BERGERON PROCESS(GROW

TH OF ICE CRYSTAL)

BYABINASH PRADHAN

REGD NO.130711M.Sc.2nd Year

BATCH-A

THE BERGERON PROCESS The Bergeron Process Named for Swedish meteorologist Tor Bergeron and

this process is also known as the cold rain or ice crystal process, is the formation of precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth.

The equilibrium vapor pressure over water is greater than the saturation vapor pressure over ice, at the same temperature.

Therefore in a mixed phase cloud , the liquid water will be out of vapor pressure equilibrium and will evaporate to reach equilibrium.

The water droplets will move towards the lower pressure over the ice and diffuse onto the ice crystals.

The vapor will be condensed and freeze onto the ice crystal, causing it to grow large.

THE FORMATION OF ICE-CRYSTALS The most common way to form an ice crystal, starts with

an ice nucleus in the cloud. Ice crystals can form from heterogeneous deposition, contact, immersion, or freezing after condensation.

In heterogeneous deposition, an ice nuclei is simply coated with water.

For contact, ice nuclei will collide with water droplets that freeze upon impact.

During immersion, an ice nucleus will heat a water droplet and instantly freeze it. Water can also condense onto ice nuclei and then freeze.

Water will freeze at different temperatures depending upon the type of nuclei present. Ice nuclei cause water to freeze at higher temperature. For pure water to freeze spontaneously, called homogenous nucleation, cloud temperatures would have to be -42°Celcius.

ICE MULTIPLICATION As the ice crystals grow, they can bump

into each other and splinter and fracture, resulting in many new ice crystals.

There are many shapes of ice crystals to bump into each other.

These shapes include hexagons, cubes, columns, and dendrites.

AGGREGATION The process of ice crystals sticking

together is called aggregation This happens when ice crystals are slick

and sticky at temperature of -5°C and above, because of the coating of water surrounding the crystal.

The different sizes and shapes of crystals fall at different terminal velocities and commonly collide and stick.

ACCRETION When an ice crystal

collides with super cooled water it is called accretion.

Droplets freeze upon impact and can form graupel.

PRECIPITATION When air is saturated (100% relative

humidity), with respect to liquid droplets, it is supersaturated with respect to ice crystals.

PRECIPITATION

PRECIPITATION So, how does precipitation form? Picture a cloud at a temperature of -10°

C (14°F) Each ice crystal is surrounded by

thousands of liquid droplets. Because the air was initially saturated

100% with respect to liquid water, it will be supersaturated (over 100%) with respect to the newly formed ice crystals.

As a result of this supersaturated condition, ice crystals continue to gather water moisture and they grow.

PRECIPITATION AND THE BERGERON PROCESS

PRECIPITATION AND THE BERGERON PROCESS

Because the level of super saturation with respect to ice can be great, the growth of snow crystals continues and generates crystals large enough to fall.

These crystals in turn are enlarged as they pass through the cloud by collision with water droplets.

Air movement in the cloud can cause some of these crystals to break apart, and they become freezing nuclei for other liquid droplets.

PRECIPITATION AND THE BERGERON PROCESS A chain reaction develops and produces

many snow crystals. These snow crystals, through a process

called accretion, form into larger masses called snowflakes.

Large snowflakes may consist of 10 to 30 individual crystals.

PRECIPITATION AND THE BERGERON PROCESS

In summary, the Bergeron process can produce precipitation throughout the year in the middle latitudes so long as the upper portions of the clouds are cold enough for the generation of ice crystals.

The type of precipitation that reaches the ground (rain, snow, sleet, freezing rain) depends on temperature in the lower few kilometers of the atmosphere.

ANY QUERY……..?