bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical transport of sulfur dioxide and dimethyl sulfide in deep convection and its role in new particle formation
Authors: Thornton D. C. , Bandy A. R. , Blomquist B. W. , Bradshaw J. D. , Blake D. R.
Published: February 2004

The NASA Pacific Exploratory Mission‐West experiment in 1991 and 1994 covered large portions of the western Pacific Ocean troposphere and transects of the troposphere of the equatorial and subtropical North Pacific Ocean. Sulfur dioxide and dimethyl sulfide were concurrently measured from the surface to 12 km. In 1991, sulfur dioxide had significant anthropogenic and volcanic sources. In 1994, sulfur dioxide aloft was significantly lower than in 1991. During both periods, deep convection was responsible for the distribution of sulfur dioxide and dimethyl sulfide. An assessment is made of the proportion of sulfur dioxide that could be made from dimethyl sulfide convected to high altitude. The subsequent formation of new aerosol particles from sulfur dioxide at high altitude is evaluated.
Seasonal variations of stable hydrogen and carbon isotope ratios in methane from a Chinese rice paddy
Authors: Bergamaschi Peter
Published: February 2004

Variations in the isotopic composition (δ13C, δD) of methane emitted from a rice paddy in Suzhou, China (31.2°N, 120.4°E) were investigated during a whole rice‐growing season in 1995. Isotope analysis was performed using our tunable diode laser based methane isotopomer spectrometer (MISOS). Both δ13C and δD of the emitted CH4 show a pronounced seasonal variation with δ13C ranging between −51.6 and −70.8‰ V‐PDB (mean −63.8±4.9‰ (1σ); n=28) and δD between −352 and −311‰ V‐SMOW (mean −335.7±10.1‰; n=19). The shapes of the seasonal δ13C and δD variations were very similar between plots with two different fertilizer treatments. Gas bubbles, collected from the stirred sediment throughout the season, show a smaller variation in their isotopic composition (δ13C=−64.1±3.0‰ V‐PBB, n=13; δD=−349.2±4.7‰ V‐SMOW, n=12). In comparison, CH4 emitted into the atmosphere is enriched both in δ13C and δD during the first 30 days after flooding, indicating the influence of partial oxidation by methanotrophic bacteria. Between days 60 and 90 after flooding, however, emitted CH4 becomes depleted in δ13C but remains enriched in δD. Possible explanations are (17) the existence of different CH4 reservoirs, for which the partitioning of methanogenic pathways is different, or (2) a combination of isotope fractionation by CH4 oxidation and molecular diffusion during the diffusive transport through the rhizosphere. The seasonal variation in δ13C of emitted CH4 resembles that found in a previous study on a Japanese rice paddy [Tyler et al., 1994] suggesting (1) a typical behavior due to systematic changes related to CH4 production, transport, and oxidation during the vegetation cycle and (2) a significant impact on atmospheric δ13C signals.
Jet detrainment at a stratified interface
Authors: Cotel A. J. , Breidenthal R. E.
Published: February 2004

Using laboratory water‐tank experiments, detrainment from a vertical jet rising through a density interface is explored. The experiments reveal that detrainment only occurs for a specific range of two governing parameters, the Richardson number associated with the vortices and the normalized interface height. The shape of the detrainment domain is explained with simple physical arguments involving velocity gradients, baroclinic torques between the pure unmixed fluid and the environment, and baroclinic torques between the mixed fluid and the surrounding fluid. Detrainment is only observed when the penetrating jet consists of fluid with two different densities.
A comparison of water vapor observations with AMIPI simulations
Authors: Bates John J. , Jackson Darren L.
Published: February 2004

Water vapor simulations from the Atmospheric Model Intercomparison Project have been compared with satellite observations of precipitable water and upper tropospheric humidity. The model means and standard deviations of precipitable water compare favorably with observations and most models also reproduce the observed seasonal cycle well. The models show a regional dependence in reproducing the observed interannual variability of precipitable water, doing better in the deep tropics than in the subtropics and midlatitudes. The skill in reproducing the observed interannual variability in the deep tropics is attributed to accurate reproduction of anomalies during the 1982–1983 El Niño‐Southern Oscillation event. Comparisons between modeled and observed upper tropospheric humidity are more problematic, but significant differences are found in both the mean values and the ability of the models to produce the observed seasonal and interannual variability. Additional comparisons of both models and observations are required to resolve these discrepancies. Examination of leading modes of interannual variability shows that models that do a better job in simulating the observed all‐sky outgoing longwave radiation in the tropics also do a better job of simulating the observed upper tropospheric humidity.
Absorption of solar radiation by the cloudy atmosphere: Interpretations of collocated aircraft measurements
Authors: Valero Francisco P. J. , Cess Robert D. , Zhang Minghua , Pope Shelly K. , Bucholtz Anthony , Bush Brett , Vitko John
Published: February 2004

As part of the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE), we have obtained and analyzed measurements made from collocated aircraft of the absorption of solar radiation within the atmospheric column between the two aircraft. The measurements were taken during October 1995 at the ARM site in Oklahoma. Relative to a theoretical radiative transfer model, we find no evidence for excess solar absorption in the clear atmosphere and significant evidence for its existence in the cloudy atmosphere. This excess cloud solar absorption appears to occur in both visible (0.224–0.68 μm) and near‐infrared (0.68–3.30 μm) spectral regions, although not at 0.5 μm for the visible contribution, and it is shown to be true absorption rather than an artifact of sampling errors caused by measuring three‐dimensional clouds.
Observational evidence of wave ducting and evanescence in the mesosphere
Authors: Isler Joseph R. , Taylor Michael J. , Fritts David C.
Published: February 2004

