bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameterization of shortwave ice cloud optical properties for various particle habits
Authors: Key Jeffrey R. , Yang Ping , Baum Bryan A. , Nasiri Shaima L.
Published: October 2002

The relative importance of ice clouds in the climate system is highly uncertain. Measurements of their microphysical properties are sparse, especially given their complex structure and large variability in particle size, shape, and density. To better understand the role of ice clouds in the climate system, parameterizations of their radiative properties are needed. The shortwave bulk optical properties of seven ice particle shapes, or “habits,” are parameterized as a function of the effective “radius” and ice water content by integrating the scattering properties over 30 in situ size distributions. The particle habits are solid and hollow hexagonal columns, hexagonal plates, two‐ and three‐dimensional bullet rosettes, aggregates of columns, and dendrites. Parameterizations of the volume extinction coefficient, single‐scattering albedo, and the asymmetry parameter are presented for 6, 24, and 56 band shortwave schemes from 0.2 to 5.0 μm. Applications to downwelling flux and upwelling radiance calculations indicate that differences in fluxes for various habits can be more than 15%, and differences in retrievals of cloud optical depth from satellite visible reflectances can be more than 50%.
Physical properties of maritime low clouds as retrieved by combined use of Tropical Rainfall Measurement Mission Microwave Imager and Visible/Infrared Scanner: Algorithm
Authors: Masunaga Hirohiko , Nakajima Takashi Y. , Nakajima Teruyuki , Kachi Misako , Oki Riko , Kuroda Shunsuke
Published: October 2002

Satellite remote sensing studies on the microphysical and optical properties of clouds have constructed an active research field in the last decades. Clouds are observed over a wide spectral range from the visible/infrared to the microwave, and either shortwave or microwave measurement is used to evaluate the liquid water path (LWP). On the other hand, to date, there have been few cloud studies based on combined measurement by a visible/infrared imager and a microwave radiometer aboard the same platform. In this paper a physical inversion algorithm for the combined use of visible/infrared and microwave sensors is proposed to retrieve the cloud physical quantities such as LWP and the effective droplet radius, each of which is determined in two different ways. The current version of the algorithm has been developed for application to the Tropical Rainfall Measurement Mission (TRMM) sensors, i.e., Visible and Infrared Scanner (VIRS) and TRMM Microwave Imager (TMI). The cloud top temperature obtained from the VIRS analysis is used as an input to the TMI analysis to reduce uncertainties in estimation of LWP. Total errors in LWP are estimated to range from 11 to 30 g/m2. In the algorithm the beam‐filling efficiency of clouds for TMI footprints is corrected by the cloud fraction evaluated from the VIRS measurements. For application, global analysis is performed with 3‐monthly data from January to March 2000. The scatter diagram of the shortwave‐retrieved LWP (LWPshrt) versus the microwave‐retrieved LWP (LWPmicr) shows characteristic trends for both precipitating and nonprecipitating clouds. Vertical inhomogeneity of the cloud droplet size accounts for small excess of LWPshrt over LWPmicr for nonprecipitating clouds, while precipitating clouds produce LWPmicr larger than LWPshrt, owing to the presence of raindrops. These tendencies are reinforced by examination of the global distributions of the shortwave‐retrieved droplet radius Re(NV) and the microwave counterpart defined by LWP divided by the cloud optical thickness Re(MV). The result implies that difference in those effective radii reflects a microphysical mechanism to expedite or suppress the conversion of the cloud water into rainfall.
Comparison of two schemes for derivation of atmospheric motion vectors
Authors: Xu J. , Holmlund K. , Zhang Q. , Schmetz J.
Published: October 2002

This paper presents the operational scheme of the National Satellite Meteorological Center (NSMC) of the China Meteorological Administration (CMA) to derive atmospheric motion vectors. The NSMC scheme is compared with a method developed at the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) in preparation for Meteosat Second Generation. Both schemes employ similar basic principles in terms of feature tracking and height assignment, however there are also some important differences. Furthermore, the EUMETSAT scheme assigns quality indicators to each wind vector at the end of the processing chain, whereas the NMSC scheme has inbuilt quality checking at different processing steps allowing for reinstatement of winds rejected by a first quality check. The evaluation of the performance is gained from two periods: a week in January and a week in July 1999. European Centre for Medium‐Range Weather Forecast analyses and radiosonde data are used as independent data for evaluation of the two schemes. It is shown that correlating infrared image data with water vapor data before height adjustment, as performed in the NSMC scheme, has a great potential to better distinguish high and low cloud and to provide high‐density wind fields. The utilization of radiative transfer calculations for the estimation of the height of thin clouds in the EUMETSAT scheme is shown to be imperative for good quality wind fields. Finally, the feature of the EUMETSAT scheme to assign quality indicators improves the utility of the wind vectors for use in numerical weather prediction models. It is suggested that a combination of the different features of both schemes potentially provide highly increased spatial density in the wind field with improved quality.
Probing near‐surface atmospheric turbulence with high‐resolution lidar measurements and models
Authors: Kao C.‐Y. J. , Cooper D. I. , Reisner J. M. , Eichinger W. E. , Ghil M.
Published: October 2002

