Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the twentieth century

Hiroaki Kawase, Toshihiko Takemura, Toru Nozawa

    Research output: Contribution to journalArticle

    8 Citations (Scopus)

    Abstract

    We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results.

    Original languageEnglish
    Article numberD18116
    JournalJournal of Geophysical Research Atmospheres
    Volume116
    Issue number18
    DOIs
    Publication statusPublished - Jan 1 2011

    Fingerprint

    aerosols
    Aerosols
    twentieth century
    summer
    aerosol
    Soot
    black carbon
    solar radiation
    atmospheric heating
    Carbon black
    anomalies
    drying
    trends
    anomaly
    Drying
    Atlantic Ocean
    carbon
    Solar radiation
    evaporation
    Evaporation

    All Science Journal Classification (ASJC) codes

    • Geophysics
    • Forestry
    • Oceanography
    • Aquatic Science
    • Ecology
    • Water Science and Technology
    • Soil Science
    • Geochemistry and Petrology
    • Earth-Surface Processes
    • Atmospheric Science
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science
    • Palaeontology

    Cite this

    Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the twentieth century. / Kawase, Hiroaki; Takemura, Toshihiko; Nozawa, Toru.

    In: Journal of Geophysical Research Atmospheres, Vol. 116, No. 18, D18116, 01.01.2011.

    Research output: Contribution to journalArticle

    @article{2e83a2ec988e4379bf4c93fac0cf58bc,
    title = "Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the twentieth century",
    abstract = "We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results.",
    author = "Hiroaki Kawase and Toshihiko Takemura and Toru Nozawa",
    year = "2011",
    month = "1",
    day = "1",
    doi = "10.1029/2011JD015933",
    language = "English",
    volume = "116",
    journal = "Journal of Geophysical Research",
    issn = "0148-0227",
    number = "18",

    }

    TY - JOUR

    T1 - Impact of carbonaceous aerosols on precipitation in tropical Africa during the austral summer in the twentieth century

    AU - Kawase, Hiroaki

    AU - Takemura, Toshihiko

    AU - Nozawa, Toru

    PY - 2011/1/1

    Y1 - 2011/1/1

    N2 - We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results.

    AB - We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results.

    UR - http://www.scopus.com/inward/record.url?scp=80053615076&partnerID=8YFLogxK

    UR - http://www.scopus.com/inward/citedby.url?scp=80053615076&partnerID=8YFLogxK

    U2 - 10.1029/2011JD015933

    DO - 10.1029/2011JD015933

    M3 - Article

    AN - SCOPUS:80053615076

    VL - 116

    JO - Journal of Geophysical Research

    JF - Journal of Geophysical Research

    SN - 0148-0227

    IS - 18

    M1 - D18116

    ER -