Meteorology is the scientific study of the atmosphere.

There are many examples: from a sunny morning to a rainy afternoon (convectional thunderstorms); from a warm, rainy afternoon to a cold, clear night (following a cold front); from a cool rainy night to a warm, humid morning (following a warm front) or from a warm, humid day followed by a violent stormy evening (approaching hurricane). All these examples demonstrate how quickly the atmospheric conditions can change.

Climate is based on observations of weather that have been accumulated over many decades. Long term changes in a region’s climate may include increases or decreases in monthly or yearly temperature and/or precipitation as well as alterations in the variations and extremes usually observed in the region. These changes may occur due to natural fluctuations, such as changes in solar variability, or human activities, such as an increase in “greenhouse” gases.

Atmospheric hazards include lightning, thunderstorms, hurricanes, tornadoes, blizzards, hail, freezing rain, heat waves, cold waves, fog, and drought.

A scientific hypothesis is a proposed explanation for a certain phenomenon that occurs in the natural world. When a hypothesis has survived extensive scrutiny and when competing hypotheses have been eliminated, it may be elevated to the status of a scientific theory. A theory is a well-tested and widely accepted view that best explains certain observable facts.

The scientific method enables us to discern the underlying patterns in the natural world and then to use the knowledge gained to make predictions about what should or should not be expected, given certain facts or circumstances.

The four spheres that constitute the Earth system are: the geosphere, or solid portion of Earth; the hydrosphere, or water portion of Earth; the atmosphere, Earth’s gaseous envelope of air; and the biosphere, the totality of life on Earth.

Oceans cover 71% of the Earth’s surface.

A system is a group of interacting, or interdependent, parts that form a complex whole. The independent components of the Earth system listed in question 7 (land, water, air and life-forms) are interconnected, producing a complex and continuously interacting whole.

The hydrologic cycle is shown in Figure 1.13. Water enters the atmosphere through evaporation from Earth’s surface and transpiration from plants. Water vapor (water in the gaseous state) condenses in the atmosphere to form clouds, which in turn produce precipitation that falls back to Earth’s surface. Some of the rain that falls onto the land infiltrates (soaks into the ground) and is later taken up by plants or is stored as groundwater, while some flows across the surface toward the ocean.

The earth’s atmosphere is composed of nitrogen, oxygen, argon, carbon dioxide, water vapor, aerosols and stratospheric ozone. Today the last four demonstrate the most variability.

Water vapor is important as the source of all cloud and precipitation but also for its ability to absorb, transport and release heat energy across the Earth’s surface. 

Aerosols are tiny solid and liquid particles suspended in the atmosphere. Many act as surfaces on which water vapor may condense, a critical function in the formation of clouds and fog. Aerosols can also absorb or reflect incoming solar radiation. Finally, aerosols contribute to the optical phenomenon of the varied hues of red and orange at sunrise and sunset.

Stratospheric ozone absorbs much of the potentially harmful ultraviolet (UV) radiation from the Sun, allowing life to flourish on land.

Atmospheric pressure is simply the weight of the air above.

Atmospheric pressure falls as one ascends through the atmosphere because there is less air (fewer air molecules) above these higher altitudes.

Figure 1.20. The troposphere is the zone of all weather, where temperature decreases with height. Temperatures rise in the stratosphere due to the presence of heat-absorbing ozone. Temperatures fall again in the mesosphere where ozone ceases to form. Finally, the extremely rarified air in the thermosphere boasts the highest temperatures of all as oxygen and nitrogen atoms absorb very shortwave, high-energy solar radiation.

Temperatures rise in the stratosphere due to the presence of heat-absorbing ozone.

The electrically charged layer known as the ionosphere is located between 80 and 400 kilometers (50 to 250 miles) above Earth’s surface. Here molecules of nitrogen and atoms of oxygen are readily ionized as they absorb high-energy shortwave solar radiation. 

Auroral displays are aligned with Earth’s magnetic poles and closely correlated with large solar storms, such as solar flares. As these charged particles (ions) approach Earth, they are captured by its magnetic field, which in turn guides them toward the magnetic poles. Then, as the ions impinge on the ionosphere, they energize the atoms of oxygen and molecules of nitrogen and cause them to emit light—the glow of the auroras.