Condensation trails (contrails) over Spain in May 2005.
24 May 2022
23 May 2005
By Jochen Kerkmann (EUMETSAT)
As in many other European countries, air traffic has significantly increased over the Iberian Peninsula in the last decades leading to an increase of high-level cirrus cloudiness in the form of condensation trails (contrails). While it is difficult to detect these thin clouds in the visible (solar) channels, they usually appear as narrow, grey stripes in the IR and WV channels.
The detection of these man-made clouds can be further improved by using the Brightness Temperature Difference (BTD) between the IR8.7, IR10.8 and IR12.0 channels (see Contrails over the Benelux countries on 5 September 2004). This is well demonstrated in the dust RGB composite image (Figure 1), where the condensation trails appear with a dark blue colour.
As can be seen in the animation (Figure 2), the contrails, while moving in a easterly direction, transform later during the day into a more compact cloud layer in the area of the Balearic Islands, thus, forming a kind of cirrostratus 'contrail genitus' cloud.
The case shown here is not such a rare event as one might think: similar cases have been observed in anticyclonic conditions over various parts of Europe and it has been demonstrated that a large percentage of cirrus clouds observed over Europe are actually man-made.
As high-level cirrus clouds have the same effect as a greenhouse gas (solar radiation passes through, infra-red radiation gets absorbed), one can imagine the impact that an increase of high-level clouds would have on our global climate. Thus, long-term monitoring of cloud coverage, as operationally performed by the Satellite Application Faciliy (SAF) on Climate Monitoring (see Climate SAF website) and the International Satellite Cloud Climatology Project (see ISCCP homepage) is a very important contribution to climate monitoring.