bluuebunny/crossref_metadata_2025 huggingface dataset:
A model analysis of the tropical South Atlantic Ocean tropospheric ozone maximum: The interaction of transport and chemistry
Authors: Moxim W. J. , Levy H.
Published: February 2004

The meteorological and photochemical nature of the South Atlantic Ocean tropospheric column ozone maximum is examined by analyzing the Geophysical Fluid Dynamics Laboratory (GFDL) Global Chemical Transport Model (GCTM) simulation during the Southern Hemisphere late winter. An ozone maximum of greater than 40 Dobson units is produced by the GCTM over the South Atlantic Ocean. The model is evaluated against available meteorological and ozone data and found to be in good qualitative agreement with observed wind fields, satellite measurements of tropospheric column ozone, tropospheric column ozone produced from ozonesonde data, and vertical profiles from ozonesondes. A quantitative analysis is performed over an area of the South Atlantic Ocean essentially devoid of local NOx sources and for a time, September, when the regional tropospheric ozone mass is at a maximum. The tropospheric mass of reactive nitrogen transported into the region is a result of source contributions from lightning (49%), biomass burning (36%), and 15% from the remaining NOx sources (fossil fuel plus biogenic plus stratosphere plus aircraft). Even with the removal of biomass burning NOx from the ozone photochemical system, the GCTM still produces an oceanic tropospheric column ozone maximum, suggesting the ozone phenomenon existed before agricultural burning by humans. The structure of clean air CO/CH4 net chemistry consists of ozone production in the upper troposphere (+2.2 Tg/month), weak destruction in the middle troposphere (−1.8 Tg/month), and strong destruction in the lower troposphere (−4.2 Tg/month). Through photochemistry, the two largest NOx sources help control the vertical profile of ozone with lightning dominating in the upper troposphere, while the relative importance of biomass burning is virtually constant throughout the troposphere. A mass budget analysis of ozone over the tropospheric South Atlantic Ocean reveals that net mass transport of ozone into the domain is nearly balanced by net chemical destruction and deposition and that the mass transport into and out of the region are comparable to the chemical production and destruction terms. The three‐dimensional circulation governing the ozone vertical structure is one of horizontal mass convergence and net chemical production supplying ozone to the upper troposphere which is fluxed downward by subsidence and removed in the boundary layer by net chemical destruction, deposition, and horizontal mass divergence.
Interannual Atmosphere‐Biosphere Variation: Implications for observation and modeling
Authors: Prince S. D. , Goward S. N. , Goetz S. , Czajkowski K.
Published: February 2004

Climate‐land surface interactions have been mainly investigated either in terms of short‐term modification of fluxes of matter, momentum, and energy, which primarily affect the atmosphere, or in the long‐term, biogeographical impacts of climatic conditions on the type of vegetation that occupies a site. Logically, there must be time and space scales at which these short‐term and biogeographical climate‐land surface interactions are both relevant. It is proposed that it is these intermediate scales, at which physiological and biogeographical processes cannot easily be separated, which are most relevant in the study of climate change, and that new analytical and modeling approaches are needed which include both. Moreover, periods of rapid climate change and periods of increasing anthropogenic impacts on the land surface can be expected to induce a wide range of transient vegetation dynamics. The timescale of interest here excludes equilibria and demands a consideration of the outcomes of processes that have a wide variety of temporal frequencies. A recent workshop brought together ecologists and climatologists with interests in observing, modeling, and predicting the dynamics of land‐atmosphere processes at the inteannual to decadal timescale. The result was a proposal to exploit recently developed archives of remotely sensed data and others such as paleobotanical and paleoclimatological records in order to advance beyond the polarized concept of land‐atmosphere processes which comes from a consideration only of short and long time periods, while ignoring their interactions. The new demands of this agenda for observational and analytical methods are considered.
Parameter estimation of GOES precipitation index at different calibration timescales
Authors: Xu Liming , Gao Xiaogang , Sorooshian Soroosh , Imam Bisher
Published: February 2004

We examined two techniques that adjust the parameters of the GOES Precipitation Index (GPI) by combining the polar microwave and the geosynchronous infrared observations at three frequencies: daily, pentad, and monthly. The first technique is the adjusted GPI (AGPI), and the second is the universally adjusted GPI (UAGPI). The study shows that rainfall estimates can be improved by frequent calibrations providing there is sufficient superior (microwave) rainfall sampling within the calibration time and space domain. For this work, daily and pentad calibrations produce monthly rainfall estimates almost as good as monthly calibration. The daily calibration produced better daily rainfall estimates than pentad and monthly calibration, but it generates similar pentad rainfall estimates to these of the pentad calibration. The monthly calibrated scheme is not suitable for the daily and pentad rainfall estimates. Under the current twice‐per‐day sampling rate of polar‐orbiting microwave observations, the pentad calibration scheme is suggested for the monthly, pentad, and daily rainfall. The potentials of applying the UAGPI and the AGPI techniques for daily rainfall estimation are also investigated.
Evolution and chemical consequences of lightning‐produced NOx observed in the North Atlantic upper troposphere
Authors: Crawford J. , Davis D. , Olson J. , Chen G. , Liu S. , Fuelberg H. , Hannan J. , Kondo Y. , Anderson B. , Gregory G. , Sachse G. , Talbot R. , Viggiano A. , Heikes B. , Snow J. , Singh H. , Blake D.
Published: February 2004

