Supercells - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 232

Figure 4.46. Idealized illustration of how moving the storm motion vector away from the
hodograph increases SREH. SREH, which is proportional to the area swept out by the
storm-relative wind vector between the ground (0) and height H, increases when the storm
motion vector defined by the line joining the origin to C1 is moved to C2. In this case, more
deviant storm motion to the right of the hodograph is accompanied by increased SREH even
for a unidirectional hodograph.
Figure 4.47. Illustration of the computation of SREH between the ground and 3 km AGL for a
quarter-circle hodograph (wind speed in m s 1 ) having a radius of 10m s 1 and a storm motion
from the west to the east of 10m s 1 . The area swept out by the storm-relative wind is 4 the area
of a circle having a radius of 10m s 1 . Twice this quantity is the SREH.
If a convective storm updraft moves along with the pressure-weighted mean
wind and if the hodograph is straight, there is no SREH. If the updraft propa-
gates off the shear vector (e.g., as a result of the nonlinear pressure term, created
through the tilting of environmental horizontal vorticity onto the vertical), then
SREH develops as the updraft splits; positive and negative SREH develop in the