bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure‐forced seiches of large amplitude in inlets of the Balearic Islands: 2. Observational study
Authors: Garcies M. , Gomis D. , Monserrat S.
Published: February 2004

In part 1 of this study, Gomis et al. [1993] proposed a possible mechanism for the generation of large‐amplitude seiches observed in inlets of the Balearic Islands. In part 2, we revise the proposed mechanism in light of recent observations. These consist of simultaneous records of sea level/bottom pressure measured at three locations inside and outside Ciutadella inlet and atmospheric pressure measured at four sites inland nearby. First, results that support the existence of offshore surface waves of atmospheric origin are shown. Next, a detailed analysis of atmospheric data reveals the passage of non dispersive waves with a predominant direction and phase speed that seem to be about the same during seiche events. Finally, coherence, phase difference, and admittance functions estimated for different pairs of instruments are compared with the theoretical results. All observations indicate that large‐amplitude seiches observed in Ciutadella are likely the result of a resonant coupling between offshore surface waves generated by atmospheric disturbances and the fundamental mode of that inlet, as suggested in part 1. However, the analytical model used in part 1 is clearly too simple to explain the observed characteristics of the offshore surface waves.
Air‐sea exchange of water vapor and sensible heat: The Humidity Exchange Over the Sea (HEXOS) results
Authors: DeCosmo J. , Katsaros K. B. , Smith S. D. , Anderson R. J. , Oost W. A. , Bumke K. , Chadwick H.
Published: February 2004

Surface layer fluxes of sensible heat and water vapor were measured from a fixed platform in the North Sea during the Humidity Exchange over the Sea (HEXOS) Main Experiment (HEXMAX). Eddy wind stress and other relevant atmospheric and oceanic parameters were measured simultaneously and are used to interpret the heat and water vapor flux results. One of the main goals of the HEXOS program was to find accurate empirical heat and water vapor flux parameterization formulas for high wind conditions over the sea. It had been postulated that breaking waves and sea spray, which dominate the air‐sea interface at high wind speeds, would significantly affect the air‐sea heat and water vapor exchange for wind speeds above 15 m/s. Water vapor flux has been measured at wind speeds up to 18 m/s, sufficient to test these predictions, and sensible heat flux was measured at wind speeds up to 23 m/s. Within experimental error, the HEXMAX data do not show significant variation of the flux exchange coefficients with wind speed, indicating that modification of the models is needed. Roughness lengths for heat and water vapor derived from these direct flux measurements are slightly lower in value but closely parallel the decreasing trend with increasing wind speed predicted by the surface renewal model of Liu et al. [1979], created for lower wind speed regimes, which does not include effects of wave breaking. This suggests that either wave breaking does not significantly affect the surface layer fluxes for the wind speed range in the HEXMAX data, or that a compensating negative feedback process is at work in the lower atmosphere. The implication of the feedback hypothesis is that the moisture gained in the lower atmosphere from evaporation of sea spray over rough seas may be largely offset by decreased vapor flux from the air‐sea interface.
The water masses between Mindanao and New Guinea
Authors: Kashino Yuji , Aoyama Michio , Kawano Takeshi , Hendiarti Nani , Syaefudin  , Anantasena Yudi , Muneyama Kei , Watanabe Hidetoshi
Published: February 2004

Water masses between Mindanao and New Guinea are investigated, using hydrographic data, during two R/V Kaiyo World Ocean Circulation Experiment cruises conducted in October 1992 and February 1994. The analysis of this data indicates that the South Pacific Tropical Water (SPTW), which is formed in the southern hemisphere, reached the area of Morotai Island in 1992 and farther north in 1994. The Antarctic Intermediate Water (AAIW) exists in the southwestern area of the southernmost Philippine Sea. There is northeastward flow between Talaud Islands and Morotai Island, which is probably a part of the retroflection of the Mindanao Current. The remnant of the North Pacific Intermediate Water, advected by the flow from the Celebes Sea, was found in 1992. The New Guinea Coastal Undercurrent, transporting SPTW and AAIW from the southern hemisphere, is divided into at least two parts because the retroflection of the Mindanao Current prevents its shallow part from reaching farther north; the shallow part of SPTW turns eastward as a source water of North Equatorial Countercurrent and retroflects toward the southeast. AAIW and the lower part of SPTW flow northward and seem to be linked with the Mindanao Undercurrent.
A study of the Kuroshio's seasonal variabilities using an altimetric‐gravimetric geoid and TOPEX/POSEIDON altimeter data
Authors: Hwang Cheinway
Published: February 2004

