College Level Meteorology

Page 96

HOW PRECIPITATION FORMS While everyone has experienced precipitation, few people understand how it forms the different names for precipitation. Let's discuss the different kinds of precipitation and how they happen. Of course, precipitation falls often in the form of rain. Have you ever wondered why some rain is gentle with small misty raindrops, while other rain is literally a downpour with giant raindrops? Why do you see some clouds that look like rain is coming, but they don't rain at all? Actually, the average raindrop inside a cloud is only 20 micrometers in diameter. This is very small. The raindrops you feel are nowhere near that small; there are reasons for this that we will discuss. The average raindrop you feel will be about 2 millimeters in diameter. This is literally 10,000 times the size of the average condensation nucleus. If you measure the size of a cloud droplet, a raindrop will be 100 times its size. The size of a raindrop can be as little as 0.2 millimeters or as large as 2.5 millimeters in diameter. This is why you feel such a difference when you feel drizzle as opposed to a downpour. You can imagine that a raindrop will grow in size inside the cloud until it becomes too heavy. Friction caused by the air itself will cause the raindrop to break up, with several smaller droplets falling to the earth. In other words, while cloud droplets have a negligible fall velocity, raindrops do not and they will fall. The aerosol that causes water vapor to condense must be hygroscopic. The term hygroscopic means it loves to attach to water and absorb it. Salt particles above the ocean are very hygroscopic, so these will attract water vapor at the lowest humidity possible. Other particles are not as hygroscopic as salt. There is an equation called the Stoke's drag law, which calculates the drag force and ultimately the velocity of any raindrop. The calculation indicates that the drag force and velocity of a raindrop is directly proportional to the diameter of the sphere, which is essentially the sphere of any raindrop. What you would see from this calculation is that it might take hours or days, if ever, for a cloud droplet to fall from the cloud to the ground. This is because the friction caused by air keeps it suspended within the cloud.

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Course Answers

28min
pages 321-340

Chapter Fourteen

2min
pages 319-320

Chapter Thirteen

1min
page 318

Chapter Eleven

1min
page 316

Chapter Twelve

1min
page 317

Chapter Ten

1min
page 315

Chapter Nine

1min
page 314

Chapter Eight

1min
page 313

Chapter Seven

1min
page 312

Chapter Three

1min
page 308

Chapter Six

1min
page 311

Chapter Five

1min
page 310

Chapter Four

1min
page 309

Chapter Two

1min
page 307

Summary

6min
pages 259-262

Chapter Fourteen: Questions

1min
pages 257-258

Key Points in This Chapter

1min
page 256

Rainbows

1min
page 254

Halos, Sundogs, and Sun Pillars

2min
pages 252-253

Cloud Iridescence

1min
page 255

What is Green Flash?

2min
page 251

Moon Phenomena and their Meaning

3min
pages 249-250

Chapter Thirteen: Questions

1min
pages 244-246

Key Points In This Chapter

0
page 243

Role of Wind and Inversions on Air Pollution

5min
pages 237-239

Sources of Air Pollution in the Atmosphere

1min
page 234

Key Points in this Chapter

0
page 228

Chapter Twelve: Questions

2min
pages 229-231

Global Warming and Future Expectations

3min
pages 226-227

Human-influenced Climate Changes

3min
pages 224-225

Ozone and its Effects

2min
pages 235-236

Temperature Extremes

1min
page 221

Wet Seasons

1min
page 220

Milankovitch Cycles

4min
pages 215-217

Chapter Eleven: Questions

1min
pages 209-211

Famous Hurricanes

1min
page 207

Naming Hurricanes

1min
page 206

Important Points in This Chapter

1min
page 208

Tracking Hurricanes

1min
page 205

Proper Tools for a Tropical Cyclone

1min
page 201

Chapter Ten: Questions

1min
pages 198-199

Life cycle of a Tornado

2min
pages 195-196

Key Points in this Chapter

0
page 197

Classification of Thunderstorms

3min
pages 187-188

Chapter Nine: Questions

1min
pages 183-185

Tornado Characteristics

1min
page 194

Key Points in this Chapter

0
page 182

Tropical Watches and Warnings

1min
page 181

Advisories related to Temperature

1min
page 180

Coastal or Lakeshore Hazard Warnings

1min
page 178

Marine Hazard Watches and Warnings

1min
page 179

Tornado and Thunderstorm Advisories

5min
pages 174-176

Winter-related Advisories

1min
page 173

Fire-Related Weather Emergencies

1min
page 177

Severe Weather Watches and Warnings

1min
page 172

Terms Related to Winter Weather

1min
page 171

Terms Related to Floods

1min
page 170

Chapter Eight: Questions

2min
pages 159-161

Important Points in this Chapter

1min
page 146

Mid-latitude Cyclone Storms

4min
pages 155-157

Chapter Seven: Questions

2min
pages 147-149

Weather Fronts

1min
page 154

Lake Effects

1min
page 140

El Niño and La Niña

2min
pages 144-145

Air Pockets and Eddies

3min
pages 138-139

Local Wind Systems

1min
page 137

How Air moves in the Atmosphere around the Globe

2min
pages 119-122

Chapter Six: Questions

2min
pages 131-133

Measuring Wind Direction and Wind Speed

1min
page 129

Types of Wind Instruments

1min
pages 127-128

Key Points from This Chapter

1min
page 130

Surface and Upper Air Charts

3min
pages 124-126

Wind Flow

6min
pages 114-118

Chapter Five: Questions

1min
pages 107-109

Key Points from This Chapter

0
page 106

Types of Precipitation

2min
pages 101-102

Moist Adiabatic Lapse Rate

0
page 92

What is the dry adiabatic lapse rate?

4min
pages 90-91

Measuring Precipitation

3min
pages 103-105

How Precipitation Forms

7min
pages 96-100

Clouds and Convection

4min
pages 93-95

What is the Atmosphere made of?

2min
page 73
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