Observed and Simulated Spatial and Temporal Variability of Aerosol Properties During TCAP: Impact on Radiative Forcing

 

Authors

Richard A. Ferrare — NASA - Langley Research Center
Jennifer M. Comstock — Pacific Northwest National Laboratory
Larry Berg — Pacific Northwest National Laboratory
Chris A. Hostetler — NASA Langley Research Center
John W. Hair — NASA - Langley Research Center
Jason Tomlinson — Pacific Northwest National Laboratory
Alla Zelenyuk-Imre — Pacific Northwest National Laboratory
Sharon P Burton — NASA - Langley Research Center
Arthur J Sedlacek — Brookhaven National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Duli Chand — Pacific Northwest National Laboratory
Kai Zhang — Pacific Northwest National Laboratory
Jacqueline Mary Wilson — Pacific Northwest National Laboratory

Category

Absorbing Aerosol

Description

The Two Column Aerosol Project (TCAP) was designed to improve our understanding of aerosol chemical and optical properties downwind of North America and to provide a comprehensive dataset for evaluation of regional and global models. We present findings from the summertime Intensive Observation Period (IOP) that highlight the marked differences in the chemical and optical properties of aerosol in the column located over the ARM Mobile Facility (AMF) site on Cape Cod compared to the remote column located over the western Atlantic Ocean. The in situ and remote sensing measurements, completed using the DOE Gulfstream 1 (G-1) and NASA King Air B200, show that there are significant differences in the aerosol mass loading between the two columns. Observed differences in the aerosol extinction and absorption are consistent with the differences in the mass loading of organic, sulfate, and black carbon aerosols. The observed single scattering albedo (SSA) is found to be larger in the first half of the study, when the aerosol mass loading is greatest suggesting systematic differences in the aerosol during TCAP. Elevated aerosol layers were observed on four of six nearly cloud free flight days during the first IOP, some of which are associated with biomass burning events. Analysis of data collected using the NASA High Spectral Resolution Lidar (HSRL) shows that these layers are found to contribute up to 60% of the AOD within the column. In addition to the above analysis, TCAP data have also been used to evaluate simulations from the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) and the Community Atmospheric Model version 5 (CAM5) performed using a range of horizontal resolutions. Both models do a reasonable job representing the aerosol mass loading and aerosol optical properties observed in the two columns, although the performance is found to vary from day-to-day and the errors in simulated composition and size are not the same between the two models. Large variations are also found in the aerosol direct radiative forcing simulated using both models within the TCAP domain. We use the surface and aircraft measurements to help identify processes in each model that are driving the errors in simulated aerosol optical properties that potentially contribute to errors in the estimate of the direct radiative forcing.