Airborne observations of NO during the Subsonics Assessment Ozone and Nitrogen Oxides Experiment (SONEX) reveal episodes of high NOx in the upper troposphere believed to be associated with lightning. Linkage to specific periods of lightning activity is possible through back trajectories and data from the National Lightning Detection Network. Lagrangian model calculations are used to explore the evolution of these high NOx plumes over the 1–2 days between their introduction and subsequent sampling by NASA's DC‐8 aircraft. Simulations include expected changes in HNO3, H2O2, CH3OOH, HO2, and OH. Depending on the time of injection and dilution rate, initial NOx concentrations are estimated to range from 1 to 7 ppbv. Similar to many previous studies, simulated HNO3 concentrations tend to be greater than observations. Several possible explanations for this difference are explored. H2O2 observations are shown to be consistent with removal in convective activity. While it is possible that upper tropospheric CH3OOH is enhanced by convection, simulations show such increases in CH3OOH can be short‐lived (e.g., <12 hours) with no perceptible trace remaining at the time of sampling. High NO levels further prevent elevated levels of CH3OOH from propagating into increases in H2O2. HO2 is suppressed through reaction with NO in all cases. Simulated increases in OH exceeded a factor of 2 for some cases, but for the highest NOx levels, loss of OH via OH+NO2 offset production from HO2+NO. Additional increases in OH of 30–60% could result from convection of CH3OOH. A final point of discussion concerns how the chemistry within these plumes, their long‐range transport, and their potential importance in sustaining background NOx far from source regions present a challenge to global and regional model simulations.
Enthalpy and entropy changes in formation of gas phase sulfnric acid monohydrates and dihydrates as a result of fitting to experimental pressure data
Authors: Noppel Madis
Published: February 2004

The values of enthalpy change ΔH1 = −44.3 kJ/mol and entropy change ΔS1 = −94.6 J/mol in the gas phase addition of a water molecule to a sulfuric acid molecule and entropy change ΔS2 = −145 J/mol in hydration of a sulfuric acid monohydrate are obtained by a fitting procedure. The procedure uses experimental data from the literature on total pressure of sulfuric acid hydrates and free molecules. The enthalpy change in monohydrate hydration is taken, based on the results of ab initio calculations given in literature, to be ΔH2 = ΔH1 ‐ 10 kJ/mol. The estimate of covariance matrix of uncertainties of these values is obtained. The standard errors of estimates of ΔH1, ΔS1, and ΔS2 are 43%, 63%, and 45% of the above values, respectively. Uncertainties are strongly correlated. The sulfuric acid hydration model is proposed for geophysical applications. The model converts total acid to free acid in accordance with experimental measurements and increases the predicted values of sulfuric acid‐water nucleation rate by 102–107 times compared with the classical liquid drop hydrate model.
Shortwave, single‐scattering properties of arctic ice clouds
Authors: Garrett Timothy J. , Hobbs Peter V. , Gerber H.
Published: February 2004

The first direct airborne measurements of the asymmetry parameter (g) and extinction coefficient (βext) of clouds are analyzed. The measurements were obtained with a Cloud‐Integrating Nephelometer (CIN) in arctic clouds in May and June 1998. The CIN was evaluated by comparing its measurements of the single‐scattering properties of water clouds with values from Mie theory using measurements of the droplet size spectra. These results are used to interpret CIN measurements of the single‐scattering properties of ice and mixed‐phase clouds. For cirrus clouds composed solely of ice crystals the derived value of g was 0.74±0.03 (or 0.76±0.03 if ice crystal faces are assumed to be perfectly smooth and parallel); this value is significantly lower than that calculated assuming the ice crystals to be hexagonal prisms or bullet rosettes. The CIN measurements of βext for cirrus clouds were several times greater than values derived from measurements of the cross‐sectional areas and concentrations of the ice crystals. Several possible explanations for the differences between calculated and measured optical properties of the ice clouds are discussed. The measured values of g for mixed‐phase clouds depended on the relative concentrations of water and ice. These results are used to show that the albedo of clouds is particularly sensitive to the onset of ice formation. Weak convective clouds and clouds saturated with respect to liquid water generally had higher values of g than those for nonconvective clouds or clouds saturated with respect to ice but subsaturated with respect to liquid water.
Water vapor density effect on measurements of trace gas mixing ratio and flux with a massflow controller
Authors: Lee Xuhui
Published: February 2004

One configuration in measurements of trace species in the atmosphere uses a massflow controller to regulate airflow through a device that traps the species of interest. Because the flow controller is calibrated with dry air, correction should be made to account for the density effect of water vapor in the ambient air. A common type of massflow controller regulates the flow by measuring temperature difference along a heated tube. It is shown that for these units the true mixing ratioSc(ratio of mass of trace speciescto mass of dry air) is related to the apparent mixing ratioSc(measurement before correction), asSc= (1+1.85r)Sc, whereris water vapor mixing ratio of the ambient air, typically varying in the range 0–0.04. Correction should also be made to the surface‐air flux measured with such an apparatus in conjunction with micrometeorological flux gradient or relaxed eddy accumulation method and flux chambers; this involves a correction term proportional to surface evaporation rate and for some measurement configurations the same scale factor (1+1.85r) as forSc. Examples are given for gaseous mercury to illustrate the magnitude of these corrections. No correction is needed if moisture is removed from the airstream before it enters the massflow controller.
Analysis of residual mean transport in the stratosphere: 1. Model description and comparison with satellite data
Authors: Schneider Hans R. , Jones Dylan B. A. , McElroy Michael B. , Shi Guang‐Yu
Published: February 2004

