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
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 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 flooding, soil erosion and
plants are vulnerable to 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.
A thunderstorm is a common occurrence and an important source of
environmental change, loss of life and property destruction. A
thunderstorm features wind, rain, snow, hail, lightning and thunder.
Severe thunderstorms, known as super cells, and tornadoes rotate in the form of
a brief, localized cyclone ( hurricane). Damage is inflicted by downburst winds,
large hailstones , lightning and flash flooding caused by heavy precipitation.
These storms move toward source of heat and moisture. Tornadoes are the most
dramatic events that move variable distances destroying everything in their path
Lightning is a sudden movement of free electrons that accumulate in an around
clouds. The electron flows occur between electrically charged regions of a
cloud, between two clouds, or between a cloud and the ground .Thunder is
the sound of lightning. Night photos of the earth from the space station
show a continuous display of lighting distributed across the earth’s surface
with a frequency of 40–50 times a second ( 1.4 billion flashes
per year). The average duration is 0.2 seconds. The main charging area occurs in
the central part of the storm where air is moving upward rapidly and
temperatures range from -15 to -25 Celsius. The upper thunderstorm cloud becomes
positively charged while the middle to lower part of the cloud becomes
negatively charged. A strike reaching the ground is a channel of ionized air
leading from a charged region in the thundercloud. Damage is done by
large electric current flows along the plasma channel from the cloud to the
ground. An important hazard of a lightning strike is igniting wildfires .
Lightning currents traveling through a tree may vaporize its sap, causing a
steam explosion that bursts the trunk. 90% of people struck by lightning
survive but may suffer severe injury due to internal organ and nervous system
damage. Buildings or tall structures hit by lightning may be damaged as the
lightning seeks unintended paths to ground. By safely conducting a lightning
strike to ground, a lightning protection system can reduce property