Forms of Condensation and Precipitation
CHAPTER 5: FORMS OF CONDENSATION AND PRECIPITATION
INSTRUCTOR: DR. BAYRON
ENERGY IN PHASE CHANGES
Key Phase Changes:
Sublimation: Transition from solid to gas.
Melting: Transition from solid to liquid.
Evaporation: Transition from liquid to gas.
Deposition: Transition from gas to solid.
Freezing: Transition from liquid to solid.
Condensation: Transition from gas to liquid.
Energy Dynamics:
Energy Absorbed/Gained: During phases of melting, evaporation, and sublimation.
Energy Released/Lost: During phases of freezing, condensation, and deposition.
WHAT IS SATURATION AND HOW DOES IT OCCUR?
Saturation Definition: Describes a state in the atmosphere where the air cannot hold any more water vapor (100% relative humidity).
Ways Saturation is Reached:
Cooling the Air:
Commonly achieved through adiabatic cooling (air rises and cools).
Adding Moisture:
Occurs when a cool, unsaturated air mass moves over a warm body of water.
Lifting Condensation Level (LCL):
Height in the atmosphere where air reaches saturation, leading to cloud formation (100% Relative Humidity).
WHAT ARE CLOUDS AND HOW DO THEY GROW?
Definition of Clouds: A collection of small liquid water droplets and solid ice crystals suspended in the atmosphere.
Formation Process:
Almost all clouds form by heterogeneous nucleation: water vapor condensing or depositing onto small existing solid particles in the atmosphere known as cloud condensation nuclei.
NUCLEATION
Homogeneous Nucleation:
Refers to condensation, freezing, or sublimation occurring without a surface ("out of thin air").
Heterogeneous Nucleation:
Requires less energy barrier to overcome compared to homogeneous nucleation.
TYPES OF CLOUDS
Cloud Classification: Based on form (shape) and height.
Cumulus: Globular, puffy clouds resembling cotton balls.
Stratus: Clouds that form sheets or layers covering much or all of the sky.
Cirrus: High, thin, white clouds forming delicate veil-like patches or wisplike strands.
Alto- and Nimbo-: Prefixes/suffixes indicating middle level or rain clouds.
CLOUD GROUPS
High Clouds (Above 6000 m or 20,000 ft):
Cirrus: Fibrous trails.
Cirrostratus: Smooth clouds producing halos around the sun.
Cirrocumulus: White patches or globules in ripples.
Middle Clouds (2000-6000 m or 6500-20,000 ft):
Alto-cumulus: Rounded masses or rolls larger and denser than cirrocumulus.
Alto-stratus: Grayish clouds which may produce light rain.
Low Clouds (0-2000 m or 0-6500 ft):
Stratus: Light gray clouds blanketing the sky.
Stratocumulus: Long parallel rolls, broken patches.
Nimbostratus: Clouds covering the sky, bringing moderate rain.
Clouds of Vertical Development:
Cumulus: Puffy cotton ball-like masses formed under clear conditions.
Cumulonimbus: Dense, billowy clouds forming tall towers, associated with severe weather.
WEIRD CLOUD FORMATIONS
Lenticular Clouds:
Form due to moist air moving over mountainous terrain, causing standing wave turbulence that forms clouds at wave crests.
Arcus Clouds:
Form from gust fronts of thunderstorms or shallow cool air currents from sea breezes or cold fronts.
Mammatus Clouds:
Poorly understood, possibly form from localized evaporation pockets leading to cooling and sinking within clouds.
CONTRAILS
Form from condensation or deposition of water vapor in jet engine exhaust encountering much cooler atmosphere.
WING CLOUDS
Low pressure above wings results in temporary temperature decrease, leading to condensation and temporary wing clouds.
CLOUDS IN SPACE
Jupiter:
Great Red Spot, approximately two Earth diameters wide, over 300 years old, mainly composed of ammonia and water.
Neptune:
Great Dark Spot, similar in size to Earth, thought to exist for shorter periods than Jupiter's Great Red Spot, with dark color possibly from methane cloud holes.
Venus:
Clouds composed of sulfuric acid; majority of atmosphere is carbon dioxide; atmospheric height is 160 miles; greenhouse effect makes it the hottest planet.
TYPES OF FOG
Overview: Fog is defined as a cloud with its base at or near the ground with no structural or appearance differences from clouds.
Evaporation Fog: Formed by addition of water vapor.
Steam Fog: Occurs when cool air moves over warm water, causing saturation and fog formation, commonly seen over lakes and rivers on crisp fall mornings.
Frontal Fog: Formed when warm, moist air rises over cooler, drier air, generating fog through evaporated raindrops.
Cooling-Induced Fog Types:
Radiation Fog: Develops from ground cooling on clear nights, dissipates after sunrise.
Advection Fog: Occurs when warm, moist air moves over cold surfaces, causing condensation.
Upslope Fog: Forms when warm, moist air rises over landforms or steep mountains, cooling adiabatically to produce fog.
PRECIPITATION FROM COLD CLOUDS
Freezing Dynamics: Most atmospheric water doesn't freeze at 0°C; pure water doesn't freeze until approximately -40°C.
Supercooled Water: Water in liquid state below 32°F, which freezes upon contact with solid particles.
Temperature Ranges and Cloud Composition:
$0$ to $-15$ °C: Supercooled water droplets.
$-15$ to $-40$ °C: Supercooled water droplets mixed with ice crystals.
$<-40$ °C: Ice crystals only.
Bergeron Process: Ice crystals in cold clouds grow by freezing and deposition, forming snowflakes that fall when too large to remain suspended. Type of precipitation determined by surface temperature.
PRECIPITATION FROM WARM CLOUDS
Collision-Coalescence Process: Growth of water droplets in warm clouds (> -15°C), involving multiple collisions of tiny cloud droplets coalescing into raindrops.
TYPES OF PRECIPITATION
Measurement of Droplet Size:
Mist: 0.005 - 0.05 mm diameter.
Drizzle: 0.05 - 0.5 mm diameter.
Rain: 0.5 - 5 mm diameter.
Virga: Rain that completely evaporates before reaching the ground.
CLOUD BURST & MEASURING RAINFALL
Cloudburst Records:
Documented events of extreme rainfall in short time frames, with notable instances and rainfall totals detailed.
Rainfall Measurement Methods:
Various Gauge Types: Simple, standard, tipping-bucket gauge measurements with formulas for calculating rainfall height.
Doppler Radar: Determines storm intensity and structure by sending radio wave pulses, useful for short-term forecasting; limitations include lack of ocean coverage.
Satellite Detection: Used to measure rainfall from space, tracking hurricanes and processes over oceans.
PLANNED WEATHER MODIFICATION
Methods that can increase precipitation by about 10% through cloud seeding, requiring supercooled water droplets and hygroscopic particles.
INADVERTENT WEATHER MODIFICATION
Contrails: May affect temperature variations.
Industrialization: Increases particulate matter, leading to higher cloudiness and precipitation in urban areas and downwind.