ATMS 100 EXAM 2 Study Guide
ATMS 100 EXAM 2 Study Guide ATMS 100
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This 27 page Study Guide was uploaded by Stef Antonopoulos on Monday March 28, 2016. The Study Guide belongs to ATMS 100 at University of Illinois at Urbana-Champaign taught by Jeffrey Frame in Spring 2016. Since its upload, it has received 32 views. For similar materials see Introduction to Meteorology in General Science at University of Illinois at Urbana-Champaign.
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Date Created: 03/28/16
ATMS100: EXAM II REVIEW SHEET AND SAMPLE QUESTIONS Exam: Wednesday, March 30, IN CLASS. You will have 50 minutes to take the xam. NO CELL PHONES. Please bring a #2 pencil and your ICard to th exam. Study aids: This sheet, lecture notes, textbook, lab as ignments. Learn and be able to apply concepts; do NOT simply memorize acts. Questions? Come to office hours, ask your TA, post to the discussion board on Compass. Please note that many of these same concepts also appear on t e Labs. FROM BEFORE: What is the difference between weather and climate? weather is the atmospheric conditions at a particular time and place while climate is the average weather over a long period of time (10 years) What is the difference between satellites and radar? Satellites look at clouds from the atmosphere, radars measure precipitation from the ground How is wind direction defined? The way the wind is coming from. A wind coming from the north heading south would be a north wind How do winds blow around high and low pressure systems in the Northern Hemisphere? Around high pressure systems, winds blow clockwise and outward. Around low pressure systems, winds blow counterclockwise and inward How do the winds around high and low pressure systems influence temperature? Around high pressure systems, the weather is clear and calm. Around low systems, it is cloudy and thunderstorms What is pressure and how does it change with height? Pressure is the weight of the molecules above you, and pressure ALWAYS DECREASES with height. What is density and how does it change with height? Air density is how much "stuff" is in a given space, calculated mass/volume. It, like pressure ALWAYS DECREASE with height because gravity pulls most air molecules closest to the surface. What is an inversion? Layers in the atmosphere in which temperature increases with height instead of decreases. Stratosphere, Thermosphere How does temperature and moisture content affect air density? Warm air is less dense, because molecules move faster, collide more, and are prone to rise. Cold air is more dense because move slower, collide less, and are prone to sink. What is advection? Transfer of heat or moisture through horizontal movements of air (lake or ocean breeze) How does the sun heat the lower atmosphere? The sun heats the surface through conduction. This air expands, becomes less dense, and begins to rise. The rising air transports heat upward from the surface through convection. The troposphere is therefore heated from the bottom up. Cooler air sinks and is later heated by the surface again How does the temperature of air change as it rises and sinks? Why? As the hot air parcel (blob of air) rises, the pressure around it decreases, so the parcel expands. It requires energy to expand, so it cools as it rises and expands. As an air parcel sinks, the pressure around it increases, so the air parcel is compressed. So compression transfers energy to the parcel, making it warm. How does water influence seasonal temperatures? It takes a lot more time and energy to heat water so therefore, inward land experiences greater seasonal differences than the coasts. How do clouds influence daily temperatures? During the daytime it keeps it cool by blocking sun, and during night, it keeps it warm by trapping warm air at the surface What is saturation? What mathematical relationships are true at saturation? Water vapor concentration in the air at which evaporation and condensation rates are equal VP= SVP RH = 100% Condensation Rate = Evaporation Rate Temp = Dew Point Temp What is relative humidity? What are the two ways to change it? ratio of water vapor in the air to that required for saturation High RH means air is closer to saturation 1.) Increase RH Add moisture increase VP Cool air decrease SVP 2.) Decrease RH Remove moisture decrease VP Warm air increase SVP What is dewpoint? Why is it useful? Dewpoint is the temperature at which saturation occurs. It is always below temperature. It is useful because a higher dewpoint ALWAYS means there is more moisture in the air, regardless of the actual temperature. It determines how much water vapor is in the air, giving a good estimate of what the air will feel like. At dewpoint the liquid will condense and evaporate at the same time. Below depoint and condensation will happen. Why is rising air crucial to cloud formation? Most clouds form in RISING air. As temperature decreases, relative humidity increases. Air eventually rises high enough (cools enough) to become saturated (RH = 100%). When air saturates, a cloud forms. As air rises, it expands and cools. The amount of water vapor in the air does not change as the air rises. What mechanisms can force air to rise? 1.) Orographic lift (air is