bluuebunny/crossref_metadata_2025 huggingface dataset:
ATMOS version 3 water vapor measurements: Comparisons with observations from two ER‐2 Lyman‐α hygrometers, MkIV, HALOE, SAGE II, MAS, and MLS
Authors: Michelsen H. A. , Manney G. L. , Irion F. W. , Toon G. C. , Gunson M. R. , Rinsland C. P. , Zander R. , Mahieu E. , Newchurch M. J. , Purcell P. N. , Remsberg E. E. , Russell J. M. , Pumphrey H. C. , Waters J. W. , Bevilacqua R. M. , Kelly K. K. , Hintsa E. J. , Weinstock E. M. , Chiou E.‐W. , Chu W. P. , McCormick M. P. , Webster C. R.
Published: October 2002

We have compared a new version of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) retrievals (version 3) of stratospheric and mesospheric water vapor with observations from shuttleborne, satelliteborne, balloonborne, and aircraftborne instruments. These retrievals show agreement to within 5% with the MkIV observations in the middle and lower stratosphere. ATMOS agrees with the National Oceanic and Atmospheric Administration (NOAA) Lyman‐α hygrometer to within 5% except for features with spatial scales less than the vertical resolution of ATMOS (such as the lower stratospheric seasonal cycle). ATMOS observations are 10–16% lower than measurements from the Harvard Lyman‐α hygrometer in the lower stratosphere and are 7–14% higher than those from the Microwave Limb Sounder (MLS; prototype version 0104) throughout most of the stratosphere. Agreement is within 7% with the Millimeter‐Wave Atmospheric Sounder (MAS; version 20) in the middle and upper stratosphere, but differences are closer to 13% in the lower stratosphere. Throughout the stratosphere, agreement is within 8% with the Halogen Occultation Experiment (HALOE; version 19). ATMOS data from 1994 show agreement with the Stratospheric Aerosol and Gas Experiment II (SAGE II; version 6) values to within 8% in the middle stratosphere, but ATMOS observations are systematically higher than those from SAGE II by as much as 41% in the lower stratosphere. In contrast, ATMOS 1985 values are systematically ∼50% lower than SAGE II values from sunset occultations in the lower stratosphere near 70 hPa but appear to be in better agreement with sunrise occultations. Version 3 retrievals in the upper stratosphere and lower mesosphere are typically 5–10% lower than version 2 values between 1 and 0.05 hPa. This reduction improves agreement with HALOE, MAS, and MLS upper atmospheric observations, but ATMOS values still tend to be higher than values from these instruments in the middle mesosphere. Agreement among the instruments compared here (except for SAGE II) is generally within 15% in the middle to lower stratosphere and mesosphere and within 10% in the middle to upper stratosphere. At altitudes near 30 km, all instruments (including SAGE II) agree to within 10%.
How linear is the Arctic Oscillation response to greenhouse gases?
Authors: Gillett Nathan P. , Allen Myles R. , McDonald Ruth E. , Senior Catherine A. , Shindell Drew T. , Schmidt Gavin A.
Published: October 2002

We examine the sensitivity of the Arctic Oscillation (AO) index to increases in greenhouse gas concentrations in integrations of five climate models (the Hadley Centre coupled models (HadCM2 and HadCM3), the European Centre/Hamburg models (ECHAM3 and ECHAM4), and the Goddard Institute for Space Studies stratosphere‐resolving (GISS‐S) model) and in the National Centers for Environmental Prediction reanalysis. With the exception of HadCM2 all the models show a significant positive AO response to greenhouse gas forcing, but in the models lacking a well‐resolved stratosphere that response is smaller than observed. In these models the AO index is linearly dependent on the radiative forcing, even up to ∼20 times current CO2 levels. By contrast, the GISS‐S stratosphere‐resolving model shows an AO response comparable to that observed, but the sensitivity of the model to further increases in forcing is reduced when CO2 levels exceed ∼1.5 times preindustrial values. It has been suggested that greenhouse gas forcing results in the equatorward deflection of planetary waves, which leads to a cooling and strengthening of the polar vortex and hence an increase in the surface Arctic Oscillation. In the observations the number of sudden warmings has reduced dramatically, consistent with this planetary wave effect, leading to a large mean cooling of the vortex. However, neither the GISS‐S nor the HadCM3 models are able to reproduce the observed temperature changes, suggesting that this explanation for the impact of the inclusion of a stratosphere in the model may be incomplete.
Disjunct eddy covariance measurements of oxygenated volatile organic compounds fluxes from an alfalfa field before and after cutting
Authors: Warneke C. , Luxembourg S. L. , de Gouw J. A. , Rinne H. J. I. , Guenther A. B. , Fall R.
Published: October 2002

There is interest in and significant uncertainty about the emissions of oxygenated volatile organic compounds (oxVOCs) from vegetation to the atmosphere. Here, we measured the fluxes of selected oxVOCs from an alfalfa field, before, during, and after cutting, using a combination of disjunct eddy covariance and proton‐transfer‐reaction mass spectrometry. Over the course of 1 day a significant methanol flux of 4 mg m−2 h−1 was observed from undisturbed alfalfa with a maximum at 0800 LT, possibly caused by the evaporation of dew. A smaller release of hexenals during this day (0.04 mg m−2 h−1) demonstrated the sensitivity of the method. Other results suggested that acetaldehyde and acetone were released in the afternoon but were lost by dry deposition in the evening and morning; deposition velocities were estimated to be 0.2 cm s−1 (acetaldehyde) and 0.09 cm s−1 (acetone). After the alfalfa was cut the emissions of methanol, acetaldehyde, acetone, and hexenals were significantly enhanced and remained high for three days during which the alfalfa was drying. After a rainstorm the oxVOC emissions from the cut, wet alfalfa increased even more. Nighttime measurements yielded low oxVOC fluxes in general, but the high variability of the concentrations during the night and the high degree of correlation between different oxVOCs suggest that the nighttime releases of oxVOCs from alfalfa were nonzero. This work suggests that the global source of oxVOCs due to the production of hay is of minor importance. The emission flux of methanol from vegetation during the growing season may be very large on a global basis.
Characteristics of Arctic polar stratospheric clouds in the winter of 1996/1997 inferred from ILAS measurements
Authors: Saitoh N. , Hayashida S. , Sasano Y. , Pan L. L.
Published: October 2002

The Improved Limb Atmospheric Spectrometer (ILAS) captured many polar stratospheric cloud (PSC) events in the Northern Hemisphere during the winter and early spring of 1997. Simultaneous measurements of nitric acid and aerosols by ILAS made it possible to infer PSC composition. The aerosol extinction coefficient and nitric acid data were compared with the theoretically predicted values for supercooled ternary solution (STS), nitric acid dihydrate (NAD), and nitric acid trihydrate (NAT) at thermodynamic equilibrium to classify PSC types. The observations showed that in 1997, both nitric‐acid‐containing solid and liquid PSCs formed over the Arctic during winter and early spring, until mid‐March. The STS PSCs were observed early in the PSC season, in mid‐January. Most of the PSCs observed late in the PSC season had features of nitric‐acid‐containing hydrates. An intensive analysis of the temperature histories suggested that most of the STS events observed in January had experienced the thermal conditions necessary for the formation of liquid PSCs. The nitric‐acid‐containing hydrates observed in March seemed not to have been influenced by any mountain‐induced lee waves. The process of nitric‐acid‐containing hydrate formation based on synoptic scale temperature change is discussed.
Efficient parameterization of the infrared effective beam emissivity of semitransparent atmospheric layers
Authors: Rathke Carsten , Fischer Jürgen
Published: October 2002

A novel parameterization is provided that relates the effective beam emissivity of a semitransparent atmospheric layer (emissivity between 0.05 and 0.95) to its optical depth, single‐scattering albedo, and asymmetry factor and to the zenith viewing angle and estimates of the incoming radiation. It is derived from discrete ordinate radiative transfer calculations performed for optical properties representative for liquid water and ice clouds as well as aerosols. The formulation is kept simple and general and can be applied to any infrared window wavelength between 3 and 40 microns. It enables the efficient consideration of scattering of infrared radiation in fast radiative transfer models and remote‐sensing algorithms. The greatest improvement over other straightforward approximations occurs when the single‐scattering albedo is larger than 0.50. The parameterization also permits a better interpretation of the ratio of the effective optical depths at two wavelengths, which is highly correlated with cloud and aerosol microphysics. The possibilities are illustrated by a sample analysis of an advanced very high resolution radiometer image containing infrared signatures of contrails and stratocumulus clouds.
Intradiurnal and seasonal variability of soil temperature, heat flux, soil moisture content, and thermal properties under forest and pasture in Rondônia
Authors: Alvalá R. C. S. , Gielow R. , da Rocha H. R. , Freitas H. C. , Lopes J. M. , Manzi A. O. , von Randow C. , Dias M. A. F. S. , Cabral O. M. R. , Waterloo M. J.
Published: October 2002

Soil temperatures depend on the soil heat flux, an important parameter in meteorological and plant growth‐energy balance models. Thus, they were measured, together with soil moisture contents, within the LBA program at forest (Reserva Jaru) and pasture (Fazenda Nossa Senhora) sites in Rondônia, Brazilian Amazonia during wet (February) and dry (August) periods of 1999. The wet period showed maxima of the heat flux into the soil around five to six times smaller at the forest than at the pasture, except for some spikes that are related to stronger solar forcing, such as those due to sunspecks in the forest. This pattern remained during the dry period, but with doubled maximum values. Also, the soil heat flux and the soil temperatures responded very significantly to the passage of cold fronts in both periods at both sites. Temperature profiles measured in the 0.10–0.40 m soil layer showed daily averages and ranges smaller at the forest than at the pasture. The daily average of the soil moisture content in the same layer, during the wet season, increased with depth at both sites, with consistently lower values at the forest. However, their ranges were smaller at the pasture, except for the 0.40 m depth. During the dry period, these ranges were much higher at the pasture, but with nearer average values. Finally, the computed daily apparent soil thermal diffusivities, volumetric heat contents, and thermal conductivities are presented, with the first ones crossed with the measured soil moisture content.
Relationship between photolysis frequencies derived from spectroscopic measurements of actinic fluxes and irradiances during the IPMMI campaign
Authors: McKenzie Richard , Johnston Paul , Hofzumahaus Andreas , Kraus Alexander , Madronich Sasha , Cantrell Chris , Calvert Jack , Shetter Rick
Published: October 2002

