First ISCCP Regional Experiment (FIRE)

PROJECT DESCRIPTION

The First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) took place off the coast of California during the summer of 1987. The objective of the experiment was to provide researchers with a detailed multi-platform data set on the extensive fields of stratocumulus clouds that often form in the subtropics. Special attention was paid to the measurement of the formation, maintenance, and dissipation of these marine stratocumulus clouds.

The dates of the experiment were 29 June to 19 July 1987. Ground-based remote sensing equipment was located on San Nicholas Island (SNI) and operated throughout the duration of the experiment. Detailed satellite imagery was taken during FIRE as well as in situ measurements from multiple aircraft. Tethered balloons provided turbulence, cloud microphysical, and cloud radiative data. For more information on the FIRE, the reader is referred to Albrecht et al. (1988).

Excellent conditions for the experiment existed during the time period. The subtropical high was strongly evident during most of the experiment, providing extended periods of stratocumulus cloudiness in the target area. The case day chosen for this study, 7 July 1987, was chosen because on this day, a long-lived stratocumulus deck began to dissipate, from west to east.

CASE STUDY

On 7 July 1987, a subtropical high pressure system was located over the eastern Pacific Ocean, with a ridge that extended into the southern California area. At the same time, a thermal low had developed over Arizona, which created a strong pressure gradient across the FIRE area. Strong north to northwesterly winds from 10-15 m/sec were observed over the FIRE region from the surface up to the 700 hPa level.

The start of the model simulation, 0000 UTC, corresponds to 4:00p.m. local time. During the night, strong long wave cooling caused a strengthening of the inversion and stratocumulus cloud deck. After sunrise and during the day, the cloud deck was observed to begin to dissipate on its western edge. As the day progressed, the area where the clouds had broken up moved further and further east. By 1830 UTC, a strong cloud transition was captured on satellite with the LANDSAT Thematic Mapper (2.08 - 2.35 micron band). West of the transition clear conditions were observed. At the transition, scattered cumuli were observed, becoming broken stratocumulus further to the east. East of the transition, nearly solid stratocumulus was found.

References