bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of water‐soluble organic matter isolated from atmospheric fine aerosol
Authors: Kiss Gyula , Varga Bálint , Galambos István , Ganszky Ildikó
Published: December 2002

Atmospheric fine aerosol (dp < 1.5 μm) was collected at a rural site in Hungary from January to September 2000. The total carbon concentration ranged from 5 to 13 μg m−3 and from 3 to 6 μg m−3 in the first three months and the rest of the sampling period, respectively. On average, water‐soluble organic carbon (WSOC) accounted for 66% of the total carbon concentration independent of the season. A variable fraction of the water‐soluble organic constituents (38–72% of WSOC depending on the sample) was separated from inorganic ions and isolated in pure organic form by using solid phase extraction on a copolymer sorbent. This fraction was experimentally characterized by an organic matter to organic carbon mass ratio of 1.9, and this value did not change with the seasons. Furthermore, the average elemental composition (molar ratio) of C:H:N:O ≈ 24:34:1:14 of the isolated fraction indicated the predominance of oxygenated functional groups, and the low hydrogen to carbon ratio implied the presence of unsaturated or polyconjugated structures. These conclusions were confirmed by UV, fluorescence, and Fourier transform infrared (FTIR) studies. On the basis of theoretical considerations, the organic matter to organic carbon mass ratio was estimated to be 2.3 for the nonisolated water‐soluble organic fraction, resulting in an overall ratio of 2.1 for the WSOC. In order to extend the scope of this estimation to the total organic carbon, which is usually required in mass closure calculations, the aqueous extraction was followed by sequential extraction with acetone and 0.01 M NaOH solution. As a result, a total organic matter to total organic carbon mass ratio of 1.9–2.0 was estimated, but largely on the basis of experimental data.
Global observations of the carbon budget 3. Initial assessment of the impact of satellite orbit, scan geometry, and cloud on measuring CO2 from space
Authors: Rayner P. J. , Law R. M. , O'Brien D. M. , Butler T. M. , Dilley A. C.
Published: December 2002

In this third of three companion papers we assess the utility of column‐integrated measurements of CO2 in constraining surface source estimates. The measurements have error characteristics defined by O'Brien and Rayner [2002]. There we described a retrieval algorithm which appeared capable of unbiased retrievals. An assessment of the sensitivity to dominant sources of error in these measurements suggested a precision about 0.5% of the background mixing ratio. We include this information along with the probability of clear sky and the sampling pattern imposed by a particular orbit and scan geometry. We carry out a synthesis inversion to recover specified surface sources. The uncertainty of the inferred sources quantifies the strength of the constraint offered by such measurements. The difference between input and retrieved sources demonstrates biases in the whole procedure. We show that source uncertainties are low in the presence of a sunlit surface but rise dramatically at high latitudes in winter. Provided we use sufficient spatial resolution for the sources we estimate, the inversion can also produce relatively accurate estimates. The inversion procedure is sensitive to biases caused by poor sampling of the diurnal cycle. Errors that isotropically affect all measured mixing ratios do not cause biases in estimated sources.
Organic compounds in biomass smoke from residential wood combustion: Emissions characterization at a continental scale
Authors: Fine Philip M. , Cass Glen R. , Simoneit Bernd R. T.
Published: December 2002

Wood smoke in the atmosphere often accounts for 20–30% of the ambient fine‐particle concentrations. In communities where wood is burned for home heating, wood smoke can at times contribute the majority of the atmospheric fine‐particle burden. Chemical mass balance receptor models that use organic compounds as tracers can be used to determine the contributions of different emission sources, including wood smoke, to atmospheric fine‐particle samples. In order for organic chemical tracer techniques to be applied to communities across the United States, differences in wood smoke composition that arise from differences in the type of wood burned in various regions must be understood. A continental‐scale accounting of particulate organic compound emissions from residential wood combustion has been constructed which helps to quantify the regional differences in wood smoke composition that exist between different parts of the United States. Data from a series of source tests conducted on 22 North American wood species have been used to assemble a national inventory of emissions for more than 250 individual organic compounds that are released from wood combustion in fireplaces and wood stoves in the United States. The emission rates of important wood smoke markers, such as levoglucosan, certain substituted syringols and guaiacols, and phytosterols vary greatly with wood type and combustor type. These differences at the level of individual wood type and combustion conditions translate into regional differences in the aggregate composition of ambient wood smoke. By weighting the source test results in proportion to the availability of firewood from specific tree species and the quantities of wood burned in each locale, it is possible to investigate systematic differences that exist between wood smokes from different regions of North America. The relative abundance of 10 major wood smoke components averaged over the emissions inventory in different regions of the United States is computed and then used to illustrate the extent to which wood smoke composition differs from region to region in North America.
Cloud liquid water and ice measurements from spectrally resolved near‐infrared observations: A new technique
Authors: Daniel J. S. , Solomon S. , Portmann R. W. , Langford A. O. , Eubank C. S. , Dutton E. G. , Madsen W.
Published: December 2002

