bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and validation of Arctic radiation and clouds in a regional climate model
Authors: Rinke Annette , Dethloff Klaus , Christensen Jens H. , Botzet Michael , Machenhauer Bennert
Published: February 2004

A regional atmospheric climate model has been applied to simulate the Arctic climate north of 65°N at a 50 km horizontal resolution for January and July 1990. The monthly mean components of the surface radiative balance and clouds using ECHAM3 parameterization have been described and compared with data. The model overestimates the incoming shortwave flux, overestimates clouds during January, and underestimates clouds during July. The high‐resolution simulations show many regional details due to regionally different surface temperatures, clouds, surface albedo, and snow depths. The bias in the model simulation can be reduced by using the ECHAM4 parameterization. The use of the ECHAM4 radiation parameterization clearly improves the results, due to the better description of atmospheric absorption. Sensitivity experiments with different cloud parameters (drop size, droplet concentration, cloud phase) have been described. The simulated changes due to these cloud parameter changes occur in a very small spatial scale and are of similar order as the model bias itself.
Measurement and analysis of C2‐C10 hydrocarbons at Whiteface Mountain, New York
Authors: Gong Qing , Demerjian Kenneth L.
Published: February 2004

Canister‐based sampling and gas chromatography‐flame ionization detection analytical techniques were developed and employed in the field measurement of hydrocarbons conducted from June 1994 through December 1995 at the summit (1400 m) and lodge (600 m) of Whiteface Mountain (WFM). More than 50 ambient hydrocarbon species, including C2‐C10 alkanes, C2‐C6 alkenes, benzene and a select group of alkylated aromatics, and isoprene were analyzed using these techniques with an estimated accuracy of ±20%. The instrumental limit of detection was ∼20 parts per trillion carbon (pptC). Quality assurance of the analysis was performed, in part, via participation in the Nonmethane Hydrocarbon Intercomparison Experiment (NOMHICE). The NOMHICE results showed that for the majority of the target hydrocarbon species the percent differences between our analyses and those of the referee group were <10% for the standard mixtures and <20% for the whole air sample. Analyses of the hydrocarbon data indicate that WFM is routinely in the path of aged photochemical regional air masses which have been influenced by urban emission upwind of the site. The distribution of hydrocarbon species observed at WFM matches that of mobile sources. The seasonal variation of anthropogenic hydrocarbons at WFM is consistent with the expected seasonal variation in OH. The observed changes in the ratios of toluene/benzene from the summers of 1994–1995 are indicative of a greater reduction in the benzene emissions relative to toluene emissions over this period. One possible explanation for this change is the introduction of reformulated gasoline in many areas in the region starting in 1995. The concentrations of naturally emitted isoprene show a strong seasonal variation and temperature dependence.
Vertical structure of humidity and temperature budget residuals over the Mississippi River basin
Authors: Roads J. O. , Chen S.‐C. , Kanamitsu M. , Juang H.
Published: February 2004

Analyses have systematic tendencies or budget residuals that are not small. Unlike the budgets in general circulation model simulations, these budget residuals are an important component of analyses’ water and energy budgets. We can either get good budgets or good climates, but not both. To better understand the character of the residuals in the National Centers for Environmental Prediction's (NCEP) global analysis and reanalysis water and energy budgets, the vertical structure of the budget residuals in NCEP's global analyses pertinent to the Mississippi River basin water and energy budgets are described herein. The vertical structure of the residuals is obtained by using NCEP's reanalysis modeling system, which is initialized (started) from NCEP's operational Global Data Assimilation System analyses as well as from the new NCEP reanalyses; forecasts of 1 day duration, 4 times a day, are then made for several years. The budget residuals in the forecasts after the first 6 hours are similar to the original residuals in the analyses and reanalyses. The residuals appear to be related to a summertime “spin‐down” and wintertime “spin‐up” in cumulus convection, an adjustment in boundary layer diffusive transports near the surface and near the top of the boundary layer, and adjustments in large‐scale transports of moisture and temperature. These residuals may thus be providing clues as to what needs to be improved in analysis systems.
Airborne measurements of carbonaceous aerosols on the East Coast of the United States
Authors: Novakov T. , Hegg Dean A. , Hobbs Peter V.
Published: February 2004

In this paper we report results of aircraft measurements of mass concentrations of carbonaceous aerosols, total aerosol mass, and simultaneously determined light scattering and absorption coefficients onshore and offshore of the eastern coast of the United States. We describe the sampling and analytical methodology used to derive spatially resolved aerosol carbon concentrations and discuss these in the context of other concurrently collected data. The carbon mass was, on average, 50% of the total dry aerosol mass. The carbon mass fraction tended to increase with altitude, suggesting that ground‐based measurements can significantly underestimate the importance of carbon species in the column aerosol mass budget. The aerosol carbon mass was significantly correlated with aerosol light absorption, suggesting that the black and organic carbon components have, at least in part, common combustion sources. A regression of the light absorption coefficient onto carbon mass suggests that ∼10% of the carbon mass is in the form of black (light‐absorbing) carbon.
Remote sensing of mesospheric temperature and O2(1Σ) band volume emission rates with the high‐resolution Doppler imager
Authors: Ortland D. A. , Hays P. B. , Skinner W. R. , Yee J.‐H.
Published: February 2004

