheric clouds (PSCs), carried out at the Amundsen Scott South Pole Station by lidar from May 1992 through October 1993, are reported and compared with previously obtained results. At that time the Antarctic stratosphere was loaded with sulfuric acid aerosol due to the eruptions of Mount Pinatubo, primarily, and of Mount Hudson. The seasonal evolution of the backscatter profiles has been investigated in relation to the presence of the volcanic aerosol and to the processes of PSC formation, particle sedimentation, and dehydration. During the first winter after the eruptions the PSC activity was more intense than in the following year, particularly above 12.5 km, where the amount of volcanic aerosol was larger in 1992 than in 1993. At lower altitudes the volcanic aerosol loading as well as the PSC phenomenon were comparable during the 2 years. No substantial changes in the signal due to the volcanic aerosol has been observed comparing the backscattering profiles before and after the PSC periods (June‐September), except for a downward shift, attributed to the subsidence of the air inside the polar vortex. It is concluded that only a small fraction of the aerosol particles, probably those with the largest radii, were involved in the nucleation of PSC particles.
Airborne measurements of boundary layer chemistry during the Southern Oxidant Study: A case study
Authors: Berkowitz Carl M. , Shaw William J.
Published: February 2004

Measurements of chemical and meteorological variables were made at several altitudes over a surface chemistry site near Nashville, Tennessee, during the 1995 Southern Oxidants Study. The measurements were designed to reveal the effects of turbulent mixing on atmospheric chemistry. They were made under conditions of clear skies and light winds during the morning transition from nocturnal stable stratification to the afternoon convective mixed layer. Early morning ozone mixing ratios measured by the aircraft were ∼70 parts per billion (ppb), while those measured by surface instrumentation were ∼25 ppb. Corresponding to growth of the morning turbulent layer, surface ozone values steadily increased with time until they matched the 70 ppb values aloft by midmorning. The mixing ratios of isoprene at altitudes above the surface increased by several orders of magnitude with the onset of turbulence at each measurement altitude. The slope of O3 as a function of NOy for each of the flight legs was also sensitive to the presence of turbulence. Measurements from nonturbulent flight legs yielded slopes that were considerably steeper than those from measurements made in turbulence. This study shows that the concentration of ozone precursors aloft is clearly dependent on the presence of turbulence, and turbulent mixing could explain the evolution of ozone concentrations at the surface. In general, conclusions regarding pollutant concentrations must account for both chemical and local dynamic processes.
Evaluation of a reduced Jacobian chemical solver
Authors: Sandilands J. W. , McConnell J. C.
Published: February 2004

To allow the use of detailed chemical modules in three‐dimensional global forecast and climate models, it is necessary to have efficient and accurate solvers for the chemical species that allow for diurnal forcing. The aim of this work was to develop a fast chemistry solver based on the implicit Euler finite difference approximation to the chemical continuity equation for a set of chemical species. This finite difference form of the continuity equation is appealing because of its mass‐conserving properties. We employ two algorithms for solution: a basic Newton solver and a modification of this method, which we have dubbed the reduced Jacobian (RJ) solver. Both methods yield equivalent solutions, but the RJ solver can be 10 times more efficient on a scalar machine for fixed time stepping. Both methods are evaluated for accuracy and timing against the Gear solver. The RJ algorithm breaks the Jacobian matrix into smaller units that may be solved more efficiently. To do this, we have made use of the interactiveness of “family” species. The reduction in computational time makes this method a good candidate for three‐dimensional modeling of atmospheric chemistry. In this paper we discuss the method and present a chemical box model comparison of these three techniques for a chemical set comprising Ox, HOx, NOx, ClOx, BrOx, and CH4 oxidation gas‐phase chemistry, at various heights in the atmosphere ranging from the upper troposphere to the mesosphere. We have also tested a modification that reduces errors at sunrise and sunset without seriously compromising the efficiency of the method. From our tests it would appear that the RJ solver is robust at all heights tested and should be readily adapted to other chemical mechanisms.
Idealized simulations of the Antarctic katabatic wind system with a three‐dimensional mesoscale model
Authors: Heinemann Günther
Published: February 2004

