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2005 .

(8 publications)

T. L. Anderson, R. J. Charlson, N. Bellouin, O. Boucher, M. Chin, S. A. Christopher, J. Haywood, Y. J. Kaufman, S. Kinne, J. A. Ogren, L. A. Remer, T. Takemura, D. Tanré, O. Torres, C. R. Trepte, B. A. Wielicki, D. M. Winker, and H. Yu. An ”A-Train” Strategy for Quantifying Direct Climate Forcing by Anthropogenic Aerosols. Bulletin of the American Meteorological Society, 86:1795-1809, December 2005. [ bib | DOI | ADS link ]

This document outlines a practical strategy for achieving an observationally based quantification of direct climate forcing by anthropogenic aerosols. The strategy involves a four-step program for shifting the current assumption-laden estimates to an increasingly empirical basis using satellite observations coordinated with suborbital remote and in situ measurements and with chemical transport models. Conceptually, the problem is framed as a need for complete global mapping of four parameters: clear-sky aerosol optical depth δ, radiative efficiency per unit optical depth E, fine-mode fraction of optical depth ff, and the anthropogenic fraction of the fine mode faf. The first three parameters can be retrieved from satellites, but correlative, suborbital measurements are required for quantifying the aerosol properties that control E, for validating the retrieval of ff, and for partitioning fine-mode δ between natural and anthropogenic components. The satellite focus is on the ”A-Train,” a constellation of six spacecraft that will fly in formation from about 2005 to 2008. Key satellite instruments for this report are the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) radiometers on Aqua, the Ozone Monitoring Instrument (OMI) radiometer on Aura, the Polarization and Directionality of Earth's Reflectances (POLDER) polarimeter on the Polarization and Anistropy of Reflectances for Atmospheric Sciences Coupled with Observations from a Lidar (PARASOL), and the Cloud and Aerosol Lider with Orthogonal Polarization (CALIOP) lidar on the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). This strategy is offered as an initial frameworksubject to improvement over timefor scientists around the world to participate in the A-Train opportunity. It is a specific implementation of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) program, presented earlier in this journal, which identified the integration of diverse data as the central challenge to progress in quantifying global-scale aerosol effects. By designing a strategy around this need for integration, we develop recommendations for both satellite data interpretation and correlative suborbital activities that represent, in many respects, departures from current practice.

P. Peylin, P. J. Rayner, P. Bousquet, C. Carouge, F. Hourdin, P. Heinrich, P. Ciais, and A. Contributors. Daily CO2 flux estimates over Europe from continuous atmospheric measurements: 1, inverse methodology. Atmospheric Chemistry & Physics, 5:3173-3186, November 2005. [ bib | ADS link ]

This paper presents an inverse method for inferring trace gas fluxes at high temporal (daily) and spatial (model grid) resolution from continuous atmospheric concentration measurements. The method is designed for regional applications and for use in intensive campaigns. We apply the method to a one month inversion of fluxes over Europe. We show that the information added by the measurements depends critically on the smoothness constraint assumed among the source components. We show that the initial condition affects the inversion for 20 days, provided one has enough observing sites to constrain regional fluxes. We show that the impact of the far-field fluxes grows throughout the inversion and hence a reasonable global flux field is a prerequisite for a regional inversion.

M. H. Zhang, W. Y. Lin, S. A. Klein, J. T. Bacmeister, S. Bony, R. T. Cederwall, A. D. Del Genio, J. J. Hack, N. G. Loeb, U. Lohmann, P. Minnis, I. Musat, R. Pincus, P. Stier, M. J. Suarez, M. J. Webb, J. B. Wu, S. C. Xie, M.-S. Yao, and J. H. Zhang. Comparing clouds and their seasonal variations in 10 atmospheric general circulation models with satellite measurements. Journal of Geophysical Research (Atmospheres), 110:15, August 2005. [ bib | DOI | ADS link ]

To assess the current status of climate models in simulating clouds, basic cloud climatologies from ten atmospheric general circulation models are compared with satellite measurements from the International Satellite Cloud Climatology Project (ISCCP) and the Clouds and Earth's Radiant Energy System (CERES) program. An ISCCP simulator is employed in all models to facilitate the comparison. Models simulated a four-fold difference in high-top clouds. There are also, however, large uncertainties in satellite high thin clouds to effectively constrain the models. The majority of models only simulated 30-40% of middle-top clouds in the ISCCP and CERES data sets. Half of the models underestimated low clouds, while none overestimated them at a statistically significant level. When stratified in the optical thickness ranges, the majority of the models simulated optically thick clouds more than twice the satellite observations. Most models, however, underestimated optically intermediate and thin clouds. Compensations of these clouds biases are used to explain the simulated longwave and shortwave cloud radiative forcing at the top of the atmosphere. Seasonal sensitivities of clouds are also analyzed to compare with observations. Models are shown to simulate seasonal variations better for high clouds than for low clouds. Latitudinal distribution of the seasonal variations correlate with satellite measurements at 0.9, 0.6-0.9, and -0.2-0.7 levels for high, middle, and low clouds, respectively. The seasonal sensitivities of cloud types are found to strongly depend on the basic cloud climatology in the models. Models that systematically underestimate middle clouds also underestimate seasonal variations, while those that overestimate optically thick clouds also overestimate their seasonal sensitivities. Possible causes of the systematic cloud biases in the models are discussed.

