LOCAL, REGIONAL AND GLOBAL SCALE WINDS, EL NIÑO AND SOUTHERN OSCILLATION (ENSO)

LOCAL SCALE WINDSSea Breeze-Land Breeze Circulation

Due to temperature differences between coastal and inland regions

For southern California, the most likely time for Sea-Breeze is Summer, late afternoon: Warmer regions inland set up conditions to build

thermal low air pressure Cooler water along coastal regions sets up

conditions to build thermal high air pressure Air always moves from areas of higher pressure to

areas of lower pressure.

Sea Breeze CirculationAfternoon warming of valley floors, produces thermals of warm rising air – Thermal Low develops over valleys.

Over the ocean, cooler water produces a Thermal High with cool sinking air.

Result: Cool, moist air flows onshore toward valleys in late afternoons.

Effects: Decrease in temperature and an increase in relative humidity.

Locally, sea breeze from Santa Monica Bay flows onshore and makes its way into the surrounding Los Angeles Basin, even into the San Fernando Valley

Land Breeze CirculationDuring night, radiational cooling in the local

valleys lifts warmer air away from valley flo0rs creating an inversion layer in the atmosphere

Valley regions are cooler at the surface producing a thermal high pressure.

C0astal areas are slightly warmer than adjacent valleys, producing a thermal low pressure.

Time for the greatest difference in temperatures is close to sunrise, setting up conditions for a land breeze, as air is moved offshore from valleys to coast.

Differences in temperature between adjacent valleys and coastal area set up conditions for offshore flow of air

Similar to the land and sea breeze in its diurnal cycle are the valley and mountain breezes. Valley breezes occur in the day because air along mountain slopes is heated more intensely than air at the same elevation over a valley floor.

Rapid radiational heat loss in the evening reverses the process to produce a mountain breeze.

Santa Ana WindsSanta Ana Winds are warm, dry, high velocity

winds that flow into southern California.The winds usually begin in late summer-early

fall and extend to December; typically ending with the arrival of the winter rainy season.

The source region for the winds is northeast of southern California near Utah.

In the late summer-early summer, a large high pressure system (The Great Basin High) develops near the area of Utah, western United States.

Average elevation in Utah is ~5000 feet, while average elevation in southern California is ~ 500 feet : a 4500 foot difference.Descending air is heated by compression (dry rate of

heating at 100C/1000 meters or 5.50 F/1000 feet).250 F added to the air temperature as it descends from the

high towards southern CaliforniaWarmed air is funneled between Sierra Nevada on west and

Wasatch Mountains to the East.Air flows over Mojave Desert – lowering specific humidity.Acceleration of the air occurs two ways:

Funneling through the canyons of the Transverse RangesFlowing downslope the Transverse Ranges under gravity

Great Basin High forming near Utah, producing conditions for development of Santa Ana Winds in southern California.

Note the isobaric pressure near Utah, compared to southern California.

Temperatures near Utah are in the mid-50s F, while temperatures in southern California are in the high 80s F.

CONTINENTAL SCALE WINDS: MONSOONSMonsoon - from Arabic word “mausim” – means “

changing wind directions with a change in season”.

Monsoon are associated with heavy precipitation.There are monsoons in many areas of the world,

including western United States.Arizona, for example, receives most of its annual

precipitation during its summer monsoonal seasonMost described are the monsoons in southern

Asia – India.India has two monsoons: Winter and Summer

Winter Monsoon in IndiaDuring the winter, the Asian landmass

becomes very cold, producing a large high pressure system over most of the southern Asian region.

This high pressure rotates air clockwise, out from the center; pushing the cool, relatively dry air off the subcontinent.

The warmer waters of the Indian Ocean produce a relatively weak low pressure system.

Summer Monsoons in IndiaIn summer, the Asian continental landmass

heats up producing very large thermal Low air pressure systems

Over the relatively cooler Indian Ocean, a thermal high pressure develops

The large continental Low draws in the cool, high humidity air from the Indian Ocean.

The cool humid air is lifted along the Himalayan Mountains, producing massive amounts of precipitation in the northern regions of India

Bangladesh

Summer Monsoon, India

UPWELLING AND OCEAN CURRENTSCold ocean currents flow almost parallel to the

west coast of large continentsCalifornia Current, North AmericaHumboldt (Peru) Current, South AmericaBenguela Current, Africa

The Earth's rotation and strong seasonal winds push the surface water away from the western coast of North America, South America and Africa. 

Upwelling of the nutrient rich water occurs on the western edge of the continental shelf replacing the warmer waters. The abundant marine life within the Galapagos Archipelago

thrives in these nutrient rich waters.

UPWELLING PROCESS

Peru

Humboldt Current

Upwelling along west coast of South America:

Humboldt Current flows north along west coast of South America. Coriolis Force pulls the surface water away from coastline, allowing upwelling of nutrient-rich deep and cold water.

El NiñoEl Niño originally referred to the warm ocean

current that appears along the Pacific coast of South America each year around Christmas

El Niño is an atmospheric and oceanic disturbance in the tropical Pacific Ocean. The name was given by Peruvian fishermen owing

to the timing of the appearance of this disturbance.During an El Niño event the following events

occur:Dwindling of trade windsChanges in barometric pressure across the PacificSea surface temperature anomalies are recordedRainfall patterns are disrupted

El Niño and the Humboldt CurrentThe Humboldt Current is a northward flowing

current along the west side of South AmericaCoriolis Force and surface winds act to pull

surface water away from the coast – creating Upwelling along the west coast of South America

Upwelling promotes:Plankton growth as they follow the cold water

pulled up from depthAnchovies follow the plankton – major food sourceSea birds follow the anchoviesGuano is deposited on local islands by the sea

birds

El Niño and Peruvian Fishing IndustryDuring an El Niño, the fishing industry in Peru

experiences a strong declinePeru’s fishing industry accounts for a significant

portion of Peru’s economyWorld’s foremost producer and exporter of

fishmeal Fishmeal a major component of all animal feed globally In historic El Niño events, cost of animal feed increased

around the world due to the collapse of Peruvian fishing

1972-73 El NiñoAnchovy catch reduced from 10.3 million metric

tons (1971) to 4.6 million metric tons (1972)1982-83 El Niño

Anchovy catch reduced by 50% from 1981 catch

El Niño – Southern Oscillation Events (ENSO)

• Upwelling along Peruvian coast ceases• Trade winds weaken• Weak equatorial eastward current develops• Moisture and temperature patterns alter as air

pressure systems ‘flip-flop’ : • Normal high pressure near Peru moves toward

western Pacific creating droughts in Australia• Normal low pressure near mid-Pacific moves toward

Peru, creating records storms, floods and landslides