Atmospheric Sciences - Weather, Climate, and Prediction Models

Earth's Atmosphere

Layers of Earth's Atmosphere

  • Troposphere: The layer we live in, where weather occurs.
  • Stratosphere: Contains the ozone layer, which filters UV radiation.
  • Mesosphere: The middle layer, characterized as the coldest.
  • Thermosphere: The outer edge of the atmosphere, very hot, and where satellites and space shuttles are located.

Atmospheric Pressure

  • The atmosphere is held in place by Earth's gravity.
  • Air pressure is affected by elevation, humidity, and temperature.
    • Altitude increase = air pressure decrease
    • Temperature increase = air pressure decrease
    • Humidity increase = air pressure decrease
  • Measured using a barometer.

Atmospheric Temperature

  • As altitude changes, temperature varies:
    • Troposphere: Temperature decreases with altitude.
    • Stratosphere: Temperature increases with altitude.
    • Mesosphere: Temperature decreases with altitude.
    • Thermosphere: Temperature increases with altitude.

The Water Cycle

  • Water is constantly cycled throughout Earth in various forms: solid (ice), liquid (water), gas (water vapor/steam).
  • Evaporation: Liquid water changes into water vapor (gas).
  • Condensation: Water vapor cools and changes from a gas to a liquid; clouds form by this process.
  • Precipitation: Rain, snow, sleet, or hail falls from clouds onto Earth's surface.
  • Runoff: Water flows across land and collects in rivers, streams, and eventually the ocean.

Humidity

  • Relative Humidity: Percentage of water vapor in the air compared to the maximum vapor potential at that temperature.
    • Relative\ Humidity = \frac{actual \ H2O \ in \ air}{H2O \ potential \ of \ air} \times 100\%%
  • Warm air holds more water.
  • Cold air holds less water.

Dew Point

  • The temperature to which air must be cooled for water vapor to condense into liquid.
  • If relative humidity is 100%, then dew point = actual temperature.

Condensation

  • Process by which a gas turns into liquid.
  • Water vapor condenses as air temperatures cool.
  • Condensation is visible in the form of clouds.
  • Clouds form as warm, moist air rises.

Cloud Types

  • Cumulus: Puffy, white clouds with flat bottoms (vertical motion).
  • Stratus: Layered, low altitude clouds (horizontal motion).
  • Cirrus: Thin, feathery, white, high altitude clouds, made of ice crystals.

Clouds and Weather

  • Poor weather:
    • Cumulus and stratus clouds produce precipitation.
    • Root word "nimbus" or "nimbo" indicates clouds that produce precipitation.
      • Cumulonimbus: thunderstorms and severe weather.
      • Nimbostratus: light, long-lasting precipitation.
  • Fair weather:
    • Cirrus clouds indicate good weather.

Global Winds

Why Air Moves

  • Differences in pressure.
  • On a global scale, air rises at the equator and sinks at the poles, creating high pressure at the poles and low pressure at the equator, due to convection.
  • Pressure belts every 30°: bands of high and low pressure.

Coriolis Effect

  • Curving of the path of currents due to Earth's rotation.
  • Both air and water are subject to this effect.
  • Earth's winds do not blow in straight paths; instead, they are deflected.
    • Clockwise in the Northern Hemisphere.
    • Counterclockwise in the Southern Hemisphere.

Types of Global Winds

  • Polar Easterlies: Wind belts from the poles (90°) to 60° latitude in N & S hemispheres (East to West).
  • Westerlies: Wind belts found between 30° and 60° in N & S hemispheres (West to East).
  • Trade Winds: Wind blowing from 30° to the equator in N & S hemispheres (East to West).

Jet Streams

  • Act like conveyor belts.
  • Current of fast-moving air in the upper troposphere and lower stratosphere.
  • The location of the jet stream marks large temperature contrast.
  • Winter: strong jet streams.
  • Summer: weak jet streams.

Climate Zones/Biomes

  • Low-latitude: Equator - 25°N & S
    • Rainforest: High humidity, heavy precipitation, constant high temperatures (e.g., Amazon, Congo, Indonesia).
    • Savanna: Seasonal changes from wet to dry, and hot to slightly cooler (e.g., India, S. Africa, S. America).
    • Desert: Low humidity, low precipitation, high day temp, lower night temp (e.g., N & S Africa, Mexico, Australia).
  • Mid-latitude: 30°-55° N & S
    • Steppe: Grasslands, semi-arid, warm/hot summer, cold winter (e.g., Great Plains, Gobi Desert).
    • Mediterranean (Chaparral): Wet winter, dry summer (e.g., California, Mediterranean, Chile, Cape Town).
    • Grasslands: Dry, cold winter, warm summer (e.g., Great Basin, interior Europe).
    • Deciduous Forest: Huge temperature swings from summer to winter, wet (e.g., eastern US, Canada, Korea, Japan, Eastern Europe).
  • High-latitude climates
    • Taiga: Interior, long, frigid winter, short, cool summer, little precipitation, largest temperature range of any zone (e.g., Alaska, Canada, N Europe, Siberia).
    • Tundra: Coastal, long, cold winter, short, mild season, very little precipitation (e.g., Hudson Bay, Greenland).
    • Alpine: Cool/cold, mountains/high plateaus, moderate temperatures similar to surrounding zones (e.g., Rocky Mountains, Alps, Himalayas, Andes).