The relationship between photolysis frequencies derived from spectroscopic measurements of actinic fluxes and irradiances was determined during a coordinated measurement campaign (International Photolysis Frequency Measurement and Modeling Intercomparison campaign (IPMMI)). When differences in viewing geometries are taken into account, the measurements are in close agreement. An empirical relationship, which is useful for high sun (noon) conditions or for daily integrals, was found to convert irradiance data to photolysis frequencies. For low‐sun conditions (large solar zenith angle), model calculations were shown to improve the accuracy. However, the input parameters to the model are site specific and the conversion depends on diffuse/direct ratios. During cloudy conditions, significant improvements in the conversion can be achieved by assuming the radiation field to comprise entirely diffuse isotropic radiation when the UVA transmission by cloud is less than 0.8. Changing cloud conditions remain the greatest limitation, but they tend to bias the results away from the clear‐sky case in a systematic way. Furthermore, although the cloud effects on the photolysis rates of nitrogen dioxide (J(NO2)) are rather large, they are much smaller for ozone photolysis (J(O3 → O(1D))), which is of prime importance in tropospheric chemistry. The study shows the potential for deriving historical and geographical differences in actinic fluxes from the extensive records of ground‐based measurements of spectral irradiance.
Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry
Authors: Birkett C. M. , Mertes L. A. K. , Dunne T. , Costa M. H. , Jasinski M. J.
Published: October 2002

Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large wetlands, rivers, and associated floodplains. A clear advantage is the provision of data where traditional gauges are absent. As part of an international program, a complete altimetric analysis of the Amazon Basin is being undertaken. Here, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first ∼7.5 years of the mission. With an initial study group of 230 targets, height variability at many ungauged locations can be observed for 30–50%, the range reflecting the clarity of the variations in lieu of instrument limitations. An assessment of the instrument performance confirms that the minimum river width attainable is ∼1 km in the presence of some inundated floodplain. This constraint does allow observation of the main stem (Solimões/Amazon) and the larger tributaries, but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval. First‐order validation exercises with the deduced 1992–1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters (mean ∼1.1 m rms). Altimetric water levels in the Solimões and Amazon are particularly well defined with amplitudes <13 m and variations in peak‐level timing from May to July. The water‐surface gradient of the main stem is found to vary both spatially and temporally, with values ranging from 1.5 cm/km downstream to 4.0 cm/km for more upstream reaches. In agreement with ground‐based estimates, the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be ∼0.35 m/s. Overall, the altimetric results demonstrate that the T/P mission is successfully monitoring the transient flood waves of this continental‐scale river basin.
Stratospheric ozone loss in the 1996/1997 Arctic winter: Evaluation based on multiple trajectory analysis for double‐sounded air parcels by ILAS
Authors: Terao Yukio , Sasano Yasuhiro , Nakajima Hideaki , Tanaka H. L. , Yasunari Tetsuzo
Published: October 2002

Quantitative chemical ozone loss rates and amounts in the Arctic polar vortex for the spring of 1997 are analyzed based on ozone profile data obtained by the Improved Limb Atmospheric Spectrometer (ILAS) using an extension of the Match technique. In this study, we calculated additional multiple trajectories and set very strict criteria to overcome the weakness of the satellite sensor data (lower vertical resolution and larger sampling air mass volume) and to identify more accurately a double‐sounded air mass. On the average inside the inner edge of the vortex boundary (north of about 70°N equivalent latitude), the local ozone loss rate was 50–80 ppbv/day at the maximum during late February between the levels of 450 and 500 K potential temperatures. The integrated ozone loss during February to March reached 2.0 ± 0.1 ppmv at 475–529 K levels, and the column ozone loss between 400 and 600 K during the 2 months was 96 ± 0.3 DU. Using a relative potential vorticity (rPV) scale, the vortex was divided into some rPV belts, and it was shown that the magnitude of the ozone loss increased gradually toward the vortex center from the edge. The maximum ozone loss rate of 6.0 ± 0.6 ppbv/sunlit hour near the vortex center was higher than near the vortex edge by a factor of 2–3. When we expanded the area of interest to include all the data obtained inside the vortex edge (north of about 65°N equivalent latitude), the local ozone loss rate was about 50 ppbv/day at the maximum. This value is slightly larger than that estimated by the Match analysis using ozonesondes for the same winter by ∼10 ppbv/day. Temperature histories of double‐sounded air parcels indicated that the extreme ozone loss in the innermost part of the vortex was observed when the air parcel experienced temperatures below TNAT during the two soundings and had experienced temperatures near Tice in the 10 days prior to the first sounding. These facts suggest that the high ozone loss rate deep inside the vortex in the 1997 Arctic early spring correlates with the presence of type Ia polar stratospheric clouds (PSCs).
Global observations of the carbon budget, 2, CO2 column from differential absorption of reflected sunlight in the 1.61 μm band of CO2
Authors: O'Brien D. M. , Rayner P. J.
Published: October 2002

