bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparisons of observed ozone trends and solar effects in the stratosphere through examination of ground‐based Umkehr and combined solar backscattered ultraviolet (SBUV) and SBUV 2 satellite data
Authors: Miller A. J. , Hollandsworth S. M. , Flynn L. E. , Tiao G. C. , Reinsel G. C. , Bishop L. , McPeters R. D. , Planet W. G. , DeLuisi J. J. , Mateer C. L. , Wuebbles D. , Kerr J. , Nagatani R. M.
Published: February 2004

Within the past year, two papers have been published which present updated profile ozone trends from the recently revised ground‐based Umkehr record [Miller et al., 1995] and the combined Nimbus 7 solar backscattered ultraviolet (SBUV) and NOAA 11 SBUV 2 satellite data record [Hollandsworth et al., 1995]. In this paper we compare the ozone trends and responses to the 11‐year solar cycle (represented by the F10.7 cm radio flux) derived from these two data sets for the period June 1977 to June 1991 (November 1978 to June 1991 for the satellite data). We consider data at northern midlatitudes (30°–50°N) at altitudes between 25 and 45 km derived from these two data sets. In particular, we investigate the effects of spatial sampling differences between the data sets on the derived signals. The trends derived from the two independent data sets are nearly identical at all levels except 35 km, where the Umkehr data indicate a somewhat more negative trend. The trend is approximately zero near 25 km but becomes more negative in the upper stratosphere, reaching nearly −7% per decade in the 40–45 km region. The upper stratospheric decreases are consistent with model results and are associated with the gas‐phase chemical effect of chlorofluorocarbons CFC's and other ozone‐destroying chemicals [World Meteorological Organization, 1995]. The ozone correlations in the two data sets with the F10.7 cm solar flux are similar, with near‐zero solar‐induced ozone variations in the 25–30 km region and statistically significant in‐phase variations at higher altitudes. Estimates of the solar cycle in the ozone time series at 40–45 km from a regression model indicate variations of about 4.5% from solar cycle maximum to minimum. Analysis of the satellite overpass data at the Umkehr station locations shows that the average of the data from the 11 Umkehr stations is a good approximation for the 30°–50°N zonal mean.
Interpretation of TOVS water vapor radiances in terms of layer‐average relative humidities: Method and climatology for the upper, middle, and lower troposphere
Authors: Soden Brian J. , Bretherton Francis P.
Published: February 2004

This study presents an analytical expression, derived from radiative theory, for relating water vapor radiances to layer‐average relative humidities. This “radiance‐to‐humidity transformation” provides a simple, yet reliable, means of interpreting satellite observations of the upwelling radiation in the 6.3‐μm water vapor absorption band in terms of a more familiar water vapor quantity. Despite its simplicity, when compared to detailed radiative transfer calculations of the upper (6.7 μm) tropospheric water vapor radiance, the transformation is demonstrated to be accurate to within ∼1 K. Similar levels of accuracy are found when the transformation is compared to detailed calculations of the middle (7.3 μm) and lower (8.3 μm) tropospheric water vapor radiance, provided that the emission from the underlying surface is taken into account. On the basis of these results, the radiance‐to‐humidity transformation is used to interpret TIROS operational vertical sounder observed water vapor radiances in terms of the relative humidity averaged over deep layers of the upper, middle, and lower troposphere. We then present near‐global maps of the geographic distribution and climatological variations of upper, middle, and lower‐tropospheric humidity for the period 1981–1991. These maps clearly depict the role of the large‐scale circulation in regulating the location and temporal variation of tropospheric water vapor.
Emissions of ethene, propene, and 1‐butene by a midlatitude forest
Authors: Goldstein A. H. , Fan S. M. , Goulden M. L. , Munger J. W. , Wofsy S. C.
Published: February 2004

Measurements of nonmethane hydrocarbon concentrations and gradients above Harvard Forest (42°32′ N, 72°11′ W) are reported for January through December 1993, along with inferred whole‐ecosystem emission rates for ethene, propene, and 1‐butene. Emissions were calculated using a micrometeorological technique where the ratio of observed CO2 fluxes and gradients were multiplied by the observed hydrocarbon gradients. Average emissions of ethene, propene, and 1‐butene during summer were 2.63, 1.13, and 0.41 × 1010 molecules cm−2 s−1, respectively. Emission of these olefins was correlated with incident solar radiation, implying a source associated with photosynthesis. In the northeastern United States, summertime biogenic emissions of propene and 1‐butene exceed anthropogenic emissions, and biogenic emissions of ethene contribute approximately 50% of anthropogenic sources. Our measurements suggest that terrestrial biogenic emissions of C2‐C4 olefins may be significant for atmospheric photochemistry.
Water‐soluble fractions of aerosol and their relations to number size distributions based on aircraft measurements from the North Atlantic Regional Experiment
Authors: Li Shao‐Meng , Banic C. M. , Leaitch W. R. , Liu P. S. K. , Isaac G. A. , Zhou X.‐L. , Lee Y.‐N.
Published: February 2004

