bluuebunny/crossref_metadata_2025 huggingface dataset:
Retrieval of the real part of the refractive index of smoke particles from Sun/sky measurements during SCAR‐B
Authors: Yamasoe M. A. , Kaufman Y. J. , Dubovik O. , Remer L. A. , Holben B. N. , Artaxo P.
Published: February 2004

A method is used to retrieve the real part of the refractive index of ambient aerosol particles in the entire vertical column using ground‐based measurements of the angular dependence of the spectral sky radiance. The method is applied to smoke aerosol particles using spectral Sun/sky data measured by the AERONET (Aerosol Robotic Network) radiometers in Cuiabá, Brazil, during the SCAR‐B (Smoke, Clouds, and Radiation‐Brazil) experiment in 1995. The refractive index is retrieved from comparison between measurements taken in the solar almucantar and calculations using Mie theory. First the aerosol size distribution is derived from sky radiance at scattering angles less then 40°, then the refractive index is derived from sky radiances for angles of 20°–100°. Simulations and sensitivity studies are presented showing that the expected error is ±0.03, Application of the method to the Cuiabá region, which is dominated by smoke from cerrado vegetation burning, resulted in a mean value for the real part of the index of refraction of 1.53±0.04, 1.55±0.04, 1.59±0.02, and 1.58±0.01, respectively, for wavelengths of 438, 670, 870, and 1020 nm. Though we do not have independent verification of the results, we tested the effect of water vapor on the refractive index. The low humidification factors measured in Brazil and the lack of high relative humidities suggested a small effect of water vapor. In fact, as expected, a nonsignificant correlation was observed between the retrieved values of refractive index and total precipitable water vapor. Application to aerosol in the eastern United States (not reported here), with high humidity and high humidification factors, did show a strong reduction of the refractive index with increase of the total precipitable water vapor, thus generating confidence in the methodology.
Scale properties of microscale convection in the marine surface layer
Authors: Hagelberg C. R. , Cooper D. I. , Winter C. L. , Eichinger W. E.
Published: February 2004

We analyze the scale distribution of coherent water vapor structures in the marine atmospheric boundary layer as measured by a shipboard Raman lidar during the Combined Sensor Program (March 1996) using a two‐dimensional continuous wavelet transform. Coherent structures in the lidar measured water vapor concentration field correspond to locations where covariance with the wavelet is a local extremum. Scales of the significant structures are identified using a filtered wavelet variance (detection density) derived from 24 “images” in a horizontal plane. A dominant radius of 14 m is identified using complimentary approaches to the analysis.
Simulation of enclosure‐based methods for measuring gas emissions from soil to the atmosphere
Authors: Gao Fang , Yates Scott R.
Published: February 2004

Enclosure‐based methods (i.e., flux chambers) have been widely used in agricultural, ecological, geophysical, and engineering studies to estimate gas exchanges at the soil‐atmosphere and the water‐atmosphere interfaces. In this study, the flux chambers are analyzed using diffusion theory and mass balance principle. Mathematical models are developed to simulate the general behavior of both closed and dynamic chambers. Simulation for the closed chamber behavior shows that the flux from the enclosed soil matrix into the chamber decreases with time after chamber placement. This indicates that application of a simple linear model to calculate flux may underestimate the real flux, even though the concentration data obtained from the chamber headspace shows a relatively linear increase with respect to time. It is recommended that nonlinear models be considered whenever possible for calculating flux for closed chambers. Simulations of dynamic chambers show that (1) these chambers can reach a steady state rapidly after placement and (2) the proper measurement of flux depends on both chamber operational conditions and soil permeability to air. A dynamic chamber may underestimate the actual flux when operating on low permeable soils. On soils with high air permeability a dynamic chamber may give an underestimate of the actual flux when operating at low airflow rate but an overestimate when the airflow rate is high. Theoretically, both closed and dynamic chambers may produce accurate flux estimates if they operate under ideal conditions and appropriated models are used in flux calculations. In practice, however, a dynamic chamber should be more desirable.
Estimates of radiative forcing due to modeled increases in tropospheric ozone
Authors: Haywood J. M. , Schwarzkopf M. D. , Ramaswamy V.
Published: February 2004

The GFDL R30 general circulation model (GCM) and a fixed dynamical heating model (FDHM) are used to assess the instantaneous and adjusted radiative forcing due to changes in tropospheric ozone caused by anthropogenic activity. Ozone perturbations from the GFDL global chemical transport model are applied to the GCM, and the instantaneous solar and terrestrial radiative forcings are calculated excluding and including clouds. The FDHM is used to calculate the adjusted radiative forcing at the tropopause. The net global annual mean adjusted radiative forcing, including clouds, ranges from +0.29 to +0.35 W m−2 with ∼80% of this forcing being in the terrestrial spectrum. If stratospheric adjustment is ignored, the forcing increases by ∼10%, and if clouds are ignored, the radiative forcing increases by a further 20–30%. These results are in reasonable agreement with earlier studies and suggest that changes in tropospheric ozone due to anthropogenic emissions exert a global mean radiative forcing that is of similar magnitude but of opposite sign to the direct forcing of sulfate aerosols.
Remote sensing of CO, CH4, and O3 using a spaceborne nadir‐viewing interferometer
Authors: Clerbaux C. , Chazette P. , Hadji‐Lazaro J. , Mégie G. , Müller J.‐F. , Clough S. A.
Published: February 2004

