Chapter 5: Forms of Condensation and Precipitation
Water vapor's role in the Earth's weather is major. Its the product of evaporation. It is lifted up, condenses and forms clouds. It is also a greenhouse gas that is a major climate regulator. It usually makes up between 0.00 to 4.00% of the total atmosphere.
Water vapor's role in the Earth's weather is major (cont.) Water vapor once forming into clouds can act as insulation holding solar energy during the sun's absence at night limiting temperature drops.
Water vapor's role in the Earth's weather is major (cont.) The primary role is that it controls and regulates weather patterns in two ways 1. maintains constant climate temperate zones. 2. distributes weather cooling or warming weather patterns.
Cloud Formation
Cloud Formation A cloud is a visible aggregate of small water droplets.
How do we get water droplets in the atmosphere? We will consider our air parcel 10 0 C discussed in chapter 4 and examine the steps it must undergo to have water drops form in it. 20 0 C 30 0 C
We begin by establishing our in initial conditions 1. The air parcel has a temperature of 30 0 C. 2. The air parcel has an initial amount of water vapor. 3. The parcel will not mix with the environment and therefore: 10 0 C a. the amount of water vapor in the parcel will remain constant. b. no heat (energy) will be added to or taken away from the air parcel (adiabatic process). 20 0 C adiabatic process is one that occurs without transfer of heat or matter 30 0 C between a thermodynamic system and its surroundings
Now our air parcel begins to rise* 0 0 C 10 0 C 20 0 C As the air parcel ascends in the atmosphere It will cool at the dry adiabatic lapse rate 10 0 C per 1000 meters. 30 0 C The method by which the air parcel is lifted is not important for this example.
A Review of Relative Humidity As the temperature of air cools Its ability to hold water vapor decreases. The result is that the relative humidity of the parcel increases.
30 0 C Lifting condensation level 10 0 C Cloud base Once 100 % relative humidity is reached the water vapor 20 0 C 30 0 C condenses into water droplets.
What happens after condensation occurs? As condensation occurs heat is released into the parcel as it continues to rise in the atmosphere.
Adiabatic Temperature Changes above the lifting condensation level When air ascends above the lifting condensation level, the rate at which it cools is reduced. The slower rate of cooling is called the wet adiabatic rate which varies from 5 C/1000m to 9 C/1000m.
Cloud Formation
Cloud Formation
Cloud Formation Growth of cloud droplets: Hygroscopic (water-seeking) nuclei are most effective for condensation. Growth is rapid at first, then slows as water vapor is consumed.
Now we will examine the clouds
Cloud Classification Clouds are classified on the basis of two criteria. Form Height
Cloud Classification Form (3 TYPES): Cirrus are high, white, and thin. Cumulus clouds are globular, usually exhibiting a flat base. Stratus clouds are best described as layers covering much of the sky.
Cloud Classification Height (3 HEIGHTS + 1) High clouds are above 6000 m. Middle clouds range between 2000 6000 m. Low clouds are at altitudes of less than 2000 m Clouds of vertical development extend upward to span more than one height range.
All three forms cirrus, alto and stratus occur at all three altitudes, low, middle and high
High Clouds cirrus cirrostratus cirrocumulus
Middle Clouds Altocumulus Altostratus
Low Clouds Stratus Stratocumulus Nimbostratus
Clouds of Vertical Development Cumulus Cumulonimbus
Cloud Classification Internationally recognized 10 cloud types
Cloud Classification High clouds: Cirrus Cirrostratus Cirrocumulus Middle clouds: Altocumulus Altostratus Clouds of vertical development: Cumulonimbus Cumulus humilis Cumulus congestus Low clouds: Stratus Stratocumulus Nimbostratus
Cloud Classification Cloud varieties: Uncinus are hooked shaped clouds, often precursors to bad weather.
Cloud Classification Cloud varieties: Mammatus clouds have udder-shaped protuberances on their bottom surfaces and are associated with stormy weather.
Cloud Classification Cloud varieties: Fractus or fractured clouds are stratus or cumulus clouds that appear broken.
Cloud Classification Cloud varieties: Lenticular clouds are lens shaped and are common in rugged or mountainous topographies.
Concept Check 5.2 * 2. Why are high clouds always thin in comparison to low and middle clouds? High clouds are always thin because of the low temperatures and thus the small quantity of water vapor available at the altitudes where they form.
Give It Some Thought 2. Chapter 5 (pp 157). Which of the three basic cloud forms (cirrus, cumulus or stratus) is illustrated by each of the images below? a) cumulus; b) cirrus; c) cumulus; d) stratus; e) cumulus; f) stratus
How Precipitation Forms
How Precipitation Forms The Bergeron process (precipitation from cold clouds) depends on the coexistence of water vapor, liquid cloud droplets, and ice crystals.
How Precipitation Forms
How Precipitation Forms The collision-coalescence process precipitation from warm clouds located below the freezing level especially in the tropics. Small droplets hit other droplets and become larger. They collide with more droplets and their falling velocity increases.
How Precipitation Forms Q Problem # 4
Forms of Precipitation
Forms of Precipitation Rain is restricted to droplets of water with a diameter at least 0.5mm. Cloudbursts are unusually heavy rainfalls. Drizzle are fine, uniform droplets with a diameter less than 0.5mm. Virga is rain that evaporates above ground. Mist contains the smallest droplets.
Forms of Precipitation Snow is precipitation in the form of ice crystals or aggregates of ice crystals. Sleet is clear to translucent particles of ice, rain drops freeze while falling. Freezing rain (glaze) are rain drops that become super-cooled, hit a surface, and freeze immediately.
Forms of Precipitation Hail is precipitation in the form of hard, rounded pellets of ice. It is produced in cumulonimbus clouds. Hail stones begin as small ice pellets and grow as they are propelled by updrafts and downdrafts through the cloud.
Forms of Precipitation Rime is a deposit of ice crystals, formed on surface objects by super-cooled fog or cloud droplets. It occurs when the surface temperature of an object is below freezing.
Concept Check 5.11 * 2. What is different about how rain and snow are made? Rain is made at a below freezing temperature but falls into warm air and melts before reaching the ground. Snow is made at a below freezing temperature but falls into cold air and does not melt before reaching the ground.
Intentional Weather Modification Intentional weather modification, such as cloud seeding, is deliberate human intervention to influence processes that constitute the weather. Snow and rain making Silver iodide crystals act as freezing nuceli. Fog and cloud dispersal Cloud seeding with dry ice into super-cooled fog or stratus clouds helps to disperse them to improve visibility.
End Chapter 5