ATM OCN (Meteorology) 100 - Lecture 3

THE THEORY OF WINDS:
PART III - RESULTANT ATMOSPHERIC MOTIONS

Fall 1997

Lectures #19, 20 & 21 Scheduled for:

17 OCT 1997 (F), 20 OCT 1997 (M) and 22 Oct 1997 (W)

Recommended Readings from Moran and Morgan (1997):

pages 210-217; 119-120; 217-218; 288-297; 302-304.

Objectives:

• To explain how forces are joined in hydrostatic equilibrium, geostrophic wind, gradient wind and surface winds.
• To describe the hydrostatic equilibrium concept and its implications.
• To explain why the Coriolis effect is important only in global and synoptic scale circulation systems.
• To list the assumptions and properties of the geostrophic wind approximation.
• To compare and contrast geostrophic winds and surface winds.
• To describe the effect of friction upon the speed and direction of the horizontal surface winds.
• To sketch a diagram (isobars and wind arrows) showing the winds associated with cyclones and anticyclones in both the Northern and Southern hemisphere.
• To explain the relationship between horizontal and vertical motions.
• To demonstrate Dines' Compensation Principle and to present examples of how the vertical motion of the air is linked to the horizontal motion of air.
• To explain why cyclones are typically cloudy and stormy, while anticyclones are commonly fair weather systems.
• To describe the formation of a sea breeze and discuss the principle it illustrates.

Outline:

Continues from THE THEORY OF WINDS: PART II - FUNDAMENTAL FORCES

A. INTRODUCTION

• Overview
• Fundamental assumptions

B. HORIZONTAL EQUATION OF ATMOSPHERIC MOTION

• The Hydrostatic Balance Concept
• The Horizontal Pressure Gradient Force

C. FLOW RESPONDING TO PRESSURE GRADIENT FORCE - LOCAL WINDS

• Assumptions
• Sea-Land Breeze Circulation
• Mountain-Valley Breeze Circulation
• City-Country Circulation

D. STRAIGHT-LINE, BALANCED, FRICTIONLESS MOTION - GEOSTROPHIC FLOW

• Definition
• Assumptions
• Concept of Geostrophic Balance
• Resultant Diagrams
• Implications of the Geostrophic Balance

E. BALANCED FLOW IN THE FRICTION LAYER

• The Nature of Friction
• The Friction Layer
• The Effect of Friction upon the Geostrophic Wind
• Resultant Diagrams
• Variations of Near Surface Winds with Height

F. CURVED, HORIZONTAL BALANCED MOTION - GRADIENT FLOW

• Assumptions
• Forces (accelerations) Associated with Curved Flow
• Gradient flow without Friction

G. GRADIENT FLOW WITH FRICTION

• Applicability to the Atmosphere
• Situation
• Resultant Diagrams

H. RELATIONSHIPS BETWEEN HORIZONTAL & VERTICAL MOTIONS

• Dilemma
• Convergence / Divergence
• Principle of Mass Continuity
• Dines' Compensation
• Resultant Vertical Motions
• Implications of Dines' Compensation

I. VORTICES AND VORTICITY

• Definitions
• Characteristic Vortex Features

Last revision 26 October 1997

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