Physical Geography study guide // Exam 2

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### Atmospheric Moisture & Weather – Core Topics Explained

#### Humidity Concepts

* Relative Humidity (RH): Ratio (%) of the actual water vapor in the air to the maximum amount the air can hold at that temp.

* Specific Humidity (SH): Mass of water vapor per mass of air (g/kg); does not change with temp.

* Temp vs. RH: As air temp rises, RH drops (if SH stays the same). Warm air holds more moisture.

* Dew Point: Temp at which air becomes saturated (RH = 100%). A high dew point means high SH.

#### Daily RH Pattern

* Lowest in mid-afternoon (hottest part of day), highest around dawn (coldest time).

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### Fog & Cloud Formation

* Types of Fog:

* Radiation Fog: Forms overnight as ground cools.

* Advection Fog: Warm moist air over a cool surface (coastal).

* Upslope Fog: Moist air pushed uphill cools.

* Orographic Lifting:

* Air rises on windward side → cools → RH ↑ → condensation → clouds/precip.

* LCL (Lifted Condensation Level): Height where dew point is reached and clouds form.

* On leeward side: air descends, warms → RH ↓ → dry conditions.

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### Lifting Mechanisms

1. Orographic: Air lifted over mountains.

2. Convectional: Sun heats surface → warm air rises.

3. Frontal: Warm air forced over cold at fronts.

4. Convergent: Air flows toward low pressure → rises.

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### Clouds

* Cumulus: Puffy, fair weather.

* Stratus: Layered, overcast skies.

* Nimbostratus: Steady rain.

* Cumulonimbus: Thunderstorms, hail, lightning.

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### Precipitation Processes

* Collision-Coalescence: Common in warm clouds (tropics).

* Bergeron Process: Common in cold clouds; involves ice crystals growing at the expense of supercooled droplets.

* Hail: Forms in cumulonimbus clouds with strong updrafts cycling ice pellets.

* Lightning/Thunder: Charge separation in clouds → discharge (lightning), rapid heating causes thunder.

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### Latent Heat

* Released: During condensation, freezing, deposition → fuels storms.

* Absorbed: During evaporation, melting, sublimation → cools environment.

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### Air Masses & Fronts

* Air Mass Types:

* mT: maritime tropical (warm, humid)

* cT: continental tropical (hot, dry)

* mP: maritime polar (cool, moist)

* cP: continental polar (cold, dry)

* Fronts:

* Cold Front: Fast, steep slope; short, intense rain; temps drop after.

* Warm Front: Slower, gradual slope; long, steady rain; temps rise after.

* Occluded Front: Cold catches warm front; mix of weather.

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### Mid-Latitude Cyclones

* Structure: Low pressure system with warm and cold fronts.

* Movement: West to east (guided by polar jet stream).

* Rotation: Counterclockwise in Northern Hemisphere.

* Precip & Wind:

* Ahead of warm front: Light/moderate rain.

* At cold front: Thunderstorms possible.

* Behind cold front: Clearer, cooler.

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### Thunderstorms

* Three Stages:

1. Cumulus: Rising warm air; updrafts dominate.

2. Mature: Up & downdrafts; most intense weather.

3. Dissipating: Downdrafts dominate, storm dies out.

* Cloud: Cumulonimbus.

* Duration: Typically 30 mins to a few hours.

* WA Connection: West side cooler, more stable (less storms); East side warmer, drier (more storms with lifting).

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