A coupled two‐dimensional model of the dynamics, chemistry, and radiation of the stratosphere is described. The effects of Rossby wave mixing are parameterized by externally specified coefficients Kyy, which are used consistently in the zonal mean momentum equation and the diffusion term of the tracer transport equation. Rossby wave mixing is reduced in the tropics. Transport between the tropics and midlatitudes is controlled by advection in the model. It is shown that subtropical tracer gradients [e.g., Trepte and Hitchman, 1992; Randel et al., 1993] are produced as a consequence of the difference between advective timescales in the tropics and the diffusive time scale in midlatitudes. In the annual mean, the flow of air is directed from the tropics toward midlatitudes. However, advection between tropics and midlatitudes takes place in both directions at stratospheric altitudes at any given time. Calculated temperatures show some discrepancies with observations in the polar regions. Distributions of long‐lived tracers are compared with observations made by instruments aboard the Upper Atmospheric Research Satellite and data from the Atmospheric Trace Molecule Spectroscopy Experiment. Tropical and midlatitude profiles calculated by the model are in reasonable agreement with observations. The sensitivity of calculated temperatures and distributions of long‐lived tracers to the choice of large‐scale diffusion coefficients, Kyy, is shown to be small due to the dual role of Kyy in determining diffusive tracer transport and providing a forcing term for the mean circulation [Holton, 1986].
Determining the source of strong LF/VLF TIPP events: Implications for association with NPBPs and NNBPs
Authors: Zuelsdorf R. S. , Franz R. C. , Strangeway R. J. , Russell C. T.
Published: February 2004

Transionospheric pulse pairs (TIPPs) as detected by the Blackbeard VHF radio instrument onboard the ALEXIS satellite have been shown to correlate with pulses detected by stations in the National Lightning Detection Network (NLDN). The short peak‐to‐zero time of these NLDN‐detected pulses (<10 μs) are indicative of interior cloud processes, as opposed to the longer pulses associated with cloud‐to‐ground discharges. TIPPs are most probably generated by the same discharge responsible for narrow bipolar pulses (NBPs), which have been detected on the ground but are also believed to be generated entirely inside the cloud. Here we report on five TIPPs detected by Blackbeard that are correlated with cloud‐generated pulses detected by multiple stations in the NLDN during powerful storms. Previously, a maximum of two stations at a time showed such a correlation. Given the greater area of detection, these pulses radiate more powerfully in the LF/VLF frequencies than those previously detected as TIPPs by Blackbeard. We are able to place the sources of the TIPPs in Hurricane Fausto off the coast of Mexico, and in a remnant of the same storm eight days later over Texas. The heights of the sources are higher than those previously determined for TIPPs. The higher altitudes and the greater power of the TIPP‐correlating signals may be related to the intensity of the storms. Two of these five TIPPs were also correlated with the ground detection of HF signals, and the TIPPs and HF signals were determined to originate from the same source region. These HF signals are similar to those previously recorded with the field change signature of narrow positive bipolar pulses (NPBPs), but we find that both polarities are detected, four out of the five being negative. This indicates that TIPPs correlate with narrow negative bipolar pulses (NNBPs) as well as NPBPs. The detection of NNBPs, which has previously been much rarer than NPBPs, may also be related to the intensity of the storms and the resultant higher‐altitude sources.
A convective kinematic trajectory technique for low‐resolution atmospheric models
Authors: Freitas S. R. , Dias M. A. F. Silva , Dias P. L. Silva , Longo K. M. , Artaxo P. , Andreae M. O. , Fischer H.
Published: February 2004

This paper presents a simple methodology to take into account the subgrid effects of wet convective processes to trace vertical motion of air parcels for low‐resolution atmospheric models. Such models are used for wind field simulations that serve as input for trajectory models. Air parcels in moist convective regions can thus be vertically transported to the cumulus top level with the short timescale associated with cumulus updrafts. Two cases are presented: wet and dry seasons in Amazonia, showing the differences of trajectories followed by air parcels with and without the methodology. The implications for the interpretation of air chemistry measurements are discussed, and an example using LBA/CLAIRE data is used to point out the usefulness of the convective kinematic trajectory technique presented here.
Comparison of model‐estimated and measured diffuse downward irradiance at surface in cloud‐free skies
Authors: Halthore Rangasayi N. , Schwartz Stephen E.
Published: February 2004