This paper investigates the impact of uncertainty in atmospheric composition and state upon the feasibility of measuring the CO2 column from spectral analysis of sunlight reflected to space in the 1.61 μm absorption band of CO2. In principle, measurements of clear sky radiance at two frequencies, one where CO2 absorbs strongly and the other weakly, allow the difference between the optical thicknesses of the atmosphere at the two frequencies to be determined precisely. That difference, denoted by L, is a linear functional of the CO2 density profile, which depends strongly on the CO2 amount and only weakly upon its vertical distribution, thus suggesting that the CO2 column may be estimated from L. A simple model for the radiance reflected to space is used to estimate the magnitude of the error in the CO2 column inferred from L when the atmosphere contains thin cloud and aerosol. It emerges that measurements in two channels in the 1.61 μm CO2 absorption band are too sensitive to cloud and aerosol to allow the CO2 column to be inferred with precision better than a few percent in the presence of thin cloud and aerosol. However, simultaneous measurements of optical thickness in the nearby 1.27 μm absorption band of O2 are tightly correlated with those for CO2, even in the presence of aerosol and thin cirrus, and therefore may allow the CO2 column to be determined relative to the O2 column, provided that the latter is known independently from surface pressure. The correlation between O2 and CO2 optical thicknesses depends upon the mean scattering height, but this quantity may be estimated with sufficient accuracy from radiances measured in the O2 band. A prototype algorithm is developed to estimate the CO2 column from data in two CO2 channels and three O2 channels. The algorithm is used to estimate the probable bias and standard error of measurements of CO2 column from space under conditions where the optical thicknesses of aerosol and cirrus may be as large as 0.2 and 0.1, respectively, and where the temperature profile is known to within ±1 K. The simulations suggest that the error in the estimated CO2 column caused by these sources is approximately 0.5%. This conclusion is interpreted cautiously because the analysis assumes inter alia that the spectroscopic properties of both CO2 and O2 are known accurately, that the surface reflectance and the scattering properties of aerosol and cirrus vary predictably between 1.27 μm and 1.61 μm, and that difficult technical issues associated with high spectral resolution measurements can be resolved. Nevertheless, the importance of global measurements of CO2 is such that the method warrants further investigation.
Chemical loss of ozone during the Arctic winter of 1999/2000: An analysis based on balloon‐borne observations
Authors: Salawitch R. J. , Margitan J. J. , Sen B. , Toon G. C. , Osterman G. B. , Rex M. , Elkins J. W. , Ray E. A. , Moore F. L. , Hurst D. F. , Romashkin P. A. , Bevilacqua R. M. , Hoppel K. W. , Richard E. C. , Bui T. P.
Published: October 2002

Simultaneous balloon‐borne observations of ozone (O3) and nitrous oxide (N2O), a long‐lived tracer of dynamical motion, are used to quantify the chemical loss of ozone in the Arctic vortex during the winter of 1999/2000. Chemical loss of ozone occurred between altitudes of about 14 and 22 km (pressures from ∼120 to 30 mbar) and resulted in a 61 ± 13 Dobson unit reduction in total column ozone between late November 1999 and 5 March 2000 (the date of the last balloon‐borne measurement considered here). This loss estimate is valid for the core of the vortex during the time period covered by the observations. It is shown that the observed changes in the O3 versus N2O relation were almost entirely due to chemistry and could not have been caused by dynamics. The chemical loss of column ozone inferred from the balloon‐borne measurements using the “ozone versus tracer” technique is shown to compare well with estimates of chemical loss found using both the Match technique (as applied to independent ozonesonde data) and the “vortex‐averaged descent” technique (as applied to Polar Ozone and Aerosol Measurement (POAM) III satellite measurements of ozone). This comparison establishes the validity of each approach for estimating chemical loss of column ozone for the Arctic winter of 1999/2000.
Ice core evidence of rapid air temperature increases since 1960 in alpine areas of the Wind River Range, Wyoming, United States
Authors: Naftz David L. , Susong David D. , Schuster Paul F. , Cecil L. DeWayne , Dettinger Michael D. , Michel Robert L. , Kendall Carol
Published: October 2002

