repetisjon kap1 kap8

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Information about repetisjon kap1 kap8

Published on April 7, 2008

Author: Sophia


Slide1:  Chapter One Composition and Structure of the Atmosphere Slide2:  Atmospheric gases are often categorized as being permanent or variable, depending on whether their concentration is stable. Permanent gases are those that form a constant proportion of the atmospheric mass. Permanent Gases of the Atmosphere Slide3:  Permanent gases account for the greater part of the atmospheric mass—99.999 percent—and occur in a constant proportion throughout the atmosphere’s lowest 80 km (50 mi). Because of its chemical homogeneity, this region within 80 km of Earth’s surface is called the homosphere. Above the homosphere is the heterosphere, where lighter gases (such as hydrogen and helium) become increasingly dominant with increasing altitude. Because its composition varies with altitude, the heterosphere contains no truly permanent gases. Slide4:  Variable gases are those whose distribution in the atmosphere varies in both time and space. The most abundant of the variable gases, water vapor, occupies about one-quarter of 1 percent of the total mass of the atmosphere. Most atmospheric water vapor is found in the lowest 5 km (3 mi) of the atmosphere. Metan CH4 Slide5:  Since the 1950s, the concentration of carbon dioxide has increased at a rate of about 1.8 ppm per year. The increase has occurred mainly because of anthropogenic combustion and deforestation of large tracts of woodland. Carbon dioxide increase since the 1950s Slide6:  Small solid particles and liquid droplets in the air (excluding cloud droplets and precipitation) are collectively known as aerosols. Aerosols play a major role in the formation of cloud droplets because virtually all cloud droplets that form in nature do so on suspended aerosols called condensation nuclei. Slide7:  The density of any substance is the amount of mass of the substance contained in a unit of volume. At lower altitudes, there is more overlying atmospheric mass than is the case higher up. Because air is compressible and subjected to greater compression at lower elevations, the density of the air at lower levels is greater than that aloft. Slide8:  Temperature profile of the atmosphere Slide9:  Chapter Two Solar Radiation and the Seasons Slide10:  Energy is defined as “the ability to do work.” The standard unit of energy in the International System (SI) used in scientific applications is the joule (J). Power is the rate at which energy is released, transferred, or received. The unit of power is the watt (W), which corresponds to 1 joule per second (1 joule = 0.239 calories). Slide12:  Conduction is the movement of heat through a substance without the movement of molecules in the direction of heat transfer. Convection is the transfer of heat by mixing of a fluid. Radiation is the only one energy transfer that can be Propagated without a transfer medium Slide13:  Electromagnetic radiation consists of an electric wave (E) and a magnetic wave (M). You need the amplitude and the wavelenght to describe the wave. The amplitude gives the quantity of radiation The wavelenght gives the type of radiation Slide14:  It is convenient to specify wavelengths using small units called micrometers (or microns). 1 micrometer equals one-millionth of a meter. Slide15:  This relationship is represented by the Stefan-Boltzmann law, expressed as I = εσT4 I is the intensity of radiation in watts per square meter, ε is the emissivity σ is a constant (5.67 x 10-8 watts per square meter) T is the temperature of the body in kelvins. Slide16:  Celsius Temperature = (oF - 32) / 1.8 Fahrenheit Temperature = (1.8 x oC) + 32 Kelvin Temperature = oC + 273 Slide17:  Solar radiation is most intense in the visible portion of the spectrum. Most of the radiation has wavelengths less than 4 micrometers which we generically refer to as shortwave radiation. Radiation emanating from Earth’s surface and atmosphere consists mainly of that having wavelengths longer than 4 micrometers. This type of electromagnetic energy is called longwave radiation. Slide18:  Energy radiated by substances occurs over a wide range of wavelengths. Because of its higher temperature, emission from a unit of area of the Sun (a) is 160,000 times more intense than that of the same area on Earth (b). Solar radiation is also composed of shorter wavelengths than that emitted by Earth. Slide20:  Chapter 3 Energy Balance and Temperature Slide21:  Atmospheric gases, particulates, and droplets all reduce the intensity of solar radiation (insolation) by absorption, a process in which radiation is captured by a molecule. It is important to note that absorption represents an energy transfer to the absorber. This transfer has two effects: the absorber gains energy and warms, while the amount of energy delivered to the surface is reduced. Slide22:  The reflection of energy is a process whereby radiation making contact with some material is simply redirected away from the surface without being absorbed. The percentage of visible light reflected by an object or substance is called its albedo. When a beam is reflected from an object as a larger number of weaker rays traveling in different directions, it is called diffuse reflection, or