ATM OCN 100 Summer 2002 LECTURE 31

1
ATM OCN 100 - Summer 2002LECTURE 31

• MID-LATITUDE WEATHER SYSTEMSPART IV
  SURFACE-UPPER AIR LINKAGE
• A. INTRODUCTION
• How do surface weather features develop and move?
• How do surface upper air weather features
  relate?

2
B. UPPER AIR WEATHER CONDITIONS

• Jet Stream Structure
• Types of Major Jet Streams
• Polar Jet
• Subtropical Jet
• Seasonal Variations in Jet Streams
• Reasons for Jet Streams
• The Thermal Wind Relationship

3
Formation of a Jet Stream
4
Reasons for Jet Stream

• The Thermal Wind Relationship
• Wind speed increases with height in region of
  strong horizontal temperature contrast
• Wind direction turns with height to parallel
  lower-level isotherms, with...Colder air to left
  in Northern Hemisphere.

5
Waves in the Jet -- A ridge- An intrusion of
warm air
6
Waves in the Jet -- A trough- An intrusion of
cold air
7
An upper air chart example
8
The Surface Low the Jet
9
C. RELATING SURFACE UPPER AIR CIRCULATION
SYSTEMS

• Weather Regimes
• Types of Flow Patterns Aloft
• Zonal Flow
• Meridional Flow
• Cutoff Lows
• Blocking Patterns

10
Zonal Circulation RegimeFigure 10.10 Moran
Morgan (1997)
11
Meridional Circulation RegimeFigure 10.10 Moran
Morgan (1997)
12
Stagnant Circulation Regime with Cut-off Lows
Blocking HighsFigure 10.13 Moran Morgan (1997)