Precipitation

Сентябрь 3, 2022

Содержание

2. Lecture 26 Precipitation
3. Water drops and ice crystals falling out or any product of the condensation of atmospheric water
4. Hydrometeor The term meteor describes an object from outer space which has entered the Earth's atmosphere
5. The amount of Precipitation falling out per a unit of time is called Precipitation intensity mm/s
6. Liquid drops formed on the surfaces after water vapor condensation against chilled surfaces. Example: Over thin
7. Rain, snow, or ice pellets may fall steadily or in showers. Steady precipitation may be intermittent
8. All precipitation types are called hydrometeors, of which additional forms are clouds, fog, wet haze, mist,
9. Duration of precipitation Brief -Short duration. Intermittent -Precipitation which ceases at times. Occasional -Precipitation which while
10. Can you guess the shape of raindrops? They are actually shaped like hamburgers! As they fall,
11. http://www.wxdude.com/page3.html
12. 1- avearge values of cloud thickness 2- downpour precipitation is not included
13. http://ga.water.usgs.gov/edu/watercycleprecipitation.html Precipitation rates vary geographically and over time
14. Precipitation size and speed http://ga.water.usgs.gov/edu/watercycleprecipitation.html
15. Virga http://en.wikipedia.org/wiki/Virga In meteorology, virga is an observable streak or shaft of precipitation that falls from
16. Virga http://en.wikipedia.org/wiki/Virga Virga can cause varying weather effects, because as rain is changed from liquid to
17. Virga http://en.wikipedia.org/wiki/Virga The word virga is derived from Latin, twig or branch. A backronym sometimes found
18. Virga http://en.wikipedia.org/wiki/Virga
20. 1- w.v. supersaturation with respect to cloud droplet surface 2- w.v. condensation process 3- if ice
21. Coagulation ? rain drop, ice crystal grow up to few mm, snowflakes, hailstones –up to few
22. Precipitation from stratiform clouds. Scheme of formation
23. The rate of fall for solid and liquid particles in the atmosphere Atm. Particle is affected
24. According to Stocks law for ball like particles (26.2) is valid for low Reynolds number Re*
25. dimensionless numberdimensionless number, gives a measure of the ratiodimensionless number, gives a measure of the ratio
26. Ball-like particle fall under influence of gravity, small Re External force= gravity + buoyancy forces Acting
27. Owing to the fact that F and G are directed along vertical line, Using (26.2) and
28. Steady state motion ? dV/dt=0 Vs is a speed of steady state motion So, Vs ~
29. Unsteady motion ? dV/dt ≠ 0 let’s use an eq-on of the particle motion Since V=dx/dt,
30. At t=τ V ↓ in e times as compared with V0 ? physical meaning of relaxation
32. Скачать презентацию

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Lecture 26 Precipitation

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Water drops and ice crystals falling out
or
any product of 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

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Hydrometeor
The term meteor describes an object from outer space which has

entered the Earth's atmosphere and produces a light phenomenon

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The amount of Precipitation falling out per a unit of 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

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Liquid drops formed on the surfaces after water vapor condensation 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.

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Rain, snow, or ice pellets may fall steadily or in 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.

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All precipitation types are called hydrometeors, of which additional forms 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.

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Duration of precipitation
Brief -Short duration.
Intermittent -Precipitation which ceases at times.
Occasional -Precipitation which while 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.

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Can you guess the shape of raindrops?
They are 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

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http://www.wxdude.com/page3.html

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1- avearge values of cloud thickness 2- downpour precipitation is not included

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http://ga.water.usgs.gov/edu/watercycleprecipitation.html
Precipitation rates vary geographically and over time

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Precipitation size and speed
http://ga.water.usgs.gov/edu/watercycleprecipitation.html

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Virga http://en.wikipedia.org/wiki/Virga
In meteorology, virga is an observable streak or shaft of 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.

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Virga http://en.wikipedia.org/wiki/Virga
Virga can cause varying weather effects, because as rain is 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.

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Virga http://en.wikipedia.org/wiki/Virga
The word virga is derived from Latin, twig or branch. 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.

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Virga http://en.wikipedia.org/wiki/Virga

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1- w.v. supersaturation with respect to cloud droplet surface
2- w.v. 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

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Coagulation ?
rain drop, ice crystal grow up to few mm,

snowflakes, hailstones –up to few cm
Rate of droplet enlargement due to coagulation ~ r
Rate of droplet enlargement due to condensation ~ 1/r

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Precipitation from stratiform clouds. Scheme of formation

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The rate of fall for solid and liquid particles in 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

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According to Stocks law for ball like particles
(26.2) is valid for

low Reynolds number Re*<3
According to experiments
(26.3) is correct for 3 < Re < 400

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dimensionless numberdimensionless number, gives a measure of the ratiodimensionless number, 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)

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Ball-like particle fall under influence of gravity, small Re
External force= gravity

+ buoyancy forces
Acting downward acting upward air density

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Owing to the fact that F and G are directed along

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

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Steady state motion ? dV/dt=0
Vs is a speed of steady state

motion
So, Vs ~ r2 at small Re (or small r)

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Unsteady motion ? dV/dt ≠ 0
let’s use an eq-on of

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

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At t=τ V ↓ in e times as compared with V0

? physical meaning of relaxation time
Assuming
All above is true for ball-like particle

Precipitation

Содержание

Lecture 26 Precipitation

Water drops and ice crystals falling out orany product of the

HydrometeorThe term meteor describes an object from outer space which has

The amount of Precipitation falling out per a unit of time

Liquid drops formed on the surfaces after water vapor condensation against

Rain, snow, or ice pellets may fall steadily or in showers.

All precipitation types are called hydrometeors, of which additional forms are

Duration of precipitationBrief -Short duration.Intermittent -Precipitation which ceases at times.Occasional -Precipitation which while not

Can you guess the shape of raindrops? They are actually

http://www.wxdude.com/page3.html

1- avearge values of cloud thickness 2- downpour precipitation is not included

http://ga.water.usgs.gov/edu/watercycleprecipitation.htmlPrecipitation rates vary geographically and over time

Precipitation size and speedhttp://ga.water.usgs.gov/edu/watercycleprecipitation.html

Virga http://en.wikipedia.org/wiki/VirgaIn meteorology, virga is an observable streak or shaft of precipitation

Virga http://en.wikipedia.org/wiki/VirgaVirga can cause varying weather effects, because as rain is changed

Virga http://en.wikipedia.org/wiki/VirgaThe word virga is derived from Latin, twig or branch. A