Mesoscale convective systems - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 300

Figure 5.28. Idealized illustration showing how a downward-directed dynamic pressure gradi-
ent force (blue arrow) is present above a mesovortex (red surface), which suppresses new
updrafts and fractures the convective line. The gust front/leading edge of the cold pool is
denoted by a cold front symbol. A rear-inflow jet is shown descending to the surface south of
the mesovortex and producing an area of enhanced surface wind (stippled). Enhanced surface
winds are also indicated just southwest of the mesovortex (from Trapp and Weisman, 2003).
MCVs in linear (or ''quasi-linear'') MCSs are supercell mesocyclones and produce
supercell-associated severe weather phenomena.
When environmental vertical shear is relatively strong, there may be high
straight line winds at the surface, which may inflict damage at the apex of the
bow echo, in between two counter-rotating vortices, perhaps closer to the cyclonic
member of the pair as it has become stronger than the anticyclonic member in
response to the Coriolis force. On the other hand, when vertical shear is weaker,
well-defined mesovortices may not form and strong straight line winds occur from
a rear-inflow jet that has descended to the ground some distance to the rear of the
leading edge of the cold pool. Long-lived MCSs that move rapidly and produce
widespread strong straight-line winds at the surface are called derechos (from the
Spanish word for ''straight ahead''), as opposed to tornadoes (from the Spanish
word for ''to turn'').