## 1 Introduction  
Radiative fluxes--leaving the Earth-Atmosphere system through Top-of-Atmosphere (TOA) and inferred from satellite measurements--are a key variable in diagnosing the system's current energy balance and--when observed repeatedly--to assess the radiative effects of clouds and aerosols (e.g., [1]). Clouds impact the energy balance through: (1) the emission of terrestrial radiation--largely regulated through their cloud-top temperature; and (2) the reflection of solar radiation--mainly driven by their cloud micro- and macrophysical properties. Marine boundary layer clouds are predominantly found in regions of large-scale subsidence and reflect solar radiation--where a much darker ocean would otherwise absorb--while emitting terrestrial radiation similar to cloud-free conditions (since their low altitude leads to a near-surface temperature at cloud-top) (e.g., [2]). This radiative response affects the prediction of tropical clouds in a future climate [3], and large uncertainties in the radiative feedback of low-level clouds arise from inaccurately predicted properties in general circulation models [4]. A main factor altering cloud properties is aerosols. In the presence of aerosols, cloud liquid water may distribute over more numerous and smaller droplets which crucially alters cloud optical properties and ultimately affects solar reflection [5]. Marine boundary layer clouds are especially exposed to and affected by various aerosol types (e.g., [6]), including biomass burning (e.g., [7; 8]) from nearby continents as well as volcanic emissions and exhaust from ships (e.g., [9; 10; 11]). The covariance of aerosol with meteorological conditions, such as humidity above clouds (hereafter referred to as cloud-topped moisture) complicates the assessment of cloud-aerosol interaction (e.g., [12]). To convert instantaneous TOA broadband radiance measurements into corresponding TOA fluxes, satellite missions [13; 14] have been relying on CERES ADMs (latest version \"CERES SSF Edition 4\" as described in [15]). The conversion for solar radiances to fluxes above clouds is--apart from viewing and illumination conditions--a function of cloud phase and cloud optical depth. The conversion factor, anisotropy, is resolved by viewing geometry (relative azimuth angles \(\phi\) and viewing zenith angle \(\theta_{v}\)) given a certain illumination geometry (solar zenith angle \(\theta_{s}\)). Anisotropy is mainly characterized by the cloud glory (the direct reflection back to the sun), the cloud bow (the direction of reflection at a scattering angle of about 140-145\({}^{\circ}\)), and higher intensity at larger \(\theta_{v}\) in the forward-scattering direction. In theory, features of the scattering phase function, such as cloud bow and glory, should correspond to the size distribution of cloud droplets. This correlation is illustrated in Figure 1. Stratocumulus clouds and their cloud-aerosol interaction should distribute reflected solar radiation differently depending on their droplet size distribution (given a constant cloud optical depth). Additionally, low clouds can have vast amounts of water vapor aloft. Such absorbing gas (acting mainly beyond 0.8 \(\upmu\)m) should have a stronger effect on upwelling radiances at larger \(\theta_{v}\) than at smaller ones due to respective atmospheric path lengths. Accordingly, anisotropy should be dependent on levels of water vapor. Figure 1: Broadband phase functions for three different cloud droplet effective radii \(R_{e}\). Phase functions were spectrally integrated over the solar regime (0.25–4.00 \(\upmu\)m) and are based on Mie calculation in spectral subintervals, assuming a Gamma–Hansen distribution with an effective variance of 0.11. Contributions from each subinterval were weighted by corresponding spectral cloud extinction and solar constant. Note that the y-axis of the inset is logarithmic, while the main plot is shown in linear scale.