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  • 1
    Online Resource
    Online Resource
    Simulation of the tropospheric sulfur cycle in a global model with a physically based cloud scheme
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research: Atmospheres Vol. 107, No. D21 ( 2002-11-16)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 107, No. D21 ( 2002-11-16)
    Abstract: The treatment of the sulfur cycle in the CSIRO global climate model (GCM) is described. It is substantially based on the scheme developed previously for the European Center/Hamburg (ECHAM) model, but the treatment of wet scavenging has been completely rewritten to better reflect the different properties of liquid and frozen precipitation, and the treatment of these in the model's cloud microphysical scheme. The model is able to reproduce the observed finding that wet deposition of sulfur over Europe and North America is larger in summer than in winter, but the seasonal cycle of sulfate over Europe is not well simulated. The latter is improved when the amplitude of the seasonal cycle of European emissions is increased. Below‐cloud scavenging makes an important contribution in our scheme: On omitting it, the global sulfate burden increases from 0.67 to 0.93 Tg S. On reverting to the less efficient scavenging treatment used in ECHAM, the global sulfate burden again increases from 0.67 to 0.93 Tg S, and excessive sulfate concentrations are obtained in Europe and North America. Some deficiencies in the simulation are investigated via further sensitivity tests. In particular, during the Arctic winter, the modeled sulfur dioxide (SO 2 ) concentrations are too large, and the modeled sulfate concentrations are too small (as in most global sulfur‐cycle models). Recent laboratory experiments suggest that SO 2 oxidation in ice clouds is nonnegligible. We obtain a much improved Arctic simulation when a simple treatment of SO 2 oxidation in ice clouds is included.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD002128
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
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  • 2
    Online Resource
    Online Resource
    Enhancement of dust source area during past glacial periods due to changes of the Hadley circulation
    American Geophysical Union (AGU) ; 2001
    In:  Journal of Geophysical Research: Atmospheres Vol. 106, No. D16 ( 2001-08-27), p. 18477-18485
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 106, No. D16 ( 2001-08-27), p. 18477-18485
    Abstract: Tropical deserts (e.g., Sahara, Arabian desert, Australian desert) are located within the Hadley circulation. Most of the dust uplifted from these deserts is carried by trade winds and deposited in tropical oceans with very little, if any, transported to polar regions. During glacial periods the dust concentrations in polar ice cores were a factor of 10 to 100 higher than during interglacial periods, including the current Holocene. The early general circulation model simulations of the past glacial climate were not able to reproduce these high mineral dust concentrations; the most recent attempts achieve an increased dust transport to polar regions by extending dust source areas to higher latitudes. We present a hypothesis that during glacial periods the Hadley cell is confined closer to the equator. This contraction of the Hadley circulation leads to the geographical change of the boundary between the tropical and the midlatitude circulation regimes. During the glacial periods a considerable fraction of the current tropical deserts was located outside the region of the Hadley circulation. This allowed the dust to be uplifted and transported by midlatitude storm systems to the polar regions. We present a model for the contraction of the Hadley circulation during the past glacial periods based on the Schneider‐Lindzen and Held‐Hou model of symmetric tropical circulation and on the assumption that the tropical sea surface temperatures were lower during glacial periods than they are today.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2000JD900583
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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  • 3
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    Can aerosols spin down the water cycle in a warmer and moister world? : GLOBAL WARMING, AEROSOL AND WATER CYCLE
    American Geophysical Union (AGU) ; 2004
    In:  Geophysical Research Letters Vol. 31, No. 6 ( 2004-03), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 31, No. 6 ( 2004-03), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2003GL019060
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2004
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  • 4
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    A Comparison of Surface Observations and ECHAM4-GCM Experiments and Its Relevance to the Indirect Aerosol Effect
    American Meteorological Society ; 2001
    In:  Journal of Climate Vol. 14, No. 6 ( 2001-03), p. 1078-1091
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 14, No. 6 ( 2001-03), p. 1078-1091
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/1520-0442(2001)014〈1078:ACOSOA〉2.0.CO;2
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2001
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  • 5
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    Stronger Constraints on the Anthropogenic Indirect Aerosol Effect
    American Association for the Advancement of Science (AAAS) ; 2002
    In:  Science Vol. 298, No. 5595 ( 2002-11), p. 1012-1015
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 298, No. 5595 ( 2002-11), p. 1012-1015
    Abstract: The anthropogenic indirect aerosol effects of modifying cloud albedo and cloud lifetime cannot be deduced from observations alone but require a modeling component. Here we validate a climate model, with and without indirect aerosol effects, by using satellite observations. The model agrees better with observations when both indirect aerosol effects are included. However, the simulated clouds are more susceptible to aerosols than the observed clouds from the POLDER satellite, thus overestimating the indirect aerosol effect. By taking the difference in susceptibilities into account, the global mean total anthropogenic aerosol effect is reduced from –1.4 to –0.85 watts per square meter.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1075405
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2002
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  • 6
    Online Resource
    Online Resource
    IMPORTANCE OF ORGANIC AEROSOLS AS CLOUD CONDENSATION NUCLEI IN THE ARCTIC
    Elsevier BV ; 2004
    In:  Journal of Aerosol Science Vol. 35 ( 2004-07), p. S733-S734
    Details
    In: Journal of Aerosol Science, Elsevier BV, Vol. 35 ( 2004-07), p. S733-S734
    Type of Medium: Online Resource
    ISSN: 0021-8502
    URL: Article
    DOI: 10.1016/S0021-8502(19)30121-1
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2004
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  • 7
    Online Resource
    Online Resource
    Why is the cloud albedo — Particle size relationship different in optically thick and optically thin clouds?