The katabatic wind system represents a key factor for the near‐surface wind field of the Antarctic region. Idealized simulations with a three‐dimensional mesoscale model are performed to investigate the development of the Antarctic katabatic wind system and its sensitivity to physical boundary conditions, in particular channeling effects and the thermodynamic forcing close to the coastline. The simulated cases represent wintertime cases with complete sea ice coverage and no sea ice, as well as a realistic summertime situation. For the wintertime situations a large impact of the presence of open water on the three‐dimensional structure of the wind field close to the coast can be shown, whereas the effects on the katabatic wind over the continent are relatively small. Near‐surface wind speeds over the continental slope for the summertime case have strengths comparable to those of the wintertime cases but reveal a distinct daily cycle due to the daily course of the radiation fluxes. The formation of shallow mesoscale circulations is simulated after 2–4 days of simulation in ice‐free coastal areas. In these regions, low‐level convergence, diabatic heating, and the cold air advection associated with the katabatic flow leads to low‐level baroclinicity and cyclonic vorticity production.
Rocket soundings of ozone profiles in the stratosphere over the Korean Peninsula
Authors: Kim Jhoon , Park Chang‐Joon , Lee Ki‐Young , Lee Dong Hoon , Cho Hi‐Ku , Kim Young‐Ok , Cho Gwang Rae , Park Jae H.
Published: February 2004

Two stratospheric ozone profiles have been obtained using rocket‐based solar absorption UV radiometry over Anheung, Korea on June 4 and September 1, 1993. The ozone sensor consists of four radiometers, measuring the attenuation of solar ultraviolet radiation as a function of altitude during ascent. The retrieved ozone density profiles cover altitudes of 15 to 35 km from the first sounding Korean Sounding Rocket‐1 (KSR‐1 ) and 15 to 45 km from the second sounding (KSR‐2). Retrieved profiles have random errors (1σ) of approximately 7% for altitudes between 20 and 30 km for KSR‐1 and between 20 and 40 km for KSR‐2 and ∼15–20% for other regions. Both profiles compare reasonably well with near‐coincident ground‐based lidar and Umkehr measurements as well as with satellite measurements of the Halogen Occultation Experiment on board UARS. The KSR‐1 and KSR‐2 soundings provided the first near in situ measurements of ozone concentrations over the Korean Peninsula. The significance of these measurements at this geographical location will be discussed.
Comparison of two complex land surface schemes coupled to the National Center for Atmospheric Research general circulation model
Authors: Peylin Philippe , Polcher Jan , Bonan Gordon , Williamson David L. , Laval Katia
Published: February 2004

Two climate simulations with the National Center for Atmospheric Research general circulation model (version CCM2) coupled either to the Biosphere Atmosphere Transfer Scheme (BATS) or to Sechiba land surface scheme are compared. Both parameterizations of surface‐atmosphere exchanges may be considered as complex but represent the soil hydrology and the role of vegetation in very different ways. The global impact of the change in land surface scheme on the simulated climate appears to be small. Changes are smaller than those obtained when comparing either one of these schemes to the fixed hydrology used in the standard CCM2. Nevertheless, at the regional scale, changing the land‐surface scheme can have a large impact on the local climate. As one example, wre detail how circulation patterns are modified above the Tibetan plateau during the monsoon season. Elsewhere, mainly over land, changes can also be important. In the tropics, during the dry season, Sechiba produces warmer surface temperatures than does BATS. This warming arises from differences in the soil hydrology, both storage capacity and the dynamics of soil water transport. Over the Tundra biotype, the formulation of the transpiration induces significant differences in the energy balance.
Climatology of the three coastal Antarctic stations Dumont d'Urville, Neumayer, and Halley
Authors: König‐Langlo G. , King J. C. , Pettré P.
Published: February 2004

