Wednesday, 25 January 2012
Parameterization of Bulk Radiative Properties for Use in Climate Models
Global radiative forcing (RF) of contrails is an important issue in understanding the influence of human activities on climate change. It has been commonly recognized that contrails and contrail cirrus have an increasing warming effect on the Earth due to the rapid growth of air travel. Nevertheless, uncertainties in modeling contrail ice crystals and their scattering properties may cause significant biases in the current estimates of contrail RF. In this study, we developed a new parameterization for the bulk-scattering properties of contrail and contrail cirrus for incorporation in radiative transfer and climate models. We analyzed the contrail information using the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The MODIS contrail mask was detected by a manually detection algorithm and an automated contrail detection algorithm (CDA). The collocated contrail data of 2006 and 2007 and a new scattering and absorption database of ice crystals were used to quantitatively understand the fractions of ice crystals with a variety of morphological habits and surface roughness conditions. An accurate representation of contrail radiative properties was given to minimize the uncertainties raised by the assumption of a particular contrail model. A parameterization of shortwave and longwave radiative properties of contrails was then developed for global and regional climate model applications.