Lidar technology provides fast data collection at a resolution of meters in a three‐dimensional atmospheric volume. A modeling counterpart of this lidar capability can greatly enhance our understanding of near‐surface atmospheric turbulence. This paper describes an integrated research capability on the basis of data from a scanning water vapor lidar and a high‐resolution hydrodynamic model (HIGRAD) equipped with a visualization routine (VIEWER) which simulates the lidar scanning. The purpose is to better understand the degree to which the lidar measurements represent faithfully the spatial and temporal features of the atmospheric boundary layer and to extend the utility of the measurements in studying turbulent fields in this layer. Raman lidar water vapor data collected over the Pacific warm pool and the HIGRAD simulations thereof are first compared with each other. The results are then used to identify the potential aliasing effects of lidar measurements due to the relatively long duration of the lidar scanning. This integrated lidar‐model capability also helps improve the trade‐off between the spatial and the temporal resolution of the lidar measurements on the one hand and their coverage on the other.
Spectroscopic measurements of tropospheric CO, C2H6, C2H2, and HCN in northern Japan
Authors: Zhao Y. , Strong K. , Kondo Y. , Koike M. , Matsumi Y. , Irie H. , Rinsland C. P. , Jones N. B. , Suzuki K. , Nakajima H. , Nakane H. , Murata I.
Published: October 2002

Tropospheric column amounts and mixing ratios of CO, C2H6, C2H2, and HCN were retrieved from ground‐based infrared solar spectra using a vertical profile retrieval algorithm (SFIT2). The spectra were recorded with high spectral resolution Fourier transform infrared (FTIR) spectrometers at Moshiri (44.4°N) and Rikubetsu (43.5°N) in northern Japan from May 1995 to June 2000. The retrievals show significant seasonal variations in the tropospheric content of the four molecules over northern Japan with maxima in winter‐spring (February–April) for CO, C2H6, and C2H2 and in summer (May–July) for HCN. Good correlations between CO, C2H6, and C2H2 indicated that they had similar sources and underwent similar dilution processes. Deviation of HCN relative to its seasonal mean value (ΔHCN) is correlated with the similar deviation of CO (ΔCO), indicating that enhancements of CO and HCN above the mean levels were probably due to the same sources. Linear trends in tropospheric CO, C2H6, and C2H2 from May 1995 to June 2000 (excluding 1998) were (−2.10 ± 0.30), (−2.53 ± 0.30), and (−3.99 ± 0.57)%/yr, respectively, while the trend of (−0.93 ± 0.49)%/yr in HCN was relatively small. Abnormally high tropospheric amounts of the four molecules were recorded in 1998. HCN amounts were found to be much higher than its seasonal mean value throughout 1998 with a 65% maximum increase in August 1998. Significant increases of CO, C2H6, and C2H2 took place in August–October 1998. Trajectory calculations, global fire maps, and satellite smoke images revealed that biomass burning in eastern Siberia from mid‐July to early October 1998 was the major cause of the elevated levels in tropospheric CO, C2H6, C2H2, and HCN observed in northern Japan in 1998.
Global mapping of vegetation parameters from POLDER multiangular measurements for studies of surface‐atmosphere interactions: A pragmatic method and its validation
Authors: Roujean Jean‐Louis , Lacaze Roselyne
Published: October 2002

This paper presents a pragmatic method to produce global maps of vegetation parameters, which offer essential data for weather forecast and climate modeling. The crucial variables are leaf area index (LAI), fractional vegetation cover (FVC), and fraction of absorbed photosynthetically active radiation (fAPAR). The approach relies on the use of spectral and directional vegetation indices simulated by a bidirectional reflectance model and calibrated against sets of satellite data. The model belongs to the kernel‐driven category, and the coefficients obtained, as the result of linear inversion, are the basis of the proposed method. The strategy presented relies upon the existence of suitable angular measurements to derive each biophysical parameter. An application is shown with the global POLDER/ADEOS‐I database. Special attention is given here to the future production of LAI and fAPAR since the albedo is a product already disseminated by the POLDER production center. Terrestrial ecosystems show a high level of aggregation and, in practice, only effective LAI can be measured. Therefore a correction factor, namely the clumping index, must be applied to help resolve the scaling issue. Clumping corrections are performed biome by biome, using empirical equations where it appears that LAI assessments for boreal and tropical forests would otherwise be significantly inaccurate. However, the effect of clumping will be less on FVC and fAPAR. The relevance of the proposed method is demonstrated through a comparison of POLDER‐derived LAI values with a varied set of ground LAI measurements, including their coherence with the corresponding fAPAR.
Radiative effects of aerosols on the evolution of the atmospheric boundary layer
Authors: Yu Hongbin , Liu S. C. , Dickinson R. E.
Published: October 2002

