bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of H2O emissions from cryoplanes and kerosene aircraft on the atmosphere
Authors: Gauss M. , Isaksen I. S. A. , Wong S. , Wang W.‐C.
Published: May 2003

Perturbations in H2O caused by aircraft in the year 2015 are calculated with a chemical transport model (CTM) and used as input for radiative forcing calculations. The focus is on a hypothetical fleet of cryoplanes, i.e., liquid‐hydrogen‐powered aircraft. For comparison, the effects of subsonic and supersonic kerosene aircraft are assessed. The CTM applies the accurate second‐order moment scheme for advective transport and is run in T42 resolution (2.8° × 2.8°) with 40 layers between the surface and 10 hPa. Aircraft emissions are taken from NASA inventories for the year 2015. In the cryoplane experiments the projected subsonic kerosene fleet is replaced completely by cryoplanes, which emit 2.55 times as much H2O. Longwave and shortwave components of radiative forcing due to the modeled H2O increases are calculated for different seasons. In northern midlatitudes near the tropopause, the fleet of cryoplanes is calculated to increase zonal‐mean H2O by more than 250 ppbv on an annual average. The resulting radiative forcing at the tropopause strongly depends on season, ranging from 0.0027 W/m2 in October to 0.0135 W/m2 in April on a global average. Subsonic kerosene aircraft are found to have a rather small impact on H2O levels and lead to an annually averaged global‐mean radiative forcing of 0.0026 W/m2. Supersonic kerosene‐powered aircraft have a more pronounced impact on H2O concentrations than subsonic cryoplanes and cause a radiative forcing of nearly 0.05 W/m2. Several sensitivity studies are performed for cryoplanes, dealing with cruising altitude, tropopause height, tropospheric lifetime, and stratospheric sinks of aircraft‐emitted water vapor.
Radiative forcing in the 21st century due to ozone changes in the troposphere and the lower stratosphere
Authors: Gauss M. , Myhre G. , Pitari G. , Prather M. J. , Isaksen I. S. A. , Berntsen T. K. , Brasseur G. P. , Dentener F. J. , Derwent R. G. , Hauglustaine D. A. , Horowitz L. W. , Jacob D. J. , Johnson M. , Law K. S. , Mickley L. J. , Müller J.‐F. , Plantevin P.‐H. , Pyle J. A. , Rogers H. L. , Stevenson D. S. , Sundet J. K. , van Weele M. , Wild O.
Published: May 2003

Radiative forcing due to changes in ozone is expected for the 21st century. An assessment on changes in the tropospheric oxidative state through a model intercomparison (“OxComp”) was conducted for the IPCC Third Assessment Report (IPCC‐TAR). OxComp estimated tropospheric changes in ozone and other oxidants during the 21st century based on the “SRES” A2p emission scenario. In this study we analyze the results of 11 chemical transport models (CTMs) that participated in OxComp and use them as input for detailed radiative forcing calculations. We also address future ozone recovery in the lower stratosphere and its impact on radiative forcing by applying two models that calculate both tropospheric and stratospheric changes. The results of OxComp suggest an increase in global‐mean tropospheric ozone between 11.4 and 20.5 DU for the 21st century, representing the model uncertainty range for the A2p scenario. As the A2p scenario constitutes the worst case proposed in IPCC‐TAR we consider these results as an upper estimate. The radiative transfer model yields a positive radiative forcing ranging from 0.40 to 0.78 W m−2 on a global and annual average. The lower stratosphere contributes an additional 7.5–9.3 DU to the calculated increase in the ozone column, increasing radiative forcing by 0.15–0.17 W m−2. The modeled radiative forcing depends on the height distribution and geographical pattern of predicted ozone changes and shows a distinct seasonal variation. Despite the large variations between the 11 participating models, the calculated range for normalized radiative forcing is within 25%, indicating the ability to scale radiative forcing to global‐mean ozone column change.
Characterization of soil dust aerosol in China and its transport and distribution during 2001 ACE‐Asia: 2. Model simulation and validation
Authors: Gong S. L. , Zhang X. Y. , Zhao T. L. , McKendry I. G. , Jaffe D. A. , Lu N. M.
Published: May 2003

A size‐segregated soil dust emission and transport model, Northern Aerosol Regional Climate Model (NARCM), was used to simulate the production and transport of Asian soil dust during the Aerosol Characterization Experiment‐Asia (ACE‐Asia) period from March to May 2001. The model is driven by the NCEP reanalyzed meteorology and has all the atmospheric aerosol physical processes of soil dust: production, transport, growth, coagulation, and dry and wet deposition. A Chinese soil texture map that infers the soil grain‐size distribution with 12 categories was generated to drive the size‐distributed soil dust emission scheme [Alfaro et al., 1997; Marticorena and Bergametti, 1995]. The size distribution of vertical dust flux was derived from the observed surface dust‐size distribution in the desert regions. Parameters applicable to the Asian deserts for the dust emission scheme are assessed. Model simulations were compared with ground‐based measurements in East Asia and North America and with satellite measurements for the same period of time. The model captured most of the dust mobilization episodes during this period in China and reasonably simulated the concentrations in source regions and downwind areas from East China to western North America. About 252.8 Mt of soil dust below d < 40 μm was estimated to be emitted in the East Asian deserts between 1 March and 31 May 2001 with ∼60% attributed to four major dust storms. The vertical dust loadings above 700 hPa correlate reasonably well with Total Ozone Mapping Spectrometer aerosol index (TOMS AI) observations. The sensitivity analysis of model performance to soil size distribution, water moisture, and meteorology was carried out with the observational data to establish the most appropriate parameters and conditions for the Chinese soil dust production and transport.
Variability of ozone loss during Arctic winter (1991–2000) estimated from UARS Microwave Limb Sounder measurements
Authors: Manney Gloria L. , Froidevaux Lucien , Santee Michelle L. , Livesey Nathaniel J. , Sabutis Joseph L. , Waters Joe W.
Published: May 2003

