Chapter Five - Test Two Flashcards
During clear, calm nights:
The ground cools very rapidly thru ____
The air that comes in contact with the ground cools thru ____.
radiational cooling; conduction
If the T cools down to Td (i.e. RH = 100%), ____ occurs.
saturation
If the T (which equals Td)) are greater than 32oF :
The water vapor molecules will condense into liquid water forming visible droplets on objects (i.e. grass, car) called ____.
Dew Formation; dew
If the T (which equals Td)) are less than 32oF :
The water vapor molecules deposit directly into ____
(White) Frost Formation; frost
Nights that favor dew/frost formation are those that experience “maximum radiational cooling” (discussed earlier):
- Clear skies
- Calm Winds
- Long nights
Neither dew nor frost “fall” from the sky, rather they are formed ____ (in place).
insitu
There is a less know phenomenon called “____”, which occurs when dew first forms thru condensation and then later freezes into tiny ice spheres.
frozen dew
visible aggregate (collection) of liquid water droplets and/or ice crystals suspended in the atmosphere
clouds
when an air parcel rises, it cools adiabatically and if the parcel’s T cools down to the Td, saturation and subsequently condensation occurs and:
a cloud is formed, beginning at the LCL
Just as dew/frost needs a surface to form on (i.e. grass), there must be a surface upon which water vapor can condense (deposit) in the air:
Cloud Condensation Nuclei (CCN)
Growth of Cloud Droplets
As the water vapor molecules cool, they:
- lose energy,
- move more slowly
until they eventually adhere to the CCN.
Picture the water vapor molecules “getting tired” and needing a place to rest.
Because CCN are so small and light
they can remain suspended for weeks
Even “clean” air contains over: ____ CCN/cm ^3
1,000
CCN enter the atmosphere through a variety of pathways, both:
Natural: dust, salt spray, volcanic ash, fires, pollen
Anthropogenic: sulfates, nitrates from fossil fuel burning (acid rain), fugitive dust
Some CCN are:
Hygroscopic (water seeking)
Hydrophobic (water repelling)
Cloud Classification
Classification developed around 1800 by ____ on the basis of:
Luke Howard
Form and Height: Combinations of these forms and height give us ten major cloud types
Cloud Forms:
cirrus form - (Latin for wisp)
cumulus form - (Latin for heap)
stratus form - (Latin for Layer)
nimbus form - (Latin for rain)
Cloud Heights:
High - ( > 6 km)
Middle - (2 to 6 km)
Low - ( 6 km)
High Clouds (> 6 km)
- thin (tens of meters thick)
- comprised solely of ice crystals
- non-precipitating
- form in slowly rising
Cirrus (Ci), Cirrostratus (Cs), Cirrocumulus (Cc)
Cirrus (Ci) (Figure 5.3a)
- most common high cloud
- called “Mare’s Tails”
Cirrostratus (Cs) (Figure 5.3b)
- often produce Halo around sun or moon, which is due to the refraction of light by ice crystals
- often precedes precipitation
Cirrocumulus (Cc) (Figure 5.3c)
- form in a more turbulent environment
- “Mackerel Sky”
Middle Clouds (2 - 6 km)
- thicker (hundreds of meters thick)
- comprised mostly of liq. Droplets w/some ice crystals
- also non-precipitating
Altocumulus (Ac) , Altostratus (As)
Altocumulus (Ac) (Figure 5.4a)
- often occur in large patches
- bases are darker
Altostratus (As) (Figure 5.4b)
- no definite configuration (formless)
- sun/moon barely visible
Low Clouds (
- thick (thousands of meters thick)
- comprised mostly of liquid droplets with some ice crystals
- some types produce precipitation
Stratus (St), Stratocumulus (Sc), Nimbostratus (Ns)
Stratus (St)
- resembles a fog that doesn’t reach the surface
- sun is not visible
- can produce drizzle
Stratocumulus (Sc)
- appear in long parallel rows or patches
- rarely precipitate
- 1 km thick
Nimbostratus (Ns) (Figure 5.5)
- produces continuous, generally light precipitation
- completely blocks out the sun/moon
- 2 to 4 km thick
90% of world’s snow falls out of this cloud
Clouds with Vertical Development (2 km to > 6 km)
- very thick (tens of thousands of meters thick)
- comprised of liquid droplets and ice crystals
- associated with unstable air
- some produce precipitation
Cumulus (Cu), Cumulonimbus (Cb)
Cumulus (Cu) (Figure 5.6)
- 1 to 5 km thick
- mostly liquid water
- resemble cotton balls
- dark, flat bases (LCL)
- “Fair weather” clouds
Cumulonimbus (Cb) (Figure 5.7)
- 5 to 20 km thick
- thunderstorm cloud
- very strong updrafts, downdrafts
- produce intense rain
- produce lightning and thunder, hail and tornadoes
Lenticular (Lens) Clouds (Figures 5.8)
- lens shape cloud that forms over and to the leeward side of the tall mountain ranges
Mammatus (Mammary) Clouds
- Form in severe thunderstorms
Anthropogenic Clouds
Contrail Clouds (Figure 5.A,B)
- Cirrus-like clouds that often form on exhaust of high-flying jets
Defined as a cloud with its base at or near the surface:
Fog; restricts visibility to 1 km or less
Produced when cooling of the air reduces T to Td, hence saturation and condensation occurs.
