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Physics Quiz 4

by: Emily Mason

Physics Quiz 4 PHYS 2400

Emily Mason

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These notes cover the discussion questions and notes from chapters 14, 16, and 17
Physics of Weather
Miguel Larson
Study Guide
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This 27 page Study Guide was uploaded by Emily Mason on Thursday April 21, 2016. The Study Guide belongs to PHYS 2400 at Clemson University taught by Miguel Larson in Winter 2016. Since its upload, it has received 45 views. For similar materials see Physics of Weather in Physics 2 at Clemson University.


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Date Created: 04/21/16
Chapter 13 FORECASTING ● National Weather Service (NWS) : the official agency for weather forecasting in the US ● Advanced Weather Interactive Processing System (AWIPS) : workstation that allows forecasters to simultaneously display maps of current weather conditions, output of computer forecast models, satellite and radar images, forecast advisories, and more. ● Forecasting Methods: 398 ○ Zone forecast- a forecast issued at designated times each day and extending out to a week in the future ○ Climatological forecasts- weather forecast based on the use of long-term climatic averages ○ Analog approach- one tries to recognize similarities between current conditions and similar well-studied patterns from before ■ requires knowledge of a long history of local and regional weather conditions ○ Numerical weather forecast (399)- the most dominant forecasting approach ■ Based on computer programs that attempt to mimic the actual behavior of the atmosphere ○ Persistence forecast- a forecast that relies completely on current conditions with no reference to climatology ■ Use this in everyday life; when we see clear skies we assume it will be this way all day ● Types of Forecasting: 399 ○ Qualitative forecasts- provide only a categorical value for the predicted variable ■ Ex: “rain/no rain,” “hurricane/no hurricane” ○ Probability forecasts- The chance of some event is stated. ■ Most common is the probability of precipitation ■ Precipitation forecasts are least accurate of all meteorological predictions because moisture is discontinuous ● Assessing Forecasts: 400 ○ Must consider forecast quality: The agreement between forecasts and observations ■ Concerned with forecast accuracy: on average how close the forecast value is to the true value ■ Need information about forecast bias: a forecast whose average is above or below the true average ■ Also must take into consideration forecast skill: the improvement provided by a forecast over and above some reference to accuracy ○ Forecast value: The usefulness of a forecast ■ Depends of applying a forecast to a particular problem or decision ● Data Acquisition and Dissemination: 401 ○ Starting point for almost all weather forecasting is info about the current state of the atmosphere ○ The World Meteorological Organization (WMO) is a collection of weather data across the globe from its 179 member nation ○ Data from all countries is send to three World Meteorological Centers in Washington D.C., Moscow, Russia, and Melbourne, Australia ○ Radiosondes (401), hydrogen filled balloons carrying weather instrument packages, are launched twice a day and about 800 are launched worldwide ■ Observe and transmit to ground recording stations the pressure, air temperature, and wet bulb temperature ■ Tracked by radars called rawinsondes ● Forecast Procedures and Products ○ Phases in Numerical Modeling (403) ■ Analysis phase: observations are used to supply values corresponding to the starting state of the atmosphere for all variables carried in the model ● Converts irregular observations into uniform initial values ■ Prediction Phase: a number of calculations are made based on input data and the application of physical laws ■ Postprocessing Phase (403): The conditions forecast are represented on a grid for mapping and other display purposes ● A series of maps might be produced for each of the 12, 24, 36, and 48 hour periods depicting forecasting distributions for Sea level pressure, 850 mb heights and temperature, 700 mb heights and vertical velocities, 500 mb heights and absolute vorticity values, and Precipitation amounts ● Models Employed: 404 ○ North American Mesoscale Forecast System (NAM) - Model run four times each times each day and uses a grid system in which large areas are overlaid by widely spaced grids ○ Rapid Refresh model (RAP)- rapidly changes the model with the changing weather conditions ○ Medium-range forecasts (MRFs)- Weather predictions 3 or 4 days in advance ■ European Center for Medium Range Weather Forecasting (ECMWF)- generates forecasts for up to 15 days ■ Best forecast model in operation**** ○ Ensemble Forecasting- a number of forecasts are performed for the same period since small disturbances can turn into large disturbances ■ uses several runs for the same forecast period ○ Chaos- the condition that occurs in physical systems that makes it impossible to precisely predict how a system will appear some time in the future. ■ Arises from small errors in the input value of a variable ○ Long range forecasts- a weather prediction extending beyond 7 days ● Weather Maps and Images ○ Surface maps (410) - present a general depiction of sea- level pressure distribution and the location of frontal boundaries. ■ Can also observe wind speeds ○ Station Models (410)- temperature, dewpoint, pressure, and other weather elements can be represented on these models ■ Also indicates cloud cover, and wind speed and direction ■ INTERPRETATION OF THESE MAPS ON PAGE 412 ■ 850, 700, 500, 300, AND 200 MB MAPS ON PAGE 412 ○ Isotachs (414)- lines of equal wind speed ● Satellite Images: 415 ○ Visible images- they view the atmosphere the way an astronaut in space would by registering the intensity of reflected shortwave radiation ■ Only available in daytime ○ Infrared Images- based on measurements of longwave radiation emitted from below. ○ Water vapor images- depict the distribution of water vapor and cloud cover ■ Useful for tracking the flow of moisture across wide regions and helping identify the location of frontal boundaries ● Radar Images: 416 ○ Radar images- used to observe internal cloud conditions by measuring the amount of radiation backscattered by precipitation ■ Covers distances up to about 400 km (250 miles) ● Thermodynamic Diagrams: 416 ○ Thermodynamic diagrams- plot vertical profiles of temperature and dew point data observed by radiosondes ■ A Stuve Chart is a simple thermodynamic