Diffuse downward shortwave irradiance at the surface arises from the scattering of radiation by molecules and aerosol particles. Recently, we reported that pyranometer‐measured diffuse solar irradiance in cloud‐free atmospheres is overestimated by radiative transfer models at two low‐altitude sites by an amount that exceeds modeling and measurement uncertainties but is correctly estimated within these uncertainties at two high‐altitude sites [Halthore et al., 1998]. Here we explore this phenomenon in detail, with more cases and improved uncertainty analysis, confirming that the excess in modeled diffuse irradiance cannot be explained by uncertainties in measurements or aerosol‐scattering properties that are input into the radiative transfer models or by errors in multiple‐scattering schemes. The phenomenon is observed for all comparisons with data obtained intermittently over a 5‐year period at the low‐altitude sites. Model computations also exceed radiometer‐measured sky radiance along the solar almucantar. Despite the inconsistencies between measured and modeled diffuse irradiance, atmospheric transmittance models correctly compute direct normal solar irradiance at all sites. These results indicate that at low altitudes a continuum atmospheric absorption process accounting for 0.022±0.01 in vertical optical thickness at 550 nm, corresponding to 4±2% absorptance, may need to be included in radiative transfer models and in models that retrieve aerosol optical thickness from extinction measurements. This is a substantial excess absorption with major implications for climate modeling and weather forecasting. In remote sensing studies, neglect of this excess absorption would lead to substantial errors in satellite sensor calibration and satellite inferred top‐of‐atmosphere flux. An agent or process for this absorption has not yet been identified.
On temperate sources of bromoform and other reactive organic bromine gases
Authors: Carpenter L. J. , Liss P. S.
Published: February 2004

Current estimates of annual bromoform production by temperate marine algae underestimate, by at least an order of magnitude, the flux required to sustain atmospheric concentrations. In the light of recent evidence of the potential of bromoform to deplete upper‐tropospheric/lower‐stratospheric ozone, such a substantial discrepancy in global emission rates is of considerable concern. Here we present new information on air and seawater CHBr3, CH2Br2, and CHBr2Cl concentrations in the coastal east Atlantic and review previous data from widespread locations which suggest that concentrations and ratios of reactive organobromines are consistent with marine macroalgal emissions. Detailed reviews of algal halocarbon emissions and biomass estimates imply that macroalgae produce around 70% of the world's bromoform, rather than only ∼20% as previously thought, and that the underestimation was most likely caused by over conservative biomass estimates. Our total global source strength estimate of 2.2×1011 g CHBr3 yr−1 agrees well with recent calculations derived from atmospheric data. Given the dominant role of macroalgae in producing bromoform, the effect of changing climate and environment on seaweed populations and consequent effect on biogenic bromine emissions should be investigated.
Dynamical climatology of the NASA Langley Research Center Interactive Modeling Project for Atmospheric Chemistry and Transport (IMPACT) model
Authors: Pierce R. Bradley , Al‐Saadi Jassim A. , Eckman Richard S. , Fairlie T. Duncan , Grose William L. , Kleb Mary M. , Natarajan Murali , Olson Jennifer R.
Published: February 2004

A comparison of the NASA Langley Research Center (LaRC) Interactive Modeling Project for Atmospheric Chemistry and Transport (IMPACT) model's dynamical characteristics with assimilated data sets and observations is presented to demonstrate the ability of the model to represent the dynamical characteristics of Earth's troposphere and stratosphere. The LaRC IMPACT model is a coupled chemical/dynamical general circulation model (GCM) of the Earth's atmosphere extending from the surface to the lower mesosphere. It has been developed as a tool for assessing the effects of chemical, dynamical, and radiative coupling in the stratosphere on the Earth's climate. The LaRC IMPACT model winds and temperatures are found to be in fairly good agreement with Upper Atmospheric Research Satellite (UARS) United Kingdom Meteorological Office (UKMO) assimilated winds and temperatures in the lower stratosphere. The model upper stratospheric zonal mean temperatures are also in good agreement with the UARS‐UKMO climatology except for a cold winter pole which results from the upward extension of the cold vortex temperatures and an elevated winter stratopause in the model. The cold pole bias is consistent with the overprediction of the winter stratospheric jet strength, and is characteristic of stratospheric GCMs in general. The model northern and southern hemisphere stratospheric eddy heat and momentum fluxes are within the expected interannual variability of the UARS‐UKMO climatology. The combined effects of water vapor transport, radiative, convective, and planetary boundary layer parameterizations are shown to produce tropospheric winds and circulation statistics that are in good agreement with the UARS‐UKMO climatology, although the model tropopause and upper tropospheric temperatures are generally cold relative to the UARS‐UKMO temperatures. Comparisons between the model and UARS‐UKMO climatology indicate that the model does a reasonable job in reproducing the frequency of observed synoptic‐scale storms during the northern and southern hemisphere winters. Generally good agreement is found between the model and observations in the distribution of outgoing longwave radiation and precipitable water. However, the model precipitation and cloud distributions are influenced by spectral truncation errors which indicate that the T32 spectral resolution of the model is probably not adequate to accurately represent coupling between localized convection and large‐scale water vapor transport. The agreement between the observed and model stratospheric circulation and temperatures, reasonableness of the model stratospheric wave driving, and stability of the model climatology provides confidence that the LaRC IMPACT model is appropriate for multiyear coupled radiation/chemistry/dynamics studies of the stratosphere.
Episodic modeling of the chemical structure of the troposphere as revealed during the spring MLOPEX 2 intensive
Authors: Hess P. G. , Flocke S. , Lamarque J.‐F. , Barth M. C. , Madronich S.
Published: February 2004

