Aerosol forcing at Niamey during RADAGAST from the CERES perspective

Poster PDF

Description

The ARM Mobile Facility (AMF), deployed at Niamey, Niger, during the RADAGAST experiment in 2006, accumulated a year-long set of detailed surface observations allowing for in-depth study of aerosol forcing to atmospheric radiation. NASA’s Clouds and the Earth’s Radiant Energy System experiment (CERES) instruments onboard the Terra and Aqua satellites measured top of atmosphere (TOA) radiation above the region and calculated flux profiles beneath CERES footprints simultaneously. Results are archived in the CERES Clouds and Radiative Swath (CRS) data product, which uses the Langley Fu & Liou two-stream radiation transfer model. Input for the model includes satellite remotely sensed variables such as clouds and aerosols and the Goddard Modeling and Assimilation Office GEOS-4 re-analysis for atmospheric conditions. Aerosol optical depth (AOD) is specified, over deserts in particular, by the Model for Atmospheric Transport and Chemistry (MATCH) and AOD from the MODIS MOD04 data product. Aerosol properties are specified by the MATCH model. We show results from the CRS compared to surface observations for CERES footprints whose centers fall within 25 km of the AMF. Reported calculations are instantaneous at satellite overpass time, not daily averages (expect large RMSs), for all- and clear-sky conditions and are presented with aerosol radiative forcing estimates from both satellites. On average Aqua CRS all-sky results show mean insolation for the year of 756 W with a bias of 24 W, and RMS of 91 W. Clear sky (defined as CERES footprint is cloud-free) results in mean insolation of 817 W, bias of 20 W, and RMS of 32 W. Mean shortwave aerosol forcing (calculated using clear-sky footprint results differenced from calculation without aerosol) is -51 W to surface insolation and +11 W reflection at TOA. The poster will show seasonal changes along with Terra results as well as consider impact of surface albedo on calculations. Key to these calculations is input AOD. The primary source for CRS calculations is the MATCH model with secondary source being MODIS MOD04. These estimates are compared to independent AOD observations from the ground (at 550 nm) from September–December 2006 using AERONET and to AOD derived from the MISR instrument onboard Terra for the entire year. Comparisons are relatively good and shown in accompanying image with biases of the CERES input values near 10% of MISR and AERONET observations with Aqua comparisons on top, Terra across the bottom.