Entropic Balance Theory and Radar Observation for Prospective Tornado Data Assimilation - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 438

Fig. 18.11 Baroclinic case
of the entropic balance
expressed in the right hand
rule

The transition to the mature stage of a tornado is characterized by the transition from
the asymmetric baroclinic stage to the symmetric barotropic stage as discussed in
Sect. 18.5 ,

H ˇ ) H ˛; BC C Wrap-around mechanism ) H ˛; BT : (18.37)

18.7.4 Wrap-Around Mechanism

The wrap-around mechanism is proposed to be responsible for the transition from
the supercell stage to the mature tornado stage. In Fig. 18.9 , the supercell baroclinic
stage is shown at the top, and the mature tornado stage is at the bottom.

S 0

is the entropy anomaly. S 0 >0 due primarily to condensation, and S 0 <0 due to

evaporation in the supercell storm. Tighter wrap-around causes steeper, axially
symmetric entropy gradients in and closely around the trapped core of tornado,
consequently creating intense vorticity, according to the entropic balance theory.
The wrap-around mechanism and the corresponding baker's transformation are
schematically shown in Figs. 18.9 and 18.10 respectively.
The supercell stage is baroclinic, ¤ 0 , created by the axially asymmetric

entropy anomaly distribution, due to S 0 >0 (condensation in the storm) and S 0 <0

(evaporation of the overshot hydrometeors against the head-wind westerlies in the
west of storm). The baroclinicity is created by the solenoid. The mature tornadic
stage is created by the field of circular band of positive S 0 wrapping around the
tornado core of negative S 0 . The trapped tornado core and the environment in
an small area is like barotropic over all by a nonlinear wrap-around mechanism
(Figs. 18.3 , 18.4 , 18.5 , 18.6 , 18.7 , 18.8 , 18.9 , 18.10 , 18.11 ,and 18.12 ).