An episodic regional chemical transport model (CTM) is described and applied to modeling the vertical chemical structure of the troposphere, as revealed from aircraft flights in the vicinity of Hawaii during the springtime Mauna Loa Observatory Photochemistry Experiment 2c intensive. The CTM simulates the chemistry and transport of 50 species within the North Pacific basin. It is driven by output fields from the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Modeling System. The modeled meteorology is highly correlated with European Centre for Medium‐Range Weather Forecasts analyses on the large scale but is not accurate enough to correctly simulate the long‐range transport of chemical plumes. The simulated total cloud cover is approximately correct when compared with International Satellite Cloud Climatology Project cloud cover. However, the coverage of low‐lying clouds is overpredicted, while the upper level cloudiness is underpredicted. Modeled and satellite‐derived deep convection are reasonably correlated. The measured concentrations of H2O2, CH3OOH, CO, NOy, and O3 are compared with simulated concentrations from the marine boundary layer to approximately 9 km. Although pronounced chemical plumes and vertical layering complicate the model‐measurement comparison, modeled and measured concentrations are generally within a factor of 2. with H2O2 particularly well simulated. A number of measured transient chemical events are examined. This study provides the necessary background for subsequent papers examining the chemistry and transport of the Pacific basin in more detail.
Identification of a transient electric dipole over a conducting half space using a simulated annealing algorithm
Authors: Popov M. , He S.
Published: February 2004

Identification of a transient electric dipole over a conducting half‐space by measuring fields at two ground points is considered. A simulated annealing algorithm (a global optimization method which mimics the slow cooling behavior of an atomic system with many degrees of freedom) is used to reconstruct the location, the orientation, and the transient moment of the dipole in multiple steps. Numerical examples are studied for a dipole (tested at three different positions) over three typical conducting half‐spaces, namely, seawater, dry earth, and fresh water. The identification results based on a ‘perfectly conducting half‐space model’ search and a ‘finitely conducting half‐space model’ search are compared.
Factors controlling nitrate in ice cores: Evidence from the Dome C deep ice core
Authors: Röthlisberger Regine , Hutterli Manuel A. , Sommer Stefan , Wolff Eric W. , Mulvaney Robert
Published: February 2004

In order to estimate past changes in atmospheric NOx concentration, nitrate, an oxidation product of NOx, has often been measured in polar ice cores. In the frame of the European Project for Ice Coring in Antarctica (EPICA), a high‐resolution nitrate record was obtained by continuous flow analysis (CFA) of a new deep ice core drilled at Dome C. This record allows a detailed comparison of nitrate with other chemical trace substances in polar snow under different climatic regimes. Previous studies showed that it would be difficult to make firm conclusions about atmospheric NOx concentrations based on ice core nitrate without a better understanding of the factors controlling NO3− deposition and preservation. At Dome C, initially high nitrate concentrations (over 500 ppb) decrease within the top meter to steady low values around 15 ppb that are maintained throughout the Holocene ice. Much higher concentrations (averaging 53 ppb) are found in ice from the Last Glacial Maximum (LGM). Combining this information with data from previous sampling elsewhere in Antarctica, it seems that under climatic conditions of the Holocene, temperature and accumulation rate are the key factors determining the NO3− concentration in the ice. Furthermore, ice layers with high acidity show a depletion of NO3−, but higher concentrations are found before and after the acidity layer, indicating that NO3− has been redistributed after deposition. Under glacial conditions, where NO3− shows a higher concentration level and also a larger variability, non‐sea‐salt calcium seems to act as a stabilizer, preventing volatilization of NO3− from the surface snow layers.
Interannual variability of global terrestrial primary production: Results of a model driven with satellite observations
Authors: Goetz Scott J. , Prince Stephen D. , Small Jennifer , Gleason Arthur C. R.
Published: February 2004

Interannual variation in terrestrial net primary production (NPP) was modeled using the global production efficiency model (GLO‐PEM), a semimechanistic plant photosynthesis and respiration model driven entirely with satellite advanced very high resolution radiometer (AVHRR) observations. The model also estimated a wide range of biophysical variables at 10‐day intervals for the period 1982–1989, including air temperature, vapor pressure deficit, soil moisture, biomass, autotrophic respiration, canopy‐absorbed photosynthetically active radiation, gross primary production, and light use efficiency. The accuracy of the simulated variables has previously been shown to be within 10–30% of field measurements, depending on the specific variable. We analyze here interannual changes in NPP, which showed large spatial variability (0–1500 gC m−2 yr−1) and trends that differed regionally over the 8‐year period. Annually integrated global NPP was found to vary as much as 12% between years and was very sensitive to air temperature. The coefficient of variation in NPP of sparsely vegetated areas (mostly semiarid) on an interannual basis was as much as 80%, whereas densely vegetated areas (broadleaf evergreen and seasonally deciduous forests) varied comparatively little (0–10%). Mean annual NPP of the latter decreased 36 gC m−2 yr−1 over the time series examined. There was extreme seasonal and moderate interannual variation (10–60%) in NPP of middle‐ to high‐latitude regions (temperate and boreal forests) with evidence for a slight trend toward increased values through time (+3 to 12 gC m−2 yr−1). The results indicate significant interannual and regional differences in responses to climate variability, with boreal regions increasing 39 gC m−2 yr−1 compared to a decrease of 116 gC m−2 yr−1 in tropical regions for each 1°C rise in air temperature. We explore a few of the possible reasons for these observations and discuss some of the issues and limitations to the use of the current global AVHRR observational record.
Surface water balance of the continental United States, 1963–1995: Regional evaluation of a terrestrial biosphere model and the NCEP/NCAR reanalysis
Authors: Lenters John D. , Coe Michael T. , Foley Jonathan A.
Published: February 2004

