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GLOBAL CLIMATES & BIOMES APES CH. 4 Slide 2 Weather vs Climate Weather: Climate : The state of the atmosphere at this moment. Scales of seconds to days. Can only be predicted (forecast) no more than a few days into the future. The average weather that occurs over a region over a long period, Usually decades to millennia. Can make general observations regarding temperature & precipitation. Processes that effect these are: uneven heating of Earth, convection currents, Earths rotation, tilt, & ocean currents. Slide 3 Earths Atmosphere Slide 4 Atmospheric Layers Troposphere: Densest layer due to gravity. Air molecules packed closer to Earth. Nitrogen, oxygen & water vapor - gases Weather is confined to this layer. Air flow is vertically Air rises & falls due to temperature/humidity differences (in other words density). Rising & falling air is called CONVECTION Slide 5 Warm moist air rises less dense Humid air is less dense than dry air Warm air is less dense than dry air Cooler dry air sinks more dense Dry air is more dense than moist air Cool air is more dense than warm air Slide 6 Atmospheric Layers Stratosphere: Temperature inversion air warms as it increases in altitude. Ozone layer interacting with UV radiation heats this layer. Ozone (O 3 ) absorbs most UV-B & all of UV-C radiation. Air flow is horizontal Jet stream narrow band of high wind that moves W to E (~ 200 mph) Influences weather; approx. three in each hemisphere Slide 7 Slide 8 Temperature Inversions Temperature inversions are when air warms as you increase in altitude. Stratosphere and Thermosphere have temperature inversions. Thermosphere is heated directly by suns radiation Temperature inversion in the troposphere can occur: Traps pollution near surface; affects weather; prevents mixing of air Slide 9 Uneven Heating of the Earth Three Causes of Uneven Heating: a. Variation of Angle Suns rays strike mid-latitudes & polar regions at a more oblique angle Suns rays strike the equator (tropics) at perpendicular (90 degree) angle. Causes radiation to travel through more atmosphere at the poles = loss of solar energy more energy reaches the tropics than at the mid-latitude & polar regions Slide 10 Earth is Unevenly Heated Slide 11 Uneven Heating Cont. b. Surface Area Heated by Sun Perpendicular angle causes energy to be distributed over a smaller surface area @ equator. Thus tropical areas receive more solar energy per square meter than higher latitudes Slide 12 Uneven Heating c. Albedo the percentage of incoming sunlight is reflected from a surface. The higher the albedo for a surface, more solar energy it reflects, and less it absorbs. Slide 13 Properties of Air Air has four properties that determine how air circulates in the troposphere: 1. Density 2. Water vapor capacity 3. Adiabatic heating or cooling 4. Latent heat release Slide 14 Density & Water Vapor Capacity Density determines the movement: Less dense = rises; areas of rising air have low air pressure More dense = sinks; areas of sinking air have high air pressure Water Vapor Capacity is related to temperature: Warm air can hold more water vapor than cool air Maximum amount of water vapor that can be in the air at a given temperature is called Saturation Point. That given temperature is called Dew point. The temperature at which water vapor condenses. Humidity is = 100% Slide 15 Relative humidity is the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature. Slide 16 Adiabatic Cooling & Heating As air rises air pressure decreases, so it expands and cools. As air sinks air pressure increases, so it contracts and heats. These processes are called Adiabatic cooling & heating respectively. The adiabatic lapse rate is a decrease of 3.5F/1,000 ft (6.4C/km) of altitude under normal conditions. Varies. Slide 17 Dew Point Slide 18 Latent Heat Release Condensation, changing from vapor to liquid, releases heat (energy). This is known as Latent Heat Release: Energy released in condensation can warm the air such as in storms. Slide 19 Atmospheric Convection Currents Global patterns of air movement that are initiated by the uneven heating of the Earth. As air rises at the equator: 1. Density decreases, moisture increases, and air pressure decreases. 2. Air reaches saturation point (humidity = 100%) 3. Condensation occurs and clouds/precipitation form 4. Condensation releases latent heat which causes air to expand and rise more rapidly 5. These processes cause air to continuously rise near equator forming a river of air upward. 6. This is considered an area of LOW PRESSURE!! Slide 20 Slide 21 Atmospheric Convection Currents Global patterns of air movement that are initiated by the uneven heating of the Earth. As air is chilled at the top of the troposphere by adiabatic cooling (Air sinking): 1. Air at this point had little water vapor. 2. It is displaced N or S by the less dense rising moist air 3. Displaced air sinks to about 30 N or S latitude 4. Air contracts and heats up as it sinks due to adiabatic heating 5. This warm, dry is considered an area of HIGH PRESSURE!! Slide 22 Slide 23 Slide 24 High & Low Pressure Systems High pressure systems are described as sinking dry air. These are associated with fair weather because no condensation is occurring Low pressure systems are described as rising, moist air. These are associated with stormy weather because condensation occurs. Air always moves horizontally across the surface from high pressure to low pressure = WIND!!!!