Stratocumulus Drizzle Measurements Using High Spectral Resolution Lidar and Radar Data During the MAGIC Campaign

Abstract:

Marine stratus clouds are an important feature of the global climate system. Drizzle plays an important role in the determining cloud lifetime. Drizzle not only removes water from the cloud but evaporation of the falling droplets cools the sub-cloud layer acting to suppress convection. Drizzle rates are often very small and difficult to measure.

The ratio of millimeter radar and High Spectral Resolution Lidar (HSRL) backscatter is used to determine drizzle rates and these are compared to conventional ground based measurements. The robustly calibrated HSRL backscatter cross section provides advantages over measurements made with traditional lidars.

Several investigators have used simultaneous lidar and radar observations to determine particle size. However, measurements made with conventional lidar are hampered by: 1) changes in the transmission of the output window caused by water accumulation, 2) the difficulty of correcting the backscatter signal for atmospheric extinction, 3) the effects of multiple scattering, and 4) the need to convert backscatter measurements to extinction. The use of High Spectral Resolution Lidar(HSRL) data avoids many of these problems. HSRL backscatter measurements are referenced to the known molecular scattering cross-section at each point in the profile and are thus independent of changes in window and atmospheric transmission.
This study uses data collected during the US Department of Energy Atmospheric Sciences program MAGIC campaign. Instruments including a suite of conventional precipitation gages, a High Spectral Resolution Lidar, along with 3.2 mm wavelength WACR and a 8.6 mm wavelength KAZR radars, were installed on the container ship Horizon Spirit as it made repeated trips between Long Beach, CA and Honolulu, HI.