Transcript Document
Clouds
Moisture in the air
Humidity
-the amount of moisture in the air
Relative humidity
- the amount of moisture in the air compared to the amount it could hold at a given temperature.
Dew point
-the temperature at which moisture in the air condenses.
Saturated
-when air is holding all the moisture it can.
Cloud development
As air rises it cools when it reaches the dew point it condenses.
It needs something to condense on. This is called a
condensation nuclei
. This can be a speck of dust etc. Sometimes the relative humidity can be above 100%. If the air is too clean there is nothing for the moisture to condense on. This is when
cloud seeding
may be effective. Silver iodide is shot into the air to give the moisture the needed nucleus.
FOUR MAJOR CLOUD TYPES High Middle Low Clouds with Vertical Development
HIGH--above 6000 m(cirro-high) Cirrus
thin and wispy Most common high cloud Composed of ice crystals Occur in fair weather Point in the direction of movement
Cirrocumulus
Cirrocumulus are thin, white patches, sheets or a layer of clouds without shading, composed of very small elements in the form of merged or separate, and more or less
regularly arranged
A patch or layer of cloud consisting of tiny individual cloudlets at high-level is called cirrocumulus
grains, ripples
Cirrocumulus are composed almost exclusively of ice crystals. , etc.,
Cirrocumulus
Cirrocumulus differs from Altocumulus in that most of its elements are and very small without shading .
Cirrocumulus
cloudlets differs from Cirrus and Cirrostratus in that it is rippled or subdivided into very small
Cirrocumulus
Sometimes they look like the scales on a fish - a "
mackerel
" sky that may mean that unsettled weather is on its way Like all high-level clouds, cirrocumulus is made of ice crystals
Formation of Cirrocumulus
It forms when cirrus or cirrostratus is warmed gently from below. This causes air to rise and sink inside the cloud. Some of the ice crystals change into water vapor, and gaps appear. It can be difficult to tell cirrocumulus from altocumulus Cirrocumulus has no shading (which altocumulus usually has), and because it is so much higher, the cloudlets of cirrocumulus are much smaller than those of altocumulus
Cirrocumulus
Mackerel Sky
Cirrostratus
sheet-like and nearly transparent
Cirrostratus
can cover the entire sky and be up to several thousand feet thick they are relatively transparent, as the sun or the moon can easily be seen through them These high-level clouds typically form when a broad layer of air is lifted by large-scale convergence
Halo
Sometimes the only indication of their presence is given by an observed or moon. to crystals.
halo
Halos result from the refraction of light by the cloud's ice crystals.
Cirrostratus clouds, however, tend
thicken
around the sun as a warm front approaches, signifying an increased production of ice As a result, the halo gradually disappears and the sun (or moon) becomes less visible.
MIDDLE-- (2000-6000m)
Altostratus Altocumulus
Altostratus
Altostratus clouds
are gray or blue-gray mid-level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky. Altostratus clouds often form ahead of storms with
continuous
rain or snow.
Altocumulus
parallel bands or rounded masses Typically a portion of an altocumulus cloud is shaded , a characteristic which makes them distinguishable from the high-level cirrocumulus.
Altocumulus
Altocumulus clouds usually form by convection in an unstable layer aloft, which may result from the gradual lifting of air in advance of a cold
front.
The presence of warm and altocumulus clouds on a humid summer morning commonly followed by in the day thunderstorms is later
LOW
Stratus— layered uniformly gray, often cover the entire sky
Stratocumulus
low, lumpy layer of clouds that is sometimes accompanied by weak intensity
precipitation
Stratocumulus vary in color from dark gray
to light gray
may appear as rounded masses, rolls, etc., with breaks of clear sky in between.
Nimbostratus
dark, low-level clouds with precipitation Nimbus means rain Stratus means sheet
Nimbostratus
light to moderately falling precipitation
Low clouds are primarily composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters) However, when temperatures are cold enough, these clouds may also contain ice particles and snow
CLOUDS HAVING VERTICAL DEVELOPMENT
Cumulus Form where temperatures change quickly with height Cumulus means heap Cumulonimbus
Fair Weather Cumulus
puffy cotton balls floating in the sky
Lifetime of 5-40 minutes
Fair weather cumulus
Known for their flat bases and distinct outlines, fair weather cumulus exhibit only slight vertical growth, with the cloud tops designating the limit of the rising air Given suitable conditions, however, harmless fair weather cumulus can later develop into towering cumulonimbus clouds associated with powerful thunderstorms called
supercells
.
Cumulonimbus Clouds (Cb)
Cumulonimbus clouds much larger and more
vertically developed
than fair weather cumulus They can exist as individual towers or form a line of towers called a
squall line Fueled by vigorous, convective updrafts
the tops of cumulonimbus clouds can easily reach 39,000 feet (12,000 meters) or higher, reaching high into the atmosphere
Mammatus
sagging
pouch-like
structures
Mammatus
are pouch-like cloud structures and a rare example of clouds in sinking air
Mammatus Clouds
Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form; a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed
Mammatus
CONTRAIL
A contrail, also known as a condensation trail, is a cirrus-like trail of condensed water vapor often resembling the tail of a kite. Contrails are produced at high altitudes where extremely cold temperatures freeze water droplets in a matter of seconds before they can evaporate.
Lenticular Clouds
Lenticular clouds
are caused by a wave wind pattern created by the mountains. They look like discs or flying saucers that form near mountains.
Cloud Types at Fronts
Fronts
Fronts form where air masses collide Cold front Cold air invades warm air Warm front Warm air invades cold air We find a variety of weather at fronts
When the two masses meet, the differences in temperature, moisture and pressure can cause one air mass to override the other.
If cold air invades warm air--
cold front
If warm air moves into cold air-
-warm front
If neither air mass is moving a
stationary front
Fronts are accompanied by wind, clouds, rain, and storms.
Approaching cold front
Approaching warm front
Less dense air gradually rises over the cold denser air ¨ ¨ ¨ ¨ ¨ Less obvious and more gradual than cold front Cirrus clouds Thicken into altocumulus and altostratus Sky turns gray Light to moderate rain or snow develops At front rain or snow turns to drizzle
Warm front animation
source: http://www.learn-line.nrw.de/angebote/klima/medio/bilder/wfront.gif
Thunderstorm Formation
As cold air pushes into warm moist air, the cold more dense air stays low and the warmer less dense air is pushed up rapidly This rapid upward movement forms thunderstorms