The splitting analysis method can be used to study the relation of the low-level jet (LLJ) and heavy rainfall. The vertical circulation in the entrance and exit region associated with the jet results from the adjustment process in response to the imbalance caused by advection along the jet.
Under the conditionally unstable and nearly saturated atmosphere, if the equivalent horizontal scale R<L0, where L0 is the characteristic scale of the adjustment process, then the adjustment process can lead to an instability of the gravity-inertia wave, whose mechanism is the positive feedback between the nonthermal wind and the vertical circulation. The coupling of upper tropospheric jet and LLJ and its relation to heavy rains have been discussed. The triggering effect of LLJ and the fact that the ageostropheric wind often occurs in LLJ over the heavy rain area and some other synoptic analysis results have also been explained.
The available potential energy for the unstable gravity inertia wave is generated by the condensation heating in the relatively warm area, which can increase the horizontal temperature gradient and make the gravity-inertia wave developing in the adjustment process. Its energy source is quite different from that of a several local storm which results from the energy of the static stability.