Koeppen's Climate Classification

  • Includes Tropical (A), Dry (B), Temperate (C), Cold (D), and Polar (E) climates.

Local Winds

High Pressure Systems (Anticyclones)

  • Located where measured air pressure is highest compared to surroundings.
  • Indicated on a weather map by a blue "H".
  • Winds flow clockwise around a high-pressure center in the northern hemisphere and counterclockwise in the southern hemisphere.
  • Sinking air prevents cloud formation and precipitation, resulting in fair weather.

Low Pressure Systems (Cyclones)

  • Located where measured air pressure is lowest compared to surroundings.
  • Indicated on a weather map by a red "L".
  • Winds flow counterclockwise around a low in the northern hemisphere and clockwise in the southern hemisphere.
  • Rising air facilitates the development of clouds and precipitation.

Air Masses

  • Large bodies of air with similar temperature and moisture properties.

  • Five basic types of air masses determine the USA's weather:

    • Continental Arctic (CA): Extremely cold temperatures and very little moisture.
    • Continental polar (CP): Cool and dry, but not as cold as Arctic air masses.
    • Maritime polar (MP): Cool and moist.
    • Maritime tropical (mT): Warm temperatures with copious moisture.
    • Continental Tropical (CT): Hot and very dry.

Fronts

  • Clashing air masses spark weather events; the boundaries are known as FRONTS.

Cold Fronts

  • Cold air moves under warm air.
  • Moves from NW to SE.
  • Air behind cold front is colder and drier than the air it replaces.

Characteristics Associated with Cold Fronts

  • Winds:
    • Before Passing: South-southwest.
    • While Passing: Gusty, shifting.
    • After Passing: West-northwest.
  • Temperature:
    • Before Passing: Warm.
    • While Passing: Sudden drop.
    • After Passing: Steadily dropping.
  • Pressure:
    • Before Passing: Falling steadily.
    • While Passing: Minimum, then sharp rise.
    • After Passing: Rising steadily.
  • Clouds:
    • Before Passing: Increasing Ci, Cs, and Cb.
    • While Passing: Cb.
    • After Passing: Cu.
  • Precipitation:
    • Before Passing: Short period of showers.
    • While Passing: Heavy rains, sometimes with hail, thunder, and lightning.
    • After Passing: Showers, then clearing.
  • Visibility:
    • Before Passing: Fair to poor in haze.
    • While Passing: Poor, followed by improving.
    • After Passing: Good, except in showers.
  • Dew Point:
    • Before Passing: High; remains steady.
    • While Passing: Sharp drop.
    • After Passing: Lowering.

Warm Fronts

  • Warm air moves over cold, dense air.
  • Move from SW to NE.
  • Air behind warm front is warmer and more humid than air it replaces.

Characteristics Associated with Warm Fronts

  • Winds:
    • Before Passing: south-southeast
    • While Passing: variable
    • After Passing: south-southwest
  • Temperature:
    • Before Passing: cool-cold, slow warming
    • While Passing: steady rise
    • After Passing: warmer, then steady
  • Pressure:
    • Before Passing: usually falling
    • While Passing: leveling off
    • After Passing: slight rise, followed by fall
  • Clouds:
    • Before Passing: in this order: Ci, Cs, As, Ns, St, and fog; occasionally Cb in summer
    • While Passing: stratus-type
    • After Passing: clearing with scattered Sc; occasionally Cb in summer
  • Precipitation:
    • Before Passing: light-to-moderate rain, snow, sleet, or drizzle
    • While Passing: drizzle or none
    • After Passing: usually none, sometimes light rain or showers
  • Visibility:
    • Before Passing: poor
    • While Passing: poor, but improving
    • After Passing: fair in haze
  • Dew Point:
    • Before Passing: steady rise
    • While Passing: steady
    • After Passing: rise, then steady

Severe Weather

Thunderstorms

  • Strong/severe storm that produces lightning and thunder.
  • Lightning: Electric discharge up to 54,000°F
  • Thunder: Shockwave produced by lightning.
  • Also produce hail, high winds, flash floods, and tornadoes.

Tornadoes

  • Spinning column of air with high wind speeds and low pressure that touches the ground.
  • Form when a funnel cloud pokes out the bottom of a cumulonimbus cloud and becomes a tornado when it touches the ground.
  • Measured using the Fujita Scale (1-5) based on damage.

Hurricanes

  • Form from a series of thunderstorms over tropical water.
  • Winds in different directions cause storms to spin.
  • Wind speeds range from 120-150 km/hr.
  • Measured using the Saffir-Simpson Scale (1-5) based on winds and storm surge.

Recap

Weather versus Climate

  • The difference between weather and climate is a matter of time.
  • Weather refers to short-term changes in the atmosphere (minute-to-minute, hour-to-hour, and day-to-day).
  • Climate describes the average weather conditions in a specific area over a long period of time (30 years or more).