An algorithm for obtaining temperatures and volume emission rate profiles in the mesosphere and lower thermosphere from HRDI measurements is described. Temperature and volume emission rates are derived via perturbation theory by comparing measured brightness to brightness computed from the forward model described here. Error analysis shows that the method recovers the temperatures with an error of 7° K and volume emission rates with an error of 3% from 80 to 100 km, providing global measurements of these fields in this altitude range for the first time. Results show the structure of the cold summer mesopause near the poles, the semiannual oscillation, and the diurnal tidal oscillations at the equator.
Estimation of water cloud properties from satellite microwave, infrared and visible measurements in oceanic environments: 1. Microwave brightness temperature simulations
Authors: Lin Bing , Wielicki Bruce , Minnis Patrick , Rossow William
Published: February 2004

Theoretical calculations are used to examine the spectral characteristics of SSM/I (special sensor microwave/imager) brightness temperature (Tb) values for non‐precipitating clouds over oceans. It was found that liquid water path (LWP) and the cloud water temperature (Tw) could be derived simultaneously with a technique using the SSM/I 37‐GHz and 85‐GHz brightness temperatures. Uncertainties in column water vapor (CWV) are the most important error sources in the estimation of LWP and Tw, while ice particles smaller than 100 μm in nonprecipitating clouds have a very weak effect (<1 K) on the Tb values at the relevant SSM/I frequencies. When all SSM/I instrument noise and error sources associated with sea surface temperature, wind speed, and CWV are considered, the biases in LWP from current microwave methods are very small (≤0.01 mm) and the standard deviations vary from 0.02 to 0.04 mm. The Tw bias and standard deviation decrease with increasing LWP from about 6 and 8 K, respectively, for clouds with low LWP to <1 K for LWP >0.4 mm. For most marine stratocumulus clouds (LWP ∼0.1 to 0.2 mm) the Tw bias and standard deviation are about 2 and 4 K, respectively, resulting in cloud height errors of ∼1 to 2 km. The method should yield an improvement in the accuracy of retrieved LWP because it more closely approximates cloud temperature than previous techniques. To use the radiative transfer results, it is necessary to normalize or calibrate them to the observations. This relative calibration using 22‐GHz brightness temperatures reveals differences of 2.86 K and −1.93 K for the 37‐GHz horizontal and 85‐GHz vertical channels, respectively, between the SSM/I observations and the model simulations. In multilayered cloud conditions, this new microwave analysis method, when combined with infrared data, should make it possible to determine cloud temperature for an upperlevel ice cloud from the infrared brightness temperatures while simultaneously deriving Tw and LWP for the lower liquid water cloud with the microwave data.
Growth and distribution of halons in the atmosphere
Authors: Butler James H. , Montzka Stephen A. , Clarke Andrew D. , Lobert Jürgen M. , Elkins James W.
Published: February 2004

The atmospheric burden of halons has continued to increase in recent years, despite an international ban on their production and sales in developed nations as of January 1, 1994. Halon emissions persist because of a lack of suitable substitutes for critical uses as fire extinguishants. As of January 1, 1997, halons H‐1301 (CBrF3), H‐1211 (CBrClF2), and H‐2402 (CBr2F4) were present in the troposphere at 2.3±0.1, 3.5±0.1, and 0.45±0.03 pmol mol−1. During 1995–1996 the tropospheric mole fraction of H‐1301 increased at 0.044±0.011 pmol mol−1 yr−1, while that for H‐1211 grew at 0.16±0.016 pmol mol−1 yr−1. These increases are significant and of concern because of the efficiency of bromine in depleting stratospheric ozone and because of the long atmospheric lifetimes of these gases. Given the current atmospheric record and the reported amount of halon produced before the ban on production, emission of H‐1301 at the 1995–1996 rate could continue for another 40 years, but H‐1211 would be depleted in 8–12 years. Exemptions to the ban on production may extend these periods. Tropospheric H‐2402 is increasing at 9±1 fmol mol−1 yr−1, but historical data on its production and use are lacking.
Ground‐based infrared solar spectroscopic measurements of carbon monoxide during 1994 Measurement of Air Pollution From Space flights
Authors: Pougatchev N. S. , Jones N. B. , Connor B. J. , Rinsland C. P. , Becker E. , Coffey M. T. , Connors V. S. , Demoulin P. , Dzhola A. V. , Fast H. , Grechko E. I. , Hannigan J. W. , Koike M. , Kondo Y. , Mahieu E. , Mankin W. G. , Mittermeier R. L. , Notholt J. , Reichle H. G. , Sen B. , Steele L. P. , Toon G. C. , Yurganov L. N. , Zander R. , Zhao Y.
Published: February 2004