A collaborative radar and imaging study of gravity waves over the Hawaiian Islands was performed during October 1993 as part of the Airborne Lidar and Observations of Hawaiian Airglow 1993/Coupling and Dynamics of Regions Equatorial (ALOHA‐93/CADRE) campaign to investigate the propagation characteristics of short‐period (<1 hour) waves at nightglow altitudes. The horizontal wavelengths and apparent phase speeds of quasi‐monochromatic wave events were measured in four separate nightglow emissions using data obtained by a high‐resolution CCD imager. This information was correlated with simultaneous MF radar wind measurements over the same height interval (∼80–100 km) to infer intrinsic wave parameters in each case. Correlating the two data sets allowed the determination of the local vertical wavenumber for each event, in particular whether it be real (indicative of freely propagating waves) or imaginary (indicative of ducted or evanescent waves). The results of this study indicate a preponderance of ducted or evanescent waves at 80–100 km during the time of the observations, with up to ∼75% of the events recorded exhibiting ducted or evanescent behavior. Also noted was a tendency for ducted behavior to be more prevalent among waves with shorter horizontal wavelengths, in agreement with Doppler ducting theory. These results suggest that ducted waves are relatively common in the upper mesosphere and lower thermosphere region, at least over the mid‐Pacific Ocean. As small‐scale waves which are ducted have the potential to travel much longer horizontal distances than freely propagating waves, the frequency of their occurrence should be taken into account in efforts to quantify gravity wave effects at these altitudes.
Estimating mean weighted temperature of the atmosphere for Global Positioning System applications
Authors: Ross Rebecca J. , Rosenfeld Simon
Published: February 2004

A water‐vapor‐weighted vertically averaged mean temperature of the atmosphere, Tm, is a key parameter in the retrieval of total water content from the measurements of Global Positioning System signal delays. The accuracy of precipitable water estimates is proportional to the accuracy of Tm. The geographic and seasonal variability of Tm based on 23 years of radiosonde soundings at 53 globally distributed stations is presented. Several methods for estimating Tm were evaluated by comparing the estimates against the actual Tm values. Sitespecific climatology or site‐specific linear regression was superior to the geographically and seasonally invariant regression relationship typically used to estimate Tm. Relative errors at most stations were less than 2%, which corresponds to absolute errors of precipitable water of 0.1–0.5 mm The station‐specific linear regression was superior to climatological means as an estimator except in the tropics, where correlations between Tm and Tsfc were not high. Also, a physical model was developed to indicate the relationship between Tm and other commonly used atmospheric variables.
A new inverse method for trace gas flux estimation: 2. Application to tropospheric CFCl3 fluxes
Authors: Mulquiney John E. , Taylor John A. , Jakeman Anthony J. , Norton John P. , Prinn Ronald G.
Published: February 2004

An initial application of a new inverse method for the estimation of flux strengths of long‐lived atmospheric trace gases is presented. CFCl3 is studied using the Australian National University's Chemical Transport Model. Unit‐pulse responses are derived from the model, and used to identify a time‐varying state‐space model of tropospheric CFCl3. This in turn is used in a Kaiman filter to perform two input‐estimation studies. The first uses model generated measurements to estimate known flux strengths. This demonstrates the robustness of the method, although it is found that instantaneous stratospheric loss rates are not well‐estimated using only surface concentration measurements. Emissions however, are robustly estimated. A time‐aver aged tropospheric lifetime can be estimated however, with an accuracy of ±5 years. Thirteen years of Atmospheric Lifetime Experiment Global Atmospheric Gases Experiment CFCl3 measurements are used in the second flux estimation experiment. The estimated fluxes though are outside known physical limits for CFCl3, and it is concluded that either a more accurate/appropriate transport model, or more measurement locations, are needed to obtain useful information regarding regional tropospheric CFCl3 fluxes.
Transport of sulfur dioxide from the Asian Pacific Rim to the North Pacific troposphere
Authors: Thornton Donald C. , Bandy Alan R. , Blomquist Byron W. , Talbot Robert W. , Dibb Jack E.
Published: February 2004

The NASA Pacific Exploratory Mission over the Western Pacific Ocean (PEM‐West B) field experiment provided an opportunity to study sulfur dioxide (SO2) in the troposphere over the western Pacific Ocean from the tropics to 60°N during February–March 1993. The large suite of chemical and physical measurements yielded a complex matrix in which to understand the distribution of sulfur dioxide over the western Pacific region. In contrast to the late summer period of Pacific Exploratory Mission‐West A (PEM‐West A) (1991) over this same area, SO2 showed little increase with altitude, and concentrations were much lower in the free troposphere than during the PEM‐West B period. Volcanic impacts on the upper troposphere were again found as a result of deep convection in the tropics. Extensive emission of SO2 from the Pacific Rim land masses were primarily observed in the lower well‐mixed part of the boundary layer but also in the upper part of the boundary layer. Analyses of the SO2 data with aerosol sulfate, beryllium‐7, and lead‐210 indicated that SO2 contributed to half or more of the observed total oxidized sulfur (SO2 plus aerosol sulfate) in free tropospheric air. The combined data set suggests that SO2 above 8.5 km is transported from the surface but with aerosol sulfate being removed more effectively than SO2. Cloud processing and rain appeared to be responsible for lower SO2 levels between 3 and 8.5 km than above or below this region.
Ozone mass exchange between the stratosphere and troposphere for background and volcanic sulfate aerosol conditions
Authors: Tie XueXi , Hess Peter
Published: February 2004