forced to rise over a mountainous barrier), 2.) Frontal lift/wedging (where warmer, less dense air is forced over cooler, denser air along a front) 3.) Convergence (a pileup of horizontal air flow resulting in an upward flow), 4.) Convective lift (unequal surface heating causes localized pockets of air to rise because of their buoyancy) How much liquid water typically results from melting a foot of snow? 1 inch What environmental factors are required to support sleet and freezing rain? Sleet: Raindrops that fall into a deep layer of cold air and refreeze into ice pellets. Thin above freezing layer of air aloft; deep below freezing layer on surface Freezing Rain: falling supercooled raindrops. Deep above freezing layer of air aloft; thin below freezing layer near surface How do you read a station model? LECTURE 9 What is a constant pressure surface? a surface in the atmosphere where the pressure is equal everywhere along that surface. For example, the 100 millibar (mb) surface is the surface in the atmosphere where the pressure at every point along that surface is 100 mb. How are low and high heights related to temperatures below that pressure surface? High heights are indicative of warm air below that pressure level Low heights are indicative of cold air below that pressure level How do you identify ridges and troughs on an upperair map? Trough Valley; low heights (pressures) elongated area of relatively low pressure. Pressure decreases as it elongates Ridge High heights (pressures) elongated area of relatively high pressure. Pressure increases as it elongates Do NOT just look at shape of contour lines look at values!!! What is the pressure gradient force? In what direction does it act? Air molecules want to flow from where there is greater pressure to where there is less pressure. Acts perpendicular to isobars (or height contours). TOWARD LOW PRESSURES. Tightly packed isobars Strong pressure gradient Big change over small distance Widely spaced isobars Weak pressure gradient Small change over big distance What is the relationship between the pressure gradient force and wind speed? Stronger PGF = stronger wind speeds What is the Coriolis force? In what direction relative to the flow does it act in the Northern Hemisphere? Apparent force due to rotation of the earth toward the right in the northern hemisphere, towards the left in the southern hemisphere How does the Coriolis force depend on wind speed? I think stronger coriolis force = weaker winds? bc it opposes the pgf Does the Coriolis force influence smallscale flows such as flushing toilets? Why or why not? No; only where wind blows over vast regions is the force in effect LECTURE 10 How do you determine the upperlevel winds given height contours? they blow parallel to the height contours or isobars How do you determine the pressure gradient and Coriolis forces from height contours on an upperlevel map? PGF acts perpendicular to height lines; towards low heights Coriolis force acts perpendicular and to the right of the wind direction (opposite of PGF) What is the geostrophic wind? PGF and Coriolis forces are equal and opposite; moving parallel to height contours What is gradient wind balance? When does it apply? Curved flow aloft; applies when imbalance of PGF and Coriolis force Lows: PGF > Coriolis Highs: Coriolis > PGF Net force inward toward center of circle, says wind speed will be faster around highs and slower around lows How does the wind aloft around highs (ridges) and lows (troughs) compare to the geostrophic? wind? High: PGF directed outward from center of high, Coriolis force directed to right of winds (opposite PGF and greater than PGF), net flow inward towards center of high Low: PGF directed inward towards center of low and greater than Coriolis, Coriolis toward right of winds; outward net flow inward towards center of low What is a cyclone? An anticyclone? Cyclone is a low pressure system NH: Flow counterclockwise SH: Flow clockwise Anticyclone is high pressure systems NH: Flow clockwise SH: Flow counterclockwise What force is important at the surface that is not important aloft? Friction What is friction? What does it do? Opposes motion, slowing winds and weakening Coriolis force Disrupts force balances seen with upper level flow How do you determine the surface winds from isobars on a surface map? Opposes motion, slowing winds and weakening Coriolis force Disrupts force balances seen with upper level flow LECTURE 11 What is an air mass? A large body of air with similar temperature and moisture concentrations in the horizontal What is the center of an air mass? Centers of air masses are surface high pressure systems How are air masses classified? Classified based on moisture and temperature Twoletter classification First letter refers to moisture, second letter refers to temperature Where are different air masses typically found with respect to a midlatitude cyclone? CP: top left CT: bottom left MP: top right MT: bottom right What is a front? boundaries between air masses How are fronts represented on weather maps? triangles and semicircles that point in the direction the front is moving How are fronts identified from wind direction? By the wind direction (relative to the front) in COLD AIR Cold front: winds in cold air blow towards front Stationary