15-1    Changes of state:

1. Common states: Solid, liquid, and gas

   

2. Where is the heat? Heat stored, called latent heat.

3. Melting point: the temperature at which solid changes into liquid.

4. Boiling point: the temperature at which liquid changes into gas.

   • At melting point and boiling point: temperature remains constant.

5. To maintain T constant at M. P. and B. P., heat is wither absorbed from the environment or released to the environment.

15-2    Humidity:

1. Vapor pressure: water has vapor, vapor contribute to pressure. When equilibrated at a particular T, if water evaporation = water condensation ==> saturation of water vapor in air. It is T dependent. As T increases, saturation increases.

2. Humidity: describe the amount of water vapor per amount of air.

3. Specific humidity:

4. Relative humidity (R. H.): water vapor content of air divided by maximum water vapor content of the air, e.g. at 85 F, max water vapor content = 26.5 g. If air has 13.3 g of water, the relative humidity = 13.5/ 26.5 = 0.5 = 50 %.

5. Changes in R. H.: R. H. is a function of T. As the T increases, R. H. decreases. E. g. at 68 F, maximum water vapor content = 14 g. If the air has 13.5 g of water vapor, the relative humidity = 13.5/14 = 100 %. 

6. Dew point: the T at which R. H. = 100 %.

7. Measurement: one type: use the hair length. Longer when R. H. is high. The other type: use evaporation of water to cool a thermometer.

15-3    Clouds:

1. Adiabatic temperature change:

   • When air compressed, T increases, and when air expanded, T decreases. The former can be felt by pumping a bicycle and the latter by release of a balloon.

   • For unsaturated air: when air goes up, P decreases, thus, air expand, thus T decreases. Therefore, T decreases by 10 degrees per 1000 m.

   • For saturated air: air is already at dew point, heat due to condensation is released, which offset the soling rate. Therefore, T decreases 5 degrees per 1000 m.

2. Cloud formation:

   • Like fog and dew, due to saturation of water moisture and condensation of water molecules, cloud forms due to adiabatic temperature changes.

3. Stable air vs. unstable air:

   • Environmental lapse rate: T decreases in the troposphere ~ 6.5°C/1000 m. Varies. Dry adiabatic rate is: ~ 10°C/1000 m, while wet adiabatic rate is: ~ 5°C/1000 m. Fig 15.9. So, as the air heated up, it rises. As it rises, it cools adiabatically.

   • Stable Fig. 15.11: Dry air. Air at 25°C at the surface. At 1000 m, outside the cloud, the T is 20°C, due to environmental lapse rate. But inside the cloud, it is 15°C, due to dry air rate. Thus, it has tendency to sink. Therefore, air doesn't rise infinitely ==> Stable.

   • Absolute stability: Environmental lapse rate < wet adiabatic rate, e.g. Fig. 15.12. Thus, as air rise the difference between T inside and outside a cloud gets bigger.

   • Temperature inversion: Atop warm air above a cool air, e.g. Fig. 15B. Warm air behave as a cover to prevent air rise further.

   • Absolute instability: Environmental lapse rate > dry air rate. Fig. 15.13, in this case, air keeps rising.

   • Conditional instability: Wet adiabatic rate < environmental lapse rate < dry adiabatic rate. In this case, the cloud is stable when air is not saturated, but not stable when air is saturated. Fig. 15.14.

   • Summary: stable: resist vertical movement. Unstable: rise vertically.

15-4    Air lifting process:

1. Orographic lifting: Mountains behaves as a barrier, air lift when meet with the mountain. Fig. 15.16. Typical, e.g. Mt. Olympic. Consequences: windward: wet, precipitation on mountain; leeward: dry, desert.

2. Frontal wedging: when warm air meets with cool air, warm air wedge up, often associated with precipitation. Fig. 15.18.

3. Convergence: Two air masses flow toward each other, resulting lift, e.g. Florida.

15-5    Air Cloud formation:

To form cloud, fog, or dew, saturation reaches first.

1. Two ways to cause saturation: (a) when air temperature decreases; (b) when more water vapor introduced.

2. Supersaturation vs. condensation: When relative humidity ~ 100 %, water vapor reaches saturation, but to form condensation (like dew drops) nuclei needed. Otherwise, the relative humidity > 100% is needed to cause condensation.

3. Types of nuclei: microparticles and dusts. They are hydroscopic (means like water). Initial droplets are tiny, gravitational pulling is negligible.

4. Cloud: consists of water droplets, ice crystals (if T < 0°C), or both.

15-6    Types of clouds:

• Based on forms and heights.

  • Forms: 

    • Cirrus: thin, thread or veil like.

    • Cumulus: globular mass, tall.

    • Stratus: sheet or layers.

  • Height: 

    • High cloud: > 6000 m.

    • Mid cloud: 2000-6000 m.

    • Low cloud: < 2000 m.

  • Combination of different forms allowed, e.g. cirrocumulus, cirrostratus, etc.

• High cloud: associated with cirro. 

  • T low, moisture low.

  • thin and white.

  • not precipitation maker.

• Middle cloud: alto as prefix.

• Low cloud: 

  • thicker and gray.

  • associated with precipitation.

  • nimbostratus: cloud causing large area rain.

  • cumulonimbus: cloud causing T-storm.

• Nimbus: rain.

15-7    Fog:

A type of special cloud whose base is near the surface.

Types of fog:

1. Advection fog: warm, moist air over cool surface, e.g. fog in Oregon. Warm air from Pacific over cold current ==> fog ==> wind carried to land.

2. Radiation fog: occurs at night. T decreases due to radiation, dissipation of heat, air cool, and reach due point. Form fog pockets in low area.

3. Due to addition of moisture: over lake in Fall, water warm, produced warm air, meeting cold air and fog forms below cold air.

15-8    Precipitation:

1. Bergeron Process: due to supercooling and supersaturation.T of water is below 0°C. Why not ice? due to lack of nuclei for crystallization. Under this condition, the relative humidity is > 100 % with respect to ice. Thus, ice grows bigger and consume more water from vapor. Fig. 15.24. 

   • Results: ice crystals get bigger and water droplets get smaller. As crystal size grow big, free fall starts to form precipitation. If the T > 0°C, form rain, otherwise, snow.

2. Collision-coalescence process: large droplets coalescence smaller droplets for form even larger one. If too large, > 5 mm, they break. Fig. 15.25.

15-9    Types of precipitation:

1. Rain drizzle: depending on rain drop size. Rain > 0.5 mm.

2. Snow: ice crystals. As T decreases, moisture decreases, not enough water to crystallize ==> fluff snow.

3. Sleet: T at upper layer is > 0°C. Thus, water droplets form. But bottom layer cold ==> sleet forms.

4. Hail: upward movement of cloud faster to hold large particles against the gravitational force.

Homework:

• Read chapter summary on p.436.

• Use your own word to explain the key terms on page 437.

• Answer the review questions on page 437.