ATMOSPHERE AND CLOUDS

By Anton Weissenberg

TABLE OF CONTENTS

Part 1 ATMOSPHEREI. Composition of the atmosphereII. Layers of the atmosphereIII. Energy transfer throughout the

atmosphereIV. AurorasV. OzoneVI. Properties of the atmosphere, how

they interact, and how they change

with altitude.

TABLE OF CONTENTS continued…

Part 2 CLOUDS

I. How clouds are formed

II. Basic cloud types and groups

III. The Water Cycle

IV. Orthographic Lifting

Composition of the Atmosphere

The atmosphere is the envelope of gases surrounding earth which are held in place by gravity. The atmosphere is composed of: 78% Nitrogen, 21% Oxygen, 1% Argon, 0.03% Carbon Dioxide, and 0.01% other gases (including water).

Layers of the Atmosphere

There are three main layers of the earth’s atmosphere. The lowest layer is the troposphere which extends from the ground to about 18,000 km. This layer contains half of the earth’s atmosphere. Weather also takes place in this layer… The mesosphere (literally middle sphere) is the third highest layer in our atmosphere, occupying the region 50 km to 80 km above the surface of the Earth, above the troposphere and stratosphere, and below the thermosphere. Next is the stratosphere which extends from 18,000km to 50,000km. The ozone layer (10,000km to 50,000km) is mostly in this layer of the atmosphere. Then there is the Ionosphere. This layer is between 65 and 100,000 km above the earth. Ions and electrons reflect radio waves off of this layer, hence the name.

Tropopause: The boundary zone or transition layer between the stratosphere and the mesosphere. Characterized by a

decrease in temperature with increasing altitude.

Energy transfer

Radiation: the transfer of heat as electromagnetic radiation (i.e. sunlight).

Conduction: The transfer of heat due to contact (heat always flows from hotter objects to cooler objects).

Advection: the transfer of warm or cold air by horizontal winds.

Convection: it is the transfer of heat due to movement of a fluid (air or water). Warmer air expands, becomes less dense, and thus rises forming a convection current. So, essentially, it is simply air mass rising.

Auroras

The beautiful, dancing patterns of light in the sky known as auroras are created by the radiant energy emission from the sun and its interaction with the earth's upper atmosphere over the middle and high latitudes. They are seen near the magnetic poles of each hemisphere. In the Northern Hemisphere, they are known as the aurora borealis or Northern Lights, especially in Alaska, obviously… In the Southern Hemisphere, these phenomena are called the aurora australis. Typical auroras are 100 to 250 km above the ground.

Once in a lifetime (literally), very rare auroras occur that are a deep blood red (usually with a little bit of yellow in the “centers”

Ozone

Ozone is a gaseous molecule that contains three oxygen atoms (O3). Ozone exists high in the atmosphere, where it shields the Earth against harmful ultraviolet rays from the sun. Depletion of stratospheric ozone by manmade chlorofluorocarbons (CFCs) is a serious global concern due to the potential increase in ultraviolet radiation that may reach the surface of the Earth as a result of stratospheric ozone layer thinning.

Terms

Temperature inversion: when the air at the surface is colder than the air above it.

Temperature: the amount of molecular kinetic energy in a substance.

Heat: transfer of energy that occurs because of a difference in temperature between substances.

Humidity: The amount of water vapor in the air.

Terms continued… Relative Humidity: The how much water vapor the air

is capable of holding.

Density: measure of how much mass is contained in a given unit volume

Wind: air moving (sometimes with considerable force) from an area of high pressure to an area of low pressure.

Air Pressure: the force exerted on a surface by the weight of the air above it

These properties interact several different ways. Take dew point for example. Dew point: the temp. to which air must be cooled at constant pressure to reach saturation. So obviously, the temp. plays a huge factor in the dew point, which is explained in its (the dew points) definition.

Also, the relative humidity varies with temperature. As the temp. increases, the air would most likely hold more moist air.

Temperature and Pressure: If an air mass usually maintains a certain

density, it proportionally increases or decreases with the temp.

Temperature and Density: If an air mass maintains a certain

pressure, as temp. increases, density decreases and vice versa. So, in other words, air becomes less dense

CLOUDS

The formation of clouds can be linked back to convection and more in the previous section.

Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere. The air is normally cooled by expansion during its upward movement. Upward flow of air in the atmosphere may be caused by convection resulting from intense solar heating of the ground; by a cold wedge of air (cold front) near the ground causing a mass of warm air to be forced aloft; or by a mountain range at an angle to the wind. Clouds are occasionally produced by a reduction of pressure aloft or by the mixing of warmer and cooler air currents.

How clouds form.

Cloud groups

There are essentially four cloud types:High clouds: 6-13km

Middle Clouds: 2-6 km

Low Clouds: Ground level to 2km

Clouds with vertical development: as the name suggests, these clouds usually start low in the atmosphere and extend far up into the upper layers.

High Clouds Cirrus: these are white clouds that are described as

“feather” and/or “wispy”. Many people know these clouds as “mares tails”. Usually, these clouds are a sign of bad weather to come…

Cirrocumulus: white louds that look like ripples or waves. One of the more popular descriptions for these clouds is “globular” or “globular masses”. These clouds indicate fair weather, but might indicate the coming of a storm.

Cirrostratus: these “halo” clouds are veillike and layer. They usually cause rings to appear around the moon or sun. The same weather predictions can be gotten from these as cirrocumulus.

Cirrus

Cirrocumulus

Cirrostratus

Middle Clouds

Altocumulus: these light gray clouds look like broken-up cirrocumulus clouds. They are small patches in the sky. Usually, these are associated with fair weather, but can cause thunderstorms.

Altostratus: these clouds are blanket layers, and can be either gray or bluish. On occasion, the produce light rain.

Altocumulus

Altostratus

Low Clouds

Stratocumulus: these are soft, gray patches that may for a continuous layer.

Stratus: these are dense, lower layers of gray clouds. They sometimes cover the entire sky. Sometimes associated with light rain. When these clouds are low to the ground, they are called fog.

Nimbostratus: a large, thick layer of dark clouds that, on occasion, block out the sun. These are usually associated with steady, drawn out precipitation.

Stratocumulus

Stratus

Nimbostratus

The Water Cycle The Sun's heat provides energy to evaporate water

from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.

Orographic Lifting

Orographic Lifting: where the flow of air is forced up and over barriers such as highlands or mountains. Moist air being forced aloft begins to cool, thus condensation forms, and rain or snow begins to fall. By the time the air reaches the leeward side of the barrier, it sinks and warms, resulting in decreasing relative humidity, ending of precipitation, and the dissipation of clouds.