A diagnostic study of the long-term balance of kinetic energy of atmospheric large scale motion over the British Isles

✍ Scribed by E. O. Holopainen; K. Eerola

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: English
• Weight: 573 KB
• Volume: 105
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49710544609

✦ Synopsis

Abstract

Calculations of the various terms in the kinetic energy budget of the atmosphere were carried out for the area of the British Isles using aerological data for the period 1974–76. The residual term (‘dissipation’) necessary to balance the equation is interpreted as representing the forcing effect of sub‐grid scale processes. The results are compared with earlier calculations for the same area, and with corresponding results for the area of North America.

The results show that the annual mean dissipation of kinetic energy in the boundary layer (below 850 mb) is 3.4 Wm^−2^, which is considerably larger than that found for the area of North America. The corresponding values for winter, spring, summer and autumn are 6.2, 2.3, 2.0 and 3.2 Wm^−2^, respectively.

Results for the British Isles in the free atmosphere are very different from those for North America. Whereas there is, on average, generation of kinetic energy by pressure forces (−V.▽Φ > 0) and net export of kinetic energy over North America, the contrary is true over the British Isles.

The mean residual term in the kinetic energy equation over the British Isles is relatively small between about 850 and 400 mb. However, higher up, the term is definitely positive, indicating (if interpreted physically) an energy input from sub‐grid scales to the synoptic scale: a situation opposite to that prevailing, in the annual mean, over North America. It is suggested that this ‘negative viscosity’ phenomenon may in general be typical for diffluent flows (such as are found in the exit areas of jet streams) and could be due to horizontal and vertical convergence of momentum flux associated with jet streaks and other sub‐grid scale phenomena.