bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracking upper tropospheric water vapor radiances: A satellite perspective
Authors: Soden Brian J.
Published: February 2004

Hourly observations of 6.7 μm “water vapor” radiances from geostationary satellites are used in conjunction with an objective pattern‐tracking algorithm to trace upper tropospheric water vapor features from sequential images. Analysis of measurements covering the 3 month period of June‐August 1987 illustrates a close relationship between the upper tropospheric moisture and the tropical circulation. Over humid tropical regions the movement of water vapor patterns reveals a diverging upper level flow away from centers of deep convection. Likewise, arid subtropical regions are characterized by converging upper level water vapor patterns indicating sinking air. The evolution of upper tropospheric moisture is also explored from a Lagrangian perspective by considering the change in moisture of a pattern as it is tracked from one image to the next. This analysis reveals that the clear‐sky upper troposphere in both tropical and subtropical regions becomes increasingly drier with time reflecting the impact of large‐scale subsidence in drying the troposphere. When separated according to cloud amount, water vapor patterns associated with clouds are observed to dry substantially slower than those without clouds, presumably due to the evaporation of cloud condensate. Trajectories of upper tropospheric moisture are also constructed by iteratively tracking water vapor patterns from successive satellite images. The trajectories reveal two distinct paths for water vapor patterns entering the dry subsidence region of the subtropical South Pacific. One path highlights the southward propagation of convective outflow from the tropics while the other path reflects the injection of moisture from eastward propagating subtropical disturbances. The existence of two distinct source regions suggests that a complete picture of the processes regulating the driest and most radiatively transparent regions of the subtropics will require an understanding of both types of convective systems.
Derivation of a global land elevation data set from satellite radar altimeter data for topographic mapping
Authors: Bamber Jonathan L. , Muller Jan‐Peter
Published: February 2004

Radar altimeter data from the 336 day cycle of the geodetic phase of ERS‐1 has been processed over all land surfaces to produce a consistent, homogenous data set for topographic mapping purposes. Several processing steps were required to achieve this, the most important of which were waveform retracking and data filtering. No slope correction was applied to the data as this was found not to improve the accuracy. The original radar altimeter data set was 145 Gb in size and a more compact, higher‐level product was required for land topography applications. Three higher‐level products were created: 1) an unaveraged data set comprising elevation, position, backscatter and a small number of auxiliary parameters; 2) an averaged data set of quasi‐regular mean elevations, position, and standard deviation at 5 arc min resolution; 3) a 5 arc min digital elevation model interpolated and extrapolated from the second data set. The accuracy of the radar altimeter data was investigated using six point data sets of both global and regional coverage, including airport runway elevations, national geodetic data, gravity station heights, and navigation beacon heights. A small number of erroneous elevations in both the radar and the point data sets were identified. After removing outliers with a difference of greater than 300 m the mean différence between the radar and point data was −0.5 m ±44 m full width at half maximum.
Resistances to ozone deposition to a flark fen in the northern aapa mire zone
Authors: Tuovinen Juha‐Pekka , Aurela Mika , Laurila Tuomas
Published: February 2004

We present results of eddy covariance measurements of ozone deposition to a subarctic aapa mire. The measurements were performed in northern Finland in August‐September 1995. The aim of the study is to quantify the ozone flux to this specific surface type and interpret the observations in terms of the resistance analogy model for dry deposition. The dry deposition velocity of ozone had a weak diurnal cycle, the hourly means within this cycle ranging from 0.15 to 0.2 cm s−1. The bulk surface resistance was on average about 400 s m−1 during the daytime and 480 s m−1 in the dark. The small day‐to‐night difference indicates only a weak dependence on radiation. The independence of the sublayer Stanton number on flow, which is approximately valid for surfaces of permeable vegetation, was found to fail for the present surface, which exhibits a pronounced hummock‐hollow pattern. This adds to the uncertainty in determining the surface resistance as a residual in the resistance system. Comparisons of observations with two general‐purpose parameterizations of the surface resistance indicate that these tend to overestimate the light sensitivity of surface‐related resistances. The overall performance of these schemes much depends on the actual implementation with respect to land‐use data and seasonal definitions.
Temperature climatology of the middle atmosphere from long‐term lidar measurements at middle and low latitudes
Authors: Leblanc Thierry , McDermid I. Stuart , Keckhut Philippe , Hauchecorne Alain , She C. Y. , Krueger David A.
Published: February 2004

