- During the mature stage of an MCS, the convective cells spread
rearward transporting warm air aloft. The surface cold pool also extends rearward due to
the rearward expanding rainfield
- The juxtaposition of the warm air aloft over a cold pool
produces lower pressure at mid levels, leading to mid-level convergence. The flow that
converges in from the rear of the system at mid levels is known as the rear-inflow jet
- The formation of the RIJ can also be explained by the
horizontal buoyancy gradients at with the back edge of the system, which generate a
vertically stacked horizontal vorticity couplet that induces the rear-inflow jet
- The strength of the RIJ is directly related to the strength of
those buoyancy gradients, i.e., the relative warmth of the FTR current and the relative
coolness of the cold pool
- The RIJ strength is also affected by the strength of the
vertical wind shear. Stronger shear produces enhanced lifting at the leading edge of the
system, which leads to a stronger FTR current and enhanced warm pool
- In weak shear, lower CAPE environments,
the warm pool aloft tends to be weaker than the cold pool. In this
case, the RIJ descends further back in the system
- In stronger shear/higher CAPE environments,
the warm pool aloft tends to be comparable to the cold pool. This
keeps the RIJ elevated until much closer to the leading line convection.
This is usually the case with severe bow echoes
- Storm-relative RIJ strengths vary from a few m/s for weak
systems, to 10-15 m/s for moderately strong systems, to 25 to 30 m/s for the most severe
systems, such as bow echoes
- In general, RIJ strength increases for increasing CAPE and
increasing vertical wind shear
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The Rear-Inflow Jet Summary