    American Geophysical Union (AGU) ; 2000
    In:  Geophysical Research Letters Vol. 27, No. 8 ( 2000-04-15), p. 1099-1102
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 27, No. 8 ( 2000-04-15), p. 1099-1102
    Abstract: Recent studies have analyzed satellite data in terms of the relationship of cloud albedo with droplet size for warm clouds. It was found that for optically thick marine clouds (τ 〉 15) the cloud albedo increases with decreasing cloud droplet effective radius ( r e ). For optically thinner marine clouds (τ 〈 15) cloud albedo increases with increasing r e as to be expected if the liquid water content is adiabatic. Hypotheses for the change in sign in the τ ‐ r e relationship are deviations from an adiabatic liquid water content or the presence of single layer versus multi layer clouds. In this study, the ECHAM model, which exhibits this sign change in the τ ‐ r e correlation for optically thin and thick marine clouds, is used to test these hypotheses. Probability density functions of τ ‐ r e show that the change in sign of the correlation can be attributed to precipitating versus non‐precipitating clouds, but not to the difference in single layer versus multi‐layer clouds.
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/1999GL011098
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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  • 8
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    Indirect effect of sulfate and carbonaceous aerosols: A mechanistic treatment
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Atmospheres Vol. 105, No. D10 ( 2000-05-27), p. 12193-12206
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D10 ( 2000-05-27), p. 12193-12206
    Abstract: The indirect effect of anthropogenic aerosols, whereby aerosol particles change cloud optical properties, is the most uncertain component of climate forcing over the past 100 years. Here we use a mechanistic treatment of droplet nucleation and a prognostic treatment of the number of cloud droplets to study the indirect aerosol effect from changes in carbonaceous and sulfate aerosols. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and an activation parameter, which takes into account the mechanism of sulfate aerosol formation. Where previous studies focussed either on sulfate aerosols or carbonaceous aerosols only, here we estimate the combined effect. The combined indirect aerosol effect amounts to −1.1 W m −2 for an internally mixed aerosol and −1.5 W m −2 for an externally mixed aerosol compared to −1.4 W m −2 , which we obtained by empirically relating sulfate mass to cloud droplet number. In the case of an internally mixed aerosol, the contribution from increasing carbonaceous and sulfate aerosols is close to being additive as the individual simulations yield an indirect effect of −0.4 W m −2 due to anthropogenic sulfate aerosols and −0.9 W m −2 due to anthropogenic carbonaceous aerosols. The contribution of anthropogenic sulfate to the indirect effect is close to zero if an externally mixed aerosol is assumed, while the contribution of carbonaceous aerosols increases to −1.3 W m −2 . The effect of sulfate in the external mixture approach is much smaller than that of carbonaceous aerosols because its burden only increases by a third of that of carbonaceous aerosols and because the mode radius of sulfate is much larger than that of black and organic carbon.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD901199
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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  • 9
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    Impact of improved near-infrared water vapor line data in simulations with the ECHAM4 general circulation model
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research Vol. 107, No. D16 ( 2002)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 107, No. D16 ( 2002)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2001JD001101
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
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  • 10
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    A new statistically based autoconversion rate parameterization for use in large‐scale models
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research: Atmospheres Vol. 107, No. D24 ( 2002-12-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 107, No. D24 ( 2002-12-27)
    Abstract: The autoconversion rate is a key process for the formation of precipitation in warm clouds. In climate models, physical processes such as autoconversion rate, which are calculated from grid mean values, are biased, because they do not take subgrid variability into account. Recently, statistical cloud schemes have been introduced in large‐scale models to account for partially cloud‐covered grid boxes. However, these schemes do not include the in‐cloud variability in their parameterizations. In this paper, a new statistically based autoconversion rate considering the in‐cloud variability is introduced and tested in three cases using the Canadian Single Column Model (SCM) of the global climate model. The results show that the new autoconversion rate improves the model simulation, especially in terms of liquid water path in all three case studies.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2001JD001484
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
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