Essential Concepts in Meteorology and Oceanography

Essential Concepts in Earth's Atmosphere and Oceans

Thermodynamics and Heat Transfer

Temperature

The average kinetic energy of molecules or atoms in a material, representing the kinetic energy of a substance.

Heat

The total energy of molecules or atoms in a material. You can have a large amount of heat but low temperatures, or high temperatures but little heat (depending on the mass of the substance).

Latent Heat

The amount of heat required to completely change a quantity of water from phase A to phase B with no corresponding change in temperature. The term “Latent” means “hidden.”

Latent Heat vs. Sensible Heat

Latent and sensible heat are types of energy released or absorbed in the atmosphere.

• Latent Heat: Related to changes in phase (e.g., melting, evaporation) between liquids, gases, and solids.
• Sensible Heat: Related to changes in temperature of a gas or object with no change in phase.

Atmospheric Moisture and Stability

Dew-Point Temperature

The temperature to which air must be cooled, at a given pressure and water-vapor content, for it to reach saturation; the temperature at which dew begins to form.

Relative Humidity

The ratio of water vapor content to water vapor capacity. The water vapor capacity is equal to the Saturated Mixing Ratio, which is temperature dependent.

Relative Humidity = (Vapor Content / Saturated Mixing Ratio)

Adiabatic Temperature Change

Temperature change that is brought about through changes in volume, such as expansion or contraction (e.g., rising air expands and cools).

Atmospheric Dynamics and Pressure

Air Pressure

The weight of the atmosphere pressing down on the Earth. It is measured by a barometer in units called millibars.

The Pressure-Gradient Force

The force that results when there is a difference in pressure across a surface. In general, pressure is defined as a force per unit area across a surface.

Friction

The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact.

Coriolis Effect

The rotation of the Earth causes a phenomenon on free-moving objects. Objects in the Northern Hemisphere are deflected to the right, while objects in the Southern Hemisphere are deflected to the left. The Coriolis effect thus tries to force winds to shift towards the right or left.

Wind Systems and Air Masses

Wind Regimes (Trades, Westerlies, Easterlies)

The trade winds are the prevailing pattern of surface winds from the east toward the west (easterly) found in the tropics, within the lower portion of the Earth's atmosphere.

Local Winds

Winds that blow over a limited area, typically between small low and high pressure systems. The main types of local winds are sea breezes and land breezes.

Air Masses

A volume of air defined by its temperature and water vapor content. Air masses cover many hundreds or thousands of miles, adapting to the characteristics of the surface below them. They are classified according to latitude and their continental or maritime source regions.

Lifting Mechanisms and Fronts

Orographic Lifting

Occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain.

Frontal Systems

• Cold Front: The transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it.
• Warm Front: A density discontinuity located at the leading edge of a homogeneous warm air mass, typically located on the equator-facing edge of an isotherm gradient. Cold fronts move faster than warm fronts.

Other Uplift Mechanisms

• Frontal Wedging: Where cold air meets warm air, forcing the warm air up.
• Convergence: When winds from two directions meet, and the only way for the air to go is up.
• Convective Uplift: Where the sun heats the surface, causing the heated air above it to rise.

Storm Systems

Cyclones and Anticyclones

• Cyclones: A storm or system of winds that rotates around a center of low atmospheric pressure (counter-clockwise in the Northern Hemisphere).
• Anticyclones: A system of winds that rotates around a center of high atmospheric pressure.

A Mid-latitude Cyclone is an area of low pressure around which the winds flow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Thunderstorms

Small-scale severe weather events associated with frequent lightning, high winds, and heavy rainfall.

Tornadoes

Violent storms that strike as a powerful rotating mixture of wind and thunderstorm clouds, extending from the clouds to the ground in a funnel shape.

Hurricanes

A type of cyclone—a generic term for any powerful, rotating storm that originates in warm tropical oceans and creates strong winds and heavy rain.

Oceanography and Coastal Processes

Residence Times

The residence time of a species is calculated as: Mass (or volume) in reservoir / Rate of inflow or outflow.

Ocean Currents and Gyres

One of the driving forces of global air and ocean currents is the uneven heating of the Earth's surface. Ocean currents (including wind-driven and boundary currents, both warm and cold) are driven by wind and density differences, forming large rotating systems called gyres.

Deep Ocean Circulation

Deep ocean currents are driven primarily by density and temperature gradients (thermohaline circulation).

Coastal Upwelling

Upwelling often happens where wind blows along a coastline. The wind causes the water at the ocean surface to move perpendicular to it, away from the coast, bringing cold, nutrient-rich water to the surface.

Ocean Waves (Characteristics, Motion)

Waves transmit energy, not water, and are commonly caused by the wind as it blows across the ocean, lakes, and rivers. Waves caused by the gravitational pull of the Moon and the Sun are called tides.

Refraction and Longshore Transport

• Refraction: The fact or phenomenon of light, radio waves, or water waves being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density.
• Longshore Transport: The movement of sediment parallel to the shore, often caused by waves approaching the coast at an angle.

Tides (Causes, Variation in Cycles and Patterns)

Gravity is one major force that creates tides. Sir Isaac Newton explained that ocean tides result from the gravitational attraction of the Sun and Moon on the oceans of the Earth.

Coastal Erosion and Shoreline Stabilization

Cliff erosion is a common storm-induced hazard along the West Coast. While coastal erosion affects all regions of the USA, erosion rates and potential impacts are highly localized. Erosion is the gradual, although sometimes rapid, removal of sediments from the shoreline. It is caused by a number of factors including storms, wave action, rain, ice, and winds.

Related concepts include coastal features, barrier islands, and shoreline stabilization techniques used to mitigate erosion.