First ISCCP Regional Experiment (FIRE) Atlantic Stratocumulus Transition Experiment (ASTEX) NASA ER-2 Cloud Lidar System Data

The development of parameterizations requires an understanding of the processes that generate, maintain, and dissipate boundary layer clouds. This development is currently impeded by lack of understanding of the transition from stratocumulus clouds to trade cumulus clouds and the factors that control cloud type and amount in the boundary layer. ASTEX was designed to address key issues related to stratocumulus to trade cumulus transition and mode selection.

ASTEX involved intensive measurements from several platforms operating from June 1-28, 1992 in the area of the Azores and Madeira Islands. The purpose was to study how the transition and mode selection are effected by 1) cloud-top entrainment instability, 2) diurnal decoupling and clearing due to solar absorption, 3) patchy drizzle and a transition to horizontally inhomogeneous clouds through decoupling, 4) mesoscale variability in cloud thickness and associated mesoscale circulations, and 5) episodic strong subsidence lowering the inversion below the LCL.

Detailed descriptions of the scientific goals of ASTEX are in the FIRE Phase II: Research plan (1989) and in the ASTEX Operations Plan (1992). The Cloud Lidar System (CLS) instrument was flown aboard the NASA ER-2 airplane. This instrument was used to determine cloud altitudes.

Information pertaining to the number of cloud layers detected; the heights of the boundaries for up to 5 cloud layers; geo-physical location information; and time were recorded.Four channels of data were recorded. The first channel recorded wave lengths at 532 nanometers in the parallel plane. The second channel recorded wave lengths of 532 nanometers in the perpendicular plane.

The third channel recorded wavelengths of 1064 nanometers total. The forth channel was a linear amplifier which received the digitized signal from one of the three previously mentioned CLS detectors. The data are organized so that there is a single header record for the file.

This header record is followed by a series of pairs of records. The first record of each pair contains the CLS calibrated data and the second record of the pair contains the CLS analyzed data.