Like this study set? Create a free account to save it.

Sign up for an account

Already have a Quizlet account? .

Create an account

Simplified precipitation process

H2OV ------> liquid water (Clouds)--------> precipitation

cloud droplet size
compared to raindrop?

-avg. size is about 20 microns in diameter & fall very slowly, 1000 m/48 hrs; usually evaporate
-1 raindrop = about 1 million cloud droplets

how do cloud droplets avoid evaporation?

they must coalesce (join together to form a raindrop)

2 mechanisms to explain precipitation formation:

1) Bergeron Process: or Ice-Crystal Process
2) Collision-Coalescence Process

Bergeron Process

-discovered by a Swedish meteorologist, Tor Bergeron in early 1930's
-primarily process for forming rain in the mid and high latitudes

2 properties of water that the Bergeron Process uses

1. pure water in the air doesn't freeze until -40 degrees C
2. saturation vapor pressure over ice crystals is much lower than over suspercooled(water<0 degree C) liquid water

other conditions needed for Bergeron Process

-need freezing nuclei to initiate deposition of water vapor
-need T°'s below -10°C; at T°'s between -10° & -20°C will have both liquid drops & ice crystals
-difference in vapor pressure allows for supersaturation to exist; RH's > 100%

what happens under supersaturation conditions?

-ice crystals collect more water vapor than they lose & thus grow
- as they grow, may break-up & these pieces act as freezing nuclei to make more ice crystals
-these join to make snow crystals & then snowflakes

Collision-Coalescence Process

-primary process in tropics for rain drop formation
-need larger cloud droplets to form "large" condensation nuclei or hydroscopic nuclei
-small droplets don't coalesce & collide by themselves very well
-max size of a raindrop =5mm; if it gets bigger then it gets pulled apart by friction
-this process is the idea behind cloud seeding.

Fall or Terminal Velocities of Rain

Type Diameter Velocity
(mm) (kph) (mph)
Typical cloud
droplet .02 04 .03
Drizzle .5 7 4
Raindrop 2 - 5 23 - 33 14 - 20

precipitation types

-freezing rain


at least .5 mm to 5 mm in size; from nimbostratus and cumulonimbus clouds

following Bergeron Process
frozen(cloud)-------melts ---------> liquid (before it hits ground)

following collision coalescence process
frozen(cloud)--------------> liquid (as it hits ground)


1 - 2 mm in size; water vapor deposited as ice crystals that stay frozen

Bergeron Process only

frozen(cloud)----------> frozen (as it hits ground)

equivalent of snow to rain

10 inches of snow =1 inch of rainfall
(does vary with heaviness of snow)


0.5 - 5 mm in size; freezes as it falls and is a frozen raindrop before it hits the ground

frozen(cloud)---melts----->liquid(in atmo) ------>freezes (refreezes before it hits the ground)

frozen(cloud)---------> liquid(in atmo) ------->freezes (before it hits the ground)

freezing rain

0.5 - 5 mm in size; supercooled raindrops which
freeze on contact with solid objects/surfaces

frozen(cloud)------>liquid (liquid as it hits the it then refreezes)-------->liquid/frozen (melts in atmo as it falls)


liquid(cloud)---------> liquid/frozen (liquid as it hits the ground then refreezes)


5 mm - 10 cm+; hard, rounded pellets or lumps of ice; only produced in large cumulonimbus clouds/ thunderstorms
- largest reported hailstone = 1.67 lbs. & over 5.5" in diameter
-have a series/network of updrafts and down drafts within the thunderstorm that move hail up and down in clouds

things that affect precipitation
Idealized Continent for precipitation:

Pressure systems, winds, seasonality, and Landmasses & Ocean

Pressure systems

-the areas of uplift (ITCZ) and subsidence (STH) affect precipitation patterns


-don't blow in nice straight paths and where they meet, like in the polar front, are turbulent


these pressure belts and winds shift from season to season

Landmasses & Ocean

-mountains get in the way of winds and moisture
-differential heating

Some exceptions to the Idealized pattern which give us a truer picture of precipitation patterns:

1. Subtropical high pressure cells (STHs)
2.Rainshadow deserts
3. Monsoon

Subtropical high pressure cells (STHs)

-don't have the same characteristics on both the east and west side

Eastside of STH:

-subsidence, temp increase, and upwelling of cold ocean currents lead to stable, dry condition

EX: Subtropical deserts; Sahara of N. Africa, deserts of Baja California

Westside of STH:

--little subsidence, more uplifting, convergence, and warm ocean currents lead to greater instability, and wet conditions
EX: Southeastern U.S., esp. Florida

Rainshadow deserts

-due to mountain barriers and orographic effects
-leeward side often much drier than windward side
-in the Gobi desert in China

EX: Nevada deserts of western U.S., Patagonia in southern South America


-an annual cycle of dryness and wetness with seasonally, shifting winds produced by changing atmospheric pressure systems

EX: southern Asia(India); also the southwestern U.S.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions and try again


Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

Voice Recording