Within the next 5 years, several instruments launched on polar orbiting satellites will provide high‐resolution infrared remote‐sensing measurements of CO, CH4, and O3 on a global scale. The upwelling spectral radiances to be recorded by a nadir‐looking remote sensor have been simulated using a high‐resolution radiative code (line‐by‐line radiative transfer model (LBLRTM)) coupled to a three‐dimensional chemical transport model (intermediate model of the annual and global evolution of species (IMAGES)). The instrumental specifications of the Fourier transform interferometric monitor for greenhouse gases/Advanced Earth Observing System (IMG/ADEOS) and infrared atmospheric sounding interferometer (IASI/METOP) were used to generate realistic data. Calculations have been performed to assess the sensitivity of the nadir spectral radiances to changes in the gas concentration, temperature profile and to instrumental characteristics. We provide spectral intervals for an efficient retrieval of these species, together with a set of climatological tropospheric standard mixing ratio profiles.
A scalar similarity study based on surface layer ozone measurements over cotton during the California Ozone Deposition Experiment
Authors: Pearson R. J. , Oncley S. P. , Delany A. C.
Published: February 2004

This paper reports the first power spectra of ozone (O3) in the surface layer for which the data quality approaches that of high‐quality spectra of meteorological properties. These results are employed in a surface layer scalar similarity study involving temperature, moisture, and O3 measurements over cotton. All data were obtained during the California Ozone Deposition Experiment, in the San Joaquin Valley of California, during July and August, 1991. A detailed comparison of nondimensional scalar power spectra during unstable conditions showed that the three scalars behaved similarly, thereby providing the first completely general test of scalar similarity theory.
Clear‐sky atmospheric solar transmission: An analysis based on FIRE 1991 field experiment data
Authors: Kinne S. , Bergstrom R. , Toon O. B. , Dutton E. , Shiobara M.
Published: February 2004

We consider explanations for disagreements between models and measurements of clear‐sky solar transmission. Data from four cloud‐free days during the FIRE 1991 field experiment are studied. Our model simulations of solar broadband fluxes exceed measurements by about 10%. About half of this discrepancy occurs in the near‐infrared spectral region. About half of this discrepancy can be linked to the direct irradiance. These deviations suggest (1) model underestimates in near‐infrared trace‐gas absorption and (2) errors in visible diffuse fluxes. The near‐infrared error in other models is generally less than the one associated with our model. Other models suggest more trace‐gas absorption. However, variations among models are so large that they swamp current measurement errors such as uncertainties of the water vapor column. The visible diffuse flux error cannot be easily explained. We illustrate that a poor cosine response of solar flux instruments could have contributed. Also, underestimates of aerosol absorption could be a factor. There is clearly a need for measurements and comparisons at high spectral resolution to better quantify the sources of these errors. However, these comparisons will only be fruitful if we have confidence in the accuracy of our models and the accuracy of the data.
1973–1996 Trends in depth‐averaged tropospheric temperature
Authors: Pielke R. A. , Eastman J. , Chase T. N. , Knaff J. , Kittel T. G. F.
Published: February 2004

The analysis of thickness derived from the National Center for Environmental Prediction (NCEP) reanalysis indicates that there has been no statistically significant warming trend in layer‐averaged global tropospheric temperatures during the period 1979–1996. While this result is at variance with data based on surface information, NCEP trends and interannual variations are closely related to tropospheric mean‐layer temperatures obtained from the satellite‐based microwave sounding unit (MSU) lower‐tropospheric data set. When a longer period, 1973–1996, is used for the NCEP analysis, a warming trend within a 95% confidence interval is derived. However, it is nearly half the magnitude of the surface‐derived trends. Strong correlations of the yearly global surface temperature anomalies and those calculated for several layers in the NCEP data indicate coincident interannual temperature variations throughout the depth of the troposphere. The disagreement of both our analysis and satellite‐derived estimates with surface data could be due to a land surface measurement bias, a result of land use changes such as deforestation and agricultural expansion whose effects are not yet accounted for in the global temperature records, and/or a decoupling between surface and lower‐tropospheric temperature over the last several years.
Estimates of cloud charge densities in thunderstorms
Authors: Marshall Thomas C. , Stolzenburg Maribeth
Published: February 2004