Long‐term measurements from several lidar instruments (Rayleigh and sodium) located at 44.0°N, 40.6°N, 34.4°N, and 19.5°N have been used to develop a new climatology of the middle atmosphere temperature. For each instrument, the measurements on every individual day of the year over the entire long‐term record were averaged to build a composite year of temperature profiles. These profiles were then interpolated to provide temperature values at 1‐km altitude intervals so that the climatology comprises daily temperature values at integer altitudes between 15 and 110 km, depending on the instrument. The climatologies for each lidar were then compared to the CIRA‐86 model and to each other. Large differences between the lidar temperatures and the CIRA‐86 temperatures are identified and explained. When compared to all instruments, CIRA‐86 appears systematically much too cold between 90 and 95 km, by 20 K or more, and possibly 6–8 K too warm around 80 km, making its use as a reference atmosphere model questionable at these altitudes. The annual and semiannual components of the seasonal variability and the 2‐ to 33‐day period variability were investigated. An annual cycle with 6–7 K amplitude in the upper stratosphere, increasing to 15–20 K at 80 km, is observed at midlatitudes. This cycle is in phase with the solar flux in the stratosphere and in opposite phase in the mesosphere with a very cold summer mesopause at 85 km, in good agreement with previous climatologies. At lower latitudes, a semiannual oscillation propagates downward from 85 to 30 km and is characterized by a stronger first cycle than the second (4 and 2 K amplitude respectively). The 2‐ to 33‐day variability at midlatitudes shows a maximum during winter around 40 km and in the mésosphère. The first peak is associated with planetary wave activity and stratospheric warmings and the second to the occurrence of mesospheric temperature inversions. Finally, sudden seasonal transitions, highly consistent between all instruments, have been observed. In particular, in the early winter midlatitudes a two‐step warming of the winter mésosphère between 65 and 85 km as well as a cooling of the lower mésosphère appear to be real climatological events rather than some short‐term geophysical or instrumental random variability.
Nitric oxide production by simulated lightning: Dependence on current, energy, and pressure
Authors: Wang Y. , DeSilva A. W. , Goldenbaum G. C. , Dickerson R. R.
Published: February 2004

The production of NO has been studied by means of arc discharges in the laboratory which simulate natural lightning in current waveform and amplitude (≃30 kA). Observations are compared to the results of a computational model that includes the dynamics of energy deposition and channel expansion, combined with the Zel'dovich equations to model the relevant chemical reactions. Results are expressed as NO produced per meter of arc length, and are measured as functions of dissipated energy and of peak current. It is found that at atmospheric pressure, the NO production per joule of dissipated energy is not constant. NO production per meter discharge length as a function of peak current appears to provide a more appropriate scaling factor for estimates of total global NO production. Production of NO2 was less than 10% of the production of NO, and by implication the production of O3 less still. From these data, and using published estimates of global lightning frequency, we derive an estimate of global NO production of 2.5 Tg(N)/yr for 30 flashes per second to 8.3 Tg(N)/yr for 100 flashes per second.
Distributions and recent changes of carbon monoxide in the lower troposphere
Authors: Novelli P. C. , Masarie K. A. , Lang P. M.
Published: February 2004

Since 1988, the distribution of carbon monoxide (CO) in the lower troposphere has been determined using a globally distributed air sampling network. Site locations range from 82°N to 90°S, with wide longitudinal coverage, and represent the marine boundary layer, regionally polluted atmospheres, and the free troposphere. These measurements present a unique, intercalibrated, and internally consistent data set that are used to better define the global temporal and spatial distribution of CO. In this paper, times series from 49 sites are discussed. With an average lifetime of ∼2 months, CO showed significant concentration gradients. In the marine boundary layer, mixing ratios were greatest in the northern winter (200–220 ppb) and lowest in the southern summer (35–45 ppb). The interhemispheric gradient showed strong seasonality with a maximum difference between the high latitudes of the northern and southern hemispheres (160–180 ppb) in February and March and a minimum in July and August (10–20 ppb). Higher CO was found in regions near human development relative to those over more remote areas. The distributions provide additional evidence of the widespread pollution of the lower atmosphere. Remote areas in the high northern hemisphere are polluted by anthropogenic activities in the middle latitudes, and those in the southern hemisphere are heavily influenced by the burning of biomass in the tropics. While tropospheric concentrations of CO exhibit periods of increase and decrease, the globally averaged CO mixing ratio over the period from 1990 through 1995 decreased at a rate of approximately 2 ppb yr−1.
An evaluation and intercomparison of four new advection schemes for use in global chemistry models
Authors: Petersen Arthur C. , Spee Edwin J. , van Dop Han , Hundsdorfer Willem
Published: February 2004

The need to use a higher spatial resolution and to include more chemical species in global atmospheric chemistry models has led to a demand for efficient advection schemes with high accuracy. We test four newly developed three‐dimensional advection schemes named Mol‐rg, Split‐u, Split‐us, and Split‐rg. We compare the new schemes with the existing schemes Slopes and Second Moments, both implemented on a uniform grid. Mol‐rg and Split‐rg make use of a reduced grid. Split‐us is an unconditionally stable scheme on a uniform grid. Two tests are performed with all schemes: a solid‐body rotation test and a radon transport test. The radon transport test is performed with the off‐line global tracer model TM2. The solid‐body rotation test shows that none of the new schemes generates undershoot and overshoot and that all of them are mass conservative. Slopes and Second Moments both generate small undershoot and overshoot at all resolutions. The accuracy of the new and old schemes for rotation of a smooth profile is similar for the horizontal resolutions studied. Since the new schemes are slightly more diffusive than the old schemes, they perform worse for rotation of a cone. The radon test shows that the errors related to the numerical schemes are much smaller than other model errors. The main advantage of the new schemes is that they use 75% and 90% less memory than Slopes and Second Moments, respectively. At horizontal resolutions higher than 5° × 5° Split‐us and Split‐rg are the most efficient of the schemes in terms of cpu time. The new advection schemes are available through Internet.
Arctic chemical ozone depletion during the 1994–1995 winter deduced from POAM II satellite observations and the REPROBUS three‐dimensional model
Authors: Deniel C. , Bevilacqua R. M. , Pommereau J. P. , Lefèvre F.
Published: February 2004

Chemical ozone depletion during the unusually cold 1994–1995 Arctic winter is quantified using ozone profile measurements from the space‐based Polar Ozone and Aerosol Measurement (POAM II) instrument and the REPROBUS three‐dimensional chemistry transport model. The model is first used to determine the dynamical component of the observed variations, allowing the chemical component to be quantified from the observations. This technique has been previously used to estimate ozone loss from ground‐based total column measurements. In the present study, it has been adapted to the POAM II vertical profile measurements in order to document the vertical evolution of ozone chemical loss throughout the winter both inside and outside the polar vortex. The cumulative ozone loss thus obtained inside the vortex at the end of the winter is found to reach a maximum of 51% (with respect to the REPROBUS dynamics‐only prediction) at the 430 K potential temperature level. The largest ozone depletion rates were observed in late January when record low temperatures were reported, and the vortex was largely displaced towards midlatitudes. The maximum depletion rate was 1.4%/d occurring at the 470 K potential temperature level. Smaller but significant chemical ozone depletion was also found outside the vortex, where cumulative ozone losses of 19% were observed in the lower stratosphere. Finally, comparison of chemical ozone loss inferred from the POAM measurements with that obtained from the REPROBUS model indicates that the model underestimates cumulative ozone loss inside the vortex (by ∼30% in the lower stratosphere).
Validation of Millimeter‐wave Atmospheric Sounder (MAS) ozone measurements
Authors: Daehler M. , Bevilacqua R. M. , Kriebel‐Hamilton D. L. , Goldizen D. , Olivero J. J. , Hartmann G. K. , Degenhardt W. , Richards M. L. , Connor B. J. , Aellig C. P.
Published: February 2004

This paper discusses the validation of measurements of O3 distribution in the Earth's atmosphere made by the Millimeter‐wave Atmospheric Sounder (MAS), a component of NASA's ATLAS spacelab shuttle package. Measurements of 184 GHz O3 emission from the Earth's limb at tangent altitudes between 20 and 80 km were made with a 50 channel radiometer having a spectral resolution of 200 KHz. In three missions the emissions of O3, H2O, ClO, and O2 were measured between 70°S and 70°N latitudes. O3 mixing ratio calculations and error analysis were performed with the Rodgers optimal estimation method. Data binned in 128 s batches yield mixing ratio profiles with an altitude resolution of 7 km at the O3 peak and an estimated accuracy of 5%. Additional retrievals made with all data from each mission binned in 5° latitude zones yield mixing ratios with about 5 km altitude resolution and somewhat improved accuracy. Comparisons with coincident measurements from other space platforms indicate a general agreement within approximately 5%. The data are publicly available through the German Remote Sensing Data Center.
Meteorological factors associated with inhomogeneous ozone concentrations within the Mexico City basin
Authors: Fast Jerome D. , Zhong Shiyuan
Published: February 2004

Meteorological processes associated with inhomogeneous ozone concentrations over Mexico City are examined by using observations from a recent field campaign and a mesoscale dynamics and dispersion modeling system. During this 4‐week field campaign, meteorological measurements of the spatial flow structure within the Mexico City basin were obtained for the first time. A mesoscale model that employs four‐dimensional data assimilation is used to create analyses that describe the boundary layer characteristics and local and regional circulations in the vicinity of Mexico City. The mesoscale analyses are then used to drive a Lagrangian particle dispersion model to simulate pollutant transport and diffusion. The resemblance between the calculated particle concentration fields and the observed spatial ozone patterns indicates that the mesoscale analyses, based on the model and the observed profiles of wind, temperature, and humidity, captured the main flow features responsible for the inhomogeneous ozone concentrations within the basin. The highest particle concentrations usually occurred in the vicinity of the peak ozone concentrations during the afternoon. The observations and mesoscale analyses provided evidence that the circulations are highly complex, and relatively weak upper level synoptic systems had an impact on the local and regional thermally driven flows in the area. In addition to horizontal advection and vertical diffusion, vertical wind shears, recirculation patterns associated with venting and entrainment processes, and mean vertical motions due to convergence within the basin also played an important role in producing the spatial variations in the near‐surface particle distributions. The contribution of emissions from the previous day was found to be relatively minor for the periods examined in this study, even though the nocturnal wind speeds were light, suggesting that the high ozone concentrations are not due to multiday accumulation of pollutants.
Redistribution by deep convection and long‐range transport of CO and CH4 emissions from the Amazon basin, as observed by the airborne campaign TROPOZ II during the wet season
Authors: Jonquières Isabelle , Marenco Alain
Published: February 2004

