Dr. Hongyu Liu

I contribute to the general development of the LaRC/UW Regional Air Quality Modeling System (RAQMS) and its application to some tropospheric chemistry issues including the interpretation of NASA Global Tropospheric Experiment aircraft observations. RAQMS was jointly developed by the NASA Langley Research Center (LaRC) and University of Wisconsin-Madison (UW) under the leadership of Brad Pierce (LaRC), and it has been used to predict the tropospheric ozone budget over East Asia during the NASA TRACE-P aircraft mission [Pierce et al., 2003]. We have recently implemented a fast and accurate numerical method (Fast-J2) for calculating photolysis rates [Bian and Prather, 2002] in the RAQMS regional component (RAQMSr) in order to take account of the impact of cloud and aerosol layers on tropospheric chemistry. We have also evaluated two parameterization schemes for cloud optical depth calculations in RAQMSr using satellite observations. I work closely with LaRC scientists, in particular, Brad Pierce (LaRC), Jim Crawford (LaRC), Jassim Al-Saadi (LaRC), and Chieko Kittaka (SAIC/LaRC).

Clouds exert an important influence on tropospheric photochemistry through modification of solar radiation which determines photolysis rates (J-values). Enhanced photolysis rates have been found above and in the upper levels of clouds, while reduced rates have been found below optically thick clouds and absorbing aerosols. The objective of this study is to assess the radiative impact of clouds on global tropospheric chemistry including the effect of cloud overlap, using a state-of-the-art three-dimensional tropospheric chemistry and transport model (GEOS-CHEM). Collaborators: Jim Crawford (LaRC), Brad Pierce (LaRC), Peter Norris (GSFC/UMBC), Steve Platnick (GSFC), and Daniel Jacob's group (Harvard). Also see my GEOS-CHEM Activities page.

A recent analysis of trace gas distributions during NASA's TRACE-P aircraft mission (February-April, 2001) revealed significant enhancements of CO (and many other anthropogenic tracers) in cloudy regions as compared to clear areas, while distributions for ozone did not show clear differences between the two regions [Crawford et al., 2003]. I am using the RAQMS regional model to further examine these associations between cloud and trace gases in the springtime Asian pollution outflow. The GEOS-CHEM model is also used to extend this study to the globe and all seasons. Collaborators: Brad Pierce (LaRC), Jim Crawford (LaRC), Jassim Al-Saadi (LaRC), Chieko Kittaka (SAIC/LaRC), and Daniel Jacob's group (Harvard).

The Global Modeling Initiative (GMI) is a NASA-led activity to develop and maintain a state-of-the-art modular three-dimensional chemistry and transport model that can be used for assessment of the impacts of anthropogenic and natural perturbations on atmospheric composition and chemistry. The GMI model can be driven by a variety of meteorological archives such as GEOS DAS, fvGCM, ECMWF, CCM3, and GISS II'. One advantage of GMI is that it allows us to assess the impact of using different meteorological archives on the simulated tropospheric chemistry and thus the uncertainty of assessments. In support of GMI, we are currently evaluating the cloud physical/radiative properties in the GMI meteorological archives against satellite observations, with a particular focus on the statistical characterizations of global daily/monthly cloud optical depth and cloud fraction. Collaborators: David Considine (LaRC), Jim Crawford (LaRC), Peter Norris (GSFC/UMBC), Steve Platnick (GSFC), and the GMI core team (GSFC).