A comprehensive analysis of version 5 (V5) Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS) ozone data using a Lagrangian transport (LT) model provides estimates of chemical ozone depletion for the 1991–1992 through 1997–1998 Arctic winters. These new estimates give a consistent, three‐dimensional picture of ozone loss during seven Arctic winters; previous Arctic ozone loss estimates from MLS were based on various earlier data versions and were done only for late winter and only for a subset of the years observed by MLS. We find large interannual variability in the amount, timing, and patterns of ozone depletion and in the degree to which chemical loss is masked by dynamical processes. Analyses of long‐lived trace gas data suggest that the LT model sometimes overestimates descent at levels above ∼520 K, so we have most confidence in the results at lower levels. When the vortex is shifted off the pole and the cold region is near the vortex edge (e.g., late winter 1993 and 1996), most rapid ozone depletion occurs near the vortex edge; when the vortex and cold region are pole‐centered (e.g., late winter 1994 and 1997), most ozone loss takes place in the vortex core. MLS observed the most severe ozone depletion in 1995–1996, with about 1.3 ppmv cumulative loss for the winter at 465 K by 3 March 1996; ∼1.0 ppmv cumulative loss is seen at 465 K by mid‐March 1993. Analyses of MLS data show significant ozone loss during January in most years, ranging from ∼0.3 to 0.6 ppmv at 465 K. A modified LT model used with the limited MLS data in 2000 gives rough estimates of ∼0.04 and 0.006–0.012 ppmv/day during 2–12 February and 12 February–29 March 2000, respectively, broadly consistent with other studies of the 1999–2000 winter. Estimates of depletion in MLS column ozone above 100 hPa are considerably smaller than other reported column loss estimates, primarily because many estimates include loss below 100 hPa and because MLS does not continuously observe the Arctic after early spring. Our results from analyses of MLS data confirm previous conclusions of broad overall agreement between many ozone loss estimates in the Arctic lower stratosphere near 450–480 K.
A northern hemispheric climatology of cross‐tropopause exchange for the ERA15 time period (1979–1993)
Authors: Sprenger Michael , Wernli Heini
Published: May 2003

A 15‐year climatology of cross‐tropopause exchange in the extratropical Northern Hemisphere is presented based upon a previously developed Lagrangian methodology and reanalysis data from the European Centre for Medium‐Range Weather Forecasts (ECMWF) for the years 1979–1993. For this time period, no apparent trends exist for upward (troposphere‐to‐stratosphere, TST) and downward (stratosphere‐to‐troposphere, STT) cross‐tropopause transport. The seasonal cycles of hemispherically integrated TST and STT and the zonally integrated meridional exchange distributions show relatively little interannual variability. The 15‐year averaged geographical distribution of STT reveals significant deviations from zonal symmetry and pronounced seasonal variability. STT occurs predominantly over the Atlantic and Pacific storm track regions during winter, spring, and autumn and also over the Mediterranean in winter and spring. In contrast, during summer, STT maxima are located over the continents, particularly over southeastern Europe and central Asia. TST is less variable and is strongest near the southern tip of Greenland and the Aleutian Islands during all seasons. Aspects of the interannual variability of the geographical exchange distributions are investigated. Over the Atlantic, STT varies significantly in line with the changing storm tracks during different phases of the North Atlantic Oscillation (NAO), whereas TST does less so. Special consideration is given to vertically deep exchange, where the exchange air parcels transfer rapidly from the lowermost stratosphere to the boundary layer (or vice versa). These processes occur mainly during winter and exhibit pronounced maxima over the North American west (deep STT) and east (deep TST) coasts.
A 15‐year climatology of stratosphere‐troposphere exchange with a Lagrangian particle dispersion model: 1. Methodology and validation
Authors: James P. , Stohl A. , Forster C. , Eckhardt S. , Seibert P. , Frank A.
Published: May 2003

The Lagrangian particle dispersion model, FLEXPART, which includes additional parametrizations for transport by subgrid‐scale convection and turbulent eddies, is employed to investigate stratosphere‐troposphere exchange (STE), based on 15 years of ECMWF global atmospheric reanalysis data (ERA‐15). The model was initialized with 500,000 particles, distributed randomly throughout the atmosphere, and these were subsequently advected continually over the reanalysis period. The methodology employed in FLEXPART, allowing various age properties and pathways of air masses to be traced permanently on a very wide range of timescales, is described in detail. Empirical validation of the model results is presented. It is shown that typically more than 95% of the mass of the troposphere at any one time has been in the stratosphere within the preceding year, emphasizing the significance of STE. Cross‐tropopause fluxes reveal regions of mean downward net flux in the subtropics flanked by mean upward net flux in the tropics and, more weakly, in the polar regions. Estimates of the mean net downward cross‐tropopause flux in the northern extratropics agree well with other studies but are shown to be highly sensitive to the choice of latitude at which the extratropics are defined to begin. The mean age of tropospheric (stratospheric) air in the stratosphere (troposphere) is derived and shown to be somewhat underestimated, especially for tropospheric air at higher levels of the stratosphere, due largely to deficiencies in the vertical resolution of the ERA‐15 stratosphere.
A Fram Strait cyclone: Properties and impact on ice drift as measured by aircraft and buoys
Authors: Brümmer Burghard , Müller Gerd , Hoeber Heinrich
Published: May 2003