A new technique is presented for the simultaneous measurement of water vapor, liquid water, and water ice in clouds using spectral observations of scattered sunlight between 0.865 and 1.065 μm. A nonlinear least squares approach is used to fit the measurements with the absorption spectral signatures of the vapor, liquid, and solid phases of water. This allows for the retrieval of the total path‐integrated column abundances of vapor, liquid, and ice and directly yields the fractional absorption by all three phases of water within clouds at these wavelengths. Laboratory, ground‐based, and aircraft‐based observations are presented that illustrate the application of this technique and its comparison to other methods of measuring liquid water in widely varying conditions. The results suggest that the retrieval of liquid water is relatively insensitive to interference from other absorbers. The measurement of ice is less accurate and precise than that of liquid and is affected to some degree by the absorption of water vapor and liquid; uncertainty estimates are given. The method provides key information for radiative balance studies and has the potential to aid aviation safety. An extension of this technique to include scattered sunlight at longer wavelengths is likely to produce more accurate results and lower detection limits for both liquid and ice. Applying the technique to shorter wavelengths should allow for retrievals that are less sensitive to photon path distribution uncertainties.
January and July regional climate simulation over South America
Authors: Nicolini M. , Salio P. , Katzfey J. J. , McGregor J. L. , Saulo A. C.
Published: December 2002

This work presents results, over the South American region, from the CSIRO Division of Atmospheric Research limited area model (DARLAM) and from the nine‐level general circulation model (GCM) of CSIRO (CSIRO Mk 2), within which it was nested in a one‐way mode. Ten separate 30‐day DARLAM simulations were performed for both January and July with a resolution of 125 km and were averaged to obtain a climatology for those months. This paper presents for the first time simulations of the January South American climate using a limited area model; previous similar studies simulated only the July climate. The goal of this study was to examine the capability of the CSIRO Mk 2 ‐ DARLAM nested modeling system for simulating the climate in the South American region. Further, it was desired to investigate whether the higher resolution of DARLAM improves the simulated climate over various subregions, compared with the GCM and observations. With this purpose, a representative set of variables was analyzed and statistically compared. Overall, the fields simulated by the nesting system provide a better representation of the South American climate than the GCM. In particular, significant improvements are found in the nested model climatology for near‐surface temperature and mean sea level pressure. Comparison of the January and July simulations shows a better wintertime performance. Some significant summertime features, like the Bolivian High, are reasonably well simulated by DARLAM, but not by the GCM.
Springtime photochemical ozone production observed in the upper troposphere over east Asia
Authors: Miyazaki Y. , Kita K. , Kondo Y. , Koike M. , Ko M. , Hu W. , Kawakami S. , Blake D. R. , Ogawa T.
Published: December 2002

Aircraft observations of ozone and its precursors (NO, NOy, CO, and nonmethane hydrocarbons) were made near Japan (26°–44°N) between 21 and 24 April 1998 to investigate the effect of transport and chemistry on the tropospheric ozone over east Asia in spring. The average mixing ratios of ozone and its precursors in the upper troposphere were higher than those observed during February–March 1994. Significantly higher values of CO indicate that the influence of surface sources mediated by convection was large throughout the troposphere during the period. Highly polluted air masses were observed in the upper troposphere at 8–11 km over the Japan Sea on 24 April. These air masses were influenced by cumulus convection associated with a cold front over northeast China about 1 day prior to the observation. However, the majority of observed air masses in the upper troposphere were not directly affected by the recent emissions of the ozone precursors from east Asia. Instead, convection over other regions in the northern midlatitude, followed by long‐range transport, affected the abundances of ozone precursors in the upper troposphere. In these air masses, ozone was positively correlated with NOx and C3H8, indicating the effect of photochemical ozone production. The diurnal‐average column‐integrated rate of ozone production, estimated by a photochemical box model, was larger than the NH average and local stratospheric flux at NH midlatitudes in spring by a factor of 3–20. The net production rates in the majority of the air masses were estimated to be 0.5–4.4 ppbv d−1 in the upper troposphere. These results indicate the important role photochemistry plays in controlling the upper tropospheric ozone abundance in spring.
Spectroscopic database for ozone in the fundamental spectral regions
Authors: Wagner G. , Birk M. , Schreier F. , Flaud J.‐M.
Published: December 2002

High‐resolution Fourier transform infrared measurements of the three ozone fundamentals have been performed. A total of 16 spectra have been recorded, including pure as well as oxygen‐ and nitrogen‐broadened ozone at room temperature and 200 K. Focus was set on quality assurance for sample preparation and on prevention of instrumental and retrieval errors. Line positions, line strengths and pressure‐broadened half widths have been determined. A quantum mechanical analysis of line positions and line strengths was performed, and improved molecular constants were obtained. Individual pressure‐broadening parameters and temperature exponents were calculated and represented as polynomials in the m quantum number for differently binned sets of subbands. Accuracies of better than 2% were achieved for both line strengths and pressure broadening of many strong transitions. The new data are suited for update of line‐by‐line spectroscopic databases.
Decomposition of peat from upland boreal forest: Temperature dependence and sources of respired carbon
Authors: Dioumaeva Irina , Trumbore Susan , Schuur Edward A. G. , Goulden Michael L. , Litvak Marcy , Hirsch Adam I.
Published: December 2002

