Humidity and Adiabatic Processes

• Evaporation cools the environment, while condensation warms it.
• Evaporation rate is affected by air/water temperature, air saturation, and windiness.

Measures of Humidity

• Absolute humidity is the weight of water in a given volume of air, changing with altitude.
  • It's calculated as the mass of water vapor divided by the volume of air.
• Specific humidity is the weight of water in a given weight of air.
  • It's calculated as the mass of water vapor divided by the total mass of air.
• Relative humidity is the percentage of water in air compared to saturation.
  • Water Vapor Content/Water Vapor Capacity = Actual Vapor Pressure/ Saturation Vapor Pressure x 100%
• Temperature and water amount differences influence relative humidity.
• Condensation can occur at high temperatures when vapor pressure reaches saturation.

Adiabatic Processes

• Rising or falling air experiences temperature changes.
• As altitude increases:
  • Temperature, pressure, and density decrease.
  • Relative humidity and air volume increase.
• Air expansion leads to temperature drops.
• Windward sides involve air rising under dry and wet adiabatic conditions.
• Leeward sides involve air descending under dry adiabatic conditions.

Vapor Pressure and Boiling

• Higher altitudes increase cooking times.
• The boiling point of water changes with atmospheric pressure.

Conditions for Condensation

• Air must be saturated (RH=100%).
• A surface must be available for condensation.

Formation of Fog

• Radiation Fog:
  • Forms near the ground on clear, calm nights.
  • Ground heat loss cools the air above it to the dew point, causing condensation.
• Advection Fog:
  • Warm, moist air moves horizontally over a cold surface.
  • Cooling causes the air to reach its dew point, forming fog.
• Upslope Fog:
  • Moist, stable air is pushed uphill by wind.
  • Air expands and cools to its dew point, forming fog along the slope.
• Evaporation Fog:
  • Cold air passes over a warmer, moist surface.
  • Water evaporates, mixes with cooler air, and reaches the dew point.

Cloud Types

• Cirriform, Stratiform, and Cumuliform are common cloud patterns.
• Thunderstorms come from Mesocyclone clouds.
• Clouds are categorized by altitude: high, middle, low, and vertical development.

Forms of Precipitation

• Includes rain, snow, sleet, and hail.
• Collision and coalescence of water droplets is responsible for droplet growth.
• Droplet form shape is not tear drop, but circular.
• Precipitation type depends on the time the snow or droplet is falling.

Causes of Lifting Air and Precipitation

• Convective Lifting: Warm, moist air rises.
• Orographic Lifting: Air rises due to elevation on the windward side.
• Convergence of Air: Low pressure causes air to rise.
• Frontal Lifting: Air rises along frontal boundaries.

Converging and Diverging Air

• Strong Cyclone: Upper-level divergence exceeds surface convergence, lowering surface pressure.
• Weak Cyclone: Upper-level divergence is less than surface convergence, increasing surface pressure.
• Strong Anticyclone: Upper-level convergence exceeds low-level divergence, increasing surface pressure.
• Weak Anticyclone: Upper-level convergence is less than low-level divergence, decreasing surface pressure.

Air Mass Source and Classification

• Air Mass: Large air body with similar temperature and moisture.
• Two-letter codes:
  • First letter: 'm' (maritime, moist) or 'c' (continental, dry).
  • Second letter: E (Equatorial, very warm), T (Tropical, warm), P (Polar, cold), A (Arctic, very cold).
• Examples: cT (Continental Tropical), mE (Maritime Equatorial).

Fronts

• Fronts separate air masses and do not readily mix.
• Fronts are sloping boundaries where warmer, lighter air rises over cooler, denser air, causing frontal uplift.

Types of Fronts

• Warm Front:
  • Warm air mass invades a colder region.
  • Gentle slope, less violent weather.
• Cold Front:
  • Cold air mass moves into a warmer air mass.
  • Steeper slope, sharp changes in temperature, pressure, and wind.
  • Can cause heavy precipitation and violent thunderstorms.
• Stationary Front:
  • Frontal boundary with little movement due to small temperature and pressure gradients.
  • Light wind and precipitation, overcast conditions.
• Occluded Front:
  • Cyclonic systems.

Movement and Modification of Air Masses

• Changes when air mass moves away from source region:
  • Thermal modification
  • Dynamic modification
  • Moisture addition or subtraction.

Major Atmospheric Disturbances: Extratropical Cyclones

• Mid-latitudes cyclone are the battle ground for air masses.
• Move within the Westerlies.
• Cold front moves faster.
• Life cycle of 4 to 7 days.

Major Atmospheric Disturbances: Hurricanes

• Tropical Depression: Winds less than 36 mph.
• Tropical Storm: Winds between 36-74 mph.
• Hurricane: Winds greater than 74 mph.
• Low-pressure center with strong cyclonic winds spiraling inwards.
• Smaller than extratropical cyclones (100-600 miles diameter).
• Eye diameter is 10-25 miles.
• Energy from latent heat evaporated from tropical oceans.
• Require warm ocean water (>27°C to 50m deep), weak vertical wind shear, and position >8° N/S.
• Hurricanes never form over the Equator due to the lack of the Coriolis effect.
• Hurricanes weaken over land due to lack of warm water.

Coriolis Effect

• Earth's rotation that influences hurricanes.
• Hurricane-free ocean areas: E. South Pacific Ocean, South Atlantic, and Equator due to cold water. Hurricane season peaks in August, September, and October.
• Hurricanes are measured on a 1-5 category scale.
• Hurricane Names:
  • Australia: Willy-Willy
  • Caribbean: Hurricane
  • Haiti: Taino
  • Indian Ocean: Cyclone
  • Philippines: Baguio
  • S. Pacific: Typhoon
• Hurricane names are reused every seven years and alternate
• Hurricane structure is a eye with clear sky, and the eye wall has the highest wind speed.

Hurricane Development

• Develop over warm ocean areas, not over the Equator, South Pacific Ocean, and South Atlantic Ocean.
• Mid-latitude cyclones develop over land.
• Necessary Ingredients:
  • Ocean water > 27°C to 50 meters deep.
  • Weak vertical wind shear.
  • Position >8 degrees N/S.

Anatomy Terms

• Eye: Patch of clear sky.
• Eye Wall: Violent, destructive, intense low-pressure system.

Intensity Scales

• Tornado: Enhanced Fujita Scale
• Hurricane: Saffir-Simpson scale/ Category

Minor Disturbances: Tornados and Thunderstorms

• Tornado Ally is centered in: Texas, through Oklahoma, Kansas, Nebraska, South Dakota, Iowa.
• Seasonal Tornado Activity:
  • Deep South: JAN/FEB/MAR
  • Ally: APR/MAY/JUN
  • Mid: JUL/AUG/SEPT

Thunderstorm Development

• Cumulus stage: Heated air rises.
• Mature stage: Up and down drafts.
• Dissipating stage: Descending air.
• Microburst: Sudden, powerful, localized air current.

Lightening

• Earth's surface has a positive charge.
• Ice crystals in the top of a thunderstorm cloud have a positive (+) charge, while hailstone below have a negative (-) charge.
• Electrical flow rushes toward earth when the negative charge is large enough to overcome air resistance.