R. N. Halthore, D. Crisp, S. E. Schwartz, G. P. Anderson, A. Berk, B. Bonnel, O. Boucher, F.-L. Chang, M.-D. Chou, E. E. Clothiaux, P. Dubuisson, B. Fomin, Y. Fouquart, S. Freidenreich, C. Gautier, S. Kato, I. Laszlo, Z. Li, J. H. Mather, A. Plana-Fattori, V. Ramaswamy, P. Ricchiazzi, Y. Shiren, A. Trishchenko, and W. Wiscombe. Intercomparison of shortwave radiative transfer codes and measurements. Journal of Geophysical Research (Atmospheres), 110:11206, June 2005. [ bib | DOI | ADS link ]

Computation of components of shortwave (SW) or solar irradiance in the surface-atmospheric system forms the basis of intercomparison between 16 radiative transfer models of varying spectral resolution ranging from line-by-line models to broadband and general circulation models. In order of increasing complexity the components are: direct solar irradiance at the surface, diffuse irradiance at the surface, diffuse upward flux at the surface, and diffuse upward flux at the top of the atmosphere. These components allow computation of the atmospheric absorptance. Four cases are considered from pure molecular atmospheres to atmospheres with aerosols and atmosphere with a simple uniform cloud. The molecular and aerosol cases allow comparison of aerosol forcing calculation among models. A cloud-free case with measured atmospheric and aerosol properties and measured shortwave radiation components provides an absolute basis for evaluating the models. For the aerosol-free and cloud-free dry atmospheres, models agree to within 1% (root mean square deviation as a percentage of mean) in broadband direct solar irradiance at surface; the agreement is relatively poor at 5% for a humid atmosphere. A comparison of atmospheric absorptance, computed from components of SW radiation, shows that agreement among models is understandably much worse at 3% and 10% for dry and humid atmospheres, respectively. Inclusion of aerosols generally makes the agreement among models worse than when no aerosols are present, with some exceptions. Modeled diffuse surface irradiance is higher than measurements for all models for the same model inputs. Inclusion of an optically thick low-cloud in a tropical atmosphere, a stringent test for multiple scattering calculations, produces, in general, better agreement among models for a low solar zenith angle (SZA = 30deg) than for a high SZA (75deg). All models show about a 30% increase in broadband absorptance for 30deg SZA relative to the clear-sky case and almost no enhancement in absorptance for a higher SZA of 75deg, possibly due to water vapor line saturation in the atmosphere above the cloud.

X. B. Wang, J. C. Tuo, Z. X. Li, and H. Yan. Distribution of radioactive uranium and radon in sedimentary environments. Geochimica et Cosmochimica Acta Supplement, 69:480, May 2005. [ bib | ADS link ]

S. Fueglistaler, M. Bonazzola, P. H. Haynes, and T. Peter. Stratospheric water vapor predicted from the Lagrangian temperature history of air entering the stratosphere in the tropics. Journal of Geophysical Research (Atmospheres), 110:8107, April 2005. [ bib | DOI | ADS link ]

We present results of Lagrangian troposphere-to-stratosphere transport (TST) in the tropics based on trajectory calculations for the period 1979-2001. The trajectories and corresponding temperature histories are calculated from wind and temperature fields provided by the reanalysis data ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF). The water vapor mixing ratio of air entering the tropical stratosphere is calculated from the minimum saturation mixing ratio over ice encountered by each trajectory. We show that this Lagrangian approach, which considers the global-scale to synoptic-scale dynamics of tropical TST but neglects mesoscale dynamics and details of cloud microphysics, substantially improves estimates of stratospheric humidity compared to calculations based on Eulerian mean tropical tropopause temperatures. For the period 1979-2001 we estimate from the Lagrangian calculation that the mean water mixing ratio of air entering the stratosphere is 3.5 ppmv, which is in good agreement with measurements during the same period, ranging from 3.3 ppmv to 4 ppmv, whereas an estimate based on an Eulerian mean calculation is about 6 ppmv. The amplitude of the annual cycle in water vapor mixing ratio at a potential temperature of 400 K in the tropics estimated from the Lagrangian calculation is compared with measurements of water vapor from the Halogen Occultation Experiment (HALOE). For the period 1992-2001, when HALOE measurements and ERA-40 data overlap, we calculate a peak-to-peak amplitude of 1.7 ppmv, in good agreement with 1.6 ppmv seen in HALOE data. On average, the Lagrangian calculations have a moist bias of 0.2 ppmv, equivalent to a warm bias of the Lagrangian cold point of about 0.5 K. We conclude that the Lagrangian calculation based on synoptic-scale velocity and temperature fields yields estimates for stratospheric water vapor in good agreement with observations and that mesoscale and cloud microphysical processes need not be invoked, at first order, to explain annual mean and seasonal variation of water vapor mixing ratios in the tropical lower stratosphere.