Results of the comparison of carbon monoxide ground‐based infrared solar spectroscopic measurements with data obtained during 1994 Measurement of Air Pollution From Space (MAPS) flights are presented. Spectroscopic measurements were performed correlatively with April and October MAPS flights by nine research groups from Belgium, Canada, Germany, Japan, New Zealand, Russia, and the United States. Characterization of the techniques and error analysis were performed. The role of the CO a priori profile used in the retrieval was estimated. In most cases an agreement between spectroscopic and MAPS data is within estimated MAPS accuracy of ±10%.
Ozonolysis of nonmethane hydrocarbons as a source of the observed mass independent oxygen isotope enrichment in tropospheric CO
Authors: Röckmann Thomas , Brenninkmeijer Carl A. M. , Neeb Peter , Crutzen Paul J.
Published: February 2004

Combined 17O and 18O measurements of tropospheric CO from two northern hemisphere (NH) sites reveal systematically enhanced 17O levels, confirming the existence of significant mass independent oxygen isotope enrichment in this important trace gas. When CO levels increase in the NH winter, the mass independent enrichment decreases proportionally. A possible source of this rare isotope effect in CO is transfer of the mass independent enrichment from O3 to the CO pool via ozonolysis of unsaturated hydrocarbons such as isoprene and terpenes. Laboratory ozonolysis experiments indeed confirm that this process is a potentially important source of mass independently enriched CO. The extra 17O enrichment found in ozonolysis‐derived CO is similar to the mass independent fractionation measured on ozone. If ozonolysis is the only source of mass independent enrichment in CO, it is estimated that about 10% of all CO in middle to high latitude winter, at ground level, originates from the ozonolysis of unsaturated hydrocarbons. While the laboratory experiments prove that ozonolysis is a source of mass independent enrichment in CO, a further problem unfolds. Because tropospheric O3 is strongly enriched in 18O as well, this enrichment is also transferred to the CO inventory. When 10% of the CO inventory has the strong 18O enrichment, the measured low 18O abundance of atmospheric CO requires for compensation the existence of a strongly 18O depleted CO source, or a selective isotopic modification due to isotope fractionation. No such source has been identified to date, and thus ozonolysis may not be the only source of mass independent fractionation in atmospheric CO. Because the mass independent isotopic enrichment is by its nature indestructible by common (i.e., mass dependent) fractionation processes, it is an ideal tracer.
Atmospheric ionization patterns at 4 m above ground level in correlation to meteorological events
Authors: Breton J. , Breton V. , Legoff Y.
Published: February 2004

We report data on small positive and negative atmospheric ion density at 4m above the ground correlated to meteorological parameters. Between November 1994 and June 1995, we recorded 75,000 measurements continuously using an ionometer located in Arcachon, a resort on the French Atlantic coast. Compared to meteorological parameters, the data show a strong correlation between the passage of active cold fronts and a large rise of ionic density.
Sulfate aerosol formation in the Arctic boundary layer
Authors: Pirjola Liisa , Laaksonen Ari , Aalto Pasi , Kulmala Markku
Published: February 2004

Aerosol size distributions were measured in the Finnish Arctic over a continuous period of 1‐year using diffusion battery and condensation particle counter. Numerous nucleation bursts were observed. Some of the nucleation events were associated with marine air clean of SO2, while others were associated with SO2‐pollution events originating from smelters located in the Kola Peninsula. Six nucleation events were analyzed with a combined gas phase chemistry‐aerosol dynamical model that used meteorological input data taken from calculated back trajectories. The assumed homogeneous nucleation mechanism of sulfuric acid and water explains the observed pollution‐related nucleation events well but does not explain the marine nucleation events.
A model for the response of the atomic oxygen 557.7nm and the OH Meinel airglow to atmospheric gravity waves in a realistic atmosphere
Authors: Makhlouf U. B. , Picard R. H. , Winick J. R. , Tuan T. F.
Published: February 2004

We describe a model for the response of atomic oxygen and hydroxyl airglow to a gravity wave. The airglow models uses a realistic atmospheric‐gravity‐wave model, describing the wave velocity and pressure fluctuations in the presence of a nonisothermal background temperature profile and background winds. The gravity‐wave model is coupled to the OH photochemical model of Makhlouf et al. [1995] and to a simple chemical model for the 557.7 nm airglow as described below. It is shown that the chemistry of the 557.7 nm airglow does not affect the phase of the Krassovsky η, due to the short chemical lifetime of the O(1S) and the O2(c ∑u−) precursor states, whereas for the OH airglow the chemistry and dynamics couple for wave periods of 10–25 min, and chemistry does affect the phase of η. The effect of standing waves and traveling waves on the phase of η is shown to be different, and this behavior can be used to differentiate between freely propagating waves and ducted waves. These effects are illustrated by applying the model to examples of Airborne Lidar and Observations of Hawaiian Airglow (ALOHA‐93) campaign data. A combination of model prediction and ground‐based measurements from the ALOHA‐93 campaign are used to estimate the vertical eddy diffusivity Dzz due to nonlinear gravity waves following the formulation of Weinstock [1976]. The estimated values of Dzz vary between 1.0 × 102 and 5.0 × 103 m2/s, which is in the range of measured and inferred values.
Physical modeling of an outflow event in Howe Sound, British Columbia
Authors: Finnigan Timothy D. , Allen Susan E. , Lawrence Gregory A.
Published: February 2004

