ScienceDaily (Jan. 2, 2009) —
One of the largest sources of uncertainty in weather prediction
involves how microscale structures influence larger-scale phenomena.
For instance, previous studies have demonstrated that the structure,
dynamics, and evolution of thunderstorms are very sensitive to cloud
However, those studies used resolutions too coarse to resolve
tornadoes or tornado-like circulations and were therefore not able to
study the sensitivity of tornadogenesis to microphysics. Snook and Xue
have now conducted simulations of severe tornadic thunderstorms using a
grid of 100-meter (328-feet) spacing.
They find that when the sizes of rain and hail drops are large,
weaker cold pools due to reduced evaporative cooling/melting over
smaller geographic regions result. Such weak cold pools are found to
produce conditions that enhance low-level rotation.
The authors’ simulations show that strong, sustained vertical
updrafts are positioned near and above the low-level circulation
centers, providing strong dynamic lifting and vertical stretching to
the air at the lower levels, which favors the creation of tornadoes.
- Nathan Snook. Effects of microphysical drop size distribution on tornadogenesis in supercell thunderstorms. Geophysical Research Letters, DOI: 10.1029/2008GL035866