Flights performed over South America in the Austral summer, during the airborne campaign Tropospheric Ozone Experiment (TROPOZ II, January 1991), have shown an upper tropospheric maximum (UTM) of carbon monoxide, methane, and relative humidity above 7 km altitude and between 30°S and 5°N. The study of chemical characteristics and convective/transport processes associated with this UTM shows that the air came from the Amazon basin boundary layer, was lifted by convective processes to upper levels, and was then redistributed over South America, and even across the South Atlantic toward the African coast, by the upper level anticyclone present during the wet season over tropical South America. The chemical composition of this UTM (high CO, CH4, and relative humidity; medium NOy, NO, and alkanes; low ozone and acetylene) agrees with the observations from the Atmospheric Boundary Layer Expedition ABLE 2B over the Amazon basin during the wet season and supports a biogenic origin for methane and carbon monoxide. The slow (or even absent) photochemical activity associated with this UTM can be explained by the low levels of active hydrocarbons and reactive nitrogen species. The TROPOZ II results complete and extend observations from previous expeditions by demonstrating that large biogenic emissions of ozone precursors from the Amazon basin can enter the upper general circulation during the Austral summer (December‐January‐February) and, though they do not contribute significantly to the ozone budget over South America, on being exported to the rest of the global circulation they will certainly become involved in the global ozone budget.
Soluble species in aerosol and snow and their relationship at Glacier 1, Tien Shan, China
Authors: Sun Junying , Qin Dahe , Mayewski Paul A. , Dibb Jack E. , Whitlow Sallie , Li Zhongqin , Yang Qinzhao
Published: February 2004

Simultaneous sampling of aerosol (n = 20) and snow (n = 114) was made at Glacier 1, Tien Shan, between May 19 and June 29, 1996. Similar temporal patterns of some major ion (calcium, magnesium, potassium, sodium, chloride, and sulfate) concentrations between snow and aerosol show that snow chemistry basically reflects changes in the chemistry of the atmosphere. This gives us confidence in the reconstruction of past atmospheric change using some snow data. There are no significant correlations between aerosol and snow samples for ammonium and nitrate. This suggests that postdepositional and/or postcollection processes may alter ammonium and nitrate concentrations in snow. The fact that the measured cations in aerosol and snow always exceed the measured anions suggests that the atmosphere is alkaline over Glacier 1, Tien Shan. In aerosol and snow samples, calcium is the dominant cationic species, with sulfate and presumed carbonate being the dominant anions. There is a very good inverse relationship (r = 0.96) between the equivalence ratio of calcium to sulfate and the ratio of ammonium to sulfate in aerosols, but this relationship does not hold for snow. This further suggests that postdepositional and/or postcollection processes exert important controls on ammonium concentrations in snow. Although melt‐freeze cycles might increase the concentration of all crustal species through progressive dissolution of dust, these cycles seem most important for magnesium and carbonate.
Contribution to the circulation climatology of the eastern equatorial Pacific: Lower‐atmospheric jets
Authors: Hastenrath Stefan
Published: February 2004

Novel data sets have been evaluated to reappraise the annual cycle of atmospheric circulation over the Pacific. In the eastern Pacific, cross‐equatorial surface winds from the southern hemisphere generate an oceanic cold tongue immediately to the south of the equator. The associated lower‐tropospheric thickness pattern entails a minimum of absolute topography in the midtroposphere near the equator, and together with the small Coriolis parameter this causes a jet stream of up to 10 ms−1 at 700–600 mbar centered at 0°‐2°N. The jet is most intense in late boreal winter because then the near‐equatorial surface low‐pressure trough is flat. The jet is fed by lower‐tropospheric convergence over equatorial South America and by upper tropospheric convergence and subsidence over a narrow equatorial zone of the eastern Pacific. Over the central Pacific a jet of up to 10 ms−1 is found at 10°–12°N and 925–850 mbar, while friction brakes the flow in the layer of steepest meridional pressure gradient near the surface. This lower‐tropospheric jet, as the surface pressure gradient, is also strongest in late boreal winter. Overall, the NCEP analyses resolve the near‐surface circulation less well than the long‐term ship observations. However, the midtropospheric equatorial jet over the eastern Pacific is also borne out by the 1967–1971 radiosoundings over Galapagos, and the lower‐tropospheric trade wind jet over the central Pacific was also identified from the intense radiosonde program of the March‐April 1967 Line Islands Experiment.
Characteristics of cryogenic soils along a latitudinal transect in arctic Alaska
Authors: Ping C. L. , Bockheim J. G. , Kimble J. M. , Michaelson G. J. , Walker D. A.
Published: February 2004