The first year of TOPEX/POSEIDON (T/P) altimeter data were used to study the seasonal variabilities of the Kuroshio Current. The intercomparison between the T/P and gauge sea levels at selected tide gauge stations around Taiwan shows that the two have a correlation of about 0.9 at the immediate vicinity of the deep ocean, and both show an annual cycle with an amplitude of 15 cm. A 3′ × 3′ geoid for the Western Pacific was constructed by least squares collocation using gravity anomalies and sea surface gradients derived from Seasat, Geosat, ERS 1, and T/P altimetry. To account for the oceanographic signal in the altimeter data, we derived a covariance function for the gradients of the sea surface topography (SST) based on a global averaging concept and a spherical harmonic expansion of the Levitus SST to degree 50. The accuracy of the geoid ranges from 5 to 40 cm. The SST values derived from the geoid and the data along T/P's descending tracks were fitted to the hyperbolic functions in a two‐step procedure to find the Kuroshio's seasonal axes and the parameters that describe its characteristics. The mean variabilities in the Kuroshio's path, maximum velocity, baroclinic transport, and width are 22 km, 19 cm, 8 Sv, and 27 km, respectively. The averaged percentage variability of all quantities is 25%. All the variabilities are relatively large near the northeast coast of Taiwan and the starting point of the Kuroshio Extension. The large‐scale circulations over the Western Pacific were obtained by median filtering the SST. At the 1334‐km spatial scale, the Pacific's subtropical gyre is clearly visible, and it shows different features over the four seasons and its kinetic energy shows possible correlations with the determined parameters. Over the South China Sea, a warm ring with a radius of 300–400 km and a center at 15°N, 113°E was detected in the spring and summer.
Seasonal variations of the Indonesian throughflow in a general ocean circulation model
Authors: Masumoto Yukio , Yamagata Toshio
Published: February 2004

Seasonal variability of the depth‐integrated transport in the Indonesian Seas is investigated in detail, together with its driving mechanism, by use of an Indo‐Pacific ocean general circulation model that allows the circulation around Australasia. Modeled net throughflow shows an annual mean transport of 9.5 Sv from the Pacific to the Indian Ocean with a maximum (minimum) transport of 11.6 Sv (6.0 Sv) in August (January). Seventy‐five percent of this transport flows through the Lombok Strait in the present model. Comparison with the result of Masumoto and Yamagata [1993], in which the circulation around Australasia was not permitted, clarifies that the magnitude of the net interbasin throughflow does not affect the seasonal variations in the depth‐integrated transport through the Lombok Strait. Several additional experiments are also carried out by masking winds over particular regions to identify which part of winds is actually effective in the seasonal variations in the depth‐integrated transport through the Timor Sea as well as the Lombok Strait. It turns out that the seasonal variability of the transport through the Lombok Strait is almost perfectly governed by the winds over the equatorial Indian and Pacific Oceans. On the other hand, the coastally trapped waves generated by the winds along the western and southern coast of Australia play an important role in the seasonal transport variation through the Timor Sea.
Numerical modeling of ship tracks produced by injections of cloud condensation nuclei into marine stratiform clouds
Authors: Ackerman Andrew S. , Toon Owen B. , Hobbs Peter V.
Published: February 2004

Ship tracks are long‐lived, linear regions of enhanced reflectivity in low‐lying marine clouds that appear in satellite imagery downwind of ships. Ship tracks were first observed as cloud lines in visible satellite imagery (type 1). A second (and more common) type of ship track (type 2), which is masked at visible wavelengths by natural variability in cloud reflectivity, is seen at near‐infrared wavelengths in satellite imagery. A one‐dimensional numerical model is used to simulate measurements of both types of ship tracks and to investigate interactions between aerosol and cloud microphysics, radiative transfer, and turbulent mixing in the cloud‐topped marine boundary layer that lead to the formation and provide for the persistence of ship tracks. We find that cloud condensation nuclei (CCN) injections can account for many of the observed properties of ship tracks. Higher CCN concentrations produce increased droplet concentrations, which enhance cloud reflectivity by reducing droplet radius and increasing droplet cross‐sectional area. The smaller droplets also reduce the drizzle rate, which can allow cloud water to increase under some conditions, thereby leading to higher cloud reflectivity. However, smaller droplets also evaporate more readily below cloud base. Increased evaporation reduces mixing between the cloud and the subcloud layers during daytime, which causes a decrease in cloud water. The distinction between the two types of ship tracks is suggested to be due to differences in ambient concentrations of CCN that cause variations in turbulent mixing in the boundary layer, through the effect of cloud droplet concentrations on cloud‐top longwave radiative cooling. The model predicts lifetimes of > 1 day and > 2 days for the simulated type 1 and type 2 ship tracks, respectively. In the atmosphere, processes not treated in the model, such as horizontal dispersion and changes in large‐scale atmospheric conditions, may limit ship track lifetimes.
Henry's law solubilities and Śetchenow coefficients for biogenic reduced sulfur species obtained from gas‐liquid uptake measurements
Authors: De Bruyn W. J. , Swartz E. , Hu J. H. , Shorter Jeffrey A. , Davidovits P. , Worsnop D. R. , Zahniser M. S. , Kolb C. E.
Published: February 2004

