science
ademola
Nov11_weather_part1.pptxFinal Variable: air motion Two types
Vertical: Convection where have we seen this before?
transfers heat from hot to cold
Air rises when heated, cool air moves in to fill the space
this sets up a convection current
Last time
2. Horizontal: Wind
From high to low pressure
This time
Rising air from Convection
We discussed this (rising air leads to cooling saturation condensation)
and your homework explores that this is heating of the ground which
then heats the air (2 step process)
Question: heating of the ground will be very different if you have
direct vs. indirect rays. How does this vary around the globe?
Different heating around the globe
More here, near equator
because of direct rays
Less here, near pole
because of indirect rays
Different heating around the globe
Rising air here, near equator.
Note the cloud- rising air will
cause clouds/rain.
Sinking air, near pole
Different heating around the globe
Tropical convection
(where the most heating is)
Warm rising air is lighter
low pressure
Cold dry air is heavier High pressure
Different heating around the globe
The arrows complete the
circuit. Air rises, moves to the pole, sinks at the pole.
Then comes back to the
equator
Global Heating and Air Circulation
Unequal heating of the Earth causes general air circulation. As we have discovered, equatorial regions receive more direct radiation and therefore have higher temperatures.
The warmer equatorial air rises and moves toward the polar regions (cooling as it goes). The colder polar air sinks and is drawn toward the equator.
Another view of atmospheric circulation
But life is complicated
The earth rotates. Air won’t go in a
straight line. Think of throwing a ball off of
a merry-go-round. Would it go straight?
A cute demonstration
Global Heating and Air Circulation
The fact that the Earth rotates complicates the circulation. Free-moving objects appear to deviate from straight-line paths as the Earth spins. This deflection due to Earth’s rotation is called the Coriolis effect.
Coriolis Effect- Deflects objects moving N and S
An “apparent” deflection- because it started where the
earth’s rotation speed was fast and is carrying that
momentum to regions where its slower.
Really is the same as throwing a ball off of a merry go round where
the ball has the momentum from the spinning carousel.
Consequence of Coriolis
Global pattern of highs and lows are created
Alternating patterns of rising and sinking air
This simple circulation becomes This
Air tries to blow straight from H L pressure but
gets deflected to the R in the N. Hemisphere
In the end, it spirals around the low: counterclockwise
For high pressure, it spirals the opposite way around
clockwise
Horizontal winds tend to go in circles or spirals. This
is why its called atmospheric circulation.
H
Consequence of Coriolis
Can you see the spiraling wind patterns?
Note: spiraling
Pattern in SH is reversed
from NH. We won’t pursue
this further here.
C:\Users\David2\Documents\PG_1210_fall20\lecture_ppts\GOES16-AL292020-GEOCOLOR-1000x1000.gif
Horizontal winds tend to go in circles or spirals. This
is why its called atmospheric circulation.
Example of recent hurricane in the Gulf of Mexico. Watch it spin!
Note: I don’t think I can post this on Bb- its an enormous file. You can go to this general site
And click around to see satellite images of hurricanes
https://www.star.nesdis.noaa.gov/GOES/floater.php?stormid=AL292020#homePageLink
H
L
Air curves around Low pressure counter clockwise
and clockwise around High pressure
Cold N
Wind
(wind from the N)
warm S
Wind
(wind from the S)
Cold N
wind
This pattern of L-H-L-H etc. typically alternates around the globe
Thus cold and warm alternate
Importance of wind direction
South winds: bring air from the south where its warmer
south winds are warm
North winds: bring air from the north where its normally colder
north winds are cold
Rising air saturation
View from side
View from above
Surface winds blow counterclockwise around a cyclone and converge inwards
We call low pressure systems: Cyclones (highs are anticyclones)
Linked with clouds and precipitation due to rising air.
This is the 2nd way we get rising air (first was convection)
Three dimensions: Air converges inward and then rises up
View in 3D: rising at lows, sinking at highs
Sinking air at anticyclones dries air out. Highs are clearer and dry
Blobs of high and low pressure
Can you see wind spirals?
Real life
www.climateanalyzer.org
Why was it so warm yesterday? From Capital Weather Gang (WaPost):
The impressive heat comes from a sprawling dome of high pressure
centered just off the East Coast. Clockwise flow on the western
periphery of the high was pumping in warm air from the south
Make maps of pressure with contour lines: Isobars
Unit is millibar (“bar” is like barometer). Average pressure at
sea level (0 elevation) is 1013 mb.
High pressure: can go up to 1024-1028 mb.
Low pressure: can go down to 996 mb
Whats the contour interval here?
What is the likely pressure at the center of the high pressure?
H
1004
1008
4 mb
A bit over 1020 mb
Winds: warm or cold?
H
1004
1008
Warm side
Cold side
Note: winds are sort of parallel to the isobars as a result of
Coriolis
Practice with a low
L
1004
1000
X
What is the pressure at the center of the low
What is the possible pressure at X?
A bit less than 988 mb
Between 996 and 1000 mb
Practice with a low
L
1004
1000
X
Draw winds and identify cold and warm sides
General pattern: warm air to the East of the low, Cold air to the West
N
E
S
W
How fast does the wind blow?
H
Like a steep altitude gradient which causes water to flow fast and
cause more erosion, a steep pressure gradient (contour lines close
together) causes the wind to blow faster.
Pressure pattern can tell you warm or cold and gradient can tell you wind speed
Slower wind
Faster wind
Weather typically moves W E
(you need this for your homework)
H
L
Cold N
Wind
(wind from the N)
warm S
Wind
(wind from the S)
Cold N
wind
X
What can X expect to happen? Can we issue a forecast?
Falling pressures
Some sort of precipitation
After low passes by, clearing colder, N wind
Preparing for 2nd part of homework. Need to look at a
real weather map with symbols
Weather stations are circles
Cloudy
Clear
Partly cloudy
Preparing for 2nd part of homework. Need to look at a
real weather map with symbols
Weather stations are circles- with tails
Cloudy
Wind from North
Wind from South
Preparing for 2nd part of homework. Need to look at a
real weather map with symbols
Weather stations are circles- with tails and numbers
Cloudy
Wind from North
Temperature = 40
Wind from South
Temperature = 70
40
70
Preparing for 2nd part of homework. Need to look at a
real weather map with symbols
Other things: other numbers and feathers on the tails
Cloudy
Little feather-
gentle breeze
More feathers
Stronger breeze
40
70
30
50
069
Other numbers near the dots refer to humidity and pressure
don’t worry about them for now
You will have to draw your own isotherms
https://courseware.e-education.psu.edu/courses/meteo101/javascript/Lesson2/contour_tool_t.html
Play with this first! The key here is that it helps you
figure out what to do if you don’t have exact values, i.e.
you have to draw a 40F contour, but your data is not
exactly 40, but a whole range of temperatures
Remember this?
PSC 121 Prince George's Community College
10
20
30
Y
?
40
If the value of Y is 42, how should you draw the contour line labeled 40?
50
Note spacing between isotherms (gradients)
Temperature gradients now
Something interesting is happening in Kansas, Iowa, Wisconsin.
Temperature in Iowa drops from 20C (68F) in SE part of state
To near 0C (32F) in NW part of state. A steep, sharp gradient in temperature
Why do we care about steep, sharp temperature gradients?
See you Monday
(but you are in position to look for this on the 2nd part of
the homework after you draw your isotherms)
Final part combines isobars and isotherms- need Monday’s class for that
