On the frictional influence of horizontal wind shear on vertical motion

✍ Scribed by C. H. B. Priestley

• Publisher: John Wiley and Sons
• Year: 1946
• Tongue: English
• Weight: 332 KB
• Volume: 72
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49707231403

✦ Synopsis

Abstract

It is suggested that a reason for the association between anticyclonic vorticity and subsidence lies in the divergence produced by the frictional forces when a strong horizontal wind shear is present. In particular the region just to the south of a strong westerly upper wind (northern latitudes) is favourable for subsidence.

A case in which such conditions remained steady for five days has been examined quantitatively, and it is found that a subsidence velocity of a few centimetres per second is accounted for by assuming an isentropic turbulent interchange coefficient (K) of 5 × 10^9^ cms^2^/sec. This is the value found by Rossby and independently by Grimminger in investigation of other phenomena on a similar scale.

The frictional divergence depends on the third space derivative of velocity across the current, and so can only be obtained when the velocity field is mapped in very exact detail. Scope for practical application of this theory in synoptic work is therefore limited.