Biogenically produced reduced sulfur compounds, including dimethylsulfide (DMS, CH3SCH3), hydrogen sulfide (H2S), carbon disulfide (CS2), methyl mercaptan (CH3SH), and carbonyl sulfide (OCS), are a major source of sulfur in the marine atmosphere. This source is estimated to contribute 25–40% of global sulfur emissions. These species and their oxidation products, dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), and methane sulfonic acid (MSA), dominate the production of aerosol and cloud condensation nuclei (CCN) in the clean marine atmosphere. The multiphase chemical processes for these species must be understood in order to study the evolving role of combustion‐produced sulfur oxides over the oceans. Using a newly developed bubble column apparatus, a series of aqueous phase uptake studies have been completed for the reduced sulfur species DMS, H2S, CS2, CH3SH, and OCS. Aqueous phase uptake has been studied as a function of temperature (278–298 K), pH (1–14), H2O2 concentration (0–1 M), NaCl concentration (0–5 M), and (NH4)2SO4 concentration (0–4 M). The Henry's law coefficients for CH3SH and CS2 were determined for the first time, as were the Setchenow coefficients for all the species studied.
Empirical model of global soil‐biogenic NOχemissions
Authors: Yienger J. J. , Levy H.
Published: February 2004

We construct a global, temperature and precipitation dependent, empirical model of soil‐biogenic NOxemissions using 6‐hour general circulation model forcing. New features of this source relative to the latest published ones by Dignon et al. [1992] and Muller [1992] include synoptic‐scale modeling of “pulsing” (the emissions burst following the wetting of a dry soil), a biome dependent scheme to estimate canopy recapture of NOχ, and an explicit linear dependence of emission on N fertilizer rate for agricultural soils. Our best estimate for annual above‐canopy emissions is 5.5 Tg N (NOχ) with a range of 3.3–7.7 Tg N. Globally, the strongest emitters are agriculture, grasslands, and tropical rain forests, accounting for 41%, 35%, and 16% of the annual budget, respectively. “Pulsing” contributes 1.3 Tg N annually. In temperate regions, agriculture dominates emission, and in tropical regions, grassland dominates. Canopy recapture is significant, consuming, on average, possibly 50% of soil emissions. In temperate regions, periodic temperature changes associated with synoptic‐scale disturbances can cause emission fluctuations of up to 20 ng N m−2s−1, indicating a close correlation between emission and warm weather events favorable to O3/smog formation. By the year 2025, increasing use of nitrogen fertilizer may raise total annual emissions to 6.9 Tg N with agriculture accounting for more than 50% of the global source. Finally, biomass burning may add up to an additional 0.6 Tg N globally by stimulating emissions for a short period after the burn.
Carboxylic acids in the rural continental atmosphere over the eastern United States during the Shenandoah Cloud and Photochemistry Experiment
Authors: Talbot Robert W. , Mosher Byard W. , Heikes Brian G. , Jacob Daniel J. , Munger J. William , Daube Bruce C. , Keene William C. , Maben John R. , Artz Richard S.
Published: February 2004

The Shenandoah Cloud and Photochemistry Experiment (SCAPE) was conducted during September 1990 in the rural continental atmosphere at a mountain top site (1014 m) in Shenandoah National Park, Virginia. We report here the extensive set of trace gas measurements performed during clear sky periods of SCAPE, with particular focus on the carboxylic acids, formic, acetic, and pyruvic. Median mixing ratios were 5.4 and 2.1 parts per billion by volume (ppbv) for formic and acetic acid, respectively, and they did not exhibit the diurnal variation characteristic of low‐elevation sites. Mixing ratios of formic acid often approached or exceeded 10 ppbv, which are the largest values yet reported for the nonurban troposphere. Over the rural eastern United States, formic and acetic acid appear to have significant nonphotochemical sources. Secondary production from suspected pathways appears to be relatively unimportant. The observed lack of correlation between formic and acetic acid with peroxide species argues against a significant source from permutation reactions of peroxy radicals. In addition, model calculations using the SCAPE data indicate minimal production of carboxylics from olefin/O3 oxidation reactions. The tight correlation (r2 = 0.88) between mixing ratios of formic and acetic acid is strongly suggestive of a commonality in their sources. The seasonal cycle of carboxylic acids in the atmosphere and precipitation over the eastern United States is evidence that combustion emissions are not a principal source of these species. It appears that direct biogenic emissions from vegetation and soils cannot be ruled out as important sources. In particular, the correlation between the seasonal variation of formic and acetic acid and the ambient temperature is consistent with a soil microbial source. Similar conclusions were reached for pyruvic acid, with its mixing ratio ranging 4–266 parts per trillion by volume (pptv) (median = 63) and most likely supported by biogenic emissions and possibly photochemical sources.
Formaldehyde, glyoxal, and methylglyoxal in air and cloudwater at a rural mountain site in central Virginia
Authors: Munger J. William , Jacob D. J. , Daube B. C. , Horowitz L. W. , Keene W. C. , Heikes B. G.
Published: February 2004

