ATM OCN 100 - Summer 2002 LECTURE 31 MID-LATITUDE WEATHER SYSTEMS: PART IV: SURFACE-UPPER AIR LINKAGE A. INTRODUCTION How do surface weather features develop and move? How do surface & upper air weather features relate?

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

Formation of a Jet Stream

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.

Waves in the Jet -- A ridge - An intrusion of warm air

Waves in the Jet -- A trough - An intrusion of cold air

An upper air chart example

The Surface Low & the Jet

C. RELATING SURFACE & UPPER AIR CIRCULATION SYSTEMS Weather Regimes Types of Flow Patterns Aloft Zonal Flow Meridional Flow Cutoff Lows Blocking Patterns

Zonal Circulation Regime Figure 10.10 Moran & Morgan (1997)

Meridional Circulation Regime Figure 10.10 Moran & Morgan (1997)

Stagnant Circulation Regime with Cut-off Lows & Blocking Highs Figure 10.13 Moran & Morgan (1997)