|HOW DOES DYNAMIC LIFT COMPARE TO CONVECTIVE LIFT?
METEOROLOGIST JEFF HABY
Dynamic lifting is a forced lifting of air. It is much slower than convective lifting but over time dynamic lifting can produce a significant
amount of vertical uplift. If the uplift occurs with saturated air then clouds and precipitation will be produced. Dynamic uplift is slow
enough that the units are measured in centimeters per second (cm/s). This slow lift can produce a significant vertical
motion given several hours.
In comparing dynamic lift to convective lift, dynamic lift of moderate intensity is around 6 cm/s. Convective motion on the other
hand of moderate intensity is about 40 meters per second (m/s). Notice the different units. If the 40 m/s is converted to cm/s, it
works out to 4,000 cm/s. This gives a moderate convective updraft a speed that is about 667 times as fast as moderate dynamic lifting. Convective
updrafts of moderate intensity typically lead to thunderstorms. Dynamic lifting typically does not produce much thunder but it still
can produce significant precipitation since dynamic lift can occur over time scales of many hours. Convective lifting can lift the air
through the troposphere in just a few minutes. Dynamic lifting can produce significant lifting also since
it acts on longer time scales.
Convective lifting and dynamic lifting are like the story of the rabbit and the turtle that race. Convective lifting is
like the rabbit that produces vertical lifting in quick bursts while dynamic lifting is like the turtle that moves slow
but can still travel a significant distance when given enough time.
Dynamic lifting is produced by lifting mechanisms such as frontal lifting, surface convergence boundaries, low level warm air
advection and upper level divergence from positive vorticity advection or jet streak divergence. These lifting mechanisms produce
a slow but steady rising of the air. Convective lifting is air rising due to positive buoyancy similar to the process of how a
helium balloon rises quickly into the air since the air in the balloon is less dense than the surrounding air. This mechanism
of rising air is very quick. Thus, convective uplift often produces thunderstorms while dynamic lift produces light to moderate
precipitation. Often these two mechanisms work together in that dynamic lift allows air to rise high enough that it can be
exposed to an environment that produces convective lift. An example is dynamic lift such as a low level convergence boundary
that lifts air through a capping inversion and into an unstable layer of air where it can convectively lift.