6. Cirrus (Often in Polar Bands) or Cirrostratus Advancing Over the 



Sky, and More Than 45° Above the Horizon (47). 



The definition of tliis type is exactly the same as the previous one, 

 with the sole exception that the edge of the sheet is more than 45° 

 above the horizon. 



This type is found in the front part of a typical disturbance, a little 

 nearer the center than the former type. 



The same remarks on the limits of the cloud sheet apply as for 



7. Veil of Cirrostratus Covering the Whole Sky (48). 



There are two cases: 



A. Thin, very uniform nebulous veil sometimes hardly visible, 

 sometimes relatively dense, always without definite detail, but always 

 producing halo phenomena (halo, sun pillar) round the sun or moon. 



B. A white fibrous sheet with more or less clearly defined fibers, 

 often like a sheet of fibrous cirrus, from which indeed it may be 

 derived. 



This type is found in a typical disturbance immediately in front 

 of the central area. 



8. Cirrostratus not Increasing, and not Covering the Whole Sky 



(49, 50). 



This is a case of a veil or sheet of cirrostratus reaching the horizon 

 in one direction but leaving a segment of blue sky in the other direc- 

 tion; tliis segment of blue sky does not grow smaller. Generally the 

 edge of this sheet is clear cut, and does not tail off into scattered 

 cirrus. 



This type is found on the north lateral edge of a disturbance, the 

 aspect of the cloud being generally very different from that of the 

 clouds on the south lateral edge. (The terms north and south apply 

 to the most frequent case of a disturbance moving from west to east.) 



If the segment of blue sky is diminisliing the cloud must be coded 

 as (7ff=6 or Cs=5 according as to whether the elevation of the sheet 

 of cirrostratus is greater or less than 45°. 



9. Cirrocumulus Predominating, Associated With a Small Quantity 



of Cirrus (51, 52). 



An absolutely necessary characteristic of cirrocumulus, according 

 to the new definition of tliis cloud, is its relationship to cirrus or 

 cirrostratus. 



This type is found on the front or lateral edges of a weak 

 disturbance. 



If the cirrus fibers, or the sheet of cirrostratus merely becomes 

 slightly corrugated in parts the cirrocumulus is neglected. But 

 if the bank of cirrus or of cirrostratus degenerates wholly into 

 cirrocumulus it is coded as (7^=9; this is an important sign of the 

 weakening of a disturbance. 



31 