M. Haeffelin, L. Barthès, O. Bock, C. Boitel, S. Bony, D. Bouniol, H. Chepfer, M. Chiriaco, J. Cuesta, J. Delanoë, P. Drobinski, J.-L. Dufresne, C. Flamant, M. Grall, A. Hodzic, F. Hourdin, F. Lapouge, Y. Lemaître, A. Mathieu, Y. Morille, C. Naud, V. Noël, W. O'Hirok, J. Pelon, C. Pietras, A. Protat, B. Romand, G. Scialom, and R. Vautard. SIRTA, a ground-based atmospheric observatory for cloud and aerosol research. Annales Geophysicae, 23:253-275, February 2005. [ bib | DOI | ADS link ]

Ground-based remote sensing observatories have a crucial role to play in providing data to improve our understanding of atmospheric processes, to test the performance of atmospheric models, and to develop new methods for future space-borne observations. Institut Pierre Simon Laplace, a French research institute in environmental sciences, created the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA), an atmospheric observatory with these goals in mind. Today SIRTA, located 20km south of Paris, operates a suite a state-of-the-art active and passive remote sensing instruments dedicated to routine monitoring of cloud and aerosol properties, and key atmospheric parameters. Detailed description of the state of the atmospheric column is progressively archived and made accessible to the scientific community. This paper describes the SIRTA infrastructure and database, and provides an overview of the scientific research associated with the observatory. Researchers using SIRTA data conduct research on atmospheric processes involving complex interactions between clouds, aerosols and radiative and dynamic processes in the atmospheric column. Atmospheric modellers working with SIRTA observations develop new methods to test their models and innovative analyses to improve parametric representations of sub-grid processes that must be accounted for in the model. SIRTA provides the means to develop data interpretation tools for future active remote sensing missions in space (e.g. CloudSat and CALIPSO). SIRTA observation and research activities take place in networks of atmospheric observatories that allow scientists to access consistent data sets from diverse regions on the globe.

J.-L. Bertaux, O. Korablev, D. Fonteyn, S. Guibert, E. Chassefière, F. Lefèvre, E. Dimarellis, J. P. Dubois, A. Hauchecorne, M. Cabane, P. Rannou, A. C. Levasseur-Regourd, G. Cernogora, E. Quémerais, C. Hermans, G. Kockarts, C. Lippens, M. de Maziere, D. Moreau, C. Muller, E. Neefs, P. C. Simon, F. Forget, F. Hourdin, O. Talagrand, V. I. Moroz, A. Rodin, B. Sandel, and A. Stern. Global structure and composition of the martian atmosphere with SPICAM on Mars express. Advances in Space Research, 35:31-36, 2005. [ bib | DOI | ADS link ]

SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) Light, a light-weight (4.7 kg) UV-IR instrument to be flown on Mars Express orbiter, is dedicated to the study of the atmosphere and ionosphere of Mars. A UV spectrometer (118-320 nm, resolution 0.8 nm) is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H2O, aerosols, atmospheric vertical temperature structure and ionospheric studies. UV observations of the upper atmosphere will allow studies of the ionosphere through the emissions of CO, CO+, and CO2+, and its direct interaction with the solar wind. An IR spectrometer (1.0-1.7 μm, resolution 0.5-1.2 nm) is dedicated primarily to nadir measurements of H2O abundances simultaneously with ozone measured in the UV, and to vertical profiling during solar occultation of H2O, CO2, and aerosols. The SPICAM Light near-IR sensor employs a pioneering technology acousto-optical tunable filter (AOTF), leading to a compact and light design. Overall, SPICAM Light is an ideal candidate for future orbiter studies of Mars, after Mars Express, in order to study the interannual variability of martian atmospheric processes. The potential contribution to a Mars International Reference Atmosphere is clear.

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