The land surface water balance of the continental United States is analyzed from 1963 to 1995 using a terrestrial biosphere model (IBIS), reanalysis data from NCEP/NCAR, a hydrologic routing model (HYDRA), and numerous observational data sets. Emphasis is placed on evaluating the performance of IBIS and the reanalysis, particularly over the central United States. IBIS is forced with daily climatic inputs from NCEP; an additional simulation is performed using observed precipitation. The NCEP reanalysis is found to have excessive precipitation and evapotranspiration over the central United States (particularly in the summertime), an exaggerated seasonal cycle of runoff, and low snow depths. The net surface water balance exhibits a dry bias that is corrected by nudging soil moisture toward climatology. Unfortunately, this correction term is large and appears to have a detrimental impact on other water balance components (particularly runoff). Fields that are reasonably well simulated in the reanalysis include fall and winter precipitation over the central United States, soil moisture in Illinois, and interannual variations in runoff. Results from the IBIS simulations show generally better agreement with observations than the NCEP reanalysis but continue to have nontrivial errors in certain fields. Over the central United States, these discrepancies include high winter/spring evapotranspiration (1 mm d−1 too high), low snow depth, and weak spring runoff (30–50% too low). The errors are at least partially caused by underestimated cloud cover and early spring green‐up. A spatial analysis of the U.S. water balance reveals that some of the strongest seasonal and interannual variations in precipitation, evapotranspiration, and soil moisture occur over the central United States.
The evolution of the boundary layer and its effect on air chemistry in the Phoenix area
Authors: Fast J. D. , Doran J. C. , Shaw W. J. , Coulter R. L. , Martin T. J.
Published: February 2004

During a 4‐week period in May and June of 1998, meteorological and chemical measurements were made as part of a field campaign carried out in the Phoenix area. Data from the field campaign provide the first detailed measurements of the properties of the convective boundary layer in this area and of the effects of these properties on ozone levels. The meteorological and chemical measurements have been combined with results from a set of meteorological, particle, and chemistry models to study ozone production, transport, and mixing in the vicinity of Phoenix. Good agreement between the simulations and observations was obtained, and the results have been used to illustrate several important factors affecting ozone patterns in the region. Heating of the higher terrain north and east of Phoenix regularly produced thermally driven circulations from the south and southwest through most of the boundary layer during the afternoon, carrying the urban ozone plume to the northeast. The combination of deep mixed layers and moderate winds aloft provided good ventilation of the Phoenix area on most days so that multiday buildups of locally produced ozone did not appear to contribute significantly to ozone levels during the study period. Sensitivity simulations determined that 20 to 40% of the afternoon surface ozone mixing ratios (corresponding to 15 to 35 ppb) were due to vertical mixing processes that entrained reservoirs of ozone into the growing convective boundary layer. The model results also indicated that ozone production in the region is volatile organic compound limited.
NDSC millimeter wave ozone observations at Lauder, New Zealand, 1992–1998: Improved methodology, validation, and variation study
Authors: Tsou J. J. , Connor B. J. , Parrish A. , Pierce R. B. , Boyd I. S. , Bodeker G. E. , Chu W. P. , Russell J. M , Swart D. P. J. , McGee T. J.
Published: February 2004

A ground‐based millimeter wave radiometer for the Network for the Detection of Stratospheric Change (NDSC) was installed at Lauder, New Zealand (45°S, 169.7°E) in November 1992. It has been monitoring the middle atmospheric ozone with nearly continuous operation since then. Owing to special complications in the observing conditions at this southern midlatitude site, three refinements to the data analysis and calibration techniques were proposed: (1) the use of a radiative model of local tropospheric climate adopted to the low surface elevation of the observing site, (2) the correction of observing angle measurements due to the settling of the foundation of the site, and (3) the improved method of radiometric temperature determination of calibration sources. All data from 1992 to 1998 were reprocessed with these modifications implemented. The retrieved ozone profiles are compared to sonde, two lidars, and satellite (Halogen Occultation Experiment (HALOE), Stratospheric Aerosol and Gas Experiment (SAGE II)) overpass measurements. The agreement is very good, with mean differences from 56 to 1 mbar of generally 2–3% for the comparisons with sonde, HALOE, and SAGE II, and generally <5% for the comparisons with lidars when large samples are considered. The root‐mean‐square scatter about the mean differences is mostly consistent with the expected (combined) precision. In comparisons with these correlative measurements, the millimeter wave ozone observations are found to have no seasonal bias, no comparison bias due to the a priori profiles used in millimeter wave data retrievals, and no observable instrument drift from 1992 to 1998. Better agreement is found in the comparison with sonde data if suspected vertical shifts in the sonde profiles are considered. The variations seen in the 6 year millimeter wave ozone data are shown to be mostly in line with photochemistry and dynamic transport processes in the mid austral latitudes. These processes, however, are apparently modulated somewhat by the Antarctic polar vortex circulation in winter seasons in the upper stratosphere.
Model study of stratospheric chlorine activation and ozone loss during the 1996/1997 winter
Authors: van den Broek M. M. P. , Bregman A. , Lelieveld J.
Published: February 2004