Site‐specific transfer functions relating delta oxygen 18 (δ18O) values in snow to the average air temperature (TA) during storms on Upper Fremont Glacier (UFG) were used in conjunction with δ18O records from UFG ice cores to reconstruct long‐term trends in air temperature from alpine areas in the Wind River Range, Wyoming. Transfer functions were determined by using data collected from four seasonal snowpacks (1989–1990, 1997–1998, 1998–1999, and 1999–2000). The timing and amount of each storm was determined from an automated snowpack telemetry (SNOTEL) site, 22 km northeast of UFG, and ∼1060 m in elevation below UFG. Statistically significant and positive correlations between δ18O values in the snow and TA were consistently found in three of the four seasonal snowpacks. The snowpack with the poor correlation was deposited in 1997–1998 during the 1997–1998 El Niño Southern Oscillation (ENSO). An ultrasonic snow‐depth sensor installed on UFG provided valuable insights into site‐specific storms and postdepositional processes that occur on UFG. The timing of storms recorded at the UFG and Cold Springs SNOTEL sites were similar; however, selected storms did not correlate. Snow from storms occurring after mid‐October and followed by high winds was most susceptible to redeposition of snow. This removal of lower temperature snowfall could potentially bias the δ18O values preserved in ice core records to environmental conditions reflecting higher air temperatures and lower wind speeds. Transfer functions derived from seasonal snow cover on UFG were used to reconstruct TA values from δ18O values determined from two ice cores collected from UFG. Reconstructed air temperatures from the ice core data indicate an increase in TA of ∼3.5°C from the mid‐1960s to the early 1990s in the alpine areas of northwestern Wyoming. Reconstructed TA from the ice core records between the end of the Little Ice Age (LIA), mid‐1800s, and the early 1990s indicate a TA increase of ∼5°C. The historically reconstructed TA values from the UFG were significantly higher than the global average observed during the 20th Century but were in agreement with TA increases observed at selected, high‐altitude and high‐latitude sites in other parts of the world. Additional research is required to determine if part of the observed trend toward heavier δ18O values in ice from the UFG since the LIA (and increased TA) is due to an increased proportion of snowfall from southerly storm tracks and moisture sources, as seems to have been the situation in 1997–1998.
Energy and water dynamics of a central Amazonian rain forest
Authors: Malhi Y. , Pegoraro E. , Nobre A. D. , Pereira M. G. P. , Grace J. , Culf A. D. , Clement R.
Published: October 2002

This paper presents measurements of the energy and water budgets of a tropical rain forest near Manaus, Brazil, in central Amazonia, collected between September 1995 and August 1996. Fluxes of sensible and latent heat were measured using a three‐dimensional eddy covariance system mounted above the forest canopy. Using a new approach to analysis of eddy covariance data, we found that the measured fluxes increased significantly when turbulent transport on timescales of 1 to 4 hours was taken into account. With this new analysis, the measured turbulent fluxes almost balanced the incoming net radiation, giving increased confidence in the accuracy of the measured fluxes. Of the 5.56 GJ m−2 yr−1 of solar radiation supplied over the year, 11% were reflected, 15% were lost as net thermal emission, 27% were transported through sensible heat convection, 46% used in evapotranspiration, and 0.5% were used in net carbon fixation. Total annual evapotranspiration was calculated to be 1123 mm, accounting for 54% of total precipitation. Seasonality was an important influence: limited water availability during the dry season caused evapotranspiration to reduce by 50%. Total canopy conductance was linearly correlated to soil moisture content, with typical midday values ranging between 0.8 mol m−2 s−1 in the wet season and 0.3 mol m−2 s−1 in the dry season. Such seasonal behavior is likely to be prevalent in most tropical forest regions, and correct description of dry‐season evapotranspiration will require accurate modeling of plant and soil hydraulic properties and knowledge of root distributions.
Development of analytical methods and measurements of 13C/12C in atmospheric CH4 from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network
Authors: Miller John B. , Mack Kenneth A. , Dissly Richard , White James W. C. , Dlugokencky Edward J. , Tans Pieter P.
Published: October 2002

We describe the development of an automated gas chromatography‐isotope ratio mass spectrometry (GC‐IRMS) system capable of measuring the carbon isotopic composition of atmospheric methane (δ13CH4) with a precision of better than 0.1‰. The system requires 200 mL of air and completes a single analysis in 15 min. The combination of small sample size, fast analysis time, and high precision has allowed us to measure background variations in atmospheric δ13CH4 through the NOAA Climate Monitoring and Diagnostics Laboratory Cooperative Air Sampling Network. We then present a record of δ13CH4 obtained from six surface sites of the network between January 1998 and December 1999. The sites are Barrow, Alaska (71°N); Niwot Ridge, Colorado (40°N); Mauna Loa, Hawaii (20°N); American Samoa (14°S); Cape Grim, Tasmania (41°S); and the South Pole (90°S). For the years 1998 and 1999, the globally averaged surface δ13C value was −47.1‰, and the average difference between Barrow and the South Pole was 0.6‰. Consistent seasonal variations were seen only in the Northern Hemisphere, especially at Barrow, where the average amplitude was 0.5‰. Seasonal variations in 1998, however, were evident at all sites, the cause of which is unknown. We also use a two‐box model to examine the extent to which annual average δ13C and CH4 mole fraction measurements can constrain broad categories of source emissions. We find that the biggest sources of error are not the atmospheric δ13C measurements but instead the radiocarbon‐derived fossil fuel emission estimates, rate coefficients for methane destruction, and isotopic ratios of source emissions.
Linear relationships between root‐zone soil moisture and atmospheric processes in the planetary boundary layer
Authors: Basara Jeffrey B. , Crawford Kenneth C.
Published: October 2002

