UPCAT General Science (Extended) — Atmosphere, Weather & ClimateRevision Notes
Quick revision notes for Atmosphere, Weather & Climate — the one-page refresher for UPCAT aspirants. Every item on this page has appeared in recent UPCAT General Science (Extended) papers, so revising these is the shortest path to a confident performance in University of the Philippines's UPCAT 2026.
Exam context
The University of the Philippines College Admission Test is conducted by University of the Philippines and is scheduled for Mid-2026 (announced by UP Admissions). The General Science (Extended) subtest is marked as "Extended coverage for UP Science programs" in the official pattern, and Atmosphere, Weather & Climate appears in position 4th of 6 in the UPCAT General Science (Extended) review rotation. Passing mark: UPG ≤ 2.2 typical. Recent UPCAT 2026 papers have drawn roughly 20 questions from this subject.
Atmosphere, Weather & Climate - Revision notes
The atmosphere is Earth's protective blanket of gases that sustains life and creates weather patterns. Understanding atmospheric composition, layers, weather phenomena, and climate patterns is essential for UPCAT and other college entrance exams. This chapter covers the structure of the atmosphere, weather systems, climate factors, and ocean movements that influence our planet's environmental conditions.
Sections
Formulas
Example
At sea level, normal air pressure is 1013.25 millibars
Formula
Air Pressure = Force/Area
Variables
Force (weight of air), Area (surface area)
Application
Understanding atmospheric pressure changes with altitude
Exam Tips
- Remember the atmospheric layers using 'Tropical Storm Makes Thunder Explode'
- Memorize exact percentages: N₂ 78%, O₂ 21%
- Know that temperature patterns differ in each layer
Key Points
- Atmosphere composition: 78% nitrogen, 21% oxygen, 0.93% argon, 0.03% carbon dioxide, 0.04% other gases
- Five main atmospheric layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere
- Troposphere (0-10 km): Where we live, contains 99% of water vapor, weather occurs here
- Stratosphere (10-50 km): Contains ozone layer that absorbs UV rays, commercial jets fly here
- Mesosphere (50-85 km): Meteors burn up, temperature decreases with altitude
- Thermosphere (85+ km): Absorbs X-rays and UV radiation, satellites orbit here, auroras occur
- Exosphere: Outermost layer where atmospheric particles escape to space
- Ionosphere: Region in mesosphere and thermosphere where atoms are ionized, reflects radio waves
Definitions
Term
Atmosphere
Definition
The layer of gases surrounding Earth, held in place by gravity
Importance
Essential for life, weather formation, and protection from harmful radiation
Term
Ozone Layer
Definition
A region in the stratosphere containing high concentrations of ozone (O₃) that absorbs UV radiation
Importance
Protects Earth from harmful ultraviolet radiation from the sun
Term
Ionosphere
Definition
Region where solar radiation ionizes atoms and molecules, freeing electrons
Importance
Enables radio wave communication by reflecting radio signals back to Earth
Section Title
Atmospheric Composition and Structure
Common Mistakes
- Confusing the order of atmospheric layers
- Thinking all weather occurs in the stratosphere instead of troposphere
- Mixing up the percentages of atmospheric gases
Formulas
Example
If air contains 10g of vapor but can hold 20g at that temperature, RH = 50%
Formula
Relative Humidity = (Actual vapor/Maximum vapor) × 100%
Variables
Actual vapor (current water vapor), Maximum vapor (capacity at given temperature)
Application
Calculating moisture content in air
Exam Tips
- Remember: Low pressure = clouds/rain, High pressure = clear skies
- Cumulonimbus clouds indicate severe weather (thunderstorms)
- Wind deflects right in Northern Hemisphere, left in Southern Hemisphere
Key Points
- Weather describes atmospheric conditions at a specific time and place
- Six main weather components: temperature, humidity, pressure, wind, precipitation, cloudiness
- Temperature measures heat energy in air using thermometer (Celsius/Fahrenheit)
- Atmospheric pressure measured in millibars using barometer, decreases with altitude
- Low pressure systems bring clouds and precipitation, high pressure brings clear weather
- Wind flows from high pressure to low pressure areas due to temperature differences
- Humidity is water vapor amount in air, measured with psychrometer
- Precipitation occurs when water vapor cools and condenses
- Eight main cloud types: cirrus, cirrostratus, cirrocumulus, stratocumulus, nimbostratus, stratus, cumulus, cumulonimbus
Definitions
Term
Weather
Definition
The state of atmospheric conditions at a specific time and place
Importance
Affects daily activities, agriculture, and human safety
Term
Atmospheric Pressure
Definition
The pressure exerted by the weight of air above a surface
Importance
Influences weather patterns and predicts storm systems
Term
Coriolis Effect
Definition
The deflection of moving objects (including wind) due to Earth's rotation
Importance
Explains wind patterns and storm circulation in different hemispheres
Section Title
Weather Components and Phenomena
Common Mistakes
- Confusing weather and climate definitions
- Mixing up cloud types and their weather indications
- Not understanding that low pressure means bad weather
Exam Tips
- Amihan = cool and dry, Habagat = hot and wet
- Sea breeze = day time, Land breeze = night time
- Remember monsoon directions: NE (Amihan) vs SW (Habagat)
Key Points
- Three major wind systems affect the Philippines
- Hanging Amihan (Northeast Monsoon): November-March, cold temperatures, little rainfall, wind from east/Siberia
- Hanging Habagat (Southwest Monsoon): June-October, hot humid weather, heavy rainfall in western Philippines, wind from Australia
- Trade Winds: March-May, brings rain to eastern Philippines, wind from North Pacific Ocean
- Sea breeze occurs during day when land heats faster than water
- Land breeze occurs at night when land cools faster than water
- These breezes result from different heat capacities of land and water
Definitions
Term
Monsoon
Definition
Seasonal wind patterns that bring distinct wet and dry periods
Importance
Determines Philippines' climate patterns and agricultural seasons
Term
Heat Capacity
Definition
The amount of heat energy required to raise temperature of a substance
