Weekly log: environmental studies: earth science2

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Chapter 4 Atmospheric Moisture and Precipitation

Visualizing Physical Geography by Timothy Foresman & Alan Strahler

Chapter Overview

Water and the Hydrosphere

Humidity

Adiabatic Processes

Clouds and Fog

Precipitation

Human Impacts on Clouds and Precipitation

Water and the Hydrosphere

The Three States of Water

Solid (ice)

Liquid (water)

Gas (water vapor)

Latent heat is transferred when water changes states

Release of energy occurs when...

Absorption of energy occurs when…

Water and the Hydrosphere

The Three States of Water

Evaporation

Freezing

Condensation

Sublimation

Deposition (e.g., Frost)

On a cold, dry day, snow covering a sidewalk slowly disappears, and there is no visible melting. Which process is at work?

a. sublimation

b. deposition

c. condensation

d. evaporation?

Water and the Hydrosphere

The Hydrosphere

The total water realm of the Earth’s surface, including the oceans (97.5%) and freshwater (2.5%).

Freshwater includes glaciers (68.7%), ground water (30%), permafrost (0.8%), and the surface waters of the lands and water held in the atmosphere make up 0.4%.

Water and the Hydrosphere

The Hydrosphere

Oceans

Ice sheets and glaciers

Surface water

©John Wiley & Sons, Inc.

Water and the Hydrosphere

The Hydrosphere

The small blue sphere represents the planet’s total water volume in proportion to the Earth’s size, demonstrating the limits on this critical resource

Water and the Hydrosphere

The Hydrologic Cycle

Water moves among the ocean, atmosphere and land

Evaporation

Precipitation

Transpiration

Evapotranspiration

Runoff

Sinks into soil

Recharge of groundwater

Water and the Hydrosphere

Humidity

The amount of water vapor in the air

The maximum volume of water vapor, or humidity, of a mass of air increases sharply with rising temperature

Air at room temperature (20°C [68°F]) can hold about three times as much water vapor as freezing air (0°C [32°F])

Water and the Hydrosphere

Humidity

The low humidity of Death Valley in California creates a warm but comfortable day for a trek across the sand

High-humidity conditions of a Florida wetland, the same temperature reading can be unbearably hot

Water and the Hydrosphere

Relative Humidity (RH)

Compares the amount of water vapor present to the maximum amount that the air can hold at that temperature

Expressed as a percentage

Air holding ½ its capacity has a RH of 50%

Can change in two ways:

Gain or lose moisture

Change in temperature

Water and the Hydrosphere

Specific Humidity

The actual amount of water vapor held by a parcel of air (g/kg)

When air cools, capacity is reduced

When air warms, capacity increases

Specific humidity and temperature values are high at low latitudes

Specific humidity values fall as temperature in high latitude regions

Water and the Hydrosphere

Specific Humidity

Water and the Hydrosphere

Dew Point

The temperature at which air with a given humidity will reach saturation when cooled without changing its pressure

Dew

Frost

What happens as air is cooled below the dew-point temperature at temperatures above freezing?

Adiabatic Processes

As a parcel of air is lifted, atmospheric pressure becomes lower, and the parcel expands and cools

As air cools to the dew point, clouds form

As air descends, air is compressed and warms

Adiabatic processes = process in which the temperature of a parcel of air changes in responses to a change in atmospheric pressure

Adiabatic Processes

The Dry Adiabatic Lapse Rate

The rate at which rising air cools or descending air warms when no condensation is occurring

10°C per 1000 m

5.5°F per 1000 ft

Adiabatic Processes

The Moist Adiabatic Lapse Rate

The rate at which rising air is cooled by expansion when condensation is occurring; ranges from:

4 to 9°C per 1000 m

2.2 to 4.9°F per 1000 ft

Adiabatic Processes

1. Suppose the air parcel shown contained more water vapor. How would that affect the lifting condensation level?

2. What would be the effect if there were less water vapor in the air parcel?

Clouds and Fog

Clouds consist of water droplets, ice crystals, or both

Condensation nucleus = a tiny bit of solid matter (aerosol) in the atmosphere, on which water vapor condenses to form a tiny water droplet

Clouds and Fog

Clouds Classification by Height

Cloud Families: High clouds, middle clouds, low clouds, clouds of vertical development

Clouds and Fog

Cirroform clouds = at the top of the troposphere, these clouds are high, thin, wispy clouds drawn out into streaks. They are composed of ice crystals and form when moisture is present high in the air

Cirrus Clouds

Clouds and Fog

Stratiform clouds = are blanket-like layers that cover large areas. A common type is stratus clouds, which often cover the entire sky. In this photo, high cumulus clouds (left) grade into a high stratus layer (right).