A three‐dimensional global chemical/dynamical model is used to study ozone mass exchange between the stratosphere and the troposphere. The ozone budget is calculated in the northern and southern extratropical lowermost stratosphere and in the tropical upper troposphere during both perturbed and background aerosol conditions. The stratospheric ozone mass flux into the troposphere is highest during the spring months in both hemispheres and higher in the northern hemisphere than in the southern hemisphere. During background aerosol conditions the net modeled stratospheric flux of ozone to the troposphere is 792 Tg/yr. The results suggest that the heterogeneous chemical reactions occurring on the surface of sulfate aerosols can have a significant impact on the ozone mass flux across the tropopause, leading to a possible 15% reduction in the annual global ozone mass transported from the stratosphere to the troposphere after a large volcanic eruption. Most of the reduction in ozone mass flux occurs in the northern hemisphere. In the southern hemisphere winter and spring the ozone concentration is already significantly perturbed by the heterogeneous reactions occurring on the surface of polar stratospheric clouds over Antarctica. The further increase in heterogeneous conversion due to the enhanced sulfate aerosol produces a smaller increase in active chlorine (ClO) than in the northern hemisphere, leading to a smaller increase in ozone destruction.
Ozone nighttime recovery in the marine boundary layer: Measurement and simulation of the ozone diurnal cycle at Reunion Island
Authors: Bremaud P. J. , Taupin F. , Thompson A. M. , Chaumerliac N.
Published: February 2004

We describe the diurnal cycle of ozone in the marine boundary layer measured at Reunion Island (21°S, 55°E) in the western part of the Indian Ocean in August‐September 1995. Results from a box chemistry model are compared with ozone measurements at Reunion Island. We focus on the peak‐to‐peak amplitude of ozone concentration, since our measurements show a variation of about 4 parts per billion by volume, which is close to the value obtained by Johnson et al. [1990] during the Soviet‐American Gases and Aerosols (SAGA) 1987 Indian Ocean cruise. Different dynamical mechanisms are examined in order to reproduce such a variation. We conclude that the most important one is the exchange between the ozone‐rich free troposphere and the ozone‐poor boundary layer. This exchange is supposed to be more important during the night than during the day, allowing ozone nighttime recovery. This is the key point of the observed diurnal cycle, since daytime ozone photochemistry is well described by the model. Then we assume an entrainment velocity equal to 1 mm s−1 during the day and 14 mm s−1 during the night to closely match our measurements. Topography influences, together with clouds, are presumed to be responsible for this difference between nighttime and daytime entrainment velocities of free tropospheric air into the boundary layer at Reunion Island. Over the open ocean the difference of the turbulent flux of sensible heat between the day and the night explains the strong ozone nighttime recovery observed by us and by Johnson et al. [1990].
Long‐range transport of ozone, carbon monoxide, and acidic trace gases at Oki Island, Japan, during PEM‐WEST B/PEACAMPOT B campaign
Authors: Kajii Yoshizumi , Akimoto Hajime , Komazaki Yuichi , Tanaka Shigeru , Mukai Hitoshi , Murano Kentaro , Merrill John T.
Published: February 2004

Ground based measurements of ozone, CO, HNO3 SO2, HCl, and formic acid were carried out at Oki, a remote island site in the Sea of Japan, during Feburuary 26 to March 16, 1994, as the Pacific Exploratory Mission in the Western Pacific/Perturbation by East Asian Continental Air Mass to the Pacific Oceanic Troposphere (PEM‐West B/PEACAMPOT B) campaign. According to trajectory analysis, the air mass reaching Oki was classified into four groups: northerly, northwesterly, west‐northwesterly, and westerly flows. Clear dependence of gas concentrations on flow direction of air mass was found for all species studied. Lowest concentrations were observed in the northerly airflow originating from the Bering Sea. The mean concentrations of ozone and CO in northerly flow were 37.6±1.9 and 151±1 ppbv, respectively. The mean values of HNO3, SO2, HCl, and formic acid in the northerly flow were 34±10, 41±5, 107±23, and 54±81 pptv, respectively. The highest concentrations of all species were observed in the westerly flow passing through a lower boundary layer over the Yellow Sea and South Korean Peninsula. The mean concentrations of ozone and CO in the westerly flow were 45.9±4.0 and 292±44 ppbv, respectively. The mean values of HNO3, SO2, HCl, and formic acid in the westerly flow were 137±37, 2075±1307, 515±214, and 264±183 pptv, respectively. Clear seasonal variation of the “background” concentrations of ozone and CO were identified by comparison with the data from the PEM‐West A/PEACAMPOT A campaign conducted in the fall. In contrast to other species, strong diurnal variation of formic acid with a daytime maximum was observed. The possibility of photochemical formation of formic acid from HCHO and the HO2 radical is discussed.
Ground‐based intercomparison of nitric acid measurement techniques
Authors: Fehsenfeld Fred C. , Huey L. Greg , Sueper Donna T. , Norton Richard B. , Williams Eric J. , Eisele Fred L. , Mauldin R. Lee , Tanner David J.
Published: February 2004