Aerosol chemical and physical measurements were made at altitudes from 0.27 to 3 km near the coast of southern Nova Scotia, Canada, during the 1993 North Atlantic Regional Experiment. The volume distributions of aerosol with diameters between 0.005 and 3 μm were dominated by accumulation mode particles. The mass and volume ratios (Rm and Rυ) of the sum of soluble organics (SumOrg) to non‐sea‐salt (nss) SO4= were relatively invariant for estimated total particle mass (TPM) in excess of 13 μg m−3 (high TPM) but increased sharply with decreasing TPM below 13 μg m−3 (low TPM). Overall, the relationships between TPM and Rm and Rυ were found to be Rm = −(0.17±0.44) + (3.5±1.0)TPM−(0.69±0.39) and Rυ = −(0.35±0.70) + (5.7±1.7)TPM−(0.68±0.39). The high TPM aerosols originated in eastern North America and had average composition of 46% nssSO4=, 8% NH4+, and 8% SumOrg. In contrast, low TPM aerosols were found to be of background continental or marine tropospheric origins and had average composition of 23% nssSO4=, 9% NH4+, and 20% SumOrg. The aerosols in both TPM regimes were separated into two groups based on the mode of the volume distributions. The correlation between the mass of each species and the particle volume distribution was investigated for these groups.
Measurement of tropospheric OH by long‐path laser absorption at Fritz Peak Observatory, Colorado, during the OH Photochemistry Experiment, fall 1993
Authors: Mount George H. , Brault James W. , Johnston Paul V. , Marovich Edward , Jakoubek Roger O. , Volpe Cassandra J. , Harder Jerald , Olson Jane
Published: February 2004

The determination of the concentration of hydroxyl (OH) in the Earth's troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. This paper describes the results from the laser long‐path spectroscopic OH experiment used in the Tropospheric OH Photochemistry Experiment (TOHPE) held at Fritz Peak, Colorado, in fall 1993. A primary goal of TOHPE was to compare the OH concentrations measured using a variety of different techniques: a long‐path spectroscopic instrument [Mount, 1992], an in situ ion‐assisted chemical conversion instrument (Eisele and Tanner, 1991, 1993), a laser resonance fluorescence instrument [Stevens et al., 1994), and a liquid scrubber instrument (X. Chen and K. Mopper, unpublished data,; 1996), all with sensitivities at or below 1×106 molecules cm−3. In addition to the OH measurements, a nearly complete suite of trace gas species that affect the OH concentration were measured simultaneously, using both in situ and/or long‐path techniques, to provide the information necessary to understand the OH variation and concentration differences observed. Measurements of OH, NO2, CH2O, SO2, H2O, and O3 were made using long‐path spectroscopic absorption of white light or laser light and OH, NO, NO2, NOy, O3, CO, SO2, CH2O, j(O3), j(NO2), RO2/HO2, HO2, H2O, SO2, PAN, PPN, HNO3, and aerosols (size and composition) and ozone and nitrogen dioxide j‐values were measured using in situ instruments. Meteorological parameters at each end of the long path and at the Idaho Hill in situ site were also measured. The comparison of the long‐path and in situ species from this set of complementary measurements provides an effective way of interpreting air masses over the long path with those at the in situ site; this is a critical issue since the long‐path spectroscopic OH determinations provide a nonchemical and well‐calibrated measurement of OH which must be compared in a meaningful manner with the in situ determinations. Over the period of the TOHPE experiment, OH concentrations were typically low during periods of clean and clear airflow, averaging about 4×106 molecules cm−3 at noon. In contrast, during the well‐defined pollution episodes which occurred during the campaign, OH concentrations rose as high as 15×106 molecules cm−3.
Meteorological overview of the 1993 OH Photochemistry Experiment
Authors: Olson Jane A. , Baumann Karsten , Volpe Cassandra J. , Harder Jerald W. , Williams Eric J. , Mount George H.
Published: February 2004

Meteorological data from three weather stations in the Fritz Peak region of the Colorado Front Range are presented to aid in the interpretation of photochemical results from the tropospheric OH Photochemistry Experiment. The field site, its surrounding topography, and pollution sources are described. Meteorological data show a transition during the campaign from the summer into the fall season, marked by decreasing temperatures and cloud cover, along with increasing wind speeds and westerly flow. Mountainous terrain significantly influences the meteorology over the site and thereby complicates the comparisons of chemical measurements. The meteorological data suggest that an appropriate time to make comparisons between measurement techniques is under conditions of strong westerly airflow, though synchronous upslope wind events should not be excluded.
Model study of polar stratospheric clouds and their effect on stratospheric ozone: 2. Model results
Authors: Tie Xuexi , Brassuer Guy P. , Granier Claire , De Rudder Anne , Larsen Niels
Published: February 2004

