GEOG 1200 SMU Module 2: HUMIDITY

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Question Description

Module 2:HUMIDITY

Objectives

  • To study the concept of humidity.
  • To understand use of the saturation curve graph.
  • Learn about how relative humidity is measured using a sling psychrometer.

SAINT MARY’S UNIVERSITY GEOG 1200 DEPARTMENT OF GEOGRAPHY FUNDAMENTALS OF PHYSICAL GEOGRAPHY Module 2: HUMIDITY Objectives 1. To study the concept of humidity. 2. To understand use of the saturation curve graph. 3. Learn about how relative humidity is measured using a sling psychrometer. Section 1: Understanding Humidity Terminology Air can hold up to a certain amount of water vapour (water in a gaseous state) but the amount varies depending on the temperature. Humidity is a general term that refers to the amount of moisture in air. Some other important terms to know when dealing with moisture in the atmosphere are: Specific Humidity (SH): the actual quantity of water vapour in the air, in grams per kilogram (g/kg). Maximum Specific Humidity (MSH): the maximum quantity of water vapour that could be held in the air at a given temperature (g/kg). If the air is unsaturated, the SH is less than the MSH. Relative Humidity (RH): the ratio of SH to MSH, expressed as a percentage: Equation 1: Specific Humidity RH (%) = ----------------------------------Maximum Specific Humidity x 100 Dew-Point Temperature (DT): the temperature at which air saturation and condensation occur for a given value of specific humidity. Condensation is the change of water from a gaseous state to a liquid state. Saturation Curve: a graph (on a separate sheet) showing the relationship between air saturation and temperature. Once the saturation point is reached, the RH is 100% and no more water vapour can be evaporated into the air. Example For reference, an example using the Saturation Curve Graph is given. Follow the example of how to correctly read the graph. a. A sample of air is collected and determined to lie at Point X on the graph. b. The air temperature is 30C. c. The SH is 10.0g/kg (grams of water vapour per kilogram of air). d. What is the MSH? e. What is the RH, rounded to the nearest %? f. What is the DT? 1 Answers Air Temperature (C) X 30 Specific Humidity (g / kg) 10 Maximum Spec. Humidity (g / kg) Relative Humidity (%) Dew-Point Temperature (C) 27.5 36 12.5 2 Section 2: Using the Saturation Curve Graph • Recall from the previous section that relative humidity is the ratio between specific humidity and maximum specific humidity expressed as a percentage. • It is possible for the specific humidity to be lower than or equal to, but not higher than, the maximum specific humidity. A point on the graph can only lie on or below the line. • A series of values will be used to demonstrate the relationships between temperature and humidity of air. • In this example, the temperature of the air changes, forcing changes in the relative humidity values. A starting point was selected with an air temperature of 20C and a specific humidity of 10 g / kg. Air Temperature (C) Specific Humidity (g / kg) A 20 10 B 13 10 C 0 4 D 10 4 Maximum Spec. Humidity (g / kg) Relative Humidity (%) Dew-Point Temperature (C) Use the Saturation Curve Graph to complete the table (above or attached). Section 3: Measuring Relative Humidity with a Sling Psychrometer Background • A device for measuring relative humidity is called a sling psychrometer. • The paragraphs below describe the sling psychrometer and its operation – For the on-line course you will not be using the instrument, however you will learn about it . The Sling Psychrometer • The sling psychrometer contains two thermometers housed in a plastic casing attached to a handle. • The casing is designed to be spun around the handle, vigourously. • The upper thermometer is a standard mercury thermometer with a Celcius temperature scale – this is the dry-bulb thermometer it measures the air temperature. • The lower thermometer is similar, except it is covered by a wick at the far end- this is the wet-bulb thermometer. If the wick is dry, unscrew the plastic cap and add water to the reservoir. • The difference between the dry bulb and wet bulb temperatures is called the wet-bulb depression (or depression of the wet bulb). How the Sling Psychrometer Works • When the psychrometer is spun, evaporation causes the wet-bulb temperature to be lowered. 3 • The amount of evaporation from the wick is related to the relative humidity (RH). The amount of evaporation is determined by the amount of water vapour already in the air (the specific humidity) compared to the maximum amount of water vapour that can be held at that temperature (maximum specific humidity). • If the RH is high, there will be relatively little evaporation and the dry and wet bulb temperatures will be close to each other. • If the RH is low, there will be relatively more evaporation and the dry and wet bulb temperatures will be further apart. Using the Psychrometer • To use, spin the psychrometer vigourously for 30-40 seconds. • Read off the two temperatures to the nearest half degree and calculate the wet-bulb depression. • On a separate sheet is a chart that will tell you the relative humidity for the air temperature you measure (dry-bulb temperature) and the corresponding wet-bulb