HONORS GEOGRAPHY: INTRO TO METEOROLOGY PART I

QUESTIONS TO ASK - how are weather and climate affected by the relative positions of the earth and sun? - how do wind and ocean currents redistribute the sun’s heat - what factors influence the world’s climate regions? - why is climatic change a cause for concern KEY TERMS weather solstice continental climate climate equinox rotation precipitation revolution front MAIN IDEA: Climate is influence by many factors, such as the relationship between the earth and sun, latitude, ocean currents and elevation. Samuel Langhorn Clemens (Mark Twain) once said, “Everybody talks about the weather, but nobody does anything about.” Another quote of his was “The coldest winter I’ve ever experienced was a summer in San Francisco.” - No matter where you come from, continent, country, state, city, town, village, there is an expression to “tell” the weather. - ex.; “Red sky in the morning, sailors take warning. Red sky at night, sailor’s delight.” - India, “when the frog croaks in the meadow, there will be rain in 3 hours.” - In England and America they say, “Rain before seven, sun by eleven.” - There is nothing in your life that isn’t affected by weather; - where you’re going to live, - what you’re going to wear, - planting and harvesting your crops. - Sometimes even your very survival depends on what you know about weather and climate. WEATHER AND CLIMATE - the definition of weather is the condition of the bottom layer of the earth’s atmosphere in one place over a short period of time. - the atmosphere is actually several layers - bands of gases, water vapor and dust in the sky - descriptions usually include temperature, moisture or precipitation, and wind - a day might be warm, dry and calm - or cold, snowy, and windy - weather is always changing - sometimes drastically in one day - from very hot to very cold in the same place - weather in one region can influence weather in another region far away - ex: weather in Nevada can affect the weather in central and southern CA - ex: weather in Korea or Japan can affect the W. coast of the U.S. and Canada - climate, on the other hand defines weather patterns experienced over a long period of time - the climate depends on several factors - elevation - latitude - nearby landforms - nearby bodies of water - climate CAN change, but this takes place over longer periods of time - ex: global warming - so weather and climate are related, but not synonymous - distinction is the difference between specifics and generalities - old farmer’s expression: - “climate is what you expect, weather is what you get” THE SUN AND THE EARTH - all weather on earth (and life for that matter), gets its source from one place - the Sun - some 93 million miles away - the star is intensely hot and gives off energy and light - essential for almost all life on earth THE GREENHOUSE EFFECT - only a small amount of the sun’s radiation makes it to the surface of the earth - some is reflected back into space by the atmosphere and earth’s surface - enough reaches us to warm the land and water - the atmosphere also helps keep heat from escaping back into space - so in essence, the atmosphere is like several glass walls in a greenhouse - traps the sun’s warmth so plants and animals can grow - this is called the greenhouse effect - without it earth would be too cold for life - only half of the earth gets heat and light at the same time - day, night, seasons, and different climates - all determined by the relative position of the sun and earth RELATION AND REVOLUTION - as Earth spins through space is spins on its axis like a top - this is called rotation - the axis is an invisible line through the center of the earth - from the south pole to the north pole - it rotates once about every 24 hours - actually every 24 hours, 56 minutes, and 4.2 seconds - the side facing the sun is day - the side away from the sun is night - the earth spins from west to east - so the sun rises in the east and sets in the west - earth also revolves around the sun in a nearly circular path - this is called an orbit - a revolution is one complete orbit around the sun - one complete orbit takes 365.25 days - the length of a year - because of the .25 days, every four years is a leap year - adding another day to February - brings the calendar back to 365 days - as the earth revolves around the sun its position changes - it is not straight up and down - our planet wobbles - tilted 23.5 degrees on its axis - so the Tropic of Cancer is 23.5 degrees North - and the Tropic of Capricorn is 23.5 degrees South - this marks the part of the earth that gets the most light and heat - this tilt also explains why sunlight strikes different parts of the earth more directly - at different times of the year - you can see this in your textbook on page 64 - you can see the North Pole tilted toward the sun - when the sun falls more directly over the Northern Hemisphere - making the days longer and warmer in the summer - and shorter and colder in the winter - this causes summer in the Northern Hemisphere - and winter in the Southern Hemisphere - as the earth moves to the opposite side of the sun the tilt changes - now the Southern Hemisphere is tilted toward the sun - these changes in season are marked by two distinct calendar days - the summer and winter solstices - usually around June 21 and December 21 - these dates are when the sun is directly overhead - the Tropics of Cancer and Capricorn - there are other “markers” for seasonal change - usually on March 21 and September 23 - these are called the Spring and Fall Equinoxes - on these days the sun is directly over the Equator - making the length of days and nights equal all over the earth LATITUDE AND CLIMATE - the angle of the sun’s rays affect weather and climate in other ways - because