This study investigates the impacts of tropospheric aerosols on the evolution of the atmospheric boundary layer (ABL) for dry subsiding regions by conducting simulations with a high‐resolution ABL model. The scattering and absorption of aerosols diminish the surface radiation, inhibiting the sensible heat flux and evaporation and inducing feedbacks such as the enhanced stratification and change in relative humidity in the surface layer. The reduced sensible heat due to aerosol backscattering lowers the air temperature and suppresses the growth of the ABL. The resultant reduction of entrainment heating contributes to an additional cooling. The decreased entrainment drying competes with the reduced surface evaporation, so that the net effect can be either an increase or a decrease of the ABL moisture, depending on the soil moisture. Aerosol absorption decreases the turbulent heating but simultaneously increases the solar heating, increasing the air temperature and decreasing the strength of capping inversion. The resultant rise of the top of the ABL compensates the lowering due to the reduced buoyancy flux. With strong aerosol absorption, the increased entrainment heating enhances the ABL warming. Both the increased entrainment drying and the reduced evaporation decrease the ABL moisture. The increased warmth and dryness of the ABL imply that absorbing aerosols within the ABL decrease the probability of formation of boundary layer clouds, causing additional warming through cloud‐feedbacks. The results are sensitive to the vertical distribution of absorbing aerosols. Absorbing aerosol above the ABL increases the strength of capping inversion and reduces the top of the ABL, hence decreasing the entrainment drying and moistening the ABL.
Spatial variability of Antarctic Peninsula net surface mass balance
Authors: Turner J. , Lachlan‐Cope T. A. , Marshall G. J. , Morris E. M. , Mulvaney R. , Winter W.
Published: October 2002

Measurements from ice cores and snow pits collected over the last 50 years are used to examine how net surface mass balance varies across the Antarctic Peninsula to give the first detailed map of mass balance for the region. A total of 211 reliable mass balance measurements were available for the preparation of the map, but some areas were found to be very data sparse. The analysis suggests that the largest values of mass balance are found along the spine of the northern part of the peninsula, where over 2.5 m yr−1 water equivalent (WE) has been measured. A secondary peak of more than 2.0 m yr−1 WE is determined along the mountains of eastern Alexander Island. Precipitation minus evaporation (P‐E) fields from the European Centre for Medium‐Range Weather Forecasts reanalysis project are compared with our analysis of in situ data. The model fields are found to have peak values of P‐E of only half the amounts found from the measurements; the greatest model values are located on the western side of the peninsula. Areas where a high density of in situ data is available, including King George VI Sound and the high south central plateau part of the peninsula, show a high spatial variability of net surface mass balance, suggesting that local orographic features play a major part in dictating the mass balance.
Mesospheric inversions and their relationship to planetary wave structure
Authors: Salby Murry , Sassi Fabrizio , Callaghan Patrick , Wu Dong , Keckhut Philippe , Hauchecorne Alain
Published: October 2002

Mesospheric inversions are studied in vertical soundings from the French lidar at Observatoire de Haute‐Provence and in synoptic global structure that was observed simultaneously by the UARS satellite. The latter provides the instantaneous three‐dimensional (3‐D) structure of the circulation that accompanies mesospheric inversions. A numerical simulation with a 3‐D primitive equation model is then shown to reproduce major features of the observed behavior. Both reveal an extensive pattern of inverted thermal structure. The behavior is closely related to planetary waves, which, in the model, experience strong absorption in the upper mesosphere and lower thermosphere. Inverted thermal structure mirrors the synoptic pattern of potential vorticity, which marks the polar night vortex. Both are strongly distorted during stratospheric warmings, when inverted thermal structure at midlatitudes is favored. The region of negative lapse rate coincides with those altitudes where planetary wave temperature undergoes an abrupt phase shift. Wave temperature is then driven out of phase with wave geopotential. This alters the vertical structure of planetary waves, from westward tilt and upward amplification below the inversion to nearly barotropic structure and upward decay above the inversion. Accompanying the upward decay of planetary waves above the inversion is a decay of flow distortion, as the disturbed vortex is gradually restored toward polar symmetry.
Biogenic contributions to atmospheric volatile organic compounds in Azusa, California
Authors: Klouda George A. , Lewis Charles W. , Stiles David C. , Marolf Julie L. , Ellenson William D. , Lonneman William A.
Published: October 2002

An objective of the 1997 Southern California Ozone Study (SCOS97) was to provide an up‐to‐date assessment of the importance of biogenic emissions for tropospheric ozone production in the South Coast Air Basin. To this end, ambient air samples were collected during September 1997 at the Azusa air‐monitoring station for subsequent measurement of their radiocarbon (14C) content of the atmospheric nonmethane volatile organic compound (VOC) fraction. The 14C/12C ratio is proportional to the fraction of a sample's carbon that is biogenic. The proportionality constant was determined from local samples of vegetation, gasoline, and ambient CO2 collected during the same period. The median fraction of biogenic VOC observed from 0600 to 0900 hours (LT) was 7% (n = 5) with a range of −8% to 24%, from 1300 to 1600 hours it was 27% (n = 4) with a range of 11% to 39%, and from 1700 to 2000 hours it was 34 ± 7% for a single sample. On the basis of calculated 24‐hour back trajectories the dominant source region for the air masses associated with periods of high biogenic VOC‐C levels was a sector extending from the north to the east. Over all time and space that the samples represent, the median fraction of biogenic VOC was 18% (n = 10). Expressed as an atmospheric mixing ratio, the overall (median and 95% confidence interval) biogenic VOC‐carbon contribution was 80 ± 50 nmol mol−1 which may be representative of the natural VOC‐C background for the Los Angeles air basin.
Effects of long‐range transport and clouds on cloud condensation nuclei in the springtime Arctic
Authors: Wylie Donald P. , Hudson James G.
Published: October 2002