The total charge density and the precipitation charge density inferred from six balloon soundings of electric field and precipitation charge are compared in order to examine the distribution of cloud charge density in small New Mexican mountain thunderstorms. Cloud charge density magnitudes were typically less than 2.0 nC m−3, and the maximum cloud charge densities were −2.1 and +6.7 nC m−3. The cloud charge density made a significant contribution to the total charge density in most of the thunderstorm depth, especially in the upper positive and upper negative charge regions, where all the charge was typically on cloud particles. The largest positive cloud charge densities were found just above the main negative charge region. In the lower part of the main negative charge region, the cloud charge density was the major contributor to the total charge density, and the precipitation charge played a minor role. The cloud charge density was often zero in lower positive charge regions but was 20–50% of the total charge density in two cases. Between the upper positive charge region and the bottom of the main negative charge region the cloud charge density changes polarity and tends to become increasingly negative with decreasing altitude.
Hydroclimatology of Illinois: A comparison of monthly evaporation estimates based on atmospheric water balance and soil water balance
Authors: Yeh Pat Jen‐Feng , Irizarry Michelle , Eltahir Elfatih A. B.
Published: February 2004

Here we describe the regional‐scale hydrological cycle of Illinois, including both the land and atmospheric branches, using a data set on most of the hydrological variables, i.e., precipitation, streamflow, soil water content, snow depth, groundwater level, and atmospheric flux of water vapor. Since direct observations of evaporation are not available, two different approaches, soil water balance and atmospheric water balance, were applied to estimate the regional evaporation over Illinois from 1983 to 1994. The availability of a comprehensive hydrological data set covering the large area of Illinois facilitated a comparison between these two approaches for estimation of evaporation. To our knowledge, this is the first time such a comparison has been made. The climatologies of the monthly evaporation estimates from the two approaches agree reasonably well and within a 10% error; however, substantial differences exist between the two estimates of evaporation for individual months. The seasonal variability of the evaporation estimates based on soil water balance is largely balanced by the seasonal pattern of subsurface storage, whereas the seasonal variability of evaporation estimates from the atmospheric water balance is almost entirely balanced by the seasonal pattern of lateral fluxes of water vapor. This contrast reflects a fundamental difference in the hydrology of the land and atmospheric branches of the regional water cycle. In light of the fact that independent data sets were used in the two approaches, our results are encouraging: The atmospheric water balance approach has the potential for the accurate estimation of the climatology of regional evaporation, at least for humid regions at a scale similar to that of Illinois (∼105 km2). However, sensitivity analysis suggests that the accuracy of atmospheric water balance computations is rather poor for the scale smaller than 105 km2. For the calculation of evaporation using the soil water balance approach in regions where the groundwater table is rather shallow, the incorporation of the change in groundwater storage is indispensable since groundwater aquifers provide a significant portion of water storage at the monthly timescale.
Vertically stacked temperature disturbances near the equatorial stratopause as seen in cryogenic limb array etalon spectrometer data
Authors: Hayashi Hiroo , Shiotani Masato , Gille John C.
Published: February 2004

Temperature data derived from the cryogenic limb array etalon spectrometer (CLAES) on board the Upper Atmosphere Research Satellite (UARS) are used to investigate planetary‐scale temperature disturbances near the equatorial stratopause for January 1992 to May 1993. The disturbances are characterized by vertically stacked temperature extrema of alternating sign with a vertical scale of about 10 km and have a localized and stationary nature in the longitudinal direction with persistence of about 1 week. These are nearly identical to so‐called “pancake structures” first identified by Hitchman et al. [1987] using data from the limb infrared monitor of the stratosphere (LIMS). Their analysis suggested that pancake structures are consistent with those predicted by inertial instability theory and that their appearance is synchronized with strong planetary waves in the winter midlatitude, though the LIMS observations were made only during the northern winter. Using the CLAES data for about 14 months, this study shows that pancake structures occur not only during the northern winter but also during the southern winter. In addition, it is found that an equatorial pancake structure has its counterpart with reversed phase in the winter midlatitude, suggesting clear evidence for inertial instability. Further analyses on the basis of Ertel's potential vorticity show that inertially unstable regions intrude locally far into the winter hemisphere around pancake structures that appear when planetary wave breaking is going on. This implies a mechanism of localized inertial instability and resulting pancake structures caused by midlatitude planetary waves in the winter hemisphere, as some numerical studies have inferred.
A modeling study of the formation of cloud condensation nuclei in the jet regime of aircraft plumes
Authors: Gleitsmann G. , Zellner R.
Published: February 2004

