Injected VLF waves and lightning-induced whistlers, if intense enough, are able to excite lower hybrid waves and field-aligned density striations in the ionosphere within a few seconds. This instability can also be triggered in the magnetosphere by the injected VLF waves if the transmitter is operated continuously for several minutes. This instability can be excited in a broad whistler frequency range in two domains, wherein either the nonoscillatory beating current or the thermal pressure force is the dominant nonlinear effect. The excitation of this instability may be responsible for the airglow effects associated with the VLF transmitter cycle and may possibly be the cause of the lower hybrid waves correlated with the occurrence of lightning storms.