Outflow winds occur when differing air masses are separated by a coastal mountain barrier. In extreme cases the cross‐barrier pressure gradient and the high degree of stratification (often approaching a distinct layered structure) result in channel winds which exhibit hydraulic features. We present a study of outflow winds in Howe Sound, British Columbia. A field investigation, aimed specifically at locating and quantifying hydraulic effects, was undertaken during the winter months of 1992/1993. Microbarographs positioned in the region recorded pressure changes at discrete locations in the streamwise direction. The pressures obtained during a severe outflow wind event, which occurred from December 27, 1992 to January 1, 1993, show a highly variable lower‐layer depth suggestive of hydraulic control. Experiments were conducted with a three‐dimensional physical model that is geometrically and kinematically similar to Howe Sound. Synoptic conditions recorded during the outflow wind event in Howe Sound in December 1992 were used to determine appropriate model flow forcing. The expanse of supercritical flow area was observed to be relatively sensitive to changes in along‐channel pressure gradient and downstream depth, when compared to changes in discharge. Channel sinuosity and local topography appeared to force critical conditions at specific locations. For example, a channel bend combined with headlands was observed to force a situation where subcritical and supercritical streams flow side by side. Flow separation, resulting in lateral shear discontinuities, produced similar conditions. These effects are discussed and put into context with field observations. Field and model results show good agreement.
DMS oxidation in the Antarctic marine boundary layer: Comparison of model simulations and held observations of DMS, DMSO, DMSO2, H2SO4(g), MSA(g), and MSA(p)
Authors: Davis D. , Chen G. , Kasibhatla P. , Jefferson A. , Tanner D. , Eisele F. , Lenschow D. , Neff W. , Berresheim H.
Published: February 2004

A sulfur field study (SCATE) at Palmer Station Antarctica (January 18 to February 25) has revealed several major new findings concerning (dimethyl sulfide) DMS oxidation chemistry and the cycling of sulfur within the Antarctic environment. Significant evidence was found supporting the notion that the OH/DMS addition reaction is a major source of dimethyl sulfoxide (DMSO). Methane sulfonic acid (MSA(g)) levels were also found to be consistent with an OH/DMS addition mechanism involving the sequential oxidation of the products DMSO and methane sulfinic acid (MSIA). Evidence supporting the hypothesis that the OH/DMS addition reaction, as well as follow‐on reactions involving OH/DMSO, are a major source of SO2 was significant, but not conclusive. No evidence could be found supporting the notion that reactive intermediates (i.e., SO3) other than SO2 were an important source of H2SO4. Quite clearly, one of the major findings of SCATE was the recognition that a large fraction of the Antarctic oxidative cycle for DMS (near Palmer Station) took place above the boundary layer (BL) in what we have labeled here as the atmospheric buffer layer (BuL). Although still speculative in places, the overall picture emerging from the SCATE field/modeling results is one involving major coupling between chemistry and dynamics in the Antarctic. At Palmer the evidence points to frequent episodes of rapid vertical transport from a very shallow marine BL into the overlying BuL. Due to the combination of a long photochemical lifetime for DMS and the frequency of shallow convective events, a large fraction of ocean released DMS is transported into the BuL while still in its unoxidized state. There, in the presence of elevated OH and low aerosol scavenging, high levels of oxidized sulfur accumulate. Parcels of this BuL air are then episodically entrained back into the BL, thereby providing a controlling influence on BL SO2, DMSO, and DMSO2. Additionally, because SO2 and DMSO are major precursors to H2SO4 and MSA, BuL chemistry, in conjunction with vertical transport, also act to control BL levels of the latter species. Although many uncertainties remain in our understanding of Antarctic DMS chemistry, the above picture already suggests that previous chemical interpretations of Antarctic field data may need to be altered.
Spatial distribution of dimethylsulfide and dimethylsulfoniopropionate in the Australasian sector of the Southern Ocean
Authors: Curran Mark A. J. , Jones Graham B. , Burton Harry
Published: February 2004

During 1991–1995, seven voyages were made to the Southern Ocean to determine the distribution of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in seawater and air in the Australasian sector (60°E to 165°E). Measurements of DMSP in sea ice were also made. During the summer months the Subtropical Convergence (STC) and Antarctic Convergence (AC) were identified as important source regions of these sulfur compounds. In the Seasonal Ice zone (SIZ) there were marked longitudinal differences possibly reflecting higher productivity and the extent of the sea ice in this region. Levels of DMSP in sea ice cores were consistent with this regional difference. High and variable concentrations of DMSP also occurred in the Subantarctic Zone (SAZ) (45°‐53°S), decreasing to lower levels around 64°S, close to the Antarctic Divergence (AD). Upwelling of deep water around the AD is suggested to have been responsible for the low biological activity and low DMSP levels. While there was generally a good relationship between DMSPp and biomass, there was a marked difference in the DMSPp:chlorophyll a ratio between regions, and between years. DMSP was generally negatively correlated with dissolved nitrate, however, it was unclear if the level of nitrate directly affected DMSP production. DMSwlevels were highest in the mixed layer, with lower, yet detectable, levels in the deeper ocean. DMSwwas occasionally elevated in Antarctic Bottom Water (AABW), suggesting that ice shelf water transports this substance to deeper waters. DMSP was not found above detection limits below the mixed layer, but some evidence was found that DMSP may be transported to deeper waters, close to the Antarctic continent.
Estimation of polar stratospheric cloud volume and area densities from UARS, stratospheric aerosol measurement II and polar ozone and aerosol measurement II extinction data
Authors: Massie Steven T. , Baumgardner Darrel , Dye James E.
Published: February 2004