The response of large stores of carbon in boreal forest soils to global warming is a major uncertainty in predicting the future carbon budget. We measured the temperature dependence of decomposition for upland boreal peat under black spruce forest with sphagnum and feather moss understory using incubation experiments. CO2efflux rates clearly responded to temperature, which ranged from −10° to +8°C by ∼2°C increments. At temperatures below 0°C, significant decomposition was observed in feather moss peat but not in wetter sphagnum peat. Above 0°C, decomposition was exponentially related to temperature, corresponding to a Q(10) (the ratio of the rate of CO2evolution at one temperature divided by that at a temperature 10°C cooler) of 4.4 for feather moss and 3.1 for sphagnum peat. The greatest change in CO2evolution rate with temperature occurred between −2° and 0°C, which coincided with the phase transition of soil water. We saw no large change in the rate of CO2evolution between incubation experiments separated by a 6 month storage period for feather moss peat. Stable C isotope measurements of evolved CO2and the rate of change of CO2evolution with time suggest different substrates are used to sustain heterotrophic respiration above and below freezing. Radiocarbon signatures of CO2respired from both types of peat reflected significant contributions from C fixed in the last 35 years (“bomb”14C) as well as C fixed prior to 1950. We observed no change in the Δ14C of respired CO2with temperature. Isotopic signatures of peat components showed that a combination of substrates must contribute to the CO2evolved in our incubations. Decomposition of fine roots (which made up less than 7% of the total peat C) accounted for ∼50% of respired CO2in feather moss peat and for ∼30% of respired CO2in sphagnum peat. Fine‐grained (<1 mm), more humified material that makes up 60–70% of the bulk peat organic carbon contributed significantly to heterotrophic respiration (∼30% in feather moss and ∼50% in sphagnum moss peat), despite slow decomposition rates. Increased temperatures caused enhanced decomposition from all pools without changing their relative contributions. Because the contribution of peat decomposition is a small portion of total soil respiration at the study site, increased respiration rates would be difficult to measure as increased fluxes in the field. Nonetheless, sustained warming could lead to significant loss of C from these peat layers.
A scaling analysis of ER‐2 data in the inner Arctic vortex during January–March 2000
Authors: Tuck A. F. , Hovde S. J. , Richard E. C. , Fahey D. W. , Gao R. S. , Bui T. P.
Published: December 2002

We apply multifractal analysis using exponents H1, C1, and α to straight and level stratospheric flight legs of the ER‐2 high‐altitude research aircraft in the inner vortex (defined as having wind speed <30 ms−1). The quantities so analyzed were ozone, wind speed s and temperature T, with the more gappy NOy data being analyzed by H1 alone. The results for ozone, wind, and temperature are presented as time‐dependent data on the three possible planes of the exponents and are compared for the different variables. We relate values of H1 found in January observations of NOy to those found for ozone. Inner vortex mixing does not remove the small‐scale polar stratospheric cloud‐induced antipersistence (negative correlation between neighboring intervals for all choices of interval) in ozone by mid‐March. Given that large particles were in evidence on all flights examined up to and including 7 March (although in greatly decreased numbers compared to January), this is reasonable. The value of α for ozone did, however, show an increase by mid‐March, consistent with the widespread ozone loss evident from time series of histograms of ozone and methane. The histograms also demonstrate that inhomogeneity, with long tails in the probability distributions, is maintained throughout at the 15–25% level in both species. Interpretation is made in terms of polar stratospheric cloud (PSC) induced antipersistence competing with persistence induced by the large‐scale insolation field, with the balance increasingly favoring the latter as time proceeds. Results are compared with inner vortex data obtained during earlier ER‐2 flights in the Antarctic (1987) and in the Arctic (1989). The inner vortex over Antarctica showed significant increases in H1(O3) and α during mid to late September. The correlated increases are consistent with latitudinal excursions of the outer vortex after the cessation of PSC processing, with increased solar exposure increasing H1(O3) and a greater variety of filaments increasing α(O3). It is concluded that the results have implications for the calculation of photochemical ozone loss in the vortex as a function of time and show that the combined effects of Bolgiano‐Obukhov k−11/5 vertical scaling and Kolmogorov k−5/3 horizontal scaling predict the scaling behavior of wind speed observed by the aircraft. Rates of change of scaling exponents are linked to horizontal mixing rates and are combined with rates of change of methane to estimate diabatic descent and ozone loss rates for the inner vortex.
Remote sensing from the infrared atmospheric sounding interferometer instrument 1. Compression, denoising, and first‐guess retrieval algorithms
Authors: Aires F. , Rossow W. B. , Scott N. A. , Chédin A.
Published: December 2002

A principal component analysis (PCA) scheme is developed for treatment of observations from the high spectral resolution Infrared Atmospheric Interferometer (IASI) spaceborne instrument. Compression and denoising of IASI observations are performed using this PCA. This preprocessing methodology also allows for a fast pattern recognition to obtain a first guess from a climatological data set. The performance of the compression, denoising, and multivariate first‐guess retrieval are evaluated with a large diversified data set of radiosondes atmospheres including rare events. Overall, the instrumental noise in the overall observed IASI spectrum goes from 0.9 to 0.2 K after denoising. This analysis procedure will be used by Aires et al. [2002c] to retrieve simultaneously temperature, water vapor and ozone atmospheric profiles.
Global tracer modeling during SOLVE: High‐latitude descent and mixing
Authors: Plumb R. Alan , Heres William , Neu Jessica L. , Mahowald Natalie M. , del Corral John , Toon Geoffrey C. , Ray Eric , Moore Fred , Andrews Arlyn E.
Published: December 2002