Variations in cloud condensation nuclei (CCN) concentration vertical profiles during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment/Arctic Clouds Experiment (FIRE/ACE) flights over the Arctic Ocean were investigated using back trajectories and satellite photos. In contrast with CCN measurements over other oceans, concentrations over the Arctic generally increased with altitude. Although land masses did not seem to have as much of an immediate effect on concentrations over the Arctic as over other oceans, the small size of the Arctic Ocean may leave it open to greater overall continental/anthropogenic influences. Cloud scavenging seemed to be the most likely cause of decreased CCN concentrations. More efficient scavenging by liquid clouds, because of their higher concentrations and surface areas than cirrus clouds, probably accounted for decreasing concentrations at lower altitudes.
Multidecadal solar radiation trends in the United States and Germany and direct tropospheric aerosol forcing
Authors: Liepert Beate , Tegen Ina
Published: October 2002

In recent studies, anthropogenic aerosols have been recognized as important radiative forcing factors of climate because of their ability to scatter and/or absorb sunlight. At clear‐sky conditions the direct aerosol forcing at ground is negative and implies less solar heating of the surface because of aerosols. In this study, an intensified direct aerosol forcing of −7 to −8 W/m2 has been detected in the United States for the interval from 1960 to 1990. In Germany a weakened aerosol forcing of +3 W/m2 was observed during the same time period. Even though the aerosol forcing is stronger in the eastern United States compared to the western United States, the positive trend is almost equal. We attained these results by scrutinizing clear‐sky global solar radiation recordings for these regions and this time period. Additionally, the diurnal cycle and the direct to diffuse ratio of solar radiation were used for constraining the observed trends. Increased absorption and declined light scattering are presumably responsible for the intensified direct aerosol forcing in the United States. While at the same time in Germany, both aerosol absorption and scattering must have declined to explain the parallel weakened aerosol forcing and the increased direct/diffuse ratio. To estimate the possible anthropogenic portion of these observed changes, we compared the observational results with modeled aerosol forcing scenarios retrieved from the Goddard Institute for Space Studies general circulation model (GISS GCM). Modeled surface solar radiation, aerosol optical thickness, and single‐scattering albedo are derived from emission trends of anthropogenic sulfate and carbonaceous aerosols. The emission distributions are calculated from fossil fuel consumption databases. On the basis of these simulations we suspect that the declining trend of sulfate burden over Germany between 1960 and 1990 was stronger than estimated with the model. Over the United States the simulated small increase in the carbonaceous aerosol burden was exaggerated in order to explain the observed changes in surface solar radiation, diurnal cycle, and direct/diffuse ratio of surface solar radiation. In addition to emission changes from fossil fuel burning, other reasons explaining the solar radiation trends are also discussed.
Chemical ozone loss in the tropopause region on subvisible ice clouds, calculated with a chemistry‐transport model
Authors: Bregman Bram , Wang P.‐H. , Lelieveld Jos
Published: October 2002

A global chemistry‐transport model has been used to investigate the role of subvisible ice clouds in chemical ozone loss in the tropopause region. The three‐dimensional subvisible cloud representation is based on 6‐hourly European Centre for Medium‐Range Weather Forecasts high cloud fields, assuming observed cloud particle radii and densities. The resulting seasonal average subvisible cloud occurrence agrees well with that observed by the Stratospheric Aerosol and Gas Experiment (SAGE) II instrument. The clouds are located along cold and warm fronts, associated with cyclonic activity. On the ice clouds, heterogeneous reactions occur similarly as on polar stratospheric clouds. The calculated chemical perturbations show high spatial variability, owing to the relatively detailed cloud representation. Halogen activation occurs only when the clouds are located at or above potential vorticity levels of 2–3 PVU. The cloud‐induced chlorine activation is stronger in June than in December with maximum ClO levels close to 100 pptv. Consequently, the calculated chemical ozone loss is stronger in June than in December with local maxima of ∼4%. The calculated chlorine activation is significantly lower compared to previous model results and shows an opposite seasonal behavior. Changing the cloud composition to a mix of liquid and ice reduces the chlorine activation even further. This illustrates the strong sensitivity to cloud properties. In addition, the reactive gas uptake on the ice cloud surfaces is poorly described for midlatitude tropopause conditions. Although these uncertainties prevent an accurate calculation of chemical ozone loss, it seems unlikely that heterogeneous chemistry on subvisible clouds can explain the observed negative ozone trends in the midlatitude lowermost stratosphere. Nevertheless, the ozone loss cannot be neglected, being of comparable magnitude as ozone formation by NOx from commercial air traffic.
An application of statistical downscaling to estimate surface air temperature in Japan
Authors: Oshima Naoko , Kato Hisashi , Kadokura Shinji
Published: October 2002