Particle size distributions, measured by the forward scattering spectrometer probe (FSSP 300), are used in Mie calculations to specify polynomial expressions by which polar stratospheric cloud (PSC) extinction data can be converted into volume and area density values for type I, liquid phase PSCs. The calculations are carried out at the wavelengths observed by experiments on the Upper Atmosphere Research Satellite (UARS) and at the stratospheric aerosol measurement (SAM II), stratospheric aerosol and gas experiment (SAGE II), and polar ozone and aerosol measurement (POAM II) wavelength of 1 μm. The calculations use laboratory indices that approximate values for ternary solution and sulfuric acid droplets. Validation calculations intercompare the SAM II and FSSP 300 area densities, and SAM II and cryogenic limb array etalon spectrometer (CLAES) area densities.
Contribution of rice straw carbon to CH4 emission from rice paddies using 13C‐enriched rice straw
Authors: Watanabe Akira , Yoshida Mariko , Kimura Makoto
Published: February 2004

It is generally recognized that the application of rice straw (RS) increases CH4 emission from rice paddies. To estimate the contribution of RS carbon to CH4 emission, a pot experiment was conducted using 13C‐enriched RS. The percentage contributions of RS carbon to CH4 emission throughout the rice growth period were 10±1, 32±3, and 43±3% for the treatments with RS applied at the rates of 2, 4, and 6 g kg−1 soil, respectively. The increase in the rate of application of RS increased CH4 emission derived from both RS carbon and other carbon sources. The percentage contribution of RS carbon to CH4 emission was larger in the earlier period (maximum 96%) when the decomposition rate of RS was larger. After RS decomposition had slowed, CH4 emission derived from RS carbon decreased. However, the δ13C values of CH4 emitted from the pots with 13C‐enriched RS applied at rates of 4 and 6 g kg−1 soil were significantly higher than those from the pots with natural RS until the harvesting stage. An increased atom‐13C% of roots of rice plants growing in the pots with 6 g kg−1 of 13C‐enriched RS at around the maximum tiller number stage and a decrease during the following 2 months suggested that rice plants assimilated RS carbon once and then released a portion of it. This supply of RS carbon from roots may be one of the sources of CH4 in the late period of rice growth.
Interhemispheric ratio and annual cycle of carbonyl sulfide (OCS) total column from ground‐based solar FTIR spectra
Authors: Griffith David W. T. , Jones Nicholas B. , Matthews W. Andrew
Published: February 2004

We have made extensive measurements of total column OCS by ground‐based high‐resolution solar Fourier transform infrared absorption spectroscopy from two southern hemisphere sites to complement earlier measurements in the northern hemisphere and to investigate the interhemispheric ratio, variability, and seasonal cycles of OCS in the atmosphere. The measurements were made at Lauder, New Zealand (45.0°S, 169.7°E, 370 m asl, 547 spectra March 1993 through April 1997), and Wollongong, Australia (34.45°S, 150.88°E, 30 m asl, 358 spectra May 1996 through April 1997). The annual mean column amounts are 9.15×1015 molecules cm−2 above Lauder and 9.84×1015 molecules cm−2 above Wollongong, corresponding to tropospheric mixing ratios of 480 and 490 parts per trillion by volume, respectively, with the assumed mixing ratio vertical profiles. The secular trend in total column OCS is less than 1% per year. Variability of all measurements about the means implies an atmospheric lifetime for OCS of at least 2.8 years. Comparison with earlier measurements in the northern hemisphere yields a north/south interhemispheric ratio in the range 1.1–1.2. There are peak‐to‐peak apparent annual cycles in total column OCS of 6% at Lauder and 18% at Wollongong with a late summer maximum. Seasonal tropopause height variation accounts for a 5–6% amplitude, and the remainder of the amplitude in Wollongong is assumed to be due to changes in the tropospheric mixing ratio.
Electrical structure in thunderstorm convective regions: 2. Isolated storms
Authors: Stolzenburg Maribeth , Rust W. David , Marshall Thomas C.
Published: February 2004

Electric field (E) soundings through the convective regions of two types of isolated thunderstorms are examined. Analysis of seven soundings through strong updrafts of isolated supercell storms show that the basic E structure there has three |E| peaks: a positive peak near 8 km height, a negative peak near 10.5 km, and a positive peak near 12 km. Strong updraft soundings are those with average balloon ascent rates in excess of 10 m s−1. The basic charge structure in strong updrafts of supercells has four charge regions of alternating polarity. The lowermost charge is positive, between about 4 and 8 km, and the uppermost region is negative. All the supercell updraft soundings are incomplete due to balloon burst or lightning‐induced instrument destruction below cloud top. Six supercell soundings that ascended outside strong updrafts are used to show that the E and charge structures there are more complex than within the strong updrafts. Analysis of 15 new or previously published soundings through small, New Mexican mountain thunderstorms indicates that the basic E structure in or near their convective cores consists of three |E| peaks: a lower positive peak at about 5 km height, a midlevel negative peak near 6.5 km, and an upper positive peak near 9.5 km. The basic charge structure near the center of New Mexican storm convection has four charge regions, alternating in polarity, with a positive charge region lowest. Soundings in New Mexican convection that did not ascend near the convective cores show more complex E profiles and charge structures.
Climatology of mesospheric gravity wave activity over Urbana, Illinois (40°N, 88°W)
Authors: Thorsen Denise , Franke Steven J.
Published: February 2004