diagram (Diagram page 417) ● Show the rate of temperature change for an unsaturated air parcel, plot the dry adiabatic lapse rate, show temperature changes in a rising saturated parcel, depict the mixing ratio, and tell us the wind speed and direction at different altitudes ● Lifted Index: 417 ○ Lifted index- The difference between the sounding temperature at 500 mb and the calculated parcel temperature ■ useful for forecasting thunderstorms ■ computed by imagining a parcel at the predicted high temperature for the day is lifted adiabatically to the 500 mb level ■ If the parcel is colder, the index is positive, reflecting stable conditions ■ If the parcel is warm, the index is negative, reflecting unstable conditions ● K-Index: 418 ○ K-index- similar to lifted index, but works better for predicting air mass thunderstorms and heavy rain than for severe weather ■ useful for forecasting thunderstorms ■ Uses values of temperature and dew point surface and the 850, 700, and 500 mb levels ● Numerical Forecast Models: 418 ○ Domain- the region of the globe being represented ■ This is the fundamental difference among models ○ Parameterizations- predict small-scale weather phenomena whose sizes are less than those of the distance between the model observation points (like localized thunderstorms) ■ Rely on the relationships between variables rather than on applying physics directly to calculations ■ Large-domain numerical forecast models predict air mass thunderstorms using parameterizations ○ Horizontal Representation ■ Grid representation- the domain is subdivided into a lattice of grid points ■ Spectral representation- alternative to horizontal representation in which the variables are represented as a series of waves in a space, each having a characteristic wavelength ****SUMMARY PAGE 419***** 1. 850 mb maps are capable of showing geostrophic flow 2. A central circle on a circle station model that is 75 percent black and 25 percent white tells you the cloud cover ranges over 70 to 80 percent of the sky 3. Current consensus among scientists is that the limit to numerical weather prediction is about 14 days 4. The present weather depicted by this station model is light rain 5. The steepness of the temperature profiles relative to the dry and wet adiabats indicates that stability 6. This is an example of a quantitative forecast 7. 500 mb maps are commonly used to represent conditions in the middle atmosphere 8. Wind profilers are used to obtain measurements of horizontal winds for up to 72 different levels Chapter 14 1. Describe the general atmospheric conditions under which a superior mirage would form. Give a specific example of a location and the associated conditions where you would expect to see this type of mirage. Explain why the conditions at the location are favorable. A superior mirage forms when images are displaced upward. Light rays are bent concave downward as a result of decreasing density with increasing height. This condition always occurs in the atmosphere, to some extent, since the density in a hydrostatic atmosphere always decreases with height. The mirage becomes noticeable, however, when the normal density gradient is enhanced. This occurs when warm (less dense) air lies above cold air, i.e., when there is a strong inversion. Conditions like this most often occur when there is a large area of ice or cool water. The enhanced albedo of the ice or the natural cooling associated with the water can create colder temperatures near the surface than aloft, thus producing the required strong inversion. 2. Describe the important aspects of wind speed and direction on dispersal of air pollution. A wind will obviously move pollution away from the pollution source, but the wind also leads to cross-flow dispersal in both the horizontal and vertical direction. Why does that occur? How is the effect related to the wind speed? Strong winds disperse pollutants in two ways. They rapidly transport emissions away from their source region and spread them over a wide horizontal area. Greater wind speeds also lower the pollution concentration indirectly. As discussed in Chapter 3, air does not flow uniformly in a given direction but contains small, swirling motions, called turbulent eddies, that mix the air both vertically and horizontally. The turbulent fluctuations in the flow increase with wind speed and, as a result, strong winds create greater vertical and cross-wind horizontal dispersion. 3. First define particulates. Then discuss their sources, the physical processes that remove them from the atmosphere, and the effects of particulates on health. In Fairbanks, Alaska, there are several air quality emergencies every winter. Why might you expect that to occur? What factors are likely contributing to the process? Particulates (also called aerosols) are solid and liquid materials in the air that are of natural or anthropogenic (human- made) origin. Some of the particulates are primary pollutants put directly into the atmosphere, whereas others are secondary pollutants formed by the transformation of preexisting gases or from the growth of smaller particulates into larger ones by coagulation. Particulates introduced directly into the air can originate from natural fires, volcanic eruptions, the ejection of salt crystals by breaking ocean waves, and by the entrainment of pollen by wind. Several different processes remove particulates from the air. Gravitational settling, the process wherein particulates fall from the air (even if very slowly), effectively removes larger particulates. The smaller ones are less susceptible to this process because even very small eddies can keep them in suspension. Precipitation, on the other hand, removes both large and small particulates in two ways. First, the particulates that served as condensation nuclei in clouds are removed when the droplets that they are part of fall as rain or snow. Other particulates are removed by scavenging, the process in which falling droplets and crystals collide with particulates in their path. Upon collision, the precipitation incorporates the particulate and carries it to the surface. The scavenging of particulates largely explains why the air is so much cleaner and visibility is enhanced after a rain shower. A certain class of particulates–those smaller than 10 !m in diameter (called PM10)–most readily enters the lungs and brings about the most serious tissue damage. A large body of research analyzing the effects of particulates has shown that a more specific class of particulates– those smaller than 2.5 !m (called PM2.5)–also presents serious health problems. The frequent air emergencies in Fairbanks are associated with two effects. One is the increased wood burning in the winter to heat homes, which produces a large quantity of particulates. The other is the limited solar insolation which, together with radiational cooling, leads to strong inversions that are very stable and reduce the dispersion of the pollutants. 