Stratiform Clouds

Clouds and Fog

Cumuliform clouds = globular masses of cloud that are

associated with small to large parcels of moist rising air. In this

photo, puffy, fair-weather cumulus clouds drift over a lake.

Cumulus Clouds

Clouds and Fog

Nimbus clouds = are clouds of any of type that produce

precipitation. An isolated cumulonimbus cell discharges

its water volume as precipitation in this photo.

Cumulonimbus Clouds

Clouds and Fog

Fog

Radiation fog: formed when temperature of the air at ground level falls below dew point

Advection fog: forms when warm moist air moves over a cold surface

Common over oceans (“sea fog”)

West Coast of US and Canada

Precipitation

Types of Precipitation

Rain

Snow

Hail

Ice storm

Precipitation

Annual rates of precipitation vary greatly around the world

Tropical regions

Wet-dry regions

Deserts

Equatorial regions

Precipitation

Globally, rainfall ranges from tropical to desert to polar

This profoundly influence landforms, the biosphere, and human activities

Most species have evolved to survive within narrow ranges of annual precipitation

Tropical regions

Deserts

Precipitation

Precipitation forms in clouds by two different processes:

Warm Cloud = Collision Coalescence

Cold Cloud = Ice crystal process

Warm cloud shown above = Formation of precipitation through coalescence of water droplets

Precipitation

Review Figure 4.10 and answer this question. Which type of cloud is represented in this figure?

a. cirrus

b. altostratus

c. cumulonimbus

d. cirrostratus

Precipitation

Cold Cloud = Ice crystal process

Precipitation forms as water vapor evaporates from super cooled liquid cloud drops. The water vapor is then deposited on ice crystals, forming snowflakes

Precipitation

Types of Precipitation

Rain and snow

Freezing rain

Measuring Precipitation = U.S. National Weather Service’s NEXRAD (Next Generation Radar)

Courtesy NOAA

Precipitation

Types of Precipitation

Hail can form during thunderstorms when there are strong updrafts

Precipitation

Atmospheric Lifting

Air can move upward in four ways: through orographic, convective, frontal, or convergent lifting

Precipitation

Atmospheric Lifting

Orographic precipitation = Precipitation that is induced when moist air is forced vertically over a mountain barrier

Convective precipitation = Precipitation that is induced when warm, moist air is heated at the ground surface, rises, cools, and condenses to form water droplets, raindrops, and eventually rainfall

Precipitation

Orographic Lifting

Precipitation

Convective Lifting

Precipitation

Convective Lifting

If the environmental lapse rate increased (that is, if it were cooler at higher altitudes), how would the lifting condensation level change?

a. It would be higher.

b. It would be lower.

c. It would stay the same.

d. It is impossible to determine.

Precipitation

Convergent Lifting

Precipitation

Frontal Lifting

Human Impacts on Clouds and Precipitation

Acid Rain

Also called acid deposition

made up of raindrops that have been chemically acidified by industrial air pollutants such as sulfur dioxide (SO2) and nitric oxide (NO2)

Acids have a low pH value, less than that of distilled water (pH = 7)

The lower the pH value, the more acidic the liquid.

Acidity of rainwater in U.S., 2005

Human Impacts on Clouds and Precipitation

Effects of Acid Rain

Acid streams and lakes affect aquatic life

Damage to forests

Damage to soils

Damage to buildings

Consider the pattern of acid rain deposition in the northeastern United States. What is the implication for international relations?

Human Impacts on Clouds and Precipitation

Cloud Cover, Precipitation, and Global Warming

Clouds: Longwave warming or shortwave cooling?

Increased Precipitation?

Any rise in sea-surface temperature will increase the rate of evaporation, and an increase in evaporation will raise the average atmospheric content of water vapor. What effect will this have on climate?