bluuebunny/crossref_metadata_2025 huggingface dataset:
Clouds at the tropical tropopause: A case study during the APE‐THESEO campaign over the western Indian Ocean
Authors: Santacesaria Vincenzo , Carla Roberto , MacKenzie Robert , Adriani Alberto , Cairo Francesco , Didonfrancesco Guido , Kiemle Christoph , Redaelli Gianluca , Beuermann Jürgen , Schiller Cornelius , Peter Thomas , Luo Beiping , Wernli Heini , Ravegnani Fabrizio , Ulanovsky Alexey , Yushkov Vladimir , Sitnikov Nikolay , Balestri Stefano , Stefanutti Leopoldo
Published: May 2003

In this paper, we report a detailed description of a thin cirrus at the tropopause above a cumulonimbus (Cb) convective cluster observed during the Airborne Platform for Earth Observation–Third European Stratospheric Experiment for Ozone (APE‐THESEO) campaign in February–March 1999 in the western Indian Ocean. The thin cirrus (Ci) has an optical depth at 532 nm below 0.1, with extended subvisible stretches, and is located directly below the tropopause, which was supersaturated with respect to ice. A direct comparison between the optical depth retrieved by Meteosat and that obtained by means of the hygrometers installed on the M55‐Geophysica aircraft is discussed showing discrepancies ranging from 10 to 20%. Combining satellite and aircraft data, we show that the observed Ci is not due to cirrus outflow from Cb anvils. In the absence of any deeply convective clouds reaching altitudes above 15 km, we propose a possible mechanism of Ci formation based on a net mesoscale transport of water vapor from altitudes above 16 km to the tropopause region around 18 km. This transport could be driven by the critical layer and turbulence induced by gravity waves that could have been generated by lower level Cb cluster activity. The proposed mechanism for high‐altitude Ci formation corroborates the new paradigm of a tropical tropopause layer (TTL) or “substratosphere,” several kilometers thick, which is decoupled from the convection‐dominated lower troposphere.
Erosion and mixing of filaments in the arctic lower stratosphere revealed by airborne lidar measurements
Authors: Flentje Harald , Kiemle Christoph
Published: May 2003

The extent of ozone depletion in the Arctic stratosphere is limited by the dynamical instability of the winter circulation. During January 1999, transport across the polar vortex boundary occurred with intrusions of midlatitude air into the vortex and via peeling of filaments off the vortex edge, followed by intensive stirring. Contour advection simulations follow the reduction of the scales. The structures are evident as heterogeneities in two‐dimensional (2‐D) airborne lidar sections of aerosol backscatter ratio, along flight paths inside the vortex during January/February 1999. Large gradients of the particle backscatter ratio indicate that microscopic mixing is slow in the presence of continuous intensive macroscopic stirring. The gradients persist several weeks after the vortex recovered and isentropic stirring started. The filament boundary layers typically extend over 100 m vertically and a few kilometers in the horizontal. Under typical stratospheric conditions, it takes about two weeks until 3‐D turbulence takes over and effectively mixes air masses at these scales. In late January 1999 only about 10–13% of the air probed during the flights inside the vortex are mixed microscopically, which, however, is a prerequisite for their chemical and microphysical interaction. As chemical transport models cannot distinguish subgrid‐scale stirring from molecular mixing, the incomplete mixing implies that homogenization would occur prematurely in a model run and interaction rates would be overestimated.
Winter‐spring evolution and variability of HOx reservoir species, hydrogen peroxide, and methyl hydroperoxide, in the northern middle to high latitudes
Authors: Snow Julie A. , Heikes Brian G. , Merrill John T. , Wimmers Anthony J. , Moody Jennie L. , Cantrell Christopher A.
Published: May 2003

The Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment examined the evolution of tropospheric chemical compositions from February to May 2000 over North America, 40 to 85 N. Hydrogen peroxide (H2O2) and methyl hydroperoxide (CH3OOH) were investigated using instrumental observations aboard the NCAR C‐130 research aircraft. Primary TOPSE results indicate both photochemistry and atmospheric dynamics are critical factors controlling the variability of peroxides in this region. From February to May, H2O2 and CH3OOH mixing ratios increased with the greatest relative changes at mid‐altitudes. H2O2 ranged from below the detection limit (BDL = 25 pptv) to 380 pptv in winter and from BDL to 1330 pptv during spring. Winter measurements of CH3OOH were from BDL (35 pptv) to 740 pptv with higher levels of BDL to 1400 pptv measured during spring. Peroxides also decreased with latitude at all altitudes. These findings are consistent with those expected from photochemical theory. Evidence also supports a source of CH3OOH to the Arctic from the transport of subtropical air masses. Air mass back trajectories and GOES‐derived specific humidity products indicate transport of moist tropical air to the study region coincides with elevated levels of CH3OOH up to 940 pptv. The concurrence of this transport regime with episodic elevated CH3OOH events suggests a source of HOx to the Arctic. However, evidence from this study shows CH3OOH does not greatly contribute to total HOx production which is dominated primarily by reactions of O(1D) and H2O at low latitudes and CH2O at high latitudes.
Arctic oscillation signals in the East Asian summer monsoon
Authors: Gong Dao‐Yi , Ho Chang‐Hoi
Published: May 2003