An informal intercomparison of gas‐phase nitric acid (HNO3) measuring techniques was carried out. The intercomparison involved two new chemical ionization mass spectrometers (CIMSs) that have been developed for the measurement of HNO3 along with an older, more established filter pack (FP) technique. The filter pack was composed of a teflon prefilter which collected aerosols followed by a nylon filter which collected the gas‐phase HNO3. The study was carried out during the late winter and early spring of 1996 at a site located on the western edge of the Denver metropolitan area. Throughout the study the two CIMS techniques were in general agreement. However, under certain conditions the HNO3 levels obtained from the nylon filter of the FP gave values for the gas‐phase concentration of HNO3 that were somewhat higher than that recorded by the two CIMS systems. The formation of ammonium nitrate (NH4NO3) containing aerosols is common during the colder months in this area. An analysis of these results suggests that the HNO3 collected by the nylon filter in the FP suffers an interference associated with the disproportionation of NH4NO3 from aerosols containing that compound that were initially collected on the teflon prefilter. This problem with the FP technique has been suggested from results obtained in previous intercomparisons.
Interannual variability of deep convection over the tropical warm pool
Authors: Chen Shuyi S. , Houze R. A.
Published: February 2004

Satellite data show that the total amount of deep convection was nearly constant from year to year over the “warm pool” region of the tropical Indian and Pacific oceans, but the spatial distribution varied. In the 1986–1987 warm El Niño/Southern Oscillation event, the maximum of deep convective activity was over the high sea surface temperature (SST) of the west central Pacific, with a local minimum over the eastern Indian Ocean. In the 1988–1989 cold ENSO event the maximum convective activity switched to the eastern Indian Ocean, with a minimum over the west central Pacific. The SST changed very little over the eastern Indian Ocean from year to year, and the centers of convective activity were always collocated with the four‐month mean low‐level westerlies in each year. The latitude of the cloudy region of the intraseasonal oscillation (ISO) varied interannually. The interannual differences in deep convective activity over the warm pool were accounted for almost exclusively by the occurrence or nonoccurrence of extremely large, long‐lasting, deep mesoscale cloud systems (cloud tops <208 K with horizontal dimensions ∼300–700 km). Such cloud systems occurred more frequently than normal over the western Pacific during the warm ENSO event and over the eastern Indian Ocean during the cold event. They occurred more frequently over the tropical eastern Indian and western Pacific oceans than over the maritime continent, thus accounting for the seesaw pattern of the observed cold cloudiness between the two oceanic regions on both interannual and intraseasonal timescales.
Distribution of tropospheric methane over Siberia in July 1993
Authors: Tohjima Y. , Wakita H. , Maksyutov S. , Machida T. , Inoue G. , Vinnichenko N. , Khattatov V.
Published: February 2004

Airborne observations of atmospheric methane (CH4) mixing ratio were carried out over Siberia during July 15–30, 1993, using a continuous measurement system. The distribution of CH4in the upper troposphere at an altitude of about 7 km was highly variable (1.72–1.91 parts per million, or ppm), being affected by intrusion of stratospheric air, long‐range transport of CH4from the source region, and a synoptic‐scale mixing process. During flights along nearly constant latitude between Yakutsk (62.10°N, 129.50°E) and Nizhnevartovsk (60.57°N, 76.40°E) on July 19 and 28 we observed large‐scale enhancements of CH4from near 90° to 100°E with a horizontal scale of more than 500km. Accompanied by high humidity and low mixing ratios of CO2and O3, the air masses with enhanced CH4mixing ratio were considered to be affected by lower tropospheric air. The probable source region of the CH4was inferred to be the West Siberian Lowland, which contains vast wetlands and huge oil/gas fields. The distribution of CH4in the lower troposphere (0.1–3 km) over the boreal wetlands in the West Siberian Lowland, ranging from 1.85 ppm to 2.75 ppm, showed large accumulations near the ground in the morning. The shortterm temporal variations in the vertical profile of CH4mixing ratio revealed that the accumulated CH4was transported to the free troposphere with the growth of the mixed layer. On the other hand, the distribution of CH4(0.1–1 km) over the tundra areas in the Siberian Arctic was less variable (1.81–1.84 ppm), and little accumulation was observed.
Biomass‐burning influence on tropospheric ozone over New Guinea and South America
Authors: Kim Jae H. , Newchurch M. J.
Published: February 2004