Fogs Formed by Cooling
Radiation, Advection
Radiation Fog
`Occurs at Night, over Land: when radiational cooling reduces T to Td
- generally associated with High Pressure
- light winds –> Maximum Radiational
- clear skies –> Cooling
- occurs more often in winter (long nights)
Advection Fog (Fig. 5.10)
occurs when warm, moist air is advected over a cooler surface reducing T to Td
- unlike radiation fog, advection fog requires the Movement of air
- San Francisco’s golden gate
- warm air moving over snow cover
Fogs Formed by Evaporation
Steam Fog (Fig. 5.11)
Steam Fog (Fig. 5.11)
occurs when cold air moves over warm water
- the air immediately over the water surface first warms and gathers water vapor through Evaporation
- it then rises (because it’s less dense) allowing T will cool to Td
- Occurs over ponds/lakes in autumn and winter
Average annual frequency of days with heavy fog
Pacific Coast States (> 40 days) Advection
New England Coast (> 40 days) Advection
Appalachian Mtns.(> 40 days) Radiation (valley)
Raleigh (25-30 days) Radiation (valley)
Satellites in Weather Forecasting
GOES (Geostationary Operational Environmental Satellite)
POES (Polar Operational Environmental Satellite)
GOES (Geostationary Operational Environmental Satellite)
- orbit above the equator at 36,000 km at the same rate the earth rotates (Fig 12.17b)
- remain stationary above a fixed location
- allows for continuous observation above a location
- limited resolution
POES (Polar Operational Environmental Satellite)
- orbit north-south at less than 1,000 km passing over both poles allowing the earth to rotate beneath (Fig. 12.17a)
- allows for complete coverage of earth, twice per day
- better resolution
What Weather Satellites Provide
- Visible images (Fig. 12.18)
- IR images (fig. 12.19)
- Water vapor images (fig. 12.20)
Though necessary, the processes of condensation is entirely too ____ to produce precipitation alone. Even under the most “ideal” conditions, it would take several days to produce a small ____ solely thru condensation
slow, rain drop
Cloud Drop
(r= 10µ)
Rain Drop
(r= 1000µ)
A cloud droplet must increase its volume by ____ in order to grow to the size of a rain drop.
- and condensation alone cannot do this.
1 million or (1 x10^6)
Clouds can form and precipitate in less than hour through two processes:
1) Bergeron (ice Crystals) Process
2) Collision- Coalescence Process
Precipitation from Cold Clouds:
The Bergeron Process
The Bergeron Process
Most clouds (outside of tropical latitudes) form in areas of the ____ where temperatures are well below freezing.
Surprisingly: these clouds are mostly comprised of ____ droplets, despite the fact that their temp. is well below freezing!
Such droplets are called:
troposphere; liquid
Super Cooled Cloud Droplets
The Bergeron Process
In order for deposition to take place the water vapor molecules must come in contact with unique particles that have a ____ shape.
Such particles are called: ____
crystal lattice
Ice Crystal or Deposition Nuclei
- that act as nuclei for the formation of ice crystals through deposition.
The Bergeron Process
The need for a deposition nuclei to initiate deposition is similar to the need of CCN to initiate condensation.
However, there are far ____ deposition nuclei than CCN
- 1:____ ratio
So even in cold clouds, the number of liquid water cloud droplets greatly exceeds the number of ice crystals, as a result:
- Millions of liquid droplets will ____ each ice crystal.
fewer; 1,000,000; surround
The Bergeron Process
Because of a subtle difference in the saturation mixing ratio (MRs) over an ice surface compared to that of a liquid surface, water vapor molecules will: ____ away from the liquid droplet, and
____ onto the ice crystal
Evaporate; Deposit
Ice crystals grow at the expense of the liquid water droplets. This growth process is called the:
Bergeron Process
after the Swedish meteorologist that discovered it (Fig. 5.14).