Importance
Explains why land and water heat and cool at different rates, creating breezes
Section Title
Philippine Wind Systems and Monsoons
Common Mistakes
- Confusing Amihan and Habagat seasons and characteristics
- Not understanding the direction of sea and land breezes
- Mixing up the source regions of different monsoons
Exam Tips
- Cold fronts move faster and create more violent weather
- Warm fronts bring gentler, longer-lasting precipitation
- Occluded fronts combine characteristics of both warm and cold fronts
Key Points
- Front occurs when two different air masses meet, creating weather changes
- Warm Front: warm air replaces cold air, brings light rain then clearer weather
- Cold Front: cold air replaces warm air, brings violent weather and thunderstorms
- Stationary Front: air masses meet but don't move, prolonged rain and clouds
- Occluded Front: cold front overtakes warm front, heavy rain and cooler weather
- Air mass characteristics depend on temperature and humidity of source region
Definitions
Term
Air Mass
Definition
Large body of air with uniform temperature and humidity characteristics
Importance
Determines weather conditions when it moves into a region
Term
Front
Definition
Boundary zone where two different air masses meet
Importance
Creates weather changes and can produce severe weather phenomena
Section Title
Weather Fronts and Air Masses
Common Mistakes
- Confusing warm and cold front weather patterns
- Not understanding that fronts create weather changes
- Mixing up the movement directions of different fronts
Exam Tips
- Remember water distribution: ~97% salt, ~3% fresh
- Surface currents = wind driven, Deep currents = density driven
- Upwelling brings nutrients up, supporting marine ecosystems
Key Points
- Earth is 75% covered in water: 97.2% saltwater, 2.8% freshwater
- Hydrosphere includes all water forms: surface water, groundwater, atmospheric water
- Surface currents: horizontal water movement caused by wind
- Deep currents: vertical water flow driven by temperature and salinity differences
- Polar creep: cold, salty water from poles moves to warmer regions and sinks
- Upwelling: deep nutrient-rich water rises to surface, supporting marine life
- Ocean movements distribute heat, nutrients, and oxygen globally
Definitions
Term
Hydrosphere
Definition
All water on Earth including oceans, lakes, rivers, groundwater, and atmospheric water
Importance
Essential for life and influences weather and climate patterns
Term
Upwelling
Definition
Process where deep ocean water rises to the surface bringing nutrients
Importance
Creates productive fishing areas and affects regional climate
Term
Thermohaline Circulation
Definition
Global ocean circulation driven by temperature and salinity differences
Importance
Distributes heat around the globe and affects climate patterns
Section Title
Hydrosphere and Ocean Movements
Common Mistakes
- Confusing surface currents with deep currents
- Not understanding the role of temperature and salinity in ocean circulation
- Forgetting that most of Earth's water is saltwater
Exam Tips
- Weather = daily conditions, Climate = long-term average (30+ years)
- Climate determines what you plant, weather determines when you water it
- Philippines climate is tropical with monsoon influences
Key Points
- Climate is average weather conditions over long periods (minimum 30 years)
- Weather is short-term atmospheric conditions at specific time and place
- Climate factors include latitude, altitude, proximity to water bodies, ocean currents
- Philippines has tropical climate with wet and dry seasons
- Global climate patterns influenced by solar radiation distribution and Earth's tilt
- Climate change refers to long-term shifts in global climate patterns
Definitions
Term
Climate
Definition
Long-term average weather conditions (minimum 30 years) for a specific region
Importance
Determines ecosystem types, agriculture patterns, and human settlements
Term
Meteorology
Definition
Science concerned with atmospheric processes and weather forecasting
Importance
Helps predict weather patterns and prepare for weather-related hazards
Section Title
Climate vs Weather and Long-term Patterns
Common Mistakes
- Using weather and climate interchangeably
- Not understanding the time scale difference between weather and climate
- Confusing local weather events with climate patterns
Connections
- Atmospheric pressure changes connect to weather prediction and storm formation
- Ocean currents influence coastal climate patterns and weather systems
- Philippine monsoon systems directly relate to agricultural seasons and typhoon patterns
- Atmospheric layers connect to satellite communication and space exploration
- Cloud formation processes link to precipitation and water cycle
- Wind patterns relate to global climate distribution and ocean current systems
Exam Strategy
Focus on memorizing atmospheric composition percentages, layer characteristics, and Philippine monsoon systems. Understand the relationships between pressure, temperature, and weather patterns. Practice identifying cloud types and their associated weather. Remember that weather describes current conditions while climate describes long-term patterns. Connect ocean movements to climate influence and understand the role of the hydrosphere in weather systems.
Quick Review Questions
What are the percentages of nitrogen and oxygen in Earth's atmosphere?
These are the two most abundant gases in our atmosphere, making up 99% of the total atmospheric composition.
In which atmospheric layer do we live and where does most weather occur?
The troposphere extends from 0-10 km altitude and contains 99% of atmospheric water vapor, making it the weather layer.
What is the difference between Hanging Amihan and Hanging Habagat?
These are the two major monsoon systems affecting the Philippines, bringing distinct seasonal weather patterns.
Which type of front brings violent weather and thunderstorms?
Cold fronts move faster and create more unstable atmospheric conditions, leading to severe weather phenomena.
What percentage of Earth's water is saltwater versus freshwater?
The vast majority of Earth's water is in the oceans, with only a small fraction being freshwater available for human use.
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