The present study examines the relationship between the Arctic Oscillation (AO) and the East Asian summer monsoon. Two rainfall data sets are used. One is obtained from 10 stations along the Yangtze River to the southern Japan and the other from gridded global land rainfall data for the period 1900–1998. All data are high‐pass filtered before analyzing to highlight the interannual variability. Results show that the AO significantly influences on year‐to‐year variations in the East Asian summer monsoon rainfall. When AO leads by one month, the correlation between May–July AO and summer total rainfall is −0.44. When AO leads by two months, correlation becomes −0.32. Of all monthly, May AO shows the strongest connection to the summer monsoon rainfall. Correlation coefficient between them is −0.45. The large‐scale atmospheric circulation patterns in East Asia in association with the AO are also evident. A positive phase of the AO in late spring is found to lead to a northward shift in the summertime upper tropospheric jet stream over East Asia. This northward shift of the jet stream is closely related to anomalous sinking motion in 20°–40°N and rising motion in surrounding regions. These changes give rise to a drier condition over the region extending from the Yangtze River valley to the southern Japan and a wetter condition in the southern China. Possible mechanisms connecting the late spring AO and summer monsoon rainfall are suggested.
Steady state free radical budgets and ozone photochemistry during TOPSE
Authors: Cantrell Christopher A. , Mauldin L. , Zondlo M. , Eisele F. , Kosciuch E. , Shetter R. , Lefer B. , Hall S. , Campos T. , Ridley B. , Walega J. , Fried A. , Wert B. , Flocke F. , Weinheimer A. , Hannigan J. , Coffey M. , Atlas E. , Stephens S. , Heikes B. , Snow J. , Blake D. , Blake N. , Katzenstein A. , Lopez J. , Browell E. V. , Dibb J. , Scheuer E. , Seid G. , Talbot R.
Published: May 2003

A steady state model, constrained by a number of measured quantities, was used to derive peroxy radical levels for the conditions of the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign. The analysis is made using data collected aboard the NCAR/NSF C‐130 aircraft from February through May 2000 at latitudes from 40° to 85°N, and at altitudes from the surface to 7.6 km. HO2 + RO2 radical concentrations were measured during the experiment, which are compared with model results over the domain of the study showing good agreement on the average. Average measurement/model ratios are 1.04 (σ = 0.73) and 0.96 (σ = 0.52) for the MLB and HLB, respectively. Budgets of total peroxy radical levels as well as of individual free radical members were constructed, which reveal interesting differences compared to studies at lower latitudes. The midlatitude part of the study region is a significant net source of ozone, while the high latitudes constitute a small net sink leading to the hypothesis that transport from the middle latitudes can explain the observed increase in ozone in the high latitudes. Radical reservoir species concentrations are modeled and compared with the observations. For most conditions, the model does a good job of reproducing the formaldehyde observations, but the peroxide observations are significantly less than steady state for this study. Photostationary state (PSS) derived total peroxy radical levels and NO/NO2 ratios are compared with the measurements and the model; PSS‐derived results are higher than observations or the steady state model at low NO concentrations.
Statistics of calendar month averages of surface temperature: A possible relationship to climate sensitivity
Authors: Wu Qigang , North Gerald R.
Published: May 2003

This study makes use of calendar month averages of surface temperature taken from the long control runs of 13 coupled atmosphere/ocean general circulation models (GCMs) as well as from the record of observational surface temperature measurements. After aggregating the data into global averages, we examine the mean seasonal cycle as well as the anomaly statistics. We find a large range of different results for the models in the seasonal cycle of anomaly statistics. There appears to be an “empirical” relationship between the published sensitivity of the models to CO2 doubling and the seasonal cycle of the anomaly statistics. We draw an inference about the sensitivity of the real climate based upon this relationship. The relationship appears to be plausible based upon simple considerations of the land–sea distribution and the wintertime variance of climatic noise forcing. This inference leads us to estimate the sensitivity of climate to a doubling of CO2 to be about 2.7°C with the 95% confidence interval (2.3°C, 3.1°C).
The mean physical and optical properties of regional haze dominated by biomass burning aerosol measured from the C‐130 aircraft during SAFARI 2000
Authors: Haywood Jim M. , Osborne Simon R. , Francis Pete N. , Keil Andreas , Formenti Paola , Andreae Meinrat O. , Kaye Paul H.
Published: May 2003

Instrumentation on the Met Office C‐130 aircraft measured aerosol physical and optical properties during the Southern African Regional Science Initiative (SAFARI 2000) in September 2002 while flying from Windhoek, Namibia. Filter measurements of aged regional haze suggest a ratio of apparent elemental carbon (ECa) to organic carbon (OC) of 0.12 ± 0.02 and mass fractions of 5% ECa, 25% inorganic compounds, and 70% organic matter (OC plus associated elements). The submicron size distribution of aged regional haze may be fitted with three lognormal distributions with geometric mean radii (rn) of 0.12 ± 0.01, 0.26 ± 0.01, and 0.80 ± 0.01 μm and geometric standard deviations (σ) of 1.3 ± 0.1, 1.5 ± 0.1, and 1.9 ± 0.4. Measurements over 2500 km from the emission region show similar rn and σ for the smallest two modes, while the third mode is absent presumably as a result of sedimentation. At a wavelength (λ) of 0.55 μm, effective medium approximations suggest a refractive index of 1.54 − 0.018i for aged regional haze aerosol. The single scattering albedo (ωoλ) derived using this refractive index and measured size distributions are consistent with those from the nephelometer and Particle Soot Absorption Photometer (PSAP). The optical parameters for aged regional haze a few days old are specific extinction coefficient (keλ=0.55) of 5.0 ± 0.8 m2 g−1, asymmetry factor (gλ=0.55) of 0.59 ± 0.02, and ωoλ=0.55 of 0.91 ± 0.04. Measurements of fresh biomass burning aerosol a few minutes old show smaller more absorbing particles. Vertical profiles of carbon monoxide, aerosol concentration, and aerosol scattering show a good correlation. Over land, aerosols become well mixed in the vertical from the surface to approximately 500 hPa. Over ocean, the aerosols can be separated from underlying stratocumulus cloud by a clear gap and a strong inversion, which may limit the indirect effect.
Modeling clouds observed at SHEBA using a bulk microphysics parameterization implemented into a single‐column model
Authors: Morrison H. , Shupe M. D. , Curry J. A.
Published: May 2003