the earth is “nearly” round the sun’s rays fall at or near the Equator - again, look at your book on page 64 - the rays grow less and less direct as they fall closer to the Poles - so most places near the Equator stay warm - and areas far from the Equator are cold - geographers use latitude to divide the world into zones - latitude is the distance from the Equator - tropical zones are low latitude zones - again 23.5 degrees north and south of the Equator - most places in the tropics are hot year round - the earth’s 2 temperate zones are in th middle latitudes - 23.5 degrees N to 66.5 degrees N - 23.5 degrees S to 66..5 degrees S - climate is generally cooler than the tropics - daily temperature change can vary widely - the polar zones are in the high latitudes - 66.5 degrees N and 66.5 degree S to the poles - the sun never hits these latitudes directly - meaning the suns rays are spread out more - the climate is always cool - or bitterly cold - you can see a diagram of these latitudes on page 66 DISTRIBUTING THE SUN’S HEAT - the sun’s heat doesn’t stay where it falls - if it did, the tropics would get hotter each year - and the polar regions colder - instead, heat is distributed by a process called convection - the transfer of heat from one place to another - convection occurs because warm gases/liquids are less dense than cool gases/liquids - warm gases/liquids tend to rise - cool gases/liquids tend to sink - pushing out lighter gases/liquids on the surface - lighter gases being pushed out are called winds - lighter liquids being pushed out are called currents - warm air and water tend to flow from the Equator to the Poles - cold air and water tend to flow from the Poles to the Equator - this is the simple explanation - but there’s much more - there are smaller, more complex patters that affect weather and climate - WIND - the weight of the atmosphere on top of us is called atmospheric pressure - warm air rising from the surface to the atmosphere leaves a “hole” below/ - the air that is pushed out is called wind - it is the movement of winds worldwide that redistribute heat over the earth’s surface - winds patterns begin when light warm air rises from the Equator and flows northward and southward - toward the poles - at the same time cold air from the poles sinks to the surface and moves toward the Equator - if the world were standing still the winds would blow in a straight line - but remember the earth is rotating - the spin deflects, or bends the winds - this is called the Coriolis effect - in the north, the winds curve to the right - and in the south winds curve to the left - the diagram on page 66 shows the wind currents of our planet WIND PATTERNS - in each latitude zone, temperature and air pressure combine to create a pattern - called prevailing (or dominant) winds - at the Equator, rising warm air causes calm weather or light breezes - this area is called the Doldrums - two other regions of light and unpredictable winds are about 30 degrees N and S latitudes - cool air sinks to the surface - sailing ships had trouble getting enough winds to travel - these latitudes are called the Horse Latitudes - during the Spanish exploration era, their ships would be stuck - in order to lighten the ship, the threw their horses overboard - making the boat lighter and easier for the wind to move - between the Horse Latitudes and Equator are where you can find the Trade Winds - blowing steadily toward the Equator from the NE and SE - merchants would sail using these winds - in order to trade with other countries on the other side of the ocean - hence the name Trade Winds CURRENTS - the ocean water also help to redistribute heat on the surface of the earth - the ocean convection patterns are very similar to those of the atmosphere - heat rises, cold sinks - warmer water at the surface (because it’s nearer to the sun) - much colder water at the depths (where there is little to no sun) - again, this convection moves warm water towards the poles - and cold water towards the Equator - wind and the Coriolis effect influence the currents of the ocean - usually in circular patterns - the map on page 67 shows the major ocean currents, both warm and cold PRECIPITATION - humidity is the amount of water vapor in the atmosphere - precipitation on the other hand is all forms of water that fall from the sky to the surface - the timing and volume (how much) of precipitation are important aspects of climate - warm less dense air absorbs moisture in the air in the form of water vapor - the warmer the air, the more water vapor the atmosphere can hold - when it cools, it can’t hold on to the water vapor - then water vapor condenses and becomes liquid - tiny droplets of water - these gather together to form clouds - precipitation happens when the clouds have more water than they can hold - and falls to the ground - snow, rain, sleet, or hail depending on the temperature and wind conditions - the water cycle is an excellent graph to show how precipitation works - you can see this on page 68 of your textbook - meteorologists divide precipitation into three types - convectional, orographic, and frontal - page 69 of your book shows these different types of precipitation CONVECTIONAL PRECIPITATION - this occurs when hot, humid air rises from the surface and cools - thereby, because the air is cooler, it cannot hold a lot of water vapor - causing rain - this is common near the Equator and the tropics - where there is LOTS of heat and humid air - convectional rainfall produces rain that feed lush, tropical forests OROGRAPHIC PRECIPITATION - sometimes warm moist air is forced up a landform - like a mountain or a cliff - this effect is called orographic precipitation - it is common along seacoasts and mountains - warm moist ocean winds blow toward the