ISSN:
1420-9136
Keywords:
Blocking
;
Dynamic meteorology
;
Planetary waves
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract 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 velocityv gr in blocking processes, becausev gr controls the energy transfer in the wave field. Using a ‘Newtonian Cooling’ —type of forcing with a phase differencek to the main field and taking the linearized version of a two-level model, the phase speedc r, the group velocityv gr and the growth ratekc i have been obtained as analytical functions of the mean zonal windU, the thermal windU T, the coefficient of diabatic heating x, the phase differencek and the wavelengthL. Now the hypothesis is introduced, that a blocking should be expected, ifv gr has a maximum value in the vicinity ofL o, for whichc r vanishes and thee-folding timet=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 valuesL o with an appropriate phase differencek exist, which satisfy the conditions mentioned above (for values see Table 2). TherebyL 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00876114
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