Transcript Slide 1

“The Weather”
Fronts
Mountains
Heat Capacity
Latent Heat
Clouds and Rain
Warm air holds more moisture than cold air.
As warm air rises, it cools and cannot hold moisture
Cloud formation and precipitation is
determined ultimately
by the vertical movement of air.
Upward motion enhances cloud formation
Cloud formation leads to rainfall.
Clouds
Clouds form when moisture condenses from the atmosphere
.
When the moisture in clouds is sufficiently abundant,
raindrops or snow falls to the earth’s surface.
If clouds are condensed moisture (liquid water),
how do clouds float in the air?
How do Clouds Float?
Updrafts
Evaporation
Terminal Velocity
Size: 10 micons
Velocity: 0.3 cm/sec or 10 meters/hr
ETA: 350 hours (3500 m or 10,500 ft)
120 to 200 mph
It takes about 15 million cloud droplets to form the typical raindrop
Precipitation: Rainfall
Rainfall
70% of earth surface covered by oceans
Ocean evaporation accounts for 90% of precipitation.
10% to land
Evaporation
90% to Oceans
4,200 bgd
Residence time
in atmosphere: 14 days
Rainfall and Rainfall Types
Frontal
Orographic
Convective
Frontal
Two masses of air of different temperature, humidity and density meet
Warm air is “lighter” than cool air. Warm air rises over cool air.
Cold Fronts and Warm Fronts
Orographic Rainfall
Warm moisture-laden wind blowing in to the
land from the sea encounters a natural barrier
Orographic Lifting
Rainfall
Dry Air
Prevailing wind
Air cools
mountain
Warm Moist air
Ocean
Rain shadow
Low rainfall
High rainfall
Prevailing
wind
wet
dry
110”
39”
18”
The Mojave Desert
Sierra-Nevada
5000-13,000 ft.
Convective
Rising of warm, moist air due to surface heating
Equatorial Regions
Florida
Southeast
cools
Low pressure
Sun warms water or land
Hurricanes are Convective Storms
High Amounts of Solar Heating
Moist Air
When?
Where?
Hurricane season = June - November
*
When?
June
September
23.26o
Atlantic Hurricanes develop between 8o and 20o latitude
30o N
wind
equator
Warm water and Coriolis circulation
Ordinary Thunderstorm
Cooling and Rainfall
Releases 580 cal/g of heat
580 cal/g heat
Water Evaporates
Warms water
Solar heat
Rising air
Condensation and release
of latent heat (580 Cal/g)
Rising air
Rising air
Cooling and Condensation
Release of latent heat (580 Cal/g)
Rising moist air
Contains 580 cal/g heat.
inflow
Low
Pressure
Intensifies
inflow
Increasing pressure
vent
vent
Condensation and release
of latent heat (580 Cal/g)
Condensation and release
of latent heat (580 Cal/g)
Rising moist air
inflow
Low
Pressure
inflow
Tropical Disturbance
1st sign of hurricane genesis
Large cluster of
thunderstorms
forming over
tropical waters.
Intensify or
Dissipate
Tropical Storm
Lower
pressure
Organization and
cyclonic circulation
Heat
Moisture
Circulation
Hurricane
Low
pressure
Warm moist air
Pressure: 1013.25 mbars is normal, 882 is record.
Hurricane Formation as Convective Storms
Easterly wind
Cyclonic
Tropical depression – a closed low pressure area with
organized convection, heavy rain, and winds up to 38 mph
Tropical Storm – cyclone in which the maximum sustained
surface wind speed ranges from 39 mph to73 mph
Hurricanes: Saffir-Simpson Scale
Category 1 -- Winds 74-95 mph
Category 2 -- Winds 96-110 mph
Category 3 -- Winds 111-130 mph
Category 4 -- Winds 131-155 mph
Category 5 -- Winds over 155 mph.
Central Pressure – pressure at the center of the storm
low pressures indicate strong storms
Wind shear – upper level winds which can prevent
rapid rising of air and decreased pressure
Wind Shear
Wind shear or high upper level winds can dissipate a hurricane
Cooler water can also dissipate a hurricane
Extra Credit Question:
Identify the 3 types of rainfall discussed.
Answer on the back of the lecture question sheet
(You may use your notes)
Other Extreme Weather
Rainfall Extremes
<10in
Records
HIGHEST AVERAGE ANNUAL RAINFALL
Tutunendo, Colombia - 463.4 inches (38.6 ft)
HIGHEST IN ONE YEAR
Cherrapunji, India 1,042 inches (86.8 ft)
HIGHEST IN 24 HOURS
Fac Fac, La Reunion Island 72 inches (6 ft)
Reunion Island
Time Period
Amount
12 hr
1144 mm (45.0")
24 hr
1825 mm (71.8")
48 hr
2467 mm (97.1")
18.5 ft rainfall in 10 days
72 hr
3240 mm (127.6")
10 day
5678 mm (223.5")
Driest Weather
Arica, Chile
0.8 mm/yr
0.03 in/yr
the longest rainless period in the world
14 years
Cool water
U.S. Weather
Phoenix 7.6 in
Chicago 36
NYC
41
Miami
59
767 rainless days at Bagdad
50 - 60 in
yr
Continental United States
Location
Quillayute, Washington
Astoria, Oregon
Inches
101.7
67.1
Mobile, Alabama
Pensacola, Florida
New Orleans, Louisiana
66.3
64.3
64.2
Tallahassee, Florida
Baton Rouge, Louisiana
West Palm Beach, Florida
63.2
63.1
61.4
Mt. Waialeale
Highest annual rainfall in the U.S.
most rainy days/yr
3000 ft in ½ mile
Orographic Rainfall
Gainesville
52 inches
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Avg. High
65°
68°
74°
80°
86°
88°
90°
90°
87°
81°
74°
68°
Avg. Low
42°
44°
50°
55°
62°
68°
70°
71°
68°
58°
50°
44°
Mean
54°
56°
64°
68°
74°
78°
81°
81°
78°
70°
62°
56°
3.4 in
4.3 in
3.7 in
2.6 in
3.8 in
6.8 in
6.8 in
8.0 in
5.3 in
1.8 in
2.3 in
3.3 in
Avg.
Precip.
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