Air, Atmosphere, Weather
The atmosphere of the earth is a thin, layered collection of gases, water vapor and particles. Most living creatures live in the atmosphere. The troposphere is the surface layer of air that absorbs visible sunlight. Heating, cooling, and water evaporation in the troposphere are expressed as weather. The weight of air around an object exerts pressure. At sea-level the weight of air molecules above each square inch is about 14.7 pounds. Air pressure varies with temperature and weather patterns are described in terms of low pressure fronts interacting with higher pressure fronts.
Air and storm systems travel over the Earth's surface. This global circulation is determined by several factors : Earth’s rotation, the Earth’s tilt relative to the sun, and the Earth’s water which is in constant motion. The sun heats the entire surface -more when it is directly overhead. The equator becomes very hot with the hot air rising into the upper atmosphere. This air moves toward the poles where it becomes cold and sinks, returning to the equator . The earth’s rotation, tilt, and the greater land mass in the northern hemisphere complicate the circulation patterns .
Air is a mixture of gases and aerosols. Humans add thousands of volatile gases to air, creating a chemical soup that changes light transmission through the atmosphere and exposes all living creatures to toxins and carcinogens. Suspended particles in the air (aerosol) are important to the behavior of the atmosphere and to human diseases.
Overland up to a quarter of the total airborne particulates are pollens, fungal spores, bacteria, viruses, plant and animal matter. The air inside buildings contains local aerosols that are often more concentrated and more toxic than outdoor air. The term dust refers to the larger particles in the aerosol that settle on walls and furniture. A smoker in the living room of a house produces a toxic aerosol that permeates the rest of the house. Smoke particles settle on walls and every object in a room so that a smoker leaves a trail of contamination that non-smokers smell as soon as they enter the room.
The air thins as you ascend above the Earth; air pressure and temperature drops. The stratosphere begins at about 12 miles altitude at the equator; about 5 miles at the poles. Solar ultraviolet radiation is absorbed by oxygen and ozone. The "ozone layer" is about 30 miles high; 90% is located within 10 miles above the Earth's surface. The atmosphere thins progressively in the mesosphere, the outer layer that extend to 53 miles altitude. Atmospheric gases eventually disappear into relatively empty, cold space.
Stratospheric ozone absorbs ultraviolet sunlight providing heat and protection for living creatures in the lower atmosphere. At the Earth's surface, ozone from human industry is toxic. In the 20th century, it became obvious that gases created by human activity changed the chemical composition of the troposphere and stratosphere with negative impacts on human survival. Large ozone holes appeared over the Antarctic and the Arctic Polar regions. Smaller areas of ozone depletion were recorded over other, more-populated regions of the Earth.
Winds are strongest immediately under the tropopause (the area between troposphere and stratosphere) except locally, during tornadoes, tropical cyclones or other anomalous situations. If two air masses of different temperatures or densities meet, the resulting pressure difference caused by the density difference (which ultimately causes wind) is highest within the transition zone. The wind does not flow directly from the hot to the cold area, but is deflected by the Coriolis effect and flows along the boundary of the two air masses.
I live on the Pacific edge of the coastal rain forest. The abundant rainfall in the winter supports vibrant forests with big trees and dense forest floors. Rain is the product of evaporation from oceans and ground waters on land. Rain and snow supply most of the fresh water on the planet and are therefore a critical determinants of environments. Precipitation, especially rain, has a dramatic effect on agriculture. A regular rain pattern is usually vital to healthy plants, too much or too little rainfall can be devastating to crops. Drought can kill crops and increase erosion while overly wet weather can cause harmful fungus growth. Plants need varying amounts of rainfall to survive. Animals have adaptation and survival strategies based on precipitation patterns. Mass migrations of African animals , for example, follow annual patterns based on precipitation.
Evaporated water rises in the atmosphere forming clouds. Mountains have heavy precipitation on windward side as the upward slopes cause moist air to rise, cool and condense. The leeward side of mountains is relatively dry. The air is less moist as the down slope flow heats and dries the air mass. Mountains accumulate snow which provide many areas with summer water as the snow melts. Snow that fails to melt becomes compacted and forms glacier ice which becomes long-term water storage. Melting glaciers is a major concern as the earth warms. Glacial water added to the oceans will raise ocean water levels and threaten coastal communities.
The water in clouds occurs as droplets, ice crystals and snow. When the water droplets-crystals grow heavier, they fall as rain, hail or snow. Droplets and ice crystal tend to form around particles. Fine particulate matter produced by car exhaust and other human sources of pollution forms cloud condensation nuclei increasing the likelihood of rain. As commuters and commercial traffic cause pollution to build up over cities, the likelihood of rain peaks by Saturday after five days of weekday pollution.