bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of the cloudy boundary layer during the autumnal freezing of the Beaufort Sea
Authors: Curry J. A. , Pinto J. O. , Benner T. , Tschudi M.
Published: February 2004

The Beaufort and Arctic Seas Experiment (BASE) occurred during September and October 1994, off the Canadian Beaufort coast. In this paper, we provide a description of the characteristics of the the cloudy boundary layer that were observed from a research aircraft during BASE and provide an interpretation for the coevolution of the atmospheric boundary layer and sea ice characteristics during the autumnal freezing of the Beaufort Sea. Observations from a total of 12 research flights are presented. During the course of the experiment the underlying surface made a transition from late summer melt conditions to full‐fledged winter conditions. All of the observed boundary layer cloud decks are associated with stable temperature profiles, with temperature inversions occurring either above or within each of the cloud decks. Unlike observations of summertime boundary layer clouds, no multiple‐layered clouds in the boundary layer were observed. Examination of the cloud phase indicates a transition from predominantly liquid phase clouds at the beginning of the experiment to predominantly crystalline clouds at the end of the experiment. Local interactions between the clouds and underlying surface were examined in several case studies, including the effects of leads. Using a time series of soundings over a period of 5 days in conjunction with the the National Center for Environmental Prediction analyses, an air mass modification event was examined that began after the intrusion of warm air from the Pacific Ocean. The evolution of the air mass is apparent in decreasing temperatures in the lower atmosphere and formation of a low‐level mixed phase cloud that evolves with time into a deeper cloud layer that is crystalline.
A practical method for predicting midlatitude total column ozone from operational forecast temperature fields
Authors: Stanford J. L. , Ziemke J. R.
Published: February 2004

Accurate forecasts of total column ozone (Ω) are important because, among other reasons, forecasts of clear‐air biologically important solar ultraviolet (UVB) reaching the Earth's surface are exponentially sensitive to Ω. We present a simple method for predicting Ω using forecast lower stratospheric temperatures and a precalculated lookup table based on ozone climatology from several years of satellite observations. Compared with observations, the simple method gives 1‐day forecast Ω errors of ∼1–2% (∼2–3%) in northern (southern) hemisphere summers, comparable with current multivariate UVB forecast models being used by national weather services in several countries. The advantage of the prediction method described here is its simplicity: a convenient lookup table based on ozone climatology is used, without the need for recalculation in each forecast. The method may prove useful for surface UVB forecasts, especially in the biologically important summer seasons of both hemispheres.
Long‐term aerosol and trace acidic gas collection at Mauna Loa Observatory 1979–1991
Authors: Holmes Jennifer , Samberg Tristine , McInnes Lynn , Zieman Jonathon , Zoller William , Harris Joyce
Published: February 2004

Weekly aerosol samples have been collected and analyzed consistently at Mauna Loa Observatory from February 1979 through June of 1991. Previous studies reported data through April of 1985. This paper focuses mainly on the data from May 1985 to June 1991. However, previous data have been included when appropriate to examine the entire data record. Elemental concentrations, enrichment factors, principal component analysis and chemical mass balancing have been used to examine this 12 year data record. Yearly Asian dust episodes are the major contributor to trace metal concentrations and variance. Marine material contributes only a third of the trace metal mass compared to the crustal contribution. Anthropogenic and biogenic material usually contribute less than 5% of the trace element mass (excluding carbon and sulfate). Sulfate, which was measured by ion chromatography for part of the period, contributes a mass similar to crustal mineral; however, it does not have a strong seasonal pattern. A pollution episode in 1989 increased the budget of several elements by an order of magnitude or more. The trace acidic gas data support the conclusion that marine material in the free troposphere has been weathered, leading to a chlorine depletion in marine particles.
Characteristics of Kelvin waves and gravity waves observed with radiosondes over Indonesia
Authors: Shimizu Atsushi , Tsuda Toshitaka
Published: February 2004

Profiles of wind velocity and temperature at 0–35 km were observed by means of radiosondes in west Java, Indonesia, during November 1992 and April 1993 and used to study the behavior of various atmospheric waves in the equatorial atmosphere. An oscillation, of zonal winds with a period of about 27 days was found in the troposphere, which was associated with variations in humidity and cloud top height. Kelvin waves showed phase progression beginning at cloud top height (13–16 km) and were particularly enhanced near the tropopause. The Kelvin waves strongly modulated the tropopause structure including the tropopause height, minimum temperature, and atmospheric stability. A hodograph analysis was applied to determine the propagation characteristics of inertial gravity waves. Height variation of the vertical group velocity suggests that the gravity waves were generated in the troposphere, while the horizontal phase velocity distribution suggests that they were interacting with the background mean zonal winds. These wave activities were enhanced when tall, convective clouds passed over the site, suggesting that cumulus convection seems to play a key role in generating these waves in the equatorial region.
Volcanic sulfur emissions: Estimates of source strength and its contribution to the global sulfate distribution
Authors: Graf Hans‐F. , Feichter Johann , Langmann Bärbel
Published: February 2004

