ATM OCN (Meteorology) 100

PRECIPITATION:
A FUNDAMENTAL WEATHER ELEMENT

PART I: MEASUREMENTS, TYPES & 
   FORMATION MECHANISM THEORIES

Summer 1999

Lecture #10 Scheduled for:

29 JUN 1999 (T)

Recommended Readings from Moran and Morgan (1997):

pages 179-187.

Continues in next lecture as Precipitation: Artifical Weather Modification

Today's Lecture Objectives:

• To enumerate the factors that tend to inhibit precipitation formation.
• To describe the various mechanisms (e.g.  the ice-crystal and collision-coalescence theories) involved in drop growth in clouds.
• 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 freezing precipitation and frozen precipitation, describing the circumstances under which each of these precipitation types 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
• Requirements
• Direct Observations using Rain Gauges
• Doppler Radar estimated rainfall
• Satellite estimated rainfall
• 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

Links to Other References:

• The precipitation module from Weather World 2010 (Univ. of Illinois-Urbana-Champaign)
• All-time 24 hour maximum precipitation totals by state (from NCDC).

Last revision 26 May 1999