Lab 6: Moisture and Forms of Condensation

Forms of Condensation

Water Molecule Properties

• Chemical Formula: H₂O
• Polarity: Water is a polar molecule, leading to unique properties like high surface tension.
• Transparency: High transparency allows sunlight penetration.
• Specific Heat: High specific heat capacity enables water to absorb a lot of heat without significant temperature changes.
• Surface Tension: Water has high surface tension due to hydrogen bonding.
• Dissolving Power: Water is known as the "universal solvent" because it can dissolve many substances.
• Mobility: Water molecules can move easily in different states.
• Latent Heat: High latent heat implying significant energy release or absorption during phase changes.
• Density: Maximum density occurs at 39ºF.
• States in Atmosphere: Can coexist as solid, liquid, or gas at various temperatures.
• Liquid at Low Temperatures: Can remain liquid at temperatures as low as -40ºF.

Humidity Concepts

Relative Humidity (RH)

• Definition: Ratio (%) of water vapor present in the atmosphere.
• Formula: RH = \frac{MR}{C} where:
  • MR = Mixing Ratio: actual amount of water vapor in air
  • C = Capacity: maximum amount of water vapor air can hold at a certain temperature
• Relationships:
  • Lower temperature results in lower capacity for water vapor.
  • Higher temperature results in higher capacity for water vapor.

Dew Point

• Definition: The temperature at which air must be cooled to reach full saturation (100% RH).

Mixing Ratio and Capacity

• Mixing Ratio (MR): Actual water vapor amount in air.
• Capacity (C): Maximum water vapor amount the air can hold.
• Examples of Calculating RH, C, MR:
  • Given MR of 20 g/kg and C of 57 g/kg, calculate RH:
  • [ RH = \frac{20}{57} \approx 0.351 \text{ or } 35\% ]
  • Given RH of 15% and MR of 43 g/kg, calculate C:
  • [ C = \frac{MR}{RH} = \frac{43}{0.15} = 286.67 \text{ g/kg} ]
  • Given RH of 77% and C of 103 g/kg, calculate MR:
  • [ MR = RH * C = 0.77 * 103 = 79.31 \text{ g/kg} ]

Capacity of Saturated Air

• Example values showing varying capacities based on temperature:
  • -40°F: 0.113 g/kg
  • 70°F: 15.810 g/kg
  • 80°F: 21.537 g/kg
  • 90°F: 30.052 g/kg

Dew Point Calculation Using Capacity Chart

• Determine the dew point by matching the closest mixing ratio from a chart to find its associated temperature.
• Example: Mixing ratio of 8.200 g/kg; dew point = 53°.

Phase Changes of Water

Key Processes

• Sublimation: Ice (solid) changes directly to water vapor (gas).
• Condensation: Water vapor (gas) changes to liquid water.
• Deposition: Water vapor (gas) changes to ice (solid).

Dew and Frost

• Dew: Forms through condensation when temperature drops and air cannot hold moisture.
• Frost: Forms through deposition under freezing temperatures (≤ 32°F).

Types of Precipitation

Hail

• Forms in cumulonimbus clouds; consists of layers of ice due to repeated updrafts and downdrafts.

Snow

• Solid precipitation converting directly from water vapor to ice crystals, forming branched flakes.

Fog

• Definition: A suspension of water droplets and/or ice crystals near the Earth's surface.
• Fog is formed by non-adiabatic processes and is not classified as a cloud.

Types of Fog

• Radiation Fog: Forms from radiational cooling in low areas, dissipating as temperature rises.
• Advection Fog: Occurs when warm, moist air moves over a cold surface, often persistent.
• Steam Fog: Forms over warm water when overlain by colder air (e.g., lakes in fall).

Cooling Mechanisms

1. Radiational: Surface loses heat, emitting radiation.
2. Conductional: Warm air moves over cooler surfaces.
3. Mixing: Warm surface air combines with cooler air aloft.
4. Adiabatic: Cooling occurs due to air expansion as it rises in the atmosphere.