NATS 101 Lecture 18 Local Winds

Supplemental References for Today’s Lecture Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp. McGraw-Hill. (ISBN )

Review: Forces for Curved Flow 5700 m 5640 m Centripetal = CF + PGF Centripetal << CF or PGF Gradient Wind Balance Wind Geo Wind PGF CF Assume PGF constant size along entire channel Trough Ridge

Sub-geostrophic Super-geostrophic

Divergence and Convergence Divergence Mass Loss Convergence Mass Gain Mass transport in channel Large Small Trough Ridge

Convergence Divergenc e Divergence Convergence

Convergence Divergence Convergence Divergence

Gedzelman, p249 Vertical Motion Mass Conservation leads to Upward motion beneath regions of divergence Downward motion beneath regions of convergence Trough Ridge

PGF PGF CF CF

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

Surface Roughness 1004 mb 1008 mb The decrease in wind speed and deviation to lower pressure depends on surface roughness. Smooth surfaces (water) show least slowing and deviation (typically 20 o -30 o from geostrophic). Rough surfaces (mtns) show most slowing and deviations (typically 30 o -40 o from geostrophic). Mtns Water 20 o -30 o 30 o -40 o

Gedzelman, p249 LowsHighs Flow at Surface Lows and Highs Spirals Outward Divergence Spirals Inward Convergence

upward motion downward motion Ahrens, Fig 6.21 Friction Induced Vertical Motion

Atmospheric Scales of Motion Ahrens, Fig 7.1

Examples of Different Scales Danielson et al

Review: Thermally Direct Circulation Heat WarmColdRisingSinking DIV CON Heat

Sea Breeze Development (Courtesy of Mohan Ramamurthy, WW2010) 12 34

56 7 RisingSinking DIV CON Heat

Mature Sea Breeze isobars  Coriolis Turning Ahrens, Fig 7.4 PGF 2 km 

Coriolis Impact on Sea Breeze Danielson et al, Fig 11.15

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 ~10 o C Nose of cool air can trigger thunderstorms Florida Satellite Loop

Lake Breeze Ahrens, Older Ed.

Mountain-Valley Breeze Ahrens, Older Ed. Sun warms slopes Density decreases Air rises IR cools slopes Density increases Air drains Mountain-Valley circulation important to Tucson Convection over Catalinas during PM summer. SE drainage flows during early AM all year.

Mountain-Valley Breeze Ahrens, Older Ed. Sun warms slopes Density decreases Air rises IR cools slopes Density increases Air drains RisingSinking DIVCON Heat CON DIV Mountain-Valley circulation important to Tucson Convection over Catalinas during PM summer. SE drainage flows during early AM all year.

Phoenix-Tucson Diurnal Winds 5 PM 5 AM PM heating AM cooling 5 PM5 AM PM heating AM cooling PM AMTUS PM AMPHX

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.

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 prestigious Darwin “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 the Darwin "National Selection" Award

Summary Land-Sea Breeze Due to differential heating between land-sea Gives diurnal reversal in temperature contrast Onshore 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 Problems - 7.5