Ordinary-cell convective storms - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 153

Figure 3.46. Conceptual model of the three stages in the life cycle of an ordinary convective cell
within a mature, multicellular, squall line mesoscale convective system. Equivalent potential
temperature (gray shaded) and vertical velocity (contoured) in a reference frame fixed to the
cell's principal updraft. Solid (dashed) contours indicate rising (sinking) motion. Buoyancy-
induced vertical circulations are depicted by elliptical streamlines. During the initiation stage,
the buoyancy-induced vertical circulation ingests potentially warm air from below. During the
maturation stage, the cell's buoyancy-induced vertical circulation acts to weaken forced lifting
as subsidence occurs on the flanks of the cell, cutting off the cell from any older, earlier cell;
stable, potentially cold air mixes into the cell's inflow region from below, reducing buoyancy. It
is the rearward movement of the cell with respect to the leading edge of the cold pool that
results in the cell's inflow being cut off from the potentially warmest air. During the dissipation
stage, the cell's buoyancy-induced vertical circulation on the front-facing flank (with respect to
the front-to-rear motion of subcloud air, which is dominant during the mature stage when the
cold pool's circulation is dominant) weakens as potentially cooler air is ingested. The poten-
tially warmest air in the cell detrains from the updraft and some moves in the direction the cold
pool is moving, reducing buoyancy there and thus suppressing upward motion on the cell's
rear-facing side (adapted from Fovell and Tan, 1998).
the ingestion of cooler air by the vertical circulations suppresses convective growth
for a while. When the new updraft has propagated back toward the rear side of
the convective storm, if it ever does, then a new updraft may be triggered as the
suppression of new-cell growth ceases. Moreover, in some simulations the moist
boundary layer is deepened upstream from the region where new convective
growth is suppressed and new-cell growth is accelerated.