Effective radiative properties of bounded cascade absorbing clouds: Definition of an effective single‐scattering albedo

Abstract

Abstract. We applied the equivalent homogeneous cloud approximation (EHCA) to the bounded cascade inhomogeneous absorbing clouds and defined their effective radiative properties. It is found that we have to introduce an effective singlescattering albedo in addition to an effective optical depth to treat the inhomogeneous absorbing clouds under the plane-parallel homogeneous cloud assumption. For an inhomogeneous absorbing cloud, a pair of the effective parameters can be estimated from each one of three possible pairs taken fi'om the area-averaged reflectance, transmittance and absorptance. We found that the behavior of these effective properties was quite similar to •hose observed ibr the inhomogeneous non absorbing clouds except, that two effective parameters were to be examined instead of only one e•ct, ive parameter for the nonabsorbing clouds. Empirical relations for both the effective optical depth and the single-s{:attering albedo were given as a function of the local mean opt•ical depth and relative local clo•d inhomogeneity. We showed tha[ tile effbctive sin/_;le-sca, tterin• albedo could not be properly introduced ,re(let t•he effe(:tiv(' thi(:kn(•ss approximation (ETA), which indicates an important ('on(:eptu•fi (tifi'eren(:e between the EHCA and the ETA. Finally, we discussed t)ossi})lc (:onsequenccs of the effective single-scattering albedo, defined in this st, udy, with respe(:t to the anomalous absorption phenomenon.

Simplifying the interaction of land surfaces with radiation for relating remote sensing products to climate models

“…The use of effective radiative state variables to express the properties of 3‐D vegetation canopy systems guarantees the correct simulation of the scattered, transmitted and absorbed radiant fluxes (in vegetation [ Pinty et al , 2004]). This requirement is not specific to vegetation canopy systems but applies, in principle, to all radiative systems with significant 3‐D structural effects (in clouds [e.g., Boissé , 1990; Cahalan et al , 1994; Szczap et al , 2000; Cairns et al , 2000]). In our approach, the values of the effective variables are estimated by inverting a 1‐D radiant flux model against fluxes generated by a 3‐D model.…”

Neural network retrieval of cloud parameters of inhomogeneous clouds from multispectral and multiscale radiance data: Feasibility study

“…The inverse cloud used in this study is a cloud with vertically uniform microphysical and optical properties, and it is defined with 6 cloud parameters: mean optical thickness ( p ), mean effective radius ( p ), standard deviation of optical thickness (σ τ, p ), standard deviation of effective radius (σ r , p ), fractional cloud cover ( p ), and cloud top temperature ( p ). Theses cloud parameters have been defined by assuming that the effect of exact spatial distribution of fluctuations within an observation pixel can be neglected as first order approximation [ Szczap et al , 2000a, 2000b]. For such an inverse cloud, the one‐to‐one correspondence between target vectors and input vectors is only an approximate one with inherent dispersions as shown in FIG01.…”

Two case studies of winter continental‐type water and mixed‐phase stratocumuli over the sea 2. Absorption of solar radiation

“…We summarize numerical values of the VIS‐band and NIR‐band absorptances averaged over each leg in Table 1. Since the leg‐mean VIS‐band absorptances scatter about zero with magnitudes exceeding the measurement accuracy of ±0.02, the leg distance of about 40 km seems to be too short to get rid of influences due to cloud inhomogeneity for the highly heterogeneous thick clouds at the oblique solar incidence [ Szczap et al , 2000a, 2000b]. However, the VIS‐band absorptance averaged over all of the three legs is almost zero, indicating that the mixed‐phase stratocumulus cloud did not substantially absorb the visible solar radiation.…”