Chlorine activation and ozone depletion in the Arctic winter stratosphere of 1996–1997 have been studied with a newly developed stratospheric chemistry‐transport model (CTM). The chemistry scheme, using a Euler Backward Iterative approximation method, includes a comprehensive set of reactions on ternary aerosol and ice particles, which has been tested against a numerically exact solver. Tracer transports in the CTM are calculated from European Centre for Medium‐Range Weather Forecasts (ECMWF) meteorological analyses. Comparisons have been made with O3 and ClO measurements, and with ozone loss rates derived from observations during February and March 1997. ClO production and ozone depletion are somewhat underestimated by the model. Furthermore, uncertainties regarding the aerosol phase are tested. Assuming nitric acid trihydrate (NAT) particles to form at their melting point, while liquid aerosol is present simultaneously in the model, gives rise to the largest ClO production and the strongest ozone depletion. By correcting for an ECMWF temperature warm bias we obtain a similar large effect on calculated ClO production and ozone depletion for the 1996/1997 Arctic winter, whereas uncertainties in the chlorine abundance seem less important. An average warm bias of 1.3 K at polar stratospheric cloud temperatures on the 50 hPa model level reduces the calculated ozone depletion rates over February and March by 35%. Observations of ClO are reproduced when lower temperatures and maximum Cly abundance are assumed, but ozone depletion is slightly overestimated in that case.
Mass balance of the atmospheric aerosol in a South African subtropical savanna (Nylsvley, May 1997)
Authors: Puxbaum H. , Rendl J. , Allabashi R. , Otter L. , Scholes M. C.
Published: February 2004

Aerosol samples were collected at Nylsvley Natural Reserve in northeastern South Africa at the beginning of the dry season, when large‐scale fires were absent. Aerosol was collected on quartz fiber filters with open face stack filters in an inlet with an upper cutoff mass median diameter of 30 μm;. The samples were analyzed for soluble ions (Cl−, NO3−, SO42−, oxalate, NH4+, Na+, K+, Ca2+, Mg2+), trace metals and crustal elements (Fe, Mn, Ca, Mg, Pb, Cu, Ag, Cd), “black carbon” (BC), total carbon (TC); and in selected samples for aerosol humidity, for mono‐ and dicarboxylic acids and other polar organic components, and for cellulose as a tracer for plant debris. Aerosol mass balances for the individual samples were constructed from the sum of following groups: Humidity (determined as weight loss at 100°C with a microthermobalance), ammonium sulfate, Cl− and NO3−, organic material, BC, and soil dust. On the average, the fit between the sum of the determined groups of components and the gravimetrically determined mass was within 6%, whereas deviations ranged for individual samples from −12 to +27% relative to the gravimetrically determined mass. The main component in aerosol was soil dust (36%), followed by organic material (28%), and ammonium sulfate (27%). Humidity was 6%, BC was 2%, and Cl− and v were 1% of aerosol mass. The low BC/TC ratio of 0.09 indicated little influence from combustion sources. The diurnal trend of the BC/TC ratio of 0.06 during day and 0.14 during night indicated a daytime source for organic components with no BC associated. As there were no industrial or other anthropogenic sources evident, the daytime source of organic components is assumed to be gas‐particle conversion from biogenic emissions. Plant debris and organic acids were the major analytically accessible groups; however, together they form only 7.2% of the carbonaceous material. With 0.4% other polar organics and 5.7% BC in this group, 86.7% of the carbonaceous material remains unidentified.
Detecting radiances in the O2A band using polarization‐sensitive satellite instruments with application to the Global Ozone Monitoring Experiment
Authors: Stam D. M. , De Haan J. F. , Hovenier J. W. , Aben I.
Published: February 2004

