Geoscience Reference
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Figure 3.5. Cumulonimbus anvil on September 9, 2009, in Boulder, CO. Three separate bursts
of convection are evident (each burst indicated by an arrow) (photograph by the author).
reach the upper troposphere is referred to as ''convective initiation'', the qualifier
''deep'' being understood and that the result is typically a cumulonimbus.
To reach the LFC, convective inhibition (CIN) must be overcome. CIN is
defined as
ð LFC
z 0 ½ T c ð z 0 Þ T 0 ð z 0 Þ=
T 0 ð z 0 Þ dz 0
CIN ¼ g
ð 3
:
4 Þ
where z 0 is the height or representative height of the air parcel that is forcibly
lifted to its LFC. Because the air is originally stable, the temperature difference
between the air parcel (T c ) and its surroundings (T 0 ) is negative, so that CIN is
negative.
One can use (3.4) and (2.70), less the dynamic vertical perturbation pressure
gradient terms, and buoyancy defined by (2.19) to estimate what initial upward
vertical velocity (in the rising branch of mesoscale circulations) is necessary so
that there is enough kinetic energy available to reach the LFC (in the absence of
friction, entrainment, and vertical dynamic pressure gradient forces)
Dt ¼ g½ T c ð z 0 Þ T 0 ð z 0 Þ=
T 0 ð z 0 Þ
Dw
=
ð 3
:
5 Þ
Then, if w is steady state, at the center of the updraft
w 0 ¼ 2g ð LFC
1 = 2
z 0 ½ T c ð z 0 Þ T 0 ð z 0 Þ=
T 0 ð z 0 Þ dz 0
1
=
2
¼ð 2 CIN Þ
ð 3
:
6 Þ
 
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