UPCAT General Science (Extended) — Atmosphere, Weather & ClimateStudy Notes

The atmosphere is a mixture of gases that surrounds Earth, held in place by gravity. Understanding its composition is crucial for understanding weather and climate patterns. The atmosphere consists of: Nitrogen (78%) - the most abundant gas, essential for protein production in living organisms through nitrogen fixation; Oxygen (21%) - necessary for respiration and combustion processes; Argon (0.93%) - an inert gas that doesn't react with other substances; Carbon dioxide (0.03%) - important for photosynthesis and the greenhouse effect; Other gases (0.04%) - including water vapor, ozone, and trace gases. These percentages remain relatively constant up to about 80 kilometers above Earth's surface, though the concentration of water vapor varies significantly depending on location and weather conditions.

The atmosphere is divided into five distinct layers based on temperature changes with altitude. Each layer has unique characteristics and plays specific roles in weather and climate formation. Troposphere (0-10 km): This is where we live and where all weather occurs. Temperature decreases with altitude at about 6.5°C per kilometer. Contains 99% of atmospheric water vapor and 75% of atmospheric mass. Commercial aviation occurs in the upper troposphere. Stratosphere (10-50 km): Contains the ozone layer which absorbs harmful UV radiation. Temperature increases with altitude due to ozone absorption of UV rays. Commercial jets cruise in the lower stratosphere for fuel efficiency. Mesosphere (50-85 km): Temperature decreases with altitude, reaching as low as -90°C. Meteors burn up in this layer, creating shooting stars. Also called the 'middle sphere.' Thermosphere (85-600 km): Temperature increases dramatically due to absorption of high-energy solar radiation. Home to the International Space Station and most satellites. Aurora phenomena occur here. Exosphere (600+ km): The outermost layer where atmospheric particles gradually escape to space. Represents the transition between Earth's atmosphere and outer space.

Weather refers to the short-term atmospheric conditions at a specific time and place. Six main components define weather: temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness. Temperature measures the average kinetic energy of air molecules, typically measured with thermometers in degrees Celsius. It's influenced by solar radiation, latitude, altitude, and local geographic features. Atmospheric Pressure is the weight of air above a given point, measured with barometers in millibars or pascals. High pressure systems typically bring clear skies, while low pressure systems often produce clouds and precipitation. Wind results from pressure differences caused by unequal heating of Earth's surface. Air moves from high-pressure areas (cold air) to low-pressure areas (warm air). The Coriolis effect, caused by Earth's rotation, deflects wind to the right in the Northern Hemisphere and left in the Southern Hemisphere. Humidity measures water vapor content in air, expressed as relative humidity (percentage of maximum moisture air can hold at that temperature). High humidity can make temperatures feel hotter. Precipitation occurs when water vapor condenses and becomes too heavy to remain suspended in air. Forms include rain, snow, sleet, and hail. Cloudiness refers to cloud cover, which affects temperature and precipitation patterns.

Clouds are classified based on their altitude and appearance, serving as natural weather predictors. Understanding cloud types helps forecast weather changes. High Clouds (6-18 km altitude): Cirrus clouds appear as thin, wispy strands resembling hair. Fair weather indicators when scattered. Cirrostratus clouds form thin sheets that create halos around the sun or moon, indicating rain within 12-24 hours. Cirrocumulus clouds appear as small white patches in rows, sometimes called 'mackerel sky.' In tropics, may indicate approaching hurricanes. Middle Clouds (2-6 km altitude): Altocumulus clouds appear as gray or white patches in waves or bands. Often indicate thunderstorms later in the day. Altostratus clouds form gray or blue-gray sheets, often covering the entire sky before storms. Low Clouds (0-2 km altitude): Stratus clouds form gray layers that may produce light mist or drizzle. Stratocumulus clouds appear as low, puffy gray masses indicating dry weather. Nimbostratus clouds are thick, dark gray layers that produce steady rain. Vertical Development Clouds: Cumulus clouds are puffy, cotton-like fair weather clouds. Cumulonimbus clouds are towering thunderheads that produce severe weather including lightning, heavy rain, hail, and tornadoes.

Air masses are large bodies of air with uniform temperature and humidity characteristics acquired from spending time over uniform surfaces. When different air masses meet, they create fronts that produce weather changes. Warm Fronts form when warm air gradually rises over cold air. They produce light to moderate precipitation over wide areas, followed by clearing skies and warmer temperatures. The weather change is gradual. Cold Fronts occur when dense cold air pushes under warm air, forcing it to rise rapidly. This creates sudden weather changes with heavy rain, thunderstorms, and sometimes severe weather, followed by clearing and cooler temperatures. Occluded Fronts develop when a cold front overtakes a warm front, lifting warm air completely off the ground. They produce mixed precipitation types and complex weather patterns. Stationary Fronts form when air masses meet but neither advances. They can produce days of clouds and light precipitation. The movement and interaction of these fronts determine regional weather patterns and are crucial for weather forecasting.