4. How could urban heat islands affect the study of global warming? Do you expect that this type of effect is a significant problem in the interpretation of global climate data? Explain why or why not. a. Most cities with long-running weather stations have undergone considerable growth during the past century. Thus, we must contend with the problem of enhanced urban heat islands influencing the data, which means that records from large urban areas are not representative of the surrounding region. The effect can be mitigated by moving the measurement sites to locations outside the cities. By comparing the measurements for the urban and nearby non-urban location, the temperature records can be normalized so that they are more representative of general conditions rather than the city environment. This process is not entirely accurate, but it mostly removes biases introduced by heat island effects. HUMAN EFFECTS ON THE ATMOSPHERE ● Atmospheric Pollutants: 424 ○ Air pollution- the introduction of undesirable gases and particulates by humans ■ ***Pollution Sources graph page 424*** ○ 2 CATEGORIES ■ Primary Pollutants- emitted directly into the atmosphere ■ Secondary Pollutants- do not go directly into the atmosphere but result ● May start out non toxic but can become a noxious gas after combining with other emissions or naturally occurring compounds ● Particulates: 424 ○ Particulates- also called aerosols which are solid and liquid materials in the air that are of natural or anthropogenic (man-made) origin. ■ Can be primary or secondary pollutants ○ SOURCES OF PARTICULATES: 424 ■ Particulates introduced directly in air can come from natural fires, volcanic eruptions, the ejection of salt crystals by breaking ocean waves, and by plants whose pollen is picked up by carried winds ■ Human activities involving combustion produce primary and secondary particulates ■ Some secondary particulates form by the coagulation of gases ● This process is most rapid with high humidity ● Promotes the formation of fog or cloud droplets ● Humid areas with a high concentration of industrial activities can become foggy at relative humidities considerably below 100% ○ REMOVAL OF PARTICULATES: 425 ■ Large ones remain in the air for only a few hours, while smaller ones can exist for weeks ■ Gravitational settling is a process wherein particulates fall from the air (even if very slowly), effectively removing larger particulates. ● Small droplets are less susceptible ■ Precipitation removes both large and small particulates in two ways: ● 1: particulates that served as condensation nuclei in clouds are removed when the droplets that they are part of fall as rain or snow ● 2: Scavenging- a process in which falling droplets and crystals collide with particulates in their path. The precipitation incorporates the particulate and carries it to the surface. This is why air is cleaner and has better visibility after a rain shower ○ EFFECTS OF PARTICULATES: 426 ■ Reduce visibility by increasing scattering of visible radiation ■ Enter the lungs and damages tissue ● Carbon Oxides: 426 ○ Carbon oxides- ■ Include carbon monoxide and carbon dioxide ■ Carbon monoxide, in cities, has inputs exceeding the rate of removal ■ In the US, CO is mostly from cars ■ CO is extremely toxic and can contribute to heart disease ● Sulfur Compounds: 427 ○ Can occur in gaseous or aerosol form ○ Most originate from natural processes ○ Cause minimal respiratory/pulmonary (lung) health problems ○ Man-made compounds released in the air are sulfur dioxide and sulfur trioxide ○ SO2 is a primary pollutant released by the burning of sulfur containing fossil fuels (like coal or oil) ■ Highly corrosive and irritates human respiratory systems ○ SO3 can be a primary pollutant but is more commonly a secondary pollutant ■ Readily combines with water droplets to form sulfuric acid ■ This can form acid fog ■ In clouds, this can create acid rain or acid snow ■ Dry deposition of acid occurs when acid chemical are incorporated in dust or dry particulates and fall to surface. ○ Smokestacks on manufacturing and power plants are designed to keep emissions away from the ground near the source. However, pollutants are carried downwind where they can cause acid deposition ● Nitrogen Oxides: 429 ○ Nitric oxide and Nitrogen dioxide are the two main air pollutants ○ Together are called NOx ○ Cause pulmonary (lung) health problems ○ NITRIC OXIDE ■ Nontoxic, highly reactive and breaks down quickly ■ Forms as a by-product of high temperature combustion associated with automobile engines, industrial manufacturing, and electric power generation ■ Primary importance is that it oxidizes to form nitrogen dioxide, a major component of smog ■ 25% of the acidity of rainfall is caused by nitric acid, formed by NO ○ NITROGEN DIOXIDE ■ Toxic gas that gives polluted air a yellowish to reddish brown color and pungent odor ■ Undergoes transformations that contribute to acid deposition and other secondary pollutants ■ Rapid decay of nitrogen dioxide prevents large concentrations from occurring in rural areas ● Volatile Organic Compounds (Hydrocarbons): 429 ○ Volatile organic compounds- materials that can rapidly evaporate at normal temperatures and include a vast number of different materials ■ Found in homes, so tend to occur indoors (paint, disinfectants, air fresheners, and dry cleaning residues on clothes) ■ Can cause dizziness, visual problems, and short term memory loss, but don’t reach the level needed to produce these effects ■ Important because in the presence of sunlight they recombine with nitrogen oxides and oxygen to produce Photochemical smog ■ Hydrocarbons- VOCs found outdoors and are made entirely of carbon and hydrogen atoms (methane, butane, propane, octane) ● Most arrive in the atmosphere through natural processes ● Photochemical Smog: 430 ○ Causes burning eyes, sore lungs, a subtle unpleasant odor, and poor visibility ○ Consists of secondary pollutants: ozone (o3), NO2, peroxyacl nitrate (PAN), and formaldehyde ○ Forms when sunlight triggers numerous reactions and transformations of gases and aerosols. ○ Usually involves dry air ○ Opposite of london-type smog that combines with damp air ● Air Quality Index: 431 ○ Air Quality Index- a uniform index that is useful for air