We use the detailed microphysical/chemical/dynamical two‐dimensional model described in part I [De Rudder et al., this issue] to study the effect of heterogeneous reactions occurring on the surface of polar stratospheric clouds (PSCs) on stratospheric ozone. The calculations show that the heterogeneous reactions occurring on the surface of PSCs are the likely causes of the ozone decrease observed from 1980 to 1990 in both Antarctica and the Arctic. The calculation shows that the dense sulfate aerosol cloud produced by the eruption of Mount Pinatubo (in the Philippines, 1991) has enhanced the formation rate of type I PSCs in the Arctic and the Antarctic. In the calculation, the concentration and surface area of type I PSCs are enhanced. The effect on the ozone depletion in the Antarctic is, however, limited due to the fact that the conversion from ClONO2 to ClO on PSCs is almost “saturated” under no‐volcanic conditions. For the potential ozone depletion, the enlargement in the area covered by PSCs may therefore be more important than the increase in PSC density. The calculation also shows that, in the future, the density of PSCs in the Arctic could be enhanced owing to the potential emission of water vapor and nitrogen species by high altitude aircraft. The increase in PSC density could lead to a maximum of ozone depletion of 10% at the northern high latitudes in winter.
Model study of polar stratospheric clouds and their effect on stratospheric ozone: 1. Model description
Authors: De Rudder Anne , Larsen Niels , Tie Xuexi , Brassuer Guy P. , Granier Claire
Published: February 2004

We have included detailed microphysical processes accounting for the formation of polar stratospheric clouds (PSC) into a global chemical/dynamical two‐dimensional model to study the effect of heterogeneous reactions occurring on the surface of PSCs on stratospheric ozone. The model explicitly calculates the formation of the PSC particles (50 bin sizes) in terms of heterogeneous nucleation, condensation, and sedimentation. The transport of the particles and heterogeneous reactions on the particles are also represented in the model. The calculated PSC particles show that the distributions of PSCs in the Arctic and in Antarctica are very different. Over Antarctica, nitric acid trihydrate particles (type I PSCs) are formed from early June to late September with a maximum surface area of 15 μm2/cm3, while in the Arctic, type I PSCs are formed only in January with a maximum surface area of 5 μm2/cm3. Ice crystal clouds (type II PSCs) are present over Antarctica in August, but are not seen in the Arctic.
Application of a subgrid orographic precipitation/surface hydrology scheme to a mountain watershed
Authors: Leung L. R. , Wigmosta M. S. , Ghan S. J. , Epstein D. J. , Vail L. W.
Published: February 2004

A regional climate model including a physically based parameterization of the subgrid effects of topography on clouds and precipitation is driven by observed meteorology on its lateral boundaries for a period of 12 months. The meteorology simulated by the model for each subgrid elevation class is distributed across a mountain watershed according to the surface elevation within the watershed. The simulated meteorology is used to drive a detailed model of hydrology‐vegetation dynamics at the topographic scale described by digital elevation data, 180 m. The watershed model, which includes a two‐layer canopy model for evapotranspiration, an energy‐balance model for snow accumulation and melt, a two‐layer rooting zone model, and a quasi‐three‐dimensional saturated subsurface flow model, is used to simulate the seasonal cycle of the accumulation and melt of snow and the accumulation and discharge of surface water within a mountain watershed in northwestern Montana. Comparisons between the simulated and the recorded snow cover and river discharge at the base of the watershed indicate comparable if not better agreement than between the recorded fields and those simulated by the watershed model driven by meteorology observed at two stations within the watershed. The agreement with the recorded discharge, precipitation, and snow water equivalent is also clearly superior to simulations driven by the regional climate model run without the subgrid parameterization but with one‐third the grid size of the simulation with the subgrid parameterization.
Validation of CLAES ClONO2 measurements
Authors: Mergenthaler J. L. , Kumer J. B. , Roche A. E. , Nightingale R. W. , Potter J. F. , Gille J. C. , Massie S. T. , Bailey P. L. , Edwards D. , Connell P. S. , Kinnison D. E. , Gunson M. R. , Abrams M. C. , Toon G. C. , Sen B. , Blavier J.‐F. , Murcray D. G. , Murcray F. J. , Goldman A.
Published: February 2004

The cryogenic limb array etalon spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite has made extensive measurements of thermal infrared radiation from the Earth's limb from which vertical concentration profiles of several stratospheric gases and multiwavelength aerosol absorption coefficients have been retrieved for the period from January 9, 1992, to May 5, 1993. This work examines stratospheric ClONO2 concentrations from the current calibration and retrieval software which are designated version 7 data. These data provide the first near‐global view of this stratospheric species. This work evaluates data quality through (1) an analysis of estimated uncertainties and biases in the remote sensing process, (2) comparison with calculations using a two‐dimensional chemical model, (3) comparison with correlative data, and (4) an examination of various known limitations. The precision of CLAES ClONO2 volume mixing ratio retrievals are within 15% in the range (10 < P < 50 mbar). The upper limit on estimated systematic error is 28% in the range (10 < P < 100 mbar) based on studies of error sources in midlatitude retrievals. The global distribution of ClONO2 computed with the Lawrence Livermore National Laboratory two‐dimensional stratospheric chemistry model and the CLAES measurements agree qualitatively. However, above the profile peak the calculated concentration frequently exceeds the measurement. CLAES and ATMOS measurements show relatively good midlatitude agreement, suggesting that the major source of discrepancy is in the model. A possible explanation in terms of a missing reaction ClO + OH → HCl + O2 is suggested. Also, the ClONO2 diurnal cycle constructed from more than 30 days of CLAES data agrees well with the model. The CLAES ClONO2 data diifer from correlative data acquired on flights of the shuttle‐based ATMOS and balloon‐borne instruments by less than 25% on the average in the 10 < P < 50 mbar range. At altitudes above 10 mbar the CLAES measurement is biased low with respect to correlative measurements. This discrepancy at high altitudes is consistent with the analysis showing a large increase of systematic errors above 10 mbar. Heavy tropical volcanic aerosol from the Mount Pinatubo eruption in June 1991 apparently interfered with ClONO2 retrievals in the period before July 1992, causing anomalous peaks in the 20 < P < 30 mbar region accompanied by very small concentrations below the peak (P > 30 mbar). A similar effect associated with thick polar stratospheric clouds is identified. Overall, this validation study indicates that the majority of these data are of good quality and should be very useful in quantitative and qualitative chemical studies of the stratosphere.
Long‐term variability in the equatorial middle atmosphere zonal wind
Authors: Burrage M. D. , Vincent R. A. , Mayr H. G. , Skinner W. R. , Arnold N. F. , Hays P. B.
Published: February 2004

The high resolution Doppler imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) has provided measurements of the horizontal wind field in the stratosphere, mesosphere, and lower thermosphere since November 1991. This data set, which spans a period of more than 3 years, has facilitated an investigation of the long‐term behavior of the background circulation on a nearly global basis. At middle and high latitudes the zonal circulation is characterized by an annual oscillation. At low latitudes (±30°) the most prominent long‐term variation above the stratopause is the mesosphere semiannual oscillation (MSAO), which maximizes near the equator at an altitude of between 80 and 85 km. Further analysis of the time series reveals an additional strong variation, with an amplitude near 30 ms−1 and a period of about 2 years. This feature shows the same altitude and latitude structure as the MSAO and exhibits a phase relationship with the stratospheric quasi‐biennial oscillation (QBO). Observations from the Christmas Island MF radar (2°N, 130°W) confirm the presence of this mesospheric QBO (MQBO). These observations support recent findings from a modeling study which generates an MQBO via the selective filtering of small‐scale gravity waves by the underlying winds they traverse.
Space shuttle's impact on the stratosphere: An update
Authors: Jackman Charles H. , Considine David B. , Fleming Eric L.
Published: February 2004

To assess their impact on the stratosphere, a launch scenario of nine shuttles and three Titans per year is simulated in a two‐dimensional photochemistry and transport model that includes heterogeneous reactions on a stratospheric sulfate aerosol (SSA) layer and polar stratospheric clouds (PSCs). These rocket launches are predicted to cause small constituent changes in the stratosphere. Maximum total inorganic chlorine enhancements are computed to be about 12 parts per trillion by volume (∼0.4% on a 3 parts per billion by volume background) in the middle to upper stratosphere at northern middle to high latitudes. Maximum ozone decreases associated with these chlorine increases are calculated to be about 0.14% in the middle to upper stratosphere at northern middle to high latitudes. Column ozone decreases are predicted to be a maximum of about 0.05% at northern polar latitudes in the early spring. Model results using (1) gas phase only reactions, (2) gas phase reactions and heterogeneous reactions on the SSA layer, and (3) gas phase reactions and heterogeneous reactions on the SSA layer and PSCs have also been compared with one another. The simulations from these three versions of our model gave annually averaged global total ozone decreases of (1) 0.0056%, (2) 0.010%, and (3) 0.014%. Stratospheric effects from heterogeneous reactions promoted by the alumina emitted from these rockets could be larger than those predicted from the chlorine emissions and need to be investigated further.
A global black carbon aerosol model
Authors: Cooke William F. , Wilson Julian J. N.
Published: February 2004

A global inventory has been constructed for emissions of black carbon from fossil fuel combustion and biomass burning. This inventory has been implemented in a three‐dimensional global transport model and run for 31 model months. Results for January and July have been compared with measurements taken from the literature. The modeled values of black carbon mass concentration compare within a factor of 2 in continental regions and some remote regions but are higher than measured values in other remote marine regions and in the upper troposphere. The disagreement in remote regions can be explained by the coarse grid scale of the model (10° × 10°), the simplicity of the current deposition scheme, and possibly too much black carbon being available for transport, which would also account for the disagreement in the upper troposphere. The disagreement may also be due to problems associated with the measurement of black carbon. Emissions from this database appear to provide a reasonable estimate of the annual emissions of black carbon to the atmosphere. Biomass burning emissions amount to 5.98 Tg and that from fossil fuel amounts to 7.96 Tg. A local sensitivity analysis has been carried out and shows that black carbon has a lifetime between 6 and 10 days, depending on the transformation rate between hydrophobic and hydrophilic black carbon.
Three‐dimensional studies of the 1991/1992 northern hemisphere winter using domain‐filling trajectories with chemistry
Authors: Lutman E. R. , Pyle J. A. , Chipperfield M. P. , Lary D. J. , Kilbane‐Dawe I. , Waters J. W. , Larsen N.
Published: February 2004