coastal mountains - the warm winds cool as they rise up the windward side of the mountains - clouds form and rain or snow falls - but the time the moisture reaches the top of the mountain - there is very little moisture that can fall on the other side - the leeward side of the mountain - the air warms up again as it goes down the other side - this warm dry air is called a rain shadow - this is why there are dense forests on the western side of the Sierras - and it’s dryer on the eastern side - ex: the Mojave Desert FRONTAL PRECIPITATION - this is the most common type of precipitation - occurs when two fronts, or masses of air of different temperatures, meet - warm air is forced upward by the cold, sinking air - the warm air cools, and water vapor condenses and rain begins OTHER INFLUENCES OF CLIMATE - so temperature and precipitation are major factors affecting weather and climate - other influence may be nearby bodies of water, elevation, and location - in relation to nearby NEARBY BODIES OF WATER - land and water absorb and store heat differently - land temperatures can change drastically within a few hours - especially during the seasons - ex: Siberia temps can vary by as much as 140 degrees - from summer to winter - water temperatures change much more slowly -ex: avg. temps on ocean surfaces vary less than 10 degrees - throughout the year - because of this difference, large bodies of water affect surrounding climates - oceans or large lakes - winds that blow over water tend to become the temperature of the ward - these cooler winds blow from the ocean to the land - if the land is warm or hot, the temperature will cool - we call these sea breezes - these areas have milder climates than land at the same latitude - simply because they’re near water - coastal areas have specific climate types -ex: middle latitude areas on continental west coasts - mild, humid marine climates - prevailing westerlies supply warm, moist ocean air - marine climates are found on Pacific Coast of North America - and in Southern Chile - the British Isles and western European countries have marine climates - these countries are farther north - but winds that blow onshore from the east are warmer - because of the North Atlantic Current - bringing warm water from the Caribbean and Gulf Stream - see page 67 for examples - central areas of continents in the Northern Hemisphere have continental climates - away from the influence of the oceans - cold, snowy winters, and warm or hot summers - humidity and precipitation vary - temps often reach extremes of hot and cold - regions with this climate are the transition zones between mild and polar climates - ex: Ctl Europe, Northern Eurasia, parts of China and much of N. America ELEVATION - Mt. Kilimanjaro in Tanzania, Africa is 19,341 feet above sea level - located near the Equator - but the mountain has snow at its peak year round - so despite being in the tropics, the elevation affects its climate - this effect happens worldwide - important rule: air temperatures decrease 3.5 degrees for every 1,000 feet - this is why climbers should know the temp at the foot of a mountain and the top - it can be hot at the bottom - but it can be a blizzard nearer the top NEARBY LANDFORMS - variations in climate happen naturally - as a matter of fact, no climate is ever completely uniform - coastal mountains are landforms that affect climate - inland mountains, large deserts, lakes, forests, other natural features - all of these influence climate, too - dense cities with tall buildings can affect the climate - pavement and concrete absorb vast amounts of heat and energy - so temps in cities tend to be warmer than the surrounding area - another example can be flat areas, like a football or baseball field - the dark grass absorbs much more heat than the surrounding area - so it can be 80 degrees in the areas near the classrooms - but it can be 110 degrees on the field - football and baseball players know this phenomenon - all of these variations are called microclimates WORLD CLIMATE REGIONS - geologists and climatologists have developed many different classification systems - to define the world’s major climate regions - this can be a difficult thing to do - changing climate conditions - lack of accurate weather data in many parts of the - most efforts to classify climate regions rely on two factors - temperature and precipitation - climate classifications began in the early 1900s by Wladimir Koppen, a German scientist - these systems identify five broad climate regions - tropical, dry, moderate, continental and polar - highland climates from mountain systems are similar to the polar regions - most of these climate groups have specific subdivisions - look on page 72 of your text - it will show you the climate classification system we’ll be using in the course CHANGING CLIMATES - many changes in climate result from changes in nature - but recently more may now be caused by human actions - increasing amounts of carbon dioxide “can” affect the atmosphere - causing “global warming” - this could potentially melt the polar icecaps - causing a rise in sea levels - flooding low lying areas like Marina del Rey - and introducing vast amounts of fresh water into the salty seas - other effects of global warming could be an increase in precipitation in some areas - and less precipitation in others - fertile farmland could turn into empty deserts - now, to be fair, some scientists say that global warming is a natural effect - happening in cycles - ex: some say the Vikings came to N. America when it was warmer - but in mid-1500s North Atlantic climates cooled - lower temps made farming difficult - resulting in lower population levels - as the Greenland ice sheet grew, settlements became fewer and fewer - until they were finally abandoned