Atmospheric cyclones in the Fram Strait affect the sea ice transport from the Arctic Ocean into the Atlantic Ocean. During the field experiment FRAMZY in April 1999 a Fram Strait cyclone and its impact on the ice drift was measured using a research aircraft and an array of 15 ice buoys. The synoptic‐scale cyclone moved from the south into the area. It was discernible up to 500 hPa in the pressure field, but the horizontal temperature contrast of up to 16 K between the warm and cold sides was confined to the lowest 500 m. The average ice drift was 0.21 ms−1 toward 200° but increased to 0.6 ms−1 during the cyclone passage. The ice drift amounted to 1.6% of the geostrophic wind with a turning angle of 51° on the average. Comparisons between the aircraft measurements and operational weather model analyses show an insufficient representation of the temperature inversion and indicate an underestimate of wind speed and, thus, momentum transfer to the sea ice.
Comparing satellite rainfall estimates with rain gauge data: Optimal strategies suggested by a spectral model
Authors: Bell Thomas L. , Kundu Prasun K.
Published: May 2003

The statistical problem of comparing rain gauge measurements to satellite rain‐rate estimates over an area surrounding the gauge(s) is examined using a model of rainfall variability developed for studies of sampling error in averages of satellite data. The model is able to capture a number of important aspects of the space‐time spectrum of rain‐rate variability, including the interdependence of time and space scales of variability. Four parameters must be specified in the model. Sets of parameters have been obtained that fit the statistics of radar‐derived rain rates over the eastern tropical Atlantic (from GATE) and the western tropical Pacific (from TOGA COARE). The model predicts that there is an optimal averaging time for gauge data when gauge averages are compared to average satellite rain‐rates for a specified area around the gauge. The optimal averaging time ranges from minutes to days as the diameter of the area around the gauge is extended from 2 km to 200 km. The optimal averaging time shrinks as more gauges are added to the area viewed by the satellite, but the model suggests that even over fairly dense gauge networks it is necessary to compare averages of several hundred satellite overflights in order to bring the comparison error down to the 10% level. The possibility that comparisons of gauge data with satellite averages might be improved by weighting the gauge data differently depending on how close the gauge data are in time to the satellite overflights is investigated, and it is found that in some cases the variance of the comparison error can be reduced by a factor of two by using optimal time‐dependent weighting.
Variability of aerosol size‐resolved composition at an Indian coastal site during the Indian Ocean Experiment (INDOEX) intensive field phase
Authors: Alfaro S. C. , Gaudichet A. , Rajot J. L. , Gomes L. , Maillé M. , Cachier H.
Published: May 2003

In March 1999, that is to say, during the Indian Ocean Experiment (INDOEX) Intensive Field Phase, various aerosol characteristics have been measured on the campus of Goa University (Goa, India: 15° 24′N, 74° 48′E). This site, located on the western coast of India, is at the exit of the continent during the winter northeastern monsoon, and the variability of the aerosol characteristics measured here will certainly reflect the variability of aerosol properties over large INDOEX areas. Concentrations in total suspended matter (TPM) and fine particles (PM1) were determined by means of a two‐stage sampler. They varied greatly during the measurement period (e.g., between 30 and 120 μg/m3for the TPM) but were found to be, on the whole, of the same order of magnitude as those measured far downwind of the Indian subcontinent, namely at Kaashidhoo Climate Observatory (KCO, the Maldives). The aerosol mass composition determined by combining XRF analysis (for inorganic elements) and thermal analysis (for carbonaceous components) of filter samples shows that mineral dust (MD) and sea salt (SS) dominate this mass composition. For instance, temporary inputs of MD from distant desert sources explain the observed TPM variations. In contrast, aerosol number concentrations and size resolved composition determined by using optical particle counters, microscope observation, and low‐ or high‐pressure stage impactors, reveal that in terms of numbers, black carbon (BC) is by far the dominant species in the submicron mode. These particles are frequently coated by less absorbing matter, presumably a mixture of sulfate and condensed organic compounds. By using the time variability of the K/BC ratio, it is also shown that the origin of carbonaceous components varies during the measurement period. In early March, 70% of BC is produced by fossil fuel combustion and 30% by biomass burning, but the contribution of biomass burning increases during the period of the experiment until the previous proportions are reversed around March 25. Comparison of these results with other INDOEX measurements indicates that the spatial gradient observed for aerosol concentrations and composition in the northern part of the Indian Ocean are of the same order of magnitude as the temporal variability observed at Goa.
Spectroscopic measurements of halocarbons and hydrohalocarbons by satellite‐borne remote sensors
Authors: Coheur P. F. , Clerbaux C. , Colin R.
Published: May 2003