A 5‐year (1991–1995) climatology of mesospheric gravity wave activity observed with the Urbana medium frequency (MF) radar is presented. We focus on the monthly mean horizontal wind variances associated with gravity waves with observed periods between 10 min and 8 hours. These results are compared with the seasonal characteristics from other gravity wave observations. The total wave variance,
, displays a dominant semiannual variation (maxima summer/winter, minima spring/fall) below 87 km with little seasonal variation above 87 km. The zonal wave variance exceeds the meridional wave variance,
, except around regions of zonal wind reversal. In all seasons the observed variance scale height is greater than that of a nondissipating wave field. A simple zero mean wind model based on linear saturation theory is found to be inadequate in reproducing the seasonal characteristics of the observed wave variances. An alternative model based on critical layer filtering by a height dependent wind field can reproduce the observed semiannual oscillation in the wave variance given a specific source input.
The UV to IR transmittance of Antarctic snow
Authors: Beaglehole D. , Ramanathan B. , Rumberg J.
Published: February 2004

We report the transmittance of Antarctic snow as a function of the thickness of snow layers, in the range between 350 and 900 nm. Samples were studied near Scott Base, Ross Island, and data are presented for measurements made in early December 1996. The transmittance followed the two flux theoretical expressions well, and scattering and absorption parameters were obtained by curve fitting. Scattering dominated the transmittance at shorter wavelengths. The absorption at shorter wavelengths varied from one site to another, being lowest for snow samples measured furthest away from Ross Island, suggesting the effects of blown volcanic dust. The snow albedo derived from the transmittance parameters is compared with those of other workers.
Stable isotope ratios of rain and vapor in 1995 hurricanes
Authors: Lawrence James Robert , Gedzelman Stanley David , Zhang Xiaoping , Arnold Robert
Published: February 2004

Isotope ratios of rain and vapor samples collected at the surface from four tropical cyclones during the active 1995 Atlantic hurricane season were determined. A two‐dimensional bulk microphysics isotope model was applied to steady symmetric tropical cyclones to explain the observed low mean values and inward decrease of isotope ratios of the rain and vapor. The low mean value is caused by the tropical cyclone's relatively large size, longevity, and deep clouds. The inward decrease is due to diffusive isotope exchange between falling rain and converging vapor in the atmospheric boundary layer. Dean, a minimal tropical storm, produced relatively high isotope ratios because of its small size and youth. Rains from the extreme outer edge of Felix, a category 3 hurricane, exhibited high isotope ratios similar to normal summer rain. Isotope ratios of rains and vapors from Hurricane Luis in Puerto Rico decreased as the storm approached. Isotope ratios of rain exhibited an abrupt jump from low values in the eastern half of Puerto Rico to high values farther west which is linked to the storm's rainbands. Isotope ratios of Hurricane Opal's rains reflected the storm's asymmetric structure, with lowest values west of the point of landfall. Record low isotope ratios from a squall line that struck eastern Texas two days before landfall are linked to low‐level outflow from Opal and demonstrate that hurricanes can vent enormous quantities of vapor to the surroundings.
Simulation of freeze‐thaw cycles in a general circulation model land surface scheme
Authors: Slater A. G. , Pitman A. J. , Desborough C. E.
Published: February 2004

Using observed meteorological data collected from four sites in the former Soviet Union, a land surface scheme designed for use in climate models was integrated for 6 years. Using observed available soil moisture and freezing front data, the model simulation of freeze‐thaw cycles over the 6 years for each station was validated. The model was able to simulate the general characteristics of the seasonal freeze‐thaw cycles for all stations for all years. There were problems in the simulation of the spring period by Best Approximation of Surface Exchanges (BASE): the model simulated excess accumulation of liquid soil moisture in spring and failed to match the observed timing of total freeze and total thaw. Most problems could be linked to the parameterization of hydraulic conductivity, and when this was modified, the model was able to simulate the available soil moisture more accurately. Moreover, it was shown that the inclusion of a frozen soil parameterization is necessary in order to capture the broad seasonal cycle of soil moisture and that the impact of not accounting for frozen soil can extend beyond the spring thaw period. To improve the simulations further, it may be necessary to model the effects of cryoturbation (including macropores), freezing fronts, ice‐lensing and other periglacial processes. Given the spatial resolution of climate models, the vertical resolution of land surface schemes (1–5 layers), and the lack of suitable observed data, even if these processes could be parameterized, the quality of the simulations are unlikely to increase enough to warrant the additional computational expense.
Processes controlling the distribution of aerosol particles in the lower marine boundary layer during the First Aerosol Characterization Experiment (ACE 1)
Authors: Bates Timothy S. , Kapustin Vladimir N. , Quinn Patricia K. , Covert David S. , Coffman Derek J. , Mari Celine , Durkee Philip A. , De Bruyn Warren J. , Saltzman Eric S.
Published: February 2004