scattering. Slide23:  The sky appears blue because gases and particles in the atmosphere scatter some of the incoming solar radiation in all directions. Air molecules scatter shorter wavelengths most effectively. Thus, we perceive blue light, the shortest wavelength of the visible portion of the spectrum. Slide24:  Sunrises and sunsets appear red because sunlight travels a longer path through the atmosphere. This causes a high amount of scattering to remove shorter wavelengths from the incoming beam radiation. The result is sunlight consisting almost entirely of longer (e.g., red) wavelengths. Slide25:  The water droplets in clouds are considerably larger than suspended particulates reflecting all wavelengths of incoming radiation about equally, which is why clouds appear white or gray. Because of the absence of preference for any particular wavelength, scattering by clouds is sometimes called nonselective scattering. Slide26:  Incoming solar radiation available is subject to a number of processes as it passes through the atmosphere. The clouds and gases of the atmosphere reflect 19 and 6 units, respectively, of insolation back to space. The atmosphere absorbs another 25 units. Only half of the insolation available at the top of the atmosphere actually reaches the surface, of which another 5 units are reflected back to space. The net solar radiation absorbed by the surface is 45 units. Slide27:  sensible heat: when energy is added to a substance, an increase in temperature occurs that we physically sense Latent heat: is the energy required to change the phase of a substance (solid, liquid, or gas). In meteorology we are concerned with the heat involved in the phase changes of water. Slide28:  Both the surface and atmosphere lose exactly as much energy as they gain. The surface has a surplus of 29 units of net radiation, which is offset by the transfer of sensible and latent heat to the atmosphere. The atmosphere offsets its 29 units of radiation deficit by the receipt of sensible and latent heat from the surface. Slide29:  Chapter 4 Atmospheric Pressure and Wind Slide30:  Pressure: force exerted per unit of surface area The standard unit of pressure is the pascal (Pa). Meteorologists in the U.S. use the millibar (mb), which equals 100 Pa. Canadian meteorologists use the kilopascal (kPa), equal to 1000 Pa, or 10 mb. Air pressure at sea level is roughly 1000 mb (100 kPa) or more precisely, 1013.2 mb. Slide31:  The enclosed air molecules move about continually and exert a pressure on the interior walls of the container (a). Pressure can increase by increasing the density of the molecules (b) or increasing the temperature (c). If the air in the container is a mixture of gases, each gas exerts its own specific amount of pressure, referred to as its partial pressure. The total pressure exerted is equal to the sum of the partial pressures. This relationship is known as Dalton’s law. Slide32:  Pressure does not decrease at a constant rate. It decreases most rapidly at low elevations and at greater heights. Slide33:  The Equation of State (Ideal Gas Law) p = ρRT where p is pressure expressed in pascals, ρ (rho) is density in kilograms, R is a constant equal to 287 joules per kilogram per kelvin, T is temperature in kelvins. (på norsk ”Tilstandslikningen”) Slide34:  If the air over one region exerts a greater pressure than the air over an adjacent area, the higher-pressure air will spread out toward the zone of lower pressure as wind. The pressure gradient gives rise to the pressure gradient force, which sets the air in motion. For pressure gradients measured at constant altitude, we use the term horizontal pressure gradient force. Slide35:  The vertical pressure gradient force and the force of gravity are normally of nearly equal value and operate in opposite directions, a situation called hydrostatic equilibrium. The Hydrostatic Equation Δp Δz = -ρ g where Δp refers to a change in pressure, Δz refers to a change in altitude, and -ρ g refers to density and the acceleration of gravity. Slide36:  Two columns of air with equal temperatures, pressures, and densities (a). Heating the column on the right (b) causes it to expand upward. It still contains the same amount of mass, but it has a lower density to compensate for its greater height. Because the pressure difference between the base and top is still 500 mb, the vertical pressure gradient is smaller. Slide37:  The rotation of Earth gives rise to the Coriolis force which causes an apparent deflection (turning) of the wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The Coriolis force is zero at the equator and increases to a maximum at the poles. The Coriolis force acting on any moving object increases with the object’s speed. However, the force changes only the direction of a moving object, never its speed. Slide38:  The other factor that influences the movement of air is friction. Air in contact with the surface experiences frictional drag, which decreases wind speed. Friction is important within the lowest 1.5 km of the atmosphere (planetary boundary layer). Air in the free atmosphere, above 1.5 km, experiences negligible friction. Slide39:  The Equation of Motion Δv / Δt = Fp + Fc + Ff where Fp stands for pressure gradient, Fc stands for the Coriolis effect, and Ff stands for friction. NB! Hvis