Transcript Why Do We Have Weather?

WHY DO WE HAVE
WHY DO WE HAVE THE WEATHER ?
JUST THINK ABOUT IT!
• WHY IS THERE WIND? WHY DOES IT BLOW FROM ONE DIRECTION ONE DAY
AND ANOTHER THE NEXT?
• WHY IS IT RAINY ONE DAY AND DRY THE NEXT?
• HOW COME IT’S COLD IN THE WINTER?
• HOW CAN WE HAVE HAIL IN THE SUMMER?
• WHAT CAUSES SNOW AND FREEZING RAIN?
LET’S TAKE A LOOK AT WHY WE HAVE
WEATHER!
IF WE WERE TO PICK ONE TERM TO HELP
EXPLAIN WHY WE HAVE WEATHER, WHAT
DO YOU THINK WOULD BE A GOOD WORD?
YOU MIGHT PICK HEAT OR SUN….BUT ANOTHER GOOD CHOICE WOULD BE
CONVECTION
CONVECTION IS THE TRANSFER OF HEAT,
USUALLY IN GASES OR LIQUIDS.
AIR MASSES
• AIR MASSES HAVE DIFFERENT
TEMPERATURES
• THEY ALSO HAVE DIFFERENT
AMOUNTS OF MOISTURE
• THE SOURCE REGION IS THE AREA
OVER WHICH A PARTICULAR AIR
MASS FORMS
• IT USUALLY GIVES THE AIR MASS
ITS CHARACTERISTICS:
TEMPERATURE AND HUMIDITY!
AIR MASS
MODIFICATION
WHEN AN AIR MASS TRAVELS
OVER LAND OR WATER THAT
HAS CHARACTERISTICS
DIFFERENT FROM THOSE OF
ITS SOURCE REGION, THE AIR
MASS CAN ACQUIRE SOME
OF THE CHARACTERISTICS OF
THAT LAND OR WATER AND
UNDERGO MODIFICATION.
AFTER THE ATMOSPHERE IS WARMED BY RADIATION
AND CONDUCTION, THE HEAT IS TRANSFERRED
THROUGHOUT THE ATMOSPHERE BY CONVECTION.
• SINCE WARMED AIR HAS MORE
SPACE BETWEEN THE
MOLECULES, IT’S LESS DENSE
AND RISES
• COOLED AIR IS MORE DENSE
AND TENDS TO SINK
• IN GENERAL, AIR NEAR THE
EQUATOR TENDS TO RISE AND
AIR NEAR THE POLES TENDS TO
SINK
TAKE A LOOK AT THIS!
Notice the band
of clouds around
the equator?
• THIS IS THE ITCZ OR
INTERTROPICAL
CONVERGENCE ZONE
WHY DO YOU THINK THERE IS THIS BAND
OF CLOUDS NEAR THE EQUATOR?
DID YOU FIGURE IT OUT?
• WARM, MOIST AIR IN THE TOPICS RISES
• COLD AIR CAN HOLD LESS MOISTURE THAN WARM AIR
• AS THE MOIST AIR RISES, IT CONDENSES AND FORMS CLOUDS!
MORE ON THIS LATER
CONSEQUENCES OF ROTATION:
THE CORIOLIS EFFECT
THE WEATHER HIGHWAYS
• THE ROTATION OF THE EARTH
CREATES THE CORIOLIS EFFECT.
• THE CORIOLIS EFFECT CAUSES
THE AIR AND WATER TO BE
DEFLECTED TO THE RIGHT
NORTH OF THE EQUATOR.
• THIS CREATES GLOBAL
WEATHER HIGHWAYS
THE WESTERLIES
• BECAUSE OF OUR LATITUDE,
MOST OF OUR WEATHER COMES
FROM THE WEST
• LOOKING AT THE WEATHER MAP,
WHAT TYPE OF WEATHER MIGHT
WE EXPECT?
• WHAT TYPE OF WEATHER MIGHT
WE EXPECT IN A FEW DAYS?
LET’S BREAK FOR A SHORT REVIEW
1.TRANSFER OF HEAT IN LIQUIDS OR GASES _____
2. _____ AIR IS DENSE AND TENDS TO SINK.
3. BAND OF CLOUDS FOUND AROUND THE EQUATOR ______
4. COLD AIR HOLDS _____ MOISTURE THAN WARM AIR
5. THE CORIOLIS EFFECT CAUSES THE AIR AND WATER TO BE DEFLECTED TO
THE _____ IF YOU ARE NORTH OF THE EQUATOR
HOW DID YOU DO?
1.
CONVECTION
2. COLD
3. ITCZ
4. LESS
5. RIGHT
NOW WHAT?
• OK, SO WE KNOW THAT THE WEATHER MOVES AROUND ON THESE
HIGHWAYS AND THAT WARM AIR RISES AND COLD AIR SINKS.
• BUT WHY IS IT SUNNY ONE DAY, AND RAINY THE NEXT?
LET’S TAKE ANOTHER LOOK AT THE WEATHER
MAP
• NOTICE THAT THERE ARE
H’S AND L’S ON THE MAP
• THERE ARE ALSO BLUE
LINES WITH SPIKES AND
RED LINES WITH HALF
CIRCLES
• LET’S TAKE A CLOSER LOOK!
