Transcript Lect18_weatherpattern

Chapter 9
Weather Patterns
Why front is tilted?
Fronts
Warm Fronts
Normal situation
1:200
Warm seasons
1:200
Cold Front
1:100
Cold Fronts and Warm Fronts
Stationary Front
The surface position of the front does not move, or
moves very slowly.
Dryline
Oklahoma
Occluded Front
Warm and Cold-type Occlusions
Cool air
(b) Warm-type
Cold air
Midlatitude Cyclones
Polar-Front Theory (Norwegian Cyclone model)
Extratropical Cyclone
Category One Hurricane: Winds 74-95 mph
Category Two Hurricane: Winds 96-110 mph
Category Three Hurricane: Winds 111-130 mph
Category Four Hurricane: Winds 131-155 mph
Category Five Hurricane: Winds > 155 mph
Cloud Patterns Associated with a Mid-latitude Cyclone
Stages in the Life Cycle of a Mid-latitude Cyclone
Theories of the development of a Mid-latitude Cyclone
Mid-latitude Baroclinic instability
density surface
.
warm
cold
S
N
Release of potential energy stored in a tilted system to kinetic energy
cold
L 
 H
warm
The energy for the growth of cyclone and anti-cyclone is from the potential
energy stored in a tilted system.
Heat transport
Heat flux
unit : J2  W2
H
ms
m
Specific heat at constant pressure
Kinematic sensible heat flux, sh
sh  H
,
C
p
J
m 2s
kg
 J kgK
3
m
 ms K
Velocity X Temperature
Cp  1004 kgJK
Mid-latitude: mainly through the transient weather systems.
North
warm
northward
cold
southward
warm
northward
v' t'  0
v'  0
t'  0
v'  0
t'  0
v' t'  0
v'  0
t'  0
East
North
cold
southward
v'  0
t'  0
L
v' t'  0
warm
northward
v'  0
t'  0
H
cold
southward
v'  0
t'  0
v' t'  0
East
Major Sites of Cyclone Formation
Typical Paths of Cyclonic Storms
Steering of Mid-latitude Cyclone
Cold Anticyclone ― Blocking High
Omega blocks
Omega blocks are so-named because the
high pressure system resembles the Greek
letter omega. The typical pattern for this is
low-high-low, arranged in the west-east
direction.
Rex blocks
A Rex block resembles a "half figure 8" or
"backwards S“. The Rex block in this case is
hugging the West Coast of the U.S. A Rex block
sets up with a strong high-pressure ridge
adjacent to a strong low-pressure trough. This
causes the air to swing in loops near the same
longitude. The wind flow makes little progress to
the east.
RING OF FIRE / CUT-OFF HIGH
High pressure is common across the Southeast US in the summer time. The high
pressure cell, which can be an extension of the Bermuda-Azores high, can become
fixed over the area for several days, especially if the jet stream is weak and with a
lack of Canadian cool fronts. The air is most stable at the center of the high
pressure. At the edges of the high pressure, the cap will be weak enough to allow
afternoon convection to occur.
SPLIT FLOW
A split flow occurs when the jet stream branches into two separate branches.
Weather systems flow quickly through each branch of the jet but the weather
pattern becomes stagnant in the region between the two jets.
A Modern View: The conveyor Belt Model