Soil moisture modulates the exchange of mass and energy between the atmosphere and the land surface. This study focuses on the relationship between soil moisture and atmospheric processes at and near the Norman Mesonet site using both automated and field samples of hydrologic and atmospheric parameters. During 1999, measurements were made during an intensive observing period (IOP) that spanned the dates of 1 June to 12 August. Analysis of the observations revealed 13 days were characterized by strong radiative forcing and weak shear in the lower troposphere (defined as ideal or golden days). Though the total number of ideal study days was somewhat limited, observations were collected over a wide range of atmospheric and soil moisture conditions. The results of this study demonstrate that soil water content in the root‐zone at the Norman Mesonet site during the summer of 1999 was linearly correlated with daily‐maximum values of sensible heat flux and latent heat flux on ideal days. Furthermore, the relationship between the mean evaporative fraction calculated during daylight hours and soil water in the root‐zone was strong and linear. However, the relationship between soil water in the surface layer and the mean evaporative fraction was weak and nonlinear. Significant linear relationships were also found to exist between soil water in the root‐zone and atmospheric parameters in the planetary boundary layer including the daily maximum air temperature at 1.5 m, mean potential temperature in the 925‐850 mbar layer, mixing ratio at 1.5 m, and mean mixing ratio in the 925‐850 mbar layer.
Impact of a physically based soil water flow and soil‐plant interaction representation for modeling large‐scale land surface processes
Authors: de Rosnay P. , Polcher J. , Bruen M. , Laval K.
Published: October 2002

The aim of this paper is to improve our understanding and the representation of hydrological and energetic exchanges between the soil, the vegetation, and the atmosphere at the continental scale. The soil hydrology of the land surface scheme Schématisation des Echanges Hydriques l'Interface entre la Biosphère et l'Atmosphère (SECHIBA) is improved. It is derived from the physically based hydrological model of the Centre for Water Resources Research and is adapted to the representation of soil‐plant‐atmosphere interactions at large scale and to the coupling with an atmospheric model. In the new model, soil‐plant interactions result from root‐soil moisture profile interactions, represented on a fine vertical resolution. This allows a better control of land evapotranspiration by soil‐vegetation systems. SECHIBA in this new version takes into account a subgrid‐scale variability of soil texture. Different possibilities of interactions between soil and vegetation variabilities allow the representation of various soil‐plant‐atmosphere systems. It is shown that the distribution of vegetation on the soil and the soil texture influence the way in which soil, plants, and atmosphere interact.
Spatial and temporal variability of trace metals in aerosol from the desert region of China and the Yellow Sea
Authors: Liu C. L. , Zhang J. , Shen Z. B.
Published: October 2002

From spring to early summer of 1995 and 1996, about 180–190 aerosol samples were collected from three observatories at Northwest China desert region (i.e., Minqin), coastal suburb area (i.e., Qingdao), and an island in the Yellow Sea (i.e., Qianliyan), respectively. The samples were analyzed to determine the concentrations of trace metals (Al, Fe, Mn, Na, Cr, Zn, Cu, Co, Ni, Pb, V, Sr, and Cd). Data are examined to understand the distribution of trace metals in aerosols at an upwind desert region and downwind marine recipient under westerly flow. The result shows that trace metal composition of aerosols vary considerably in time and space. Trace metal levels display a drastic seasonal change at both Qingdao and Qianliyan, with concentrations generally 2–3 times higher in spring than summer. Daily variation of trace metal concentrations at Minqin is more significant than Qingdao and Qianliyan, however. The enrichment factors for the crustal source (EFcrust) at Minqin are relatively low and unimportant compared with those at Qingdao and Qianliyan. Some of the trace species like Pb, Zn, and Cd have relatively high contributions from the anthropogenic source (Rp), and >98% are found at Qingdao and Qianliyan, with EFcrust values 1–2 orders of magnitude higher than Minqin. Manganese is mainly from low‐temperature weathering products and the contribution from crustal source (Rc) is >70% at Qingdao and Qianliyan. The coastal atmosphere responds to the episodic dust storms in the desert region (i.e., Minqin) by an increase in aerosol level and a higher concentration of crust‐dominated materials. The percentage contributions from the crustal source (Rc) of trace metals, such as Pb, Cd, and Zn, could be increased considerably by 5–10 folds higher during the passage of cold fronts than during calm weather period over the Yellow Sea.
Diurnal variation in water vapor over North America and its implications for sampling errors in radiosonde humidity
Authors: Dai Aiguo , Wang Junhong , Ware Randolph H. , Van Hove Teresa
Published: October 2002

Diurnal variations in atmospheric water vapor are studied by analyzing 30‐min‐averaged data of atmospheric precipitable water (PW) for 1996–2000 derived from Global Position System (GPS) observations from 54 North America stations. Vertical structures in the diurnal cycle of atmospheric water vapor are examined using 3‐hourly radiosonde data from Lamont, Oklahoma, during the 1994–2000 period. Significant diurnal variations of PW are found over most of the stations. The diurnal (24 hour) cycle, S1, which explains over 50% of the subdaily variance, has an amplitude of 1.0–1.8 mm over most of the central and eastern United States during summer and is weaker in other seasons. The S1 peaks around noon in winter and from midafternoon to midnight in summer. The semidiurnal (12 hour) cycle is generally weak, with an amplitude of a few tenths of 1 mm. At Lamont, specific humidity in the free troposphere is significantly higher in the early morning (0000–0008 local solar time (LST)) than during the day (0800–1800 LST). This diurnal variation changes little from ∼4 to 16 km above the ground. Near the surface, specific humidity tends to be lower in the morning than in the afternoon and evening in all seasons except summer. This near‐surface diurnal cycle propagates upward through the lower troposphere (up to ∼4 km). Errors in seasonal mean humidity due to undersampling the diurnal cycle with twice‐daily synoptic soundings (at 0000 and 1200 UTC) are generally small (within ±3% or ±0.5 mm for PW), but it can easily reach 5–10% if there is only one random sounding per day. Several physical processes are proposed that could contribute to the diurnal variations in atmospheric water vapor.
Transport of methane in the stratosphere associated with the breakdown of the Antarctic polar vortex
Authors: Choi Wookap , Kim Sumi , Grant William B. , Shiotani Masato , Sasano Yasuhiro , Schoeberl Mark R.
Published: October 2002