A single‐column model coupled to a bulk microphysics parameterization (with prognostic cloud liquid water, cloud ice, rain, and snow mixing ratios) is evaluated using cloud properties retrieved at the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) during the period of 1 April to 16 May 1998. Overall, the model accurately simulates the cloud boundaries and total cloud fraction, but has difficulty correctly partitioning the cloud phases and predicting the condensed water contents and paths. In particular, the mean liquid water path (LWP) is underestimated by 76%. This bias is attributed to underpredicting the liquid cloud fraction, that is, underpredicting the frequency of liquid‐ or mixed‐phase clouds. The mean ice water path (IWP) is underestimated by 42%. Glaciation in the model occurs primarily through the preferential depositional growth of pristine ice initiated by deposition‐condensation nucleation at the expense of liquid water, in contrast to glaciation mechanisms inferred from observations. Sensitivity tests are conducted to elucidate the relative importance of various microphysical parameters on the modeled cloud properties and processes. The liquid cloud fraction and mean LWP are most sensitive to uncertainties in the ice crystal number concentration, while the mean IWP is sensitive to several cloud ice/snow microphysical parameters, including the collection efficiency for riming and terminal fall velocities. The model evaluation is also discussed in the context of the spatial resolution and the approach to cloud scale separation. The unique spatial scales (particularly in the vertical) associated with Arctic stratiform clouds must be taken into account in order to correctly simulate the observed cloud properties.
Daily sampling of PM2.5 in Atlanta: Results of the first year of the Assessment of Spatial Aerosol Composition in Atlanta study
Authors: Butler André J. , Andrew Michael S. , Russell Armistead G.
Published: May 2003

A monitoring network was established in metropolitan Atlanta, Georgia, to measure fine particulate mass (PM2.5) and composition for approximately one year, beginning in March 1999. Annual average mass concentrations ranged from 19.3–21.2 μg/m3, maximum 24‐hour concentrations were 44.3–51.5 μg/m3, and maximum 1‐hour concentrations were 73.3–87.9 μg/m3. Peak mass concentrations occurred typically (but not always) at the Tucker site, which was located approximately 12 miles ENE of downtown. Mass concentrations varied significantly with season and time of day. Approximately 75% of the mass was identified using various chemical speciation analyses. Of the identifiable portion, carbonaceous material, sulfate, ammonium, and nitrate were the largest constituents.
Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 2. Tropospheric variability and the zonal wave‐one
Authors: Thompson Anne M. , Witte Jacquelyn C. , Oltmans Samuel J. , Schmidlin Francis J. , Logan Jennifer A. , Fujiwara Masatomo , Kirchhoff Volker W. J. H. , Posny Françoise , Coetzee Gert J. R. , Hoegger Bruno , Kawakami Shuji , Ogawa Toshihiro , Fortuin J. P. F. , Kelder H. M.
Published: May 2003

The first view of stratospheric and tropospheric ozone variability in the Southern Hemisphere tropics is provided by a 3‐year record of ozone soundings from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (http://croc.gsfc.nasa.gov/shadoz). Observations covering 1998–2000 were made over Ascension Island, Nairobi (Kenya), Irene (South Africa), Réunion Island, Watukosek (Java), Fiji, Tahiti, American Samoa, San Cristóbal (Galapagos), and Natal (Brazil). Total, stratospheric, and tropospheric column ozone amounts usually peak between August and November. Other features are a persistent zonal wave‐one pattern in total column ozone and signatures of the quasi‐biennial oscillation (QBO) in stratospheric ozone. The wave‐one is due to a greater concentration of free tropospheric ozone over the tropical Atlantic than the Pacific and appears to be associated with tropical general circulation and seasonal pollution from biomass burning. Tropospheric ozone over the Indian and Pacific Oceans displays influences of the waning 1997–1998 El Niño, seasonal convection, and pollution transport from Africa. The most distinctive feature of SHADOZ tropospheric ozone is variability in the data, e.g., a factor of 3 in column amount at 8 of 10 stations. Seasonal and monthly means may not be robust quantities because statistics are frequently not Gaussian even at sites that are always in tropical air. Models and satellite retrievals should be evaluated on their capability for reproducing tropospheric variability and fine structure. A 1999–2000 ozone record from Paramaribo, Surinam (6°N, 55°W) (also in SHADOZ) shows a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone (ITCZ). A more representative tropospheric ozone climatology for models and satellite retrievals requires additional Northern Hemisphere tropical data.
Consistency of ARESE II cloud absorption estimates and sampling issues
Authors: Oreopoulos L. , Marshak A. , Cahalan R. F.
Published: May 2003

