Retrieving mesospheric water vapour from observations of volume scattering radiances

Abstract

Abstract. This study examines the possibility for a theoretical approach in the estimation of water vapour mixing ratios in the vicinity of polar mesospheric clouds (PMC) using satellite observations of Volume Scattering Radiances (VSR) obtained at the wavelength of 553 nm. The PMC scattering properties perturb the underlying molecular Rayleigh scattered solar radiance of the background atmosphere. As a result, the presence of PMC leads to an enhancement in the observed VSR at the altitude of the layer; the PMC VSRs are superimposed on the exponentially decreasing with height Rayleigh VSR, of the PMC-free atmosphere. The ratio between the observed and the Rayleigh VSR of the background atmosphere is used to simulate the environment in which the cloud layer is formed. In addition, a microphysical model of ice particle formation is employed to predict the PMC VSRs. The initial water vapour profile is perturbed until the modelled VSRs match the observed, at which point the corresponding temperature and water vapour profiles can be considered as a first approximation of those describing the atmosphere at the time of the observations. The role of temperature and water vapour in the cloud formation is examined by a number of sensitivity tests suggesting that the water vapour plays a dominant role in the cloud formation in agreement with experimental results. The estimated water vapour profiles are compared with independent observations to examine the model capability in the context of this study. The results obtained are in a good agreement at the peak of the PMC layer although the radiance rapidly decreases with height below the peak. This simplified scenario indicates that the technique employed can give a first approximation estimate of the water vapour mixing ratio, giving rise to the VSR observed in the presence of PMC.

The Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite: A 20 year perspective

“… Vergados and Shepherd [2009] employed the CARMA (Community Aerosol and Radiation Model for Atmospheres) model to predict PMC scattering from the ice crystals simulated by the model. These were compared with the WINDII PMC observations and the water vapor profiles adjusted to match the model results with the observations.…”

“…Richmond et al [2003],Shepherd [2011],Thuillier et al [2002] Polar mesospheric clouds were observed in an imaging mode but also in normal operations. et al[1995],Shettle et al [2002],Vergados and Shepherd [2009], Wiens et al[1995] Auroral emission rate profiles were observed both in the daytime and at night, allowing auroral excitation and the influence of geomagnetic disturbances to be studied.…”

Comparison of retrieved noctilucent cloud particle properties from Odin tomography scans and model simulations

“…This is because there is more than one solution when fitting the observed signal to the simulated T-matrix spectra for large particles and scattering angles > 90 • (see von Savigny et al, 2005, Fig. 3 for an equivalent issue).…”

“…It has been used to simulate NLCs in numerous publications (e.g. Asmus et al, 2015;Kiliani et al, 2015;Chandran et al, 2012;Megner, 2011;Megner et al, 2006;Rapp and Thomas, 2006;Merkel et al, 2009;Stevens, 2005;Vergados and Shepherd, 2009;Lübken et al, 2007). As in the majority of these studies, we use the 1-dimensional set-up of the model to simulate microphysical processes such as ice nucleation and growth, sedimentation and vertical transport.…”

Comparison of retrieved Noctilucent cloud particle properties from Odin tomography scans and model simulations

“…It has been used to simulate NLCs in numerous publications (e.g. Asmus et al, 2015;Kiliani et al, 2015;Chandran et al, 2012;Megner, 2011;Megner et al, 2006;Rapp and Thomas, 2006;Merkel et al, 2009;Stevens, 2005;Vergados and Shepherd, 2009;Lübken et al, 2007). As in the majority of these studies, we use the 1-dimensional set-up of the model to simulate microphysical processes such as ice nucleation and growth, sedimentation and vertical transport.…”