Infrared spectra recorded by the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) and the Interferometric Monitor for Greenhouse Gases (IMG) remote sensors have been analyzed by means of line‐by‐line radiative transfer calculations in order to evaluate the possibilities offered by solar occultation and by nadir instruments to monitor the cholorofluorocarbons (CFCs) and their substitutes. The reliability of the existing spectroscopic parameters has been examined, and it was found that only laboratory parameters measured at high resolution reproduce the satellite observations well. It is shown that solar occultation spectra can give information regarding the atmospheric abundance of CFC‐113, in addition to the usual retrievals of CFC‐11, CFC‐12 and HCFC‐22. Also, relying on existing emission scenarios, it is foreseen that future solar occultation experiments, such as the Atmospheric Chemistry Experiment (ACE), will be able to detect HCFC‐142b and HFC‐134a, from the year 2005 onward and at low tangent heights. As for the nadir‐looking missions, it is found that CFC‐11, CFC‐12 and HCFC‐22 can be retrieved from IMG spectra, provided that numerous measurements are averaged over space or time, thereby mitigating the usefulness of such measurements for determining surface sources. The improved geometrical scanning performances of the future nadir‐looking Infrared Atmospheric Sounding Interferometer (IASI) and the Tropospheric Emission Spectrometer (TES), however, are shown to be more promising in this respect.
PMSE dependence on aerosol charge number density and aerosol size
Authors: Rapp Markus , Lübken Franz‐Josef , Hoffmann Peter , Latteck Ralph , Baumgarten Gerd , Blix Tom A.
Published: May 2003

It is commonly accepted that the existence of polar mesosphere summer echoes (PMSEs) depends on the presence of charged aerosols since these are comparatively heavy and reduce the diffusion of free electrons due to ambipolar forces. Simple microphysical modeling suggests that this diffusivity reduction is proportional to rA2 (rA = aerosol radius) but only if a significant amount of charges is bound on the aerosols such that NA∣ZA∣/ne > 1.2 (NA = number of aerosols, ZA = aerosol charge, ne = number of free electrons). The fact that the background electron profile frequently shows large depletions (“biteouts”) at PMSE altitudes is taken as a support for this idea since within biteouts a major fraction of free electrons is missing, i.e., bound on aerosols. In this paper, we show from in situ measurements of electron densities and from radar and lidar observations that PMSEs can also exist in regions where only a minor fraction of free electrons is bound on aerosols, i.e., with no biteout and with NA∣ZA∣/ne ≪ 1. We show strong experimental evidence that it is instead the product NA∣ZA∣rA2 that is crucial for the existence of PMSEs. For example, small aerosol charge can be compensated by large aerosol radius. We show that this product replicates the main features of PMSEs, in particular the mean altitude distribution and the altitude of PMSEs in the presence of noctilucent clouds (NLCs). We therefore take this product as a “proxy” for PMSE. The agreement between this proxy and the main characteristics of PMSEs implies that simple microphysical models do not satisfactorily describe PMSE physics and need to be improved. The proxy can easily be used in models of the upper atmosphere to better understand seasonal and geographical variations of PMSEs, for example, the long debated difference between Northern and Southern hemisphere PMSEs.
Seasonally averaged ozone and nitrous oxide in the Northern Hemisphere lower stratosphere
Authors: Proffitt M. H. , Aikin K. , Tuck A. F. , Margitan J. J. , Webster C. R. , Toon G. C. , Elkins J. W.
Published: May 2003

Northern Hemisphere ozone (O3) measurements in the lower stratosphere made from 1989 to 1997 are presented along with simultaneous measurements of the conserved tracer nitrous oxide (N2O) to help separate O3 changes due to photochemistry from those due to transport. This model‐independent analysis represents 139 flights aboard the ER‐2 aircraft and 12 profiles from balloons and uses zonal, isobaric, and isentropic seasonal averages of O3 and N2O to examine seasonal changes in O3 distributions. The resulting seasonal families of curves at constant latitude are somewhat intertwined, while the families of isobaric and isentropic curves are not. Although some of the isobaric curves cross, the isentropic curves are sufficiently separated to confidently estimate O3 by specifying season, N2O, and potential temperature, then interpolating between the curves. Such estimates may be useful for testing of photochemical models with transport, and perhaps more importantly, the families of curves could serve as baseline references for estimating high latitude photochemical O3 loss and as an indicator of O3 recovery in the lower stratosphere.
Halogen Occultation Experiment and Stratospheric Aerosol and Gas Experiment II observations of tropopause cirrus and aerosol during the 1990s
Authors: Massie Steven , Randel William , Wu Fei , Baumgardner Darrel , Hervig Mark
Published: May 2003