We compare tracer observations made during the northern winter of 1999/2000 with the results of simulations with a three‐dimensional chemical transport model, driven by assimilated winds. During the course of the winter, very low concentrations of tracers of tropospheric origin (such as N2O) descend into the lower stratosphere within the polar vortex. The altitude of origin of this air has been a matter of debate in the literature; by midwinter, both observations and model results indicate a significant fraction of mesospheric air in the lower stratosphere. Observations from aircraft and balloon flights reveal markers of mesospheric air within the Arctic vortex in the lower and middle stratosphere. An artificial tracer introduced into the model mesosphere at the start of winter descends (being diluted as it does so) all the way down to the 450 K potential temperature surface by March. Modeled tracer‐tracer relationships evolve through the winter in a way similar to observations, but the separation between vortex and extravortex curves is exaggerated, suggesting that the model exhibits excessive horizontal mixing within and into the vortex. The tracer‐tracer relationships are used to identify partly mixed air as lying, in tracer‐tracer space, in a region intermediate between the characteristic vortex and midlatitude relationships. Air lying in a collar region just inside the vortex edge is thus identified as being mixed, and this indicates excessive horizontal mixing in the model across the vortex edge.
Vascular plants as regulators of methane emissions from a subarctic mire ecosystem
Authors: Öquist M. G. , Svensson B. H.
Published: December 2002

Vascular plant functions as controlling mechanisms of methane emissions were investigated at two contrasting habitat types at a subarctic peatland ecosystem in northern Sweden. One of the habitats was ombrotrophic (vegetation dominated byEriophorum vaginatumandCarex rotundata), while the other was minerotrophic (vegetation dominated byEriophorum angustifolium). Through shading manipulations we successfully reduced the gross photosynthetic rates of the vascular plant communities. At the ombrotrophic site a 25% reduction in gross photosynthesis lead to a concomitant 20% reduction in methane emission rates, indicating a strong substrate‐based coupling between the vascular plant community and the methanogenic populations. At the minerotrophic site, methane emission rates were unaffected, although plant photosynthesis was reduced by almost 50%. However, the methane emission rates at the minerotrophic site were significantly correlated with the number of vascular plants. We conclude that at the minerotrophic site the vegetation influences methane emission rates by facilitating methane transportation between the soil and the atmosphere, while at the ombrotrophic site the relationship between the vascular plant community and methane emissions is mediated by substrate‐based interactions regulated by plant photosynthetic activity.
Nonlinear characteristics of the surface air temperature over Canada
Authors: Wu Aiming , Hsieh William W. , Shabbar Amir
Published: December 2002

Nonlinear characteristics of the Canadian surface air temperature (SAT) were investigated by applying a neural‐network‐based nonlinear principal component analysis (NLPCA) method to the SAT anomaly data for individual seasons. The SAT data were separated into three subsets: data for 1900–1949 and 1900–1995 over southern Canada (south of 60°N), called S0049 and S0095, respectively, and data for 1950–1995 over the entire country, called C5095. The NLPCA was computed for the three data sets separately. The leading NLPCA modes from C5095 and S0095 show similar results: the nonlinearity is strong in winter (December, January, and February, DJF) and fall (September, October, and November, SON), but is much weaker in spring (March, April and May, MAM) and summer (June, July, and August, JJA), manifesting the seasonal dependence of the nonlinearity in the Canadian SAT. No significant nonlinearity is detected from data set S0049, even for the winter and fall seasons, indicating interdecadal dependence of the nonlinearity. The leading NLPCA mode combines the effects of Pacific‐North America (PNA) pattern and North Atlantic Oscillation (NAO) on the Canadian winter SAT. A possible reason for the existence of nonlinearity in the winter SAT only after 1950 is that the NAO manifested its strong negative phase from the 1950s to the early 1970s.
Two case studies of winter continental‐type water and mixed‐phase stratocumuli over the sea 1. Microphysical and optical properties
Authors: Gayet Jean‐François , Asano Shoji , Yamazaki Akihiro , Uchiyama Akihiro , Sinyuk Alexander , Jourdan Olivier , Auriol Frédérique
Published: December 2002

Collocated aircraft observations of microstructure and radiative properties of winter boundary layer clouds over the East China Sea and the Japan Sea have been carried out in January 1999 within the Japanese Cloud and Climate Study (JACCS) program. The first part of the paper describes the in situ measured microphysical and optical properties for two cases of boundary layer winter stratocumulus clouds, which concern, first, a rather uniform, supercooled water cloud contaminated by aerosols and, second, a highly heterogeneous, mixed‐phase stratiform cloud. Using the Polar Nephelometer, a new instrument for measuring, in situ, the scattering phase function of cloud droplets and ice particles, the polluted, continental‐type stratocumulus cloud can be optically regarded as a liquid water cloud because the measured scattering phase functions fitted very well with those calculated from Mie theory for the directly measured FSSP size distributions. In mixed‐phase cloud, the measured scattering phase function shows that ice particles strongly affect optical properties of the cloud, where large number of liquid water droplets with higher extinction coefficient and asymmetry factor values were converted into a much smaller number of large ice crystals with lower extinction coefficient and asymmetry factor. Furthermore, a quasi‐stable liquid‐topped cloud layer with precipitating ice particles was noticed; the layer may, first, affect the cloud radiative properties and, second, seriously restrict the interpretation of satellite cloud composition retrievals.
Distribution of tropical cirrus in relation to convection
Authors: Massie Steven , Gettelman Andrew , Randel William , Baumgardner Darrel
Published: December 2002