The morphological, chemical, and physical properties of arctic tundra soils were examined along a 200‐km latitudinal gradient in northern Alaska which includes two major physiographic provinces; the Arctic Coastal Plain and the Arctic Foothills. Annual air temperature and precipitation increase along the gradient from north to south. Soils on the Arctic Coastal Plain support wet, nonacidic tundra vegetation and have high carbonate contents. Soil on the Arctic Foothills support moist, nonacidic tundra in the northern part and moist acidic tundra in the southern part. Most arctic tundra soils are characterized by medium texture, poor drainage, and high organic matter content. From north to south along the transect, the base saturation of the active layer decreases and exchangeable aluminum increases from north to south. Most soils have strongly developed cryogenic features, including warped and broken horizons, ice lenses, thin platy structure, and organic matter frost‐churned into the ice‐rich upper permafrost horizons.
Effects of urban emission control strategies on the export of ozone and ozone precursors from the urban atmosphere to the troposphere
Authors: Duncan B. N. , Chameides W. L.
Published: February 2004

An urban plume model is used to simulate the photochemistry of ozone (O3) precursors and the concomitant generation of O3 within an urban plume as it advects and mixes with the background atmosphere. On the basis of these calculations, we estimate the rates at which O3 and its precursor compounds are exported to the background atmosphere and how these export rates are affected by various control strategies that might be implemented to reduce maximum O3 concentrations within the urban plume. Two model cities with different chemical characteristics are considered: case 1, where peak O3 concentrations during extreme air pollution episodes are more sensitive to nitrogen oxides (NOx = NO + NO2) and case 2, where peak O3 concentrations during these episodes are more sensitive to volatile organic compounds (VOC). The model is first run for extreme meteorological conditions conducive to the generation of high O3 concentrations to determine the most effective emission control strategies for reducing peak O3 under these conditions. The model is then run for more typical meteorological conditions, to determine how these various emission control scenarios might affect the export of O3 and its precursors from the urban to the rural and background atmosphere. The export of O3 from the urban atmosphere is found to be more sensitive to NOx emissions, even for case 2 where VOC emission controls more effectively reduced peak O3 during pollution episodes. The impact of VOC and NOx emission reductions on the export of primary and secondary O3 precursor compounds is more complex, leading to reductions in the export of some species and enhancements in the export of others.
Estimates of large‐scale divergence in the lower troposphere over the western equatorial Pacific
Authors: Hartten Leslie M. , Gutzler David S.
Published: February 2004

A network of 915‐MHz wind profilers measured half‐hourly lower‐tropospheric winds over the western equatorial Pacific with vertical resolutions as high as 100 m during November 1992 through February 1993, the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE). These wind data are used in conjunction with collocated surface wind measurements to examine the near‐surface divergent flow over the western Pacific warm pool during austral summer as well as the synoptic‐scale variability of divergence in both time and space. The synoptic‐scale wind field estimated from profiler data exhibits stronger near‐surf ace divergence than sonde‐based estimates from the same time period. Temporal variations of the lower‐tropospheric divergence profiles are described by three vertical structure functions derived from Varimax‐rotated eigenvector analysis. One vertical mode appears to be associated with deep convection, one with near‐surface processes, and one with shallower convection. These structure functions vary zonally across the COARE region, with the convective modes having convergence maxima at lower elevations to the west of the intensive flux array (IFA) than over and east of it.
Seasonal behavior of tropical to midlatitude upper tropospheric water vapor from UARS MLS
Authors: Sandor Brad J. , Read William G. , Waters Joe W. , Rosenlof Karen H.
Published: February 2004