The formation of cloud condensation nuclei in the jet regime of a B‐747 airliner at cruise has been investigated by modeling studies. Both the formation of H2O/H2SO4 clusters by homogeneous nucleation and the deposition of water vapor on soot particles activated by the adsorption of gaseous H2SO4, sulfuric acid hydrates, and H2O/H2SO4 clusters were taken into account. H2SO4 has been assumed to be formed only by OH oxidation of SO2 in the plume. Whereas at ambient temperatures between 219 and 224 K the heterogeneous condensation leads to ice particles with average diameters between 3.0 and 1.1 μm for soot emission indices of EI(soot) = (0.05 − 0.5) g/kg, respectively, no heterogeneous condensation occurs at higher temperatures. Homogeneously nucleated H2O/H2SO4 clusters, on the other hand, have diameters of less than 7 nm and do not contribute to visible contrail formation. Assuming different sulfur emission indices (0.1 g/kg≤EI(SO2)≤10 g/kg), we conclude that the contrail onset is essentially independent of this quantity and that a fractional H2SO4 surface coverage corresponding to a 0.1 monolayer (ML = 0.1) must be sufficient to activate the soot particles for H2O uptake, at least for EI(SO2)≥0.5 g/kg fuel. Calculations based on higher threshold values (i.e., 0.1<ML≤0.3) lead to results which are in disagreement with the onset of contrail formation as deduced by visual observations. Moreover, the present modeling study provides an estimate of the effect of mutual coupling of homogeneous and heterogeneous condensation pathways.
Correlations between tropopause height and total ozone: Implications for long‐term changes
Authors: Steinbrecht W. , Claude H. , Köhler U. , Hoinka K. P.
Published: February 2004

For the central European station of Hohenpeissenberg, averaging of ozone profiles grouped by tropopause height shows that the ozone mixing ratio profile in the lower stratosphere shifts up and down with the tropopause. The shift is largest near the tropopause and becomes negligible above 20 to 25 km. As a consequence a high tropopause is correlated with low total ozone and a low tropopause with high total ozone. Independent of season, total ozone decreases by 16 Dobson units (DU) per kilometer increase in tropopause height. At Hohenpeissenberg the tropopause has moved up by 150±70 m (2 σ) per decade over the last 30 years. If the −16 DU per kilometer correlation between total ozone and tropopause height is valid on the timescale of years, it is speculated that the observed increase in tropopause height could explain about 25% of the observed −10 DU per decade decrease of total ozone. This is of the same magnitude as the 30% fraction of midlatitude ozone depletion which current stratospheric models have difficulty accounting for. For Hohenpeissenberg the increase in tropopause height appears to be correlated with observed tropospheric warming: At 5 km altitude, for example, temperature has increased by 0.7±0.3 K per decade (2 σ) since 1967.
Evaluation of recent precipitation studies for Greenland Ice Sheet
Authors: Bromwich David H. , Cullather Richard I. , Chen Qiu‐shi , Csathó Beáta M.
Published: February 2004

The retrieval of an accurate spatial and temporal record of contemporary Greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales. A comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long‐term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of Greenland. There is general agreement on a long‐term Greenland average of about 35 cm yr−1 and on long‐term values for regional scales, although differences for outlying data sets exceed 50% of the observed glaciological estimate for particular regions. A fundamental problem is the inadequate topographic representation of Greenland in the numerical analyses. Nearly all of the data sets are overly dry for high‐elevation areas, as seen from comparisons with glaciological observations from Summit. The east‐central region of Greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses. In contrast, there is strong agreement among all methods on the temporal variability for the west‐central region over a 15‐year period. From the comparison it is concluded that none of the data sets is able to capture all of the regional‐scale features. In general, however, the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features. Agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of Greenland's precipitation climatology. In particular, an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses. In the north, anomalously high precipitation is associated with cyclonic development near the Fram Strait. For west‐central Greenland the close agreement among methods is related to the dominant contribution of the mean circulation.
Airborne studies of aerosol emissions from savanna fires in southern Africa: 2. Aerosol chemical composition
Authors: Andreae M. O. , Andreae T. W. , Annegarn H. , Beer J. , Cachier H. , Le Canut P. , Elbert W. , Maenhaut W. , Salma I. , Wienhold F. G. , Zenker T.
Published: February 2004

We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than ∼1–2 μm and a Teflon second filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser‐optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO2and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10–30% of the aerosol mass. K+and NH4+were the dominant cationic species in the smoke of most fires, while Cl−and SO42−were the most important anions. The aerosols were unusually rich in Cl−, probably due to the high Cl content of the semiarid vegetation. Comparison of the element budget of the fuel before and after the fires shows that the fraction of the elements released during combustion is highly variable between elements. In the case of the halogen elements, almost the entire amount released during the fire is present in the aerosol phase, while in the case of C, N, and S, only a small proportion ends up as particulate matter. This suggests that the latter elements are present predominantly as gaseous species in the fresh fire plumes studied here.
Effect of aerosols on solar UV irradiances during the Photochemical Activity and Solar Ultraviolet Radiation campaign
Authors: Kylling A. , Bais A. F. , Blumthaler M. , Schreder J. , Zerefos C. S. , Kosmidis E.
Published: February 2004