The goals of the International Global Atmospheric Chemistry (IGAC) Program's First Aerosol Characterization Experiment (ACE 1) are to determine and understand the properties and controlling factors of the aerosol in the remote marine atmosphere that are relevant to radiative forcing and climate. A key question in terms of this goal and the overall biogeochemical sulfur cycle is what factors control the formation, growth, and evolution of particles in the marine boundary layer (MBL). To address this question, simultaneous measurements of dimethylsulfide (DMS), sulfur dioxide (SO2), the aerosol chemical mass size distribution, and the aerosol number size distribution from 5 to 10,000 nm diameter were made on the National Oceanic and Atmospheric Administration (NOAA) ship Discoverer. From these data we conclude that the background MBL aerosol during ACE 1 often was composed of four distinct modes: an ultrafine (UF) mode (Dp = 5–20 nm), an Aitken mode (Dp = 20–80 nm), an accumulation mode (Dp = 80–300 nm), and a coarse mode (Dp > 300 nm). The presence of UF mode particles in the MBL could be explained by convective mixing between the free troposphere (FT) and the MBL associated with cloud pumping and subsidence following cold frontal passages. There was no evidence of major new particle production in the MBL. Oceanic emissions of DMS appeared to contribute to the growth of Aitken and accumulation mode particles. Coarse mode particles were comprised primarily of sea salt. Although these particles result from turbulence at the air‐sea interface, the instantaneous wind speed accounted for only one third of the variance in the coarse mode number concentration in this region.
A critical analysis of the Stratospheric Aerosol and Gas Experiment II spectral inversion algorithm
Authors: Fussen Didier
Published: February 2004

The ozone long‐term trends derived from the Stratospheric Aerosol and Gas Experiment II have been shown to be biased by the level of volcanic aerosol. We have investigated the spectral algorithm used to separate the partial optical thicknesses associated with ozone and aerosols. We present two possible causes of inaccuracies capable of producing relative errors on the slant path ozone optical thickness as large as 5–15%. The first one is related to the interpolation of the aerosol optical thickness at 0.6 μm which is not very well performed by solving the inverse problem of the unknown size distribution. The second error cause lies in the assumed altitude independence of the aerosol optical properties. Both error causes are discussed, and possible corrections are presented.
Emissions of volatile organic compounds (primarily oxygenated species) from pasture
Authors: Kirstine Wayne , Galbally Ian , Ye Yuerong , Hooper Martin
Published: February 2004

The volatile organic compound (VOC) emissions from pasture at a site in southeastern Victoria, Australia, were monitored over a 2 year period using a static chamber technique. Fluxes up to 23,000 μg(C) m−2 h−1 were detected, with the higher fluxes originating from clover rather than from grass species. Gas Chromatographic analyses indicated that emissions from both grass and clover were high in oxygenated hydrocarbons including methanol, ethanol, propanone, butanone, and ethanal, and extremely low in isoprene and monoterpenes. In the case of clover, butanone made up 45–50% of the total emissions. When grass and clover were freshly mown, there were significantly enhanced emissions of VOCs. These enhanced emissions included both those oxygenates emitted from uncut pasture and also C6‐oxygenates, including (Z)−3‐hexenal, (E)−2‐hexenal, (Z)−2‐hexen−1‐ol, (Z)−3‐hexen−l‐ol, and (Z)−3‐hexenyl acetate. Emissions from the undisturbed pasture increased markedly with temperature and the intensity of solar radiation, peaking at midday and ceasing at night. The fluxes, when normalized to a temperature of 30°C and a light intensity of 1000 μE m−2 s−1 were, for grass and clover respectively, about one eighth and two fifths of the equivalent fluxes reported to occur from U.S. woodlands. The annual integrated emission from the pasture was approximately 1.9 g(C) m−2 or 1.3 mg(C) g−1 (dry matter). The large transient fluxes that occurred following physical damaging of the pasture, when integrated over time, could be of the same order as those emissions that were observed from undisturbed pasture. In the case of methanol, and perhaps ethanol, the emissions from grasslands may be significant global sources of these gases.
The 15N/14N isotope fractionation in dissociative recombination of N2+
Authors: Fox J. L. , Hać Aleksander
Published: February 2004

