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Chap 4 Weather, Climate, Atmosphere Weather vs Climate • Weather is a local area’s short-term physical conditions such as temperature and precipitation. • Climate is a region’s average weather conditions over a long time. • Latitude and elevation help determine climate. • The two most important factors are temperature and precipitation. Weather • condition in the atmosphere at a given place and time. • temperature, atmospheric pressure, precipitation, cloudiness, humidity, and wind. • day-to-day winds, clouds, rains, storms, heat waves, droughts, etc Local Weather • A weather front marks the boundary between two air-masses at different densities. • A front is about 100-200 km wide and slopes where warm and cool air masses collide. Cold front Warm front Weather - Fronts • Warm Front – • The boundary between an advancing warm air mass and the cooler one it is replacing. • Because warm air is less dense than cool air, an advancing warm front will rise up over a mass of cool air. Weather - Fronts • Cold Front – • The leading edge of an advancing air mass of cold air. • Because cool air is more dense than warm air, an advancing cold front stays close to the ground and wedges underneath less dense, warmer air. • A cold front produces rapidly moving, towering clouds called thunderheads. Weather: Stationary & Occluded Front • Stationary front • is a transitional zone between two nearly stationary air masses of different density. • Occluded front • air front established when a cold front occludes (prevents the passage of) a warm front. Climate • Average weather conditions over long period of time • • • • Latitude Altitude Temperature Rainfall • Earth’ processes distributes heat & precipitation, creating climate • Unequal heating of Earth by Sun • Rotation of Earth • Earths orbit on tilted axis • Atmospheric convection currents • Ocean Currents Earth’s climate system is composed of atmosphere/ocean interactions (driven by sun) Climate - Changes with Latitude From equator moving to the poles gets colder and drier There are exceptions particularly for rainfall! Biomes – observe latitude similarities Climate - Changes with Elevation/Altitude • As you go up in elevation: • Colder & Drier • Less soil and less nutrients less plants • Less oxygen • lower air pressure thinner atmosphere less organisms • Temperatures decreases • More UV rays – limits plant growth Solar Energy: Distributing Heat • Global air circulation • driven by the uneven heating of the earth’s surface by solar energy, seasonal changes in temperature and precipitation: • Angle of rays • Surface area • Reflective surfaces Seasons: Earth’s tilted axis • The Earth’s 23.5 degree incline on its axis remains the same as it travels around the sun. As the earth spins around the sun the seasons change. VERY IMPORTANT: What causes the seasons? • The ANGLE of the sun’s rays. • Direct sunlight = summer • Direct = more sunlight in a smaller area more heat stored • Indirect sunlight = winter • Indirect = sunlight spread over larger area less heat stored Albedo • Reflectiveness • The higher the albedo of a surface, the more sun that is reflected and the less heat stored • The lower the albedo of a surface, the more sun that is absorbed and the more heat stored. Masses of air and water transfer solar energy through circulation/convection Wind connects most life on earth. • Keeps tropics from being unbearably hot. • Prevents rest of world from freezing. • http://hint.fm/wind/ Figure 5-1 Wind Cause • Wind is caused by the pressure gradient force. • High pressure means more air, and low pressure means less air. • The air moves from high to low, causing wind. Air Pressure Definition • Air pressure is pressure exerted by the weight of Earth’s atmosphere. • At sea level = 14.69 pounds per square inch. • A barometer is used to measure atmospheric pressure. Air Pressure Pressure Gradient • Changes from high to low. • A higher pressure gradient means stronger winds • the isobars on a weather map would be drawn closer together. Wind Friction • A combination of the • pressure gradient force and • the Coriolis effect. • Friction at the Earth’s surface causes winds to turn a little. Wind Upper Level Flow • There is little friction up in the upper troposphere • Jet stream • River of air • fast flowing, narrow air currents found in the upper atmosphere • https://www.youtube.com/watch?v=C_HiBj0teRY Sea, Land, Valley, & Mountain Breezes • Sea - ocean-to-land breezes • occur during the day. • Land - land-to-ocean breezes • occur at night. • Valley – • the wind blows from the plains into a valley between two mountains, • the