Surface UV irradiances were measured at two different sites in Greece during June 1996 under noncloudy conditions. The measured UV irradiances are simulated by a radiative transfer model using measured ozone density and aerosol optical depth profiles. The absolute difference between model and measurements ranges between −5% and +5% with little dependence on wavelength. The temporal and solar zenith angle dependence in the difference between model and measurement suggests that part of this difference may be explained by assumptions made about the aerosol single‐scattering albedo and phase function. Simulated spectra including aerosols are compared with calculated spectra excluding aerosols. It is found that for otherwise similar atmospheric conditions the UVB irradiance is reduced with respect to aerosol free conditions by 5% to 35% depending on the aerosol optical depth and single‐scattering albedo. For the campaign period, changes in the aerosol loading gave larger variations in the surface UV irradiances than the changes seen in the ozone column.
Simulation of satellite lidar and radiometer retrievals of a general circulation model three‐dimensional cloud data set
Authors: Doutriaux‐Boucher M. , Pelon J. , Trouillet V. , Sèze G. , Le Treut H. , Flamant P. , Desbois M.
Published: February 2004

The inclusion of a backscatter lidar on a space platform for a radiation mission, as proposed by various space agencies, aims to bring new information on three‐dimensional cloud distribution, with a special emphasis on optically thin cirrus clouds, which are presently poorly detected by passive sensors. Key issues for such cloud observational studies are the detection of multilayered cloud systems, thin cirrus, and fractional cloud cover, knowledge that would improve our understanding of the global radiation budget. To assess the impact of such lidar measurements on cloud climatology, a 1 month cloud data set has been simulated with a general circulation model (GCM). The cloud detection capability of a spaceborne scanning backscatter lidar is assessed with the use of two detection schemes, one based on limitations in the detected cloud optical depth and the other based on lidar signal‐to‐noise ratio. The cloud information retrieved from passive radiometric measurements using a procedure like that used in the International Satellite Cloud Climatology Project is also simulated from the same GCM cloud data set. It is shown that a spaceborne backscatter lidar can improve significantly the retrieval of thin cirrus clouds as well as underlying cloud layers. High‐level cloud retrieval from a spaceborne lidar therefore appears as a powerful complement to radiometric measurements for improving our knowledge of actual cloud climatology.
Solar atmospheric coupling by electrons (SOLACE): 2. Calculated stratospheric effects of precipitating electrons, 1979–1988
Authors: Callis Linwood B. , Natarajan Murali , Lambeth James D. , Baker Daniel N.
Published: February 2004

An analysis has been carried out of the effects of energetic electron precipitation (EEP) on stratospheric NOy, NO2, and O3. Solar wind observations used together with precipitating electron fluxes observed aboard TIROS spacecraft show a close relationship between the long‐ and short‐term fluctuations in the solar wind and EEP over a period of 16 years. Daily electron energy spectra for 4.25≤E≤1050 keV and energy deposition profiles are developed for both hemispheres for L≥5 and used in two‐dimensional chemical transport simulations for the period January 15, 1979, through December 31, 1987. Results indicate that globally averaged column NOy (from 25 to 40 km) increases by ≈ 12% between 1979 and 1983–1985 with a rapid decline to 1979 levels between early 1985 and 1987. Day‐by‐day comparisons of the results with the Stratospheric Aerosol and Gas Experiment (SAGE II) column NO2 and O3 for the period October 24, 1984, and December 31, 1987, show good agreement with the inclusion of EEP in the simulations. Northern near‐hemispheric decreases of column NO2 of ≈ 35% observed by SAGE II between early 1985 and 1987 are well simulated with the inclusion of EEP. Comparisons of several simulations with one another and with SAGE II NO2 data and Solar Backscattered Ultraviolet (SBUV) (V6) O3 data suggest that SOLACE represents a solar‐ terrestrial coupling mechanism which, for solar cycle 21, is as important to stratospheric O3 as solar UV flux variations.
Solar atmospheric coupling by electrons (SOLACE): 1. Effects of the May 12, 1997 solar event on the middle atmosphere
Authors: Callis Linwood B. , Natarajan Murali , Evans David S. , Lambeth James D.
Published: February 2004

An analysis is carried out of the effects on middle atmospheric NOy and O3 of a coronal mass ejection (CME) event which occurred on May 12, 1997, and which is coupled with observed solar wind fluctuations. Observations of electron fluxes by instruments aboard the SAMPEX and NOAA 12 satellites indicate large enhancements of magnetospheric electron fluxes occurring with the arrival of the high‐speed solar wind. Calculations suggest that significant formation rates of NOy should occur in the mesosphere and the lower thermosphere at mid to high latitudes. Halogen Occultation Experiment (HALOE) NO observations reveal increases of more than an order of magnitude between 85 and 120 km in both hemispheres within 1–2 days after the electron flux increases. Two dimensional chemical transport simulations were carried out to assess the fate of the NOy increases. Northern hemispheric increases were lost to photochemical destruction shortly after the event ended. Southern hemispheric increases were transported in part into the stratosphere by advective descent. By October 1997, high‐latitude NOy increases of 20–40% were calculated near 25 km leading to O3 reductions of up to ≈ 20% when compared to a simulation with no electron precipitation. A solar atmospheric coupling by electrons precipitating from the outer trapping and auroral regions of the magnetosphere, and which affects middle atmospheric NO, is clearly demonstrated by the observations alone.
Contraction of the 300 mbar north circumpolar vortex during 1963–1997 and its movement into the eastern hemisphere
Authors: Angell James K.
Published: February 2004

