Mesoscale convective systems - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 285

Figure 5.18. Vertical profiles of layer mean storm-relative pre-MCS winds for linear
MCS archetypes. Wind vectors depicted as line parallel ( , ) and line perpendicular
( ! , ) components in m s 1 (a sign indicates flow into the page; a indicates flow out
from the page). Idealized reflectivity factor (shadings) and cloud outlines (solid line outline) are
shown. Leading edges of MCSs are to the right (from Parker and Johnson 2000).
by Keith Browning and collaborators), air flows toward the MCS in a moist
boundary layer of depth h 0 at a speed of U 0 . This branch of the MCS (the rear-
ward-leaning, ascending branch) flows up and rearward, departing at the rear with
a speed of U b . Rear inflow has a speed of U c over a depth of h c and turns around
just to the rear of the leading edge of the cold pool; the retreating branch also has
a depth of h c and exits at low levels with a speed of U c . It follows that the rear-
ward-leaning, ascending branch has a depth of H 2h c at the left. At the rear of
the MCS (to the left in Figure 5.19 ), the rearward-ascending branch is character-
ized by positive buoyancy B u above z ¼ 2h c (Emanuel in his text let B ¼ B u above
z ¼ h c at the rear (left), but the air in the rear inflow in nature is not positively
buoyant and may even be negatively buoyant). At the top of the rear inflow layer
(to the left in Figure 5.19 ), there is no buoyancy; at the rear in low levels, the cold
pool has negative buoyancy, B d . This simple model, while nonlinear, is restricted