Data from three cloudy days (3, 21, and 29 March 2000) of the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment II (ARESE II) were analyzed and broadband absorptances were obtained for three sets of instruments. Grand (total flight) averages of fractional solar absorptances were ∼0.21–0.22, with the exception of 3 March when two sets of instruments gave values smaller by ∼0.03–0.04. The robustness of these values was evaluated by examining potential sampling problems with the aid of 500 nm spectral fluxes. The grand average of 500 nm apparent absorptance was statistically indistinguishable from zero for 21 and 29 March but acquired a large positive value of ∼0.10 on 3 March, which is not physically understood. We present results showing that each of the three days is unique in terms of cloud morphology and behavior of the absorptance time series. When the conditional sampling method is applied to the two days with reliable 500 nm absorptances (21 and 29 March), the resulting histogram of broadband absorptances is significantly narrower than the histogram constructed from the original time series. Corrections to the absorptance time series à la Cess et al. [1999] were successful for all three days because of the generally good correlation between broadband and 500 nm absorptances, removing the bulk of low‐end and high‐end extremes most likely associated with sampling and horizontal flux artifacts. The above two methods suggest an ARESE II range of broadband absorptances of ∼0.18–0.26. Finally, our study shows that the data set obtained on 29 March is the most self‐consistent and straightforward to analyze among the three, because this day fulfilled all the requirements of the ARESE II experimental design, namely the presence of thick, overcast, homogeneous clouds.
Comparison of aerosol size distributions, radiative properties, and optical depths determined by aircraft observations and Sun photometers during SAFARI 2000
Authors: Haywood Jim , Francis Pete , Dubovik Oleg , Glew Martin , Holben Brent
Published: May 2003

The Meteorological Office C‐130 aircraft performed a dedicated flight over the Etosha Pan surface‐based Aerosol Robotic Network (AERONET) Sun photometer site on 13 September 2000 during the Southern African Aerosol Regional Science Initiative (SAFARI 2000) intensive measurement campaign. Aerosol optical depths at different wavelengths, τaerλ, are derived from in situ measurements of the scattering and absorption coefficients and from various radiometric measurements and compared to those derived from the Sun photometer site. The estimates of τaerλ from the various measurements are shown to be in good agreement. The exception to this is when τaerλ is derived from the Passive Cavity Aerosol Spectrometer Probe (PCASP), as this method is shown to be extremely sensitive to the pitch angle of the aircraft; therefore, τaerλ differs for profile ascents and profile descents. However, the aerosol size distribution measured by the PCASP and derived from the AERONET site are in excellent agreement over the 0.05–1.0 μm radius range, which contains the majority of the optically active particles. C‐130‐derived refractive indices and single scattering albedos are also shown to be in excellent agreement with those derived from the AERONET site. The consistency between in situ and remotely sensed data suggests that, for aerosol well mixed in the vertical, data from AERONET may be used with confidence in validating satellite measurements and modeling studies of the radiative properties and effects of aerosols.
Behavior of tropopause height and atmospheric temperature in models, reanalyses, and observations: Decadal changes
Authors: Santer B. D. , Sausen R. , Wigley T. M. L. , Boyle J. S. , AchutaRao K. , Doutriaux C. , Hansen J. E. , Meehl G. A. , Roeckner E. , Ruedy R. , Schmidt G. , Taylor K. E.
Published: May 2003

We examine changes in tropopause height, a variable that has hitherto been neglected in climate change detection and attribution studies. The pressure of the lapse rate tropopause, pLRT, is diagnosed from reanalyses and from integrations performed with coupled and uncoupled climate models. In the National Centers for Environmental Prediction (NCEP) reanalysis, global‐mean pLRT decreases by 2.16 hPa/decade over 1979–2000, indicating an increase in the height of the tropopause. The shorter European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis has a global‐mean pLRT trend of −1.13 hPa/decade over 1979–1993. Simulated pLRT trends over the past several decades are consistent with reanalysis results. Superimposed on the overall increase in tropopause height in models and reanalyses are pronounced height decreases following the eruptions of El Chichón and Pinatubo. Interpreting these pLRT results requires knowledge of both T(z), the initial atmospheric temperature profile, and ΔT(z), the change in this profile in response to external forcing. T(z) has a strong latitudinal dependence, as does ΔT(z) for forcing by well‐mixed greenhouse gases and stratospheric ozone depletion. These dependencies help explain why overall tropopause height increases in reanalyses and observations are amplified toward the poles. The pronounced increases in tropopause height in the climate change integrations considered here indicate that even AGCMs with coarse vertical resolution can resolve relatively small externally forced changes in tropopause height. The simulated decadal‐scale changes in pLRT are primarily thermally driven and are an integrated measure of the anthropogenically forced warming of the troposphere and cooling of the stratosphere. Our algorithm for estimating pLRT (based on a thermal definition of tropopause height) is sufficiently sensitive to resolve these large‐scale changes in atmospheric thermal structure. Our results indicate that the simulated increase in tropopause height over 1979–1997 is a robust, zero‐order response of the climate system to forcing by well‐mixed greenhouse gases and stratospheric ozone depletion. At the global‐mean level, we find agreement between the simulated decadal‐scale pLRT changes and those estimated from reanalyses. While the agreement between simulated pLRT changes and those in NCEP is partly fortuitous (due to excessive stratospheric cooling in NCEP), it is also driven by real pattern similarities. Our work illustrates that changes in tropopause height may be a useful “fingerprint” of human effects on climate and are deserving of further attention.
Laboratory simulations and parameterization of the primary marine aerosol production
Authors: Mårtensson E. M. , Nilsson E. D. , de Leeuw G. , Cohen L. H. , Hansson H.‐C.
Published: May 2003