Using NIMBUS‐7 version‐7 Total Ozone Mapping Spectrometer (TOMS) ozone‐column measurements, we derive lower‐tropospheric ozone amounts over western South America and over the western Pacific Ocean near New Guinea from the column difference between two nearby regions with a topographic contrast, mountain and sea level. The seasonal variation of lower tropospheric‐column ozone from ozonesondes at Natal, Brazil, agrees well with the seasonal variation of lower‐tropospheric ozone over areas east and west of the Andes at the Natal latitude. This result suggests that, in the presence of the persistent easterly winds throughout the year over equatorial South America, favorable conditions exist for transporting biomass‐burning products from burning regions to western South America. The seasonal variation of lower‐tropospheric ozone over New Guinea shows a distinguishable annual cycle with a maximum in July–September and a minimum in January–February. Because the ozone monthly variation is well anticorrelated with monthly rainfall (the maximum ozone episode occurs during the dry season), biomass burning appears to be a likely precursor of the elevated ozone in a mechanism similar to the mechanism observed over South America and Africa. Overall, we observed less lower‐tropospheric ozone over western New Guinea (6.6 ±2.2 Dobson units (DU) annual mean and monthly extrema) than over the plains east of the Andes (9.0 +3.4/−2.O DU). The tropospheric‐ozone linear trend derived from a regression of the deseasonalized monthly averaged lower‐tropospheric ozone amount versus time east of New Guinea (upwind of the biomass‐burning areas) shows no significant trend; however, west of New Guinea (downwind of the biomass burning regions) we find a statistically significant increase of 0.06 ± 0.04 [DU yr−1] (95% confidence interval (c.i.)), corresponding to 1.0 ± 0.6 [% yr−1] (95% c. i.). The magnitude of this increasing trend is similar to the magnitude of the trend in the lower‐troposphere ozone in western South America.
A study of the low‐frequency inertio‐gravity waves observed during the Pyrénées Experiment
Authors: Scavuzzo C. M. , Lamfri M. A. , Teitelbaum H. , Lott F.
Published: February 2004

The purpose of this paper is to analyze and interpret the onset of some well‐characterized transient inertio‐gravity waves, observed during the PYREX (Pyrénées Experiment) campaign. The data used are the high‐resolution soundings, launched every 6 hours on both sides of the ridge. In agreement with other observations made during the field campaign, certain among those soundings often show steady mountain waves. It appears that those waves are often transients and are followed by well‐characterized inertio‐gravity waves, propagating upward and downward from the level where the initial mountain waves are large. To interpret those observations, it is suggested that the observed inertio gravity waves result from the geostrophic adjustment of the large‐scale flow that follows the transit and eventually the breaking of the main mountain wave. This hypothesis is supported by an analytical calculation of inertio‐gravity waves emission from a momentum deposit that lasts a finite time. The spatial extent of this forcing are also finite, and its maximum amplitude is a fraction of the measured mountain drag.
Soil carbon cycling at a black spruce (Picea mariana) forest stand in Saskatchewan, Canada
Authors: Nakane Kaneyuki , Kohno Takahiro , Horikoshi Takao , Nakatsubo Takayuki
Published: February 2004

Stored amounts and flow rates of soil carbon were measured simultaneously with soil environmental conditions (temperature and moisture content) periodically during the growing seasons from 1994 to 1995 at two plots (plot A was a dry soil condition, and plot B was a wet condition) in a black spruce (Picea mariana) forest stand in the Prince Albert area of Saskatchewan, Canada. Seasonal trends in litterfall rate and accumulation of the A0 layer were not observed, while the total and mineral soil respiration rates changed seasonally with soil temperature. There was no significant relationship between soil moisture content and any flow rates or accumulations of soil carbon. Soil respiration and loss of litter might have been very low during the winter (November to early May) because of the frozen soil. The annual soil carbon cycling was analyzed by a compartment model, based on the data obtained in this study. The relative decomposition rate of the A0 layer and humus in the mineral soil were estimated at 0.0632 yr−1 and 0.0045 for plot A and 0.0284 yr−1 and 0.0020 for plot B, respectively. These values indicate that the soil carbon cycling in plot A was about twice as fast as that in plot B. The slower cycling in plot B may be caused by the lower soil temperature and humid soil conditions, since the groundwater level is higher in plot B. The soil in both plots were accumulating carbon, i.e., 0.13 t C ha−1 yr−1 for plot A and 0.03 for plot B. The soil carbon cycling in the boreal forest stand was slower because of the lower soil temperature than that reported in the cool‐ and warm‐temperate forests. Soil carbon cycling in the boreal forest predominantly occurred at the surface of the mineral soil, suggesting that the decomposition response of soil organic matter in the boreal forest will be enhanced compared to other climate zone forests because of the large predicted temperature increase in the boreal zone under global warming.
Spectral reflectance measurements of boreal wetland and forest mosses
Authors: Bubier Jill L. , Rock Barrett N. , Crill Patrick M.
Published: February 2004