Anthropogenic emission of SO2 and conversion into SO42− is argued to be the most important factor damping and modulating the global greenhouse effect. Recent estimates of the relative strength of the three important sources of volatile sulfur (SO2 from fossil fuel combustion ∼78 Tg S/yr, from biomass burning ∼2 Tg S/yr, and from natural sources ∼25 Tg S/yr) suggest an over‐whelming effect of the anthropogenic emissions for climate forcing. However, the radiauvely relevant product SO42− may have different patterns due to the distribution of the sources (some very dense areas near the surface for anthropogenic SO2, formation of SO2 from dimethylsulfide in the marine boundary layer, and emission of volcanic SO2 mostly in the free atmosphere in rural areas). In this paper we study the relative contribution of volcanic SO2 emissions to the atmospheric sulfur budget applying an atmospheric general circulation model including a full sulfur cycle and prescribed source distributions. An off‐line analysis tool is applied to determine the radiative forcing of sulfate aerosols. The results show that natural S sources are at least as important as the anthropogenic ones, even though their source strength is much smaller. The reasons are different lifetimes due to different production and emission processes. Therefore, we should improve our knowledge about the volcanic volatile sources and their time‐space variability.
Results from the Intergovernmental Panel on Climatic Change Photochemical Model Intercomparison (PhotoComp)
Authors: Olson Jennifer , Prather Michael , Berntsen Terje , Carmichael Gregory , Chatfield Robert , Connell Peter , Derwent Richard , Horowitz Larry , Jin Shengxin , Kanakidou Maria , Kasibhatla Prasad , Kotamarthi Rao , Kuhn Michael , Law Kathy , Penner Joyce , Perliski Lori , Sillman Sanford , Stordal Frode , Thompson Anne , Wild Oliver
Published: February 2004

Results from the Intergovernmental Panel on Climatic Change (IPCC) tropospheric photochemical model intercomparison (PhotoComp) are presented with a brief discussion of the factors that may contribute to differences in the modeled behaviors of HOx cycling and the accompanying O3 tendencies. PhotoComp was a tightly controlled model experiment in which the IPCC 1994 assessment sought to determine the consistency among models that are used to predict changes in tropospheric ozone, an important greenhouse gas. Calculated tropospheric photodissociation rates displayed significant differences, with a root‐mean‐square (rms) error of the reported model results ranging from about ±6–9% of the mean (for O3 and NO2) to up to ±15% (H2O2 and CH2O). Models using multistream methods in radiative transfer calculations showed distinctly higher rates for photodissociation of NO2 and CH2O compared to models using two‐stream methods, and this difference accounted for up to one third of the rms error for these two rates. In general, some small but systematic differences between models were noted for the predicted chemical tendencies in cases that did not include reactions of nomnethane hydrocarbons (NMHC). These differences in modeled O3 tendencies in some cases could be identified, for example, as being due to differences in photodissociation rates, but in others they could not and must be ascribed to unidentified errors. O3 tendencies showed rms errors of about ±10% in the moist, surface level cases with NOx concentrations equal to a few tens of parts per trillion by volume. Most of these model to model differences can be traced to differences in the destruction of O3 due to reaction with HO2. Differences in HO2, in turn, are likely due to (1) inconsistent reaction rates used by the models for the conversion of HO2 to H2O2 and (2) differences in the model‐calculated photolysis of H2O2 and CH2O. In the middle tropospheric “polluted” scenario with NOx concentrations larger than a few parts per billion by volume, O3 tendencies showed rms errors of ±10–30%. These model to model differences most likely stem from differences in the calculated rates of O3 photolysis to O(1D), which provides about 80% of the HOx source under these conditions. The introduction of hydrocarbons dramatically increased both the rate of NOx loss and its model to model differences, which, in turn, are reflected in an increased spread of predicted O3. Including NMHC in the simulation approximately doubled the rms error for O3 concentration.
Stratospheric ozone response to short‐ and intermediate‐term variations of solar UV flux
Authors: Zhou Shuntai , Rottman Gary J. , Miller Alvin J.
Published: February 2004

On the basis of three years (October 1991 through September 1994) of UARS SOLSTICE (solar stellar irradiance comparison experiments) and MLS (microwave limb sounder) data, correlations between tropical ozone and spectral solar UV flux have been studied. In addition to the 27‐day period of solar rotation, this new result shows a relatively weak UV‐ozone correlation at periods of 60–80 days in the upper stratosphere. The 60–80 day correlation coefficient (∼0.5) is somewhat smaller than the 27‐day correlation (∼0.7). For the 60–80 day periodicity the overall phase lag of ozone is about 2 weeks throughout the 1–10 mbar layer, but the phase relation differs each year. This suggests that dynamical effects could be influencing the 60–80 day ozone variation. Although the 60–80 day solar variation is much smaller than the 27‐day variation, the ozone response to these solar variations is about as strong. Further investigation of the 60–80 day variation using alternate data sets for different time periods would be desirable.
Remote sensing of aerosol properties over oceans using the MODIS/EOS spectral radiances
Authors: Tanré D. , Kaufman Y. J. , Herman M. , Mattoo S.
Published: February 2004