The size of the 300 mbar north circumpolar vortex, and its partition into western and eastern hemispheres and quadrants 0°–90°W, 90°W–180°, 90°E–180°, and 0°–90°, is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean‐monthly analyses of the Institute of Meteorology of the Free University of Berlin. During 1963–1997 the trend in annual vortex size is a significant − 1.4%/decade (vortex contraction), but with the trend in the western hemisphere portion of the vortex a significant −2.1%/decade compared to −0.7%/decade in the eastern hemisphere portion, signifying a movement of the vortex farther into the eastern hemisphere. Thus, while on average 52% of the vortex was in the eastern hemisphere during 1963–1997, this value increased by a significant 0.4%/decade during the period, resulting in a substantial increase in vortex eccentricity. In winter and spring the vortex has moved mainly into the Asian quadrant 90°E–180°, whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90°E–180° and 0°–90°W, and in autumn there has been a decrease in size of quadrant 90°W–180° relative to the other quadrants. The standard deviation of the annual quadrant‐size anomalies has decreased significantly during 1963–1997, indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts. On the basis of a 41‐station northern hemisphere radiosonde network, during 1963–1997 the annual 850–300 mbar temperature increased by a significant 0.12°C/decade in the northern hemisphere as a whole, and by a significant 0.17°C/decade in the western half and by 0.06°C/decade in the eastern half of the hemisphere. The resulting association of a 1%/decade decrease in 300 mbar vortex size, with about an 0.1°C/decade increase in 850–300 mbar temperature, differs by a factor of 2 from what would be expected hydrostatically, a difference that would be eliminated by an 0.4 mbar/decade increase in midlatitude surface pressure during 1963–1997.
Effect of aircraft on ultraviolet radiation reaching the ground
Authors: Plumb I. C. , Ryan K. R.
Published: February 2004

Changes in ozone levels for a range of scenarios, including those for present and projected future aircraft emissions and for present and future halogen loadings, are calculated using the Commonwealth Scientific and Industrial Research Organization two‐dimensional chemical transport model. These changes are applied to measured ozone columns and vertical profiles based on measurements to produce vertical profiles of ozone for each scenario considered, which are traceable to measurements. A radiative transfer model is then used to investigate changes in biologically active radiation reaching the surface of the Earth resulting from current and future fleets of aircraft and those resulting from changing levels of halogen compounds in the atmosphere. It is shown that equal changes in ozone column for these scenarios do not produce equal changes in biologically weighted fluxes reaching the ground. This is because aircraft affect ozone mainly in the upper troposphere, whereas the effects of halogens are greatest in the middle and lower stratosphere. The magnitude of the ratio of the biologically weighted flux change to the ozone column change is greater for the case of the aircraft, due to the larger contribution to multiple scattering in the troposphere. For the same reason, projected fleets of supersonic aircraft are shown to have a smaller effect on UV radiation for a given change in ozone column than subsonic aircraft. While aerosols reduce the UV radiation reaching the ground for all scenarios investigated, they have minimal impact on the ratios of UV changes to ozone column changes because the bulk of the aerosol loading is below the altitudes where ozone changes due to aircraft or halogens occur.
SCAR‐B fires in the tropics: Properties and remote sensing from EOS‐MODIS
Authors: Kaufman Yoram J. , Kleidman Richard G. , King Michael D.
Published: February 2004

Two moderate resolution imaging spectroradiometer (MODIS) instruments are planned for launch in 1999 and 2000 on the NASA Earth Observing System (EOS) AM‐1 and EOS PM‐1 satellites. The MODIS instrument will sense fires with designated 3.9 and 11 μm channels that saturate at high temperatures (450 and 400 K, respectively). MODIS data will be used to detect fires, to estimate the rate of emission of radiative energy from the fire, and to estimate the fraction of biomass burned in the smoldering phase. The rate of emission of radiative energy is a measure of the rate of combustion of biomass in the fires. In the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) experiment the NASA ER‐2 aircraft flew the MODIS airborne simulator (MAS) to measure the fire thermal and mid‐IR signature with a 50 m spatial resolution. These data are used to observe the thermal properties and sizes of fires in the cerrado grassland and Amazon forests of Brazil and to simulate the performance of the MODIS 1 km resolution fire observations. Although some fires saturated the MAS 3.9 μm channel, all the fires were well within the MODIS instrument saturation levels. Analysis of MAS data over different ecosystems, shows that the fire size varied from single MAS pixels (50×50 m) to over 1 km2. The 1×1 km resolution MODIS instrument can observe only 30–40% of these fires, but the observed fires are responsible for 80 to nearly 100% of the emitted radiative energy and therefore for 80 to 100% of the rate of biomass burning in the region. The rate of emission of radiative energy from the fires correlated very well with the formation of fire burn scars (correlation coefficient = 0.97). This new remotely sensed quantity should be useful in regional estimates of biomass consumption.
The character and bioactivity of dissolved organic matter at thaw and in the spring runoff waters of the arctic tundra North Slope, Alaska
Authors: Michaelson G. J. , Ping C. L. , Kling G. W. , Hobbie J. E.
Published: February 2004