Daily values of Halogen Occultation Experiment (HALOE) aerosol extinction and Climate Diagnostics Center (CDC) outgoing longwave radiation (OLR) data are used to quantify the statistical and geographical relationships of tenuous cirrus to OLR for pressure levels near the equatorial tropopause. Daily locations of deep convection are identified by analysis of the CDC OLR data. Analysis of the HALOE and CDC data demonstrates that cirrus extinction is larger over deep convection than over clearer regions by a factor of 3. Deep convection, however, occupies only 7% of the equatorial region. Ninety percent of the cirrus clouds near the tropopause are located outside of regions of deep convection. Estimates of the equivalent H2O amount in the cirrus are calculated by applying transformations from extinction to volume density. Averaged over the HALOE 2 km vertical field of view, the amount of equivalent H2O in cirrus is 0.1–0.2 ppmv, which is 2 to 5% of the local gas phase H2O. Five‐day back trajectories near the tropopause are calculated for 1995–2000. Half of the HALOE cirrus observations over the maritime continent are consistent with formation by convective blow‐off, while the other half are consistent with in situ formation processes.
Retrieval of tropospheric ozone from simulations of limb spectral radiances as observed from space
Authors: Clough S. A. , Worden J. R. , Brown P. D. , Shephard M. W. , Rinsland C. P. , Beer R.
Published: December 2002

The frequent and direct remote sensing of the tropospheric ozone profile is a critical environmental measurement to be performed on a global scale by future satellite instruments. An approach has been developed for the retrieval of tropospheric ozone profiles from 9.6 μm limb‐viewing clear‐sky radiances generated for the spectral resolution and signal‐to‐noise of the Tropospheric Emission Spectrometer (TES). TES is a high‐resolution Fourier transform spectrometer under development for NASA's Earth Observing System Aura platform (http://eos-chem.gsfc.nasa.gov/). The simulated radiance spectra are calculated from northern hemisphere midlatitude lidar profile measurements. The ozone profile retrieval and the associated errors are obtained as a function of atmospheric pressure level using the method of nonlinear least squares with regularization. In order to accelerate convergence a two‐stage strategy has been applied in which the full profile retrieval has been preceded by a shape retrieval involving a smaller set of near independent parameters. Our analysis indicates that the O3 profile can be retrieved from the TES limb measurements with a relative uncertainty of 5% (1σ) in the middle and upper troposphere.
Particle production in the outflow of a midlatitude storm
Authors: Clement C. F. , Ford I. J. , Twohy C. H. , Weinheimer A. , Campos T.
Published: December 2002

The concentrations of atmospheric gases and condensation nuclei (CN) or aerosol in the outflow of a storm were measured aboard a NASA DC‐8 aircraft, as described in a companion paper [Twohy et al., 2002]. The data are used here to study the production of the aerosol. Major fluctuations in CN concentration are observed, in correlation with gas‐phase species, but these are shown to arise as the result of the mixing of two distinct air masses. It is deduced that the CN originated in a storm outflow air mass and that its concentration before mixing was approximately uniform over a flight distance of about 200 km. The formation of the aerosol by nucleation followed by growth and coagulation is analyzed assuming that it consists of water and sulphuric acid produced locally by the oxidation of SO2. The analysis uses analytic models, and it is concluded that a 5 min burst of nucleation was followed by growth and coagulation over a period of about 5 hours. Both the mass and number concentrations of the observed aerosol can be reproduced by this analysis within a timescale consistent with that of the storm. The final number concentration is very insensitive to the initial SO2 concentration.
Information content of the 95‐GHz cloud radar signals: Theoretical assessment of effects of nonsphericity and error evaluation of the discrete dipole approximation
Authors: Okamoto Hajime
Published: December 2002

The applicability of the discrete dipole approximation (DDA) is examined to estimate backscattering signatures of ice crystals randomly oriented in horizontal plane (2‐D) and oriented in three‐dimensional space (3‐D) for various sizes and aspect ratios at the frequency of 95 GHz (3.16 mm). Previous studies have shown that accurate estimation of the backscattering properties seem to be problematic for particles with sharp edges and fixed in one orientation with respect to the incident radar wave. Contrary, the errors in the backscattering calculations for 2‐D and 3‐D orientations are drastically reduced and turn out to be less than 10% for both radar reflectivity factor Ze and linear depolarization ratio (LDR). Exception is the LDR for hexagonal plates with 2‐D orientation, where it is not possible to achieve a converging solution. Then the size‐averaged Ze and LDR for various aspect ratios are estimated as a function of effective radius reff, for the first time, with a confidence of accuracy. The differences in Ze for different shapes or orientations are within 2 dB (40%), and thus the size is a control parameter for reff < 100 μm. LDR shows weak size dependence. For reff > 100 μm, Ze and LDR show strong dependence on shape as well as size. Due to the fact that the local minimum and maximum of Ze and LDR occur at different reff depending on the shape, nonsphericity plays a major role for reff > 100 μm, where the maximum differences between Ze for the different shapes are 8 dB and those for LDR are 14 dB. For reff > 1000 μm, the maximum differences between the LDRs for the different shapes are 5 dB, while the effect of orientations becomes comparable, although such larger particles are rare in cirrus clouds.
Equatorial Mid‐Tropospheric Easterly Jet over the eastern Pacific: Comparison from the ECMWF and NCEP‐NCAR reanalyses
Authors: Hastenrath Stefan , Polzin Dierk
Published: December 2002

