The significance of dynamic instability in atmospheric motions

A discussion is given of the criterion for a special type of dynamic instability first derived by H. Solberg, viz. :—that the anti‐cyclonic wind shear along an isentropic surface should exceed the coriolis parameter. It is concluded that this criterion has no direct bearing on the formation of extratropical cyclones but it may be important in respect of the limit which it imposes on the wind shear to the south of the “jet stream”. Dynamic instability of this type may also be important in connection with the formation of tropical cyclones and certain features of frontal structure.