Science 1206 Chapter 1 - Inquiring about Weather

Transcription

1 Science 1206 Chapter 1 - Inquiring about Weather The Atmosphere: Energy Transfer and Properties (pp ) Weather and the Atmosphere weather the physical conditions of the atmosphere at a specific time and place Weather changes constantly as conditions in the atmosphere can change within very short periods of time (hour to hour, day to day, etc) Components of weather include temperature, precipitation, atmospheric pressure, humidity, wind speed and direction, and sky cover.

2 Components of Weather (table 1.1, p. 11) Earth s Spheres The Sun s energy interacts with all of the Earth s spheres: The atmosphere (air) is a mixture of nitrogen, oxygen, and other gases that extends more than 700 km above Earth s surface. The first 12 km of the atmosphere, called the troposphere, is the region in which all weather takes place. The lithosphere (land) is made up of land-forming continental crust above sea level and oceanic crust at the ocean bottom.

3 Earth s Spheres The hydrosphere (water) is water on or near Earth s surface. It includes liquid water and solid water in oceans, rivers, ponds, and streams, as well as gaseous water vapour in the atmosphere. The biosphere consists of all the areas on and under the lithosphere, in the atmosphere, and the hydrosphere that are inhabited by and support life. Earth s Energy Budget (fig. 1.4, p. 14) Energy from the Sun travels to Earth via radiation. Radiation - thermal energy transfer in which atoms or molecules give off energy as electromagnetic waves There are several forms of radiation (visible light, X-rays, etc) in various wavelengths. When this radiation reaches Earth, it can be absorbed, reflected or transmitted. When it is absorbed, objects gain energy and become warmer. Warm objects also can give off (emit) thermal energy and some energy from the Sun can go back out into space. However, enough stays to help mantain Earth s temperature because of a natural Greenhouse Effect

4 Factors Affecting Absorption of Energy The colour of a surface affects the amount of energy it will absorb or reflect. Albedo - reflectivity of a surface; how much energy it reflects White surfaces tend to reflect more energy while darker surfaces tend to absorb more energy. The type of substance also affects absorption. For example, water absorbs more heat than land. In other words, it takes more energy to increase the temperature of water compared to land. heat sink- any substance that can absorb and retain energy without changing state Thermal Energy Transfer by Conduction, Convection and Radiation (fig. 1.6 and 1.7, pp ) conduction - thermal energy transfer between two objects or substances that are in direct contact convection - thermal energy transfer by the movement of heated material from one place to another All 3 forms of heat transfer (conduction, convection, radiation) are responsible for the transfer of heat energy. As well, advection is the horizontal, large scale movement of air in the atmosphere.

5 Atmospheric Pressure atmospheric pressure - the pressure exerted by air on its surroundings due to the weight of the air The SI unit for pressure is the pascal (Pa). Pascals are quite small, however, and typically pressure is typically reported in kilopascals (kpa). 1 kpa = 1000 Pa. As altitude (height from sea level) increases, the density of air decreases therefore pressure decreases. The movement of air at different temperatures also has an effect on atmospheric pressure. When warm air pushes into and replaces an area of cold air near the ground, the atmospheric pressure in that location decreases. When cold air pushes into and replaces a region of warm air, the atmospheric pressure in that location increases. Humidity and Air Pressure Humidity - the amount of water vapour in the air The more water that is in the air, the lighter it is (water molecules weigh less than oxygen and nitrogen molecules). More water in the air means less oxygen and/or nitrogen. This leads to a decrease in atmospheric pressure. A decrease in atmospheric pressure suggests that warm, humid air is approaching and that the temperature will increase. An increase in atmospheric pressure suggests that cool, dry weather is on its way

6 Humidity and Air Pressure As the temperature of the air increases, its capacity to hold water vapour also increases. dew point - temperature at which air is saturated with water vapour so that it condenses and falls as precipitation Usually, the amount of water vapour in the air is less than the amount required to saturate the air at a given temperature. Meteorologists refer instead to relative humidity, which compares the amount of water vapour in the air with the amount if it were totally saturated. A relative humidity of 50 percent means the air is about 50 percent saturated. A relative humidity of 100 percent means that the air is completely saturated. The Role of Water in Transferring Energy in the Atmosphere Oceans, ponds, and rivers have a low albedo and absorb about 95 percent of the incoming solar energy. The temperature of the air near large bodies of water does not vary as much as the air at great distances from bodies of water. Due to its high specific heat capacity, a lot of energy is needed to change the temperature of water. Thus, oceans and large ponds have a moderating effect on the air temperature of nearby land communities. The circulation of water between Earth s hydrosphere and atmosphere occurs through an endless and continuous cycle of evaporation and condensation the water cycle. This cycle, as you can see, also circulates matter and energy.

7 Science 1206 Chapter 1 - Inquiring about Weather The Causes of Weather (pp ) Air Masses air mass - very large mass of air with nearly uniform properties of temperature, humidity, and pressure Air masses that form over land are known as continental while ones that form over the ocean are maritime. As well, ones that form at the North or South poles are called polar while ones that form in the tropics are tropical

8 Comparing Air Masses High Pressure Systems When an air mass cools over an ocean or a cold region on land, a high pressure system forms. In the northern hemisphere, Earth s rotation causes the wind to move in a clockwise direction around the high pressure centre. As the high pressure air sinks, it becomes warmer and drier. As a result, high pressure systems often bring clear skies.

