DIURNAL AND LONG-TERM VARIATIONS OF THE KINETIC ENERGY GENERATION AND DISSIPATION FOR A FIVE-YEAR PERIOD

Abstract

The diurnal variation and long-term variation of the kinetic energy generation and dissipation are investigated with the wind and geopotential data observed twice a day at 00 and 12 gmt over North America during a 5-yr. period. The generation from the work done by the horizontal pressure force and the dissipation are significantly and consistently greater at 00 gmt than at 12 gmt. The diurnal variation is especially pronounced during the summer. The annual march of the seasons and the year-to-year variation of the kinetic energy parameters are also significant. By the use of twice-a-day observations for an extended period, the study over North America is increased in generality as an approximation to hemispherical features. However, some uncertainty remains in this respect because of the possible effects of the semidiurnal variations and unconfirmed radiation errors in the radiosonde observations. The previously reported double maxima of the generation and dissipation in the planetary boundary layer and at the jet stream level derived from limited data are confirmed in this study. The multi-annual mean of the dissipation is estimated as 4.12 watts/m.2 About half of the estimated dissipation takes place in the boundary layer, and the other half takes place in the free atmosphere.