In this study, a statistical downscaling model based on singular value decomposition was applied to estimate the monthly mean temperature field in Japan for January and July. The regression model estimated surface air temperature in Japan from upper air temperature in east Asia with root‐mean‐square errors of around 1.0°C for an independent verification period. The method was applied to the output of a CO2 transient run of NCAR‐CSM, and the result was compared with the output of NCAR‐RegCM2.5 nested in CSM. The statistical model reproduced the spatial distribution of the temperature more realistically than the CSM output. In January the results corresponded well between the models except that the climate simulated by RegCM was generally cooler than that estimated using the statistical method mainly due to the unrealistic RegCM topography. In July the results did not correspond well between the methods, since the climate is more complex and difficult to be estimated solely from the upper air temperature field. Temperature rise from 1CO2 climate to 2CO2 climate was larger in RegCM than in the statistical method for both months reflecting the influence of sea surface temperature rise. It was concluded that this statistical downscaling method can be applied to estimate the January mean temperature in Japan, although other predictor variables such as sea surface temperature should be included to improve the estimation in July.
Budget and export of anthropogenic SOx from East Asia during continental outflow conditions
Authors: Tan Qian , Huang Yan , Chameides W. L.
Published: October 2002

We examine the budget and export of anthropogenic SOx (SO2 and sulfate aerosol) emitted from East Asia during the late winter/early spring when continental outflow conditions dominate. Our study is based on simulations using a modified version of the China‐MAP coupled regional climate/chemical transport model of Qian and Giorgi [1999]. The modification involves the addition of algorithms to treat the vertical transport and removal of SOx by convective clouds. Model‐calculated anthropogenic SO2 concentrations peaked at values greater than 20 ppbv at the surface in the urban source regions of China and Korea, but averaged only about 5 pbbv in the rural areas. Midtropospheric SO2 concentrations were more than an order of magnitude less, with peak values of around 0.1–0.15 ppbv overlying the urban source regions. The model‐calculated sulfate aerosol distribution is more disperse, with peak surface concentrations of 5–10 ppbv in urban source regions, and concentrations of about 3 ppbv or less in rural areas and 1 ppbv or less in the midtroposphere. The model‐calculated SOx concentrations are generally within a factor of 2 of the relevant observed concentrations at nonurban sites. The calculations indicate that during the late winter/early spring period, about 50% of the anthropogenic SOx emitted over East Asia is removed from the continental source regions. Roughly 30% is wet and dry deposited onto the neighboring oceans, and the remaining 20% is exported out of the model domain. The vast majority of the exported SOx is in the form of sulfate aerosol and is transported into the midtroposphere overlying the North Pacific Ocean. The rate of SOx export, about 0.2 Tg S per month, is significant when compared to natural S sources to the North Pacific Ocean, suggesting that the export of anthropogenic SOx from East Asia is perturbing sulfate aerosol concentrations over the North Pacific Ocean during the late winter and early spring. On an intraregional basis we find that China is the largest contributor to the emission and export of SOx from East Asia. However, all the nations/continental subregions of East Asia appear to be net exporters of SOx, even those downwind of China.
Airborne observations of turbulence, mixing, and gravity waves in the tropopause region
Authors: Pavelin Edward , Whiteway James A. , Busen Reinhold , Hacker Jörg
Published: October 2002

In situ observations of small‐scale dynamics and compositional structure in the tropopause region are presented. The measurements were made aboard the Grob “Egrett” high‐altitude research aircraft above Aberystwyth, Wales, in the summer of 2000. The observations presented here show evidence of mixing of ozone and water vapor in a patch of intense turbulence just above the tropopause. This turbulence is shown to be the result of wind shear above a tropospheric jet stream. The value of the vertical eddy diffusion coefficient in this turbulence is estimated to be 0.9 m2 s−1. It is also shown that wavelike perturbations superimposed on the overall tracer structure can be accounted for by a gravity wave.
Pointing and temperature retrieval from millimeter‐submillimeter limb soundings
Authors: Verdes C. , Bühler S. , von Engeln A. , Kuhn T. , Künzi K. , Eriksson P. , Sinnhuber Björn‐Martin
Published: October 2002