As part of the Shenandoah Cloud and Photochemistry Experiment (SCAPE), we measured formaldehyde (HCHO), glyoxal (CHOCHO), and methylglyoxal (CH3C(O)CHO) concentrations in air and cloudwater at Pinnacles (elevation 1037 m) in Shenandoah National Park during September 1990. Mean gas‐phase concentrations of HCHO and CHOCHO were 980 and 44 pptv, respectively. The concentration of CH3C(O)CHO rarely exceeded the detection limit of 50 pptv. Mean cloudwater concentrations of HCHO and CHOCHO were 9 and 2 μM, respectively; the mean CH3C(O)CHO concentration was below its detection limit of 0.3 μM. The maximum carbonyl concentrations were observed during stagnation events with high O3, peroxides, and CO. Outside of these events the carbonyls did not correlate significantly with O3, CO, or NOy. Carbonyl concentrations and concentration ratios were consistent with a major source for the carbonyls from isoprene oxidation. Oxidation of CH4 supplies a significant background of HCHO. The carbonyl concentrations were indistinguishable in two size fractions of cloudwater having a cut at d=18 μm. Gas‐ and aqueous‐phase concentrations of HCHO from samples collected during a nighttime cloud event agree with thermodynamic equilibria within a factor of 2. Samples collected during a daytime cloud event show HCHO supersaturation by up to a factor of 4. Positive artifacts in the cloudwater samples due to hydrolysis of hydroxymethylhydroperoxide (HOCH2OOH) could perhaps account for this discrepancy.
Environmental factors influencing the variability of methane oxidation in temperate zone soils
Authors: Czepiel P. M. , Crill P. M. , Harriss R. C.
Published: February 2004

The influence of organic matter and soil moisture on the spatial distribution of methane (CH4) oxidation was examined in temperate zone soils by laboratory incubations. CH4 oxidation in soil cores exhibited distinct vertical zonation with maxima at 3 to 6 cm. The kinetic parameters of CH4 oxidation were measured in soil composites. The maximum rate of CH4 uptake, Vmax, ranged from 6.8 to 7.4 nmol hr−1 g dry soil−1 and the apparent half saturation constant, Km, ranged from 17.4 to 19.9 (parts per million by volume) ppmv. Oxidation in random samples was observed to be influenced by both soil moisture and organic matter contents. The rate of oxidation in each sample increased to a maximum with increasing water content and decreased with additional water. Maximum oxidation rates ranged from 2.2 to 9.0 nmol hr−1 g dry soil−1 at sample moisture contents of 18 to 51%. Organic matter content appears to explain the spatial variability of methane oxidation at optimal soil moisture contents. The oxidation maximum at this site was coincident with an organic matter content of 14% by weight and a gravimetric moisture content of 33%.
Generalized smoothing splines in CO2 analysis
Authors: Granek H.
Published: February 2004

A number of shortcomings associated with the use of smoothing and least squares splines for data analysis in general, and also in some specific past CO2 analyses are considered. A potentially useful alternative, through generalized smoothing (GeS) splines, which do not require the data and spline knots to coincide, is offered. This may be computationally more cost effective and, with appropriate care, produces equivalent results. The presented examples examine fits to unselected Cape Grim CO2 data and a number of preprocessed cases are also compared. In all these cases the GeS splines produce a stable output, unlike the smoothing spline, which does not possess the capability of directly handling very large data sets. A range of diagnostics may be applied to a problem to evaluate the suitability of the GeS spline as a replacement for the conventional smoothing spline in data smoothing. A proof of asymptotic equivalence between the smoothing and generalized smoothing splines is also given as an appendix.
Comparison of stratospheric temperatures from several lidars, using National Meteorological Center and microwave limb sounder data as transfer references
Authors: Wild J. D. , Gelman M. E. , Miller A. J. , Chanin M. L. , Hauchecorne A. , Keckhut P. , Farley R. , Dao P. D. , Meriwether J. W. , Gobbi G. P. , Congeduti F. , Adriani A. , McDermid I. S. , McGee T. J. , Fishbein E. F.
Published: February 2004

Stratospheric temperatures derived from five different lidars are compared. Although the lidars are in five separate geographic locations, the evaluation is accomplished by comparing each of the sets of lidar data taken over the course of a year (1991–1992) with temperatures interpolated to each location from daily global temperature analyses from the National Meteorological Center (NMC). Average differences between the lidars and NMC temperatures vary for the different lidars by up to 6.7 K. Part of this large average temperature difference is shown to be due to the real temperature variation throughout the day, and the different times of observation of the NMC data and each of the lidar systems. Microwave limb sounder (MLS) data from the upper atmosphere research satellite are used to model the diurnal and semidiurnal variations in temperature for each lidar location, for each season. After adjusting for the temperature changes caused by variations in observation time, average temperature differences are reduced among four of the five lidars, compared with the NMC temperatures, but still vary by as much as 3.9 K at stratospheric altitudes between 30 and 45 km. Results of direct comparisons at two permanent lidar sites with a mobile lidar show that sometimes agreement within 1 to 2 K is achieved, but for other cases, larger average differences are seen. Since the precision of lidar temperatures has been estimated to be better than 1 K, further research is needed to reconcile this small expected error with the larger average differences deduced here using measurements made under operational conditions.
Comparisons of observed ozone trends in the stratosphere through examination of Umkehr and balloon ozonesonde data
Authors: Miller A. J. , Tiao G. C. , Reinsel G. C. , Wuebbles D. , Bishop L. , Kerr J. , Nagatani R. M. , DeLuisi J. J. , Mateer C. L.
Published: February 2004

