Daily Contrail Observations
At Hazelrigg, and at all the other stations taking part in the Network daily observations are carried out at 9am and are recorded on the observation form shown in Figure 1. The observations that are conducted are:
The proportion of the sky that is covered by non-contrail related cloud. This is recorded in oktas and is recorded as 0 oktas (no coverage) to 8 oktas (total coverage) or 9 oktas (sky obscured by low cloud or fog).
The proportion of the sky covered by contrail related cloud. This is recorded in the same way as the proportion of the sky covered by non-contrail related cloud except that there is no option for 9 oktas and the 0 to 1 oktas scale is divided here into small sub categories, this is to account for the fact that there may be 1 or 2 contrails in the sky but these do not quite account for 1 full okta, therefore they would take up a portion of the sky between 0 and 1 okta.
Cloud cover type. This category involves the identification of the 10 major cloud types. For the observations however only the 3 major cloud types that are occurring are recorded, the main type being recorded as a number 1 next to the cloud type and the third least common being recorded as a number 2 next to the cloud type.
Number of planes within the observable sky and number of contrails within the observable sky. This involves just simple counting of what can be seen within the sky. However if there are no planes or contrails to be seen it is important to actually record this as 0 rather than simply leave the observation card as blank, which may be interpreted by others that the observation had not been carried out.
Description of contrails. The contrails that have been observed can be classified into 4 categories; persistent and dispersed (p+d), persistent and non dispersed (p+nd), non persistent and dispersed (np+d) and non persistent and non dispersed (np+nd), with the persistent and dispersed types obviously being of most importance climatologically. This classification of contrails is probably the most difficult and the most subjective of the observations as one observer may view the contrails in a different way to another observer.
Figure 1
Once each station has completed the observations for a full month they complete the monthly return form (Figure 2) to return to Lancaster.
Figure 2
