Bottom-Up Process
•This process is believed to occur as a result of tilting of the
horizontal circulation along the forward frank gust front as it moves under
the ascending updraft.
•Air behind the gust front is cool, negatively buoyant, and
descending. In the updraft air adjacent to the gust front, air is warm, positively
buoyant, and ascending.
•This leads to a sense of rotation along the interface between the
gust front and warm air.
•If this region advances under the strong
updraft of the mid-level mesocyclone, it can be tilted to the
vertical, leading to rapid rotation very close to earth’s surface.
•With further vortex stretching, the rotation
can spin up to become a ‘bottom up” tornado.