During the past several years, several authors have published results of the annual and seasonal trends depicted in the total ozone data from both satellite and ground‐based observations. The examination of the vertical profile data available from the balloon ozonesonde and Umkehr observations, however, has been generally restricted to limited periods and to nonseasonal trend calculations. Within this study, we have examined the nonseasonal and the seasonal trend behavior of the ozone profile data from both ozonesonde and Umkehr measurements in a consistent manner, covering the same extended time period, 1968–1991, thus providing the first overall comparison of results. Our results reaffirm the observation of significant negative ozone trends in both the lower stratosphere (15–20 km), about −6% per decade, and upper stratosphere (35–50 km), about −6% per decade, separated by a nodal point in the region of 25–30 km. The upper stratosphere decrease is, apparently, associated with the classic gas phase chemical effect of the chlorofluorocarbons, whereas the cause of the lower stratospheric decline is still under investigation, but may well be associated with the chlorine and bromine chemistry in this region.
Impact of a simulated severe local storm on the redistribution of sulfur dioxide
Authors: Wang Chien , Crutzen Paul J.
Published: February 2004

A series of numerical experiments in a two‐dimensional framework have been carried out in order to investigate the impact of a severe summertime, midlatitude storm on the SO2‐S(IV)‐S(VI) transport and oxidation processes by comparing results of numerical simulations with and without consideration of aqueous phase chemistry. The cloud‐transport‐only runs showed considerable dilution of boundary layer air with free tropospheric air in the cloud, such that in its upper reaches and anvil parts only 10% or less originated from the boundary layer. A substantial fraction of the SO2 transported upward into the cloud area is dissolved in the liquid phase particles. As a consequence, about 50% of the SO2 that has gone up in the cloud is removed by precipitation processes under the chosen conditions. Below‐cloud scavenging was likewise an efficient process. Most importantly, the uptake of SO2 in falling cloud drops strongly hinders the transfer of SO2 to the upper reaches of the cloud. Transport of SO2 from the boundary layer to the upper troposphere was therefore a rather inefficient process. Another result of our simulation is that only a small amount of dissolved SO2 is converted into S(VI) during the storm simulation period (1 hour). This is explained by the fact that we assumed H2O2 to be present only in the boundary layer at concentrations about 10 times lower than those of SO2, together with the higher solubility of H2O2. However, because of the large entrainment of free tropospheric air into the cloud, the H2O2 in the free troposphere would be much more efficient in oxidizing S(IV). A number of sensitivity calculations which we conducted, assuming different chemical makeups of the boundary layer did not change the main conclusions of our study.
Interhemispheric differences in springtime production of HCl and ClONO2 in the polar vortices
Authors: Douglass Anne R. , Schoeberl Mark R. , Stolarski Richard S. , Waters J. W. , Russell James M. , Roche Aidan E. , Massie Steven T.
Published: February 2004

UARS observations of O3 and ClO (Microwave Limb Sounder), ClONO2 and HNO3 (Cryogenic Array Etalon Spectrometer), NO, NO2, and HCl (Halogen Occultation Experiment), and model calculations are used to produce an exposition of the different processes through which the reservoir gases ClONO2 and HCl are reformed at the end of the polar winter. Comparison of the observations within the polar vortices shows that HCl increases more rapidly in the Antarctic vortex in spring than in the Arctic vortex. Model analysis shows that this occurs because the O3 concentrations in the southern vortex fall well below those in the northern vortex. The Cl/ClO fraction calculated for the southern hemisphere is therefore up to 30 times higher, leading to rapid HCl formation by Cl + CH4. The concentrations of NO observed by HALOE are substantially lower for the northern hemisphere than for the southern hemisphere, even for similar values of the concentration of HNO3 and the production of NOX from HNO3 through photolysis and reaction with OH. This is consistent with the dependence of the NO/NOX ratio on the O3 concentration, i.e., the daytime production rate of NO2 via NO + O3 is reduced, leading to higher NO in the southern hemisphere. This higher concentration of NO also contributes to the rapid HCl increase as Cl production from ClO + NO is enhanced.
Tropospheric circulation changes associated with stratospheric sudden warmings: A case study
Authors: Kodera Kunihiko , Chiba Masaru
Published: February 2004

It was theoretically demonstrated by Matsuno that stratospheric warmings are caused by an intensified vertical propagation of tropospheric planetary waves. However, the question of how the resultant changes in the stratospheric circulation affect the troposphere in return is left unanswered. In the present study, a case study on the 1984–1985 stratospheric warming event is conducted to clarify the changes in the tropospheric circulation associated with stratospheric sudden warmings. The results of the present study indicate that during stratospheric warmings, not only the intensification of the upward propagation of planetary waves is found in the stratosphere, but also changes in the direction of the meridional propagation of waves occur in the troposphere as well as in the stratosphere. Changes in the meridional phase structure of tropospheric planetary waves produce enhanced cold surges over the oceans, which in turn generate intense synoptic eddies. Further disturbances, such as blockings, can be produced through interactions between the planetary waves and synoptic eddies, but this may be only indirectly related with the stratospheric warmings. Comparisons between the observed changes in circulation and results of numerical model experiments suggest a potential role of the stratosphere in the tropospheric circulation through changes in meridional propagation of planetary waves.
Use of microwave brightness temperatures with a general circulation model
Authors: Shah Kathryn Pierce , Rind David
Published: February 2004