pollution monitoring across the United States ■ Applies a formula for ozone, particulates, carbon monoxide, sulfur dioxide, and nitrogen and expresses each pollutant on a scale ranging from 0 to 500. ● Effects of Wind on Horizontal Transport: 431 ○ Aid the dispersal in two ways: ○ 1: Transport emissions from their source and spread them over a wide horizontal extent. The concentration of pollution is inversely proportional to wind speed (Diagram page 432) ○ 2: Greater wind speeds lower pollution concentration indirectly. Forced wind convection increases with wind speed, creating strong winds in favor of dispersion ○ Short term variations in wind direction affect dispersion. If wind direction only changes slightly through time, pollution will be concentrated within a relatively narrow area downwind of the source ■ If wind directions are highly variable, the pollutants will spread out over a wider area ● Effect of Atmospheric Stability: 432 ○ Stable air resists vertical displacement and leads to higher pollutant concentrations near the ground ○ Unstable air enhances vertical mixing, so any material introduced near the surface is easily displaced upwards, reducing pollution concentrations near the surface ○ Inversions (when temperature increases with height) make the air extremely stable and impose the greatest restraint on vertical lifting ○ Radiation inversions have the greatest impact on pollution concentrations in the early morning since that is when they dissipate. (important in London type smog) ○ Subsidence inversions are important to photochemical smog ■ Doubles the concentration of pollutants because limits the height where air is easily mixed (DIAGRAM 433) ● The Counteroffensive on Air Pollution: 433 ○ The Clean Air Act was the first US initiate to clean the air in 1990 (DIAGRAM 433) ● Urban Heat Islands; 437 ○ Urban heat island- increased local temperatures that result from urbanization ○ Example of how not all human impacts on the atmosphere are as dramatic as the pollution of the atmosphere ○ Greatest differences between urban and rural occur greatest during the late evening and night during winter month ○ Occur because of modifications to the energy balance that result when natural surfaces are paved and built on when human activities release heat into the local environment ○ Size of the city is the main factor that influences the magnitude of the heat island effect ○ Highest temperatures are in the city core ● Radiation Balance: 438 ○ Increased particulates associated with urban activity can absorb and scatter incoming solar radiation and increase the amount of absorption and reradiation of longwave energy in the atmosphere ○ Stuff about buildings: 438 ● Changes in Heat Storage: 439 ○ Buildings have a greater capacity to store heat than most natural surfaces, making stored heat more available for transfer to lower atmosphere during the evening and nighttime, increasing nocturnal temperatures ● Sensible and Latent Heat Transfer: 439 ○ When moisture is available near the surface, the transfer of energy as latent heat can exceed sensible heat transfer, indicating that most of the surplus is consumed by evaporation ○ If the surface is dry, the surplus energy raises the surface temperature above the air temperature, and sensible heat dominates ○ The higher the ratio of sensible heat to latent heat, the greater the temperature ***SUMMARY PAGE 441**** Chapter 16 1. Describe the thermohaline circulation and how it is associated with climate change. PAGE 501 Thermohaline circulation is the movement of surface waters in the oceans due to variations in temperature and salt content. This large flow of water northward located in in Atlantic surface water delivers heat to the overlying atmosphere. After this water cools and sinks to the North Atlantic, it causes the water to flow south to the rim of Antarctica. The water then flows north into the Indian and Pacific oceans, eventually rising and returning to the southern ocean at the surface. The Atlantic portion of this system is called the Atlantic Meridional Overturning Circulation, or the MOC. In this area, rates and locations of sinking water change very abruptly, which also leads to abrupt climate jumps, at least during the last glacial period. Cold episodes are believed to be caused by pulses of freshwater released during melting episodes of an ice sheet. A layer of less dense freshwater that remains at the surface interrupts the flow of warm surface waters northward across the Atlantic. 2. Give the details of the three main components of the Milankovitch cycles. The Milankovitch cycles are a collection of three different of astronomical factors that influence the timing and intensity of the seasons. The first cycle consists of the eccentricity in the orbit. This factor is what precession, or the orientation of the Earth axis, depends on. Low values of eccentricity mitigate procession, while greater eccentricity enhances it. The second is the cycle of the tilt of Earth's axis off the perpendicular to the plane of the orbit. The tilt of the Earth's axis, or its obliquity, varies in a period of about 41,000 years, and changes between 22.1 degrees and 24.5 degrees off the perpendicular. These small changes can make high latitude regions undergo changes in available solar radiation at the top of the atmosphere of about 15%. The third cycle is of the timing of aphelion and perihelion relative to the timing of the equinoxes. This process begins when the axis of rotation gyrates so that it will eventually point at a different star called Vega instead of Polaris. This process, as mentioned before, is called precession. This process directly alters the timing and intensity of the seasons. If the orientation of the axis were toward Vega with the current timing of aphelion and perihelion, the winter solstice for the Northern Hemisphere would nearly coincide of apehlion, resulting in warmer summers and cooler winters in the Northern Hemisphere. The Southern Hemisphere, however, would experience less seasonality because its summer solstice would occur near aphelion. 3. How can Ice-albedo feedback affect climate? Page 497 There is a large portion of Earth's surface that is occupied by large continental sheets of ice that float in the sea. The cooling of the atmosphere would cool these ice masses and cause them to expand. Because ice has a higher albedo than most other natural surfaces, this expansion would reduce the amount of insolation absorbed by the surface. This then leads to further cooling, which is considered a positive feedback. However, If the atmosphere were to warm, the ice would melt. This would increase the amount of surface no longer covered in reflective ice, causing warming. This is also considered positive feedback, because it is a mechanism that favors warming or cooling once a temperature trend is initiated. 