Passive microwave limb sounding instruments like the Millimeter‐Wave Atmospheric Sounder (MAS) or the Microwave Limb Sounder (MLS) observe dedicated oxygen lines for the derivation of temperature and pointing information, since these quantities are essential for the quality of the retrieval of the trace gas mixing ratio. Emission lines of oxygen are chosen because the volume mixing ratio (VMR) profile is known. In this paper, we demonstrate the capabilities of a new and innovative method by means of which accurate temperature and pointing information can be gathered from other strong spectral features like ozone lines, without including accurate knowledge of the VMR profile of these species. For this purpose, retrievals from two observation bands with a bandwidth of about 10 GHz each, one including an oxygen line, have been compared. A full error analysis was performed with respect to critical instrument and model parameters, such as uncertainties in the antenna pattern, calibration uncertainties, random pointing error, baseline ripples, baseline discontinuities, and spectroscopic parameters. The applied inversion algorithm was the optimal estimation method. For the selected scenario and instrumental specifications we find that the retrieval of a pointing offset and the atmospheric temperature profile can be achieved with a good accuracy. The retrieval precision of the pointing offset is better than 24 m. The retrieval precision of the temperature profile is better than 2 K for altitudes ranging from 10 to 40 km. Systematic errors (due to model parameter uncertainties) are somewhat larger than these purely statistical errors. Investigations carried out for different atmospheric states or different instrumental specifications show similar results.
Polar Ozone and Aerosol Measurement III measurements of water vapor in the upper troposphere and lowermost stratosphere
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Hoppel Karl W. , Lumpe Jerry D. , Smit Herman
Published: October 2002

We present water vapor measurements made by the Polar Ozone and Aerosol Measurement (POAM) III instrument since May 1998 in the upper troposphere and lowermost stratosphere. While POAM III is primarily a stratospheric instrument, many of the POAM III occultation measurements allow for the retrieval of water vapor in the upper troposphere. The Measurements of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) instruments provide a large number of coincident measurements and thus offer the best opportunity to validate POAM measurements in the highly spatially variable regions of the upper troposphere‐lowermost stratosphere, where the mixing ratios are much larger than those found throughout most of the stratosphere. The comparison shows that there is no statistically significant difference in the response of the two instruments to changes in water vapor and that in the regime where the MOZAIC measurements are thought to be most accurate, the water vapor mixing ratios measured by POAM are 10% higher. The POAM III Northern Hemisphere measurements are taken from 55° to 71° and show a qualitatively reasonable seasonal variation, with high mixing ratios in the upper troposphere in the summer and low mixing ratios in the winter. Comparisons of the seasonal variations of the POAM measurements with those from the upper tropospheric Microwave Limb Sounder (MLS) measurements from the early 1990s show qualitative similarities. The ∼1 km vertical resolution of POAM measurements allows us to study in greater detail than other satellite instruments the complex variations in water vapor that occur in the upper troposphere and lowermost stratosphere. Among the interesting features observed is a rise in the level of the high‐latitude hygropause from April through September.
Atmospheric remote sensing using a combined extinctive and refractive stellar occultation technique 1. Overview and proof‐of‐concept observations
Authors: Yee Jeng‐Hwa , Vervack Ronald J. , DeMajistre Robert , Morgan Frank , Carbary James F. , Romick Gerald J. , Morrison Daniel , Lloyd Steven A. , DeCola Philip L. , Paxton Larry J. , Anderson Donald E. , Kumar C. Krishna , Meng Ching‐I
Published: October 2002

A new approach to optical remote sensing of the Earth's atmosphere using a combination of extinctive and refractive stellar occultation measurements is presented. In this combined method, spectrographic imagers are used to measure the wavelength‐dependent atmospheric extinction of starlight while a co‐aligned imager is used to measure the atmospheric refraction along the same line of sight. By simultaneously measuring both the refraction and extinction of the starlight, the composition‐dependent extinction measurements can more accurately probe the Earth's lower atmosphere, where refraction effects are significant. The refraction measurements provide the bulk atmospheric properties and the actual light path through the atmosphere, both of which are necessary to correctly infer the total extinction in the refractive regime. The technique is demonstrated on a proof‐of‐concept basis using data from the Ultraviolet and Visible Imagers and Spectrographic Imagers (UVISI) on the Midcourse Space Experiment (MSX) satellite. These preliminary results show that the combined approach has the potential to be a powerful, self‐calibrating method for remotely sensing the Earth's atmosphere in general and for the determination of ozone profiles in the stratosphere and upper troposphere in particular.
Atmospheric remote sensing using a combined extinctive and refractive stellar occultation technique 3. Inversion method for refraction measurements
Authors: Vervack Ronald J. , Yee Jeng‐Hwa , Carbary James F. , Morgan Frank
Published: October 2002

In this paper, an inversion algorithm for the retrieval of total density, pressure, and temperature in the Earth's lower atmosphere from refraction angle measurements by a visible‐light imager is presented. A detailed description of the retrieval algorithm is provided, and its performance under a variety of conditions is assessed, including a rigorous evaluation of the statistical and systematic uncertainties. Tests show that visible‐light images of stellar refraction can provide reasonably accurate measurements of the atmospheric bulk properties from the surface (or cloud top heights) to roughly 30 km altitude. The combined statistical and systematic uncertainties in density and temperature profiles retrieved with a vertical resolution of 1 km decrease from 3.1% and 5 K, respectively, at 30 km to 0.8% and 3.8 K at 20 km and 0.35% and 1.5 K at 10 km for an imager with a sampling rate of 10 Hz and pointing control/knowledge of 0.002° (1σ). This level of accuracy and resolution is adequate for a combined extinctive/refractive occultation technique for remotely sensing the Earth's lower atmosphere that has recently been demonstrated using data taken by the Ultraviolet and Visible Imagers and Spectrographic Imagers (UVISI) on the Midcourse Space Experiment (MSX) spacecraft.
Simulated observation of tropospheric ozone and CO with the Tropospheric Emission Spectrometer (TES) satellite instrument
Authors: Luo M. , Beer R. , Jacob D. J. , Logan J. A. , Rodgers C. D.
Published: October 2002