Averages of Halogen Occultation Experiment (HALOE) aerosol extinction at 121 hPa for 1993–1999 and Stratospheric Aerosol and Gas Experiment (SAGE II) aerosol extinction between 100 and 140 hPa for 1987–1999 are analyzed in the tropics (20°S–20°N). Multiple wavelength techniques for HALOE and SAGE II data are used to distinguish cirrus from aerosol observations following the eruption of Mount Pinatubo in 1991. SAGE II and HALOE cirrus extinction values are 34 and 28% less, respectively, in 1993 than in 1995–1999, while aerosol extinction decreases over the same time period. SAGE II and HALOE decreases in the frequency of occurrence of cirrus in 1993 are qualitatively similar to the SAGE II decreases in the frequency of occurrence of cirrus, discussed by Wang et al. [1995], after the eruption of El Chichon. Tropopause temperature anomalies in 1993 most likely do not account for the decrease in cirrus observed in 1993 by both the HALOE and SAGE II experiments.
Budget of tropospheric ozone during TOPSE from two chemical transport models
Authors: Emmons L. K. , Hess P. , Klonecki A. , Tie X. , Horowitz L. , Lamarque J.‐F. , Kinnison D. , Brasseur G. , Atlas E. , Browell E. , Cantrell C. , Eisele F. , Mauldin R. L. , Merrill J. , Ridley B. , Shetter R.
Published: May 2003

The tropospheric ozone budget during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign has been studied using two chemical transport models (CTMs): HANK and the Model of Ozone and Related chemical Tracers, version 2 (MOZART‐2). The two models have similar chemical schemes but use different meteorological fields, with HANK using MM5 (Pennsylvania State University, National Center for Atmospheric Research Mesoscale Modeling System) and MOZART‐2 driven by European Centre for Medium‐Range Weather Forecasts (ECMWF) fields. Both models simulate ozone in good agreement with the observations but underestimate NOx. The models indicate that in the troposphere, averaged over the northern middle and high latitudes, chemical production of ozone drives the increase of ozone seen in the spring. Both ozone gross chemical production and loss increase greatly over the spring months. The in situ production is much larger than the net stratospheric input, and the deposition and horizontal fluxes are relatively small in comparison to chemical destruction. The net production depends sensitively on the concentrations of H2O, HO2 and NO, which differ slightly in the two models. Both models underestimate the chemical production calculated in a steady state model using TOPSE measurements, but the chemical loss rates agree well. Measures of the stratospheric influence on tropospheric ozone in relation to in situ ozone production are discussed. Two different estimates of the stratospheric fraction of O3 in the Northern Hemisphere troposphere indicate it decreases from 30–50% in February to 15–30% in June. A sensitivity study of the effect of a perturbation in the vertical flux on tropospheric ozone indicates the contribution from the stratosphere is approximately 15%.
Seasonal/regional comparisons of rain rates and rain characteristics in West Africa using TRMM observations
Authors: Sealy Andrea , Jenkins Gregory S. , Walford Segayle C.
Published: May 2003

West African rain estimates from a number of global rain data sets (surface and satellite derived), including the TRMM precipitation radar and merged data sets are compared for the 1998–2000 May through September period. Rain intensity and classification (convective/stratiform) from the TRMM precipitation radar are also included in this study. All of the rainfall estimates, including the TRMM products, show that the highest rain rates occur during the month of August for West Africa and its sub region, the Sahel. High negative correlations (<−0.8) are found among the wet season rain estimates and outgoing longwave radiation for West Africa and the Sahel. In the Guinea region, correlations are considerably lower because of a significant longitudinal variation in OLR during the wet season. The TRMM Precipitation Radar derived rain estimates show that stratiform rain becomes increasingly important as the wet season evolves with 35–40% of the rain being stratiform during August and September. Surprisingly the total number of lightning flashes in the Sahel is higher than those in the Guinea region by a factor of 1.5. During August, the Sahelian lightning flashes outnumber those in the Guinea region by more than a factor of 4. Furthermore, in the Sahel, the majority of the flashes occur during the nighttime but during the daytime in the Guinea region. Because of spatial and temporal under‐sampling, the TRMM rain estimates are lower than other rain estimates with the TRMM PR producing the lowest rain rates.
Estimation of Arctic polar vortex ozone loss during the winter of 1999–2000 using vortex‐averaged airborne differential absorption lidar ozone measurements referenced to N2O isopleths
Authors: Grant William B. , Browell Edward V. , Butler Carolyn F. , Gibson Sharon C. , Kooi Susan A. , von der Gathen Peter
Published: May 2003

The NASA Langley UV differential absorption lidar (DIAL) system flew on the NASA DC‐8 aircraft during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) mission from 30 November 1999 to 15 March 2000. The UV DIAL system measured ozone (O3) profiles at altitudes from about 1 km above the aircraft up to about 26 km with a vertical resolution of 750 m and a horizontal resolution of 70 km below 19 km and 140 km above 19 km. In comparison with electrochemical concentration cell ozonesonde profiles, the UV DIAL O3 measurements agreed to within 5% up to 20 km and 10% from 20 to 25 km. Ozone loss during the season was determined using the UV DIAL O3 data along with air mass subsidence determined using N2O as a conservative tracer at five levels from 50 to 250 ppbv [Greenblatt et al., 2002]. O3 mixing ratios were determined inside the polar vortex, away from the collar region along these five levels during the mission. The maximum O3 loss determined from 30 November to 12 March was 1.55 ± 0.3 ppmv at the 440–450 K potential temperature (Θ) level, while the loss there between 20 January and 15 March was 1.3 ± 0.3 ppmv. These results are comparable to many of the other reported losses for these periods, but lower than several. Some of the determinations of higher losses used a different method to determine descent during the season. These results indicate that a series of vertical profiles of O3 that sample much of the vortex during the winter, along with determinations of the descent of air masses inside the vortex, can give a reasonable estimate of the O3 changes during the season.
Evolution of El Niño‐precipitation relationships from satellites and gauges
Authors: Curtis Scott , Adler Robert F.
Published: May 2003

This study uses a 23 year (1979–2001) satellite‐gauge merged community data set to further describe the relationship between El Niño‐Southern Oscillation (ENSO) and precipitation. The globally complete precipitation fields reveal coherent bands of anomalies that extend from the tropics to the polar regions. El Niño‐precipitation relationships were analyzed during the six strongest events from 1979 to 2001. El Niños were defined based on the zonal contrast in rainfall in the equatorial Pacific, and seasons of precipitation evolution (pre‐onset, onset, peak, decay, and postdecay) were identified. Areas with a consistent El Niño‐precipitation relationship were determined based on this unique definition of El Niño and season of year. The latter analysis confirms previous studies and suggests other areas of significant signal over the oceans (Gulf of Alaska). The former analysis reveals subtle shifts in tropical rainfall from onset to decay, namely negative anomalies moving from the Maritime Continent and South Pacific to the north tropical Pacific and positive anomalies from the central equatorial Pacific southeastward. These distributions of tropical convection appear to be connected to extratropical precipitation anomalies through meridional atmospheric circulations, concentrated in the eastern Indian Ocean sector during onset and in the Pacific sector during decay. The Yangtze River basin, which is known to flood during El Niño, is affected during the entire evolution.
Development of mixed‐phase clouds from multiple aerosol size distributions and the effect of the clouds on aerosol removal
Authors: Jacobson Mark Z.
Published: May 2003

This paper provides numerics for cloud and precipitation development from multiple aerosol size distributions and examines the effect of clouds and precipitation on aerosol removal. Numerical techniques are given for (1) simultaneous liquid and ice growth onto multiple aerosol size distributions, (2) diffusiophoretic, thermophoretic, gravitational, etc., coagulation among liquid, ice, and graupel, and their aerosol components, (3) contact freezing (CF) of drops by size‐resolved interstitial aerosols, (4) heterogeneous plus homogeneous freezing, (5) liquid drop breakup, (6) coagulation of cloud hydrometeors and incorporated aerosols with interstitial aerosols, (7) coagulation of precipitation hydrometeors with interstitial and below‐cloud aerosols (washout), (8) removal of precipitation and incorporated aerosols (rainout), (9) below‐cloud evaporation/sublimation to smaller hydrometeors and aerosol cores, (10) gas washout, and (11) aqueous chemistry. Major conclusions are (1) hydrometeor‐hydrometeor coagulation appears to play a substantial role in controlling aerosol‐particle number globally, (2) washout (aerosol‐hydrometeor coagulation) may be a more important in‐plus below‐cloud removal mechanism of aerosol number than rainout (the opposite is true for aerosol mass), (3) close‐in diameter dual peaks in observed cloud distributions may be in part due to different activation characteristics of different aerosol distributions, (4) evaporative cooling at liquid drop surfaces in subsaturated air may be a mechanism of drop freezing (termed “evaporative freezing” here), and (5) heterogeneous‐homogeneous freezing may freeze more upper‐tropospheric drops than CF, but neither appears to affect warm‐cloud hydrometeor distributions or aerosol scavenging substantially.
Evaluation of transport in the lower tropical stratosphere in a global chemistry and transport model
Authors: Douglass Anne R. , Schoeberl Mark R. , Rood Richard B. , Pawson Steven
Published: May 2003

Off‐line chemistry and transport models (CTMs) use meteorological information from a general circulation model (GCM) or from a data assimilation system (DAS) to calculate the evolution of stratospheric constituents. Here constituent fields from two CTM simulations are compared with each other and with observations from satellite, aircraft, and sondes to judge the realism of the tropical transport. One simulation uses winds from a GCM and the second uses winds from a DAS that has the same GCM at its core. A simulation using the GCM fields reproduces many observed features for O3, CH4, and the age of air. The same comparisons for a simulation using DAS fields show rapid upward tropical transport and excessive mixing between the tropics and middle latitudes. The assimilation system changes the temperature and wind fields to produce consistency between a GCM forecast and observations, behaving like an additional forcing has been added to the equations of motion and possibly leading to the unrealistic transport produced by the DAS fields. These comparisons highlight aspects of the transport in the lower tropical stratosphere, and suggest that while a CTM driven by DAS fields provides good short‐term simulations when event‐by‐event comparisons with observations are desired, a CTM driven by GCM fields may be more appropriate for long‐term calculations such as required to assess the impact of changes in stratospheric composition.
Modification of aerosol mass and size distribution due to aqueous‐phase SO2 oxidation in clouds: Comparisons of several models
Authors: Kreidenweis Sonia M. , Walcek Chris J. , Feingold Graham , Gong Wanmin , Jacobson Mark Z. , Kim Cheol‐Hee , Liu Xiaohong , Penner Joyce E. , Nenes Athanasios , Seinfeld John H.
Published: May 2003

Models of aerosol scavenging and aqueous‐phase oxidation of SO2 by H2O2 and O3 in a cloud updraft are compared. Bulk models considering only a single droplet size are compared with size‐resolved models that explicitly simulate multiple aerosol and drop sizes. All models simulate growth of cloud drops on a lognormal ammonium bisulfate aerosol distribution, and subsequent aqueous‐phase chemistry during adiabatic ascent. In agreement with earlier published studies, it is found that relative to bulk models, the size‐resolved cloud chemical models consistently calculate 2–3 times more oxidation via the SO2 + O3 pathway, due to calculated variability of cloud water pH among cloud drops. All models calculate high scavenging of the input dry aerosol mass, but the calculated number of cloud drops formed varies from 275–358 drops cm−3. Differences in the calculated number of cloud drops formed result from the treatment of gaseous species uptake, solution thermodynamics, applied water condensation mass accommodation coefficient, and bin size range definitions over which the input aerosol distribution is numerically approximated. The difference in calculated cloud drop number can under many conditions propagate to appreciable variations in cloud albedo. It is found that the modifications to the aerosol size and mass spectrum are sensitive to the number of cloud drops formed, and differences in the processed aerosol spectra were found to induce up to 13% differences in calculated light extinction properties of the modified particle distributions. These significant discrepancies among cloud aerosol chemistry interaction models, even when used to simulate relatively simple conditions, suggest that parameterizations of these processes used in larger‐scale cloud, regional and longer‐term climate models can contain high levels of uncertainty.
Statistical characteristics of the electric and magnetic fields and their time derivatives 15 m and 30 m from triggered lightning
Authors: Schoene J. , Uman M. A. , Rakov V. A. , Kodali V. , Rambo K. J. , Schnetzer G. H.
Published: May 2003

We present a statistical analysis of the salient characteristics of the electric and magnetic fields and their derivatives at distances of 15 m and 30 m from triggered lightning strokes that lowered negative charge to ground. Return stroke current and current derivative characteristics are also presented. The measurements were made during the summers of 1999 and 2000 at Camp Blanding, Florida. Lightning was triggered to a 1 to 2 m strike object at the center of a 70 m × 70 m metal‐grid ground plane that was buried beneath a few centimeters of soil. The strike object was mounted on the rocket launching system that was located below ground level in a pit. The experiment was designed (1) to minimize the influence of the strike object on the field and field derivative waveforms and (2) to eliminate potential distortions of the field and field derivative waveforms both due to ground surface arcing and due to the propagation of the field being over imperfectly conducting ground. Measurements were made on about 100 return strokes, although not all field quantities were successfully recorded for each stroke. We present histograms and parameters of statistical distributions for the following 28 waveform characteristics: current peak, risetime, and width; current derivative peak, risetime, and width; return‐stroke electric field change and field pulse width at 15 m and at 30 m; electric field derivative peak, risetime, and width at 15 m and at 30 m; magnetic field peak, risetime, and width at 15 m and at 30 m; and magnetic field derivative peak, risetime, and width at 15 m and at 30 m. We compare our results with those from previous studies. From this comparison we infer, among other results, that for strikes to our buried metal‐grid ground plane the current risetime and width are, on average, smaller than for strikes to concentrated grounding electrodes (vertical ground rods).
Lidar observations of equatorial cirrus clouds at Mahé Seychelles
Authors: Pace Giandomenico , Cacciani Marco , di Sarra Alcide , Fiocco Giorgio , Fuà Daniele
Published: May 2003

In February–March 1999, nocturnal observations with a ground‐based backscatter/depolarization lidar were conducted during the Airborne Platform for Earth Observation–Third European Stratospheric Experiment on Ozone (APE‐THESEO) campaign at Mahé, Seychelles (4.4°S, 55.3°E). Upper tropospheric cirrus clouds were a common feature in the lidar echoes; they were detected for about 67 hours out of a total measurement time of 125 hours. Optical and geometrical characteristics of the clouds detected at altitudes above 9 km throughout the campaign are derived and discussed. Cirri above 14.5 km present a layered structure and appear more persistent and thinner than cirri at lower altitudes. The behavior of average optical and geometrical depths, integrated depolarization, backscatter‐to‐extinction ratio, integrated backscatter, and extinction coefficient is studied as a function of midcloud temperature and is compared with results from previous measurements and models. The estimated cloud backscatter‐to‐extinction ratio ranges from 0.01 to 0.2 sr−1, with an average value of 0.051 ± 0.030 sr−1. In the temperature range between 200 and 240 K the integrated depolarization ranges between 0.27 and 0.19 and appears lower than that for midlatitude cirri. In a single night, very high values of the integrated depolarization for a layered cirrus at 16 km could be related to outflow from an active convective cell. The two highest and coldest (temperature around 188 K) layers show values of optical and geometrical depth and integrated depolarization lower than for cirri at temperatures between 190 and 200 K. The optical characteristics of the clouds decrease for temperatures from 190 to 200 K, possibly indicating different evolution phases of the clouds.
Corona emission from raindrops in strong electric fields as a possible discharge initiation: Comparison between horizontal and vertical field configurations
Authors: Coquillat Sylvain , Combal Bruno , Chauzy Serge
Published: May 2003