4. What are some of the important problems involved in defining climate change? First climate is defined as the statistical properties of atmospheric values. However, climate is more than just an average value, because the changes in climate may occur even though the mean values of precipitation, temperature, or wind may remain the same. External conditions, or boundary conditions, also might vary too quickly for climactic equilibrium to be obtained, but they are still conditions that drive climactic change and act as forcing agents. In addition, longer averaging periods reduces the sampling error, but increases the likelihood of blurring truly distinct climates. We are also unable to determine if climate change is the reason for the occurrence of unusual weather events. CLIMATE CHANGES: PAST AND FUTURE  Climate Change: 476 o Boundary Conditions- a system that responds to the configuration of external factors like the gaseous compositions of the atmosphere, its surface pressure, the average amount of incoming solar radiation, and the length of a year o Feedback Processes- the manner in which a change in one variable is muted or enhanced by its impact on another variable  Positive feedback: feedback that amplifies a given change  Ex: high albedo of snow amplifies the effect of decreasing incoming solar radiation  Negative feedback: prevents or partially offsets a change  Methods for Determining Past Climates: 477 o We gain information through proxy indicators- evidence derived from sources other than human measurements  Obtained in different places using different techniques o Proxy data give info about paleoclimates- the climates of the past o Oceanic Deposits  Scientists extract deep cores of material that has been deposited over long periods  Includes bones of animal life made of calcium carbonate  Info in the oxygen of Calcium carbonate is most important for determining past climates 16 18  Observe the ratio of ????/ ???? in the layers  Mainly help observe glacial volume o Ice cores 18  Snow that falls under warm conditions contain the ???? isotope  Provide information on the past chemistry of the atmosphere and on the incidence of past volcanic eruptions  Bubbles of ambient air trapped in ice record varying carbo0n dioxide levels  There is a strong correlation between past temperatures and concentrations of carbon dioxide and methane  High temperature coincides with high concentrations, where glacial periods coincide with reduced concentrations of these greenhouse gases  This indicates a positive feedback process in which changes in greenhouse gases amplify climate changes  Remnant Land Forms: 478 o All landforms are the end result of processes that build up and wear down features at the surface o The largest features (mountains and valleys) are produced by tectonic forces, those that produce a deformation of Earth’s crust o Once formed, such features become subject to erosional processes that remove material at the surface and transport it to other locations o Deposition occurs when the forces transporting the material are no longer capable of moving the material  Movement of water, the slow moving ice sheets expanding across the surface, wave action along coastlines, wind, and floating icebergs carrying large debris contribute to erosion and deposition  Features Associated with Ice and Water: 479 o Features associated with glaciation are related to erosion  Ex: Glaciers that expand down and widen can transform the typical V-shaped valleys associated with those cut by running water to U- shaped valleys o Glaciers also leave scratch marks on solid rock walls and valley floors, or polish exposed rocks to a smooth finish o Ice sheets are capable of moving both very large and small sediments, so poorly sorted deposits often exist along their past margins o In Streams and Rivers, the speed of the water flow affects the size of material that can be transported  Rapidly moving streams can carry large rocks  The slower the flow of water, the smaller size sediment it can move  By examining the stratigraphy (layering) of stream banks or road cuts, we see the sequencing of high and low precipitation episodes o We can examine the elevation of terraces or submerged coastal platforms of waves along coastlines to infer how much glacial ice has accumulated or melted in  Coral Reefs: 479 o Are hard ridges extending from the ocean floor to below the water surface, along shallow margins of warm, tropical oceans o Form by the growth of small marine organisms having hard shells composed largely of calcium o When the top coral die, their shells remain to provide a foundation for more to grow o Because they exist along shallow water, they can provide information on the location of past sea levels  Because chemical composition of growing coral is affected by water temperature, analysis of the changing chemistry of coral reefs with depth provides useful information on past conditions  Useful in providing information on past El Nino events  Past Vegetation: 479 o Pollen spores can be deposited and preserved on lake beds or bogs, and can be extracted and identified. o Organic material deposited with the pollen is subjected to a technique called Radiocarbon Dating  Provides an estimate of the age of material younger than 50,o00 years and can determine the distribution of vegetation species that existed during the past o Tree rings show climate changes, because each year trees increase the width of their trunks by the growth of concentric rings  the width of each ring depends on how favorable temperature and/or moisture conditions were during a given year  Past Climates: 481 o Time is divided into eras, periods, and epochs, and are based on geologic fossil evidence indicative of past environmental conditions and events  They do not have uniform climactic conditions  Significant climate events sometimes cross boundaries  The geologic columns are not absolute—the names, numbers, and durations of the time intervals are constantly revised  Warm Intervals and Ice Ages: 481 o Most of the time our planet has been warmer than it is today and mostly free of permanent ice o Earth is a warm planet that has been punctuated by multiple but brief ice ages  The earliest known ice age is about 2.8 billion years ago o The mid-Cretaceous period extended from about 120 to 90 million years ago and was very warm  Dinosaurs roamed beyond