Long term air and snowfall chemistry measurements have been performed at the three coastal Antarctic stations Dumont d'Urville (66°40′S, 140°1′E), Neumayer (70°39′S, 8°15′W), and Halley (75°35′S, 26°19′W). The results have to be interpreted and compared with respect to the regional meteorological conditions. In this study the 3‐hourly synoptic surface observations taken at the three stations between 1991 and 1995, as well as the daily upper air soundings from 1993, are analyzed to describe the aspects of station climatologies relevant for the air and snowfall chemistry measurements discussed in the papers of this special section. Although the three stations are comparable, being situated close to the coastline of Antarctica, the meteorological conditions differ. While at Dumont d'Urville katabatic winds cause predominant strong and relatively dry surface winds from the interior of Antarctica, Neumayer and Halley are frequently influenced by easterly winds associated mostly with eastward moving cyclones. From April through October the wind field above 5 km is governed by a circumpolar vortex with westerly winds increasing in intensity with height. Dumont d'Urville represents a station at the edge of this vortex with extreme stratospheric wind velocities up to above 50 m s−1. Neumayer and Halley are mostly situated within the vortex and isolated from air masses advecting from lower latitudes into the upper troposphere and lower stratosphere during the Austral winter.
Effect of vegetation on an ice‐age climate model simulation
Authors: Crowley Thomas J. , Baum Steven K.
Published: February 2004

A growing number of studies suggest that vegetation changes can significantly influence regional climate variations. Herein we utilize a climate model (GENESIS) with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum (LGM). In particular, we focus on the potential response to a significant reduction in the area of tropical rainforest. Simulations employed a global vegetation reconstruction for the LGM and Climate/Long‐Range Investigation, Mapping and Prediction (CLIMAP) sea surface temperature (SST) estimates. Results indicate that expansion of dryland vegetation causes a 15–30% additional LGM cooling for Australia (0.4°C) and Africa (0.9°C), respectively. Turnover from conifer to tundra also causes cooling of 2°–4°C or more in western Europe and Siberia. However, for the largest rainforest area (Amazon Basin), inclusion of realistic vegetation increased modeled temperatures 2°–4°C and decreased precipitation by 10–35%. These latter results are similar to those obtained with sensitivity experiments of the effects of future Amazon deforestation. Initial assessment of the potential effect of decreased stomatal resistance due to lower ice age CO2levels indicates little significant response to this effect. Comparison of model‐predicted low‐elevation LGM temperature changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the LGM results in slightly more than 50% agreement between models and data for low‐elevation sites in low‐mid latitudes. Data at variance with model predictions would appear to be explainable by considering additional changes in vegetation, ice age dust, or a 1°–2°C cooling below CLIMAP values. This conclusion is at variance with a 3°–4°C tropical cooling suggested by some studies for explaining estimated land temperature changes during the LGM. In some western European sites model temperatures are colder than proxy data by 2°–8°C. This model‐data discrepancy may be explained by less sea ice in the subpolar North Atlantic than stipulated by CLIMAP, a conclusion consistent with new marine data from that region.
The Meteor 3/total ozone mapping spectrometer version 7 data set: Calibration and analysis
Authors: Seftor C. J. , Jaross G. , Herman J. R. , Gu X. , Moy L. , Taylor S. L. , Wellemeyer C. G.
Published: February 2004

The Meteor 3/total ozone mapping spectrometer (TOMS) data set has been reprocessed using the version 7 TOMS total ozone algorithm and a recalibration of the TOMS instrument using in‐flight and revised laboratory data. To provide continuity for the analysis of long‐term trends, the absolute calibration of Meteor 3/TOMS was adjusted so that the measured radiances closely matched Nimbus 7/TOMS. The residual bias in ozone is less than 1% and shows no significant latitudinal or seasonal dependence. The calibration procedure and the differences between the current and previously used calibrations are discussed. Problems in the Meteor 3/TOMS data set caused by chopper wheel synchronization problems are described, and comparisons of the resulting data with version 7 of the Nimbus 7/TOMS data are presented.
Screening design for model sensitivity studies
Authors: Welsh James P. , Koenig George G. , Bruce Dorothy
Published: February 2004