Measurements of upper tropospheric water vapor made during 1991–1997 with the Microwave Limb Sounder instrument on the Upper Atmospheric Research Satellite are described. Zonal mean results versus day of year are presented for tropical to midlatitudes on pressure surfaces 316, 215, and 147 hPa. The latitude of greatest upper tropospheric humidity (UTH) varies with season, following the Intertropical Convergence Zone. Annual maximum UTH occurs in northern summer at north tropical latitudes, coincident with the Indian monsoon and with a June‐August maximum of water vapor transport to the lower stratosphere [Rosenlof et al, 1997]. Comparison with lower stratospheric studies supports the Rosenlof et al. [1997] conclusion that water vapor transport is a maximum from the summer northern hemisphere tropical troposphere. Seasonally adjusted UTH is higher in the northern hemisphere than at equivalent southern hemisphere latitudes. The midlatitude secondary maximum in relative humidity seen in other (lower altitude) data sets is seen on the 316 hPa surface throughout the year, only in northern hemisphere spring‐summer at 215 hPa, and does not occur at 147 hPa. These observations characterize seasonal and interhemispheric differences in strengths of midlatitude convection and of subtropical subsidence. Frequency distribution analysis of tropical measurements shows the peak (mode) of the frequency distribution to be much drier than mean and median values at 316 and 215 hPa and marginally drier than mean and median values at 147 hPa. The frequency distribution mode is drier in the tropical wet than in the dry season at 316 hPa, consistent with other data sets at 300–500 hPa [Spencer and Braswell, 1997; Chiou et al., 1997] but is wetter in the tropical wet than in the dry season at 215 and 147 hPa. The wettest values of the frequency distribution mode occur in April–May, corresponding to neither the tropical wet nor the dry season.
Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) experiment
Authors: Kaufman Y. J. , Hobbs P. V. , Kirchhoff V. W. J. H. , Artaxo P. , Remer L. A. , Holben B. N. , King M. D. , Ward D. E. , Prins E. M. , Longo K. M. , Mattos L. F. , Nobre C. A. , Spinhirne J. D. , Ji Q. , Thompson A. M. , Gleason J. F. , Christopher S. A. , Tsay S.‐C.
Published: February 2004

The Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) field project took place in the Brazilian Amazon and cerrado regions in August–September 1995 as a collaboration between Brazilian and American scientists. SCAR‐B, a comprehensive experiment to study biomass burning, emphasized measurements of surface biomass, fires, smoke aerosol and trace gases, clouds, and radiation, their climatic effects, and remote sensing from aircraft and satellites. It included aircraft and ground‐based in situ measurements of smoke emission factors and the compositions, sizes, and optical properties of the smoke particles; studies of the formation of ozone; the transport and evolution of smoke; and smoke interactions with water vapor and clouds. This overview paper introduces SCAR‐B and summarizes some of the main results obtained so far. (1) Fires: measurements of the size distribution of fires, using the 50 m resolution MODIS Airborne Simulator, show that most of the fires are small (e.g., 0.005 km2), but the satellite sensors (e.g., AVHRR and MODIS with 1 km resolution) can detect fires in Brazil which are responsible for 60–85% of the burned biomass; (2) Aerosol: smoke particles emitted from fires increase their radius by as much as 60% during their first three days in the atmosphere due to condensation and coagulation, reaching a mass median radius of 0.13–0.17 μm; (3) Radiative forcing: estimates of the globally averaged direct radiative forcing due to smoke worldwide, based on the properties of smoke measured in SCAR‐B (−0.1 to −0.3 W m−2), are smaller than previously modeled due to a lower single‐scattering albedo (0.8 to 0.9), smaller scattering efficiency (3 m2g−1at 550 nm), and low humidification factor; and (4) Effect on clouds: a good relationship was found between cloud condensation nuclei and smoke volume concentrations, thus an increase in the smoke emission is expected to affect cloud properties. In SCAR‐B, new techniques were developed for deriving the absorption and refractive index of smoke from ground‐based remote sensing. Future spaceborne radiometers (e.g., MODIS on the Earth Observing System), simulated on aircraft, proved to be very useful for monitoring smoke properties, surface properties, and the impacts of smoke on radiation and climate.
Five years of shortwave radiation budget measurements at a continental land site in southeastern Australia
Authors: Prata A. J. , Grant I. F. , Cechet R. P. , Rutter G. F.
Published: February 2004

A new data set of near‐continuous, high‐quality measurements of the components of the land surface radiation budget (SRB) at a uniform site in Australia is described. Its intended uses include the validation of SRB parameters predicted by general circulation models (GCMs), the validation of SRB parameters remotely sensed by satellites, and the study of surface processes. The site at Uardry (145.30°E, 34.39°S) near the town of Hay is the first in Australia's Continental Integrated Ground‐truth Site Network. It is located in extremely flat and homogeneous natural terrain, with grassland cover that is characteristic of much of the Australian continent, beneath an atmosphere that is characterized by low amounts of water vapor and aerosol. The measurements include the downwelling and upwelling shortwave flux densities. The upwelling measurements are made at several points across the site in order to sample the variability on a scale of 1 km, which is approximately the resolution of many current and planned satellite‐based sensors. The paper describes the shortwave component of the data set, shows some internal quality checks, presents some statistical summaries, and makes comparisons with the albedos used in GCMs. It then discusses features of the temporal variation of the albedos derived from the data set in terms of their impact on the remote sensing of land albedo. In particular, significant morning‐afternoon asymmetry is present in the diurnal variation on some days, and changes of 20% in albedo occur over a few days. Both of these characteristics violate common assumptions of algorithms used to retrieve land reflective properties from satellite measurements. Consideration of their effect is merited.
MOZART, a global chemical transport model for ozone and related chemical tracers: 1. Model description
Authors: Brasseur G. P. , Hauglustaine D. A. , Walters S. , Rasch P. J. , Müller J.‐F. , Granier C. , Tie X. X.
Published: February 2004