front: winds in cold air blow parallel to front Warm front: winds in cold air blow away from front What are cold fronts and how do they influence the weather? Cold air is advancing; have steep vertical slope; cold air is more dense and lifts the less dense air Precipitation is brief, intense, thunderstorms and showers As front passes, temp and dewpoint decrease Winds shift from S or SW to N, NW or W Cold fronts extend southward or westward from low pressure What are warm fronts and how do they influence the weather? Warm air advancing, cold air retreating; winds in cold air blow away from front Less dense warm air gradually overruns more dense cold air Gradual vertical slope Precipitation widespread mainly North of front, intensity is light to moderate, mixture of precipitation, snow/ice in winter Temperature and dewpoint increase; wind shift from E or S to SW Extends southward or eastward from low pressure; (Cold to warm) snow, sleet, freezing rain, rain What are stationary fronts? Do not move, winds in cold air move parallel to the front (generally easterly) mixed precipitation often north of front in winter How do occluded fronts influence the weather? Widespread rain or snow; temperature may rise/drop but remain cold; wind shift from E/NE to N/NW/W How do occluded fronts form? As low pressure system strengthens, wraps cold air around itself When cold front "catches up" to the warm front, warm air is forced aloft (less dense) always connect low w/another low or a low w/its warm and cold fronts What are drylines and how do they influence the weather? Separate mT air from cT air found in KS/OK/TX during spring; can trigger severe thunderstorms How do you find fronts given a surface weather map? Temperature gradient; large change in temperature w/distance; tightly packed isotherms Dewpoint gradient: tightly packed isodrosotherms, wind shift; trough of low pressure at the surface lines of clouds or precipitation What is the warm sector? Region south of warm front and ahead of cold front is called warm sector Temperatures are warm; within warm air mass What is the triple point? intersection of cold, warm and occluded fronts What is overrunning and where is it found? warm fronts; an air mass in motion aloft above another air mass of greater density at the surface LECTURE 12 What is a midlatitude cyclone? area of low pressure. Also called extratropical cyclone What do midlatitude cyclones look like on satellite imagery? comma shaped clouds Where is warm air and cold air found with respect to a surface low? bring cold air southward and warm air northward How do midlatitude cyclones influence the weather? Thunderstorms, tornadoes, blizzards, ice storms, widespread snow and rain, warm and cold fronts Where (with respect to a midlatitude cyclone and its fronts) are ice storms most likely? above the warm front between rain and snow What is a blizzard? Visibility less than 1/4 mile because of snow Winds greater than 35 mph for 3 or more hours Where are blizzards most likely with respect to a midlatitude cyclone? NW of low pressure system between snow Left of the cold front What is a Nor'Easter? An intense midlatitude cyclone that tracks along the northeastern coast of the U.S.; produce heavy rain, wind, snow Cause most economic damage Where are thunderstorms most likely with respect to a midlatitude cyclone and its fronts? along the cold fronts LECTURE 13 What is the jet stream? Where is it found? River of fast moving air in the upper atmosphere, near tropopause, moves parallel to height contours What is convergence? Divergence? Divergence: sinking air that goes clockwise and outward around a high; prevents formation of clouds Convergence: rising air that goes counterclockwise and inward around a low; forms clouds LECTURE 14 How do surface lows and highs influence lowlevel convergence and divergence? Low: divergence along pressures fall, air converges into low pressure systems at the surface High: convergence aloft causes surface pressures to rise, air diverges into high pressure systems at the surface How do convergence and divergence influence surface pressure? Convergence: surface pressure rises Divergence: surface pressure decreases What is hydrostatic balance? Strong upward PGF balanced by gravity, doesn't apply to thunderstorms or tornadoes Why is vertical motion important? Faster rising air = more interesting weather How do convergence and divergence strengthen and weaken surface lows and highs? Divergence: decreases surface pressure by losing molecules (low gets lower, high gets lower) Convergence: increases surface pressure by gaining molecules (low gets higher, high gets higher) Where are convergence and divergence found with respect to upperlevel troughs and ridges? EAST (downstream) of troughs in jet stream Where are surface lows found with respect to upperlevel troughs? EAST (downstream) of the upperair trough axis How are strengthening and weakening defined with respect to both highs and lows? Strengthen low: pressure drops Weakening low: pressure rises Strengthen high: pressure rises Weaken high: pressure drops How do surface lows move with respect to warm fronts? Cold front is to the South and warm fronts are to the E; low will move parallel to, but just N of its warm front What is cyclogenesis? In what regions