The Tropospheric Emission Spectrometer (TES) on board NASA's Aura satellite (to be launched in 2004) will provide measurements of global distributions of ozone, CO, and other key chemical species in the troposphere. In order for TES to meet a design lifetime of 5 years, it has been determined that a global survey strategy with ∼50% duty cycle must be identified. In this study, simulated concentrations of ozone and CO from the GEOS‐CHEM global three‐dimensional (3‐D) model of troposphere chemistry are used as a time‐varying synthetic atmosphere for demonstrating and assessing the capabilities of TES nadir observations. Autocorrelation analyses of the model species fields for different time lags identify a significant 1‐day correlation and support a 1‐day‐on/1‐day‐off observation strategy. Three major steps are then taken to demonstrate and evaluate TES products: (1) species profiles along the TES orbit track are sampled from the model 3‐D time‐varying fields with cloudy scenes (50‐60% of total scenes) removed; (2) nadir‐retrieved profiles (“level 2 products”) are obtained from these “true” synthetic profiles using TES retrieval characteristic functions; (3) interpolated daily global maps (“level 3 products”) are generated to compare with the original model fields. The latter comparison indicates that the error in the level 3 products relative to the true fields for ozone and CO is <10% in ∼70% of cases and <20% in 80–90% of cases. The three major sources of error lie in the asynoptic orbital sampling, the retrieval, and the level 3 global mapping.
Impact of coastal transportation emissions on inland air pollution over Israel: Utilizing numerical simulations, airborne measurements, and synoptic analyses
Authors: Ranmar D. O. , Matveev V. , Dayan U. , Peleg M. , Kaplan J. , Gertler A. W. , Luria M. , Kallos G. , Katsafados P. , Mahrer Y.
Published: October 2002

The detection of high ozone levels over large inland areas in Israel during the early, mid and late summer triggered an analysis of air mass back‐trajectories. This, in turn, pointed to the transportation system in the metropolitan coastal Tel Aviv region as the possible origin of the ozone's precursors. To link the daily dynamics of rush hour transportation emissions to inland air pollution, in general, and airborne ozone measurements, in particular, an interdisciplinary modeling system was established. The simulations of transportation‐to‐inland air pollution integrated transportation, emission factor, atmospheric, transport/diffusion, and photochemical models. The modeling results elucidated a spatial and temporal overlap between the ozone precursors and ozone production. The model simulations indicated east to southeasterly dispersion of the pollution cloud. The results agreed well with both spatial and temporal ozone levels as recorded by aircraft over central Israel, as well as with ground‐based monitoring station observations. The impact of the Tel Aviv metropolitan area as well as the Gaza Strip, as pivotal coastal transportation sources for inland air pollution in general and ozone formation in particular, is discussed. The synoptic analysis identified the conditions prevailing when elevated air pollution, and especially high ozone levels, exists over central Israel. The analysis showed that this season features a shallow mixed layer and weak zonal flow, which leads to poor ventilation rates and inhibit efficient dispersion of this secondary pollutant. These poor ventilation rates result in the slow transport of ozone precursors, enabling their photochemical transformation under intense solar radiation during their travel from the coast inland. Under these conditions, model results showed that traffic emissions during the morning rush hour from the Tel Aviv metropolitan area contribute about 60% to the observed ozone concentrations.
Comparison of spectral surface albedos and their impact on the general circulation model simulated surface climate
Authors: Roesch A. , Wild M. , Pinker R. , Ohmura A.
Published: October 2002

This study investigates the impact of spectrally resolved surface albedo on the total surface albedo. The neglect of albedo variation within the shortwave spectrum may lead to substantial errors as the atmospheric water greatly influences the spectral distribution of the incoming radiation. It is shown that ignoring the spectral dependence of the surface albedo will affect the predicted climate. The study reveals substantial changes in the climate over northern Africa when modifying the surface albedo of the Sahara deserts. Detailed information is given how the European Center/Hamburg General Circulation Model (ECHAM4) can be extended to include surface boundary conditions for both the visible and near‐infrared incoming radiation. This comprises global climatologies for both the visible and near‐infrared albedo for snow‐free conditions, as well as the corresponding albedo values over snow, land‐/sea ice and over snow covered forests. Comparisons between several available surface albedo climatologies and a newly compiled albedo data set show substantial scatter in estimated albedos. The largest albedo differences are found in snow covered forest regions as well as in arid and semi‐arid terrains.
Missing ozone at high altitude: Comparison of in situ and satellite data
Authors: Kirchhoff V. W. J. H. , Guarnieri F. L.
Published: October 2002