A major source of the primary marine aerosol is the bursting of air bubbles produced by breaking waves. Several source parameterizations are available from the literature, usually limited to particles with a dry diameter Dp > 1 μm. The objective of this work is to extend the current knowledge to submicrometer particles. Bubbles were generated in synthetic seawater using a sintered glass filter, with a size spectra that are only partly the same spectra as measured in the field. Bubble spectra, and size distributions of the resulting aerosol (0.020–20.0 μm Dp) of the resulting aerosol, were measured for different salinity, water temperature (Tw), and bubble flux. The spectra show a minimum at ∼1 μm Dp, which separates two modes, one at ∼0.1 μm, with the largest number of particles, and one at 2.5 μm Dp. The modes show different behavior with the variation of salinity and water temperature. When the water temperature increases, the number concentration Np decreases for Dp < 0.07 μm, whereas for Dp > 0.35 μm, Np increases. The salinity effect suggests different droplet formation processes for droplets smaller and larger than 0.2 μm Dp. The number of particles produced per size increment, time unit, and whitecap surface (Φ) is described as a linear function of Tw and a polynomial function of Dp. Combining Φ with the whitecap coverage fraction W (in percent), an expression results for the primary marine aerosol source flux dF0/dlogDp = W Φ (m−2 s−1). The results are compared with other commonly used formulations as well as with recent field observations. Implications for aerosol‐induced effects on climate are discussed.
Evaluation of the transport in the Goddard Space Flight Center three‐dimensional chemical transport model using the equivalent length diagnostic
Authors: Ma Jun , Waugh Darryn W. , Douglass Anne R. , Kawa S. R. , Lin S.‐J.
Published: May 2003

Transport and mixing in the extratropical stratosphere of the NASA Goddard Space Flight Center (GSFC) three‐dimensional (3‐D) chemical transport model (CTM) are evaluated using the modified Lagrangian‐mean diagnostic. The normalized equivalent length squared (ξ) has been calculated from simulated N2O and CH4 distributions using two different wind data sets and has been compared with that calculated from observations by the CLAES satellite instrument. There is generally good agreement, indicating that the CTM realistically simulates the location and seasonal evolution of mixing regions/barriers in the extratropical lower and middle stratosphere. Differences that occur between the CTM fields and observations at high latitudes in winter and spring can be attributed to interannual variability in polar meteorology. There are also some differences in northern summer: the CTM series shows regions of high ξ in the extratropics that are not observed in ξ from CLAES. These high values occur where there is small‐scale variability in N2O in regions with very weak meridional gradients. Comparison of ξ from isentropic tracer simulations using the same wind fields as used in the 3‐D CTM show good agreement except during the summer. The isentropic tracers do not have as much small‐scale variability as the 3‐D CTM tracer fields, indicating that the enhanced small‐scale structures in the CTM N2O, and high values of ξ, are produced by small‐scale horizontal variability in the vertical motions. The fact that vertical motions can influence summer values of ξ means that these ξ fields cannot be interpreted in terms of quasi‐horizontal mixing.
Agricultural ammonia emissions and ammonium concentrations associated with aerosols and precipitation in the southeast United States
Authors: Aneja Viney P. , Nelson Dena R. , Roelle Paul A. , Walker John T. , Battye William
Published: May 2003

Temporal and spatial variations in ammonia (NH3) emissions and ammonium (NH4+) concentrations associated with aerosols and volume‐weighted NH4+ concentration in precipitation are investigated over the period 1990–1998 in the southeast United States (Alabama, Florida, Georgia, Kentucky, North Carolina, South Carolina, Mississippi, and Tennessee). These variations were analyzed using an NH3 emissions inventory developed for the southeast United States and ambient NH4+ data from the various Clean Air Status and Trends Network (CASTNet) and the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). Results show that natural log‐transformed annual NH4+ concentration associated with aerosols increases with natural log‐transformed annual NH3 emission density within the same county (R2 = 0.86, p < 0.0001, N = 12). Natural log‐transformed annual volume‐weighted average NH4+ concentration in precipitation shows only a very weak positive correlation with natural log‐transformed annual NH3 emission densities within the corresponding county (R2 = 0.12, p = 0.04, N = 29). Analysis of NH4+ concentration associated with aerosols at CASTNet sites revealed that temperature, precipitation amount, and relative humidity are the most statistically significant (p < 0.05) parameters in predicting the weekly concentrations of NH4+ during the period 1990–1998. Wind speed and wind direction were also statistically significant (p < 0.05) at several CASTNet sites, but the results were less consistent. Investigation into wet NH4+ concentration in precipitation consistently yielded temperature as a statistically significant (p < 0.05) parameter at individual sites. Trends over the period 1990–1998 revealed a slight decrease in NH4+ concentration at CASTNet site SPD, Claiborne County, Tennessee (2.14–1.88 μg m−3), while positive trends in NH4+ concentration in precipitation were evident at NADP sites NC35, Sampson County, North Carolina (0.2–0.48 mg L−1) and KY35, Rowan County, Kentucky (0.2–0.35 mg L−1) over the period 1990–1998.
Analysis of OBrO, IO, and OIO absorption signature in UV‐visible spectra measured at night and at sunrise by stratospheric balloon‐borne instruments
Authors: Berthet Gwenaël , Renard Jean‐Baptiste , Chartier Michel , Pirre Michel , Robert Claude
Published: May 2003

