Tornadoes - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 403

variations in temperature and static stability. Mesocyclones in supercells are far from
steady state. A theory needs to be developed that accounts for the full complexity of
real atmospheric conditions.
Tornado formation in which the mesocylone forms first aloft as a result of
tilting of environmental vorticity and later a mesocyclone forms at low levels as a
result of baroclinic generation or advection of horizontal vorticity from the en-
vironment or both, followed by tilting and stretching, is most likely if the
mesocyclone aloft and mesocyclone at low levels are superimposed. This situation
resembles that of synoptic-scale, mid-latitude cyclogenesis, because both involve
the effects of the superposition of high-level and low-level vortices, albeit of vastly
different scales (in the case of synoptic-scale flow, 1,000 km; in the case of meso-
cyclones, 1-10 km). How the positions of mid-level and low-level mesocyclones
change with time and are influenced by storm-scale processes needs to be
understood.
It would be nice to analyze tornadogenesis as an instability process as has
been done for extratropical cyclones. Tornadogenesis, however, is highly nonlinear
and involves precipitation microphysics, which also contributes to the nonlinearity;
it is apparently not as amenable to simple analysis and certainly not linear anal-
ysis. Nevertheless, it is hoped that a definitive set of numerical simulations under
controlled conditions can be produced some day that will determine what ranges
of parameters are necessary conditions for tornadogenesis.
A wish list for improved measurement capabilities includes
a. Rapid-scan, mobile Doppler radars with very narrow beams ( 0.1-0.25
half-power beamwidths) and volumetric update times 10 s. It is likely that to
attain very narrow beams on mobile platforms the operating wavelength will
have to be short. To scan rapidly, it is likely that electronic scanning will be
necessary.
b. Probes to measure thermodynamic and moisture variables mounted on
unmanned aircraft and helicopters.
c. Doppler radars and eye-safe Doppler lidars mounted on unmanned aircraft and
helicopters. The radars and lidars will have to be small and lightweight, so they
will probably emit low power.
d. Storm-penetrating aircraft that can make in situ measurements of thermo-
dynamic, moisture, and cloud microphysics variables.
e. Downward-looking Doppler radars with polarimetric capability that can fly over
severe convective storms on manned or unmanned aircraft.
f. Development of spaced antennas or other technologies that allow the
construction of mobile Doppler radar systems with effective half-power beam-
widths 10, so that the two-dimensional wind field could be attained (over an
entire convective storm). It would be desirable to do this rapidly, about every
minute or less. It would also be desirable to have polarimetric capability. There is
more discussion on future observational capabilities in Section 7.3.