Roadmaps of Convective Storm Attributes as a Function of Environment: Part 1: Updraft Overturning and Rotation Efficiency and Steadiness

Deep convective storms can assume many intensities, sizes and
morphologies in Earth's atmosphere, reflecting varying balances of the
competing forces that arise in the diverse environmental 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 research, but much more easily to idealized parameter space
investigations using numerical models. A large 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 environmental parameters.

The basic parameters considered 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,
subcloud-layer lifting condensation level, level of free convection,
cloud-base temperature (and, therefore, also total precipitable water),
and free tropospheric relative humidity. Each of these parameters
was found to exert noteworthy independent impacts on the intensity and
morphology of the convection, with large differences in peak updraft
speed, overturning efficiency (the ratio of simulated peak updraft
speed to that predicted from pseudoadiabatic parcel theory), and
updraft steadiness (defined as the ratio of a storm's average mature
peak updraft speed to its maximum peak updraft speed. By analogy,
similar efficiency and steadiness analyses can be performed for updraft
rotational efficiency relative to environmental helicity, and the
temporal steadiness of updraft vorticity parameters.

Comprehensive results will be shown for the first time that demonstrate
the strongly patterned convective response within this large parameter
space, for both updraft overturning and rotation efficiency and their
steadiness. For example, in experiments having CAPE = 2000 J/kg and
16 m/s hodograph radius, peak updraft efficiency reaches 94% in some
cases, while in others having warmer LCL temperatures and greater water
loading, along with less favorably shaped shear profiles, that efficiency
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 extended by adding
extra dimensions to deal with other physical effects, including varying
types and distributions of aerosols and other tracers that can affect
storm microphysics and chemistry.