Atmosphere Characteristics Chapter 17.1 Atmosphere Characteristics

Earth’s atmosphere is very unique – it makes life on Earth possible. Weather is the state of the atmosphere at any given time and place. Earth’s motions and energy from the sun make all types of weather. Weather is constantly changing. Climate is based on observations of weather that have been collected over many years. Climate helps describe a place or region. Measurable properties of weather and climate are air temperature, humidity, type and amount of precipitation, air pressure, and speed and direction of the wind.

Composition of the Atmosphere Major components Air is made of many different gases and differs from time to time and place to place. Nitrogen and oxygen make up most of the air. Carbon dioxide is a very small part of air along with argon.

Variable Components of the Atmosphere Water vapor, dust particles, and ozone are very important parts of the atmosphere that vary. Water vapor is the source of all clouds and precipitation, it also absorbs heat given off by Earth and some solar energy. There are microscopic particles suspended in the atmosphere like sea salts, fine soil, smoke and soot, pollen, and microorganisms.

Ozone is a form of oxygen that combines three oxygen atoms Ozone is a form of oxygen that combines three oxygen atoms. There is very little ozone in the atmosphere. Most ozone is between Earth’s surface and the atmosphere. Ozone absorbs UV rays from the sun. If ozone did not do this life would not be possible on Earth.

Human Influence Air pollutants are airborne particles and gases that can endanger organisms. Primary pollutants come from identifiable sources. Secondary pollutants are not given off directly in air. They form in the atmosphere, when primary pollutants are changed.

Height and Structure of the Atmosphere The atmosphere thins as you move away from Earth until there are too few gas molecules to detect. That means there is no definite line between the atmosphere and space.

Pressure Changes Atmospheric pressure is the weight of the air above. At sea level atmospheric pressure is greater than at a higher altitude because there is less air pushing on you.

Temperature Changes There are 4 layers of the atmosphere due to temperature. The bottom layer, where temperature gets colder as height increases (think climbing a mountain) is called the troposphere. This is where weather occurs. The outer boundary of the troposphere is called the tropopause. The stratosphere starts at the end of the tropopause. In this area temperature is constant for a majority, but temperature will increase in the upper part of the stratosphere called the stratopause. This is wherer ozone is located.

The third layer is the mesosphere – this area the temperature decreases with height until the mesopause. The last layer is the thermosphere, this is only a small amount of the Earth’s atmosphere. Temperatures increase in this area.

Earth-Sun Relationships Almost all weather comes from the sun. Earth can only absorb a small amount of energy the sun gives off. The sun’s energy is not distributed evenly over the Earth. It will vary based on latitude, time of day, and season of the year. The unequal heating of the Earth makes winds.

Earth’s Motions Earth has rotation and revolution. Rotation is the spinning of Earth on it’s axis (the imaginary line running through the north and south poles). Our planet rotates once every 24 hours that produces day-night cycles. Revolution is the Earth’s orbit around the sun. It has an elliptical orbit around the sun.

Earth’s Orientation Seasonal changes happen because of Earth’s position relative to the sun changes as the Earth orbits around the sun. The Earth is tilted 23.5 degrees. This makes it so how the sun’s rays hit the Earth is different at different seasons. If we did not have this tilt we would not have seasons.

Solstices and Equinoxes On June 21 or 22 the Northern Hemisphere is “leaning” toward the sun. This is the summer solstice – the first day of summer. In December the Northern Hemisphere “leans” away from the sun. December 21 or 22 is the winter solstice, the first day of winter.

Equinoxes are halfway between the solstices. September 22 or 23 is the autumnal equinox. March 21 or 22 is the spring equinox. At these times the Earth is neither “leaning” toward or away from the sun.

Length of Daylight Length of daylight is also determined by Earth’s orbit. At the summer solstice the length of daylight is longer than the length of darkness. At this time, at the Arctic Circle daylight is 24 hours.