is it most likely? Development or strengthening of midlatitude cyclone; east of mountain ranges and along temperature gradients (coastlines, stationary fronts) Upperlevel divergence required How does an upperlevel trough intensify a surface cyclone? Upper level trough of low pressure must be located behind, or to the west, of the surface low How does a surface cyclone intensify an upperlevel trough? Height falls within the upperlevel trough What is the basic midlatitude cyclone life cycle? Frontal wave (development), open wave (gets stronger), mature (strongest), occlusion (weakens), cutoff cyclone (dissipates) Why do cyclones begin to dissipate? (Two reasons) Upperlevel trough moves faster than surface low because of stronger winds aloft Max divergence now east of low When the cyclone occludes, the upper level trough catches up to the surface low and eliminates upper level divergence at the center of the surface low; the inward air flow at the surface low causes pressure to rise at the center of the low; the low slowly weakens and the cyclone dissipates What force causes cyclones to dissipate? Friction; when the rate of convergence at the surface is greater than the rate of divergence aloft, so surface pressure increases and will eventually cause the low to dissipate LECTURE 15 How you can issue a weather forecast based on the motion of fronts? On the cyclone model? You can assume weather will continue to move, unchanged, in the direction they're moving How are computers used to forecast the weather? Computers use thousands of CPU's to solve equations that are too long and complicated to ever be done by hand What is a model grid and grid resolution? A model grid is a 3D grid of points that show the weather at those points; at each of these points, the model solves atmospheric equations to create a forecast; resolution is the spacing of each of the grid points; a smaller spacing does not make models more accurate, but let's smaller scale features be seen How do upperlevel troughs and ridges influence the weather? Upper level troughs influence many surface weather features, including the format and movement of surface and low pressure areas and the location of clouds and precipitation; precipitation tends to fall to the E of the trough axis and drier air tends to prevail W of the trough; air sinks on the W side of the troughs, which inhibit clouds and precipitation; upper level ridges also have a great impact on the surface weather, depending on their strength and how fast they move, they can bring record summer heat and air pollution to an area for several days; a ridge is an elongated area of high atmospheric pressure; they occur both at the earth's surface and at higher altitudes; sunny dry days to the E of the ridges and wet weather on the W side; air sinks on the E side of the ridge, inhibiting clouds and precipitation, whereas air rises on the W side, which can lead to formation of clouds and precipitation How do surface high and low pressure systems influence the weather? High pressure systems are generally associated with fair, sunny weather; high pressure is an area of sinking air and tends to dry out as it sinks leaving sunny skies Low pressure areas are generally cloud/rainy areas; where strong areas of low pressure bring out our stormiest weather because it's an area of rising air, and as air rises, it condenses into clouds and rain; air moves from higher pressure to lower pressure so if you have a high and a low nearby, it can be windy as air rushes between the two What are some sources of uncertainty in weather forecasts? Weather forecasts can always vary, due to the weather being predicted through statistical means and smaller scale weather phenomenon that is very difficult to predict, which will fall under the heading of chaos How is a television weather forecast generated? A TV weather forecast is generated upon a green street that a forecaster stands in front of What is the difference between a watch and a warning? Watch = a certain type of hazardous weather is possible (nothing has actually been sighted yet) Warning = hazardous weather is occurring (observed or detected by radar) LECTURE 16 What is latitude? measure of how far north or south you are on the earth What drives the general circulation of the atmosphere? uneven solar heating of the earth At what latitudes is rising air generally found? Sinking air? 5060°, 30° How does the general circulation influence global precipitation patterns? Most precipitation falls near equator and polar front Least precipitation falls in Subtropics and polar regions How does the general circulation influence the location of deserts and jungles around the world? Tropical rainforests predominantly found near 0° owing to ascent near equator Also see temperate rainforests near 50/60°N/S owing to enhanced precipitation. Deserts predominantly found near 30°N/S owing to sinking air at these latitudes Antarctica also desert like (little precipitation); however, it is very cold! What is a jet stream? Where are jet streams found? What causes them to form? swiftly flowing air currents typically found near tropopause How are temperature gradients related to jet streams? Jet streams are found above temperature gradients
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