The Water Cycle and Weather

• The water cycle involves the continuous movement of water between Earth’s surface and the atmosphere.
• This movement occurs through physical processes.

Movement Into the Atmosphere

• Water enters the atmosphere from oceans, lakes, and streams through evaporation.
• Evaporation is the process where liquid water turns into water vapor (a gas).
• Transpiration is another way water enters the atmosphere, involving the evaporation of water from plants.
• Both evaporation and transpiration are powered by the sun's energy.

Cloud Formation

• Condensation is how water vapor in the atmosphere forms clouds.
• Condensation is the process where water vapor transforms into liquid water.

Precipitation and Surface Water

• Precipitation is when water falls back to Earth’s surface, driven by gravity.
• Some water that reaches land flows downhill as runoff.
• Some water soaks into the ground and becomes groundwater.

Weather Defined

• Weather is the atmospheric condition at a specific place and time, characterized by factors like temperature, rain, and wind.
• Changes in weather are due to the movement of air masses.
• An air mass is a large volume of air with consistent temperature and humidity.
• Air masses generally move from areas of high pressure to areas of low pressure.

Weather Fronts

• Weather fronts form when air masses collide.
• A cold front forms when a cold air mass moves into a warm air mass, typically bringing cooler temperatures, heavy rain, or thunderstorms.
• A warm front forms when a warm air mass moves into a cold air mass, usually resulting in warmer temperatures and moderate rain.

Weather Prediction

• Scientists predict weather by gathering current data and using computer models.
• Due to the complexity of weather, predictions are probabilities, not certain outcomes.

Currents Explained

• A current is a steady flow of fluid (air or water) within a larger body of that fluid.
• Prevailing winds are air currents that predominantly blow in a single direction.
• The uneven heating of Earth’s surface causes the global pattern of prevailing winds.

Surface Currents and the Coriolis Effect

• Surface currents in the ocean are created as prevailing winds blow across the water.
• Both prevailing winds and surface currents curve because of Earth’s rotation; this is the Coriolis Effect.

Gyres

• Surface currents connect, forming large, rotating systems known as gyres.
• Gyres circulate heat around the Earth by moving warm water from the equator toward the poles.

Deep Currents and Overturning Circulation

• Density differences drive deep ocean currents.
• Denser water, which is colder and saltier, sinks; less dense water, which is warmer and less salty, rises.
• Vertical currents connect via horizontal currents at the surface and in the deep ocean.
• Together this system of currents is called the overturning circulation.

Climate Defined

• Climate is the long-term weather pattern in a specific region.
• Many factors influence a region’s climate.

Latitude's impact on Climate

• Latitude is the distance north or south from the equator.
• Higher latitudes receive less direct sunlight, resulting in cooler climates.

Elevation's impact on Climate

• Elevation is a place's height above sea level.
• Air cools as it rises to higher elevations, leading to cooler temperatures.

Geographic Features' impact on Climate

• Geographic features are elements of Earth’s surface like large bodies of water or mountain ranges.
• Large bodies of water moderate air temperatures, leading to milder climates near oceans or lakes.
• Mountain ranges can create a rain shadow, which is an area of reduced rainfall on the range's leeward side.
• Rain shadows have warmer and drier climates compared to the other side of the mountain range.