In this paper, we present numerical simulations of the radiance and the degree of linear polarization of light reflected by the terrestrial atmosphere in the O2 A absorption band, around 760 nm. Since the O2 A band is often used to derive cloud parameters, we included clouds in our model atmosphere. The simulations show that the polarization of the reflected light changes across the O2 A band, and that this change depends strongly on the spectral resolution of the instrument. The polarization of reflected light induces errors in radiances derived from observations by polarization sensitive instruments. For the Global Ozone Monitoring Experiment (GOME) satellite instrument, which measures radiances with about 0.4‐nm spectral resolution in the O2 A band, broadband polarization measurements are used to correct the narrowband radiance observations for the instrument's polarization sensitivity. Although such correction schemes significantly improve the accuracy of derived radiances in the continuum, they do not account for changes of the polarization in narrow absorption bands, such as the O2 A band. The main purpose of this paper is to investigate for cloudy atmospheres the errors in the derived radiances due to polarization changes across the O2 A band, both for a polarization sensitive instrument with a high spectral resolution and for a GOME‐like resolution. If no correction scheme is used, it is found that for nadir viewing directions, the maximum errors in the absorption band can increase by up to about 20% with decreasing width of the spectral response function when the instrument's sensitivity for radiation polarized perpendicularly to the principal plane is twice as large as that for radiation polarized parallel to this plane. If, in this case, a correction scheme based on the broadband value of the polarization is used, the radiance errors can still be up to 18% with a high spectral resolution and of the order of a few percent with a GOME‐like resolution.
A true eddy accumulation system for trace gas fluxes using disjunct eddy sampling method
Authors: Rinne H. J. I. , Delany A. C. , Greenberg J. P. , Guenther A. B.
Published: February 2004

A new true eddy accumulation flux measurement system, based on the disjunct sampling approach, has been developed and tested. In disjunct sampling, short, separate samples are taken instead of continuously sampling the air as in traditional relaxed eddy accumulation and eddy covariance systems. This method reduces the number of samples but allows more time to process them. Simulation shows that the fluxes, calculated using disjunct data, are close to those calculated using continuous data. The disjunct true eddy accumulation instrument was successfully deployed to measure monoterpene fluxes at Niwot Ridge, Colorado. The ability of the system to measure the sample flow accurately, critical for any eddy accumulation system, was tested using atmospheric CFC‐113 as a tracer, with good results. The system was capable of measuring relatively low α‐pinene fluxes, below 10 ng m−2 s−1 at T = 8°–18°C, over a subalpine forest.
Wavebreaking and mixing in the northern hemisphere summer stratosphere
Authors: Wagner Richard E. , Bowman Kenneth P.
Published: February 2004

The cause of zonal ozone variations observed by the Polar Ozone and Aerosol Measurement II (POAM II) instrument in the Northern Hemisphere summer stratosphere from ∼55° to 65°N and ∼20 to 30 km is investigated using United Kingdom Meteorological Office (UKMO) stratospheric data. Eliassen‐Palm (E‐P) flux vectors calculated from the UKMO data show that wave activity propagates vertically from the troposphere into the stratospheric easterlies during the Northern Hemisphere summer. In the layer between 20 and 30 km the E‐P flux divergence is small but nonzero. Space‐time power spectra show that wave power shifts from eastward propagating waves in the upper troposphere to predominantly westward propagating waves in the middle stratosphere, consistent with phase speed filtering following the Charney‐Drazin theorem. Air parcel trajectories and effective diffusivity calculations show substantial mixing due to breaking of westward propagating waves in the summer easterly wind regime. Changes in mixing properties during the summer season are consistent with changes in the mean state and the wave forcing. We conclude that breaking of large‐scale westward propagating waves in the summer easterlies causes meridional transport and the observed local maximum in ozone variability.
Energy balance of a high marsh on the Texas Gulf Coast: Effect of water availability
Authors: Heilman J. L. , Heinsch F. A. , Cobos D. R. , McInnes K. J.
Published: February 2004

The supply of water to the Nueces River Delta near Corpus Christi, Texas, and its estuarine marshes is limited by low tidal ranges in the Gulf of Mexico and by channelization of the Nueces River which restricts freshwater inflow. Micrometeorological measurements were made at the upper end (high marsh) of the delta to determine how daily and seasonal changes in the surface energy balance were affected by availability of water. The marsh consists of shallow ponds interconnected by narrow channels, and elevated areas containing emergent vegetation. During the spring and fall when ponds were flooded, latent and sensible heat flux averaged 67% and 30%, respectively, of net radiation. In the summer when ponds dried, energy partitioning was reversed with sensible heat flux accounting for 65% of net radiation and latent heat accounting for 27%. When ponds were flooded, heat storage in the water column was the major component of storage heat flux. When ponds dried, storage heat flux was controlled by sediment water content, largely through its effect on thermal diffusivity. The ratio of actual to equilibrium evaporation averaged 0.7 in the spring and fall, and 0.3 in the summer, indicating that the marsh behaved more like a dryland ecosystem than a wetland.
Features and trends in Atmospheric Trace Molecule Spectroscopy (ATMOS) version 3 stratospheric water vapor and methane measurements
Authors: Michelsen H. A. , Irion F. W. , Manney G. L. , Toon G. C. , Gunson M. R.
Published: February 2004

Mixing ratios of water vapor entering the stratosphere are inferred from Atmospheric Trace Molecule Spectroscopy (ATMOS) measurements to be 3.28 ppm in 1985, 3.53 ppm in 1992, 3.67 ppm in 1993, and 3.65 ppm in 1994, yielding an average increase of 0.041±0.007 (1σ) ppm/yr or 1.2±0.2%/yr between 1985 and 1994. Strong evidence for a seasonal cycle in water vapor is apparent below 45km in the tropics, and ascent rates derived from these tropical profiles are comparable to previous estimates. An enhancement in the sum [H2O]+2[CH4] apparent between 45 and 60km in the tropics appears to be consistent with remnants of a seasonal cycle in [H2O].