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국제학술지

공지 (2024. 9. 4.)

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Minor trace gas radiative forcing calculations using the k-distribution method with one-parameter scaling

Abstract: The k distribution method with one-parameter pressure and temperature scaling, first developed for water vapor, has now been applied to the minor trace gas (N2O, CH4, CFCs, and two minor bands of CO2) absorption in the infrared window region (800–1380 cm−1). The derivation of the k distributions is based upon an exponential sum fitting to the monochromatically calculated transmission functions at a predetermined reference pressure and temperature. For nonhomogeneous path lengths, one-parameter scaling is utilized in conjunction with the k distribution method. To determine the accuracies of the k distribution method as compared to the monochromatic calculations, fluxes and cooling rates are calculated for a wide variety of atmospheric conditions. For the entire 800–1380 cm−1 spectral range the effect of the minor trace gases on the fluxes calculated using the k distribution method is within 2.3% of the monochromatic method. In addition to being accurate, this method is computationally very fast. When implemented into the Goddard EOS general circulation model, the computing time for the longwave flux calculations is increased by only 20% despite the inclusion of the minor trace gas absorption bands.
- 작성자Kratz et al.
- 작성일2024.06.14
- 조회수10
- 1998
Parameterizations for cloud overlapping and shortwave single-scattering properties for use in general circulation ...

Abstract: Parameterizations for cloud single-scattering properties and the scaling of optical thickness in a partial cloudiness condition have been developed for use in atmospheric models. Cloud optical properties are parameterized for four broad bands in the solar (or shortwave) spectrum; one in the ultraviolet and visible region and three in the infrared region. The extinction coefficient, single-scattering albedo, and asymmetry factor are parameterized separately for ice and water clouds. Based on high spectral-resolution calculations, the effective single-scattering coalbedo of a broad band is determined such that errors in the fluxes at the top of the atmosphere and at the surface are minimized. This parameterization introduces errors of a few percent in the absorption of shortwave radiation in the atmosphere and at the surface. Scaling of the optical thickness is based on the maximum-random cloud-overlapping approximation. The atmosphere is divided into three height groups separated approximately by the 400- and 700-mb levels. Clouds are assumed maximally overlapped within each height group and randomly overlapped among different groups. The scaling is applied only to the maximally overlapped cloud layers in individual height groups. The scaling as a function of the optical thickness, cloud amount, and the solar zenith angle is derived from detailed calculations and empirically adjusted to minimize errors in the fluxes at the top of the atmosphere and at the surface. Different scaling is used for direct and diffuse radiation. Except for a large solar zenith angle, the error in fluxes introduced by the scaling is only a few percent. In terms of absolute error, it is within a few watts per square meter. Full title: Parameterizations for cloud overlapping and shortwave single-scattering properties for use in general circulation and cloud ensemble models
- 작성자Chou et al.
- 작성일2024.06.13
- 조회수9
- 1998
Water vapor and cloud feedback over the tropical oceans: Can we use ENSO as a surrogate for the climate change?

Abstract: Based on experiments with the Goddard Earth Observing System (GEOS) global climate model we find that the basic patterns of anomalous water vapor greenhouse effect and cloud radiative forcing during ENSO are primarily determined by the basin-wide dynamical response to large scale sea surface temperature (SST) forcing. There is no supergreenhouse effect in the sense of unstable interaction due to local thermodynamics and water vapor radiative feedback on interannual time scales. About 80% of the clear sky water vapor greenhouse sensitivity to SST-deduced from ENSO anomalies are due to the transport of water vapor by the large scale circulation. The sensitivity of water vapor greenhouse effect to SST due to radiative feedback is found to be about 1.8 Wm −2/ °C, much smaller than the values of 6~9 Wm −2/ °C previously estimated from satellite observations from ENSO conditions. Our results show that regionally based interannual variability should not be used to infer radiative feedback sensitivity for climate change unless proper corrections are made for the effect of the large scale circulation.
- 작성자Lau et al.
- 작성일2024.06.13
- 조회수8
- 1996