Spectral radiances measured at the top of the atmosphere in a wide spectral range (0.55–2.13 μm) are used to monitor the aerosol optical thickness and the aerosol size distribution (integrated on the vertical column) of the ambient (undisturbed) aerosol over the oceans. Even for the moderate resolution imaging spectrometer (MODIS) wide spectral range, only three parameters that describe the aerosol loading and size distribution can be retrieved. These three parameters are not always unique. For instance, the spectral radiance of an aerosol with a bilognormal size distribution can be simulated very well with a single lognormal aerosol with an appropriate mean radius and width of distribution. Preassumptions on the general structure of the size distribution are therefore required in the inversion of MODIS data. The retrieval of the aerosol properties is performed using lookup table computations. The volume size distribution in the lookup table is described with two lognormal modes: a single mode to describe the accumulation mode particles (radius <0.5 μm) and a single coarse mode to describe dust and/or salt particles (radius >1.0 μm). Note that two accumulation modes may be present, one dominated by gas phase processes and a second dominated by cloud phase processes. The coarse mode can also be split into several partially overlapping modes describing maritime salt particles and dust. The aerosol parameters we expect to retrieve are η, the fractional contribution of the accumulation mode to scattering; τ, the spectral optical thickness; andrm, the mean particle size of the dominant mode. Additional radiative quantities such as asymmetry parameter and effective radius are derived subsequently. The impact of the surface conditions, wind speed and chlorophyll content on the retrieval is estimated, the impact of potential sources of error like the calibration of the instrument is also tested. The algorithm has been applied successfully to actual data sets provided by the Thematic Mapper on Landsat 5 and by the MODIS airborne simulator on the ER‐2 and tested against ground and airborne measurements. A first estimate of the general accuracy is Δτ = ±0.05±0.05τ (at 550 nm), Δrm= 0.3rm, Δη = ±0.25.
Evaluation of the Geophysical Fluid Dynamic Laboratory general circulation model climate variability: 1. Variances and zonal time series
Authors: Polyak Ilya , North Gerald
Published: February 2004

This paper statistically analyzes and compares the variability of the observed and simulated (by the Geophysical Fluid Dynamic Laboratory general circulation model(GCM)) northern hemisphere monthly surface air temperatures, averaged within different latitude bands. The objects used for the analysis are: seasonal cycle of variances and univariate spectral and autocorrelation functions of zonal time series. The estimates reveal a significant latitudinal trend of all second moments. A comparison shows a statistically significant distinction of the variances of the observed and simulated stochastic systems. In some cases the shapes of the corresponding univariate spectra and autocorrelation functions are quite similar, but their numerical values and some features differ markedly, especially for the tropical regions. The approach developed gives reasonable descriptions of the univariate temperature processes, thereby providing an opportunity for solving some of the vital problems of theoretical and practical aspects surrounding validation and diagnosis of GCMs.
Evaluation of the GFDL GCM climate variability: 2. Stochastic modeling and latitude‐temporal fields
Authors: Polyak Ilya , North Gerald
Published: February 2004

This paper statistically analyzes and compares the variability of the observed and simulated (by the Geophysical Fluid Dynamic Laboratory general circulation model) northern hemisphere monthly surface air temperature latitude‐temporal fields. The objects used for the analysis are as follows: multivariate autoregressive and linear regression model parameters, the diffusion equation coefficients, and two‐dimensional spatial‐temporal spectral and correlation characteristics. The estimates reveal a significant latitudinal trend of all second moments. A comparative study of the estimates demonstrates a significant distinction between the character of the meridional circulations of the observed and simulated systems. The methodology and results presented make it clear that the variability validation problems can be formalized by applying standard statistical techniques of multivariate modeling and multidimensional spectral and correlation analysis to the data averaged spatially and temporally.
An integrated air pollution modeling system for urban and regional scales: 1. Structure and performance
Authors: Lu Rong , Turco Richard P. , Jacobson Mark Z.
Published: February 2004

A new three‐dimensional air pollution modeling system is described for urban and regional air quality studies. The system includes four major components: a meteorological model, a tracer transport code, a chemical and aerosol microphysical model, and a radiative transfer code. The meteorological model solves the equations of fluid dynamics and thermodynamics over complex terrain and incorporates physical processes such as turbulent diffusion, water vapor condensation and precipitation, solar and infrared radiative transfer, and ground surface processes. The tracer transport code computes the dispersion of gases and aerosols throughout the atmosphere, including the effects of emission sources, and dry and wet deposition. The chemistry/aerosol model treats coupled gas‐phase photochemistry and aerosol microphysics and chemistry. Aerosol processes include nucleation, coagulation, condensational growth, evaporation, sedimentation, chemical equilibrium and aqueous chemistry. A detailed radiative transfer code is attached to the dynamical and chemical models. Absorption and scattering by gases and aerosols are explicitly treated to define photodissociation rates, heating and cooling profiles, and boundary layer visibilities. The integrated modeling system, which is referred to as the surface meteorology and ozone generation (SMOG) model, is shown to be a powerful tool for studying coupled dynamical, chemical, and microphysical processes on urban and regional scales.
Observed vertical profile of sulphur hexafluoride (SF6) and its atmospheric applications
Authors: Patra Prabir K. , Lal Shyam , Subbaraya B. H. , Jackman Charles H. , Rajaratnam P.
Published: February 2004

The vertical distribution of sulphur hexafluoride (SF6) was measured during a balloon‐borne cryogenic air sampler experiment conducted from Hyderabad (17.5°N, 78.6°E) on April 16, 1994, in the altitude region of about 8–37 km. The profile shows a faster decrease in its concentration in the region between the tropopause (∼17 km) and about 27 km, which is known as the transition region. Above this region the decrease rate is almost an order of magnitude less than in the transition layer. These results indicate very little loss of SF6 due to photochemistry in the stratosphere. Based on the reported increase rate of SF6 mixing ratio at ground level and assuming that long‐lived trace gases are transported to the stratosphere without any measurable loss from the troposphere through the equatorial tropopause, the age of stratospheric air is estimated to vary from 1±0.08 years near the tropopause to 4.26±0.17 years above the transition layer. Atmospheric lifetime of SF6, inferred from the mixing ratio correlations with simultaneous measurements of N2O, and CFC‐12, is computed to be about 1937±432 years.
Photochemical calculations along air mass trajectories during ASHOE/MAESA
Authors: Pierce R. Bradley , Grooss Jens‐Uwe , Grose William L. , Russell James M. , Crutzen Paul J. , Fairlie T. Duncan , Lingenfelser Gretchen
Published: February 2004

The practicality of conducting photochemical calculations along trajectories of air masses is investigated. An isentropic trajectory package is used in conjunction with a detailed photochemical model to compare predictions of the mean chemical content of air masses initialized with the Halogen Occultation Experiment (HALOE) data with coincident in situ observations from instruments onboard the ER‐2 aircraft. Comparisons are made for 10 ER‐2 flights originating from Christchurch, New Zealand, during the May to June and October 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) deployments. Between 54 and 84 coincidences are found, depending on the species measured. Correlations between the ER‐2 and HALOE air mass/box model calculations are high (0.56–0.90) for most species considered except for H2O (0.14) and HCl (0.24). Statistically significant low biases in the prediction of HCl, H2O, and OH are found. Kolmogorov‐Smirnov (KS) significance tests are used to quantify the agreement between the distribution of species observed by the ER‐2 and predicted by the HALOE trajectory/ photochemical model. The model predictions agree with the observed variance within the distributions at significance levels greater than 0.80 (greater than 80% confidence that the predicted and observed variance are identical) for H2O, ClO, O3, and NOy. The impact of computational errors in the trajectory calculations and measurement uncertainty in the computed confidence levels are investigated using Monte Carlo techniques. Computational trajectory errors are found to play a small role in reducing confidence levels. The error analysis shows that the HALOE trajectory/photochemical model calculations reproduce the large‐scale variability found in the in situ ER‐2 constituent measurements to within the expected uncertainties in the HALOE observations for all species considered. It is concluded that the combined trajectory/photochemical model is an effective tool for interpreting in situ aircraft observations within the global perspective provided by remote satellite measurements.
Observations of the nitrate radical in the free troposphere at Izaña de Tenerife
Authors: Carslaw Nicola , Plane John M. C. , Coe Hugh , Cuevas Emilio
Published: February 2004

This paper reports direct measurements of the nitrate radical (NO3) in the lower free troposphere. The measurements were carried out at Izaña de Tenerife (2300 m altitude) in the Canary Islands during May 1994, using the technique of differential optical absorption spectroscopy (DOAS). The average nighttime NO3 concentration in very clean air from the mid‐Atlantic was found to be 8 ppt, with a maximum observed concentration of about 20 ppt. Combining the NO3 data with ancillary measurements of NO2 and O3 in a model shows that there are no important NO3 scavengers in a part of the troposphere that is characterized by a very low relative humidity and aerosol particle count, and where the concentration of NO2 is too small for significant quantities of N2O5 to form. On occasion, the presence of a trace concentration of NO or an organic species such as α‐pinene is required to explain the observations. The lifetime of NO3 at night was in excess of 2 hours, much longer than measured hitherto in the tropospheric boundary layer.
Spectral UV measurements over Europe within the Second European Stratospheric Arctic and Midlatitude Experiment activities
Authors: Bais A. F. , Blumthaler M. , Webb A. R. , Groebner J. , Kirsch P. J. , Gardiner B. G. , Zerefos C. S. , Svenoe T. , Martin T. J.
Published: February 2004

