A temporal analysis of East Pacific and East Atlantic ship-tracks

Abstract

The spatial, temporal and radiative properties of ship tracks are described with an analysis of AVHRR (Advanced Very High Resolution Radiometer) imagery. 15 cams are analyzed including 6 from the Atlantic Stratocumulus Transition Experiment (ASTEX) in the Azores islands, 6 from ship tracks observed off the coast of Oregon and 3 from the 1987 First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) (Starr, 1987). The reflectance in channel 3 (3.7 microns) of each ship track and associated background are analyzed as a function of time. The width of each ship track is also plotted as a function of time to determine their spatial and dispersive qualities. The eastern Pacific Ocean ship tracks are generally less dispersive, but two ASTEX ship tracks were more dispersive than what would be consistent over land. In individual cases, higher ambient reflectances are associated with environments that are less sensitive to ship effluent resulting in lower ship track reflectances. But in the composite of all ship track cases, higher ambient reflectances are associated with environments that are more sensitive to ship effluent resulting in higher ship track reflectances. Though the number of cases was limited due to weather and other phenomena, the reflectance, width and dispersion analysis highlight the commonalities and differences between the ship tracks from the two areas. This indicates that the state of the atmosphere has a substantial effect on ship track formation.