Brightness temperature maps from global monthly mean general circulation model (GCM) atmospheric and surface fields are calculated with a new microwave radiative transfer postprocessor. This microwave radiative transfer model uses fields from the 4° by 5° Goddard Institute for Space Studies (GISS) GCM Model II and subsequent developmental versions of the GCM. The absolute brightness temperature maps from the microwave radiative transfer model are shown to be more accurate than maps from temperature weighting functions due to the inclusion of local surface emission and local radiative transfer effects. This permits direct comparison of calculated brightness temperatures to observed brightness temperatures measured by the microwave sounding unit (MSU) channels. Microwave maps are calculated for the January and July Geophysical Fluid Dynamics Laboratory (GFDL) radiosonde upper air and surface climatology and compared to the MSU climatology. This work tests the microwave radiative transfer model and comments on two disparate tropospheric climatologies used for trend analysis and GCM validation. The microwave comparison generally finds good agreement between the MSU channel 2 and the radiosonde climatologies. January brightness temperature differences of a few degrees come from spatial coverage gaps and land biasing in the radiosonde climatology, echoing results in previous comparison studies. The July microwave comparison finds unexpected warmth brightness temperatures from the radiosonde climatology over land masses. This July warmth may be related to diurnal sampling differences and to recent study by other researchers into radiosonde time series' sensitivity to instrumentation and to solar heating of the radiosonde. Comparison of calculated GCM microwave maps to observed monthly mean MSU maps aids development of the GISS GCM. MSU channel 2R and channel 2 are used to evaluate the impacts of GCM developments near the ocean surface and the midtroposphere, respectively. These microwave channels show large sensitivity to the planetary boundary layer scheme. MSU channel 4 confirms improvements in the lower stratosphere with addition of a parameterized gravity wave drag beneath the GCM's rigid model top. Overall, the MSU climatology with its global coverage, several broad vertical samplings, and horizontal resolution comparable to GCM grid cells complements more traditional observations used to validate general circulation models.
Shenandoah Cloud and Photochemistry Experiment (SCAPE): Overview
Authors: Keene William C. , Jacob Daniel J. , Talbot Robert W. , Munger J. William
Published: February 2004

The Shenandoah Cloud and Photochemistry Experiment (SCAPE) investigated the chemistry of the atmosphere at a high‐elevation forested site in central Virginia with particular focus on the factors controlling concentrations of ozone, carbonyl compounds, and carboxylic acids. Carbonyl compounds and carboxylic acids are ubiquitous chemical constituents of the global troposphere, but many aspects of their biogeochemical cycling are poorly understood. Carbonyls are generated from the oxidation of hydrocarbons; formaldehyde (HCHO) produced via this pathway is an important precursor for OH. Thus the carbonyls are intermediates in and tracers of tropospheric photochemistry [e.g., Carlier et al., 1988]. Carboxylic acids are major natural sources of atmospheric acidity thereby partially controlling pH‐dependent chemical transformations in clouds [e.g., Keene and Galloway, 1988]. The aqueous‐phase oxidation of HCHO in clouds has been hypothesized as a significant source of formic acid (HCOOH) and the aqueous‐phase oxidation of HCOO− a potentially important in‐cloud sink for OH [Chameides and Davis, 1983; Jacob, 1986]. Under many conditions, clouds should be a net sink for tropospheric HCOOH [Jacob and Wofsy, 1988]. Specific research objectives were (1) to assess the relative importance of NOx and hydrocarbons in limiting regional ozone production, (2) to investigate sources and sinks for carbonyl compounds and caiboxylic acids, and (3) to examine the droplet‐size dependence of solute concentrations and the thermodynamics of phase partitioning for carbonyl compounds and carboxylic acids in clouds.
Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record
Authors: Masarie Kenneth A. , Tans Pieter P.
Published: February 2004

Atmospheric transport models are used to constrain sources and sinks of carbon dioxide by requiring that the modeled spatial and temporal concentration patterns are consistent with the observations. Serious obstacles to this approach are the sparsity of sampling sites and the lack of temporal continuity among observations at different locations. A procedure is presented that attempts to extend the knowledge gained during a limited period of measurements beyond the period itself resulting in records containing measurement data and extrapolated and interpolated values. From limited measurements we can define trace gas climatologies that describe average seasonal cycles, trends, and changes in trends at individual sampling sites. A comparison of the site climatologies with a reference defined over a much longer period of time constitutes the framework used in the development of the data extension procedure. Two extension methods are described. The benchmark trend method uses a deseasonalized long‐term trend from a single site as a reference to individual site climatologies. The latitude reference method utilizes measurements from many sites in constructing a reference to the climatologies. Both methods are evaluated and the advantages and limitations of each are discussed. Data extension is not based on any atmospheric models but entirely on the data themselves. The methods described here are relatively straightforward and reproducible and result in extended records that are model independent. The cooperative air sampling network maintained by the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado, provides a test bed for the development of the data extension method; we intend to integrate and extend CO2 measurement records from other laboratories providing a globally consistent atmospheric CO2 database to the modeling community.
Turbulent surface fluxes derived from radiometric surface temperature of sparse prairie grass
Authors: Stewart J. B.
Published: February 2004