In the frame of the Second European Stratospheric Arctic and Midlatitude Experiment an intensive program of spectral measurements of global solar UV radiation was organized at several European sites, extending from middle latitudes to the Arctic Circle, in March 1995. Before starting the intensive measurements, a 2‐day intercomparison was performed at each site with a traveling spectrophotometer to ensure consistency and comparability between the instruments and their measurements during the period of the study. The collected data were used to investigate the variability of solar ultraviolet irradiances at high and middle latitudes during a period of considerably varying ozone levels. The ratio of the UV erythemal irradiance to UVA irradiance was used to exclude the interference of clouds and other wavelength independent factors. Finally, a simple statistical analysis of the data showed that the variability of UV erythemal dose due to clouds can be at least of similar importance to that induced by the variability of total ozone.
Infrared radiative transfer in the 9.6‐μm band: Application to TIROS operational vertical sounder ozone retrieval
Authors: Engelen Richard J. , Stephens Graeme L.
Published: February 2004

This paper introduces a radiative transfer model for the 9.6‐μm ozone band that specifically matches the TIROS operational vertical sounder (TOVS) channel 9. The model is based on a spectral Malkmus band model for transmission. Band parameters were calculated by comparing to MODTRAN3 derived radiances. The effect of pressure on absorption is dealt with using a four‐parameter approximation, and the improvements of this approximation over the more common Van de Hulst‐Curtis‐Godson scaling approximation are assessed. While this new model is exploited in the development of the retrieval described in this paper, the result has wider applicability to ozone climate problems requiring calculation of the radiative forcing associated with changing ozone. A two‐layer version of the radiative transfer model is implemented in a retrieval scheme to obtain total ozone amounts from radiances measured by the TOVS instrument. Because the TOVS ozone channel is mainly sensitive to lower stratospheric ozone, ozone columns of the upper layer (above 30 hPa and with mean pressure of 10 hPa) are prescribed as a function of latitude. Ozone columns of the lower layer (mean pressure of 105 hPa) are then retrieved. The retrieval is based on a nonlinear optimal estimation algorithm and provides definition of error characteristics for every retrieval, which makes it possible to obtain a spatial distribution of the errors in the retrieval together with the spatial distribution of the retrieved total ozone column itself. This global distribution of the retrieval error and also of the contribution of a priori knowledge to the retrieval is presented to provide a validity of the ozone retrievals. Total ozone mapping spectrometer (TOMS) statistics are used as a priori information in the retrieval, and the 40‐layer model is used to estimate the forward model error of the two‐layer model. Comparisons of ozone retrievals for 1989 with TOMS total ozone measurements show good agreement both in time and in space with a rms difference between 1% and 3% for zonal means and 10% for global gridded measurements.
Sensitivity of spruce/moss boreal forest net ecosystem productivity to seasonal anomalies in weather
Authors: Frolking Steve
Published: February 2004

A process‐oriented, daily time step model of a spruce/moss boreal ecosystem simulated 1994 and 1995 productivity for a Boreal Ecosystem‐Atmosphere Study site near Thompson, Manitoba. Simulated black spruce net primary productivity (NPP) was 139 g C m−2 in 1994 and 112 in 1995; feathermoss NPP was 13.0 g C m−2 in 1994 and 9.7 in 1995; decomposition was 126 g C m−2 in 1994 and 130 in 1995; net ecosystem productivity (NEP) was an uptake of 26.3 g C m−2 in 1994 and 2.5 in 1995. A very dry period for the first half of the 1995 summer was the major cause of that year's lower productivity. Sensitivity simulations explored the impact of 2‐month long warmer, cooler, wetter, and drier spells on ecosystem productivity. Warmer summers decreased spruce NPP, moss NPP, and NEP; cooler summers had the opposite effect. Earlier snowmelt (due to either warmer spring temperatures or reduced winter precipitation) increased moss and spruce NPP; later snowmelt had the opposite effect. The largest effect on decomposition was a 5% reduction due to a drier summer. One‐month droughts (April through October) were also imposed on 1975 base year weather. Early summer droughts reduced moss annual NPP by ∼30–40%; summer droughts reduced spruce annual NPP by 10%; late summer droughts increased moss NPP by about 20% due to reduced respiration; May to September monthly droughts reduced heterotrophic respiration by about 10%. Variability in NEP was up to roughly ±35%. Finally, 1975 growing season precipitation was redistributed into frequent, small rainstorms and infrequent, large rainstorms. These changes had no effect on spruce NPP. Frequent rainstorms increased decomposition by a few percent, moss NPP by 50%, and NEP by 20%. Infrequent rainstorms decreased decomposition by 5%, moss NPP by 50% and NEP by 15%. The impact of anomalous weather patterns on productivity of this ecosystem depended on their timing during the year. Multiyear data sets are necessary to understand this behavior and test these types of models.
Tropospheric ozone, lightning, and climate change
Authors: Sinha Ashok , Toumi Ralf
Published: February 2004

