Because Earth is a sphere, the Sun’s light hits Earth’s curved surface more directly close to the equator and less directly closer to the poles. The difference in the angle of sunlight striking Earth’s surface at different latitudes causes uneven heating. Because of Earth’s tilt, the angle at which sunlight strikes Earth at different times of year causes the Northern and Southern Hemispheres to experience more and less intense sunlight and thus opposite periods of higher and lower average temperatures (seasons). Earth’s tilted axis results in differing amounts of daylight in an area over the course of the year. The differences in how long the Sun shines affects how much the area gets heated up by the Sun and, thus, its temperature. Ocean Currents: Surface current: top layer of the ocean; driven by temperature differences and winds Deep current: lower layer of the ocean; driven by density changes due to differences in salinity and temperature Upwelling: occurs when the surface currents move out allowing the deep currents to briefly rise to the surface; only happens in 1% of the ocean Global conveyor belt: system of deep currents that circles the entire globe; one molecule of water can take over 1000 years to travel back to it's original starting point Gulf stream: warm surface current that moves from the Gulf of Mexico, up the east coast of the United States and towards western Europe. This current greatly influences the weather in the Eastern US and Western Europe. Density: a measure of how much matter is in a given amount of space Salinity: the amount of dissolved salts in water Thermohaline circulation: large scale circulation of water due to differences in salinity and temperature Ocean currents move due to the uneven heating of earth's surface. Sun's radiation is most direct at the equator; therefor this location receives the most radiant energy. Near the equator, warm water will rise and move towards the poles, where it will cool and begin to sink. Salt does not freeze. When water freezes at the poles, salt is pushed out. Therefor the saltiest water will be found at the poles. The path of surface currents is influenced by the wind, the Coriolis effect and by continental deflection. Density is influenced by temperature and salinity; colder water will be more dense than warm water; water with more salt (high salinity) will be more dense than water with less salt. Climate: the average weather patterns in a location of a long period of time Climate is influenced by 5 factors: Latitude- more direct sun rays will cause warmer climates Altitude- greater distance from ground will be colder Mountains- winds are deflected by the mountain causing a rain shadow effect Continental position: locations close to the ocean will not get as hot/cold as cities on the same latitude but inland. Land and sea breezes: coastal cities experience more moderate weather, meaning they won't get as hot or cold as inland cities on the same latitude Weather: short-term changes in the atmosphere experienced daily Wind Currents: winds are created due to a difference in temperature and pressure. As warm, less dens air rises, cooler, more dense air moves in the fill the empty space. This movement of cooler air is wind. Global winds (prevailing winds): major winds high in the atmosphere created by uneven heating of earth's surface; move in one direction due to coriolis effect and can move air masses Coriolis effect: apparent deflection of air as it travels north to south (northern hemisphere) or south to north (southern hemisphere) Northern hemisphere winds rotate counter-clockwise; southern hemisphere winds rotate clockwise Global wind belts: smaller convection cells (Hadley, Polar and Ferrel Cells) that are created at the latitudes due to uneven heating of earth's surface. The name indicates the direction the winds come from. Winds move from colder to warmer areas. Trade winds: just above and below the equator; move east to west Westerlies: between 30-60 degree latitude; move west to east Polar easterlies: between 60-90 degree latitude; move east to west local winds (surface): closer to ground level; move short distances and in any direction Sea breeze: occur during day; cool air from water blows toward land Land breeze: occur during night; cool air from land blows toward sea Jet streams: narrow belt of very high speed winds in the upper atmosphere; can be found in different places and affect the movement of storms. Air Pressure: measured in millibars by a barometer. Air pressure decreases as you increase altitude. There are 2 main reasons for this: Gravity pulls air molecules down Air molecules get their energy from the heat of the earth's surface. As they rise and spread out, they "lose" energy. This is why air is described as being "thin" at higher altitudes. The molecules are spreading further apart as they rise in the atmosphere. High pressure: molecules are tightly packed and cooler; these molecules will move down and out Low pressure: molecules warm up and spread out more; these molecules will move up and in towards the center. Fronts: created when 2 air masses meet Cold front: occurs when strong cold air masses rushes in, forcing warm air to rise; storms and heavy rain. Cooler temperatures will occur as the cold front passes. Warm front: occurs when warm air meets cold air; warm air gently rises over cold air; gentle rains. Warmer temperatures will occur as the warm front passes. Occluded front: warm air meets a cold air mass but before it can rise another cold air masses rushes in from behind forcing warm air straight up; causes severe weather and blizzards Stationary front: warm and cold air mass meet but neither is strong enough to move past the other; causes overcast, drizzly weather for a few days Jet streams: narrow belt of very high speed winds in the upper atmosphere; can be found in different places and affect the movement of storms. Air Masses: Continental polar (cP): cold, dry air formed over land Continental tropical (cT): warm, dry air formed over land Maritime polar (mP): moist, cold air formed over water Maritime polar (mP): moist, cold air formed over water Maritime tropical (mT): moist, warm air formed over water Daily weathered is influenced by the movement of these air masses. Severe Weather: Tornadoes: when warm, humid air rises and meets colder air higher the atmosphere, clouds form. If winds at the surface are moving at a different speed or direction than winds higher in the atmosphere, horizontal rotation can occur. Air rises quickly into the thunderstorm, causing the rotation to shift vertically and a funnel cloud forms. Tornado alley is an area of states mostly in the middle of the US and towards the east that experience the most tornadoes. The United States is unique in that cold arctic air from Canada travels south while warm, moist air from the Gulf of Mexico travels north. This provides the perfect conditions for storms. The US experiences the most tornadoes in the world due to these features. Hurricanes: warm, moist air over warm ocean waters evaporates, causing the atmosphere to warm. Winds can cause even more water to evaporate. As the warm air rises, winds begin to spiral around the center. Winds 74 mph+ can be classified as a hurricane. Weather Maps: Weather maps usually show fronts and high and low pressure systems. Fronts are always shown at the beginning of the warm air or cold air mass and point in the direction they will be moving. Isobars indicate changes in air pressure. The closer the lines are, the windier it will be and possibly storms will occur in these areas. High pressure areas have "happy" weather - clear, sunny, calm. High pressure is indicated with a measurement of 1013 millibars and above. Low pressure areas have "lowsy" weather- rainy and possibly Low pressure is indicated with a measurement below 1013 millibars, typically in the 900's range. Cloud Formation and Precipitation: Dew point: the temperature at which gas condenses back in to a liquid Relative humidity: the amount of moisture the atmosphere can hold under current conditions. This is represented as a percentage. Remember the sponge analogy. Pouring one cup of water onto a small sponge may cause it to be completely saturated and leak water droplets= 100% humidity. Pouring the same amount of water on a large sponge may only fill the sponge half way = 50% humidity. When the atmosphere is at or near 100% humidity, it must release some of the moisture in the form of precipitation. The closer the dew point is to the actual temperature, the more likely precipitation will occur.