An experiment was designed to measure ozone at a site on the Andes Mountains, near La Paz, Bolivia, at a height of 3420 m, with the objective of investigating the ozone reduction seen over the mountains and the increased UV‐B radiation. A Brewer spectrophotometer was used for surface measurements of the vertical ozone column and UV‐B radiation; the spatial ozone variation around the mountain site was obtained using Total Ozone Mapping Spectrometer (TOMS) data. The ozone column values show a decrease over the mountain region, which maximizes at about 20 Dobson units, in comparison to the values in the Pacific regions, to the west, and the continental values to the east, at about the same latitude. To investigate the reason for this missing ozone, the vertical ozone distribution was measured using electrochemical concentration cell ozonesondes. The ozone profiles were integrated downward to sea level. It is shown that this integral corresponds to the missing ozone over the mountain area. The strongest consequence of the reduced atmosphere at high altitude on the UV‐B intensities is not the reduction of the ozone column but that of the Rayleigh‐ scattering effect. The absence of scattering considerably increases the UV‐B radiation at high altitudes. For example, the ozone effect on the ratios of UV‐B intensities between La Paz and Natal, a sea level station, is only 1.15, while for the Rayleigh‐scattering reduction, the ratio between stations is 1.75, at 306.3 nm. Measured UV‐B intensities at both sites show La Paz/Natal ratios of this order of magnitude.
A Lagrangian “1‐year climatology” of (deep) cross‐tropopause exchange in the extratropical Northern Hemisphere
Authors: Wernli Heini , Bourqui Michel
Published: October 2002

A Lagrangian methodology is applied to operational European Centre for Medium‐Range Weather Forecasts analyses to study upward cross‐tropopause exchange (troposphere to stratosphere exchange (TSE)) and downward cross‐tropopause exchange (stratosphere to troposphere exchange (STE)) in the extratropical Northern Hemisphere for the period from May 1995 to April 1996. A residence time criterion serves to distinguish between short‐ (<1–2 days) and long‐lasting exchange events. The adopted approach enables identification of a range of novel aspects of extratropical cross‐tropopause transport which are of primary importance when assessing its chemical impact. For the considered year the annual cycle of the hemispherically integrated net cross‐tropopause mass flux compares well with estimates from previous studies. The part of STE and TSE which occurs with equal amplitude in both directions (referred to as “symmetric two‐way exchange”) has only a weak annual cycle and, for short residence times, a larger amplitude than the net exchange. The meridional distribution of the net flux reveals an upward branch in the subtropics, pronounced downward exchange in the midlatitudes and weak upward fluxes in the Arctic region. Detailed geographical distributions show significant zonal asymmetries with maximum exchange in the Atlantic and Pacific storm track regions. It is further shown that STE (TSE) events occur typically below (slightly above) the climatological tropopause position. Deep exchange (that is, rapid vertical transport between the stratosphere and the lower troposphere) is strongest during winter and confined to the midlatitude regions of baroclinic wave activity. The localized source regions for deep TSE indicate that pollutants emitted in eastern North America and Asia have an enhanced potential for being rapidly transported into the lowermost stratosphere.
Influence of fuel sulfur on the composition of aircraft exhaust plumes: The experiments SULFUR 1–7
Authors: Schumann U. , Arnold F. , Busen R. , Curtius J. , Kärcher B. , Kiendler A. , Petzold A. , Schlager H. , Schröder F. , Wohlfrom K.‐H.
Published: October 2002

The series of SULFUR experiments was performed to determine the aerosol particle and contrail formation properties of aircraft exhaust plumes for different fuel sulfur contents (FSC, from 2 to 5500 μg/g), flight conditions, and aircraft (ATTAS, A310, A340, B707, B747, B737, DC8, DC10). This paper describes the experiments and summarizes the results obtained, including new results from SULFUR 7. The conversion fraction ε of fuel sulfur to sulfuric acid is measured in the range 0.34 to 4.5% for an older (Mk501) and 3.3 ± 1.8% for a modern engine (CFM56‐3B1). For low FSC, ε is considerably smaller than what is implied by the volume of volatile particles in the exhaust. For FSC ≥ 100 μg/g and ε as measured, sulfuric acid is the most important precursor of volatile aerosols formed in aircraft exhaust plumes of modern engines. The aerosol measured in the plumes of various aircraft and models suggests ε to vary between 0.5 and 10% depending on the engine and its state of operation. The number of particles emitted from various subsonic aircraft engines or formed in the exhaust plume per unit mass of burned fuel varies from 2 × 1014 to 3 × 1015 kg−1 for nonvolatile particles (mainly black carbon or soot) and is of order 2 × 1017 kg−1 for volatile particles >1.5 nm at plume ages of a few seconds. Chemiions (CIs) formed in kerosene combustion are found to be quite abundant and massive. CIs contain sulfur‐bearing molecules and organic matter. The concentration of CIs at engine exit is nearly 109 cm−3. Positive and negative CIs are found with masses partially exceeding 8500 atomic mass units. The measured number of volatile particles cannot be explained with binary homogeneous nucleation theory but is strongly related to the number of CIs. The number of ice particles in young contrails is close to the number of soot particles at low FSC and increases with increasing FSC. Changes in soot particles and FSC have little impact on the threshold temperature for contrail formation (less than 0.4 K).