Tropospheric O3 is an important greenhouse gas. Lightning is a major source of NOx, and thus of tropospheric O3. It has recently been suggested that due to an apparent strong correlation between lightning strike rates and surface temperatures, tropospheric O3 may significantly increase if the climate warms, resulting in a substantial positive climate forcing. This paper attempts to quantify the extent of this forcing and the associated positive climate feedback. Simulations in‐corporating a tropospheric O3‐surface temperature parameterization are performed of the last glacial maximum and of a climate in which greenhouse gas concentrations have been doubled. The O3 parameterization is based on results from a two‐dimensional chemical model. The simulations are obtained using a one‐dimensional radiative‐convective model, in which CO2, CH4, tropospheric O3, and in the case of the paleoclimate simulation the surface albedo, are varied both independently and in combination. In the paleoclimate case, the tropospheric O3 feedback has roughly two thirds of the effect on surface temperatures as the change in tropospheric O3 due to industrialization alone. During climate warming, the effect on surface temperatures is about 60% of that due to a doubling of CH4. The results indicate that a surface temperature‐lightning‐O3 feedback, currently absent in general circulation models, could significantly affect anthropogenic climate change. Improved modeling and observations are required to confirm this.
Biomass burning and deep convection in southeastern Asia: Results from ASHOE/MAESA
Authors: Folkins Ian , Chatfield R. , Baumgardner D. , Proffitt M.
Published: February 2004

There was extensive biomass burning in Indonesia, northern Australia, and New Guinea during September and October 1994. This paper discusses two accidental encounters of biomass plumes from the 1994 Airborne Southern Hemisphere Ozone Experiment and Measurements for Assessing the Effects of Stratospheric Aircraft campaign (ASHOE/MAESA). During the October 23 descent into Fiji, and an ascent from Fiji on October 24, the NASA ER‐2 passed through layers highly enhanced in NO, NOy, CO, and O3. These layers occurred near an altitude of 15 km. Back trajectories and satellite images indicate that the layers probably originated as outflow from a convective disturbance near New Guinea. The measurements indicate that deep convection can inject emissions from southeast Asian biomass burning to near tropical tropopause altitudes. Deep convection magnifies the impact of biomass burning on tropospheric chemistry because of the much longer residence times and chemical lifetimes of species in the upper tropical troposphere. Transport of the products of southeast Asian biomass burning into the upper tropical troposphere, followed by southward high‐level outflow and advection by the subtropical jet, may play a significant role in dispersing these emissions on a global scale. Anthropogenic emissions from countries in southeast Asia are likely to increase in the future as these countries become more highly industrialized. This transport mechanism may play a role in increasing the impact of these types of emissions as well.
Ten years of ozonesonde measurements at the south pole: Implications for recovery of springtime Antarctic ozone
Authors: Hofmann D. J. , Oltmans S. J. , Harris J. M. , Johnson B. J. , Lathrop J. A.
Published: February 2004

Ten years of ozonesonde data at the south pole are used to investigate trends and search for indicators that can be used to detect Antarctic ozone recovery in the future. These data indicate that there have been no systematic winter temperature trends at altitudes of 7–25 km and thus no expected changes in stratospheric cloud particle surface area, which would affect heterogeneous chemistry. Springtime ozone depletion has been very severe since about 1992, with near‐total loss of ozone in the 14‐ to 18‐km region, but has lessened somewhat in 1994 and 1995. probably because of the decay of the sulfate aerosol from the Mount Pinatubo eruption which was present at 10–16 km. Sulfate aerosol particles from the Pinatubo eruption resulted in new ozone depletion in 1992 and 1993 in the 10‐ to 12‐km region where it is too warm for polar stratospheric clouds (PSCs) to form. The volcanic aerosol also augmented depletion related to PSCs at 12–16 km. Although ozone depletion was not as severe in 1995 as in 1993, the depleted region remained intact longer than ever, with record low values throughout December in 1995. Since about 1992, a pseudo‐equilibrium seems to have been reached in which springtime ozone depletion, as measured by the total column or the ozone in the 12‐ to 20‐km main stratospheric cloud region, has remained relatively constant. Independent of volcanic aerosol, ozone depletion has extended into the upper altitudes at 22–24 km since about 1992. There is some indication that ozone depletion has also worsened at the bottom of the depletion region at 12–14 km. Extensions of the ozone hole in the vertical dimension are believed to be the result of increases in man‐made halogens and not due to changes in particle surface area or dynamics. A quasi‐biennial component in the ozone destruction rate in September, especially above 18 km, is believed to be related to variations in the transport of halogen‐bearing molecules to the polar region. A number of indicators for recovery of the ozone hole have been identified. They include an end to springtime ozone depletion at 22–24 km, a 12‐ to 20‐km mid‐September column ozone loss rate of less than about 3 Dobson Units (DU) per day, and a 12‐ to 20‐km ozone column value of more than about 70 DU on September 15. It is estimated that if the Montreal protocol and its amendments, banning and/or limiting substances that deplete the ozone layer, is adhered to, recovery of the Antarctic ozone hole may be conclusively detected from the aforementioned changes in the vertical profile of ozone as early as the year 2008. Future volcanic eruptions would affect ozone at 10–16 km, making detection more difficult, but indicators such as depletion in the 22‐ to 24‐km region will be immune to these effects.
Trace gas measurements in coastal Hong Kong during the PEM‐West B
Authors: Wang T. , Lam K. S. , Chan L. Y. , Lee A. S. Y. , Carroll M. A.
Published: February 2004

