Spectral Absorption of Solar Radiation in Cloudy Atmospheres: A 20 cm<sup>−1</sup>Model

Davies, R.; Ridgway, William L.; Kim, Kyung-Eak

doi:10.1175/1520-0469(1984)041<2126:saosri>2.0.co;2

Cited by 56 publications

(35 citation statements)

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“…Except for the study of Pilewskie and Valero (1995), which follows the traditional approach of using aircraft to directly measure cloud absorption, the other two studies deal with atmospheric column absorption using ground and TOA fluxes. Since the absorption bands of water vapor and water droplets are highly overlapping and are of similar magnitudes (Davies et al 1984), total absorption in the atmospheric column is supposed to be rather insensitive to cloud, except for modification of its vertical distribution. Having a small effect on atmospheric absorption, however, does not imply that clouds absorb little solar radiation, only that whatever absorption occurs, the bulk of it is in place of clear-sky absorption (Stephens 1996).…”

Section: Renewed Debate Since the Mid-1990smentioning

confidence: 65%

On the Solar Radiation Budget and the Cloud Absorption Anomaly Debate

2004

Observation, Theory and Modeling of Atmospheric Variability

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This paper reviews the current state of knowledge, advances and challenges in short-wave earth radiation budget (ERB) studies and the cloud absorption anomaly (CAA) debate. The ERB issues deal exclusively with the solar energy disposition between the atmosphere, clouds and the surface. The ERB and its disposition have been derived from surface observations, satellite remote sensing and general circulation modeling. Major sources of uncertainties and discrepancies between observations and modeling are highlighted. Reported discrepancies between the ERB data sets obtained by various means are discussed, especially within the context of the recent debate concerning the CAA. This debate is documented thoroughly and critically in four stages: before and after the mid-1990s, and following two dedicated field experiments: the Atmospheric Radiation Measurement Enhanced Shortwave Experiment (ARESE I and II). An attempt is made to shed light on the causes of some controversial findings. It is now clear that the CAA is largely an artifact which does not emerge from a carefully designed closure test using the state-of-the-art radiative transfer models.

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Section: Renewed Debate Since the Mid-1990smentioning

confidence: 65%

On the Solar Radiation Budget and the Cloud Absorption Anomaly Debate

2004

Observation, Theory and Modeling of Atmospheric Variability

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“…The SW heating rate is also significant above the fog due to molecular absorption (dominantly by water vapour), which indicates that water vapour absorption inside the fog can also be important for heating the fog, as discussed, e.g. by Davies et al (1984). Finally, the calculated condensation rates (Fig.…”

Section: Appendix B: Estimation Of Vertical Profiles Of Microphysicalmentioning

confidence: 81%

“…This is due to the SW radiation being largely diffused in the forward direction, rather than being absorbed, so that much SW still remains to be absorbed even far down inside an optically thick cloud. Note also that some absorption occurs even in when LWP = 0, because of absorption by water vapour inside the cloud (Davies et al, 1984). E SW is also sensitive to the sizes of the droplets: for a given LWP, the largest effective radius (10.7 µm) gives a ≈ 50 % larger evaporation rate than the smallest effective radius (4 µm), which can appear counterintuitive since the total surface area of the DSD decreases with r eff .…”

Section: Sensitivity Of Radiation-driven Condensation Andmentioning

confidence: 99%

Radiation in fog: quantification of the impact on fog liquid water based on ground-based remote sensing

Wærsted¹,

Haeffelin

Dupont

et al. 2017

Atmos. Chem. Phys.

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Abstract. Radiative cooling and heating impact the liquid water balance of fog and therefore play an important role in determining their persistence or dissipation. We demonstrate that a quantitative analysis of the radiation-driven condensation and evaporation is possible in real time using groundbased remote sensing observations (cloud radar, ceilometer, microwave radiometer). Seven continental fog events in midlatitude winter are studied, and the radiative processes are further explored through sensitivity studies. The longwave (LW) radiative cooling of the fog is able to produce 40-70 g m −2 h −1 of liquid water by condensation when the fog liquid water path exceeds 30 g m −2 and there are no clouds above the fog, which corresponds to renewing the fog water in 0.5-2 h. The variability is related to fog temperature and atmospheric humidity, with warmer fog below a drier atmosphere producing more liquid water. The appearance of a cloud layer above the fog strongly reduces the LW cooling relative to a situation with no cloud above; the effect is strongest for a low cloud, when the reduction can reach 100 %. Consequently, the appearance of clouds above will perturb the liquid water balance in the fog and may therefore induce fog dissipation. Shortwave (SW) radiative heating by absorption by fog droplets is smaller than the LW cooling, but it can contribute significantly, inducing 10-15 g m −2 h −1 of evaporation in thick fog at (winter) midday. The absorption of SW radiation by unactivated aerosols inside the fog is likely less than 30 % of the SW absorption by the water droplets, in most cases. However, the aerosols may contribute more significantly if the air mass contains a high concentration of absorbing aerosols. The absorbed radiation at the surface can reach 40-120 W m −2 during the daytime depending on the fog thickness. As in situ measurements indicate that 20-40 % of this energy is transferred to the fog as sensible heat, this surface absorption can contribute significantly to heating and evaporation of the fog, up to 30 g m −2 h −1 for thin fog, even without correcting for the typical underestimation of turbulent heat fluxes by the eddy covariance method. Since the radiative processes depend mainly on the profiles of temperature, humidity and clouds, the results of this paper are not site specific and can be generalised to fog under different dynamic conditions and formation mechanisms, and the methodology should be applicable to warmer and moister climates as well. The retrieval of approximate emissivity of clouds above fog from cloud radar should be further developed.

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“…Many physicists have recently investigated the problem of cloud inhomogeneity with renewed interest. Some have attempted to evaluate its effect on radiant flux components of the cloud radiation budget [Barker, 1992[Barker, , 1996a [Davies et al, 1984]. On the other hand, Borde and Isaka [1996] showed that its effect on the effective optical depth is linear, and it should remain small in our case.…”

Section: Introductionmentioning

confidence: 89%