HIGH PRESSURE AREAS
• WHEN COOLER AIR SINKS
AND IS WARMED, THE AIR
CAN HOLD MORE MOISTURE
• THIS USUALLY MEANS
SUNNY SKIES
• WINDS TEND TO MOVE
CLOCKWISE AROUND A
HIGH
LOW PRESSURE AREAS
• WHEN WARM AIR RISES AND IS
COOLED, THE AIR CAN NOT
HOLD AS MUCH MOISTURE
• OFTEN, THESE AREAS ARE
ASSOCIATED WITH
PRECIPITATION AND STORMY
WEATHER
• WINDS TEND TO MOVE
COUNTER CLOCKWISE AROUND
THE LOW
SO, IF YOU SEE A BIG H ON THE WEATHER
MAP OVER THE AREA YOU LIVE, YOU CAN
EXPECT FAIR WEATHER
WHEN YOU SEE A BIG L IN YOUR AREA,
THERE WILL PROBABLY BE STORMY
WEATHER
THESE HIGHS AND LOWS MOVE MORE OR
LESS ALONG THE JET STREAM AND BRING
US OUR WEATHER CHANGES
FRONTS AND AIR MASSES
• AN AIR MASS IS A LARGE BODY OF AIR WHOSE TEMPERATURE AND
MOISTURE ARE FAIRLY SIMILAR AT A GIVEN ALTITUDE
• FRONTS ARE BOUNDARIES SEPARATING DIFFERENT AIR MASSES
• THERE ARE FOUR DIFFERENT AIR MASSES THAT AFFECT THE UNITED
STATES
THE AIR MASSES
• CP( CONTINENTAL POLAR) : COLD, DRY STABLE
• CT( CONTINENTAL TROPICAL) : HOT, DRY, STABLE AIR ALOFT, UNSTABLE AT
THE SURFACE
• MP( MARITIME POLAR) : COOL, MOIST, UNSTABLE
• MT( MARITIME TROPICAL) : WARM, MOIST, UNSTABLE
THIS MAP SHOWS THE AIR MASS
SOURCE REGIONS AND THERE PATHS
OK, NOW WE SEE THE DIFFERENCE IN THE
AIR MASSES
• LET’S LOOK AT THE DIFFERENT FRONTS AND THEIR IMPACT
ON WEATHER
• CAN YOU SEE THE FOUR DIFFERENT TYPES OF FRONTS ON
THE MAP?
WARM FRONTS
• A WARM FRONT IS WARM AIR
DISPLACING COOL AIR DIAGRAM
• SHALLOW LEADING EDGE WARM AIR
MUST “OVERRUN” COLD AIR
• THESE ARE USUALLY SLOW MOVING
COLD FRONTS
• COLD AIR ADVANCES INTO
REGION OF WARM AIR
• INTENSITY OF
PRECIPITATION GREATER,
BUT SHORT LIVED
• CLEARING CONDITIONS
AFTER FRONT PASSES
• USUALLY APPROACHES FROM
W OR NW
STATIONARY FRONTS
• SURFACE POSITIONS
OF THE FRONT DO
NOT MOVE
• OFTEN A REGION OF
CLOUDS
OCCLUDED FRONTS
• COLD FRONT OVERTAKES WARM FRONT
• OFTEN FOUND CLOSE TO THE LOW
PRESSURE CENTER
READY FOR A LITTLE QUIZ?
YOU’LL NEED A SHEET OF PAPER
•WRITE YOUR ANSWERS AS WE GO
•HERE WE GO!
1.
• WINDS IN A LOW
PRESSURE SYSTEM
MOVE _____ AROUND
THE LOW
L
2.
• WHAT TYPE OF
FRONT CAN BE
FOUND CLOSE TO
POINT D ?
3.
• WHICH OF THESE
FRONTS WOULD YOU
EXPECT TO HAVE
GREATER
PRECIPITATION, BUT
BE SHORT LIVED AS
THE FRONT PASSES?
4.
• GIVE THE NAME OF THE
AIR MASS THAT
WOULD HAVE THE
FOLLOWING
CHARACTERISTICS:
• COOL, MOIST,
UNSTABLE
5.
THAT IMPORTANT WEATHER WORD THAT
REFERS TO THE TRANSFER OF HEAT
6.
IN GENERAL, AIR NEAR THE EQUATOR
TEND TO_____ ( RISE OR FALL )
7.
IT CAUSES AIR AND WATER TO BE
DEFLECTED TO THE RIGHT NORTH
OF THE EQUATOR
8.
WHICH OF THE WEATHER HIGHWAYS
USUALLY
CONTROLS OUR WEATHER
9.
WARM AIR HOLDS ( MORE OR LESS )
MOISTURE THAN COLD AIR
10.
• IF THERE IS A BIG
H ON THE
WEATHER MAP
WHERE YOU LIVE,
WOULD YOU
EXPECT FAIR OR
STORMY
WEATHER
H
HOW DID YOU DO?
LET’S CHECK THE ANSWERS!
ANSWERS
1. COUNTERCLOCKWISE
8. WESTERLIES
2. COLD
9. MORE
3. COLD
10. FAIR
4. MARITIME POLAR (MP)
5. CONVECTION
6. RISE
7. CORIOLIS