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Weather Weather Presentation Transcript

  • weather and us
  • Weather effects everything; it provides temperature changes, moist or dry spells and shapes landscapes, which define the plants that grow, further determining the animals that live among them.
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  • The landscape and vegetation in turn are responsible for the weather that occurs, continuing an infinitely changing cycle, creating the complex ecosystems which support the phenomenon of life .
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  • The following is an attempt to help understand how this cycle works and where we fit in.
    • Basic factors contributing to weather
    • Storm systems
    • California climate and us
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  • What factors make up weather?
    • Wind
    What factors make up weather?
    • Wind
    • Temperature
    What factors make up weather?
    • Wind
    • Temperature
    • Precipitation
    What factors make up weather?
  • The story of weather begins with AIR.
  • WIND is the movement of air; air always moves from areas of high pressure to areas of low pressure. Picture filling a balloon: you puff and blow until it’s full of air, air under lots of pressure, then you let it go – quickly the air blasts out of the balloon. * Winds are also created by the spin of the Earth on it’s axis; this is known as the Coriolis Effect which will later be discussed in more detail.
    • Air pressure can be effected by two main factors:
    • Altitude
    • Temperature
  • At sea level the air is under more pressure due to the added weight of all the air in the atmosphere above it.
  • Air at higher altitudes has less atmosphere above it and therefore less pressure is exerted upon it.
  • Under pressure, air (a gas) is compressed, thus the oxygen atoms are more dense: Oxygen atoms in a cubic foot of air at sea level. Oxygen atoms in a cubic foot of air at 10,000’.
  • A cubic foot of air at 10,000’ contains only 75% the oxygen of a cubic foot of air at sea level. That means you get 1/4 less oxygen in every breath you take at 10,000! No wonder you get tired hiking in the mountains!
  • Air, again, moves from areas of high pressure to areas of low pressure, thus creating winds that generally move upward in elevation.
    • Solar radiation heats up the Earth’s surface during the day, and through convection the air close to the surface is also heated. This process happens unevenly, depending on the type of surface, the cloud cover and the angle of the Earth in relation to the sun.
    • Dark colored surfaces heat more than light surfaces, e.g. a dark conifer forest vs. a white glacier (picture wearing a black shirt on a hot day vs. a white shirt).
    • Bodies of water (from small ponds to the Pacific ocean) cause cooler air temperatures.
    • Cloud cover decreases amount of solar radiation getting to the surface, but also works as an insulator, keeping solar warmth on the surface at night.
    • Equatorial regions of the Earth get more sun throughout the year, whereas toward the polar regions the amount of sun varies depending on the season.
  • As air warms, the molecules spread out, resulting in less dense, lighter air, which exerts less pressure. Cool air then sinks, moving beneath the warmer air, filling in these lower pressure areas, creating wind.
  • 10,000 ft. Earth’s surface sea level solar radiation heats surface air under greater atmospheric pressure air cools cool dense air convection occurs heating air (fills lower pressure areas by forcing lighter, warm air upward)
    • TEMPERATURE changes are effected by:
    • solar radiation (as previously discussed)
    • altitude
    • moisture content
  • As altitude increases air temperature decreases: an average of 3.6 degrees F per 1000’. Air molecules transfer heat when they collide, and, though the temperature of individual molecules increases with the decrease of pressure at altitude, there are fewer of them and therefore fewer collisions to transfer heat.
  • MOISTURE is always present in the air in the form of water vapor. The amount of moisture depends on many factors including temperature and proximity to water. Air with a large amount of water vapor will heat and cool more slowly than dry air because of the thermal conductivity of water.
  • PRECIPITATION occurs when there is too much moisture for the air to hold. The maximum amount of water that the air can hold as vapor is known as vapor capacity. The vapor capacity of air is not a specific amount, but depends on temperature; colder air has a lower vapor capacity.
  • When air cools to a certain point relative to the humidity, the vapor will condense, forming miniscule water droplets which create clouds, fog, and dew drops or (if the temperature is below freezing) frost on surfaces. This temperature is known as the dew point.
  • Clouds, such as these cumulous clouds , form with flat bottoms which indicate the elevation at which the air has cooled to dew point.
  • You see your breath when it’s cold out due to your breath’s moisture saturating the air to beyond vapor capacity.