Absorption bands of OBrO, IO, and OIO in the visible region have been investigated in the data of the AMON (“Absorption par les Minoritaires Ozone et Nox”) and SALOMON (“Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et Nox”) balloon‐borne spectrometers used to obtain measurements in the nighttime stratosphere, since 1992 and 1998 respectively. The absorption features initially detected in AMON residual spectra and attributed to OBrO are also observable in SALOMON data with better accuracy. New estimates of OBrO cross‐section amplitudes taking into account recent laboratory measurements are used for the OBrO retrieval. A consequence is that previously published OBrO concentration and mixing ratio values are revised downwards of around 40%. Further tests are performed to assess the consistency of the OBrO detection. No correlation exists between OBrO and NO2 vertical profiles which practically rules out the possibility for the structures ascribed to OBrO absorption to be due to remaining NO2 contributions. It is shown that variability of OBrO quantities at high latitudes obtained from various AMON and SALOMON flights is possibly linked to the chemical processes involving the production of OClO. At midlatitudes, the exceptional and unexpected conditions of the April 28, 1999 SALOMON flight allow us to observe the drop in OBrO concentrations just after sunrise. As expected, if previous studies of stratospheric iodine species are considered, IO and OIO absorption lines are never detected in the residual spectra. The presence of unknown structures in the residual spectra in the IO and OIO absorption regions is obvious and tends to distort the retrievals. The possibility that these remaining features result from a temperature dependence effect or uncertainties of O3 and/or NO2 cross‐sections is suggested. Thus, more accurate laboratory measurements and sets of cross‐sections for low temperature are needed.
Nitrous oxide emission inventory of German forest soils
Authors: Schulte‐Bisping Hubert , Brumme Rainer , Priesack Eckart
Published: May 2003

Annual fluxes of N2O trace gas emissions were assessed after stratifying German forest soils into Seasonal Emission Pattern (SEP) and Background Emission Pattern (BEP). Broad‐leaved forests with soil pH(KCl) ≤ 3.3 were assigned to have SEP, broad‐leaved forests with soil pH(KCl) > 3.3 and all needle‐leaved forests to have BEP. BEPs were estimated by a relationship between annual N2O emissions and carbon content of the O‐horizon. SEPs were primarily controlled by temperature and moisture and simulated by the model Expert‐N after calibration to a 9‐year record of N2O measurements. Analysis with different climate and soil properties indicated that the model reacts highly sensitive to changes in soil temperature, soil moisture, and soil texture. A geographic information system (ARC/INFO) was used for a spatial resolution of 1 km × 1 km grid where land cover, dominant soil units, and hygro climate classes were combined. The mean annual N2O emission flux from German forest soils was estimated as 0.32 kg ha−1 yr−1. Broad‐leaved forests with SEP had the highest emissions (2.05 kg ha−1 yr−1) followed by mixed forests (0.38 kg ha−1 yr−1), broad‐leaved forests (0.37 kg ha−1 yr−1), and needle‐leaved forests with BEP (0.17 kg ha−1 yr−1). The annual N2O emission from German forest soils was calculated as 3.26 Gg N2O‐N yr−1. Although needle‐leaved trees cover about 57% of the entire forest area in Germany, their contribution is low (0.96 Gg N2O‐N yr−1). Broad‐leaved forests cover about 22% of the forest area but have 55% higher emissions (1.49 Gg N2O‐N yr−1) than needle‐leaved. Mixed forests cover 21% of the area and contribute 0.81 Gg N2O‐N yr−1. Compared to the total N2O emissions in Germany of 170 Gg N yr−1, forest soils contribute only 1.9%. However, there are some uncertainties in this emission inventory, which are intensely discussed.
A multilayer biochemical dry deposition model. 1. Model formulation
Authors: Wu Yihua , Brashers Bart , Finkelstein Peter L. , Pleim Jonathan E.
Published: May 2003