the Arctic Circle  Sea level was about 150 to 200m higher, flooding 20% of continental areas  Global average temperature was thought to have been anywhere from 5 degrees Celsius to 15 degrees Celsius warmer than now o All ice ages have abundant, year round ice  Ice sheets form from sea water, lowing sea levels  Differences between ice ages and warm ages vary by latitude, with high latitudes showing greater changes than the tropics  The Pleistocene: 482 o This is what people refer to when they speak of the “ice age” o It is an epoch that occupies most of the last 2.5 million years o Glacial/interglacial cycles- oscillations in temperature and ice cover  The ice volume increases slowly and then terminates rapidly in a warming event  Cycles generally last about 100,ooo years  Ice volume changes have been largest in the Northern Hemisphere with the sheets of ice growing by a factor of 3 with each cycle o Antarctic air temperature changes are believed to match those of the north polar latitudes, with glacial period temperatures of about 10 degree Celsius lower than interglacial o The most recent glaciation period reached its maximum about 20,000 years ago  The Last Glacial Maximum: 483 o The land ice covered much more area o When the ice melted, the land surface gradually expanded upward towards its original level o On land, temperature changes varied greatly by proximity to the ice sheets and to the ocean o Most places were colder and also drier  Especially in high latitudes where precipitation amount were about 50% below today’s o This period was not uniform  The Holocene: 485 o Warming began about 15,000 years ago and was interrupted about 2000 years later by the cold period called the Younger Dryas which lasted 1200 years o Has not been uniformly warm, as seen because of the Little Ice Age  Only caused a small decrease of average temperature  Shortened growing seasons led to reductions in agricultural productivity  New data of the last 1000 years of this have suggested a more intense Little Ice Age than most other curves imply  The Last Century: 485 o Data from a network of meteorological stations established around the world give firsthand accounts of temperature and precipitation patterns  Effects of Warming on Temperature-Related Variables: 487 o Variables that have made changes consistent with a warmer planet are:  The number of days frost has decreased over Midlatitude regions  A decrease in the number of extreme cold events across the world/more warm events  Snow cover has decreases/ increasing precipitation  The breakup date for river and lake ice occurred earlier by an average of 6.5 days  From 1901 to 2002 the maximum extent of seasonally frozen ground declined byout 7% in the northern Hemisphere  Effects of Warming on Precipitation: 487 o Global warming is the only climate trend in the past 100 years o Spatial patterns are unclear  Precipitation exhibits extreme variability from year to year and from place to place  Long term changes must be very large in order to stand out, but they did not.  Factors Involved in Climactic Change: 488 o Earth’s climate has undergone significant changes possibly due to the intensity of radiation emitted by the Sun, changes in Earth’s orbit, land surface changes, and differences in the gaseous and aerosol composition of the atmosphere o These factors do not operate independently  Variations in Solar Output: 488 o The amount of energy the sun emits is not truly constant o The abundance of sunspots rises and falls which changes solar output  Solar radiation decreases as sunspots increase o The Maunder Minimum is the period of minimal sunspot activity, and supports the connection between climate and solar activity  This is because it coincided with one of the coldest periods of the Little Ice Age o It was later observed a relationship between tropospheric condition and sunspot activity  Sunspot activity was much stronger when the direction of the stratospheric winds over the tropics was taken into account  Quasi-biennial oscillation is the tow year cycle pattern in which these winds tend to reverse their direction  Changes in Earth’s orbit: 488 o The Earth’s axis of rotation is oriented at 23.5 degrees from the perpendicular plane o The orientation of the axis is constant throughout the course of the year o Points toward the North Star, Polaris o After the March equinox, the Northern Hemisphere is inclined toward the Sun, and the rest of the year the Southern Hemisphere has greater exposure to the sun o If the axis of rotation were greater than 23.5, there would be more seasonality, and vice versa o Earth’s elliptical orbit allows the planet to receive 7% more solar radiation at the top of the atmosphere during early January (perihelion) than early July (aphelion) o The Earth-Sun distance is largest during the summer and smallest during the winter in the Northern Hemisphere  Milankovitch cycles- three cycles that influence the timing and intensity of the seasons: o Eccentricity in the orbit o The tilt of Earth’s axis off the perpendicular to the plane of orbit o The timing of aphelion and perihelion relative to the timing of the equinoxes o Play a role in the expansion and retreat of glaciers during Pleistocene (490)  Eccentricity: 489 o The eccentricity of Earth’s orbit changes cyclically  Cycle lasts usually 100,000 year  The Earth-Sun distance at aphelion is about 3% greater than at perihelion  Over the last 15,000 years, there has been a steady decrease in eccentricity  Obliquity: 489 o Obliquity is the tilt of the Earth’s axis  Varies cyclically with a period of about 41,000 years  During this time it varies between 22.1 degrees and 24.5 degrees off the perpendicular  High latitude regions can undergo changes of available solar radiation of about 15% due to obliquity  Precession: 489 o The summer solstice in the Northern Hemisphere changes through time because the axis wobbles on a 27,000 year cycle o Soon will point at Vega instead of Polaris  If this occurred, the winter solstice for the Northern Hemisphere would nearly coincide with aphelion, resulting in increased seasonality (warmer summers/colder winters)  Southern Hemisphere would experience less seasonality o Change in orientation of the Earth axis is called precession  Low values of eccentricity mitigate precession while greater eccentricity amplifies it  This effect will be small over the next 50,000 years due to decreasing eccentricity  Modification of Earth’s Surface by Human Activity: 490 o Deforestation reduces evapotranspiration from the surface, leading to higher temperatures near the surface and decreasing precipitation  Decomposition of cleared vegetation increases CO2, a greenhouse gas  Leads to increase in surface albedo (491) o Alteration of arid land surfaces by overgrazing cattle makes soil compact, increasing the amount of runoff and making less water available for evaporation  Changes in Atmospheric Turbidity: 490 o Turbidity is the amount of suspended solid and liquid material (aerosols) contained in the air.  