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The BD circulation and wave forcing Influence on the QBO period
Le Kuai
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The wave-induced zonal force per unit mass
A: the vertical momentum flux at z0=16 km(z): the thermal damping rateN: the Brunt-Vaisala frequencyK: the zonal wavenumberC: phase speed
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F = Aexp(z − z0
H)R(z)exp(−P(z))
R(z) =α (z)N
k(u − c)2
P(z) = r(z')dz'z0
z
∫
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QBO period variation caused by:
• Planetary wave induced equatorial heating rate
• QBO induced circulation• Descent rate of critical line (westerly regular
and faster than easterly )• Year-to-year variability in the amplitude of
wave forcing• SAO above 30 km (Gray and Pyle, 1989)
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Case without PW: regular downward propagation of easterly and westerly phase regimes.Period:~20 month
Case with PW:leads to a stalling of more than one year in the easterly wind downwelling
Shear zone ~ 50 hPa
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197
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148:+20/-30193:+20/-20194:+25/-30195:+23/-30
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196, 1.1 westerly forcing
197, 1.2 westerly forcing
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