NATS 101

Lecture 18Local Winds

Supplemental References for Supplemental References for Today’s LectureToday’s Lecture

Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp. McGraw-Hill. (ISBN 0-697-21711-6)

Review: Forces for Curved Flow

5700 m5640 m

Centripetal = CF + PGF

Centripetal << CF or PGF

Gradient Wind Balance

Wind

Wind

Geo

Win

dPGF

PGF

PGF

CF

CF

CF

Assume PGF constant size along entire channel

Trough

Ridge

Sub-geostrophicSub-geostrophic

Super-geostrophicSuper-geostrophic

Divergence and Convergence

Diver

gence

Mas

s Los

s

Convergence

Mass G

ain

Mass transport in channel

Large

Small

Trough

Ridge

Convergence

Convergence Divergenc

Divergencee

DivergenceDivergence

ConvergenceConvergence

Convergence

Convergence

Divergence

Divergence

ConvergenceConvergence

DivergenceDivergence

Gedzelman, p249

Vertical Motion

Mass Conservation leads to Upward motion beneath regions of divergence Downward motion beneath regions of convergence

Trough RidgeRidge

Review: Friction

Pressure Gradient Force

Coriolis Force

Wind

1004 mb

1008 mb

Because PGF becomes larger than CF, air parcel will turn toward lower pressure.

Friction Turns Wind Toward Lower Pressure.

Eventually, a balance among the PGF, Coriolis and Frictional Force is achieved.

Friction

Gedzelman, p249

Flow at Surface LowsLows and HighsHighs

Spirals OutwardDivergence

Spirals InwardConvergence

www.met.tamu.edu

upward motionupward motiondownward motiondownward motion

Ahrens, Fig 6.21

Friction Induced Vertical Motion

Atmospheric Scales of Motion

Ahrens, Fig 7.1

Review:Thermally Direct Circulation

Heat Heat

WarmWarm ColdColdRisingRising SinkingSinking

DIV

DIV

CON

CON

HeatHeat

Sea Breeze Development(Courtesy of Mohan Ramamurthy, WW2010)

1 2

3 4

Sea Breeze Development(Courtesy of Mohan Ramamurthy, WW2010)

5 6

7

RisingRising SinkingSinking

DIV

DIV

CON

CONHeatHeat

Sea Breeze versus Land Breeze (Courtesy of Mohan Ramamurthy, WW2010)

Stronger Temperature contrast during PM than during AM

Sea breezes are stronger than land breezes

PM

AM

LAX Airport 4 PM upper 7 AM lower

Sea Breeze

• Regular feature of many coastal areas

California, Florida, Gulf Coast • Occurs along large lakes-Great Lakes• Typically strongest during Spring-Summer• Can penetrate inland 50 km or more • Temperatures can drop ~10oC• Nose of cool air can trigger thunderstorms

Florida Satellite Loop

Mountain-Valley Breeze

Ahrens, Older Ed.

Sun warms slopes Density decreases Air rises

IR cools slopes Density increases

Air drains

RisingRising SinkingSinking

DIV CON

HeatHeat

CON DIV

Mountain-Valley circulation important to TucsonConvection over Catalinas during PM summer.SE drainage flows during early AM all year.

Phoenix-Tucson Diurnal Winds

5 PM5 AMPM heating

AM cooling

5 PM5 AMPM heating

AM cooling

PMAM TUS TUS

PMAM PHX PHX

Darwin was Right

The Darwin "Natural Selection" Awards are given each year to bestow upon (the remains of) that individual, who through single-minded self-sacrifice, has done the most to remove undesirable elements from the human gene pool.

www.darwinawards.com

Darwin was Right

Ladies and Gentlemen...(drum roll...and envelope please)...

We proudly present: Larry Walters, who now (hopefully) realizes the value of knowing some basic meteorology.

Darwin was Right

Larry Walters is among the relatively few who have actually turned their dreams into reality.

His story is true (confirmed), though you may find it hard to believe.

Darwin was Right

Larry was a truck driver, but his lifelong dream was to fly.

When he graduated from high school, he joined the Air Force in hopes of becoming a pilot.

Unfortunately, poor eyesight disqualified him.

Darwin was Right

So when he finally left the service, he had to satisfy himself with watching others fly the fighter jets that crisscrossed the skies over his backyard.

As he sat there in his lawn chair, he dreamed about the magic of flying.

Darwin was Right

Then one day, Larry Walters got an idea.

He went down to the local army-navy surplus store and bought a tank of helium and forty-five weather balloons.

Darwin was Right

These were not your brightly colored party favors, these puppies measured 4 feet across and held 33 cubic feet of helium.

Back in his yard, Larry used straps to attach the balloons to his lawn chair, the kind of chair you have in your own yard.

Darwin was Right

He anchored the chair to the bumper of his jeep and inflated 42 of the balloons with helium.

Then he packed some sandwiches, beers and loaded a BB gun, figuring that he could pop a few balloons when it was time to return to earth.

Darwin was Right

Preparations complete, Larry Walters sat in his chair and cut the anchoring cord.

His plan was to float slowly upward a few hundred feet, pop a few balloons, and lazily float back down to terra firma.

But things didn't quite work out that way.

Darwin was Right

When Larry cut the cord, he didn't float lazily up; he bolted up as if fired from a cannon!

Nor did he go up a couple hundred feet.

He climbed and climbed and climbed until he finally leveled off at 16,000 feet!

Darwin was Right

At that height, he feared deflating any of the balloons, lest he unbalance the load and really experience flying!

So he stayed up there, drifting cold and frightened for 14 hours, totally at a loss as to how to get down.

Darwin was Right

Eventually, Larry drifted into the approach corridor for Los Angeles International Airport.

A Pan Am pilot radioed the tower about passing a guy in a lawn chair at 16,000 thousand feet with a gun in his lap. (Folks…that's a conversation I'd have given anything to have heard!)

Darwin was Right

LAX is right on the ocean, and y’all know at nightfall or aloft during the day, the winds along the coast blow offshore.

As dusk fell, Larry (alledgedly) even drifted out over the ocean for awhile.

Darwin was Right

Larry eventually gathered enough nerve to shoot a few balloons and slowly descended.

But as Larry approached the ground, he got entangled in power lines that caused a blackout in Long Beach.

Once on terra firma, he was arrested.

Darwin was Right

But as he was being led away in handcuffs, a television reported called out, "Mr. Walters, why'd you do it?"

Larry stopped, eyed the man, then replied nonchalantly, "A man can't just sit around."

Darwin was Right(Most of the Time!)

Congratulations Larry, you are a rare survivor to earn (honorable mention) for the prestigiousDarwin “Natural Selection” Award

So, what’s the moral of the story? If you don’t learn basic meteorology, then you too will be strategically positioned to receive theDarwin "National Selection" Award

Summary

• Land-Sea Breeze

Due to differential heating between land-seaGives diurnal reversal in temperature contrastOnshore winds PM - Offshore winds AM Sea Breeze PM - Land Breeze AM

• Mountain-Valley Breeze

Differential heating along mountain slopes Gives diurnal reversal in temperature contrast Upslope winds PM - Downslope winds AM Valley Breeze PM - Mountain Breeze AM

Next Lecture

• Monsoon Circulations-Seasonal Winds

Asia Monsoon

“Arizona” Monsoon

Assignment for Next Lecture

• Reading – Ahrens pg 173-175• Problems - 7.5