我想請問Holton在第九章symmetric baroclinic instability中，
講解Fig. 9.6的一段，
Because the tubes lie on the same potential temperature surface, they have the
same available potential energy. Thus a spontaneous exchange of parcels is
possible if δ(KE), the kinetic energy of the zonal flow after exchange minus
that in the initial state, is negative. Otherwise some external source of the
energy is required to furnish the kinetic energy of the meridional and vertical
motions required for the exchange.
這裡的KE應該是指Fig 9.65中的KE_1 + KE_2，1, 2代表管1和管2流體
交換後管1在原先管2的位置，管2在原先管1的位置
在沒有外加能量的情況下，
過程中KE_1 + KE_2 + (E_p1 + E_I1) + (E_p2 + E_I2) = const
如果δ(KE) = (KE_1' + KE_2') - (KE_1 + KE_2) < 0
=> (E_p1 + E_I1) + (E_p2 + E_I2) < (E_p1 + E_I1)' + (E_p2 + E_I2)'
末總位能竟然大於初總位能，怎麼可能會自發性交換位置？　
而且就算考慮到過程中動能有y和z分量，
大不了減少x分量的動能，
將它分給y和z動能分量以及總位能，
不就不需要外加能量的輸入？
想破頭都參不透這段Holton的意思
懇請強者幫忙解惑，感激不盡~~