dette er vanskelig, bruk CD’n som fulgte med i boka! Slide40:  A stationary parcel of air in the upper atmosphere subjected to a south-to- north pressure gradient force (a). If the parcel is tethered to an imaginary pole, no movement of the parcel can take place. Once the imaginary cord is cut, the horizontal pressure gradient accelerates the parcel northward (b). Initially, when the wind speed is low, the Coriolis force is small. As the parcel speeds up, the strength of the Coriolis force increases and causes greater displacement to the right (c). The wind speed increases the Coriolis force sufficiently to cause the air to flow perpendicular to the pressure gradient force. The air flow becomes unaccelerated, with unchanging speed and direction known as geostrophic flow (or geostrophic wind). Slide41:  Supergeostropic flow (a) occurs in the upper atmosphere around high-pressure systems. As the air flows, it is constantly turning to its right. This turning motion occurs because the Coriolis force has a greater magnitude than the pressure gradient force (as represented by the length of the dashed arrows). Observe the changing direction of the four solid arrows 1 through 4. Subgeostrophic flow (b) occurs in the upper atmosphere around low-pressure systems. The pressure gradient force is greater than the Coriolis force and the air turns to its left in the Northern Hemisphere. Slide42:  Geostrophic flow cannot exist near the surface. Friction slows the wind, so that the Coriolis force is less than the pressure gradient force. The air flows at an angle to the right of the pressure gradient force in the Northern Hemisphere (a) and to the left in the Southern Hemisphere (b). Slide43:  Enclosed areas of high pressure marked by roughly circular isobars or height contours are called anticyclones. The wind rotates clockwise around anticyclones in the Northern Hemisphere, as the Coriolis force deflects the air to the right and the pressure gradient force directs it outward. In the boundary layer, the air spirals out of anticyclones (a), while in the upper atmosphere it flows parallel to the height contours (b). In the Southern Hemisphere, the flow is counterclockwise (c) and (d). Slide44:  Closed low-pressure systems are called cyclones. Air spirals counterclockwise into surface cyclones in the Northern Hemisphere (a) and rotates counterclockwise around an upper-level low (b). The flow is reversed in the Southern Hemisphere (c) and (d). Slide45:  Elongated zones of high and low pressure are called ridges (a) and troughs (b), respectively. Slide46:  Direction is always given as that from which the wind blows, so that a “westerly” wind is one from the west. Slide47:  Chapter 5 Atmospheric Moisture Slide48:  evaporation condensation sublimation deposition Slide49:  Consider a hypothetical jar containing pure water with a flat surface and an overlying volume that initially contains no water vapor (a). As evaporation begins, water vapor starts to accumulate above the surface of the liquid. With increasing water vapor content, the condensation rate likewise increases (b). Eventually, the amount of water vapor above the surface is enough for the rates of condensation and evaporation to become equal. The resulting equilibrium state is called saturation (c). Slide50:  Humidity refers to the amount of water vapor in the air. The part of the total atmospheric pressure due to water vapor is referred to as the vapor pressure. The vapor pressure of a volume of air depends on both the temperature and the density of water vapor molecules. The saturation vapor pressure is an expression of the maximum water vapor that can exist. The saturation vapor pressure depends only on temperature. Slide51:  Absolute humidity is the density of water vapor, expressed as the number of grams of water vapor contained in a cubic meter of air. Specific humidity expresses the mass of water vapor existing in a given mass of air. Saturation specific humidity is the maximum specific humidity that can exist and is directly analogous to the saturation vapor pressure. The mixing ratio is a measure of the mass of water vapor relative to the mass of the other gases of the atmosphere. The maximum possible mixing ratio is called the saturation mixing ratio. Slide52:  Relative humidity, RH, relates the amount of water vapor in the air to the maximum possible at the current temperature. RH = (specific humidity/saturation specific humidity) X 100% More water vapor can exist in warm air than in cold air, so relative humidity depends on both the actual moisture content and the air temperature. If the air temperature increases, more water vapor can exist, and the ratio of the amount of water vapor in the air relative to saturation decreases. Slide53:  Processes in which temperature changes but no heat is added to or removed from a substance are said to be adiabatic. The rate at which a rising parcel of unsaturated air cools, called the dry adiabatic lapse rate (DALR), is very nearly 1.0 °C/100 m (5.5 °F/1000 ft). Slide54:  The rate at which saturated air cools is the saturated adiabatic lapse rate (SALR), which is about 0.5 °C/100 m (3.3 °F/1000 ft). Slide55:  The environmental lapse rate (ELR), applies to the vertical change in temperature through still air. A balloon rising through air with an