High‐spectral resolution reflectance data were acquired in the laboratory for several species of boreal forest and peatland mosses. Feather mosses and lichens (forests), brown mosses (rich fens), and Sphagnum species (bogs and poor fens) were collected from sites in the northern study area (NSA) of the Boreal Ecosystem‐Atmosphere Study (BOREAS) near Thompson, Manitoba, and from three peatlands in southeastern New Hampshire. Because mosses are indirect indicators of soil moisture, trace gas flux, and carbon accumulation, these data may enable hyperspectral remote sensing systems, such as the airborne visible and infrared imaging spectrometer and the compact airborne spectrographic imager (AVIRIS) (CASI), as well as future systems such as Lewis and the first New Millennium Project, to infer differences in hydrology and carbon cycling in boreal ecosystems at small spatial scales (< 1–900 m2). Mosses exhibit distinctly different spectral characteristics from vascular plants in the visible, near‐infrared (NIR) and short‐wave infrared (SWIR) regions. In the visible portion of the spectrum, mosses exhibit typical absorption in the blue and red regions but differ from vascular plants in having a “green” peak reflective of the color (red, brown, or green) of the individual species. The moss reflectance in the NIR spectral region is typically less reflective than the same region in vascular plants and is characterized by strong water absorption features located at approximately 1.00 and 1.20 μm, resulting in pronounced reflectance peaks at approximately 0.85, 1.10, and 1.30 μm (identified as NIR 1, 2, and 3, respectively). The variations in the relative brightness of the three NIR peaks in each of the three groups of mosses (Sphagnum, feather, and brown mosses) are diagnostic and may be indicative of different cellular characteristics. The slope of the NIR plateau as determined by the NIR 3/1 ratio, as well as the shape of the NIR 1 peak and relative dominance of NIR 2, separate the three groups. In addition, the NIR 1 peak in Sphagnum species is marked by a minor absorption feature at 0.85 μm, which is absent in all brown mosses and feather mosses, as well as in vascular plants. Because this absorption feature results in a narrow NIR 1 peak, and the red absorption is also narrow in Sphagnum, the standard normalized difference vegetation index/simple vegetation index ratio (NDVI/VI) methods do not work well in characterizing biomass or greenness. The overall reflectance of mosses in the SWIR region (1.50–2.50 μm) is lower than that of vascular plants because of the higher water content of the moss tissue. In lichens, reflectance in this region is higher than either mosses or vascular plants, due likely to tissue dryness. The lichens included in this study are most dissimilar from mosses and vascular plants in the visible portion of the spectrum.
Cosmic‐ray‐induced neutron intensity in Taiwan and its variations during a typhoon
Authors: Chung C. , Chen C. Y.
Published: February 2004

Cosmic neutrons as a secondary cosmic radiation, strike the ground with intensity which varies at different latitude, altitude, and solar activity. In a 3‐year extensive survey period, the cosmic neutron intensity was measured over Taiwan islandwide; the average neutron dose equivalent rate is 0.65 nSv h−1 near sea level, up to 14.5 nSv h−1 at the highest mountaintop (altitude of 3952 m). In a rare event, the cosmic neutron intensity at a monitoring station was recorded during the entire period that Typhoon Herb swept across the island in 1996. The anomalous reading of cosmic neutron intensity in the typhoon eye, 2.17±0.40 nSv h−1 (or 4 times higher than the normal reading) is reported here for the first time. The onset of cosmic neutron intensity in the typhoon is closely associated with the steady, rapid air pressure drop as well as the 6×106 km3 spiral cloud; the dips in the onset are correlated with sustained gale winds and heavy precipitation. It is believed that the air pressure drop provides thinner air within the typhoon, and the spiral cloud containing dense moisture further slows down high energy neutrons from the ground, where we observed the neutrons showering down from the stratosphere where the cosmic neutrons have the maximum density. These combined effects result in more medium‐energy neutrons penetrating down to the ground through the typhoon; while the gale wind and heavy rain deflect, attenuate, and, to a lesser extent, absorb the cosmic neutrons from the atmosphere.
A reexamination of the impact of anthropogenically fixed nitrogen on atmospheric N2O and the stratospheric O3 layer
Authors: Nevison Cynthia , Holland Elisabeth
Published: February 2004

The impact of anthropogenic nitrogen fixation on atmospheric N2O is estimated using the approach of the 1970s, which assumed that some fraction β of anthropogenically fixed nitrogen is rapidly denitrified back to the atmosphere, with a significant fraction α of the end product as N2O. Appropriate values for β and α are discussed and applied to current anthropogenic nitrogen fixation rates, which are dominated by synthetic fertilizer and crop production. These calculations yield an N2O source of about 3.5 Tg N/yr associated with anthropogenic nitrogen fixation, which accounts for most of the observed atmospheric N2O increase of 3–5 Tg N/yr. This simple nitrogen cycle‐based approach toward estimating anthropogenic N2O sources provides a useful check on the more complex approaches employed today, in which emissions from a large number of small, independent sources are estimated by extrapolating measured emissions coefficients. Such approaches can be inconsistent with considerations of the global nitrogen cycle and likely have underestimated the fertilizer N2O source and double counted other sources. A box model of atmospheric N2O which assumes an anthropogenic N2O source proportional to past and projected future rates of anthropogenic nitrogen fixation can reproduce much of the historic growth in N2O. Continued growth in the rate of anthropogenic nitrogen fixation could increase atmospheric N2O to 400–500 ppbv by the year 2100. Two‐dimensional model calculations suggest that the corresponding increase in stratospheric NOx would cause a small loss of O3, which would be superimposed upon a larger recovery due to the phaseout of anthropogenic halocarbons. An increase in N2O could put more NOx into the middle and upper stratosphere than supersonic aircraft, although the relevant time scale is considerably longer. To better understand the impact of anthropogenic nitrogen on atmospheric N2O and the stratospheric O3 layer, more information is needed about future anthropogenic nitrogen fixation rates, the N2O yields of denitrification and nitrification, net storage/loss of naturally and anthropogenically fixed nitrogen, and NOx chemistry in the stratosphere.
An evaluation of deep convective mixing in the Goddard Chemical Transport Model using International Satellite Cloud Climatology Project cloud parameters
Authors: Allen Dale J. , Pickering Kenneth E. , Molod Andrea
Published: February 2004