The upper‐air data set of the European Centre for Medium‐Range Weather Forecasts (ECM) 1979–93 Reanalysis is evaluated in comparison to the National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCP) Reanalysis for the same period. Attention is focused on the Equatorial Mid‐Tropospheric Easterly Jet (EMTEJ) over the eastern Pacific, first noted from a short series of rawin soundings at Galapagos, and then corroborated in its broad spatial context from the NCP 40‐year Reanalysis. The present follow‐up study contributes a comparison of evidence from the two sources with different model assimilations. The major characteristics of the EMTEJ are confirmed, although the winds from ECM are overall slower and those from NCP faster than the measurements over Galapagos. In both ECM and NCP the easterly speed maximum along the equator is over the eastern Pacific located around 600–700 mb and further westward at progressively lower elevations. Divergence prevails in the realm of the speed maximum and is primarily fed by subsidence from aloft. The ECM evidence differs from NCP by a more westward location of the easterly speed maximum and overall weaker flow.
Surface energy exchanges and interactions with thunderstorms during the Maritime Continent Thunderstorm Experiment (MCTEX)
Authors: Beringer Jason , Tapper Nigel
Published: December 2002

Inputs of heat and moisture through surface energy exchanges are important in the evolution of diurnally modulated thunderstorms. As part of the Maritime Continent Thunderstorm Experiment (MCTEX) conducted on the Tiwi Islands, northern Australia, we measured the surface energy exchanges above the dominant surface types (savanna, grassland, forest and shallow tidal strait). Measurements were made during the monsoon transition period (October–December) using the Bowen ratio and the aerodynamic techniques. A full radiation balance was measured at the Savanna site, where the surface albedo was determined as 0.19. The surface energy exchanges showed broad similarities between the sites, with comparable high net radiation totals averaging 11.8 MJ.m−2.day−1 over the terrestrial sites. The substrate heat fluxes were large at the Tidal strait (4.21 MJ.m−2.day−1) due to the high rates of energy absorption into water. The partitioning of net radiation into sensible and latent heat fluxes was controlled primarily by surface characteristics such as soil moisture and vegetation cover, with Bowen ratios averaging 1.08, 0.65, 0.5 and 0.40 for grassland, forest, savanna and tidal strait sites, respectively. A higher Bowen ratio was recorded at the Grassland site as this was during an earlier period that was much drier. Strong relationships were observed between the total surface convective fluxes and boundary layer development (e.g., the lifting condensation level) and between the magnitude of the daytime surface sensible heat flux and the onset time of thunderstorm convection. Observed terrestrial surface fluxes of moisture (averaging 165–265 W.m−2) were deemed insufficient for observed thunderstorm initiation and suggest that sea breeze advection of moisture is necessary. Tiwi Island thunderstorms were shown to represent a dynamic system where surface fluxes are important in generating a boundary layer sufficient to initiate the thunderstorms but where feedbacks between thunderstorms and surface fluxes eventually help terminate the storms.
On the relative role of convection, chemistry, and transport over the South Pacific Convergence Zone during PEM‐Tropics B: A case study
Authors: Mari Céline , Saüt Carine , Jacob Daniel J. , Staudt Amanda , Avery Melody A. , Brune William H. , Faloona Ian , Heikes Brian G. , Sachse Glen W. , Sandholm Scott T. , Singh Hanwant B. , Tan David
Published: December 2002

A mesoscale 3D model (Meso‐NH) is used to assess the relative importance of convection (transport and scavenging), chemistry, and advection in the vertical redistribution of HOx and their precursors in the upper tropical troposphere. The study is focused on marine deep convection over the South Pacific Convergence Zone (SPCZ) during the PEM‐Tropics B Flight 10 aircraft mission. The model reproduces well the HOx mixing ratios. Vertical variations and the contrast between north and south of the SPCZ for O3 are captured. Convection uplifted O3‐poor air at higher altitude, creating a minimum in the 9–12 km region, in both modeled and observed profiles. The model captured 60% of the observed HCHO variance but fails to reproduce a peak of HCHO mixing ratio at 300 hPa sampled during the northern spirals. Simulated HCHO mixing ratios underestimate observations in the marine boundary layer. In the model, convection is not an efficient process to increase upper tropospheric HCHO, and HCHO is unlikely to serve as a primary source of HOx. Convection plays an important role in the vertical distribution of CH3OOH with efficient vertical transport from the boundary layer to the 10–15 km region where it can act as a primary source of HOx. The SPCZ region acts as a barrier to mixing of tropical and subtropical air at the surface and at high altitudes (above 250 hPa). The 400–270 hPa region over the convergence zone was more permeable, allowing subtropical air masses from the Southern Hemisphere to mix with tropical air from NE of the SPCZ and to be entrained in the SPCZ‐related convection. In this altitude range, exchange of subtropical and tropical air also occurs via airflow, bypassing the convective region SW and proceeding toward the north of the SPCZ.
Summertime nitrous acid chemistry in the atmospheric boundary layer at a rural site in New York State
Authors: Zhou Xianliang , Civerolo Kevin , Dai Hongping , Huang Gu , Schwab James , Demerjian Kenneth
Published: December 2002