An independently derived excess resistance was used to modify the classical relationship between surface‐air temperature difference and sensible heat flux. The modified relationship was used to estimate sensible heat flux using radiometric surface temperature, air temperature, and wind speed measured at a sparse prairie site during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) 1987 and FIFE 1989. Using the classical relationship, the mean sensible heat flux is overestimated by 141 W m−2 compared to an underestimate of only 21 W m−2 using the relationship including the excess resistance, also the root‐mean‐square error decreased from 63 to 26 W m−2.
Stratospheric effects of bromine activation on/in sulfate aerosol
Authors: Danilin Michael Y. , McConnell John C.
Published: February 2004

Heterogeneous reactions on/in stratospheric sulfate aerosol and polar stratospheric clouds are important in the photochemical balance of the stratosphere. Recent laboratory measurements indicate that heterogeneous reactions with bromine compounds are possible under stratospheric conditions. We have used a box photochemical model of the stratosphere with a detailed heterogeneous module to evaluate the effect of the heterogeneous reactions of the inorganic bromine for background and volcanic conditions at 60°S and 50 mbar. For the conditions studied the most important reaction is the hydrolysis of BrONO2 on the aerosol, especially for volcanic conditions. It results in the indirect increase of the ClOχ fraction due to the suppression of NOχ (thus reducing ClONO2) and the direct release of ClOχ due to an additional consumption of HCl. The NOχ decrease is pronounced going into winter and leads to a ClO activation to about 0.5 parts per billion by volume (ppbv) 1 to 2 weeks earlier than without the heterogeneous reactions of bromine species. Due to the temperature sensitivity of the solubility of HCl, the reaction HOBr + HCl(a) → BrCl + H2O results in direct activation of ClO at temperatures below ∼205 K. The enhanced processing for the bromine reactions leads to an additional increase ∼30% in ozone depletion for volcanic conditions during the winter. The stratospheric effects of the reactions ClONO2 + HBr(a) → BrCl + HNO3, N2O5 + HBr(a) → BrNO2 + HNO3 and HOBr + HBr(a) → Br2 + H2O are limited even under volcanic conditions due to slow gas phase production rate of HBr.
Hydroxyl radical concentrations and Kuwait oil fire emission rates for March 1991
Authors: McKenna D. S. , Hord C. J. , Kent J. M.
Published: February 2004

Toward the end of the Gulf War, Iraqi troops damaged several hundred oil wells in Kuwait setting many of them on fire. Measurements made in March 1991, a few weeks after most of the fires had started (Johnson et al., 1991), were used to estimated the total burn rate and the emission rates of individual pollutants. Measurements of the principal carbon species in the plume, obtained from flask samples collected at the same time as continuous measurements of SO2 have been used to derive an “effective” sulphur content of the smoke of 2.4%, almost a third lower than the previous estimate. This sulphur content of 2.4% combined with the capping history of the fires has been used to revise the earlier estimates and provide more detailed information on the speciation of the emissions. It is now estimated that 139×106 t of crude oil were burnt during an 8‐month period, resulting in the release of 112×106 t of carbon in carbon dioxide, 3×106 t of carbon in soot, 1.6×106 t of carbon in carbon monoxide, 1.3×106 t of carbon in nonmethane hydrocarbons, 0.11×106 t of nitrogen in nitrogen oxides, and 3.11×106 t of sulphur in sulphur dioxide. In addition to measurements made close to the source of the plume, one flight successfully sampled a plume some 600 km from the fires which had experienced significant photochemical aging. These observations provided a unique data set with which to estimate the rate at which hydrocarbon pollutants in the plume degrade and to infer the hydroxyl radical concentrations which cause that degradation. Most of the aliphatic hydrocarbon concentrations determined from flask samples collected at a range of distances from the Kuwait source conform to a simple loss process proportional to hydrocarbon hydroxyl reactivity and imply a diurnally averaged hydroxyl radical concentration within the plume of 1×106 molecules cm−3. Finally, it is shown that, although theoretically, hydrocarbon concentrations can be combined to predict the difference ratio of hydrocarbon reactivity, that is, (k1 ‐ k2)/(k3 ‐ k4), in practice experimental error can give rise to apparent discrepancies between theory and observations. Earlier studies found similar discrepancies and have speculated that these arise from differences in “photochemical age” for different hydrocarbons, a parameter those studies could not determine. We have shown similar discrepancies but have been able to determine photochemical ages for several hydrocarbons and have shown that the hydrocarbon reductions are consistent with a single photochemical age (3% precision), precluding the earlier explanations. However, even though the photochemical lifetime may be determined very precisely, consideration of the computational stability of the procedures involved suggest that unavoidable experimental precision may lead to factors of 2 errors in the determination of the difference ratio, which is more than sufficient to explain the known discrepancies.
Dynamics of fine scale variables versus averaged observables in a simplified thermal convection model
Authors: Vannitsem S. , Nicolis C.
Published: February 2004