The brief spring thaw period in the arctic is an important time when carbon is transferred from terrestrial to aquatic systems as melting snow and soil waters run off into the streams, lakes, and ocean. Measurements were made of the quantity and quality of dissolved organic carbon (DOC) in thawing soil and runoff waters in the foothills region of the Kuparuk River basin of arctic Alaska, during the thaw of May 1996. Incubations were performed using DOC and soil cores at the time of thaw from the surface layers of two major tundra types of the region, nonacidic and acidic tundra. Results indicated that there are major changes in both the quantity and quality of DOC as soil waters thaw and move to the streams and lakes. DOC concentrations were found to be reduced up to 90% as soil waters thawed and became free‐flowing soil waters with leachates from thawed soil cores averaging 116 mg DOC/L at thaw and soil waters averaging 20 mg DOC/L. Stream and inlet to Toolik Lake DOC concentrations averaged 12 and 10 mg DOC/L respectively indicating further dilution of DOC. Quality differences elucidated by XAD‐8/4 resin fractionation of DOC were observed for waters at various points in the ecosystem. The hydrophilic neutral fraction (HIN) accounted for 71% of the DOC in waters of thawing soil cores, but was only 23% in flowing waters of soils, and 9–20% in stream waters. A 14 day 4°C incubation of DOC from thawing soil core waters reduced DOC an average of 39%, with 80% of that reduction occurring in the HIN fraction. Soil waters and stream waters were similar in DOC fraction composition, and fulvic acid fractions were dominant. Initial 14 day DOC respiration rates with high HIN waters were 10 mg CO2‐C/g DOC/d, and reduced to 1.2–1.7 mg CO2‐C/g DOC/d after 34 days incubation. Respiration rates of thawed cores ranged from 0.12 to 0.06 and 0.03 mg CO2‐C/g C/d for nonacidic and acidic cores, respectively.
Observations of nonmethane hydrocarbons and oxygenated volatile organic compounds at a rural site in the southeastern United States
Authors: Riemer Daniel , Pos Willer , Milne Peter , Farmer Charles , Zika Rod , Apel Eric , Olszyna Ken , Kliendienst Tad , Lonneman William , Bertman Steve , Shepson Paul , Starn Tim
Published: February 2004

Measurements of an extensive range of nonmethane hydrocarbons (NMHCs) including alkanes, alkenes, and aromatics, and oxygenated volatile organic compounds (OVOCs) including alcohols, ketones, and aldehydes were conducted for several weeks during the summer of 1995 as part of the Southern Oxidants Study (SOS) at a rural experimental site (Youth, Inc.) 32 km southeast of Nashville, Tennessee, in the southeastern United States. These measurements were conducted to (1) determine the absolute magnitude and variability of oxygenated compounds found in a contemporary rural region; (2) assess the importance of the measured ambient levels of OVOCs on a photochemical reactivity basis relative to the more commonly determined NMHCs; and (3) to evaluate our ability to accurately measure oxygenates by the current techniques employed under a field study scenario. Several other physical (temperature, insolation, etc.), meteorological (wind velocity, wind direction, atmospheric structure, and boundary layer height), and chemical (criterion pollutants, NOx, SO2, CO, O3, etc.) parameters were measured concurrently with the NMHC and OVOC measurements. During the study period, OVOCs were consistently the dominant compounds present, and methanol and acetone had the highest mixing ratios. Although OVOCs made up the majority of the volatile organic compound component on a mass basis, a substantial sink for OH was isoprene and its immediate oxidation products, methacrolein and methyl vinyl ketone. In combination with CO and formaldehyde, these compounds comprised about 85% of the observed OH reactivity at the site. Acetaldehyde and methanol were responsible for an additional 10%, with the NMHCs and remaining OVOCs making up the final 5% of the measured OH reactivity at the site. These observed patterns reinforce recent studies which find OVOCs to be an important component of the rural troposphere.
OPAL: Network for the Detection of Stratospheric Change ozone profiler assessment at Lauder, New Zealand 1. Blind intercomparison
Authors: McDermid I. S. , Bergwerff J. B. , Bodeker G. , Boyd I. S. , Brinksma E. J. , Connor B. J. , Farmer R. , Gross M. R. , Kimvilakani P. , Matthews W. A. , McGee T. J. , Ormel F. T. , Parrish A. , Singh U. , Swart D. P. J. , Tsou J. J. , Wang P. H. , Zawodny J.
Published: February 2004

