ATM OCN (Meteorology) 100 - Lecture 3

PRECIPITATION:
A FUNDAMENTAL WEATHER ELEMENT

MEASUREMENTS, TYPES & FORMATION MECHANISM THEORIES

Fall 1997

Lectures #13 & 14 Scheduled for:

1 OCT 1997 (W) & 3 OCT 1997 (F)

Recommended Readings from Moran and Morgan (1997):

pages 179-187.

Continues in next lecture as Precipitation: Artifical Weather Modification

Objectives:

• To enumerate the factors which tend to inhibit precipitation formation.
• To describe the various mechanisms -- such as the ice-crystal theory and collision-coalescence theory -- involved in drop growth in clouds.
• To outline the steps in the formation of precipitation according to the Bergeron ice-crystal process.
• To describe the formation of precipitation according to the collision - coalescence process.
• To enumerate the properties of supercooled water drops at low temperatures.
• To explain the role of sublimation.
• To identify the instruments used for precipitation measurement.
• To discuss the factors necessary to obtain an accurate measurement of rain or snow.
• To list and identify the commonly observed precipitation types
• To distinguish between sleet, glaze, and hail and describe the circumstances under which each of these forms.

Outline:

A. INTRODUCTION

• What is precipitation?
• Why is precipitation important?
• How is precipitation formed? Statement of the Problems
• How is precipitation measured?

B. BACKGROUND

• Cloud Droplet Formation - Nucleation (Birth)
• Requirements for Formation of a Raindrop
• Factors opposing Precipitation
• Typical Rain Drop Sizes

C. POSSIBLE PRECIPITATION MECHANISMS -
GROWTH OF LIQUID RAIN DROPS

• Requirements
• Simple Condensation by Diffusion Process
• The Collision - Coalescence Process
• The Ice Crystal or Bergeron-Findeisen Process

D. PRECIPITATION OBSERVATIONS

• Observational Practices
• PRECIPITATION TYPES
  • The Specific Precipitation Types
    • Liquid precipitation
    • Solid precipitation
    • Freezing precipitation
  • Special Precipitation Formation Processes
• QUANTITATIVE MEASUREMENT
  • Direct measurement by Rain gauges
  • Doppler radar estimated rainfall
  • Satellite estimated rainfall
• Excessive or Extreme Precipitation Events

E. PRECIPITATION CLIMATOLOGY

Continues in next lecture as Precipitation: Artificial Weather Modification

Last revision 14 October 1997

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