A multilayer biochemical dry deposition model has been developed based on the NOAA Multilayer Model (MLM; Meyers et al. [1998]) to study gaseous exchanges between the soil, plants, and the atmosphere. Most of the parameterizations and submodels have been updated or replaced. The numerical integration was improved, and an aerodynamic resistance based on Monin‐Obukhov theory was added. An appropriate parameterization for the leaf boundary layer resistance was chosen. A biochemical stomatal resistance model was chosen based on comparisons of four different existing stomatal resistance schemes. It describes photosynthesis and respiration and their coupling with stomatal resistance for sunlit and shaded leaves separately. Various aspects of the photosynthetic process in both C3 and C4 plants are considered in the model. To drive the photosynthesis model, the canopy radiation scheme has been updated. Leaf area index measurements are adjusted to account for stem area index. A normalized soil water stress factor was applied to potential photosynthesis to account for plant response to both drought and water‐logging stresses. A new cuticle resistance model was derived based on membrane passive transport theory and Fick's first law. It accounts for the effects of diffusivity and solubility of specific gases in the cuticle membrane, as well as the thickness of the cuticle membrane. The model is designed for use in the nationwide dry deposition networks, for example, the Clean Air Status And Trends Network (CASTNet), and mesoscale models, for example, the Community Multiscale Air Quality model (CMAQ) and even the Weather Research and Forecasting model (WRF).
Measurements of OH, H2SO4, and MSA during Tropospheric Ozone Production About the Spring Equinox (TOPSE)
Authors: Mauldin R. L. , Cantrell C. A. , Zondlo M. A. , Kosciuch E. , Ridley B. A. , Weber R. , Eisele F. E.
Published: May 2003

Data from OH, H2SO4, and MSA measurements performed during Tropospheric Ozone Production About the Spring Equinox (TOPSE) are presented. Model simulations of OH results made at solar zenith angles of 60° or less showed a tendency of the model to overestimate OH concentrations. This overestimation was a factor of 1.7 at the lower latitudes (<57°N) of the study. At higher latitudes (>57°N) the model tended toward agreement and ultimately an underestimation of OH concentrations by a factor of 0.7. Comparisons of measurements and model showed the model underestimates OH concentrations at solar zenith angles greater than 70°. The results of the present study are discussed in the context of previous studies. Possible model discrepancies are discussed. Measurements of H2SO4 showed the highest concentrations at the lowest altitudes (<2000 m) and the lowest latitudes of the study. Larger H2SO4 concentrations observed at higher latitudes were accompanied at times by particle nucleation as indicated by the presence of UCN (ultra‐fine condensation nuclei) with diameters of 3–4 nm. Concentrations of MSA were generally low with typical values of <2 × 105 molecule cm−3. High concentrations (>107 molecule cm−3) were found in layers and were accompanied by other compounds such as NOx and NOy indicating MSA may also have an industrial source.
Intercomparison of remote sounding instruments
Authors: Rodgers Clive D. , Connor Brian J.
Published: May 2003

When intercomparing measurements made by remote sounders, it is necessary to make due allowance for the differing characteristics of the observing systems, particularly their averaging kernels and error covariances. We develop the methods required to do this, applicable to any kind of retrieval method, not only to optimal estimators. We show how profiles and derived quantities such as the total column of a constituent may be properly compared, yielding different averaging kernels. We find that the effect of different averaging kernels can be reduced if the retrieval or the derived quantity of one instrument is simulated using the retrieval of the other. We also show how combinations of measured signals can be found, which can be compared directly. To illustrate these methods, we apply them to two real instruments, calculating the expected amplitudes and variabilities of the diagnostics for a comparison of CO measurements made by a ground‐based Fourier Transform spectrometer (FTIR) and the “measurement of pollution in the troposphere” instrument (MOPITT), which is mounted on the EOS Terra platform. The main conclusions for this case are the following: (1) Direct comparison of retrieved profiles is not satisfactory, because the expected standard deviation of the difference is around half of the expected natural variability of the true atmospheric profiles. (2) Comparison of the MOPITT profile retrieval with a simulation using FTIR is much more useful, though still not ideal, with expected standard deviation of differences of around 20% of the expected natural variability. (3) Direct comparison of total columns gives an expected standard deviation of about 9%, while comparison of MOPITT with a simulation derived from FTIR improved this to 8%. (4) There is only one combination of measured signals that can be usefully compared. The difference is expected to have a standard deviation of about 5.5% of the expected natural variability, which is mostly due to noise.
Land surface skin temperatures from a combined analysis of microwave and infrared satellite observations for an all‐weather evaluation of the differences between air and skin temperatures
Authors: Prigent Catherine , Aires Filipe , Rossow William B.
Published: May 2003

A neural network inversion scheme including first guess information has been developed to retrieve surface temperature Ts, along with atmospheric water vapor, cloud liquid water, and surface emissivities over land from a combined analysis of Special Sensor Microwave/Imager (SSM/I) and International Satellite Cloud Climatology Project (ISCCP) data. In the absence of routine in situ surface skin measurements, retrieved Ts values are evaluated by comparison to the surface air temperature Tair measured by the meteorological station network. The Ts − Tair difference shows all the expected variations with solar flux, soil characteristics, and cloudiness. During daytime the Ts − Tair difference is driven by the solar insulation, with positive differences that increase with increasing solar flux. With decreasing soil and vegetation moisture the evaporation rate decreases, increasing the sensible heat flux, thus requiring larger Ts − Tair differences. Nighttime Ts − Tair differences are governed by the longwave radiation balance, with Ts usually closer or lower than Tair. The presence of clouds dampens all the difference. After suppression of the variability associated to the diurnal solar flux variations, the Ts and Tair data sets show very good agreement in their synoptic variations, even for cloudy cases, with no bias and a global rms difference of ∼2.9 K. This value is an upper limit of the retrieval rms because it includes errors in the in situ data as well as errors related to imperfect time and space collocations between the satellite and in situ measurements.
Individual aerosol particles from biomass burning in southern Africa: 2, Compositions and aging of inorganic particles
Authors: Li Jia , Pósfai Mihály , Hobbs Peter V. , Buseck Peter R.
Published: May 2003

