Contrail coverage over Western Europe derived from NOAA-AVHRR-data

The mean of the heterogeneity-corrected AVHRR-derived contrail coverage reached 0.5%±0.25% over Western Europe. The authors recognize strong temporal and spatial variations in contrail coverage which match those derived by S. Bakan et al. (1994). Absolute values derived are smaller by a factor of 1.6 which is of low significance due to analysis of different time-periods. Large differences of the two investigations can also be explained by an overestimation of the visual interpretations, but also by the poor detection efficiency of the automated scheme. For the midseason month within this period the authors derive a nighttime contrail coverage of 0.2% which has to be compared to 0.7% for the same period from AVHRR-nonpassages. The observed annual cycle has its maxima during winter and spring, but might still be influenced by a differing detection efficiency. Beyond this the scheme is not able to detect atypical contrails such as very wide spread and fuzzy ones, which are hard to distinguish from natural cirrus. These man made cirrus clouds might have an important influence on the regional climate