Physics – Geophysics
Scientific paper
May 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977papge.115..459d&link_type=abstract
Pure and Applied Geophysics PAGEOPH, Volume 115, Issue 3, pp.459-471
Physics
Geophysics
Blocking, Dynamic Meteorology, Planetary Waves
Scientific paper
Considering the blocking problem as a baroclinic instability problem in a dispersive wave system with diabatic heating effects, it is of great interest to investigate the role of wavegroup velocity v gr in blocking processes, because v gr controls the energy transfer in the wave field. Using a ‘Newtonian Cooling’ —type of forcing with a phase difference k to the main field and taking the linearized version of a two-level model, the phase speed c r, the group velocity v gr and the growth rate kc i have been obtained as analytical functions of the mean zonal wind U, the thermal wind U T, the coefficient of diabatic heating x, the phase difference k and the wavelength L. Now the hypothesis is introduced, that a blocking should be expected, if v gr has a maximum value in the vicinity of L o, for which c r vanishes and the e-folding time t=1/ kc i ( kc i>0) is smaller than 6 days (see condition (20) in the text). One finds, that for special parameter combinations ( U T, U, α), where 15 m/sec≤ U T≤25m/sec, U=10m/sec, 0.8·10-5≤α≤1.5·10-5 [sec-1], certain values L o with an appropriate phase difference k exist, which satisfy the conditions mentioned above (for values see Table 2). Thereby L o varies within the range 8500 km < L o<11000 km corresponding to the preferred planetary ‘blocking’ wavenumber 2 in middle latitudes 50°<π<70° N.
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