Rear-inflow jet

The rear-inflow jet is a component of bow echoes in a mesoscale convective system that aids in creating a stronger cold pool and downdraft. The jet forms as a response to a convective circulation having upshear tilt and horizontal pressure gradients. The cold pool that comes from the outflow of a storm forms an area of high pressure at the surface. In response to the surface high and warmer temperatures aloft due to convection, a mid-level mesohigh forms behind the leading edge of the storm.

With a mid-level area of low pressure, air is drawn in under the trailing stratiform region of precipitation. As air is drawn in on the rear side of the storm, it begins to descend as it approaches the front line of the cells. Before the reaching the leading edge, the jet dives down to the ground creating strong downdrafts and straight-line winds (Houze, 2004).

Studies done by "Chong et al." [1987] and "Klimowski" [1994] concluded that any mature mesoscale convective system was capable of developing its own rear-inflow jet, but the question remained as to what decided on the strength of the jet. The diabatic effects of sublimation, melting and evaporationg were examined and found that while these did play a role, they were not able to account for strong jet cases. However, the diabatic effects were found to be responsible for the jet subsiding behind the leading edge of the MCS. "Braun and Houze" [1997] found that the sinking started when the mid level inflow first went under the trailing stratiform cloud before descending to the melting layer.

There are other factors that contribute to the strength of any rear inflow jet. "Skamarock et al." [1994] showed that the strength of a rear inflow jet can be greatly increased with induced vortices at the end of the line, called "line-end vortices" or "book-end vortices." These vortices at either end of the line will help reinforce the rear inflow towards the center of the line. The other factor that can help strengthen the jet is an evnironment in which the large scale flow is feeding/forcing mid-level air into the rear end of the storm.

See also

* Convective storm detection

References

* Braun, S.A., and R.A. Houze Jr., "The evolution of the 10-11 June 1985 PRE-SORM squall line: Initiation, development of rear inflow, and dissipation." 1997.
* Chong, M., P. Amayene, G. Scialon, and J Testud. "A tropical squall line observed during the COPT 81 esperiment in West Africa, Part 1: Kinematic structure inferred from dual-Doppler radar data." 1987
* Houze, Robert A. "Mesoscale Convective Systems" University of Washington, 2004.
* Kimowski, B.A. "Initiation and development of rear inflow within the 28-29 June 1989 North Dakota mesoconvective system." 1994.
* Skamarock, W.C., M.L. Weisman, and J.B. Klemp. "Three-dimensional evolution of simulated long-lived squall lines." 1994.

Further reading

* Jorgensen, Murphy and Wakimoto. "Rear Inflow Evolution in a Non-Severe Bow Echo Observed by Airborne Doppler Radar During Bamex."
* Houze and Smull. "Rear Inflow in Squall Lines with Trailing Stratiform Precipitation" American Meteorological Society, 1987.
* Harder, Jason. "Enhancement of the Downdraft" University of Wisconsin-Madison, 1998.