This paper describes a different approach to sensitivity studies for environmental, including atmospheric, physics models. The sensitivity studies were performed on a multispectral environmental data and scene generation capability. The capability includes environmental physics models that are used to generate data and scenes for simulation of environmental materials, features, and conditions, such as trees, clouds, soils, and snow. These studies were performed because it is difficult to obtain input data for many of the environmental variables. The problem to solve is to determine which of the 100 or so input variables, used by the generation capability, are the most important. These sensitivity studies focused on the generation capabilities needed to predict and evaluate the performance of sensor systems operating in the infrared portions of the electromagnetic spectrum. The sensitivity study approach described uses a screening design. Screening designs are analytical techniques that use a fraction of all of the combinations of the potential input variables and conditions to determine which are the most important. Specifically a 20‐run Plackett‐Burman screening design was used to study the sensitivity of eight data and scene generation capability computed response variables to 11 selected input variables. This is a two‐level design, meaning that the range of conditions is represented by two different values for each of the 11 selected variables. The eight response variables used were maximum, minimum, range, and mode of the model‐generated temperature and radiance values. The result is that six of the 11 input variables (soil moisture, solar loading, roughness length, relative humidity, surface albedo, and surface emissivity) had a statistically significant effect on the response variables.
Evaluating the role of NAT, NAD, and liquid H2SO4/H2O/HNO3 solutions in Antarctic polar stratospheric cloud aerosol: Observations and implications
Authors: Del Negro L. A. , Fahey D. W. , Donnelly S. G. , Gao R. S. , Keim E. R. , Wamsley R. C. , Woodbridge E. L. , Dye J. E. , Baumgardner D. , Gandrud B. W. , Wilson J. C. , Jonsson H. H. , Loewenstein M. , Podolske J. R. , Webster C. R. , May R. D. , Worsnop D. R. , Tabazadeh A. , Tolbert M. A. , Kelly K. K. , Chan K. R.
Published: February 2004

Airborne measurements of total reactive nitrogen (NOy) and polar stratospheric cloud (PSC) aerosol particles were made in the Antarctic (68°S) as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAES A) campaign in late July 1994. As found in both polar regions during previous studies, substantial PSC aerosol volume containing NOy was observed at temperatures above the frost point, confirming the presence of particles other than water ice. The composition of the aerosol particles is evaluated using equilibrium expressions for nitric acid trihydrate (NAT), nitric acid dihydrate (NAD), and the supercooled ternary solution (STS) composed of nitric acid (HNO3), sulfuric acid (H2SO4), and water (H2O). The equilibrium abundance of condensed HNO3 is calculated for each phase and compared to estimates made using observations of aerosol volume and NOy. The best agreement is found for STS composition, using criteria related to the onset and abundance of aerosol volume along the flight track. Throughout the PSC region, a comparison of the number of particles between 0.4 and 4.0 μm diameter with the number of available nuclei indicates that a significant fraction of the background aerosol number participates in PSC growth. Modeled STS size distributions at temperatures below 191 K compare favorably with measured size distributions of PSC aerosol. Calculations of the heterogeneous loss of chlorine nitrate (ClONO2) show that the reactivity of the observed PSC surface area is 30 to 300% greater with STS than with NAT composition for temperatures less than 195 K. The total volume of STS PSCs is shown to be more sensitive than NAT to increases in H2O, HNO3, and H2SO4 from supersonic aircraft fleet emissions. Using the current observations and perturbations predicted by the current aircraft assessments, an increase of 50 to 260% in STS aerosol volume is expected at the lowest observed temperatures (190 to 192 K), along with an extension of significant PSC activity to regions ∼0.7 K higher in temperature. These results improve our understanding of PSC aerosol formation in polar regions while strengthening the requirement to include STS aerosols in studies of polar ozone loss and the effects of aircraft emissions.
Comparative MF radar and Na lidar measurements of fluctuating winds in the mesopause region
Authors: Collins Richard L. , Thorsen Denise , Franke Steven J.
Published: February 2004

