We find that these LCSs are present not only in all of the AEW development cases, but also in other cases where there is no AEW precursor. These additional cases that are included under the LCS generalization include downstream development from existing storms, storms originating from ITCZ convection, and storms originating from other wave types including mixtures of waves. This Lagrangian paradigm for tropical cyclogenesis therefore completes the marsupial paradigm by accounting for the 'pouch' in all disturbance types, in all stages of the tropical cyclone lifecycle, and in time-dependent flows. This generalization can also be extended to other development regions.
While the location of LCSs is required to assess the permeability of the pouch, methods for the location of such structures has been difficult. We show that a relatively simple computation of a scalar field called the Lagrangian OW field reveals all LCSs in a single global or basin-wide computation. This allows for the location of developing vortices far easier than tracking easterly waves and computing translation speeds, as is required under the frame-dependent marsupial paradigm. The results from these methods are very robust since all developing storms are easily located, and many non-developing pouches are easy dismissed as being incoherent in the Lagrangian flow. Since there are very clear thresholds fro development, these methods may be used for cyclone detection in global forecast models or climate models.
![](images/flag.png)
![](images/blue_ribbon.png)