9 Low Pressure Systems Air masses that travel over warm land or oceans may develop into low pressure systems. When an air mass warms, it expands and rises, making the layer of air thicker. However, as the air rises, it cools. Water vapour in the air may condense, producing clouds or precipitation. This is why low pressure systems often bring wet weather. The wind flows counterclockwise around the low pressure centre in the northern hemisphere and clockwise in the southern hemisphere The Coriolis Effect and Wind Over long distances, wind is affected by Earth s rotation. The Coriolis effect is a change in the direction of moving air, water, or any objects on Earth s surface due to its rotation. Air moving northward from the equator travels east quickly in the same direction that Earth rotates. As a result, the Coriolis effect deflects winds to the right in the northern hemisphere and to the left in the southern hemisphere.

10 Global Wind Systems (table 1.3, p. 29) Wind systems are wide zones of prevailing winds. (When used to describe wind, prevailing refers to the usual direction from which a wind blows.) Earth has three major wind systems, which occur in both hemispheres. Sailors created the term trade winds to name the dependable winds that helped them transport and trade goods. The prevailing westerlies in the northern hemisphere are responsible for much of the weather in North America. The polar easterlies are cold, polar winds. Global Wind Systems

11 Jet Streams A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams. A jet stream is a narrow band of fast-moving wind. Its speed varies with the temperature differences between the air masses at the wind zone boundaries. A jet stream can have a speed up to 300 km/h or greater, at altitudes of 10 km to 12 km. Storms form along jet streams and generate large-scale weather systems. These systems transport cold surface air toward the tropics and warm surface air toward the poles. Weather systems generally follow the path of jet streams Fronts front - a zone that develops as a result of the meeting of two air masses with different characteristics There are 4 types of fronts - Cold front - Warm front - Stationary front - Occluded front

12 Fronts (fig 1.18, p. 31) Cold front - occurs when cold, dense air displaces warm air. It forces the warm air up along a steep slope Warm Front: Advancing warm air displaces cold air along a warm front, which develops a gradual boundary slope Stationary Front: When two air masses meet but neither advances, the boundary between them stalls. The resulting stationary front often occurs between two modified air masses with small temperature and pressure differences. The air masses can continue moving parallel to the front. Fronts (cont..) Occluded Front: Sometimes a cold air mass moves so fast that it overtakes a warm front, forcing the warm air up. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front. (Occluded means obstructed.)

13 Surface Currents in the Ocean Surface currents are created by wind. Warm currents begin at the equator while cold ones start at the poles There are five major sets of surface currents, one in each main ocean basin the north Pacific basin, the south Pacific basin, the north Atlantic basin, the south Atlantic basin, and the Indian Ocean basin Due to the Coriolis effect, the major currents in the northern hemisphere move in a clockwise direction, and those in the southern hemisphere move in a counterclockwise direction. Another result of the Coriolis effect is that currents on the western side of ocean basins tend to be narrow and fast moving. Currents on the eastern side of ocean basins are the opposite. They tend to be wider and slow-moving Deep Ocean Currents Deeper ocean water moves as a result of differences in the temperature and the salt content of water. Colder water is denser than warmer water. So colder water sinks and displaces warmer water around it. In a similar way, saltier water is denser than water that is less salty. So saltier water sinks and displaces the less salty water around it.

14 Extreme Weather - Thunderstorms Thunderstorms occur when water vapour in rising warm air condenses, releasing thermal energy. The energy further heats the air, which continues to rise. The condensation produces large thunderheads (cumulonimbus clouds), which precede and accompany thunderstorms Thunderstorms occur where atmospheric conditions are unstable. Moist air rising quickly up a mountain or within a cold air mass can produce intense thunderstorms. Sea breezes in the tropics, for example, often result in thunderstorms. Advancing cold fronts and, less often, advancing warm fronts also cause thunderstorms. Extreme Weather - Tornadoes A tornado is a violent, funnel-shaped column of rotating air that touches the ground. A tornado can form when high-altitude horizontal winds meet large thunderstorms The horizontal winds cause the rapidly rising air in the thunderstorm to rotate. This produces a spinning vortex of air called a funnel cloud. In some cases, the funnel cloud touches the ground and becomes a tornado. The tornado follows seemingly random, winding paths, hurling dust and debris in all directions. Surface winds can reach 400 km/h.

15 Extreme Weather - Hurricanes Storms that we know as hurricanes to those near the Atlantic Ocean are cyclones to people living near the Indian Ocean, and typhoons to those near the western Pacific Ocean. Hurricane season extends from late summer to early fall, the period when the oceans store the greatest amount of thermal energy. Some of the world s most violent weather results from the exchange of thermal energy in the tropics. Together, warm ocean water and winds produce conditions that lift moist air high into the atmosphere,. The water vapour condenses, producing clouds and rain. The rain releases large amounts of thermal energy transferred from the warm ocean water. At the same time, the rising air produces a low pressure area at the ocean s surface. Warm air rushes toward the low pressure area to replace the rising air. The Coriolis effect forces the air to rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere Hurricanes diagram (fig and 1.23 p. 35)

16 Extreme Weather - Nor easters Nor'easters form as a result of the interaction of two air masses. One air mass is cold, dry Arctic air that pushes down across eastern Canada and the northern United States. The other air mass is warm, humid air that has picked up thermal energy and moisture from being over water from the Gulf of Mexico or the Gulf Stream. When these two air masses meet, the difference in temperature fuels the storm. Warm air is quickly pulled up the eastern side of the developing storm, creating an area of low pressure. Nor easters rotate in a counterclockwise direction and usually occur from September to April. Extreme Weather - Blizzards A blizzard is a violent winter storm with freezing temperatures, strong winds, and blowing snow. Although snow is usually part of a blizzard, it does not have to be falling for a storm to be called a blizzard. Instead, strong winds can blow snow that has already fallen, creating low-visibility white-out conditions. In a blizzard, winds exceed 56 km/h and visibility is reduced to less than 0.5 km for at least three hours