Weather: A study in Variables Coriolis Effect & Mid- Latitude Cyclones

Review  Atmosphere  Structure  composition  Heat  Global Heat uneven  Convection, conduction, radiation  Pressure  Gravity, depth  Water, temperature  Causes wind  Atmosphere  Structure  composition  Heat  Global Heat uneven  Convection, conduction, radiation  Pressure  Gravity, depth  Water, temperature  Causes wind

Review...  Water  Relative humidity  Amount in air affected by temperature (capacity/cups)  Air masses  Consistent throughout  Don’t mix  Boundaries are fronts  Warm = less dense, cool = more dense  Water  Relative humidity  Amount in air affected by temperature (capacity/cups)  Air masses  Consistent throughout  Don’t mix  Boundaries are fronts  Warm = less dense, cool = more dense

Things are never as simple as they seem!  Let’s start with wind  Blows from areas of high pressure to areas of low pressure  Opposed by friction near the surface  Also have to account for the rotation of the Earth for any wind that travels a significant distance  Let’s start with wind  Blows from areas of high pressure to areas of low pressure  Opposed by friction near the surface  Also have to account for the rotation of the Earth for any wind that travels a significant distance

Global winds, no rotation (pg 540) Cold = High pressure Hot = Low pressure

With Rotation  Last slide = Space frame of reference  Our frame of reference = Northern hemisphere = winds curve to the RIGHT  In Southern hemisphere, winds curve to the LEFT.  Earth rotates counterclockwise when viewed from above the north pole.  Rotation makes stuff happen.  Last slide = Space frame of reference  Our frame of reference = Northern hemisphere = winds curve to the RIGHT  In Southern hemisphere, winds curve to the LEFT.  Earth rotates counterclockwise when viewed from above the north pole.  Rotation makes stuff happen.

Global Winds (Ideal, pg 541) Polar cell = Air moving South warms and rises Hadley cell = air moving North cools and sinks Notice ALL arrows! What happens to them?

Coriolis effect  Ball is rolled straight across the merry-go- round.  Due to the spin, ball does not go where it is aimed, but goes to the person next to them.  Ball is rolled straight across the merry-go- round.  Due to the spin, ball does not go where it is aimed, but goes to the person next to them.

Global Winds & Coriolis To see Coriolis effect, “stand” at the TAIL of the arrow and “look” towards the HEAD of the arrow.

Put the pieces together  We’ve got the pieces, PUZZLE time!  Mid-latitude cyclones. These things are why we get cold and rain with a low pressure system.  Let’s start with Definitions...  We’ve got the pieces, PUZZLE time!  Mid-latitude cyclones. These things are why we get cold and rain with a low pressure system.  Let’s start with Definitions...

Cyclones, Anticyclones  Cyclones =  areas of low pressure at the surface  Counterclockwise winds  Air moving inward at the surface = convergence  Anticyclones =  Areas of high pressure at the surface  Clockwise winds  Air moving outward at the surface = divergence  Cyclones =  areas of low pressure at the surface  Counterclockwise winds  Air moving inward at the surface = convergence  Anticyclones =  Areas of high pressure at the surface  Clockwise winds  Air moving outward at the surface = divergence

Air will move from high pressure areas to low. L *Air moving down in a high pressure area can’t make clouds because it is warming up! Bigger cup! wind H

L Coriolis effect causes wind to curve to the right.

L We will see these on weather maps. Instead of arrows, there will be front lines. (Air masses don’t mix.)

Fronts curve due to friction at the surface. Like playing crack the whip! Warm front = Sunday driver, “moseying” along. Gives high clouds & slow, lasting rain. Slides over the cold air and cools slowly. L Warm Air Here Coldest Air Here Cold Air Here

Cold front = Road rage. Gives thunderstorms and severe weather. Shoves under the warm air and cools it quickly. L Warm Air Here Coldest Air Here Cold Air Here

So What?  Question 1: Why does a high pressure system seem to go with clear warm days if high pressure goes with cool air?  Answer: Air moving downward can’t make clouds, because it is warming up as it sinks. Warmer air increases it’s capacity. (Cup cannot overflow)  That’s why it is sunny with a high system!  Question 1: Why does a high pressure system seem to go with clear warm days if high pressure goes with cool air?  Answer: Air moving downward can’t make clouds, because it is warming up as it sinks. Warmer air increases it’s capacity. (Cup cannot overflow)  That’s why it is sunny with a high system!

And?  Question 2: So, if warm air means less pressure, then why do we get colder rainy days with a low pressure system?  Air rushing into a low pressure area creates fronts.  Cold fronts associated with low systems push warm, wet air up where it is cooled quickly to make clouds and rain.  Question 2: So, if warm air means less pressure, then why do we get colder rainy days with a low pressure system?  Air rushing into a low pressure area creates fronts.  Cold fronts associated with low systems push warm, wet air up where it is cooled quickly to make clouds and rain.

 High pressure system on the right! Cold air sinking toward Earth will warm up. This will increase the capacity to hold water. Makes it SUNNY! Low pressure system on the left! Warm air rising will cool down. This decreases the capacity to hold water. Makes it CLOUDY! H L This represents a front line!

Convergence & Divergence  Air rushing into a low (convergence) will increase the pressure and weaken the Low.  Same for the High!  Have to have balance above, in the atmosphere, to maintain the high or low pressure system.  Divergence (moving air away) has to be maintained above in order for a low to continue at the surface.  Air rushing into a low (convergence) will increase the pressure and weaken the Low.  Same for the High!  Have to have balance above, in the atmosphere, to maintain the high or low pressure system.  Divergence (moving air away) has to be maintained above in order for a low to continue at the surface.

Convergence & Divergence L H Divergence Convergence

Recipe for a snow storm