Page 304 - (DK) The Ultimate Visual Dictionary 2nd Ed.

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

Weather Advancing cold Warm air
TYPES OF OCCLUDED FRONT
front rises up
over warm Warm
WEATHER IS DEFINED AS THE ATMOSPHERIC CONDITIONS at a particular front front
time and place; climate is the average weather conditions for a given
region over time. Weather is assessed in terms of temperature, wind, Cold air
cloud cover, and precipitation, such as rain or snow. Good weather Cool air
is associated with high-pressure areas, where air is sinking. Cloudy,
wet, changeable weather is common in low-pressure zones with WARM OCCLUSION
rising, unstable air. Such conditions occur at temperate latitudes, Warm air
Cold air Warm
where warm air meets cool air along the polar fronts. Here, spiraling front
low-pressure cells known as depressions (mid-latitude cyclones) often Cold front
form. A depression usually contains a sector of warmer air, beginning undercuts
warm Cool air
at a warm front and ending at a cold front. If the two fronts merge, front
forming an occluded front, the warm air is pushed upward. An
extreme form of low-pressure cell is a hurricane (also called a COLD OCCLUSION
typhoon or tropical cyclone), which brings torrential rain
FORMS OF PRECIPITATION
and exceptionally strong winds.
Water droplets less Water droplets
than 0.5 mm in coalesce to
TYPES OF CLOUD
diameter fall form raindrops
Cirrus Cirrostratus as drizzle 0.5–5.0 mm in
diameter
13
Rising air
Cirrocumulus 12

11
Freezing level, RAIN FROM CLOUDS NOT
above which REACHING FREEZING LEVEL
clouds consist 10
of ice crystals Ice crystal Snowflakes
Coalesced grown from
9 water droplets ice crystals
Cumulonimbus
fall as rain fall as snow
8
Snowflakes
Altocumulus 7 melt to fall
Rising air as rain
6
Altostratus
5 RAIN AND SNOW FROM CLOUDS
REACHING FREEZING LEVEL
Nimbus
Vertical air Alternate
4
currents toss freezing
Stratocumulus frozen water and melting
droplets up builds up
3
and down layers of ice
Cumulus
2
Nimbostratus Rising air Ice falls as
1 hailstones
Stratus
0
Altitude in
temperate HAIL
Condensation level
regions (km)
302