Next Week: QUIZ One question from each of week: –9 normal lectures + global warming lecture –Over main topic of lecture and homework Multiple choice, short answer, matching, map question Powerpoints:

AOS 101 April 15/17 Thickness and Thermal Wind

Thickness The vertical distance in meters between two pressure levels 1000 hPa = 0 m 500 hPa = 5600 m THICKNESS = 5600 m – 0 m = 5600 m Z

Consider a column… Cool the average temperature of the column by 20 K Air becomes more dense, mass stays the same so volume must decrease Air takes up less space COLUMN SHRINKS 1000 hPa = 0 m 500 hPa = 5600 m COOL

Consider a column… Cool the average temperature of the column by 20 K Air becomes more dense, mass stays the same so volume must decrease Air takes up less space COLUMN SHRINKS 1000 hPa = 0 m 500 hPa = 5000 m COOL Z = 5000 m

Consider a column… Warm the average temperature of the column by 20 K Air becomes less dense, mass stays the same so volume must increase Air takes up more space COLUMN EXPANDS 1000 hPa = 0 m 500 hPa = 5600 m WARM

Consider a column… Warm the average temperature of the column by 20 K Air becomes less dense, mass stays the same so volume must increase Air takes up more space COLUMN EXPANDS 1000 hPa = 0 m 500 hPa = 6200 m WARM Z = 6200 m

Summary COOL air will result in LOW THICKNESS WARM air will result in HIGH THICKNESS Thus, the thickness between two pressure layers is proportional to the average temperature of that layer Z ≈ const x T ave

Thermal Wind Not an actual wind “Blows” along thickness contours with cold (low thickness) air to the left Stronger temperature gradients imply stronger thermal wind Equal to the SHEAR of the wind (i.e. is related to the observed wind)

V 850 V 200 VTVT

VTVT 5660 m COLD WARM 5600 m 5540 m

Clockwise turning of winds with height VeeringBacking 850 hPa 300 hPa 850 hPa 300 hPa VTVT VTVT Counterclockwise turning of winds with height WARM AIR ADVECTIONCOLD AIR ADVECTION

Midlatitude Weather Upper-level winds will be much stronger than low-level winds –i.e. thermal wind will be very close to upper- level wind Consider a front with cold air to the north and warm air to the south.

COOLWARM P = 500 hPa Geostrophic wind into page Thermal wind into page LOW heightsHIGH heights NORTH PGF P = 700 hPa

Thermal Wind Balance Pressure gradient increases with height –Winds increase with height Thus, areas of strong temperature (thickness) gradient will have strong winds above them.

700 hPa Temperature hPa Thickness

500 hPa Height 500 hPa Wind Speed

hPa Thickness 500 hPa Wind Speed

Cyclone Symbols: Point in direction of front movement COLD WARM OCCLUDED STATIONARY

Warm Front COOL WARM

Associated Weather (WF) Gradual Slope Stratiform rain –long lasting light rain –occurs on cool side of front Temperature increases prior to frontal passage Wind becomes southerly after passage

Cold Front COOL WARM

Associated Weather (CF) Much Steeper Slope More intense (convective) rain –Thunderstorms for a shorter period –occurs on warm side of front Temperature decreases after frontal passage Wind becomes northerly after passage

L LIGHTER RAIN HEAVIER RAIN WARM AIR COLD AIR COOL AIR

Finding a Front Temperature (dewpoint) Gradient Change in wind direction –Converging winds at the front “Kink” or “trough” in isobars (lower pressure) Banded precipitation

Upper-level terminology TROUGH: area of lower heights RIDGE: area of higher heights L H