Individual aerosol particles collected over southern Africa during the SAFARI 2000 field study were studied using transmission electron microscopy and field‐emission scanning electron microscopy. The sizes, shapes, compositions, mixing states, surface coatings, and relative abundances of aerosol particles from biomass burning, in boundary layer hazes, and in the free troposphere were compared, with emphasis on aging and reactions of inorganic smoke particles. Potassium salts and organic particles were the predominant species in the smoke, and most were internally mixed. More KCl particles occur in young smoke, whereas more K2SO4and KNO3particles were present in aged smoke. This change indicates that with the aging of the smoke, KCl particles from the fires were converted to K2SO4and KNO3through reactions with sulfur‐ and nitrogen‐bearing species from biomass burning as well as other sources. More soot was present in smoke from flaming grass fires than bush and wood fires, probably due to the predominance of flaming combustion in grass fires. The high abundance of organic particles and soluble salts can affect the hygroscopic properties of biomass‐burning aerosols and therefore influence their role as cloud condensation nuclei. Particles from biomass burning were important constituents of the regional hazes.
Modeling the solar radiative impact of aerosols from biomass burning during the Southern African Regional Science Initiative (SAFARI‐2000) experiment
Authors: Myhre Gunnar , Berntsen Terje K. , Haywood James M. , Sundet Jostein K. , Holben Brent N. , Johnsrud Mona , Stordal Frode
Published: May 2003

In this study, we model the radiative impact of biomass burning aerosols with meteorological data for the Southern African Regional Science Initiative (SAFARI‐2000) experiment campaign period. Satellite, ground‐based, and aircraft observations are used in the validation of the modeled aerosol optical depth (AOD), vertical profiles, and radiative impact of the aerosols. The modeled pattern and magnitude of the AOD is generally in good agreement with the observations. The meteorological conditions are found to be important in determining the distribution of the aerosols. The modeled radiative impact of the biomass aerosols compares well to measurements. During September 2000, the modeled radiative impact of biomass aerosols reaches −50 W m−2 locally.
Solar radiative forcing by biomass burning aerosol particles during SAFARI 2000: A case study based on measured aerosol and cloud properties
Authors: Keil Andreas , Haywood Jim M.
Published: May 2003

This study investigates the top of atmosphere (TOA) solar radiative forcing by biomass burning aerosol from the African continent. Radiative transfer calculations are based on airborne aerosol and cloud measurements made on 7 September 2000, being representative for the aerosol optical properties and the relative location of aerosol and clouds during Southern African Fire‐Atmosphere Research Initiative (SAFARI) 2000. We focus on how the radiative effects of biomass aerosol are changed in the presence of clouds to the west of the southern African coastline. The typical scenario observed showed a clear separation between an elevated biomass aerosol layer (1.8–3.7 km altitude) and low‐level stratiform clouds (below 1 km, liquid water path 85 g m−2). The aerosol was characterized by particle concentrations of 1800 cm−3and a single scattering albedo at 550 nm wavelength of around 0.90. Presuming no effect by the biomass aerosol on the clouds themselves, the presence of clouds converted the negative TOA forcing by the biomass aerosol in clear skies into a positive one (−13.0 W m−2converted to +11.5 W m−2for average optical properties of the biomass aerosol and a solar zenith angle of 60°). As biomass aerosol was found above cloud thousands of kilometers away from the southern African coastline, positive direct TOA forcings can be expected in extended sea areas over the Namibian cloud sheet. These results suggest errors in global climate model (GCM) modeling assessments of the direct radiative forcing due to biomass aerosols. Additionally, we estimate the possibility that a potential indirect effect dominates the overall forcing, resulting generally in strong negative TOA forcings.
An estimate of the area burned in southern Africa during the 2000 dry season using SPOT‐VEGETATION satellite data
Authors: Silva João M. N. , Pereira José M. C. , Cabral Ana I. , Sá Ana C. L. , Vasconcelos Maria J. P. , Mota Bernardo , Grégoire Jean‐Marie
Published: May 2003

The area burned in southern Africa during the 2000 dry season was mapped on a monthly basis from May to November using SPOT‐VEGETATION (VGT) satellite imagery at 1 km spatial resolution. Burned areas were identified with a classification tree that relied only on the near‐infrared channel of VGT. The classification tree algorithm yielded very accurate results (Kappa = 0.93). However, when compared with burned area maps derived from 30 m resolution Landsat Enhanced Thematic Mapper (ETM+) imagery, the VGT 1 km burned area maps reveal variable accuracy, dependent on vegetation type and on the spatial pattern of the burned areas. Fire incidence was higher in the northern part of the study area, especially in Wetter Zambezian Miombo Woodland, Mosaic of Guineo‐Congolian Lowland Forest and Secondary Grassland, Edaphic and Secondary Grassland on Kalahari Sand, Drier Zambezian Miombo Woodland, and Undifferentiated North‐Zambezian Miombo Woodland. Fire incidence was lower in the eastern part of the study area and almost absent from the western and southern semiarid and desert regions. The most extensively burned countries were, in decreasing order, the Democratic Republic of Congo, Angola, Mozambique and Zambia. The total area burned was estimated at 959480 km2.