ELR of 0.5 °C/100 m passes through air whose temperature decreases from 10 °C at the surface, to 9.5 °C at 100 m, and 9.0 °C at 200 m. The air within the balloon cools at the dry adiabatic lapse rate of 1.0 °C/100 m, faster than the ELR, and therefore attains a temperature of 8 °C at the 200-m level. Slide56:  Chapter 6 Cloud Development and Forms Slide57:  1. Orographic lifting, the forcing of air above a mountain barrier 2. Frontal lifting, the displacement of one air mass over another 3. Convergence, the horizontal movement of air into an area at low levels 4. Localized convective lifting due to buoyancy Four mechanisms lift air so that condensation and cloud formation can occur: Slide58:  The air’s susceptibility to uplift is called its static stability. Statically unstable air becomes buoyant when lifted and continues to rise if given an initial upward push; statically stable air resists upward displacement and sinks back to its original level when the lifting mechanism ceases. Statically neutral air neither rises on its own following an initial lift nor sinks back to its original level; it simply comes to rest at the height to which it was displaced. Slide59:  When a parcel of unsaturated or saturated air is lifted and the Environmental Lapse Rate (ELR) is greater than the dry adiabatic lapse rate (DALR), the result is absolutely unstable air. Slide60:  When a parcel of unsaturated or saturated air is lifted and the Environmental Lapse Rate (ELR) is less than the saturated adiabatic lapse rate (SALR), the result is absolutely stable air and the parcel will resist lifting. Slide61:  When the ELR is between the dry and saturated adiabatic lapse rates the air is said to be conditionally unstable, and the tendency for a lifted parcel to sink or continue rising depends on whether or not it becomes saturated and how far it is lifted. The level of free convection is the height to which a parcel of air must be lifted for it to become buoyant and to rise on its own. Slide62:  Assume the ELR is 0.7 °C/100 m and the air is unsaturated. As a parcel of air is lifted, its temperature is less than that of the surrounding air, so it has negative buoyancy. Slide63:  A parcel starts off unsaturated but cools to the LCL, where it is cooler than the surrounding air. Further lifting cools the parcel at the SALR. At the 200-m level, it is still cooler than the surrounding air, but if taken to 300 m, it is warmer and buoyant. Slide64:  Situations in which the temperature increases with altitude are called inversions. Air parcels rising through inversions encounter ever-warmer surrounding air and have strong negative buoyancy. Inversions are extremely stable and resist vertical mixing. Radiation inversions result from cooling of the surface. Frontal inversions exist at the transition zone separating warm and cold air masses. Subsidence inversions result from sinking air. Slide65:  Chapter 7 Precipitation Processes Slide66:  Air exerts an opposing resistance to a falling object called drag. As speed increases, so does resistance, until its force equals that of gravity and the acceleration ceases. The object falls, but at a constant speed or terminal velocity. More than anything else, terminal velocity depends on size, with small objects falling much more slowly than large objects. Raindrops fall to the surface when they become large enough that gravity overcomes the effect of updrafts. In terms of radius, raindrops are about 100 times bigger than cloud droplets. Slide67:  Warm clouds are those having temperatures greater than 0 °C throughout. The largest droplet (collector drop) falls through a warm cloud and overtakes some of the smaller droplets because of its greater terminal velocity contributing to the collision–coalescence process. Slide68:  Collision and coalecence When a collector drop and a smaller drop collide, they can either combine to form a single, larger droplet or bounce apart. Most often the colliding droplets stick together. This process is called coalescence, and the percentage of colliding droplets that join together is the coalescence efficiency. Because most collisions result in coalescence, coalescence efficiencies are often near 100 percent. Slide69:  Cold clouds (a) have temperatures below 0 °C throughout and consist entirely of ice crystals, supercooled droplets, and a mixture of the two. Cool clouds (b) have temperatures above 0 °C in the lower reaches and subfreezing conditions above. Slide70:  In the Bergeron process, if enough water vapor is in the air to keep a supercooled water droplet in equilibrium, more than enough moisture is present to keep an ice crystal in equilibrium. This causes deposition (i.e., the transfer of water vapor to ice) to exceed sublimation (i.e., the transfer of ice to water vapor), and the crystal grows in size (a). This, in turn, draws water vapor out of the air, causing the water droplet to undergo net evaporation (b). Evaporation from the droplet puts more water vapor into the air and facilitates further growth of the ice crystal (c). Although this is shown here as a sequence of discrete steps, the processes occur simultaneously. Slide71:  Riming and aggregation When ice crystals fall through a cloud and collide with supercooled droplets, the liquid water freezes onto them. This process, called