Aerosols directly affect the transmission and absorption of both solar and infrared radiation  Global dimming occurs when the amount of solar radiation reaching the Earth’s surface decreases  Aerosols can increase the absorption of outgoing longwave radiation  Aerosols indirectly affect climate through their ability to serve as cloud condensation nuclei  Aerosols can also reduce cloud amount through their warming effect in the troposphere  Tropospheric Aerosols: 492 o Natural sources of tropospheric Aerosols: spraying of salt particles by ocean waves and bubbles, soot and gases from fires, the erosion of soil by wind, the dispersal of spores and pollen the emission of sulfides by marine plankton, and other biospheric processes o Humans produce particulate matter by: combustion of fossil fuels, burning wood and other biofuels, burning forests for conversion to agriculture, and plowing fields that become sources of dust  Humans have increased their concentrations  Usually occur over industrialized land areas  Do not have long life spans, so settle over these areas before they are dispersed. o Aerosol backscatter and absorption cause an atmospheric brown cloud which is essentially a local accumulation of aerosols  This promotes surface cooling  Also warms the lower atmosphere through increased absorption os solar radiation and longwave radiation  Modify absorption of solar radiation by the surface o Have a net effect of reducing surface temperatures globally  Stratospheric Aerosols: 493 o Most occur from natural processes o Can remain in the stratosphere longer because they tend to be smaller, which means they have lower terminal velocities. There is also no precipitation in the stratosphere for their removal o Shortwave and longwave radiation depend on the size of the aerosol  Aerosols vs Greenhouse Gases: 493 o The short lifetime of aerosols means that change in release rates have an immediate impact. o Greenhouse gas emissions have residence times for decades to centuries, causing more gradual climate changes  Changes in Radiation Absorbing Gases: 494 o Burning of fossil fuels and the clearing of forests have led to a steady increase in the carbon dioxide content in the atmosphere  The Mechanism of Greenhouse Warming: 494 o Because greenhouse gases absorb longwave radiation, less surface emission escapes to space and more is retained by the atmosphere o The presence of a greenhouse gas raises the effective radiating altitude, and because temperature decreases with altitude, there is less emission to space than would otherwise occur o The increase of greenhouse gases immediately darkens the atmosphere at more longwave wavelengths, causes absorbed raditation to exceed emission, warming the planet and emitting more longwave radiation  Increase in both temperature and emission of longwave continue to increase until a new radiation balance is achieved at a warmer climate  Recent Changes in Greenhouse Gases: 494 o Since the middle of the 19 century, there has been an exponential increase in the input of carbon dioxide to the atmosphere by industrial activities o Most emissions come from developed nations  90% come from the Northern Hemisphere o Fossil fuel use has been the main drivers of CO2 emission for the last few decades and is expected to continue to be so  Water Vapor and Cloud Feedback o 2 important mechanisms:  Observations and calculations that show the relative humidity tends to be constant when temperatures change even by large amounts  Water-related feedback concerns changes in the lapse rate of the troposphere  If the planet warms and the atmosphere has more water, the lapse rate at low latitudes will decrease  Lower latitude areas show the largest decrease in the lapse rate if the planet warms  Thick clouds strongly reflect solar radiation, which promotes cooling  Atmosphere-Biota Interaction: 498 o Changes in climate are linked with land-vegetation patterns o By transpiring moisture to the air, the presence of plants affects the moisture content of the atmosphere and the likelihood of precipitation o Plants also affect the albedo and the transfer of heat at the surface o Vegetation-albedo feedback are important at high latitudes, because forest cover greatly reduces the high albedo that would otherwise occur duing winter in a snow climate o Most important feedback is the influence of CO2 concentrations on the photosynthetic rates  Plants undergo enhance photosynthesis in an environment rich in carbon  This could create negative feedback in which increasing CO2 contents allow plants to suppress further increases in the greenhouse gas o More CO2 makes vegetation more dry, and more susceptible to fires o  Warming Temperatures and Sea Levels: 500 o Increases in temperatures raise sea levels mainly through the expansion of warm waters o Increase in temperature also cause glaciers to melt and release water back to the ocean o Melting of West Antarctic ice sheet could raise sea levels by 5M  Thermal Inertia of the Oceans:502 o The huge mass and high specific heat of oceans along with their vertical and horizontal mixing creates a strong thermal inertia o Makes the warming of the ocean due to atmospheric temperature very slow  Identifying the Causes of Climate Change: 502 o General Circulation Models (GCMs) are mathematical representations of the Earth atmosphere-ocean-land system that run on supercomputers o Estimate the response of Earth’s climate to a set of given external conditions know as boundary conditions  Ex: Earth topography, tilt of Earth’s axis, solar output, volcanic aerosol loading, and greenhouse gas emissions o Compute the state of the atmosphere, oceans, and land surface conditions at discrete points in time o Have limited spatial details  This means that small-scale processes can be represented only as parameterizations  Temperature Trends Through the 21 Century: 503 o We must assume varying amounts of radiative forcing- the change in the net radiation for the troposphere that would occur as a result of a change in some external factor  Ex: The amount of energy radiated by the Sun or by an increase in atmospheric carbon dioxide  An increase in the net radiation would create a disequilibrium that would lead to warming  Change in Mean Temperature: 504 o There would likely be an increase in global mean temperature of about 1 degrees Celsius that flattens out at about midcentury under the RCP2.6 o Under the RCP8.5 scenario, the temperature increases by about 4 degrees Celsius o Predicted that by the year 2100 the global average temperature will likely have increased by at least 1.5 degrees Celsius  Evaporation and Atmospheric Moisture: 505 o since the amount of water vapor that can be maintained in air is grater at higher temperatures, the average global specific humidity is expected to increase with atmospheric warming o The atmosphere’s increased saturation specific humidity will increase such that the relative humidity is likely to remain about constant.  