We describe a new and computationally efficient technique for global three‐dimensional modeling of stratospheric chemistry. This technique involves integrating a photochemical package along a large number of independent trajectories to produce a Lagrangian view of the atmosphere. Although Lagrangian chemical modeling with trajectories is an established procedure, this extension of integrating chemistry along a large number of domain‐filling trajectories is a novel technique. This technique is complementary to three‐dimensional Eulerian chemical transport modeling and avoids spurious mixing caused by low resolutions or diffusive transport schemes in these models. We illustrate the technique by studying the chlorine activation in the Arctic winter lower stratosphere. A photochemical model was integrated along large ensembles of calculated trajectories between 20 and 100 mbar for the 1991/1992 winter in order to produce a three‐dimensional chemical picture. Large amounts of chlorine was activated at low altitudes (80 to 100 mbar) as well as altitudes near 50 mbar. This activated air was well contained at all levels, with little indication of mixing into lower latitudes. Model results for early January 1992 were compared to daily Microwave Limb Sounder (MLS) ClO observations at 465 K. The structure and evolution of the activated chlorine was well reproduced, giving faith in the technique, although absolute modeled ClO amounts were smaller than the MLS data. A larger number of domain‐filling isentropic trajectories were also run at 475 K to produce a higher‐resolution picture of vortex evolution in late January 1992. The model successfully reproduced the wave breaking events which characterized this period causing transport of activated air to lower latitudes.
Measurements of aerosol optical properties in marine air
Authors: Hegg Dean A. , Covert David S. , Rood Mark J. , Hobbs Peter V.
Published: February 2004

Airborne measurements of the optical properties of aerosols near the coasts of California and Washington are presented. Parameters examined include the particle light‐scattering coefficient (for both total scattering and backscattering), the particle mass light‐scattering efficiency, the hygroscopic growth factor for particle light scattering, and aerosol optical depths computed from vertical profiles of the light‐scattering coefficient. In several instances, the measured values of these parameters differed from commonly accepted values, derived primarily from more polluted airsheds. For example, the aerosol mass scattering efficiency was found to be 2.1 ± 0.3 m2 g−1.
Diurnal winds observed in the tropical troposphere using 50 MHz wind profilers
Authors: Williams Christopher R. , Avery Susan K.
Published: February 2004

The seasonal diurnal zonal and meridional winds observed from 2 to 18 km in the tropical Pacific using five 50‐MHz wind profilers are presented. The hourly data sets ranged in length from 686 days to 2934 days of observations. The observed diurnal winds are compared with tidal model winds forced by solar absorption of water vapor that are primarily the (1,1,1) tidal mode. Similarities between observed and modeled diurnal winds off the equator (12°S) suggest these off‐equator observations are forced by solar absorption of water vapor and are global oscillations. Differences between observed and modeled winds near the equator (2°N and 1°S) suggest these observations are forced by local or mesoscale processes. The vertical structure of meridional wind near the equator supports the diurnal forcing by the radiation of cloud tops and/or cirrus clouds above 12 km or the latent heat release of precipitating clouds extending throughout the troposphere. While near‐equator observations appear to be locally forced, the global distribution of these “local” forcing mechanisms may generate global oscillations that cannot be resolved with these wind profiler data from the Pacific basin. The observed winds below 4 km appear to be affected by boundary layer processes and have different characteristics than winds above 4 km.
Linearization of a longwave radiation scheme for intermediate tropical atmospheric models
Authors: Chou Chia , Neelin J. David
Published: February 2004

A Green's function method is presented for linearizing longwave radiation schemes commonly used in general circulation models in order to produce simpler schemes suitable for use in intermediate complexity atmospheric models. Nonlocal dependence of radiative fluxes on vertical distributions of temperature, moisture, cloud fraction, and cloud top are retained, consistent with the nonlinear scheme. Treatment of several cloud cover types is used in linearizing cloud fraction. A weakly nonlinear scheme is also presented. The method is most useful if linearization about a single tropical reference profile has a sufficient range of validity. Tests are carried out using European Centre for Medium‐Range Weather Forecosts (ECMWF) analysis fields, International Satellite Cloud Climatology Project (ISCCP), Comprehensive Ocean‐Atmosphere Data Set (COADS) and outgoing longwave radiation (OLR) data, and the Harshvardhan scheme as the nonlinear scheme. The linear scheme is found to reproduce the nonlinear results with surprising accuracy in simulation of longwave radiative fluxes associated with interannual variability, seasonal variations, and even tropical climatology as a departure from its spatial average. The spatial patterns and relative magnitudes associated with various contributions are discussed to help inform and provide a target for intermediate model simulations.
Zonal asymmetries in southern hemisphere column ozone: Implications of biomass burning
Authors: Ziemke J. R. , Chandra S. , Thompson A. M. , McNamara D. P.
Published: February 2004

This study compares Nimbus 7 total ozone mapping spectrometer (TOMS) total column ozone with ozone data from two different satellite instruments measuring vertical profiles of ozone in the stratosphere. The first instrument is the microwave limb sounder (MLS) onboard the upper atmosphere research satellite (UARS) and the second is the solar backscattered ultraviolet (SBUV2) nadir sounder aboard NOAA 11. Previous studies have shown that TOMS data exhibit a zonal wave maximum (amplitudes ∼20–30 Dobson units) in total column ozone in the tropical South Atlantic region near 0° longitude. This wave structure occurs in all seasons but maximizes around August–October in association with intense biomass burning in South America and southern Africa. Results of this investigation show that MLS stratospheric column ozone integrated between 1 to 68‐hPa shows no such feature. Horizontal structures of 1 to 68‐hPa MLS column ozone are found to be incoherent with TOMS and SBUV2 total column data in the tropics in all seasons. This study provides the first evidence from a UARS data set that the southern tropical wave 1 peak in TOMS may have relatively small dependence on stratospheric ozone. Combined MLS, TOMS, SBUV2, and ozonesonde station data show that zonal asymmetries observed in total column ozone in the tropics originate primarily from tropospheric effects (dynamics coupled with biomass burning). Outside of the tropics, zonal patterns in total ozone originate mostly from stratospheric dynamics. Wave signatures in TOMS, SBUV2, and MLS column ozone all show generally coherent horizontal structures in middle and high latitudes, especially during seasons of large planetary wave events such as in the southern hemisphere during southern winter–spring.
Refining of atmospheric transport model entries by the globally observed passive tracer distributions of 85krypton and sulfur hexafluoride (SF6)
Authors: Levin Ingeborg , Hesshaimer Vago
Published: February 2004

Our high precision database of the global distribution of SF6 in the troposphere [Maiss et al., 1996] is used in a two‐dimensional atmospheric transport model (2D‐HD model) to study the behavior of this new tracer in comparison to the classical global atmospheric transport tracer krypton 85. The 2D‐HD model grid has been derived from the three‐dimensional Hamburg TM2 model with the same resolution in the vertical and meridional direction and was designed to run on any standard personal computer. The same vertical convection scheme and wind fields as in the TM2 model, reduced to two dimensions, were used in the calculations. In addition, the horizontal diffusion parameter of the model was adjusted by matching the model‐estimated mean meridional 85Kr distribution with observations over the Atlantic Ocean. To simulate global tropospheric SF6 concentrations, an almost linearly increasing SF6 source strength has been applied since 1970. The latitudinal distribution of the SF6 source was assumed to be similar to the global electrical power production. Excellent agreement between SF6 model results and observations is achieved with the 85Kr‐tuned 2D‐HD transport model with respect to the global meridional concentration distribution, and particularly in middle to high northern latitudes. In the southern hemisphere at the German Antarctic station Neumayer, a significant seasonal cycle of SF6 has been observed which is reproduced by the model, however, with a smaller amplitude. This finding may point to possible shortcomings of the model's transport scheme when simulating the seasonality of stratosphere‐troposphere exchange in high southern latitudes.
Small‐scale chemical evolution of aircraft exhaust species at cruising altitudes
Authors: Kärcher B. , Hirschberg M. M. , Fabian P.
Published: February 2004

The chemical transformation of exhaust trace species in aircraft plumes, both directly emitted by the airplane and generated in situ within the first few kilometers behind a single jet engine, is investigated. The chemical processes are strongly coupled to the turbulent dynamics of the hot jet which rapidly mixes with the surrounding atmospheric air. Key issues of the chemical reactions in the jet regime are worked out and the results of extensive parameter studies are presented. The evolution of hydrogen, oxygen, nitrogen, and sulfur species is discussed in detail and related to observations. Spatially resolved, two‐dimensional simulations are compared with box model calculations to point out specific features that result from the coupling between mixing and chemistry and to answer the question under which conditions box models can be applied to give a reasonable description of the jet plume chemistry. Main results concern the conversion efficiencies of primary into secondary exhaust products, the oxidation potential within young aircraft plumes to produce nitrous, nitric, and sulfuric acid, the sensitivity of these processes under variation of exit plane conditions, as well as the production of new aerosol particles. Open questions concerning chemical processing in near‐field exhaust plumes are addressed. The modeling framework presented in this study serves as a basis for further near‐field studies on the physics and chemistry in aircraft wakes.
Chemical species spatial distribution and relationship to elevation and snow accumulation rate over the Greenland Ice Sheet
Authors: Yang Q. , Mayewski P. A. , Linder E. , Whitlow S. , Twickler M.
Published: February 2004

Major chemical species (Cl−, NO−3, SO2−4, Na+, K+, Mg2+, Ca2+) from 24 snowpits (sampled at a resolution of 3 cm, total 2995 samples) collected from northern, central, and southern Greenland were used for this investigation. The annual and seasonal (winter and summer) concentration of each chemical species was calculated and used to study the spatial distribution of chemical species over the central portion of the Greenland Ice Sheet. A two‐sided t‐distribution test (α = 0.05) suggests that concentrations of major chemical species in snow do not vary significantly over this portion of central Greenland. The relationship between chemical concentration and snow accumulation rate was investigated using annual data from two groups of snowpits: those from coastal sites (northern and southern Greenland); and those from high‐altitude inland sites (central Greenland). The snowpit data from a single group, when examined independently of the other group, show that chemical concentrations do not vary with snow accumulation rate. However, when data from the two groups are integrated into a single data set, pseudorelationships appear, with NO−3 concentration decreasing and Na+, K+, Mg2+, and Cl− increasing as snow accumulation rate increases. Therefore we suggest that it is improper to study the relationship between chemical concentration and snow accumulation rate by using data collected from different geographic sites. The relationship between elevation and chemical concentration was investigated using the same suite of annual data sets. We find that Cl−, Na+, and Mg2+ concentrations decrease, while NO−3 concentration increases, with increasing elevation on the Greenland Ice Sheet.
Sensitivity of cirrus cloud albedo, bidirectional reflectance and optical thickness retrieval accuracy to ice particle shape
Authors: Mishchenko Michael I. , Rossow William B. , Macke Andreas , Lacis Andrew A.
Published: February 2004