wind must divert into a smaller area. • This causes high winds to form through the valleys. • Mountain – • Cool air coming from the top of the mountain • sinks down on the eastern slope, • causing increased winds on the mountain. Microclimate – Rain shadow effect • Topography, water bodies and other local features create local climate conditions known as microclimate. • For example mountains commonly result in high rainfall on the windward side and low rainfall in the rain shadow of the leeward side. Air Masses and Storms Continental vs. Maritime • Continental fronts are • generally cool and dry • Maritime (ocean) fronts are • generally warm and moist. • When these two air masses converge, • the result is usually rain. Wind Cyclones • (called hurricanes in the Atlantic and typhoons in the Pacific) • Violent storms that form over warm ocean waters and can pass over coastal land. • Giant, rotating storms with winds of at least 74 mph. The most powerful ones have wind velocities greater than 155 mph. Wind – affected by spin of Earth • Coriolis Effect • Force created by the rotation of the Earth on its axis • deflect winds to the right in the N. Hemisphere and to the left in the S.Hemisphere. Convection Cells: with No spin Wind Coriolis Effect • Global air circulation is affected by the rotation of the earth on its axis. Figure 5-4 Coriolis Effect • The spinning of the earth creates • Different wind speeds at different latitudes (faster at equator, slower at poles) • clockwise winds in the northern hemisphere • counter clockwise winds in the southern hemisphere • This movement is called the Coriolis Effect. • Watch: N. hemisphere - CLOCKWISE https://www.classzone.com/books /earth_science/terc/content/visual izations/es1904/es1904page01.cf m?chapter_no=visualization S. hemisphere COUNTER - CLOCKWISE Coriolis and Convection cells Without the Coriolis Effect, air would travel in two large cells. The warm air at the equator would rise and move toward the poles. As it moved to the poles, it would cool and sink, then move back to the equator along land, warming as it moved. DOES NOT ACTUALLY HAPPEN With the Coriolis Effect, air still travels from the equator toward the poles, but due to the wind patterns, the 2 cells are broken into 6 global cells. Warm air rises in each cell and cools as it travels through the atmosphere, then sinks and warms as it travels across the land. Coriolis Effect • The spinning of the earth creates • Different wind speeds at different latitudes (faster at equator, slower at poles) • clockwise winds in the northern hemisphere • counter clockwise winds in the southern hemisphere • This movement is called the Coriolis Effect. • Watch: https://www.classzone.com/books/earth_scie nce/terc/content/visualizations/es1904/es190 4page01.cfm?chapter_no=visualization N. hemisphere CLOCKWISE S. hemisphere COUNTER - CLOCKWISE Air Masses and Winds Polar vs. Tropical • The atmosphere has 3 prevailing winds. • Prevailing winds that blow from the North or South Pole are called Polar Easterlies. • Winds that blow in the middle latitudes (between 3o and 60 degrees) are called the Westerlies • Tropical winds that blow toward the equator are called Trade Winds. Prevailing Winds Convection Currents • Global air circulation is affected by the properties of air water, and land. Figure 5-5 Convection Cells • Heat and moisture are distributed over the earth’s surface • by vertical currents • which form six giant convection cells at different latitudes. Figure 5-6 Circulation Patterns Hadley Cells • Warm moist air rises at the equator. Rain • As air rises, it spreads out north & south, then cools and sinks at 30 degrees. Dry • This is why most of the world’s deserts are found at 30 degrees. • These are called the horse latitudes (3o degrees) because early settlers would get stuck here in their boats & couldn’t move. They would finally throw their horses overboard to lighten the load & get moving again. • Trade Winds blow towards equator Hadley Cells Circulation Patterns Ferrell Cells • Warm air rises at about 60 degrees. Rain • and sinks at around 30 degrees, dry, both north and south. • Westerlies. Predominant winds in US Circulation Patterns Polar Cells • Air rises at about 60 degrees. Rain • floats north, and sinks at around 90 degrees, both north and south. Dry • Easterlies Circulation Patterns Ocean Currents: • Ocean currents influence climate by • distributing heat from place to place and • mixing and distributing nutrients. Earth’s Current Climate Zones Figure 5-2 Ocean Currents: Transport nutrients and heat all over the globe Also called the Ocean Conveyor belt • Driven mostly by: • Wind/Coriolis • Temperature gradients (colder water sinks) THERMO • Salinity gradients (saltier water sinks) HALINE Upwelling • Occur when ocean currents pull water from the deep ocean up to the surface • Upwellings pull cold, nutrient rich water up to the surface • Good for fishing: • increases NPP • nutrients are often a limiting factor Gyre Large scale patterns of water circulation • Direction driven by the Coriolis Effect and the continents • 5 gyres: • spin clockwise in the N. hemisphere and • counter clockwise in the S. hemisphere • Redistribute heat and nutrients • Upwellings occur along the west coasts of continents Ocean Currents • There are two types of Ocean Currents: 1. Surface Currents / Surface Circulation • These waters make up about 10% of all the water in the ocean. • These waters are the upper 400 meters of the ocean. • Driven mostly by wind 2. Deep Water Currents • These waters make up the other 90% of the ocean • move around the ocean basins by density and gravity. • The density difference is a function of different temperatures and salinity…THERMOHALINE • These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase. El Nino Southern Oscillation (ENSO) • El Nino – warming event in the tropical Pacific Ocean • Caused by weak/no trade winds blowing WEST • The upwelling along the west coast of the Americas stops • Occurs in cycles every 2-7 years • La Nina – cooling event in the tropical Pacific Ocean • The opposite end of the spectrum as an El Nino • Trade winds and upwelling is strong • Both extremes cause extreme weather events globally El Nino Southern Oscillation ENSO effects – El Nino • During an El Nino event • Warmer ocean temps in the Pacific • Warmer and wetter in the western Americas • Suppresses hurricane activity in the Atlantic ocean • Major declining in fishing populations during an El Nino • Drought in the western Pacific and Australia ENSO effects – La Nina • During a La Nina event • Pacific ocean temps are colder than normal • Droughts along the west coast of the Americas (more snow in northwest US) • Active hurricane season in the Atlantic • More rain in the Western Pacific and Australia The Atmosphere • The mixture of gases known as air • protects life on Earth • by absorbing ultraviolet radiation and • reducing temperature extremes between day and night. • The atmosphere is not static. • Interactions involving the Weather occurs in the troposphere. Gaseous water molecules held together by intermolecular forces cause the formation of clouds. amount of sunlight, • the spin of the planet and • tilt of the Earth’s axis • cause ever changing atmospheric conditions. The auroras occur in the thermosphere and are caused by interactions between the Earth’s atmosphere and charged particles streaming from the Sun. Formation of the Atmosphere • Most of the Earth’s early atmosphere was lost due to the vigorous solar wind from the early Sun. • Continuous volcanic eruptions built a new atmosphere of: water vapor carbon dioxide nitrogen methane Air Density • The atmosphere consists of several layers with different temperatures, pressures, and compositions. The Atmosphere • Earth's atmosphere contains roughly: 78% nitrogen 20.95% oxygen 0.93% argon 0.038% carbon dioxide Trace gases The Earth’s atmosphere (where pressure becomes negligible) is over 140 km thick. Compared to the bulk of the planet, this is an extremely thin barrier between the hospitable and the inhospitable. 1% water vapour All images: NASA Troposphere • 75% of mass of atmosphere • 0 to 11 miles in altitude • 78% nitrogen, 21% oxygen • Location of Earth’s weather • Temperature decreases with altitude until the next layer is reached, where there is a sudden rise in temperature Stratosphere • 11 miles to 30 miles in altitude, calm • Temperature increases with altitude • Contains 1000x the ozone of the rest of the atmosphere; ozone forms in an equilibrium reaction when oxygen is converted to O3 by lightning and/or sunlight • 99% of ultraviolet radiation (especially UVB) is absorbed by the stratosphere Mesosphere & Thermosphere • Mesosphere • 30 to 50 miles in altitude • Temperature decreases with increasing altitude Thermosphere 50 to 75 miles in altitude Temperature increases with increasing altitude Very high temperatures Heat Transfer • Conduction • Warm air holds more moisture than cold air. During conduction, heat & moisture from the ocean or land moves into the atmosphere. • Ex. cold air moving over warm water (like a lake), forming steam fog. • Radiation • Radiation drives weather. Heat from the sun warms the earth, which radiates the heat back into the atmosphere. • Convection • Air & water movement