The dynamical properties of time‐ and space‐averaged observables of a simplified one‐dimensional thermal convection model are explored and compared to those of the fine scale variables. It is found that averaging reduces the domain of variability of the system, favors persistence of correlations in time and space, and reduces the “effective” dimensionality of the underlying attractor. Furthermore, space and time averages display enhanced predictability, characterized by an error growth rate smaller than the one of the fine scale variables.
Aerosol optical depth over the oceans: Analysis in terms of synoptic air mass types
Authors: Smirnov A. , Villevalde Y. , O'Neill N. T. , Royer A. , Tarussov A.
Published: February 2004

The results of spectral aerosol optical depth measurements in the Pacific Ocean, Baltic Sea, and North Atlantic are considered with regard to air mass types. It is found that the optical properties of continental and maritime air mass types differ significantly for the data employed in this study. A synoptical air mass context was also employed in demonstrating the correlation between near infrared aerosol optical depth τa(1640 nm) and wind speed as well as for investigations into the relationship between deck level relative humidity and the aerosol optical depth at 550 nm. Simulations, employing well‐known aerosol parameterization models, of the aerosol optical depth spectra for various air mass types show good agreement with the experimental results in the visible and near infrared range.
Infrared measurements of the ozone vertical distribution above Kitt Peak
Authors: Pougatchev N. S. , Connor B. J. , Rinsland C. P.
Published: February 2004

The vertical distribution of the ozone in the troposphere and the lower and middle stratosphere has been retrieved from a series 0.005–0.013 cm−1 resolution infrared solar spectra recorded with the McMath Fourier transform spectrometer at the National Solar Observatory on Kitt Peak. The analysis is based on a multilayer line‐by‐line forward model and a semiempirical version of the optimal estimation inversion method by Rodgers. The 1002.6–1003.2 cm−1 spectral interval has been selected for the analysis on the basis of synthetic spectrum calculations. The characterization and error analysis of the method have been performed. It was shown that for the Kitt Peak spectral resolution and typical signal‐to‐noise ratio (≥100) the retrieval is stable, with the vertical resolution of ≈5 km attainable near the surface degrading to ≈10 km in the stratosphere. Spectra recorded from 1980 through 1993 have been analyzed. The retrieved total ozone and vertical profiles have been compared with total ozone mapping spectrometer (TOMS) satellite total columns for the location and dates of the Kitt Peak measurements and about 100 ozone ozonesoundings and Brewer total column measurements from Palestine, Texas, from 1979 to 1985. The total ozone measurements agree to ±2%. The retrieved profiles reproduce the seasonally averaged variations with altitude, including the ozone spring maximum and fall minimum measured by Palestine sondes, but up to 15% differences in the absolute values are obtained.
Hydrologic cycle parameterization for energy balance climate models
Authors: Chu Shaoping , Ledley Tamara Shapiro
Published: February 2004

The exchange of moisture and heat between the atmosphere and the Earth's surface fundamentally affect the dynamics and thermodynamics of the climate system. In order to trace moisture flow through the climate system and examine its impact on climate, a hydrologic cycle and a land surface energy balance are incorporated into a coupled climate ‐ thermodynamic sea ice (CCSI) model. The expanded CCSI model is tested by comparing its climate simulations with available observations and GCM modeling results. In general, the expanded model does a good job in simulating the large‐scale features of the atmospheric circulation and precipitation in both space and time. The expanded model is used to examine the role of the hydrologic cycle in initiating ice sheet growth in response to changes in atmospheric composition. The results indicate that variations in summer ice melt in response to changes in the land ice albedo, and thus in air temperatures, are more important in determining the initiation of ice sheet growth than variations in precipitation.
Parameterization of subgrid‐scale land surface fluxes with emphasis on distributing mean atmospheric forcing and using satellite‐derived vegetation index
Authors: Gao W.
Published: February 2004

Atmosphere‐surface exchange fluxes can vary significantly over a large grid cell of atmospheric models and need to be estimated with subgrid‐scale variations included. The present study aims at developing a method for parameterization of subgrid‐scale (PASS) surface fluxes in atmospheric models, with emphasis on a scheme to distribute the mean atmospheric forcing from the model grid (MG) to subgrid (SG) cells and on using spectral vegetation indices derived from satellite remote sensing to estimate surface parameters at SG scales. The mean atmospheric forcing, including wind speed, temperature, and humidity, is distributed to SG cells according to spatial differences in these parameters at the surface and the strength of vertical turbulence mixing in the atmospheric boundary layer. Simulation with this scheme allows a feedback of changed SG atmospheric conditions caused by surface heterogeneity to influence the SG surface exchange. The SG surface exchange is parameterized with a suite of simplified relationships developed to infer surface conductance, aerodynamic resistance, surface albedo, and soil heat flux ratio on the basis of spectral vegetation indices available from satellite remote sensing, while empirical coefficients used in the relationships are derived for selected surface types from available field experiments. The computation of the surface flux and energy budget for a large number of SG cells is made feasible by using a rapid scheme based on an analytical solution to the surface energy budget equations. The PASS model was tested in a single‐cell mode with field measurements and evaluated in a multicell mode with limited data and a sensitivity study.