Precipitation: 507 o Predicted to increase in the latter part of the 21 century by at least 1 to 3% per every 1 degree Celsius temperature increase o Predicted there will be a shift in the nature of short-term precipitation events, with higher occurrence of intense storms  Cryosphere: 507 o Permafrost layers in the soil are predicted to be subject to the greatest warming o This will weaken the subsoil, which may become unable to support overlying buildings o This will also release carbon dioxide and methane into the air, promoting further warming o There will also be a loss of glacial ice  Change in Sea Level: 508 o Warming of oceans is expected to continue, increasing the mean sea level ****SUMMARY PAGE 510**** Chapter 17  Refraction: 518 o Defined as the bending of rays as they pass through a medium o Occurs whenever radiation travels through a medium whose density varies or whenever it passes from one medium to another having a different density o Occurs because radiation speed varies with density (The denser the medium, the slower the radiation) o Index of refraction- the speed of light in a vacuum divided by the speed of light in a medium  The degree of slowing determines this  Rays are slowed more on the denser side than on the less dense side, so they ray turns toward the denser air  Varies slightly with wavelength (shorter wavelengths refract more light) o Density increases with height, causing radiation to refract slightly, forming an arc with the concave side oriented downward o The amount and direction of refraction varies with atmospheric conditions o When light moves along a density gradient rather than across it, it slows down but is not refracted  Refraction and the Sun o Refraction of incoming solar radiation is greatest when the Sun is low over the horizon because the low solar angle causes the rays to pass through a greater amount of atmosphere o At sunset, refraction can cause direct rays to be visible even after the Sun has dropped below the horizon o Twilight occurs when the Sun is positioned slightly farther below the horizon, so its direct rays cannot be seen at the surface but its diffuse radiation illuminates the sky  Longest during the high Sun season and increases with latitude o Refraction effects the Sun’s shape and color  Longer wavelengths colors (reds and oranges) undergo less refraction than shorter wavelengths colors (blue and green).  Shorter wavelengths concentrate near the top of the sun, and longer ones locate near the bottom  Green flash is when the Sun appears momentarily to be capped by a bright green spot  Mirages: 520 o Caused by the refraction of visible light when the temperature decreases rapidly with increasing height o Applies to any apparent upward or downward displacement of an object due to refraction o Upward refraction:  A steady, steep drop in temperature with height can cause refraction patterns in which rays are bent concave upward o Inferior mirage- the viewer perceives not only a true image of an object but also an inverted image directly below  Occurs when steeper temperature gradients of the lower layer cause it to refract air more strongly than the air above it  Diffuse, visible radiation from the top of the object goes in many directions  Some light passes directly to the viewer, and some approaches the surface where intense refraction creates a second image  If light reflected by the bottom of the object is refracted more strongly, the image will appear vertically stretch/taller o Superior mirage- forms when images are displaced upward  Light rays are bent concave downwards as a result of decreasing density with increasing height  How the Sun appears higher above the horizon  To be noticeable, the normal density gradient must be enhanced by a temperature profile in which warm air lies above cold air  Compression occurs when refraction decreases with altitude, and stretching occurs when refraction increases with altitude  Rainbows: 521 o Rainbows are arcs of light that exhibit changes in color from the inner part of the ring to the outer part of the ring o Appear only when rain is falling some distance away and with a clear sky above or behind the viewer, which allows sunlight to reach the surface unobstructed o Always located in exactly the opposite direction of the Sun  Primary and Secondary Rainbows: 522 o Primary rainbows are the brightest and most common rainbows  The angular distance from one to the other always extends about 82 degrees of angle  Shortest wavelengths appear at the innermost portion, and longer are in the outermost  Form when light is refracted by raindrops twice o Secondary rainbows are often less distinct and surround primary rainbows  Cover 102 degrees of arc at the horizon  Has the reverse color scheme of the primary rainbow  From when light is refracted through raindrops and when two reflections occur at the back of the raindrop, causing the reverse color scheme  The Arc of a Rainbow: 523 o It is in the shape of an arc because the angles of reflected color look different from different angles  Rays near the top of the arc are seen in vertical cross section, and lower ones are seen more from the side  Halos, Sundogs, and Sun Pillars: 524 o Halos are circular bands of light that surround the Sun or Moon produced by Cirrostratus clouds  Occur when ice crystals are between the viewer and the Sun or Moon o Sundogs appear as whitish spots in the sky  Platelike ice crystals tend to align horizontally, and if the Sun is slightly above the horizon and behind these crystals, sundogs occur o Sun pillars occur when these platelike ice crystals reflect sunlight off their tops and bottoms  the ice crystals are almost exactly aligned horizontally, with each reflecting a portion of the incoming light differently to produce the apparent columns stretching upwa


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