The simulation of deep convective mixing in the Goddard Chemical Transport Model (GCTM) is evaluated by comparing 1990–1992 distributions of upper tropospheric convective mass flux and cloud top pressure from the Goddard Earth Observing System data assimilation system (GEOS‐1 DAS) with deep convective cloud fields from the International Satellite Cloud Climatology Project (ISCCP). Deep convective mixing in the GCTM is calculated using convective information from the GEOS‐1 DAS. Therefore errors introduced when deep convection is parameterized in the GEOS‐1 DAS affect the distribution of trace gases in the GCTM. The location of deep convective mixing in the tropics is fairly well simulated, although its north‐south extent is overestimated by >5°. The frequency of deep convective mixing also appears to be overestimated in the tropics, resulting in GCTM‐calculated upper tropospheric concentrations of carbon monoxide in the tropics that are larger and less variable than those observed. The spatial extent of deep convective mixing in the subtropics is overestimated at several locations including the Caribbean throughout the year and the South Pacific Convergence Zone during June‐August. The extent of deep convection is underestimated over midlatitude marine storm tracks. DAS‐calculated cloud top pressures differ from ISCCP cloud top pressures by less than one‐half a GCTM layer (35 hPa) at most longitudes in the tropics; however, cloud top pressures are overestimated by more than 35 hPa (i.e., the vertical extent of deep convection is underestimated) over wintertime midlatitude storm tracks and the Indian Ocean and underestimated by more than 35 hPa at locations that include the Gulf of Mexico during December–February and central South America during June–August.
Recent and future improvements in two‐photon laser‐induced fluorescence NO measurement capabilities
Authors: Sandholm S. , Smyth S. , Bai R. , Bradshaw J.
Published: February 2004

This report briefly describes modifications to the Georgia Institute of Technology's two‐photon laser‐induced fluorescence airborne nitric oxide (NO) sensors that were made to enhance sensor performance during the NASA Pacific Exploratory Measurements in the Western Pacific Ocean (PEM‐West B) field measurement program. These modifications resulted in an approximate fiftyfold improvement in sensor sensitivity and significantly enhanced our ability to make higher‐speed NO measurements at low mixing ratios. In addition, the modifications have enabled us to demonstrate that reliable quantitative measurements can be routinely carried out at the parts‐per‐trillion level that is relevant to remote tropospheric conditions.
On the relation between stratospheric chlorine/bromine loading and short‐lived tropospheric source gases
Authors: Ko Malcolm K. W. , Sze Nien‐Dak , Scott Courtney J. , Weisenstein Debra K.
Published: February 2004

Current methods for estimating the concentrations of inorganic chlorine/bromine species (Cly/Bry) in the stratosphere due to decomposition of tropospheric source gases assume that the Cly/Bry concentration in the stratosphere is determined mainly by the balance between production from in situ oxidation of the source gases in the stratosphere and removal by transport of Cly/Bry out of the stratosphere. The rationale being that for source gases whose lifetimes are of the order of several months or longer the concentration of Cly/Bry in the troposphere is small because they are produced at a relatively slow rate and also removed efficiently by washout processes. As a result of the small concentration, the rate at which Cly/Bry is transported to the stratosphere is expected to be small compared to the in situ stratospheric production. Thus the transport of Cly/Bry from the troposphere contributes little to the stratospheric concentration. In contrast, the origin of stratospheric Cly/Bry from reactive source gases with tropospheric lifetimes comparable to the washout lifetime of Cly/Bry (of the order of 10–30 days) in the troposphere is distinctly different. The in situ source in the stratosphere is expected to be significantly smaller because only a small portion of the source gas is expected to survive the troposphere to be transported into this region. At the same time these short‐lived source gases produce appreciable amounts of Cly/Bry in the troposphere such that transport to the stratosphere offers a larger source for stratospheric Cly/Bry than in situ production. Thus, for reactive source species, simple methods of estimating the concentration of stratospheric Cly/Bry that ignore the tropospheric contribution will seriously underestimate the loading. Therefore estimation of the stratospheric Cly/Bry loading requires not only measurements of tropospheric source gases but also measurements of Cly/Bry at the tropopause. This paper illustrates the mechanism by using results from a two‐dimensional chemistry‐transport model. However, in view of the importance of tropospheric transport on stratospheric loading the detailed values should be further evaluated using a three‐dimensional model with appropriate treatment of convective transport.
Polar stratospheric clouds due to vapor enhancement: HALOE observations of the Antarctic vortex in 1993
Authors: Hervig M. E. , Carslaw K. S. , Peter T. , Deshler T. , Gordley L. L. , Redaelli G. , Biermann U. , Russell J. M.
Published: February 2004