We have carried out Monte Carlo calculations of the velocity distributions and escape fractions for 14N and 15N released in dissociative recombination of 28N2+ and 29N2+, respectively, for a range of ion temperatures (Ti) and electron temperatures (Te) appropriate to the Martian exosphere. Separate calculations were carried out for each vibrational level of N2+ for 0≤ν≤6. We have taken into account the variation in the dissociative recombination cross section with relative velocity of the ion and electron, and the differences in the vibrational and rotational energy levels of 28N2+ and 29N2+. The escape probabilities and ratios are found to be quite sensitive to the temperature of the N2+ ions, but less so to the electron temperature or to the assumed rotational distribution. The escape probabilities for N2+(ν=0), with Ti=400 K and Te=2000 K and an assumed escape velocity of 4.877 kms−1, are 0.391 and 0.669 for 15N and 14N, respectively. The ratio of the escape fractions, which is a measure of the isotope differentiation effect, is 0.58. This value is close to the ratio 0.51 computed by Wallis [1978], but the individual escape fractions are smaller than his values by about a third. Sample calculations are carried out of the time evolution of the N2 abundance and of the isotope enhancement ratio to illustrate the effect of the new computed escape probabilities. It is found that the N isotopes are still predicted to be overfractionated over the last 3.8 Gyr, but the requirements on the mechanism assumed to reduce the escape, such as the existence of a dense, early atmosphere, are reduced over those required by calculations that employ the escape fractions of Wallis.
The effect of bulk density and particle size sorting on the thermal conductivity of particulate materials under Martian atmospheric pressures
Authors: Presley Marsha A. , Christensen Philip R.
Published: February 2004

Preliminary measurements of the effects of bulk density and particle size sorting on the thermal conductivity of particulate materials under Martian atmospheric pressures are presented and discussed. Concoidally fractured particles tend to form more loosely packed, less dense sedimentary structures, due to irregularities in the shape of the particles, than those formed by spherical particles of similar size. The lower bulk density of the angular‐shaped particles leads to a lower thermal conductivity of the sample. If the density difference is assumed to be the sole factor that controls the difference in conductivity in this case, then the thermal conductivity of 25–30 μm size particles appears to increase linearly with increasing bulk density and with the square root of the atmospheric pressure. Initial experiments appear to indicate that the bulk thermal conductivity of a particulate material containing a mixture of different particle sizes is the same as the thermal conductivity that a material of similar bulk density would have if it were composed entirely of the largest particle size contained within that material. More studies are, however, necessary to confirm this apparent trend.
Ambient effects on basalt and rhyolite lavas under Venusian, subaerial, and subaqueous conditions
Authors: Bridges Nathan T.
Published: February 2004

Both subaerial and subaqueous environments have been used as analog settings for Venus volcanism. To assess the merits of this, the effects of ambient conditions on the physical properties of lava on Venus, the seafloor, and land on Earth are evaluated. Rhyolites on Venus and on the surface of Earth solidify before basalts do because of their lower eruption temperatures. Rhyolite crust is thinner than basalt crust at times less than about an hour, especially on Venus. At later times, rhyolite crust is thicker because of its lower latent heat relative to basalt. The high pressure on the seafloor and Venus inhibits the exsolution of volatiles in lavas. Vesicularity and bulk density are proportional, so that lavas of the same composition should be more dense on the seafloor and less dense on land. Because viscosity depends partly upon the fraction of unvesiculated water in a melt, basalts with the same initial volatile abundance will be least viscous on the seafloor and most viscous on land. Assuming the same preemptive H2O contents, molten rhyolites on Venus will have viscosities ∼10% that of rhyolites on land. Despite lower expected viscosities, underwater flows are more buoyant and should have heights like subaerial and Venusian lavas of the same composition and extrusive history. In cases where the influence of crust is insignificant, a volume of rhyolite will have a higher aspect ratio than the same volume of basalt, no matter what the environment. If flow rheology is dominated by the presence of strong crust, aspect ratios differ little among environments or between compositions. These analyses support a rhyolitic interpretation for the composition of Venusian festooned flows and a basaltic interpretation for the composition of Venusian steep‐sided domes. Although ambient effects are significant, extrusion rate and eruption history must also be considered to explain analogous volcanic landforms on Earth and Venus.
Radar and photoclinometric studies of wrinkle ridges on Mars
Authors: Watters Thomas R. , Robinson Mark S.
Published: February 2004

Earth‐based radar altimetry and image derived photoclinometric profiles were analyzed to examine both the long‐ and short‐wavelength topography associated with wrinkle ridges on Mars. Photoclinometrically derived elevation data across wrinkle ridges were evaluated to determine the sensitivity of profiles to two empirical photoclinometric parameters, the horizontal digital number (HDN) and the scattered light value (SLV). The photoclinometric profiles are extremely sensitive to small variations in HDN. The sense of slope of a profile can be completely reversed over a range in HDN of as little as ±1. Comparably small variations in the SLV have relatively minor effects on the photoclinometrically derived elevations. The existence of elevation offsets from one side of the ridge to the other, reported in previous photoclinometric studies of martian wrinkles, were not confirmed through photoclinometry. In addition, no evidence of elevation offsets were found in Earth‐based radar altimetry profiles across wrinkle ridges. In order to more accurately model wrinkle ridge topography, we controlled photoclinometrically derived elevations with long‐wavelength topography obtained from the radar altimetry. The results of this study do not support kinematic models for the origin of planetary wrinkle ridges that involve deeply rooted thrust faults which separate crustal blocks at different elevations. A kinematic model involving buckling of shallow crustal layers into concentric folds that close, leading to the development of thrust faults, is consistent with wrinkle ridge morphology and terrestrial analogs. Recent geophysical studies of terrestrial analogs and the influence of shallow subsurface structures, particularly buried craters, on the localization of many wrinkle ridges on Mars suggest that thrust faults associated with the ridges are confined to the ridged plains material and do not extend into the lithosphere.