LASE measurements of aerosol and water vapor profiles during TARFOX

Abstract

The Lidar Atmospheric Sensing Experiment (LASE) was operated autonomously from the NASA high‐altitude ER‐2 aircraft on nine flights during July 10–26, 1996, as part of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). LASE measured high‐resolution profiles of water vapor and aerosols in regions of urban haze plumes over the U.S. eastern seaboard. Real‐time LASE aerosol measurements were used to guide the in situ aircraft to sample haze layers. In this paper the vertical and horizontal distributions of aerosol backscatter measured by LASE are presented along with the temporal evolution of the haze layers. The aerosol backscatter data also identify the presence of gradients in the aerosol plumes, the presence of low‐altitude clouds, and optically thin cirrus. This information is useful for many of the radiometeric observations made during TARFOX and can help explain observational differences among ground, airborne, and satellite observations. An iterative procedure is discussed which was used to invert lidar data to retrieve aerosol scattering ratios, extinction, and total optical depths from the LASE measurements. The sensitivity of these retrievals to assumed parameters is discussed and the results of retrievals are also compared to the well‐known Bernoulli method. LASE water vapor measurements were made across the entire troposphere using a three “line pair” method to cover the range of water vapor mixing ratio from < 0.01 g/kg near the tropopause to ∼ 20 g/kg near the surface in a single aircraft pass over the experiment region. These measurements also show two‐dimensional distributions of large spatial gradients in water vapor in the lower and upper troposphere. These observations are useful in the calculation of IR radiation fields and relative humidity fields, since relative humidity has a strong influence on the growth of aerosols and their scattering properties. Water vapor profiles, aerosol scattering ratios, aerosol extinction coefficients and aerosol optical depths were derived using the methodology presented in this paper from LASE measurements during TARFOX. These measurements are compared with other in situ and remote measurements during TARFOX in the companion papers [Ferrare et al., this issue (a, b)]