A Parameter Space Approach to Understanding Convective Storm Morphology.
Abstract
Deep convective storms assume many intensities, sizes and morphologies
in Earth’s atmosphere, reflecting varying balances of the competing
forces that arise in the diverse atmospheric conditions that promote and
support such storms. The understanding of how these forces compete with
each other lends itself only with great difficulty to observational
study, but much more easily to idealized parameter space studies using
numerical models. A parameter space study was recently designed and
executed using an eight-dimensional framework, with 2-h experiments run
using all possible combinations of reasonably chosen high and low values
of the eight independent parameters. The basic parameters are those
needed to build an idealized vertical profile of temperature, moisture
and wind: bulk convective available potential energy (CAPE), radius of
an assumed semicircular hodograph, shape of the buoyancy profile, shape
of the shear profile, lifting condensation level, level of free
convection, cloud-base temperature (roughly equivalent to total
precipitable water), and free tropospheric relative humidity. Each of
the parameters is found to exert noteworthy independent impacts on the
intensity and morphology of the convection, with drastic differences in
updraft overturning efficiency (the ratio of simulated peak updraft
speed to that predicted from pseudoadiabatic parcel theory), updraft
rotation, updraft steadiness and precipitation efficiency. Storm
rotational efficiency relative to ambient vertical shear, and its
steadiness, may also be examined. Results will be shown that demonstrate
the strongly patterned convective response within this large parameter
space, for both updraft overturning and rotational efficiency and their
temporal steadiness. For example, in experiments having CAPE = 2000
J/kg, peak updraft efficiency reaches 94% in some cases, while in
others with unfavorable combinations of parameters, that peak is less
than 20%. While the eight basic parameters used in this study cover
most of the variability of the vertical meteorological structure of the
convective atmosphere, the framework can easily be expanded by adding
new dimensions to deal with other physical effects, such as varying
types and distributions of aerosols and other tracers that influence
atmospheric chemistry.