Toward New Inferences about Cloud Structures from Multidirectional Measurements in the Oxygen A Band: Middle-of-Cloud Pressure and Cloud Geometrical Thickness from POLDER-3/PARASOL

Abstract

New evidence from collocated measurements, with support from theory and numerical simulations, that multidirectional measurements in the oxygen A band from the third Polarization and Directionality of the Earth's Reflectances (POLDER-3) instrument on the Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL) satellite platform within the ''A-Train'' can help to characterize the vertical structure of clouds is presented. In the case of monolayered clouds, the standard POLDER cloud oxygen pressure product P O2 is shown to be sensitive to the cloud geometrical thickness H in two complementary ways: 1) P O2 is, on average, close to the pressure at the geometrical middle of the cloud layer (MCP) and methods are proposed for reducing the pressure difference P O2 2 MCP and 2) the angular standard deviation of P O2 and the cloud geometrical thickness H are tightly correlated for liquid clouds. Accounting for cloud phase, there is thus the potential to obtain a statistically reasonable estimate of H. Such derivation from passive measurements, as compared with or supplementing other observations, is expected to be of interest in a broad range of applications for which it is important to define better the macrophysical cloud parameters in a practical way.

Retrieval of aerosol microphysical and optical properties above liquid clouds from POLDER/PARASOL polarization measurements

“…The apparent O 2 cloud pressure does not appear to be much perturbed by the aerosol layer and tends to slightly underestimate the true cloud top altitude. This last method provides an estimate of the cloud top height that is in-between the geometric middle of the cloud layer and the cloud top height, as expected for low-level single cloud layers (Ferlay et al, 2010). Most of the clouds observed in the POLDER image shown in Fig.…”

The O2 A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

“…However, because this method only accounts approximately for the penetration and multiple scattering of photons inside the cloud, it tends to systematically overestimate cloud-top pressures (hence, it underestimates cloud-top altitudes; Vanbauce et al 1998). The retrieved pressure appears to be more representative ofthe pressure halfway throughthe cloud (see Vanbauce et al 2003;Sneep et al 2008;Wang et al 2008;Ferlay et al 2010;Desmons et al 2013).…”

Evaluation of SCIAMACHY ESA/DLR Cloud Parameters Version 5.02 by Comparisons to Ground-Based and Other Satellite Data

“…This approach was firstly proposed by Saiedy et al (1965Saiedy et al ( , 1967, who also noticed that the assumption of a cloud as a perfect Lambertian reflector with zero transmittance leads to lower values of cloud heights. When light scattering inside and below the cloud are taken into account in the forward modeling, the geometrical thickness (CGT) of a cloud can also be retrieved, being beneficial for the accuracy of cloud top height (Fischer and Grassl, 1991;Kuji and Nakajima, 2002;Ferlay et al, 2010;Schuessler et al, 2013).…”