Abstract:
Clouds strongly modulate the radiative transfer in the atmosphere by inducing large deviations from clear-sky fluxes. This implies that the radiative effect of clouds (CRE) on their surroundings, even if small relative to CRE, will be large compared to clear-sky and significant for Earth’s energy budget.
Over the past two decades, extensive research has focused on cloud radiative signatures in their surroundings through components such as undetected clouds, 3D radiative effects, increased humidification, and more. Such studies emphasize the challenges in obtaining an adequate definition of clouds and separating clouds from aerosol. These actions are critical when quantifying CRE, aerosol direct and indirect radiative effects, and remote sensing of clear sky properties for both surface and atmosphere. So far, such studies have mostly used narrowband solar radiation — focusing on process-level understanding of what causes increased reflectance near clouds, and the biases it induces in remote sensing retrievals.
In this presentation, we will take a step further by analyzing high-resolution multi-spectral images of cloud fields measured by MODIS co-located with CERES broadband top-of-the-atmosphere radiative fluxes. We will quantify the net radiative effect of clouds coming from the supposedly clear-sky by adjusting the simple equation for radiative fluxes at the top of the atmosphere to explicitly include cloud effects in the clear-sky term. While CERES contributes robust estimates of top-of-the-atmosphere pure-clear-sky, MODIS multi-spectral and high spatial-resolution is used to include the spectral and spatial variability within the cloud field. The results show that cloud radiative effects on their neighboring clear-sky in the solar spectrum are larger than the aerosol direct radiative effect over the Ocean and that the near-cloud radiative effect in the longwave infra-red is equivalent to a large increase in greenhouse gasses.
This presentation lays the groundwork for a discussion about the benefits that Earth energy budget research can gain by separating the sky into three (i.e., cloudy, cloud-influenced, and clear sky), rather than two regimes. This has the potential to advance the development of new directions that don’t involve definitions of clouds. We’ll show that using discrete spectral information can highly contribute to such ideas.