O3, CO, NOy, and SO2 were measured at a coastal site in Hong Kong (22°13′N, 114°15′E, 60 m MSL) during the Pacific Exploratory Mission‐West B (PEM‐West B) in February and March 1994. Average concentrations determined in this study were 34±14 ppbv for O3, 458±130 ppbv for CO, 9.33±7.84 ppbv for NOy, and 1.31±1.46 ppbv for SO2. Their high and variable levels suggest that the study site was often under the impact of fresh continental emissions (including urban Hong Kong) during the season of continental outflow. Concentrations of these species were strongly influenced by the passage of cold fronts and troughs which periodically brought high levels of pollutants from the north. Outflow of continental air was indicated by dramatic changes in meteorological parameters and in the levels of trace gas species. CO appeared to be a good chemical indicator of changes of air mass type, and its variability may be attributed to the relative strength of the outflow and to the transport of urban plumes. Variations of NOy and SO2 appeared to be mainly dominated by local sources. O3 was poorly and often negatively correlated with CO and NOy, suggesting that air masses sampled in the study period were highly inhomogenous with respect to the chemical signatures and that O3 was chemically titrated by anthropogenic pollutants during the early stages of continental outflow. Calculated isentropic trajectories captured large‐scale changes of air masses, indicated also by surface meteorological and chemical data. Trajectory results offering finer resolutions would yield more insight into the histories of smaller‐scale air masses. Finally, the reasons for apparent disagreement between trajectory results, surface winds, and sometimes chemical data require further investigation.
A high precision manometric system for absolute calibrations of CO2 in dry air
Authors: Zhao Cong Long , Tans Pieter P. , Thoning Kirk W.
Published: February 2004

A high‐precision manometric system has been developed for absolute calibrations of CO2‐in‐air mixture gas. This report describes the principle of the calibration method and evaluates the performance of the manometric apparatus. The test results show that the reproducibility of the manometric system for calibrating CO2‐in‐air gas mixtures is within ±0.1 μmol mol−1 in the atmospheric CO2 concentration range of 300 to 400 μmol mol−1. Preliminary measurements indicate that the agreement with the absolute World Meteorological Organization mole fraction scale, widely used for atmospheric CO2 monitoring, is also within ±0.1 μmol mol−1 in that same range.
Vertical wavenumber spectra of wind and temperature from high‐resolution balloon soundings over Illinois
Authors: Nastrom G. D. , Van Zandt T. E. , Warnock J. M.
Published: February 2004

We spectrally analyzed high‐resolution balloon measurements of vertical profiles of temperature and horizontal wind in the troposphere and lower stratosphere over very flat terrain in Illinois. This paper is principally concerned with spectra in the power law range at vertical wavenumbers m ≥10−3 cycle/m. The logarithmic spectral slopes and amplitudes are found to have only insignificant dependencies on meteorological parameters, including time of day, season, wind speed and direction, vertical shear, etc., except that between the troposphere and stratosphere the spectral amplitude scales as (N2)q with q ∼0.3, where N is the buoyancy frequency. The mean slopes are ≈−3 in the stratosphere and ≈ −2.6 in the troposphere. On the average the individual spectra with larger amplitudes have less negative spectral slopes. The wide variation of spectral slopes (σ≈0.5) and amplitudes and the weak dependence on N2 are quite inconsistent with the predictions of theories of saturated spectra. Further, the wind spectra in the troposphere and stratosphere are correlated, which suggests some unsaturated propagation between the regions. The ratio of kinetic to potential energy spectra is constant versus m, consistent with the linear gravity wave polarization relations. The magnitude of the model ratio can be brought into agreement with the observed ratio by assuming a model intrinsic frequency spectrum varying as ω−p with p ∼5/3 to 2 plus an enhancement of energy near the inertial frequency.
Seasonal isoprene emission rates and model comparisons using whole‐tree emissions from white oak
Authors: Pier P. A. , McDuffie C.
Published: February 2004

Whole‐tree isoprene emission rates of a chambered white oak were measured throughout the growing season to develop a seasonal emissions model and to compare with emissions estimated using current leaf algorithms and forest canopy models. Emissions increased from mid‐May to a maximum in mid‐July, and the highest rates occurred late in June and throughout July. Rates decreased from early August to mid‐October. A model developed to characterize the whole‐tree emissions accounted for 80% of the variability of observed emissions over the growing season. Peak isoprene emissions and photosynthesis occurred at the same time, but peak emissions continued longer, suggesting that peak photosynthetic rates were not necessary for peak isoprene emissions. Measured light intensities 2 m and 3.3 m down into the tree canopy corresponded to intensities estimated by using current canopy models; however, intensities at l m were 14% lower than predicted by modeling. Measured median leaf‐to‐air temperature differences were 2.0°C at the canopy top and 0.5°C or less in the canopy. Median values of leaf temperatures estimated using a leaf energy balance procedure were slightly lower than air temperatures at all canopy levels, although differences were not more than 0.9°C. The most recently developed biogenic emissions model, which assumes that leaf and air temperatures are the same, predicted July whole‐tree emission rates fairly closely, although high emission rates were slightly underpredicted using the model. Leaf temperature adjustments used in previous canopy models were applied to this model, and in this case, predicted rates underestimated measured rates when measured rates exceeded 80 μg C g−1 h−1.
Observations of ozone structures in the Arctic polar vortex
Authors: Bird J. C. , Pal S. R. , Carswell A. I. , Donovan D. P. , Manney G. L. , Harris J. M. , Uchino O.
Published: February 2004