Aerosol measurements from the Halogen Occultation Experiment (HALOE) during the Antarctic spring of 1993 are compared with calculations of the volume of different types of polar stratospheric clouds (PSCs) at equilibrium. The observed volumes increased by a factor of ∼30 coincident with water vapor enhancements of ∼3 ppmv, suggesting that the enhancement of water vapor was important in determining PSC growth. The enhanced water vapor was coincident with increased methane mixing ratios, and trajectory analysis suggests that the vapor enhancements were consistent with transport from lower latitudes. The nitric acid distribution was not measured and is treated either as constant or as positively correlated with the observed water. Comparing the observed volumes with model calculations assuming constant nitric acid suggests that the PSCs were composed of liquid ternary H2SO4‐H2O‐HNO3 aerosols (LTA) rather than solid nitric acid trihydrate (NAT). However, if the water vapor intrusions were accompanied by enhanced nitric acid, the observations closely match predictions for solid NAT, and those for LTA. These comparisons highlight the importance of the vapor distributions for modeling PSC growth and suggest that vapor resupply is important for late spring PSC growth. This work also highlights some inherent limitations of large field of view limb‐viewing instruments for the observation of PSCs.
Distribution of halon‐1211 in the upper troposphere and lower stratosphere and the 1994 total bromine budget
Authors: Wamsley P. R. , Elkins J. W. , Fahey D. W. , Dutton G. S. , Volk C. M. , Myers R. C. , Montzka S. A. , Butler J. H. , Clarke A. D. , Fraser P. J. , Steele L. P. , Lucarelli M. P. , Atlas E. L. , Schauffler S. M. , Blake D. R. , Rowland F. S. , Sturges W. T. , Lee J. M. , Penkett S. A. , Engel A. , Stimpfle R. M. , Chan K. R. , Weisenstein D. K. , Ko M. K. W. , Salawitch R. J.
Published: February 2004

We report here on the details of the first, in situ, real‐time measurements of H‐1211 (CBrClF2) and sulfur hexafluoride (SF6) mixing ratios in the stratosphere up to 20 km. Stratospheric air was analyzed for these gases and others with a new gas Chromatograph, flown aboard a National Aeronautics and Space Administration ER‐2 aircraft as part of the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission conducted in 1994. The mixing ratio of SF6, with its nearly linear increase in the troposphere, was used to estimate the mean age of stratospheric air parcels along the ER‐2 flight path. Measurements of H‐1211 and mean age estimates were then combined with simultaneous measurements of CFC‐11 (CCl3F), measurements of brominated compounds in stratospheric whole air samples, and records of tropospheric organic bromine mixing ratios to calculate the dry mixing ratio of total bromine in the lower stratosphere and its partitioning between organic and inorganic forms. We estimate that the organic bromine‐containing species were almost completely photolyzed to inorganic species in the oldest air parcels sampled. Our results for inorganic bromine are consistent with those obtained from a photochemical, steady state model for stratospheric air parcels with CFC‐11 mixing ratios greater than 150 ppt. For stratospheric air parcels with CFC‐11 mixing ratios less than 50 ppt (mean age ≥5 years) we calculate inorganic bromine mixing ratios that are approximately 20% less than the photochemical, steady state model. There is a 20% reduction in calculated ozone loss resulting from bromine chemistry in old air relative to some previous estimates as a result of the lower bromine levels.
Case study modeling of turbulent and mesoscale fluxes over the BOREAS region
Authors: Vidale Pier Luigi , Pielke Roger A. , Steyaert Louis T. , Barr Alan
Published: February 2004

Results from aircraft and surface observations provided evidence for the existence of mesoscale circulations over the Boreal Ecosystem‐Atmosphere Study (BOREAS) domain. Using an integrated approach that included the use of analytical modeling, numerical modeling, and data analysis, we have found that there are substantial contributions to the total budgets of heat over the BOREAS domain generated by mesoscale circulations. This effect is largest when the synoptic flow is relatively weak, yet it is present under less favorable conditions, as shown by the case study presented here. While further analysis is warranted to document this effect, the existence of mesoscale flow is not surprising, since it is related to the presence of landscape patches, including lakes, which are of a size on the order of the local Rossby radius and which have spatial differences in maximum sensible heat flux of about 300 W m−2. We have also analyzed the vertical temperature profile simulated in our case study as well as high‐resolution soundings and we have found vertical profiles of temperature change above the boundary layer height, which we attribute in part to mesoscale contributions. Our conclusion is that in regions with organized landscapes, such as BOREAS, even with relatively strong synoptic winds, dynamical scaling criteria should be used to assess whether mesoscale effects should be parameterized or explicitly resolved in numerical models of the atmosphere.
Electrical and multiparameter radar observations of a severe hailstorm
Authors: Carey Lawrence D. , Rutledge Steven A.
Published: February 2004

Using data from the 11 cm, CSU‐CHILL multiparameter radar, the simultaneous evolution of the radar‐inferred precipitation structure and electrical characteristics of a severe hailstorm is investigated. We compare the substorm point discharge current, intracloud (IC) lightning flash rate, cloud‐to‐ground (CG) lightning flash rate, ground strike location, and flash polarity to the progression of precipitation types and amounts. This study is unique in that it presents multiparameter radar observations of a thunderstorm complex which exhibited an extremely high IC‐to‐CG ratio (IC/CG, 20–70) and predominantly positive CG lightning (over 74%) after it became severe, producing large hail and weak tornadoes. In particular, we investigate the reported relationship between large hail and positive CG lightning. Although a direct correlation is found between a rapid increase in IC/CG, the first positive CG lightning flashes, and the initial production of hail aloft, the temporal and spatial behavior of large hail and positive CG lightning appear to be anticorrelated, as broad peaks in the positive CG flash rate lag relative maxima in the fallout of large hail by up to 30 min. The majority of positive ground strikes were adjacent to the main precipitation core in a region of light rain and little or no hail at the surface. Aloft, radar data indicated that ice crystals were aligned vertically in a strong electric field. Corona point observations at the surface indicate that these regions adjacent to the convective core were characterized by net positive charge aloft. Possible mechanisms to explain these observations are discussed.