Contrail and Cirrus Observations over Europe from 6 Years of NOAA-AVHRR Data

Abstract

Thin ice clouds – cirrus and contrails – are analysed in a long-term 1 km data set from the Advanced Very High Resolution Radiometer (AVHRR). Here twice daily data received at DLR Oberpfaffenhofen covering most of Europe over the full lifetime of the NOAA-14 satellite from January 1995 until October 2001 is taken into account to derive high resolution contrail and cirrus cloud maps. The data presented here is part of the ongoing European Cloud Climatology (ECC). For the detection of thin cirrus the APOLLO (AVHRR processing scheme for the detection of clouds over land and ocean) scheme is applied and line-shaped contrails are recognised by a pattern recognition scheme. Over the almost 7 year long data set we observe strong annual variations of cirrus and contrail cover. As the monthly averages of cirrus and contrail coverage are almost synchronous there is a slight correlation between the two. Within the annual cycle the distribution patterns of both contrails and cirrus change extensively. Contrail coverage on average is rather constant during the time-span analysed here, while we observe a decrease of thin cirrus coverage from 1995 to 2001. It is still an open question whether this is caused by severe observing effects due to changes of the sensor system or actually a natural effect.