An intercomparison of ozone‐profiling instruments, two differential absorption lidars, a microwave radiometer, electrochemical concentration sondes, and the SAGE II satellite instrument is presented. The ground‐based instruments were located at the Network for the Detection of Stratospheric Change (NDSC) primary station at Lauder, New Zealand. The campaign, which took place between April 15 and 29, 1995, strictly followed the NDSC guidelines for a blind intercomparison. Agreement between the measurements was within 15% for single profiles and within 10% for the campaign average, in the region from 20 to 40 km altitude. Outside of this region the differences were greater but can generally be ascribed to the limits of a particular instrument.
The Galileo Probe Doppler Wind Experiment: Measurement of the deep zonal winds on Jupiter
Authors: Atkinson David H. , Pollack James B. , Seiff Alvin
Published: February 2004

During its descent into the upper atmosphere of Jupiter, the Galileo probe transmitted data to the orbiter for 57.5 min. Accurate measurements of the probe radio frequency, driven by an ultrastable oscillator, allowed an accurate time history of the probe motions to be reconstructed. Removal from the probe radio frequency profile of known Doppler contributions, including the orbiter trajectory, the probe descent velocity, and the rotation of Jupiter, left a measurable frequency residual due to Jupiter's zonal winds, and microdynamical motion of the probe from spin, swing under the parachute, atmospheric turbulence, and aerodynamic buffeting. From the assumption of the dominance of the zonal horizontal winds, the frequency residuals were inverted and resulted in the first in situ measurements of the vertical profile of Jupiter's deep zonal winds. A number of error sources with the capability of corrupting the frequency measurements or the interpretation of the frequency residuals were considered using reasonable assumptions and calibrations from prelaunch and in‐flight testing. It is found that beneath the cloud tops (about 700 mbar) the winds are prograde and rise rapidly to 170 m/s at 4 bars. Beyond 4 bars to the depth at which the link with the probe was lost, nearly 21 bars, the winds remain constant and strong. Corrections for the high temperatures encountered by the probe have recently been completed and provide no evidence of diminishing or strengthening of the zonal wind profile in the deeper regions explored by the Galileo probe.
Mars' surface pressure tides and their behavior during global dust storms
Authors: Bridger Alison F. C. , Murphy James R.
Published: February 2004

Simulations of Mars' atmospheric tides with the NASA‐Ames Mars general circulation model are presented and analyzed. In an annual simulation, diurnal and semidiurnal tides in the model's surface pressure field are shown to compare well with tides observed by the Viking landers throughout the Mars year. Focused simulations of global dust storms during the northern winter season show a semidiurnal tide that responds very strongly to the increased dust load during the storms, again matching well with observations. Analysis of the structure and behavior of this tide during global storms verifies that it is dominated by the gravest symmetric Hough mode (H22), as has been noted previously. However, it is shown here that additional symmetric and asymmetric modes play an important role in accounting for the structure of the tide and its variation during the dust storms. The phase advance observed between the Viking lander sites (earlier semidiurnal phase at the higher‐latitude site) is explained by the presence of these higher‐order modes. Finally, decomposition of the semidiurnal tide during a global dust storm into its component Hough modes shows that the amplitude of the
mode mirrors changes in the observed overhead visible dust opacity, while variations in higher‐order modes are indicative of the zonal (and, possibly, longitudinal) distribution of airborne dust.
The clouds of Jupiter: Results of the Galileo Jupiter Mission Probe Nephelometer Experiment
Authors: Ragent Boris , Colburn David S. , Rages Kathy A. , Knight Tony C. D. , Avrin Philip , Orton Glenn S. , Yanamandra‐Fisher Padmavati A. , Grams Gerald W.
Published: February 2004

The results of the nephelometer experiment conducted aboard the probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle‐free 5‐μm “hot spot” region of the probe's descent were documented from about 0.46 bar to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bar down to about 0.55 bar, a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 bar to a distinctive base at 1.34 bars and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud, perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other causes. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading, and column mass loading in the atmosphere encountered by the Galileo probe during its descent.
Helium in Jupiter's atmosphere: Results from the Galileo probe Helium Interferometer Experiment
Authors: von Zahn U. , Hunten D. M. , Lehmacher G.
Published: February 2004

On December 7, 1995, the NASA Galileo probe provided the first in situ measurements of the helium abundance in the atmosphere of Jupiter. Our Jamin interferometer measured precisely the refractive index of the Jovian atmosphere in the pressure region from 2 to 12 bars. From these measurements, we derive the atmospheric helium mole fraction to be 0.1359±0.0027. The corresponding helium mass fraction matches closely, but accidentally, the current helium abundance of the atmosphere of the Sun. However, both the Jovian and the solar value fall somewhat below the protosolar value. This suggests that in both Jupiter and the Sun processes are active which separate helium from hydrogen.