riming (or accretion), causes rapid growth of the ice crystals, which further increases their fall speeds and promotes even further riming. Aggregation is the joining of two ice crystals to form a single, larger one. Aggregation occurs most easily when the ice crystals have a thin coating of liquid water to make them more “adhesive.” Slide72:  Chapter 8 Atmospheric Circulation and Pressure Distributions Slide73:  George Hadley (1685-1768) proposed a simple circulation pattern called the single-cell model to describe the general movement of the atmosphere. In the single-cell model, air expands upward, diverges toward the poles, descends, and flows back toward the equator near the surface. Winds blowing east-to-west or west-to-east are referred to as zonal winds; those moving north-to-south or south-to-north are called meridional. The three-cell model divides the circulation of each hemisphere into three distinct cells: the heat-driven Hadley cell that circulates air between the Tropics and subtropics, a Ferrel cell in the middle latitudes, and a polar cell. Slide74:  Wind speeds generally increase with height between the surface and the tropopause largely because pressure gradient force is typically stronger at high altitudes. The surfaces representing the 900, 800, and 700 mb levels all slant downward to the north, but not by the same amount. Higher surfaces slope more steeply, which means that the pressure gradient force is greater. Slide75:  The polar front is a strongly sloping boundary between warm mid-latitude air and cold polar air. Within the front, the slope of the pressure surfaces increases greatly because of the abrupt horizontal change in temperature. With steeply sloping pressure surfaces there is a strong pressure gradient force, resulting in the polar jet stream situated above the polar front near the tropopause. Slide76:  This hypothetical drawing of the 500 mb surface reveals that heights decrease from south to north but also rise and fall through the ridges and troughs. Vertical changes are highly exaggerated in the figure. Actual height changes are small compared to the size of the continent. Slide77:  Features such as the Intertropical Convergence Zone, the westerlies, and large Rossby waves exist on a global scale. Smaller features, such as cyclones, anticyclones, troughs, and ridges, exist at the synoptic scale, covering hundreds or thousands of square kilometers. Mesoscale events are on the order of tens of square kilometers and last for periods as brief as half an hour. The smallest exchanges of mass and energy operate at the microscale. Slide78:  Monsoon refers to the climatic pattern in which heavy precipitation alternates with hot, dry conditions on an annual basis due to the seasonal reversal in surface winds caused by an oscillation between high- and low-pressure cells. During winter (top), dry air flows southward from the Himalayas. When summer arrives (bottom) moist air is drawn northward from the equatorial oceans. Surface heating, convergence, and a strong orographic effect cause heavy rains over the southern part of the continent. Slide79:  Foehn is the generic name for synoptic scale winds that flow down mountain slopes, warm by compression, and introduce hot, dry, and clear conditions to the adjacent lowlands. Winds warmed by compression that descend the eastern slopes of the Rocky Mountains are called chinooks. The Santa Ana winds of California, common in the fall and spring, occur when high pressure develops over the Rocky Mountains. Katabatic winds originate when air is locally chilled over a high- elevation plateau and warmed by compression as it flows down slope. Slide80:  Along the coast during the daytime, land surfaces warm more rapidly than the adjacent water (a), which causes the air column overlying the land to expand and rise upward (b). At a height of about 1 km, the rising air spreads outward (c), which causes an overall reduction in the surface air pressure. Over the adjacent water less warming takes place, so the air pressure is greater than that over land. The air over the water moves toward the low-pressure area over the land, which sets up the daytime sea breeze. At night the land surface cools more rapidly than the water. The air over the land becomes dense and generates a land breeze. Slide81:  A valley breeze (a) forms when daytime heating causes the mountain surface to become warmer than nearby air at the same altitude. The air expands upward and the air flows from the valley to replace it. Nocturnal cooling makes the air dense over the mountain and initiates a mountain breeze (b). Slide82:  El Niño is a recurrent event in the tropical eastern Pacific in which sea-surface temperatures are significantly above normal. La Niña is the inverse event (cold sea-surface temperatures). The Walker circulation is an east-west circulation pattern of the Tropics, characterized by several cells of rising and sinking air connected by horizontal motions along parallel lines of latitude. The Southern Oscillation is the reversal of surface pressure patterns over the tropical Pacific associated with El Niño events. The Pacific Decadal Oscillation is an alternating pattern of sea surface temperature in the Pacific that reverses over several decades.

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