Transport of methane associated with the polar vortex and its breakdown was observed by the data from the Improved Limb Atmospheric Spectrometer (ILAS) during November and December of 1996. The zonal mean mixing ratio in the middle stratosphere at high latitudes in the Southern Hemisphere increased rapidly during the period, and the vertical gradient of methane sometimes showed an unusual reversal. The reversal of the vertical gradient confirms that the erosion of the vortex and the subsequent breakdown occurs in the upper stratosphere first and descends with time. The variation of the tracer mixing ratio was investigated with respect to the boundary of the polar vortex. The mixing ratios inside and outside of the polar vortex evolved with distinctive patterns with time. The small difference in methane between inside and outside of the vortex in the upper stratosphere is presumably a result of the vortex erosion prior to November. Also, the small difference between inside and outside of the vortex in the lower stratosphere confirms the weak barrier effect of the polar vortex on that altitude. High concentrations of methane observed inside the vortex show mixing of lower‐latitude air into the vortex. An RDF calculation confirms the behavior of methane transport into the vortex.
Unexpected changes in soil phosphorus dynamics along pasture chronosequences in the humid tropics
Authors: Townsend Alan R. , Asner Gregory P. , Cleveland Cory C. , Lefer Margaret E. , Bustamante Mercedes M. C.
Published: October 2002

Phosphorus (P) is widely believed to limit plant growth and organic matter storage in a large fraction of the world's lowland tropical rain forests. We investigated how the most common land use change in such forests, conversion to cattle pasture, affects soil P fractions along pasture chronosequences in the central Brazilian Amazon and in southwestern Costa Rica. Our sites represent a broad range in rainfall, soil type, management strategies, and total soil P (45.2–1228.0 μg P/g soil), yet we found some unexpected and at times quite similar changes in soil P in all sites. In the Brazilian sites, where rainfall is relatively low and pasture management is more intense than in the Costa Rican sites, significant losses in total soil P and soil organic carbon (SOC) were seen with pasture age on already P‐deficient Oxisol and Entisol soils. However, P losses were from inorganic soil P fractions, while organic forms of soil P remained constant or increased with pasture age, despite the declines in SOC. In Costa Rica, SOC remained constant across the Oxisol sites and increased from forest to pasture on the Mollisols, while soil organic P increased with pasture age in both sequences.
Exchange fluxes of NO2 and O3 at soil and leaf surfaces in an Amazonian rain forest
Authors: Gut A. , Scheibe M. , Rottenberger S. , Rummel U. , Welling M. , Ammann C. , Kirkman G. A. , Kuhn U. , Meixner F. X. , Kesselmeier J. , Lehmann B. E. , Schmidt W. , Müller E. , Piedade M. T. F.
Published: October 2002

Trace gas exchange of NO2 and O3 at the soil surface of the primary rain forest in Reserva Biológica Jarú (Rondônia, Brazil) was investigated by chamber and gradient methods. The ground resistance to NO2 and O3 deposition to soil was quantified for dry and wet surface conditions using dynamic chambers and was found to be fairly constant at 340 ± 110 and 190 ± 70 s m−1, respectively. For clear‐sky conditions, the thermal stratification of the air in the first meter from the forest floor was stable during daytime and unstable during nighttime. The aerodynamic resistance to NO2 and O3 deposition to the ground in the first meter above the forest floor was determined by measurements of 220Rn and CO2 concentration gradients and CO2 surface fluxes. The aerodynamic resistance of the 1‐m layer above the ground was 1700 s m−1 during daytime and 600 s m−1 during nighttime. The deposition flux of O3 and NO2 was quantified for clear‐sky conditions from the measured concentrations and the quantified resistances. For both trace gases, deposition to the soil was generally observed. The O3 deposition flux to the soil was only significantly different from zero during daytime. The maximum of −1.2 nmol m−2 s−1 was observed at about 1800 and the mean daytime flux was −0.5 nmol m−2 s−1. The mean NO2 deposition flux during daytime was −1.6 ng N m−2 s−1 and during nighttime −2.2 ng N m−2 s−1. The NOx budget at the soil surface yielded net emission day and night. The NO2 deposition flux was 74% of the soil NO emission flux during nighttime and 34% during daytime. The plant uptake of NO2 and O3 by the leaves of Laetia corymbulosa and Pouteria glomerata, two typical plant species for the Amazon rain forest, was investigated in a greenhouse in Oldenburg (Germany) using branch cuvettes. The uptake of O3 was found to be completely under stomatal control. The uptake of NO2 was also controlled by the stomatal resistance but an additional mesophyll resistance of the same order of magnitude as the stomatal resistance was necessary to explain the observed uptake rate.
Geostrophic wind fields in the stratosphere and mesosphere from satellite data
Authors: Oberheide J. , Lehmacher G. A. , Offermann D. , Grossmann K. U. , Manson A. H. , Meek C. E. , Schmidlin F. J. , Singer W. , Hoffmann P. , Vincent R. A.
Published: October 2002