We present a new global three‐dimensional chemical‐transport model (called MOZART) developed in the framework of the NCAR Community Climate Model (CCM) and aimed at studying the distribution and budget of tropospheric ozone and its precursors. The model, developed with a horizontal resolution of 2.8° in longitude and latitude, includes 25 levels in the vertical between the Earth's surface and an upper boundary located at approximately 35 km altitude. In its present configuration the model calculates the global distribution of 56 chemical constituents with a timestep of 20 min, and accounts for surface emission and deposition, large‐scale advective transport, subscale convective and boundary layer exchanges, chemical and photochemical transformations, as well as wet scavenging. Transport is simulated “off line” from CCM with dynamical variables provided every 3 hours from preestablished history tapes. Advection is calculated using the semi‐Lagrangian transport scheme [Rasch and Williamson, 1990] developed for the MATCH model of Rasch et al. [1997]. Convective and boundary layer transports are expressed according to Hack [1994] and Holtslag and Boville [1993], respectively. A detailed evaluation of the model results is provided in a companion paper [Hauglustaine et al., this issue]. An analysis of the spatial and temporal variability in the chemical fields predicted by the model suggests that regional events such as summertime ozone episodes in polluted areas can be simulated by MOZART.
Glacial‐interglacial changes induced by pulse modulation of the incoming solar radiation
Authors: Liu Han‐Shou
Published: February 2004

The Milankovitch insolation equation as an astronomical forcing function for climate change is modified to include the frequency variation effect of the Earth's obliquity on insolation. To establish the criterion that frequency variation of the obliquity is responsible for major paleoclimatic changes, the cooperative phenomena between the obliquity frequency and the Milankovitch insolation are defined as frequency‐insolation resonances. Coupling of the orbital frequency and insolation variations has established an especially new and interesting series of these resonances, which may induce pulsation of insolation. In this paper we show that insolation pulses would modulate the Milankovitch insolation in such a way that the mode (phase or period) of the insolation variations could be locked into a 100‐kyr cycle. The pulse‐modulated Milankovitch insolation forcing is tested by energy balance climate models. The physical mechanism behind this forcing for glacial‐interglacial changes is explained and clarified in terms of pulse duration in the incoming solar radiation. It is concluded that the frequency‐insolation resonances may be the key to the puzzle of the 100‐kyr paleoclimate cycle.
Trends and variability in vertical ozone and temperature profiles measured by ozonesondes at Lauder, New Zealand: 1986–1996
Authors: Bodeker G. E. , Boyd I. S. , Matthews W. A.
Published: February 2004

A first analysis of trends in vertical ozone and temperature profiles from ozonesonde flights made at Lauder (45.045°S, 169.684°E) between August 1986 and July 1996, is presented. To calculate the trends and determine the magnitude of the forcing mechanisms underlying the variability in ozone and temperature, a linear least squares regression model was applied to ozone mixing ratios, ozone number densities, and temperatures, interpolated onto 100 pressure levels from the surface (969 hPa/370 m) to 12.1 hPa (∼30.1 km), ∼300 geopotential meters apart. Ozone trends indicate wintertime upper tropospheric decreases of more than −30±24% per decade (2σ), post vortex breakup trends in a narrow altitude region above the tropopause of −20±20% per decade (2σ), and positive trends of up to 30±14% per decade (2σ) in the lower stratosphere during late winter, spring, and early summer. The predominant temperature trend is +1.5% per decade and greater above the ∼50 hPa level during winter. Derived trends were sensitive to inclusion of tropopause height forcing which was found to influence ozone and temperature at a high level of statistical significance. Ozone at Lauder shows significant QBO dependence throughout the lower stratosphere during winter, spring, and early summer, but little or no dependence on the solar cycle. Temperatures, however, show little dependence on QBO but were influenced by the solar cycle. The Mt. Pinatubo eruption had little influence on Lauder ozone but significantly cooled the troposphere. The ENSO cycle in ozone and temperature was weak except at the uppermost analysis levels.
Stable isotope composition of precipitation over southeast Asia
Authors: Araguás‐Araguás Luis , Froehlich Klaus , Rozanski Kazimierz
Published: February 2004

Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network “Isotopes in Precipitation” and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is controlled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical‐maritime air mass originating in the northern Pacific, (4) equatorial‐maritime air mass originating in the western equatorial Pacific, and (5) equatorial‐maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain‐out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of δ18O and δ2H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June–September) is depleted in 18O by more than 6‰ with respect to winter rainfall, despite of 10°C higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average δ18O of rainfall, which in the south of China (Haikou. Hong Kong) is about 2.5‰ more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation observed in some areas of the studied region result from a complete reversal of atmospheric circulation over these areas and changing source of atmospheric moisture. High d‐excess values observed at Tokyo and Pohang during winter (15–25‰) result from interaction of dry air masses from the northern Asian continent passing the Sea of Japan and the China Sea and picking up moisture under reduced relative humidity. The isotopic composition of precipitation also provides information about the maximum extent of the ITCZ on the continent during summer.
Photoacoustic and filter measurements related to aerosol light absorption during the Northern Front Range Air Quality Study (Colorado 1996/1997)
Authors: Moosmüller H. , Arnott W. P. , Rogers C. F. , Chow J. C. , Frazier C. A. , Sherman L. E. , Dietrich D. L.
Published: February 2004

A new photoacoustic instrument for the measurement of aerosol light absorption was collocated with conventional aerosol instrumentation during the 1996–1997 winter intensive monitoring period of the Northern Front Range Air Quality Study. Measurements of the light absorption efficiency for black carbon were 5 m2/g at 685 nm and 10 m2/g at 532 nm, and for elemental carbon, they were 3.6 m2/g at 685 nm. We show that these values together with previous photoacoustic measurements of aerosol light absorption shed some light on the wavelength dependence of absorption efficiency for carbonaceous aerosol in the visible and near‐visible region. Integrating plate type filter measurements of aerosol light absorption result in far larger values than those measured with the photoacoustic instrument. We demonstrate that a recently published correction technique [Horvath, 1997] can yield improved agreement.
Measurements of nitrogen oxides from aircraft in the northeast Atlantic flight corridor
Authors: Klemm Otto , Stockwell William R. , Schlager Hans , Ziereis Helmut
Published: February 2004

We investigated the size and composition of exhaust plumes of commercial airliners in the northeast Atlantic flight corridor off the shores of Ireland and Scotland, an area with high air traffic density in the tropopause region. The primary objective was to measure the contribution of the NO and NOy emitted from aircraft to the nitrogen oxide background. We have made measurements in aircraft flight corridors by flying a research aircraft perpendicular to the routes of commercial transatlantic air traffic. Although previous studies had succeeded in identifying a few plumes, this study was the first systematic investigation of over 60 aircraft plumes through in situ NO and NOy measurements. These plumes were up to 1.5 km wide (along our flight paths) and showed NOy mixing ratios of up to 10 ppb above the background levels. The measurements showed that on larger scales the composition of NOy in the background air masses was very heterogeneous. On top of this natural variability of the NOy, we could not identify any influence of air traffic exhaust on air chemistry on scales larger than a few kilometers from our data. A secondary objective was to estimate the importance of the oxidation of NOχ to NOy in the relatively fresh plumes. The measured NO/NOy ratios were near the NO/NOχ ratios calculated from a simple photo‐stationary state assumption. This result was also consistent with calculations made with an expanding box model that included gas‐phase chemistry for the measured plume conditions. The model calculated NO/NOy and NC/NOχ ratios were almost equal, and these were consistent with the measured NO/NOy, ratios. These calculations showed that oxidation of NOχ to higher oxides played only a negligible role in our measured plumes of ages between 14 and 90 min.
Carbon dioxide transfer over a Central Amazonian rain forest
Authors: Malhi Yadvinder , Nobre Antonio D. , Grace John , Kruijt Bart , Pereira Maria G. P. , Culf Alistair , Scott Steve
Published: February 2004

Tropical rain forests are among the most important and least monitored of terrestrial ecosystems. In recent years, their influence on atmospheric concentrations of carbon dioxide and water vapor has become the subject of much speculation. Here we present results from a yearlong study of CO2 fluxes at a tropical forest in central Amazonia, using the micrometeorological technique of eddy covariance. The diurnal cycle of CO2 flux was consistent with previous short‐term studies in tropical rain forests, implying that the Amazonian rain forest shows a fair degree of spatial uniformity in bulk ecophysiological characteristics. Typical peak daytime photosynthesis rates were 24–28 μmol CO2 m−2 s−1, and respiration rates were 6–8 μmol CO2 m−2 s−1. There was significant seasonality in peak photosynthesis over the year, which appeared strongly correlated with soil moisture content. On the other hand, there was no evidence of strong seasonality in soil respiration. Central Amazonia has only a short, 3‐month dry season, not atypical of tropical rain forest, and it is therefore likely that large areas of Amazonia exhibit significant seasonality in photosynthetic capacity. The gross primary production was calculated to be 30 t C ha−1 yr−1. An analysis of data quality is included in the appendix.