Test 2 Flashcards
Describe what Raindrop formation requires
-Condensation nuclei
What are the two processes for droplet growth
- Collision - coalescence process
2. Ice-Crystal (bergeron) process
Explain collision - coalescence
- need different droplet sizes
- Terminal velocity greater for larger rain drops
- large drops overtake and collide with small drops
This is the dominant precipitation mechanism in warm phase of clouds
What effects collision-coalescence precipitation production?
- Liquid water content (LWC)
- Range of droplet size
- cloud thickness
- updraft speed
Where is the cold section in a typical cumulonimbus could
Top
What is the ice-crystal (bergeron) process
- Saturation vapor pressure over ice surface < over liquid surface
- Vapor pressure difference causes the movement of water vapor molecules from liquid to ice surface
- Ice crystals grow at the expense of liquid droplets.
What is secondary ice formation
ice crystals grow, fall, collide with super cooled droplets, which freeze on contact (accretion).
This creates larger ice crystals (graupel) which ___Missing____
What is the dominant preticipation formation in warm clouds
Collision and coalescense
List the types of precipitation
- Rain
- Virga
- Snow
- Fallstreaks
- Dendrite snowflakes
- Hail
What is virga
when rain droplets fall but evaporate before hitting the ground.
What is hail
pieces of ice
-form in cumulonibus clouds
List other types of precipitation
- sleet
- freezing rain
- Rime
- Snow grains
- snow pellets
What is sleet
Falling snowflakes partly melts in warmer air then falls through cold (<0C) surface layer of air and refreezes to ice pellet
What is freezing rain
Its the same as sleet but the cold layer is too thin. ____Missing____
What is Atmospheric Pressure?
Weight of air above a given height
- Obeys the gas law
- decreases with height (rate varies though)
what is variation in atmospheric pressure based on?
high and low pressure areas
What is the pressure gradient
horizontal pressure differences
What causes wind?
The pressure gradient
List four primary ways in which
clouds form.
- surface heating and free convection
- uplift along topography
- widespread ascent due to the fl owing together (convergence)
of surface air - uplift along weather fronts
Explain why rain shadows form
on the downwind (leeward) side
of mountains.
by forcing air to rise along their windward
slopes. -> the windward side of mountains tends to be “wet.” As air descends and warms along the leeward side, there is less likelihood of clouds and precipitation. Thus, the leeward (downwind) side of mountains tends to be “dry.”
What is the primary difference
between a cloud droplet and a
raindrop?
Rain drops -> about 2 mm and have enough mass to fall to the ground
Cloud droplet -> about 0.02 mm and do not have enough mass to fall to the ground
when does warm, moist air rise?
in conditionally unstable atmosphere
What is Rising air due to?
- Strong surface heating
- topographical forcing
- Frontal lifting
- Convergence of surface air
Where do ordinary cell (air mass) Thunderstorms form?
where there is limited vertical wind shear (wind speed/direction do not abruptly change with height)
Are Ordinary cell (air mass) Thunderstorms Isolated thunderstorm and not severe?
Yes
Are Ordinary cell (air mass) Thunderstorms short lived?
Yes (45-60 min)
What is the 3 stage life cycle of Ordinary cell (air mass) Thunderstorms?
- Cumulus or growth
- Mature
- Dissipating
What does entrainment mean?
Dry outside air drawn in side and top