Ambient measurements of HONO and HNO3, using a highly sensitive coil scrubbing/HPLC/visible detection technique, were made at a rural site in southwestern New York State from 26 June to 14 July 1998, along with concurrent measurements of NOx, NOy, O3, and various meteorological parameters. The mean (and median) half‐hour concentrations of HONO and HNO3 during this period were 63 (and 56) pptv and 418 (and 339) pptv, respectively. On average, there were two HONO concentration peaks, the first around 0200–0300 LT and the second around 0700–0800 LT, and a minimum at about 2000 LT. The sum of NOx, HONO, and HNO3 (ΣNOyi) was highly correlated with the measured NOy concentration (r2 = 0.64). The average HONO/NOx ratio was 0.07, while the average ΣNOyi/NOy ratio was 0.66. During the early morning hours, the photolysis of HONO appeared to be a dominant source of HOx radicals in boundary layer near the ground surface. The average daily radical production from HONO photolysis was 2.3 ppbv, accounting for 24% of the total production from photolyses of HONO, O3, and HCHO at the measurement height of 4 m above the ground. Diurnal patterns of HONO and relative humidity suggest that the ground and vegetation surfaces were sinks for HONO in the boundary layer when dew droplets were formed at night and that the subsequent release of the trapped nitrous acid/nitrite from the surfaces acted as a strong HONO source in the morning as the dew droplets evaporated. Our data also suggest that, in order to maintain the observed daytime HONO concentration of ∼60 pptv, there should be a strong daytime source of 220 pptv hr−1, which was much greater than the nighttime source of 13 pptv hr−1 and the estimated production of ∼ 40 pptv hr−1 from the gas‐phase NO‐OH reaction. Photolysis of HNO3, which deposits and accumulates on the ground and vegetation surfaces, may contribute significantly to the “missing” daytime HONO sources.
Intercomparison of radiative transfer codes under non‐local thermodynamic equilibrium conditions
Authors: von Clarmann T. , Dudhia A. , Edwards D. P. , Funke B. , Höpfner M. , Kerridge B. , Kostsov V. , Linden A. , López‐Puertas M. , Timofeyev Yu.
Published: December 2002

Limb infrared spectra calculated by the Optimized and Precise Radiative Transfer Algorithm (KOPRA), GENLN2, Reference Forward Model (RFM), and Simulation Program for Infrared Radiative Transfer (SPIRT) radiative transfer algorithms were intercompared for both local thermodynamic equilibrium (LTE) and non‐local thermodynamic equilibrium (non‐LTE) conditions, in the latter case for given profiles of vibrational temperatures. The overall agreement is usually better than approximately 0.5%, except for isolated phenomena that have been assessed in more detail. Most spectral radiance discrepancies occur also under LTE conditions and are attributed to different treatment of far wings of lines, integration schemes, and mass‐weighted averaging of atmospheric temperature and pressure along slant path segments as well as different spectral sampling during the calculation of monochromatic radiances.
The effect of atmospheric absorption of sunlight on the runaway greenhouse point
Authors: Pujol Toni , Fort Joaquim
Published: December 2002

The longwave emission of planetary atmospheres that contain a condensable absorbing gas in the infrared (i.e., longwave), which is in equilibrium with its liquid phase at the surface, may exhibit an upper bound. Here we analyze the effect of the atmospheric absorption of sunlight on this radiation limit. We assume that the atmospheric absorption of infrared radiation is independent of wavelength except within the spectral width of the atmospheric window, where it is zero. The temperature profile in radiative equilibrium is obtained analytically as a function of the longwave optical thickness. For illustrative purposes, numerical values for the infrared atmospheric absorption (i.e., greenhouse effect) and the liquid vapor equilibrium curve of the condensable absorbing gas refer to water. Values for the atmospheric absorption of sunlight (i.e., antigreenhouse effect) take a wide range since our aim is to provide a qualitative view of their effects. We find that atmospheres with a transparent region in the infrared spectrum do not present an absolute upper bound on the infrared emission. This result may be also found in atmospheres opaque at all infrared wavelengths if the fraction of absorbed sunlight in the atmosphere increases with the longwave opacity.
Retrieving aerosol optical depth and type in the boundary layer over land and ocean from simultaneous GOME spectrometer and ATSR‐2 radiometer measurements, 1, Method description
Authors: Holzer‐Popp T. , Schroedter M. , Gesell G.
Published: December 2002

A new aerosol retrieval method called Synergetic Aerosol Retrieval (SYNAER), using simultaneous measurements of the radiometer Along Track Scanning Radiometer (ATSR‐2) and the spectrometer Global Ozone Monitoring Experiment (GOME) in the visible and near‐infrared spectra, was developed. Both instruments are flown onboard the European Remote Sensing (ERS‐2) satellite. SYNAER delivers boundary layer aerosol optical thickness (BLAOT) and aerosol type both over land and over ocean, the latter as BLAOT percentage of six representative components from the Optical Parameters of Aerosols and Clouds (OPAC) data set. The high spatial resolution of ATSR‐2 permits accurate cloud detection. It allows BLAOT calculation over automatically selected dark pixels and surface albedo correction for a set of boundary layer aerosol mixtures. After spatial integration and colocation to GOME pixels, these parameters are used to simulate GOME spectra for the same set of aerosol mixtures. A least squares fit of these spectra to the measured and cloud‐corrected GOME spectrum chooses the aerosol mixture. First validation studies are presented in part 2 of this paper [Holzer‐Popp et al., 2002]. The method will be used for the future sensor pairs Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY)/Advanced ATSR (AATSR) on Envisat and GOME‐2/Advanced Very High Resolution Radiometer (AVHRR) on METOP. Thus, SYNAER holds the potential to extract a long‐term climatological data set.
Impact of drought on seasonal monoterpene emissions from Quercus ilex in southern France
Authors: Staudt Michael , Rambal Serge , Joffre Richard , Kesselmeier Jürgen
Published: December 2002

We studied monoterpene emissions from the evergreen oak Quercus ilex exposed to different levels of summer drought to examine the seasonal variation of emissions in the Mediterranean area and to test the role of water limitations therein. Measurements were made in seven campaigns between June and January on intact leaves of mature trees growing in two adjacent sites, in one of which the natural water supply was reduced by a ground roof. In both sites, actual emission rates as well as light‐ and temperature‐normalized emission rates (i.e., emission factor (EF)) significantly changed during the seasons: Mean EFs increased from June to July to a broad summer maximum between 5.2 and 9.4 nmol m−2 leaf area s−1 (12–21 μg g−1 leaf dry mass h−1), dropped in October and November and reached a minimum of about 0.77 nmol m−2 s−1 (1.7 μg g−1 h−1) in January. From June to July, mean EFs of the trees with reduced water supply were significantly lower than those of trees with normal water supply. The lowered EF in summer was paralleled by lower predawn water potentials, leaf transpiration, photosynthesis and stomatal conductance with respect to control trees. The results suggest that in natural Q. ilex habitats the seasonal evolution of EF follows a marked summer‐winter cycle whose shape and intensity can be modified by summer drought.
The case for rainfall on a warm, wet early Mars
Authors: Craddock Robert A. , Howard Alan D.
Published: December 2002

Valley networks provide compelling evidence that past geologic processes on Mars were different than those seen today. The generally accepted paradigm is that these features formed from groundwater circulation, which may have been driven by differential heating induced by magmatic intrusions, impact melt, or a higher primordial heat flux. Although such mechanisms may not require climatic conditions any different than today's, they fail to explain the large amount of recharge necessary for maintaining valley network systems, the spatial patterns of erosion, or how water became initially situated in the Martian regolith. In addition, there are no clear surface manifestations of any geothermal systems (e.g., mineral deposits or phreatic explosion craters). Finally, these models do not explain the style and amount of crater degradation. To the contrary, analyses of degraded crater morphometry indicate modification occurred from creep induced by rain splash combined with surface runoff and erosion; the former process appears to have continued late into Martian history. A critical analysis of the morphology and drainage density of valley networks based on Mars Global Surveyor data shows that these features are, in fact, entirely consistent with rainfall and surface runoff. The necessity for a cold, dry early Mars has been predicated on debatable astronomical and climatic arguments. A warm, wet early climate capable of supporting rainfall and surface runoff is the most plausible scenario for explaining the entire suite of geologic features in the Martian cratered highlands.
A model for large‐scale volcanic plumes on Io: Implications for eruption rates and interactions between magmas and near‐surface volatiles
Authors: Cataldo Enzo , Wilson Lionel , Lane Steve , Gilbert Jennie
Published: December 2002

Volcanic plumes deposit magmatic pyroclasts and SO2 frost on the surface of Io. We model the plume activity detected by Galileo at the Pillan and Pele sites from 1996 to 1997 assuming that magmatic eruptions incorporate liquid SO2 from near‐surface aquifers intersecting the conduit system and that the SO2 eventually forms a solid condensate on the ground. The temperature and pressure at which deposition of solid SO2 commences in the Ionian environment and the radial distance from the volcanic vent at which this process appears to occur on the surface are used together with observed vertical heights of plumes to constrain eruption conditions. The temperature, pressure, and density of the gas–magma mixtures are related to distance from the vent using continuity and conservation of energy. Similar eruption mass fluxes of order 5 × 107 kg s−1 are found for both the Pillan and the Pele plumes. The Pele plume requires a larger amount of incorporated SO2 (29–34 mass %) than the Pillan plume (up to ∼6 mass %). Implied vent diameters range from ∼90 m at Pillan to ∼500 m at Pele. The radial extents of the optically dense, isothermal, incandescent parts of the eruption plumes immediately above the vents are ∼100 m at Pillan and ∼1300 m at Pele. Gas pressures in the vents are ∼20 kPa at Pillan and ∼2 kPa at Pele and the eruption conditions appear to be supersonic in both cases, though only just so at Pele.