WINDS LOCAL, REGIONAL AND GLOBAL SCALE WINDS, EL NIÑO AND SOUTHERN OSCILLATION (ENSO)
LOCAL SCALE WINDS • Sea 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 Circulation Afternoon 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 Circulation • During 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.
Land Breeze Circulation Differences in temperature between adjacent valleys and coastal area set up conditions for offshore flow of air
Mountain and Valley Breezes 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 Winds • Santa 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 California Warmed 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 Ranges Flowing downslope the Transverse Ranges under gravity Santa Ana Winds
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: MONSOONS • Monsoon - 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 season • Most described are the monsoons in southern Asia – India. • India has two monsoons: Winter and Summer
Winter Monsoon in India • During 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 India • In 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 CURRENTS • Cold ocean currents flow almost parallel to the west coast of large continents • California Current, North America • Humboldt (Peru) Current, South America • Benguela 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 Niño • El 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 winds • Changes in barometric pressure across the Pacific • Sea surface temperature anomalies are recorded • Rainfall patterns are disrupted
El Niño and the Humboldt Current • The Humboldt Current is a northward flowing current along the west side of South America • Coriolis 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 depth • Anchovies follow the plankton – major food source • Sea birds follow the anchovies • Guano is deposited on local islands by the sea birds
El Niño and Peruvian Fishing Industry • During an El Niño, the fishing industry in Peru experiences a strong decline • Peru’s fishing industry accounts for a significant portion of Peru’s economy • World’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 Niño • Anchovy 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