Impact of radiatively interactive dust aerosols in the NASA GEOS‐5 climate model: Sensitivity to dust particle shape and refractive index
Tóm tắt
The radiative effects of Saharan dust aerosols are investigated in the NASA GEOS‐5 atmospheric general circulation model. A sectional aerosol microphysics model (CARMA) is run online in GEOS‐5. CARMA treats the dust aerosol lifecycle, and its tracers are radiatively coupled to GEOS‐5. A series of AMIP‐style simulations are performed, in which input dust optical properties (particle shape and refractive index) are varied. Simulated dust distributions for summertime Saharan dust compare well to observations, with best results found when the most absorbing dust optical properties are assumed. Dust absorption leads to a strengthening of the summertime Hadley cell circulation, increased dust lofting to higher altitudes, and a strengthening of the African easterly jet, resulting in increased dust atmospheric lifetime and farther northward and westward transport. We find a positive feedback of dust radiative forcing on emissions, in contrast with previous studies, which we attribute to our having a relatively strong longwave forcing caused by our simulating larger effective particle sizes. This longwave forcing reduces the magnitude of midday net surface cooling relative to other studies, and leads to a nighttime warming that results in higher nighttime wind speeds and dust emissions. The radiative effects of dust particle shape have only minor impact on transport and emissions, with small (~5%) impact on top of atmosphere shortwave forcing, in line with previous studies, but relatively more pronounced effects on shortwave atmospheric heating and surface forcing (~20% increase in atmospheric forcing for spheroids). Shape effects on longwave heating terms are of order ~10%.
Từ khóa
Tài liệu tham khảo
Chou M. andM. J.Suarez(1994) An efficient thermal infrared radiation parameterization for use in general circulation models Technical Report Series on Global Modeling and Data Assimilation 3 1–98.
Chou M. andM. J.Suarez(1999) A solar radiation parameterization for atmospheric studies Technical Report Series on Global Modeling and Data Assimilation 15 1–51.
Chou M. M. J.Suarez X.‐Z.Liang andM. M. H.Yan(2001) A thermal infrared radiation parameterization for atmospheric studies Technical Report Series on Global Modeling and Data Assimilation 19 1–68.
Gerber H. E.(1985) Relative‐humidity parameterization of the Navy Aerosol Model (NAM) NRL Report 8956 1–16.
IPCC, 2007, Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 996
Prospero J. M., 1996, Particle Flux in the Ocean, 19
Prospero J. M., 1989, Chemical Oceanography, 187
Pruppacher H. R., 1997, Microphysics of Clouds and Precipitation
Rienecker M. et al. (2008) The GEOS‐5 data assimilation system—Documentation of version 5.0.1 5.1.0 and 5.2.0 NASA Technical Report Series on Global Modeling and Data Assimilation 27 1–118.
Shettle E. P. andR. W.Fenn(1979) Models for the aerosols of the lower atmosphere and effects of humidity variation on their optical properties Air Force Geophysics Laboratory Tech. Rep. AFGL‐TR‐79‐0214 pp.94 Hanscom AFB Massachusetts USA.