We examine the sensitivity of cirrus cloud albedo and bidirectional reflection function to particle shape using the phase functions of liquid water spheres, regular hexagonal ice crystals, and random‐fractal ice particles calculated at a nonabsorbing visible wavelength of 0.63 μm. Accurate multiple‐scattering calculations for plane‐parallel clouds show that hexagonal ice crystal clouds have systematically larger planetary and global albedos than liquid water clouds of the same optical thickness. There is accumulating evidence that the idealized phase function of regular hexagonal crystals, which causes pronounced halos, is not necessarily the best representation of the range of reflectance characteristics of the majority of ice clouds. A more typical representation of the scattering phase function for ice clouds that are composed of a complex set of crystal shapes and sizes may be obtained using a model of randomly shaped irregular particles. Even larger cloud albedos are obtained for the random‐fractal particle model because of its smaller asymmetry parameter. Our computations also show that a larger planetary albedo does not always imply a larger reflectance and that the relative brightness of ice versus liquid water clouds is highly scattering‐geometry dependent. Use of the wrong particle shape model (crystal instead of water droplet and vice versa) in retrieving cloud optical thickness from bidirectional reflectance measurements can result in an underestimation or overestimation of the true optical thickness by a factor that can exceed 3. At some scattering geometries, use of the wrong model can give an unrealistically large optical thickness or no solution at all. Overall, bidirectional reflectance differences between random‐fractal and regular hexagonal particle shapes are significantly smaller than those between either ice crystal and liquid water spheres, except at the back scattering direction.
Filtering of air through snow as a mechanism for aerosol deposition to the Antarctic ice sheet
Authors: Harder Susan L. , Warren Stephen G. , Charlson Robert J. , Covert David S.
Published: February 2004

Aerosol particles serve as cloud condensation nuclei worldwide, and they affect the Earth's radiation budget both directly and indirectly. These particles consist mostly of sulfate compounds. Ice core measurements can be used to infer past variations of atmospheric sulfate concentration, but to do so requires knowledge of the deposition mechanisms. Significant “dry” deposition may occur by filtering when air moves through the snow due to changes in pressure caused by wind blowing over a rough surface (wind pumping). The filtering efficiency of snow was measured at South Pole Station, using an optical particle counter and a condensation nucleus counter. The number size‐distribution of ambient aerosol peaks at a dry particle diameter of 0.13 μm, the volume size‐distribution at 0.17 μm. Less than 5% of the particles have diameters >0.3 μm. Diffusion from interstitial air to snow grains appears to be the primary mechanism of dry deposition for particles <0.6 μm in diameter, but another mechanism, probably impaction, becomes significant for larger particles. Aerosol deposition by filtering occurs with an e‐folding time of 1–3 s depending on particle size, corresponding to an e‐folding depth of 0.5–1 cm for an estimated air velocity of 0.4 cm s−1 within the surface snow. Even for long residence times, a small number of particles (<0.1%) are found in filtered air, suggesting a small degree of new particle formation or reentrainment. However, both the e‐folding depth and the reentrainment rate are small enough that smoothing of the sulfate records in ice cores should be negligible. Three mathematical models for filters agree in describing filtering by snow as dominated by diffusion, but all underpredict the filter efficiency. Capture of aerosol particles is found to be 2–3 times as rapid as that assumed by Cunningham and Waddington [1993], supporting their conclusion of nearly total removal of particles from air entering the snow. Blowing snow might also be expected to collect aerosol particles; however, a calculation suggests that deposition to blowing snow on the Antarctic Plateau is insignificant. If wind pumping and diffusion contribute significantly to total deposition, the flux of air into the snow and the residence time of the air within the snow control the deposition rate. Both air flux and residence time are functions of wind speed and surface roughness, so that the aerosol flux to the snow depends on these factors as well as atmospheric concentration, complicating the interpretation of paleoclimate records for aerosol‐bound substances.
The Mauna Loa Observatory Photochemistry Experiment: Introduction
Authors: Atlas E. L. , Ridley B. A.
Published: February 2004

The Mauna Loa Observatory Photochemistry Experiments (MLOPEX) were seasonal investigations of the chemistry of the remote free troposphere over the north Pacific Ocean. This introduction describes the measurement campaign, MLOPEX 2.
A global three‐dimensional model of tropospheric sulfate
Authors: Chin Mian , Jacob Daniel J. , Gardner Geraldine M. , Foreman‐Fowler Michael S. , Spiro Peter A. , Savoie Dennis L.
Published: February 2004

