Broken-Cloud Enhancement of Solar Radiation Absorption

Byrne, Raymond; Somerville, Richard C. J.; Subasilar, B.

doi:10.1175/1520-0469(1996)053<0878:bceosr>2.0.co;2

Cited by 41 publications

(39 citation statements)

References 2 publications

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“…This apparent effect should not be mixed with the real effect of 3-D cloud in altering cloud absorption. Throughout the course of the debate, controversial findings on the magnitude of absorption enhancement have also been reported, ranging from very significant (Byrne et al 1996), significant (at steep solar zenith angles only) (O'Hirok et al 1998) to negligible (Markshak et al 1998, Barker et al 1998.…”

Section: Renewed Debate Since the Mid-1990smentioning

confidence: 99%

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: 99%

On the Solar Radiation Budget and the Cloud Absorption Anomaly Debate

2004

Observation, Theory and Modeling of Atmospheric Variability

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“…This argues for alternate mechanisms for absorption enhancement which may or may not involve clouds Arking, 1996]. However, recent simulations of broken cloudiness (with fixed cloud albedo) using stochastic radiative transfer [Byrne et al, 1996] …”

Section: Introductionmentioning

confidence: 99%

Inhomogeneity effects on cloud shortwave absorption measurements: Two‐aircraft simulations

Marshak¹,

Davis²,

Wiscombe³

et al. 1997

J. Geophys. Res.

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Abstract. We set up an Observation System Simulation in order to quantify the idiosyncratic uncertainties caused by cloud inhomogeneity in two-aircraft measurements. An independently validated fractal model is used to simulate the horizontal variability of optical depth for boundary layer stratus, with and without gaps. A spectral band between 0.9 and 1.0 gm, with a combination of strong and weak water vapor absorption and negligible weak liquid water absorption, is selected for a detailed study of column absorption. Measurements of upwelling and downwelling radiative fluxes are simulated by the Monte Carlo method at two altitudes in a realistic cloudy atmosphere. We consider three methods of estimating column absorption: cloud forcing ratio, reflectance (R) versus transmittance (T) regression, and Ackerman-Cox correction. Emphasis is on the second method, R versus T, which is shown to be biased in the direction of enhanced absorption as long as the R and T data points are affected by horizontal fluxes. In other words, to reduce the bias to an acceptable level, (R, T) measurements must be at a scale well within the regime where the independent pixel approximation is accurate. Under completely cloudy skies, radiative smoothing processes dominate the bias in the absorption estimate at small scales; hence spatial averages over at least 30 times the radiative smoothing scale, which is commensurate with cloud thickness, are required. If there are substantial gaps in the cloud cover, geometrical shadowing and cloud side-illumination effects overwhelm the radiative smoothing. As a result, the bias in R versus T methodology is worsened, and aircraft positioning becomes more critical. We also examine the effect of Sun angle and instrumental parameters such as vertical separation and horizontal offset between aircraft. The Ackerman-Cox correction offers an alternative to spatial averaging; a modification of this intrinsically small-scale approach that can virtually eliminate horizontal flux contributions in the data is presented.

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“…The major accomplishments include: (1) increased understanding of transport in 3-D media (e.g., Byrne et al 1996;Davis and Marshak, 2001; O'Hirok and Gautier 1998), (2) the development of an intercomparison of 3-D radiative transfer methods (I3RC) applied to Earth's atmosphere and (3) a study of how well 1-D solar radiative transfer codes -especially those used in numerical weather prediction (NWP) models and GCMs -interpret and handle unresolved clouds as determined directly by detailed radiation calculations applied to cloud-resolving model (CRM) output . In general, the various Monte Carlo methods for calculating radiative transport in 3-D media agree well with each other.…”

Section: -D Radiative Transfermentioning

confidence: 99%