The Philippines experiences three major wind systems that significantly influence the country's weather patterns and seasonal changes. Understanding these systems is crucial for predicting weather in the archipelago. Hanging Amihan (Northeast Monsoon) occurs from November to March, bringing cold, dry air from Siberia and northeastern Asia. This wind system is characterized by cool temperatures, little rainfall, and generally pleasant weather conditions. The northeast trade winds dominate during this period, making it the ideal time for outdoor activities and tourism. Hanging Habagat (Southwest Monsoon) dominates from June to October, bringing warm, moist air from Australia and the Indian Ocean. This system produces hot, humid weather with heavy rainfall, particularly on the western sides of islands. The southwest monsoon is responsible for the Philippines' wet season and can intensify tropical cyclones. Trade Winds occur during the transition periods from March to early May, bringing moderate rainfall primarily to the eastern parts of the country. These winds originate from the North Pacific Ocean and create relatively stable weather conditions. Local wind systems also affect Philippine weather, including land and sea breezes that occur daily along coastlines due to differential heating between land and water surfaces.

Land and sea breezes are local wind systems that occur in coastal areas due to the different heating and cooling rates of land and water. These daily wind patterns significantly affect local weather conditions and are important for understanding microclimates. Water has a high specific heat capacity, meaning it heats up and cools down slowly. Land has a low specific heat capacity, so it heats up and cools down quickly. During the day, solar radiation heats the land faster than the water. The warm land heats the air above it, causing it to expand, become less dense, and rise, creating a low-pressure area. Over the water, the air remains cooler and denser, creating a high-pressure area. Air flows from high pressure to low pressure, creating a sea breeze that moves from water to land. Sea breezes typically begin mid-morning and are strongest in mid-afternoon. At night, the land cools faster than the water. The air over the land becomes cooler and denser, creating high pressure, while the air over the water remains warmer and less dense, creating low pressure. This causes air to flow from land to water, creating a land breeze. Land breezes are typically weaker than sea breezes and occur during late night and early morning hours.

The hydrosphere encompasses all water on Earth, including oceans, lakes, rivers, groundwater, and atmospheric water vapor. Approximately 75% of Earth's surface is covered by water, with 97.2% being saltwater and only 2.8% being freshwater. Of the freshwater, most is frozen in ice caps and glaciers, making less than 1% readily available for human use. Ocean movements play crucial roles in global climate regulation and weather patterns. Surface Currents are horizontal water movements driven by wind friction on the ocean surface. These currents redistribute heat from equatorial regions toward the poles, moderating global temperatures. Major surface currents include the Gulf Stream, Kuroshio Current, and the Antarctic Circumpolar Current. Deep Currents, also called thermohaline circulation, are vertical water movements driven by differences in water density caused by temperature and salinity variations. Cold, salty water is denser and sinks, while warm, less salty water rises. Polar Creep occurs when cold, high-salinity water at the poles sinks and moves toward equatorial regions along the ocean floor, carrying oxygen to deep waters and supporting deep-sea life. Upwelling happens when deep, nutrient-rich water rises to the surface, typically along coastlines where winds push surface water away from shore. This process supports marine ecosystems by bringing nutrients to surface waters where photosynthesis occurs.

Understanding the distinction between weather and climate is fundamental to atmospheric science. Weather refers to short-term atmospheric conditions at a specific time and place, including temperature, humidity, precipitation, wind, and atmospheric pressure. Weather can change from hour to hour and day to day. Climate, on the other hand, represents the long-term average weather conditions for a specific region over a minimum period of 30 years. Climate describes patterns and trends rather than daily variations. Climate is determined by several factors: Latitude affects the angle and intensity of solar radiation received. Equatorial regions receive more direct sunlight and are generally warmer, while polar regions receive less direct sunlight and are colder. Altitude influences temperature, with higher elevations being cooler due to lower air pressure and density. Proximity to water bodies moderates temperature due to water's high heat capacity. Ocean currents redistribute heat globally, affecting regional climates. Topography creates rain shadows, where mountains block moisture-laden air, creating wet conditions on one side and dry conditions on the other. Global wind patterns distribute heat and moisture around the planet. Human activities increasingly influence both local and global climate through greenhouse gas emissions, deforestation, and urbanization.