The purpose of this work is to determine which electric field configuration (vertical or horizontal) produces corona emission from raindrops for the lowest ambient electric field. For that, a numerical modeling of the distortion of uncharged raindrops falling at terminal velocity in quiescent air in a horizontal electric field is performed. The results are compared with previous numerical study involving a vertical electric field. It is shown that the fall velocity is quite unaffected by ambient field intensities lower than 200 kV/m. The disruption and the corona onset fields are lower than those corresponding to the vertical field configuration and the larger the drop the larger the difference. For a given altitude the difference between the corona onset fields in both configurations can reach about 100 kV/m; meanwhile for a given ambient field intensity, the difference in altitude of corona emission can rise to about 1 km. These onset field intensities are, though, too high for allowing drop breakup and corona emission from an uncharged drop in permanent field conditions below 12 km height. An estimation of the critical onset field (disruption and/or corona emission) is carried out for charged drops in the horizontal field configuration. For a drop 2 mm in spherical equivalent radius carrying the quarter of its Rayleigh maximum net charge, the critical onset field is approximately equal to 290 kV/m below 7.4 km height and decreases down to 110 kV/m at 10 km. Given that present modeling does not take into account the effect of turbulence that could induce drop oscillations, the critical field intensities calculated here may be considered as upper limits.
Peroxy radical observations using chemical ionization mass spectrometry during TOPSE
Authors: Cantrell Christopher A. , Edwards G. D. , Stephens S. , Mauldin L. , Kosciuch E. , Zondlo M. , Eisele F.
Published: May 2003

Peroxy radicals (HO2 + RO2) were measured by chemical conversion‐chemical ionization mass spectroscopy in the TOPSE (Tropospheric Ozone Production about the Spring Equinox) campaign that took place February through May 2000. Instrumentation for these measurements was deployed on the NCAR/NSF C‐130 aircraft that flew at latitudes from 40 to 85°N, and altitudes from the surface to 7.5 km over the North American continent. The measurements demonstrate the evolution of photochemical activity as time progresses through the study period due to increases in free radical source rates. The increase in average peroxy radical concentration moves northward as the maximum solar elevation and length of sunlit days increase. HOxROx (HO2 + RO2) concentrations are distributed lognormally with means of 11.5 and 7.8 pptv for the middle‐latitude band (MLB) and high‐latitude band (HLB), respectively. The observations agree well on average with steady state derived concentrations; measurement‐model concentration ratios are 1.04 (MLB) and 0.94 (HLB). Concentrations within a given latitude band and altitude region sometimes appear to increase with NOx concentrations, but this correlation nearly disappears at low and moderate NOx levels when the data are parsed by radical production rate; lower radical levels are observed at the highest NOx levels measured (near 1 ppbv). These data are compared with results from other recent observations utilizing a variety of platforms.
Statistical analysis of cloud light scattering and microphysical properties obtained from airborne measurements
Authors: Jourdan Olivier , Oshchepkov Sergey , Gayet Jean‐Francois , Shcherbakov Valery , Isaka Harumi
Published: May 2003

A new statistical analysis of the in situ scattering phase function measurements performed by the Laboratoire de Météorologie Physique's airborne polar nephelometer is implemented. A principal component analysis along with neural networks leads to the classification of a large data set into three typical averaged scattering phase functions. The cloud classification in terms of particle phase composition (water droplets, mixed‐phase, and ice crystals) is done by a neural network and is validated by direct Particle Measuring Systems, Inc., probe measurements. The results show that the measured scattering phase functions carry enough information to accurately retrieve component composition and particle size distributions. For each classified cloud, we support the statement by application of an inversion method using a physical model of light scattering to the average scattering phase function. Furthermore, the retrievals are compared with size composition obtained by independent direct measurements.
Intensity of prehistoric tropical cyclones
Authors: Nott Jonathan F.
Published: May 2003

Prediction of future tropical cyclone climate scenarios requires identification of quasi‐periodicities at a variety of temporal scales. Extension of records to identify trends at century and millennial scales is important, but to date the emerging field of paleotempestology has been hindered by the lack of a suitable methodology to discern the intensity of prehistoric storms. Here a technique to quantify the central pressure of prehistoric tropical cyclones is presented in detail and demonstrated for the tropical southwest Pacific region. The importance of extending records to century time scales is highlighted for northeast Australia, where a virtual absence of category 5 cyclones during the 20th century stands in contrast to an active period of severe cyclogenesis during the previous century. Several land crossing storms during the 19th century achieved central pressures lower than that ever recorded historically and close to the theoretical thermodynamic limit of storms for the region. This technique can be applied to all tropical and subtropical regions globally and will assist in obtaining more realistic predictions for future storm scenarios with implications for insurance premiums, urban and infrastructural design, and emergency planning.
Variability and predictability of 200‐mb seasonal mean heights during summer and winter
Authors: Kumar Arun , Schubert Siegfried D. , Suarez Max S.
Published: May 2003

In this paper a comparison of the variability and predictability of 200‐mb seasonal mean heights for winter and summer is made based upon atmospheric general circulation model (AGCM) simulations. Simulations from two different AGCMs for the 1982–1999 period are used. The magnitude of seasonal predictability for the winter and summer is found to be similar. The spatial characteristics of seasonal predictability, however, had some interesting differences. For the respective hemisphere's summer the extratropical zonal mean heights had an appreciable contribution towards seasonal predictability, whereas for the winter season, predictability was dominated by eddy heights. There were also interesting interhemispheric differences in seasonal variability and predictability which are attributed to an interplay between the seasonal cycle of El Niño‐Southern Oscillation SST anomalies and the seasonal cycle of mean atmospheric circulation which governs the dynamics of tropical‐extratropical interactions.