Precipitation

of the eddy coefficient, please.
Write down the humid air state

equation and give notions to all terms.
What does convection process mean?
Write down statics’ equation and give notions to all terms.

What is the potential temperature?

Version 2

What value is higher and why: meteorological or astronomical solar constant?
Please, describe the entrainment process briefly.
Write down the dry air state equation and give notions to all terms.
How do you understand term “convergence”?
Please, give numerical form of relation between dry air gaseous constant R and specific heats at const V and p.
Write down the potential temperature formula with all notations.

Fast questionnaire

the condensation of atmospheric water vapor that is pulled down

by gravity and deposited on the Earth's surface
is called
Precipitation.


Amount of precipitation is measured by
the thickness of the liquid water layer that could be formed after precipitation fall out on a horizontal surface.
1 mm= 1 kg/m2

Definition

has entered the Earth's atmosphere and produces a light phenomenon

time is called
Precipitation intensity

mm/s (rare),
mm/h (forecasts),
mm/day,
mm/

month (climatologically texts)

Forms of Precipitation:

rain,
snow,
ice pellets (шарик,гранула),
graupel
dew
drizzle (r< 0.25 mm)
sleet

against chilled surfaces.

Example:
Over thin blades of grass and leaves at

night

Dew

In England sleet is defined as a mixture of rain and snow, or melting snow.

showers. Steady precipitation may be intermittent (перемежающийся) though lacking sudden

bursts of intensity.
Hail, small hail, and snow pellets occur only in showers.
Drizzle, snow grains, and ice crystals occur as steady precipitation.

Showers originate from instability clouds of the cumulus family, whereas
steady precipitation originates from stratiform clouds.

are clouds, fog, wet haze, mist, blowing snow, and spray.

Whenever rain or drizzle freezes on contact with the ground to form a solid coating of ice, it is called
freezing rain,
freezing drizzle,
or glazed frost;
it is also called an ice storm or a glaze storm, and sometimes is popularly known as
silver thaw (оттепель) or
erroneously (ошибочно) as a sleet storm.

not frequent, is recurrent.
Frequent -Showers occurring regularly and often.
Continuous -Precipitation which does

not cease, or ceases only briefly.
Periods of rain -Rain is expected to fall most of the times, but there will be breaks.


Distribution of showers and precipitation

Few- Indicating timing and not area.
Isolated -Showers which are well separated in space during a given period.
Local -Restricted to relatively small areas.
Patchy- Occurring irregularly distributed over an area.
Scattered -Irregularly distributed over an area. Showers, which while not widespread, can occur anywhere in an area. Implies a slightly greater incidence than isolated.
Widespread -Occurring extensively throughout an area.

actually shaped like hamburgers! As they fall, the air pushes

on the bottoms of the drops, causing the bottoms to flatten out while the tops remain round.

http://www.wxdude.com/page3.html
http://ga.water.usgs.gov/edu/watercycleprecipitation.html

included

precipitation that falls from a cloud but evaporates before reaching

the ground.

At high altitudes the precipitation falls mainly as ice crystals before melting and finally evaporating; this is usually due to compressional heating, because the air pressure increases closer to the ground.

It is very common in the desert and in temperate climates.

changed from liquid to vapor form, it removes heat from

the air due to the high heat of vaporization of water.
In some instances, these pockets of colder air can descend rapidly, creating a dry microburst which can be extremely hazardous to aviation. Conversely, precipitation evaporating at high altitude can compressionally heat as it falls, and result in a gusty downburst which may substantially and rapidly warm the surface temperature. This fairly rare phenomenon, a heat burst, also tends to be of exceedingly dry air.

Virga also has a role in seeding storm cells whereby small particles from one cloud are blown into neighboring supersaturated air and act as nucleation particles for the next thunderhead cloud to begin forming
Virga can produce dramatic and beautiful scenes, especially during a red sunset. The red light can be caught by the streamers of falling precipitation, and winds may push the bottom ends of the virga so it falls at an angle, making the clouds appear to have commas attached.

A backronym sometimes found in amateur discussions of meteorology is

"Variable Intensity Rain Gradient Aloft."
Extraterrestrial occurrences

Sulfuric acid rain in the atmosphere of Venus evaporates before reaching the ground due to the high heat near the surface. Similarly, virga happens on gas giant planets such as Jupiter. In September 2008 NASA's Phoenix lander discovered a snow variety of virga falling from Martian clouds.

condensation process
3- if ice crystal appears ? distillation
4- coalescence /coagulation

begins as droplet
r= 20…60 micrometers
result of different downward W) ? gravitational coagulation;
eddy and Brownian movements ? … coagulation;

Processes of cloud element enlargement and precipitation formation

mm,
snowflakes, hailstones –up to few cm

Rate of droplet

enlargement due to coagulation ~ r
Rate of droplet enlargement due to condensation ~ 1/r

the atmosphere
Atm. Particle is affected by:
external forces (gravity, electrostatic,

buoyancy…)
air resistance force
force of interaction between particles

According to the 2 nd Newton’s law

for low Reynolds number Re*

3 < Re < 400

gives a measure of the ratio of inertial forcesdimensionless number,

gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions.












laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion;
while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities.

V  is the mean velocity of the object relative to the fluid (SI units: m/s)
L is a characteristic linear dimension, (travelled length of the fluid; hydraulic diameter when dealing with river systems) (m)
μ is the dynamic viscosityμ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/(m·s))
ν is the kinematic viscosity (ν = μ / ρ) (m²/s)
   is the density of the fluid (kg/m³)

gravity + buoyancy forces



Acting downward

acting upward air density

along vertical line,
Using (26.2) and (26.5) :

steady state motion





So, Vs ~ r2 at small Re (or

small r)

of the particle motion








Since V=dx/dt, after integrating (26.10)

with V0 ? physical meaning of relaxation time

Assuming









All above

is true for ball-like particle

speed is determined empirically: