Routine measurements of aerosol extinction profiles by the ARM program and their validation

The vertical profile of aerosol extinction is needed as input for the assessment of direct, indirect, and semi- direct effects of aerosols on the Earth radiative balance. Since 1998 the U.S. Department of Energy Atmospheric Radiation Measurement program has continuously operated a fully automated Raman Lidar at its Southern Great Plains site in Oklahoma. Its capability of measuring profiles of aerosol extinction and water vapor has been critically assessed using remote sensing and in situ aircraft measurements from the 2003 Aerosol Intensive Operations Period (AIOP). These comparisons revealed that the Raman Lidar's sensitivity had degraded significantly and the derived extinction profiles had developed a significant positive bias. Major upgrades to the Raman Lidar made in 2004 resulted in dramatically improved sensitivity and reduced random errors. The ARM program also operates Micro Pulse Lidars (MPL) at all of its fixed and mobile sites. When combined with a ground-based measurement of aerosol optical depth (AOD), aerosol extinction profiles can be derived from MPL data. Finally from 2000- 2007 the ARM program has conducted in-situ aerosol profile (IAP) flights using a small aircraft measuring profiles of aerosol scattering and absorption. An aircraft campaign focused on quantifying the improvements of the Raman Lidar and on validating the MPL extinction profiles - the Aerosol Lidar Validation Campaign (ALIVE) - was conducted in 2005. In both the AIOP and ALIVE campaigns the NASA Ames Airborne 14-channel Sunphotometer (AATS-14) was used as the comparison basis for vertically resolved aerosol extinction measurements. Additionally, coordinated flights between the IAP aircraft and the aircraft carrying AATS-14 in AIOP and ALIVE allow an assessment of the IAP's capability to measure aerosol extinction. The AATS-14 instrument has been used for the same purpose in many campaigns outside the ARM program. It is increasingly seen as the solid benchmark against which other measurements of ambient extinction profile measurements are compared. In this paper we show the comparisons derived from the ALIVE data (and not previously published AIOP IAP vs. AATS-14 comparisons) and put these in context with the previously published AIOP comparisons.