What is RFD (Rear Flank Downdraft)?
What is RFD (Rear Flank Downdraft), and how does it help tornadoes form. Please and thanks!
- 1 decade agoFavorite Answer
Information provided by Wikipedia:
The rear flank downdraft or RFD is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes. Large hail within the rear flank downdraft often shows up brightly as a hook on weather radar images, producing the characteristic hook echo, which often indicates the presence of a tornado.
Rear-flank downdrafts have a well-established association with hook echoes. Firstly, the initial rear flank downdraft is air from aloft transported down to the surface by colliding and mixing with the storm. Secondly, hook echoes form through advection of precipitation from the rear of the main echo around the region of strong updraft. Thus, precipitation loading and evaporation cooling induced by the hook echo can enhance the downdraft. Some observations showed the presence of an enhanced downdraft in the vicinity of the strongest low-level rotation, behind the main storm updraft. Further, it was concluded that the presence of a hook echo can reflect downdraft intensification.
It has been realized by many researchers that rear flank downdrafts, especially those associated with hook echoes, are fundamentally critical to tornado formation. Fujita (1975) initiated the Recycling Hypothesis: Firstly, downdraft air is recirculated into the (developing) tornado, which results in an appreciable convergence on the back side of the (still developing) tornado. Then the downward transport of the angular momentum by precipitation, and the recycling of air into the tornado, will create a tangential acceleration required for the intensification of the tornado.
The drag force from the droplets initiates circulation in an RFD. Dry environmental air is also entrained into the downdraft and evaporative cooling helps create more negatively buoyant air. As precipitation falls and cool entrained air circulated downward and eventually reaching the surface. This circulation contributes to the circulation to form a hook echo.
So essentially when a thunderstorm reaches its mature stage, updrafts and downdrafts exist side by side with a slight tilt to allow for air flow. The energy involved with the downdraft is essential in fueling the updraft which will then suction up the rotating funnel of air on the ground causing a tornado to form.Source(s): Wikipedia I am a teacher of Meteorology and Physics.
- ToddLv 71 decade ago
A rear flank downdraft is air from aloft that is transported down to the surface from colliding with the storm. The rear flank downdraft air tends to be dry and warm since the air warms by adiabatic compression as it sinks to the surface. Adiabatically warmed air will also decrease in relative humidity if no precipitation falls into the air. The rear flank downdraft tends to be warmer than the forward flank downdraft also since rain and evaporative cooling is not as common in the rear flank. Shear is enhanced along these flanking downdraft boundaries and the shear can be magnified along where the two flanks merge. The right balance of shear and instability release can lead to tornadogenesis.
The interaction between the RFD and the forward flank downdraft generates tubes of horizontal vorticity and is important to the generation of the low level circulation necessary for tornadogenesis.
- Anonymous4 years ago
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What is RFD (Rear Flank Downdraft)?
What is RFD (Rear Flank Downdraft), and how does it help tornadoes form. Please and thanks!Source(s): rfd rear flank downdraft: https://tr.im/ZVecm