Na lidar and MF radar observations of the mesopause region (≈ 80–105 km) were made over a 2‐year period at Urbana, Illinois (40°N, 88°W). The Na lidar data yielded both temperature profiles and Na density profiles which are used to derive independent estimates of the rms horizontal winds. Estimates of the rms horizontal winds from concurrent radar and lidar measurements are obtained on 37 nights, totaling 263 hours. These three sets of rms wind estimates are processed in a common fashion. This analysis yields vertical profiles of the rms winds that do not grow exponentially with altitude, indicating that the gravity wave field is saturated throughout this altitude region. All three techniques reveal an annual maximum in the summer rms horizontal winds. However, the Na density estimates also have a semiannual variation with a second maximum in winter, which was not produced by the other techniques. Estimates of the rms winds derived from lidar Na density and Na temperature data are comparable in magnitude. The radar estimates are systematically larger than both sets of lidar estimates at higher altitudes. The discrepancy between the radar and lidar estimates is found to be greatest at those altitudes where the saturation is most pronounced.
Catalytic destruction of stratospheric ozone
Authors: Lary D. J.
Published: February 2004

This paper presents a review of the main ozone destroying catalytic cycles operating in the stratosphere. Particular attention is paid to the kinetic aspects of these cycles such as the rate limiting step and chain length. Although it is an important kinetic parameter, the chain length of the various cycles is seldom considered when the various catalytic cycles are discussed. This survey highlights that in the low stratosphere the cycles involving HO2 and halogens (notably bromine) are particularly important. In approximate order of effectiveness the most important ozone loss cycles in the polar lower stratosphere are the BrO/CIO, HO2/BrO, and OH/HO2 cycles.
On the relationships between daily circulation patterns and precipitation in Portugal
Authors: Zhang Xuebin , Wang Xiaolan L. , Corte‐Real João
Published: February 2004

Daily circulation (sea level pressure) maps over east Atlantic‐Europe were classified into six circulation patterns (CPs) by using k‐means clustering coupled with principal component analysis. The relationships between winter monthly rainfall in Portugal and the occurrence frequencies of the CPs were also examined. The CP classification scheme is effective not only in discriminating regional wet/dry weather conditions, but also in differentiating between various conditions associated with different precipitation intensities. For southern Portugal, CP6 and CP3 are the wettest patterns: under their presence the rainfall occurrence probability and the rainy day rainfall intensity are twice as high as those associated with the dry CPs; with only about 26.6% occurrence probability the two wet CPs together contribute about 66.8% of the total rainfall. For northern Portugal, CP6 and CP4 turned out to be the wettest patterns. They produce over 60% of the total rainfall with only 31% chance of occurrence. In terms of long‐term variation the precipitation is also intimately related to the occurrence frequencies of the CPs. The occurrence frequencies of CPs were found to be good predictors for the regional precipitation. In addition, it is evident that the decrease of March rainfall throughout the country in the last 3 decades has been a consequence of a reduction in the occurrence frequency of the wettest circulation pattern, CP6, which coincides with the upward trend of the North Atlantic Oscillation index and could be related to the northeastward shifting and strengthening of the Azores High.
Measurements of the dry deposition of peroxides to a Canadian boreal forest
Authors: Hall Brad D. , Claiborn Candis S.
Published: February 2004