Lidar and balloon measurements at the new observatory, AStrO (80.05°N, 86.42°W), near Eureka, in the Canadian Arctic, have revealed laminations inside the ozone layer both inside and outside the polar vortex. These observations have been conducted by the lidar group of the Institute for Space and Terrestrial Science during February–March 1993 and the winters of 1993–1994 and 1994–1995. Observations of the vortex edge region were obtained as it passed over Eureka, revealing ozone profiles rich in structure. This paper discusses the observed ozone structures and their relationship to vortex filaments, the vortex edge structure, low‐ozone pockets, motion of the vortex edge region in the ozone profiles, and observed temperatures. Complementing the observations are back trajectories, potential vorticity maps, and Lagrangian domain‐filling potential vorticity trajectories. The relations of magnitude and thickness of the laminations to their positions relative to the vortex are revealed by presenting data as a function of potential vorticity. Mechanisms for the formation and transport of the laminae are discussed, as well as their role as a possible exchange mechanism of air masses across the polar vortex boundary. From observations of the laminations and their relation to potential vorticity, it is suggested that motion of the vortex, sometimes associated with warmings, is involved in the formation of laminations, which are subsequently advected as filamentary structures.
Performance of an aircraft instrument for the measurement of NOy
Authors: Kondo Y. , Kawakami S. , Koike M. , Fahey D. W. , Nakajima H. , Zhao Y. , Toriyama N. , Kanada M. , Sachse G. W. , Gregory G. L.
Published: February 2004

Measurements of NO and NOy using a chemiluminescence technique were made on board a DC‐8 aircraft during NASA's Pacific Exploratory Mission‐West B (PEM‐West B). The gold converter to convert NOy species into NO was operated at a constant pressure using a servo‐controlled Teflon valve, which has been used for NOy measurements on board the ER‐2 aircraft. The results of laboratory tests and some flight data during PEM‐West B are presented. These experiments indicate no detectable inlet loss of HNO3 in dry air, although some loss was observed at H2O mixing ratios of 1–2%. The laboratory tests also showed small variability in the NOy artifact, high conversion efficiency for NO2 and HNO3, low HCN conversion efficiency, good repeatability of the measurements, and fast response. The control of the converter pressure during flight has been proven to be very advantageous in making reliable aircraft NOy measurements in the troposphere. The uncertainties of the NO and NOy PEM‐West B data, including the effects of HCN conversion and HNO3 inlet loss, have been estimated.
Validation of spaceborne estimates of aerosol loading from Sun photometer measurements with emphasis on polarization
Authors: Bréon F.‐M. , Deuzé J.‐L. , Tanré D. , Herman M.
Published: February 2004

Over land, aerosol products from the Polarization and Directionality of the Earth's Reflectances (POLDER) are derived from the multispectral analysis of multiangular measurements of polarized radiance. A retrieval algorithm, developed on the basis of radiative transfer simulations and airborne observations, will process all measurements during the instrument mission. An evaluation of the algorithm performance and possible improvements is needed before the release of the aerosol products to the scientific user communities. A validation effort has been planned to test the derived products against independent measurements. The validation is achieved against ground‐based Sun photometer measurements from a worldwide station network. Although both measurements depend on the optical properties of the aerosols, they differ from the surface contribution and from the different viewing geometry. In this paper, we describe the planned procedure for POLDER aerosol product validation, and we discuss possible sources of uncertainties in comparing ground‐based measurements with satellite based ones. The study shows that ground‐based aerosol products are less affected by uncertainties than satellite‐based ones and therefore constitute a reliable ground truth and a valid source of information in the process of the POLDER algorithm improvement. However, because a Sun photometer cannot observe the larger scattering angles, it may not be adapted to validate the refractive index estimate.
Bounds for the mass of the atmosphere
Authors: Sañudo J. , Membrado M. , Pacheco A. F.
Published: February 2004

Inspired by the previous work of Trenberth and collaborators and in a model‐independent way, we have calculated an upper and a lower bound for the mass of the Earth's atmosphere, m. A recent precise determination of m agrees with our bounds.
On fluctuations of the mean daily relative humidity and self‐organized critical phenomena
Authors: García J. M. , Gimenez L. M. , Pacheco A. F.
Published: February 2004

We analyze the spectral density of the fluctuations in the relative humidity of Zaragoza, Spain in the period 1951–1993. A similar study has already been carried out by Vattay and Harnos [1994] using data from Hungary. These authors claim that this spectrum shows a l/ƒα behavior. Our results indicate a different trend, which seems to show that relative humidity at ground level is not a self‐organized critical phenomenon.