  • The basic factors previously discussed result in the following weather patterns: Low pressure systems High pressure systems Warm fronts Cold fronts
  • The spin of the Earth on its axis creates the Coriolis Effect, which on a larger scale, impacts the movements of these weather patterns. Air moving from high to low pressure centers is deflected by the coriolis effect: to the right in the northern hemisphere and to the left in the southern hemisphere.
  • Low pressure systems originate near the equator and consist of warm air moving toward the polar regions; it rises, cools and condenses, pulling more warm air into the center. The coriolis effect forces low pressure systems to move counterclockwise (as viewed from above). Picture a vacuum cleaner sucking up sunflower seeds.
  • Because warm air can hold more moisture, low pressure systems carry wet air away from the equator, where it cools, condenses, and brings wet weather.
  • High pressure systems originate in polar regions and consist of cold air (high pressure) sinking as it moves toward the equator, forcing warmer air away from the center. The coriolis effect forces high pressure systems to move clockwise (as viewed from above). Picture dropping a softball into a bowl of jello.
  • As cold, dry air is brought from polar regions by high pressure systems, it continues to warm, resulting in fair weather.
  • FRONTS are boundaries between air masses of different pressures/temperatures (contained within pressure systems). Warm air Warm air Cold air Cold air Warm Fronts: warm air moves slowly up and over cold air, resulting in slow developing, sustained cloud cover and rainy weather. Cold Fronts: cold air moves quickly, forcing warm air upward, resulting in sudden heavy downpours or thunderstorms.
  • So what does all this mean for us and the climate in California?
  • Responsible for the overall weather pattern in California is the state’s geography interacting with the semi-permanent high pressure center in the northern Pacific, known as the Pacific High. The Pacific High directs weather northward leaving California with calm, warm weather in the summer, and southward bringing in very wet storms in the winter.
  • Due to the abrupt drop-off of the continental shelf off the coast of California, the ocean currents produce an upwelling of cold water from deep down on the ocean floor. This water abruptly cools the warm, moisture laden, summertime air at the water’s surface, creating fog along the coastline.
  • During the winter as weather brings air currents inland, toward higher elevations, the air, forced upward along the mountain slopes, rapidly cools and reaches vapor capacity. Thus, the mountains create clouds. This is known as orographic uplift .
  • Thus, as air currents move eastward over the Coast Ranges and the Sierra Nevada, the moisture is drawn out of the air as rain or falling snow…
  • … leaving the eastern slope of the mountains with little or no precipitation. This is known as the rainshadow effect.
  • The rainshadow effect is responsible for the climate of desert areas, such as Joshua Tree, Death Valley, Anza Borrego, and the Owen’s Valley, that lie on the leeward side of California’s larger mountains.
  • There is some water that reaches the eastern slopes; it’s primary source: the snow melt off mountain crests in the spring and summer.
  • This water, stored conveniently in the snowpack, accounts for 50% of our drinking and agricultural water in California.
  • Which, as it melts is held in reservoirs and brought to our cities via large aqueduct systems (75% of the water comes from north of Sacramento and 75% of it is used south of Sacramento).
  • As weather patterns change with the global climate, California is being hit with longer droughts and warmer, wetter storms. And, though this weather has increased the Sierra snowpack this winter, the concern, as in the last few seasons, is that the snow will melt earlier in the season due to warm weather and rain. When the snow, our primary water storage source, melts early, there is too much water in the spring, overfilling reservoirs, and leaving too little to sustain us through the dry season.
  • Conness Glacier As the snowpack melts earlier and permanent glaciers dwindle, the general weather warming increases due to the the greater heat absorption of the darker surfaces that were once covered with white snow and ice.
  • As the air warms it continues to hold more water vapor, adding to the greenhouse gases which allow more solar radiation to enter the atmosphere, but insulate it from again leaving.
  • As these changes occur on a small scale, the heating effects air pressure, moving air currents and continuing a butterfly effect of weather change throughout the globe. It may mean water scarcity for us and flooding elsewhere, colder winter temperatures and warmer summer temperatures, but as these changes occur, everything and everyone is effected. Landscapes change defining the plants that grow (including our agriculture), which determine the animals that live among them (including us).
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