The dry deposition rates of hydrogen peroxide (H2O2) and total organic peroxides (ROOH) were measured above a coniferous forest in Saskatchewan, Canada. Deposition velocities νd were obtained from gradient measurements using the modified Bowen ratio method. A diurnal pattern was observed, with highest deposition velocities occurring during the day. Daytime deposition velocities were approximately 5 cm s−1 for H2O2 and 1.6 cm s−1 for ROOH. Nighttime deposition velocities were much smaller, approximately 1 and 0.5 cm s−1, respectively. A slight seasonal trend observed in νd can be attributed to meteorological rather than physiological factors. The seasonal variation of H2O2 and ROOH concentrations, however, effects a significant seasonal variation in flux. Highest concentrations and therefore highest fluxes were observed during midsummer. On a diurnal scale, maximum deposition velocities coincide with high concentrations only during midday. Thus the highest fluxes occur primarily from 1100 to 1500 hours. The transport of H2O2 appears to be similar to that of other soluble, reactive trace gases, such as HNO3 and NH3, and a small surface resistance is suspected.
Investigations of marine aerosols over the tropical Indian Ocean
Authors: Moorthy K. Krishna , Satheesh S. K. , Murthy B. V. Krishna
Published: February 2004

Results of the studies on the characteristics of marine aerosol optical depths made in remote regions of the tropical Indian Ocean using a multiwavelength solar radiometer, taken on a scientific cruise, are presented. The dependence of the aerosol optical depths on prevailing winds in marine boundary layer and on deck level relative humidity (RH) are examined. Aerosol optical depths (τp) in far oceanic regions with marine air mass prevailing, in general, are found to increase nearly exponentially with average wind speed (Ua) as τp=τo exp(a Ua), where a = 0.16 ± 0.04. No association is seen with deck level relative humidity, as the effects of wind appear to offset the effects due to RH. The columnar size distributions retrieved from aerosol spectral optical depths reveal two modes, one at ∼0.04 μm and a secondary mode at ∼0.8 μm. The columnar mass loading estimated from the size distributions increases exponentially with wind speed and has a wind independent value of ∼28 mg m−2.
Satellite retrieval of aerosol properties over the ocean using measurements of reflected sunlight: Effect of instrumental errors and aerosol absorption
Authors: Mishchenko Michael I. , Travis Larry D.
Published: February 2004

A major task of several currently existing and planned satellite instruments is to provide accurate global monitoring of the distribution and properties of tropospheric aerosols using radiance and/or polarization measurements of the reflected sunlight. We use advanced computer simulations of radiative transfer in a realistic atmosphere‐ocean model at a wavelength of 865 nm to examine the sensitivity of several widely used and recently developed retrieval techniques to aerosol absorption and instrumental errors. We assume that nonabsorbing (e.g., sulfate) and strongly absorbing (e.g., soot) aerosol components are mixed externally and that the scattering matrix of the mixture is that of the nonabsorbing component, while the only effect of the absorbing component is to reduce the single‐scattering albedo. We show that neither algorithms using multiple‐viewing‐angle radiance measurements nor analogous polarization measurements or their combination can retrieve the aerosol single‐scattering albedo with sufficient accuracy. However, accurate retrievals of the aerosol optical thickness, refractive index, and effective radius using polarization measurements do not require a precise knowledge of the aerosol single‐scattering albedo, whereas potential uncertainties in the single‐scattering albedo can strongly influence the accuracy of aerosol retrievals based on intensity measurements alone. Another important conclusion is that the accuracy of aerosol retrievals based on intensity and/or polarization measurements of the reflected sunlight is strongly corrupted by instrumental errors. We show that nonzero measurement errors can result in the best fit of model computations to measurement data being obtained with aerosol parameters far different from the actual ones. Our results emphasize the importance of accurate and stable instrumental calibration and suggest that the absolute radiometric uncertainty should be constrained to about ±4% or better and the absolute polarization accuracy should be kept to within ±0.2%. However, less accurate polarization measurements can still be used to estimate the aerosol refractive index and effective radius with reasonable accuracy. The results of our previous paper [Mishchenko and Travis, 1997] and this one demonstrate the limited capabilities of aerosol retrieval techniques based on intensity measurements alone and suggest that high‐precision spaceborne polarimetry may potentially be the only way of retrieving aerosol characteristics with accuracy needed for long‐term monitoring of global climate forcings and feedbacks.