A three‐dimensional model is used to simulate the global tropospheric distributions of dimethylsulfide (DMS), SO2, SO42−, and methanesulfonic acid (MSA). The model uses meteorological input from a general circulation model (GCM) developed at the Goddard Institute of Space Studies (GISS) with 4° × 5° horizontal resolution, nine layers in the vertical, and a time resolution of 4 hours. Model results are compared with observations from surface sites, ships, and aircraft. The model reproduces generally to within 30% the observed SO2 and SO42− concentrations over the United States and Europe; these concentrations are highly sensitive to the supply of H2O2 as an in‐cloud SO2 oxidant. Sulfate concentrations and wet deposition fluxes observed at remote marine sites can be accounted for using a global DMS source of 22 Tg S yr−1 in the model. However, this source overestimates DMS air concentrations by a factor of 2 unless we assume the presence of another DMS oxidant besides OH and NO3. Inclusion of another DMS oxidant in our model also improves the simulation of the MSA to SO42− concentration ratio in marine air. Simulated SO42− concentrations in the northern hemispheric free troposphere are much lower than in previous global models and are more consistent with the few observations available. The difference reflects in part our accounting of efficient scavenging of SO2 and SO42− in wet convective updrafts. Global mean tropospheric lifetimes computed in our model are 1.0 days for DMS, 1.2 days for SO2, 3.9 days for SO42−, and 6.2 days for MSA. Fossil fuel combustion and industrial activities represent 68% of global non‐sea‐salt sulfur emissions. About 50% of SO2 globally is converted to SO42− aerosol (principally by in‐cloud oxidation) while the remainder is removed by deposition (30% by dry, 20% by wet). In‐cloud oxidation of SO2 represents 85% of the global SO42− source.
Accuracy of spectral UV model calculations: 1. Consideration of uncertainties in input parameters
Authors: Weihs Philipp , Webb Ann R.
Published: February 2004

Even in idealized, clear sky conditions, spectral UV models need well‐specified input parameters such as solar zenith angle, pressure, ozone and aerosol optical depth to produce realistic results. UV models based on exact analytical methods are widely considered to be absolutely accurate with errors in results widely attributed to inaccurate input parameters. The uncertainties in the standard determinations of each input parameter were determined for the following methods of specifying each parameter: (1) ozone from satellites or ground‐based Dobson spectrometer measurements; (2) aerosol optical depth from sunphotometer measurements; (3) single‐scattering albedo; three different procedures using ground‐based spectrometer measurements and radiative transfer calculations were studied; (4) ground albedo; the determination of the ground albedo is achieved using satellite measurements, which have a resolution of some 100 km; ground‐based measurements may give some information about the albedo of the ground, but the albedo needed for radiative transfer calculations is a weighted average of the surrounding albedos. The resulting inaccuracies in UV calculations from errors in input parameters were simulated with the discrete ordinate method model by Stamnes et al. [1988] using the uncertainties specified above for the different input parameters. The simulations of the errors of the spectral UV calculations were carried out for each input parameter at 0°, 50°, and 80° zenith angle and analyzed at 305 and 380 nm. The overall maximum error may be determined by combining the different errors.
Pinatubo aerosol and stratospheric ozone reduction: Observations over central Europe
Authors: Ansmann Albert , Wagner Frank , Wandinger Ulla , Mattis Ina , Görsdorf Ulrich , Dier Horst‐Dieter , Reichardt Jens
Published: February 2004

Long‐term observations of ozone profiles at Lindenberg (52.2°N, 14.1°E) and of profiles of the particle surface area concentration at Geesthacht (53.4°N, 10.4°E) are evaluated. Six time series of monthly mean ozone anomalies are formed for layers between 13.5 and 27 km height. The effects of seasonal variation, trend, quasi‐biennial oscillation (QBO), polar vortex, and North Atlantic oscillation (NAO) are eliminated. The residual anomalies indicate aerosol‐induced ozone losses between 10 and 30% in the central part of the Pinatubo layer (15–20 km height) in the winter and spring seasons of 1991–1992 and 1992–1993. Values of the monthly mean particle surface area concentration ranged from 10 to 36 mm2 m−3 during this time period. A correlation analysis, based on mean values of the ozone and aerosol data for the lower, central, and upper part of the Pinatubo layer, indicates a weak positive linear relationship between ozone depletion and surface area in each of the three layers. There is a generally strong influence of the polar vortex strength on the ozone concentration in winter. In the winter of 1992–1993, 10 to 60% of the entire ozone reduction is estimated to be related to the anomalously strong polar cyclone. After the elimination of the vortex‐induced reduction, winter mean sulfate‐related ozone losses of 10 to 20% were associated with winter mean surface area concentrations of 15 to 20 mm2 m−3 for the first two winters after the eruption. The observations are compared with other measurements at northern midlatitudes and with model calculations. In general, a good agreement is found.
Deterministic chaos versus stochasticity in analysis and modeling of point rainfall series
Authors: Koutsoyiannis Demetris , Pachakis Demetris
Published: February 2004

The differences between historic rainfall data and synthetic data obtained by a stochastic rainfall model are investigated using nonlinear analysis tools devised for description and characterization of chaotic behavior. To achieve this goal, a 6‐year point rainfall record with a time resolution of one quarter of hour is studied. A stochastic model capable of preserving important properties of the rainfall process, such as intermittency, seasonality and scaling behavior, is fitted to this data set and a synthetic time series of equal length is generated. For both data sets the correlation dimension is calculated for various embedding dimensions by the time delay embedding method. However, the applicability of this method in estimating dimensions proves limited due to the domination of voids (dry periods) in a rainfall record at a fine time resolution. Thus, in addition to time delay embedding, a Cantorian dust analogue method is developed and used to estimate dimensions. Results of both methods show that there is no substantial difference in behavior between the synthetic and the historic records. Moreover, no evidence of low‐dimensional determinism is detected in the sets examined.