Daily maps of horizontally resolved zonal and meridional geostrophic wind fields in the altitude range of 20–90 km were obtained from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment during November 1994 and August 1997. Results are compared with zonal mean zonal winds from climatological sources and with assimilated data from standard analyses. Correlative data from ground‐based and balloon‐ and rocket‐borne measurements are used to validate the CRISTA winds. The comparisons show that geostrophic wind fields from high spatial resolution satellite‐borne temperature measurements are a good approximation for the winds in the middle atmosphere up to mesopause heights. Therefore, they may be used as input for further modeling efforts particularly in the mesosphere, where no wind data from standard analyses are available.
Dynamical heating in the polar lower stratosphere and its impact on the tropopause
Authors: Zängl Günther
Published: October 2002

A radiative‐convective model is used to compute dynamical heating rates in the polar lower stratosphere. In contrast to previous studies, full annual cycles are considered, and zonal asymmetries in the Arctic are also taken into account. Moreover, the impact of dynamical heating on the polar tropopause is examined. It is found that substantial zonal asymmetries are present in the Arctic lower stratosphere except in summer when heating rates are generally close to zero. Between September and January, the heating rates outside the polar vortex are at least twice as large as in the polar vortex region. Between February and April, when the polar vortex is eroded by stratospheric warmings, zonal asymmetries decrease. However, meridional heating rate gradients are maximum in February and March since the strongest heating occurs at high latitudes. At 100 hPa, heating rates up to 1 K d−1 are found. In the Antarctic, dynamical heating in the lower stratosphere exhibits a double wave with maxima in spring and autumn and minima in summer and winter. The maximum heating rates are substantially lower than in the Arctic and amount to ∼0.4 K d−1 at 100 hPa. However, dynamical heating is significantly positive even in summer. The simulations indicate that dynamical heating has a fundamental impact on the tropopause, particularly in the north polar region. There, the annual cycle of the tropopause pressure would be entirely different without dynamical heating.
On the variability of tropospheric gases: Sampling, loss patterns, and lifetime
Authors: Johnston Nancy A. C. , Colman Jonah J. , Blake Donald R. , Prather Michael J. , Rowland F. Sherwood
Published: October 2002

The relationship between the variability (relative standard deviation, σ) in mixing ratio of a gas and its global mean lifetime (τ) has been used to estimate the τ of atmospheric gases. This can prove quite useful if it is a unique relationship. Here a three‐dimensional chemical transport model is used to investigate the variability‐lifetime relationship of tropospheric gases with two types of sources and three types of losses. The effects of sampling time and location are also explored. The relationship is best described in the form σ = ατ−β, where α and β are variable depending on the sources, sinks, and time and location of averaging. When spatially averaging over the troposphere and temporally averaging over 1 year, the model results give a β of 0.77–0.79 for τ between 0.9 and 7.0 years. The variability of a CH3Br‐like gas is also analyzed using different weightings of chemical sinks. Photochemical (OH), ocean mixed layer, and soil losses are scaled separately to maintain τ ≈ 1 year. These different scalings result in a ±17% spread in σ, which translates into a ±20% spread in τ inferred from the variability‐lifetime relationship found in the model. In addition, the model is used to simulate conditions of Pacific Exploratory Mission (PEM) Tropics A and B field campaigns. The variability‐lifetime relationships derived from the model do not compare to the field observations, except that both demonstrate a seasonal dependence of variability. This study identifies some factors controlling the variability of trace gases in the troposphere, estimates the error in using variability‐lifetime analysis to determine an unknown τ, and shows that the variability‐lifetime relation is not universal among trace gases.
Tropical snowline depression at the Last Glacial Maximum: Comparison with proxy records using a single‐cell tropical climate model
Authors: Greene Arthur M. , Seager Richard , Broecker Wallace S.
Published: October 2002

The substantial lowering of tropical snowlines at the Last Glacial Maximum (LGM), circa 21 kya, is examined using a modified version of the single‐cell tropical climate model ofBetts and Ridgway[1989]. These authors concluded that it was difficult to reconcile the large depression of snowlines at the LGM with the small reduction in mean tropical sea‐surface temperature (SST) of the Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) reconstruction. Here, climatic implications of the snowline depression are compared, not with CLIMAP, but with temperature proxies (δ18O and Sr/Ca ratios in corals, noble gas concentrations in aquifers, alkenone and Mg/Ca ratios in deep‐sea sediments and recent faunal reconstructions) whose LGM values have been interpreted as implying lower surface temperatures in the tropics. It proves difficult, in the framework of this model, to reconcile the coldest of the indicated paleotemperatures with the observed snowline depression, which by itself is found to be consistent with an SST reduction of ∼3 K. A cooling of this magnitude corresponds most closely to recent warm‐pool LGM sea‐surface temperature estimates based on Mg/Ca paleothermometry. Discordance among the various proxy reconstructions may result, at least in part, from regional variations in surface temperature change at the LGM.