As the ice crystals grow larger they eventually fall where:
- They either reach the ground intact as snowflakes, or
- they melt and reach the surface as raindrops.
Precipitation from Warm Clouds:
The Collision - Coalescence Process
The average cloud droplet has a diameter of:
20 µ (0.02 mm)
Cloud droplet sizes vary considerably, due in part to the size and type (hydrophobic, hygroscopic) of their ____
As a result, the variably sized cloud drops have variable:
Fall (or Terminal) ____
Defined as the point at which air resistance = ____ force; so that the acceleration = 0; and the drop falls at a constant velocity (Table 5.3).
CCN; Velocities; gravitational
Large drops fall faster and “overtake” small drops where they:
Collide and coalesce (combine)
After coalescing, cloud drops are larger, fall faster, further increasing the # of collisions, until, after ____ or so collisions, they are large enough to fall to the ground as a ____ drop (Fig. 5.15).
a million; rain
Rain drops resemble what shape?
Hamburger bun
Two factors important to Collision Coalescence Process:
1) Cloud Thickness
2) Cloud Updraft Strength
Thick clouds with strong ___ can produce larger drops and more intense than thin clouds with weak ones
updrafts
A warm Stratus Cloud is typically:
- Thin (~1000 m thick) and
- has weak updrafts (
A stratus cloud droplet would spend ~ 10-15 min in the cloud and at most grow to ~ 500µ (the size of drizzle).
A warm Cumulus Cloud is typically:
- thick (>5000 meters)
- Strong updrafts (> 0.6 m/s)
Therefore:
A cumulus cloud droplet could spend ~ 1-2 hours in the cloud and be able to grow to 5000µ (the size of a large raindrop).
While falling, the raindrops/snowflakes are often altered by the atmospheric conditions encountered beneath the cloud. (Table 5.4)
They can:
- change form (i.e. snow to rain)
- evaporate resulting in a phenomenon called:
Virga (Latin for streak) (fig. 5.17)
Rain (500µ
either nimbostratus or cumulonimbus clouds
Nimbostratus clouds produce ____ rain, characterized by:
stratiform
- continuous (hours to day)
- light rates (0.1- 0.2 inches per hour)
- often called “overrunning precipitation”
Cumulonimbus clouds produce ____ rain, characterized by:
convective
- generally brief (minutes to hour)
- intense rates (1-2 inches per hour)
Snow (Fig. 5.16b)
Results if the temperature remains near or below freezing between the cloud base and the surface.
Six-sided ice-crystals (Fig. 5.18)
- Small, dry powdery snowflakes are associated w/T
Sleet (Fig. 5.16c, 5.19) results, if while falling, the snow first encounters a ____ Layer in which melting occurs and then encounters a:
Deep ____ Layer
above the surface in which complete freezing recurs before the precipitation reaches the surface.
warm (T > 32º), cold (T
____ (Freezing Rain) (Fig. 5.16d, 5.20) results, if while falling, the snow first encounters a Warm Layer (T > 32º) in which melting occurs and then encounters a:
____ Cold Layer (T
Glaze, Shallow; surface
- adheres to trees/ power lines (fig. 5.20)
- can cause extensive damage
Standard Rain Gauge (Fig. 5. 25b)
Funnel shaped collector has an opening 10x wider than tube to allow for greater precision
- Can measure to nearest 0.01 inches
- Any amount less called a Trace
- Disadvantage: needs a person to record data
- Any amount less called a Trace
Standard Tipping Bucket (Fig. 5.25c)
A thimble-sized bucket fills and tips over for every 0.01” which creates an electrical signal that can be recorded
- Can be used remotely
Snow Gauge
A Standard Rain Gauge that has been modified with wind screens (Fig. 5.26) to ensure accurate collection. The snow is then melted to get: Liquid Equivalent precipitation
RADAR:
Each RADAR unit consists of a:
Transmitter:
when the energy encounters an object, a small fraction of the energy is reflected back to the:
Receiver:
Radio Detection And Ranging (Figs. 5.27, 10.27,10.28)
emits powerful pulses of energy;
which amplifies and displays the signal on a screen as an echo providing precipitation:
