A comparison of the spectral energy and enstrophy budgets of blocking versus nonblocking periods

The time mean spectral energy and enstrophy budgets for blocking versus nonblocking periods from the winters of 1978–79 and 1976–77 are calculated. The major differences in the 1978–79 cases were in the nonlinear interaction terms. A pronounced upscale cascade of kinetic energy and enstrophy from intermediate to planetary-scale wavenumbers during blocking was found. During December 1976, the energy and enstrophy budgets of a case of Atlantic blocking were very similar to the cases in 1978–79, but quite different from the persistent, greatly amplified, planetary-wave pattern that followed in January and February 1977 (as identified by Charney et al., 1981). Planetary-scale baroclinic processes were greatly increased during the 1977 event along with reduced intermediate-scale baroclinic activity and the absence of the upscale enstrophy cascade noted in the other blocking cases.

The predictability time (Lilly, 1970) based on the enstrophy flux function showed an increased predictability for the January-February 1977 event but no significant differences between the other blocking cases compared to the nonblocking sample. However, the reversal of the low wavenumber enstrophy cascade during blocking does suggest that blocking may be more persistent (due to reduced dissipation of the large-scale circulation) and therefore more predictable.