What are vortex lines

1
What are vortex lines?
A vortex line is a curve in the fluid such that
its tangent at any given point gives the
direction of the local vorticity.
When horizontal density gradients and turbulence
are absent, vortex lines are frozen in the
fluid, i.e., they are material lines
(Helmholtzs Theorem).
2
Origins of rotation
3
L
L
4
Storm splitting
the updraft-flanking vortices effect
5
(No Transcript)
6
Splitting entails an increase in motion along the
vortex lines
Bluestein V.II
7
Like a well-shot basketball
Storm moving across vortex lines crosswise
vorticity
Storm motion
Updraft-flanking vortices
Like a well-thrown football
Storm motion
Storm moving into vortex lines streamwise
vorticity
Helical (rotating) updraft
8
z 5 km
z 5 km
Ingestion of crosswise vorticity
w 10 m s-1
Vertical vorticity at 0.0025 s-1 intervals
(dashed contours indicate negative values)
25 km
9
z 5 km
Ingestion of streamwise vorticity
w 10 m s-1
Vertical vorticity at 0.0025 s-1 intervals
(dashed contours indicate negative values)
Perturbation winds
25 km
10
crosswise vorticity
streamwise vorticity
t 25 min
t 25 min
z 5 km
z 5 km
Vertical vorticity at 0.0025 s-1 intervals
(dashed contours indicate negative values)
11
3 km
Z
0 km
6 km
12
(No Transcript)
13
v
The environments flux of streamwise vorticity
into the storm is measured in terms of the
storm-relative helicity
9 km
3 km
6 km
motion of an ordinary cell
motion of a supercell
u
0 km
10 m/s
10 m/s
area100 m2/s2100 J/kg
Twice the signed area swept out by storm-relative
hodograph
14
scanned from notes by M. Weisman
MR text
15
Another source of dynamic pressure perturbations
the updraft in shear effect
16
(No Transcript)
17
Mean wind
RM
18
(No Transcript)
19
LM
Mean wind
20
Propagation

• Definition
• a. Translation of a feature that is not
  attributable to simple advection
• b. In particular (for storms), translation of a
  convective entity due to preferred formation
  and/or dissipation of storms in preferred
  directions

21
Propagation

• System motion advection propagation
• (consider a right-moving supercell)

hodograph
R
preferred dissipation of updraft
advection
propagation
observed storm motion
preferred formation of updraft
22
Propagation
3. Continuous vs. discrete propagation
preferred dissipation of updraft
advection
continuous propagation
observed storm motion
preferred formation of updraft
X
cell motion
discrete propagation
X
observed system motion
X
preferred formation of new cells
X
23
Erik Nguyen
Chuck Robertson
24
Bluestein V.II
25
courtesy M. Weisman
26
Houze
27
Cell interactions
28
Bluestein and Weisman (2000)
29
Bluestein and Weisman (2000)
French (2007)
30
dryline
KICT 0.5 Reflectivity 1732 UTC
31
KICT 0.5 Reflectivity 1802 UTC
32
KICT 0.5 Reflectivity 1831 UTC
33
KICT 0.5 Reflectivity 1858 UTC
34
KICT 0.5 Reflectivity 1910 UTC
35
KICT 0.5 Reflectivity 1931 UTC
36
KICT 0.5 Reflectivity 2001 UTC
37
KICT 0.5 Reflectivity 2030 UTC