depression. • Read the chart down to the dry-bulb temperature you recorded, and across to the wet-bulb depression to obtain the relative humidity value. • For example, if you measured a dry-bulb temperature of 34C and a wet-bulb temperature of 24.5C, the wet-bulb depression is 9.5C and the relative humidity is 46%. Use the chart to confirm how this value of relative humidity is obtained. • On the chart, if the exact dry-bulb temperature you recorded is missing, you must interpolate between given values. Before Moving On • It is essential to understand the information provided to this point before moving on. Three points that frequently require emphasis or clarification are: o Dry-bulb temperature on the psychrometer measures the air temperature. o Wet-bulb temperature is not the same as wet-bulb depression. o Wet bulb depression is the difference between dry-bulb and wet-bulb temperatures. (That is, how much lower, or “depressed”, is the temperature of the wet-bulb compared to the dry-bulb?) Section 4: Practice Exercises Using Given Sling Psychrometer Values Work out the relative humidity assuming the following temperatures were measured off a sling psychrometer: Dry-Bulb Temperature (C) Wet-Bulb Temperature (C) 30 26 5 2 45 27.5 Wet-Bulb Depression (C) Relative Humidity (%) 4 9.5 4.5 4 Section 5: Relative Humidity Measurements • I completed these measures for the class using the sling psychrometer to measure the relative humidity in three locations on the campus: 1. In room B205 2. In the lobby of the Atrium, near the entrance to the library 3. Outside, well away from any buildings or building entrances • Spaces are provided below to about the humidity conditions (using the relative humidity results and the saturation curve graph). • Equation 1 - used to calculate RH when SH and MSH are known - can be rearranged into Equation 1a to calculate SH, if RH and MSH are known. Equation 1: RH = (SH / MSH) x 100 Equation 1a: SH = (RH / 100) x MSH Make sure you include appropriate units for all values on p. 4 and 5. Location 1: In Room B205 Dry-Bulb Temperature _20.5 C ______________ Wet-Bulb Temperature 16.0 C _______ Location 2: In the lobby of the Atrium Dry-Bulb Temperature _19.5 C Wet-Bulb Temperature __18.5 C ______________ Location 3: Outside, away from buildings Dry-Bulb Temperature 6 C ________________ Wet-Bulb Temperature __2 C ______________ Location 1: In Room B205 Wet-Bulb Depression Relative Humidity ________________ ________________ Maximum specific humidity for this air temperature ________________ Specific humidity (SH = [RH / 100] x MSH) ________________ Dew-point temperature ________________ Location 2: In the Atrium, on the second floor beside the green living wall Wet-Bulb Depression Relative Humidity ________________ ________________ Maximum specific humidity for this air temperature ________________ Specific humidity (SH = [RH / 100] x MSH) ________________ Dew-point temperature ________________ 5 Location 3: Outside, away from buildings Wet-Bulb Depression Relative Humidity ________________ ________________ Maximum specific humidity for this air temperature ________________ Specific humidity (SH = [RH / 100] x MSH) ________________ Dew-point temperature ________________ For each of the three locations, plot your values of specific humidity vs. air temperature on the Saturation Curve graph. • At which location is the relative humidity highest? ________________ • Which location has the greatest amount of water vapour in the air? ________________ • Is it possible for the highest relative humidity and the greatest amount of water vapour in the air to have occurred at different locations? 6
Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 3 Air Temperature © Alberto Garcia/©Corbis Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Chapter Overview Temperature and Heat Flow Processes Daily and Annual Cycles of Air Temperature © Alberto Garcia/©Corbis Local Effects on Air Temperature Guess whether the World Patterns of Air Temperature eruption of Mt. Pinatubo had a cooling or warming The Temperature Record and effect? Global Warming Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Measuring Temperature • Temperature = level of internal motion of atoms and molecules that make up the matter • Temperature scales • Fahrenheit • Celsius • Kelvin What is the freezing and boiling point of water in oF and oC? © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Surface Temperature • • • • Air temperature is measured at 1.2 m (4 feet). Daytime ground temperatures are usually warmer than 1.2 m. Night ground temperatures tend to be cooler than at 1.2 m. Ground temperatures are often more extreme than air temperatures. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Wind Chill and Heat Index • Wind chill index = the higher the wind speed, the faster the rate at which heat leaves our bodies, and the colder we feel. If the air temperature is 0o F and the wind speed is 30 mph, what is the wind chill? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © Courtesy NOAA Temperature and Heat Flow Process Wind Chill and Heat Index • Heat index: • Higher levels of humidity raise our perception of heat. • Humid conditions reduce the amount of evaporative cooling when we sweat. If the relative humidity is 85%, at what temperature should someone exercising outdoors use “extreme caution”? © Courtesy NOAA Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Energy Transfer • Heat = internal energy transferred from one substance to another as a result of their temp differences. • Heat flows by: • Radiation = all objects emit heat (e.g., SW and LW). • Conduction = transfer by particles (atoms or molecules). • Convection = in gases or liquids (e.g., warm air rises). • Advection = a mass of air moves to a new location, bringing along its properties (temperature and moisture). Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Energy Transfer • Example: • Sunlight hits earth via SW radiation. • SW is absorbed by ground, raising its temperature. • The surface layer radiates (LW) energy to the air, and heats the soil below it through conduction. © John Wiley & Sons, Inc. Where is convection occurring in this image? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Temperature and Heat Flow Process Latent Heat • Sensible heat = flow of heat that results in a temperature change of an object or its surroundings. • Latent heat = flow of heat taken or released when a substance changes states (solid, liquid, or gas) to another. • Important energy transfer in the atmosphere/ocean: • Water evaporating into water vapor is a cooling process as heat is absorbed into the water vapor. • The latent heat stored in water vapor is released in the condensation process. • Hurricanes are fueled by warm water and this process. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Daily and Annual Cycles of Air Temperature Four important controls of air temperature: • Time of day • Season • Surface type (continental or maritime) • Latitude © NG Image Collection Other local factors involved in determining temperature (see the next section) include: • Elevation • Land use and urbanization • Ocean currents Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Daily and Annual Cycles of Air Temperature The Daily Cycle of Air Temperature •Net radiation varies daily: • Positive after sunrise • Peaks at noon • Decreases to negative by sunset What time of day would you expect the high temperature? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © John Wiley & Sons, Inc. Daily and Annual Cycles of Air Temperature The Daily Cycle of Air Temperature •Air temperature varies daily: • Minimum is just after sunrise. • Rises to a peak in mid-afternoon. • Even after noon, incoming radiation is still greater than outgoing radiation (positive net radiation); thus, the temperature continues to increase. • Temperatures begin to decrease once net radiation is negative. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © John Wiley & Sons, Inc. Daily and Annual Cycles of Air Temperature Temperatures Close to the Ground • Temperatures on the ground are usually more extreme than temperatures at standard height. • Soil, surface, and air temperatures vary throughout the day. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Annual Cycles of Insolation and Air Temperature •Insolation varies by season: • Day length longest at summer solstice = warmer temp. • Day length shortest at winter solstice = colder temp. © John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Goddard Institute for Space Studies Surface Temperature Analysis • Calculating the Earth’s surface temperature from ground, air, and satellite measurements is extremely complex. • http://data.giss.nasa.gov/gistemp/ Courtesy NASA Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Land and Water Contrasts • Specific heat = amount of heat required to raise the temperature of a unit mass of a substance by 1ºC. • Rock and soil (inland areas) have low specific heat, which means less energy is needed to raise the temperature. © John Wiley & Sons, Inc. Water has a much higher specific heat capacity. An extensive, deep body of water heats more slowly and cools more slowly than inland areas. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Inland climates have more temperature extremes than coastal climates: 1. Solar rays heat land surface, but are distributed deeper in water. 2. Water has higher heat capacity than rock and soil. 3. Water mixes. © John Wiley & Sons, Inc. 4. Water evaporates, removing latent heat. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Land and Water Contrasts • Maritime = Coastal regions have smaller daily and annual temperature ranges. • Continental = Inland regions have greater daily and annual temperature ranges. © NG Image Collection © John Wiley and Sons Publishers Inc. © NG Image Collection Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Temperature by Latitude • Annual cycle of insolation affects→ net radiation, which affects→ monthly mean air temperature. • Higher latitudes experience large annual temperature range. • Equatorial regions experience small annual temp ranges. Courtesy David H. Miller Courtesy David H. Miller Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Temperature by Latitude © NG Image Collection Courtesy David H. Miller Is the annual temperature range for Manaus, Brazil, small or large? Explain. In your explanation, describe the latitude and annual net radiation for Manaus. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Temperature by Latitude © John Wiley & Sons Courtesy David H. Miller Is the annual temperature range for Yakutsk small or large? Explain. In your explanation, describe the latitude and annual net radiation for Yakutsk. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Daily and Annual Cycles of Air Temperature Temperature by Latitude Although Yakutsk is only 9.5° further north than Hamburg, the annual temp cycles of these two cities are quite different. While summer temp are similar, winter temp at Yakutsk average –45°C compared to just about freezing at Hamburg. Which is the best explanation for this observation? a. The elevation is much higher in Yakutsk. b. The elevation is much higher in Hamburg. c. Winds bring air from the Arctic Ocean to Yakutsk. d. Winds bring air from the Atlantic Ocean to Hamburg. © John Wiley & Sons, Inc. © Gerd Ludwig/INSTITUTE Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Local Effects on Air Temperature Local factors involved in determining temperature: • Elevation • Land use and urbanization • Ocean currents Microclimates = Local atmospheric zones where the climate differs from surrounding areas © Courtesy NASA © NG Image Collection Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Local Effects on Air Temperature Effects of Elevation on Temperature • Temperature decreases with altitude in the troposphere, then increases above the troposphere. • Environmental temperature lapse rate = rate at which air temperature drops with increasing due to pressure drop and subsequently less carbon dioxide and water vapor to absorb LW. © NG Image Collection Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © NG Image Collection Local Effects on Air Temperature Effects of Elevation on Temperature • Temperature Structure of the Atmosphere © John Wiley & Sons, Inc. What gas absorbs ultraviolet radiation in the stratosphere? How does this relate to the temperature trend? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Local Effects on Air Temperature Effects of Elevation on Temperature Variation © John Wiley & Sons, Inc. What happens to temperature as one increases in elevation in the Andes mountains? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Local Effects on Air Temperature Effects of Elevation on Temperature Variation •Temperature inversion = a state of the atmosphere in which air temperature increases with elevation. © John Wiley & Sons, Inc. If you were to plant a frost-sensitive plant/tree, is it best to plant it on the valley floor or on a hill side? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Local Effects on Air Temperature Urban and Rural Environments • Urban heat island = an area at the center of a city that has a higher temperature than surrounding regions • Heat-related fatalities • Green roofs © Courtesy NASA © Courtesy NASA Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. World Patterns of Air Temperature Air Temperature Maps • Air temperature maps use isotherms to show centers of high and low temperatures. • Isotherm = line on a map drawn through all points with the same temperature. • Temperature gradient = rate of temperature change along a selected line or direction. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. World Patterns of Air Temperature Air Temperature Patterns around the Globe Three main factors explaining world isotherm patterns: 1. Latitude affects annual insolation, temperatures, and seasonal temperature variation 2. Maritime-continental contrast 3. Elevation Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Data from John E. Oliver World Patterns of Air Temperature Air Temperature Patterns around the Globe Temperature Extremes 1. Hottest = 58oC (136oF) at El Azizia, Libya (~28oN). 2. Coldest = –89°C (–128°F) at Vostok Station, Antarctica (high elevation near 85oS). 3. Within North America, temperatures range from 57°C (134°F) in Death Valley, California, to –63°C (–81°F) in Snag, Yukon, Canada. Find these locations on physical map. Use at least two temperature controls to explain the temperature extremes in Libya and Antarctica. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. World Patterns of Air Temperature Air Temperature at the Equator and Midlatitudes Locate regions that show: 1. Temperature decrease with elevation 2. Seasonal temperature differences 3. Little to no seasonal temperature difference Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Data from John E. Oliver World Patterns of Air Temperature Air Temperature at the Poles Data from John E. Oliver Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming The Temperature Record • Satellite technology allows scientists to monitor surface air temperature and sea surface temperature (SST). • Direct methods date to mid-19th century. © Courtesy NASA © Courtesy NASA In Figure 3.17b, can you identify: 1. the urban-heat island effect? 2. natural geographic features influencing temp patterns? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming The Temperature Record Indirect temperature records (proxies) • Tree rings • Ancient sediment • Coral reef coring • Ice cores from glaciers and polar regions • Oxygen isotope ratio Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © NG Image Collection The Temperature Record and Global Warming The Temperature Record •Cycles of higher and lower temperatures © John Wiley & Sons, Inc. Volcanic activity (SO2) • Eruption of Mt. Pinatubo Did the eruption of Mt. Pinatubo have a cooling or warming effect? Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Courtesy NASA The Temperature Record and Global Warming Global Warming •Earth has been getting warmer, especially in the past 50 years. •Intergovernmental Panel on Climate Change (IPCC) • 2000 statement: “Global warming is ‘unequivocal.’ ” • 2007 statement: “Climate change is occurring, is caused largely by human activities, and poses significant risks for—and in many cases is already affecting—a broad range of human and natural systems.” Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming Temperature Trends by Latitude • Small island nations express alarm at rising sea levels. • Arctic citizens are witnessing a greater rise in temperature. • Arctic region is warming at 2.5 times the global average. Courtesy NASA Temperature averages over the 1951–1980 time period by latitude Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming Causes of Global Warming • IPCC concluded that human activity is very likely the cause of climatic warming through the increase of the concentration of greenhouse gases. • IPCC conclusions are based on computer simulations. © National Academy of Sciences, U.S.A. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming Air Temperature Trends •2005 and 2010 are tied as the warmest years on record since the middle of the 19th century. •First 10 years of the 21st century are the warmest decade on record since 1400. •In the past 30 years, the Earth has warmed by 0.6°C (1.1°F). In the past century, it has warmed by 0.8°C (1.4°F). Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Temperature Record and Global Warming Consequences of Global Warming • IPCC has projected that global temperatures will warm between 1.8°C (3.2°F) and 4.0°C (7.2°F) by the year 2100. • Sea ice will melt. • Greenland ice sheet will change. © imagebroker/Alamy © National Geographic Society Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming Consequences of Global Warming •Arctic thawing •Sea-level rise •Polar sea ice melting •Habitat loss (coral reefs) © NG Image Collection © Courtesy NOAA © imagebroker/Alamy © National Snow and Ice Data Center Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Courtesy NASA The Temperature Record and Global Warming Consequences of Global Warming © Courtesy NASA © John Wiley & Sons, Inc. Review Figure 3.20 and answer this question: Where do you expect to find the largest observed changes in global temperature as a function of latitude? a. Tropical regions b. Subtropical regions c. Midlatitude regions d. Polar regions Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Temperature Record and Global Warming Climate Change • Weather seems to becoming more variable and more extreme: • Very high 24-hour precipitation—extreme snowstorms, rainstorms, sleet, and ice storms—have become more frequent since 1980, with more intense hot and cold weather. • Seasons affected—early onset of spring and the delay in fall. • Pine beetle infestations in the Pacific Northwest • Bleaching of coral reefs in the Indian Ocean • Could promote the spread of diseases such as malaria • Shifting climate range boundaries may shift, making some regions wetter and others drier • Shifts in agricultural patterns, including desert expansion, could displace large human populations Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. The Temperature Record and Global Warming International Response to Global Warming •1992 Rio de Janeiro Earth Summit •1997 Kyoto Protocol •IPCC •Carbon taxes and cap-and-trade failure or success? •China, Germany, and Scandinavian countries have reduced greenhouse gases and supported renewable energy: • Solar • Wind • Geothermal • Nuclear Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc.
Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 4 Atmospheric Moisture and Precipitation © Daniel Berehulak/Getty Images Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Chapter Overview Water and the Hydrosphere Humidity Adiabatic Processes Clouds and Fog Precipitation Human Impacts on Clouds and Precipitation © Daniel Berehulak/Getty Images Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere The Three States of Water • Solid (ice) • Liquid (water) • Gas (water vapor) • Latent heat is transferred when water changes states • Release of energy occurs when... • Absorption of energy occurs when… © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere The Three States of Water • • • • • Evaporation Freezing Condensation Sublimation Deposition (e.g., Frost) © John Wiley & Sons, Inc. On a cold, dry day, snow covering a sidewalk slowly disappears, and there is no visible melting. Which process is at work? a. sublimation b. deposition c. condensation d. evaporation? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere The Hydrosphere • The total water realm of the Earth’s surface, including the oceans (97.5%) and freshwater (2.5%). • Freshwater includes glaciers (68.7%), ground water (30%), permafrost (0.8%), and the surface waters of the lands and water held in the atmosphere make up 0.4%. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere The Hydrosphere • Oceans • Ice sheets and glaciers • Surface water ©John Wiley & Sons, Inc. © NG Image Collection © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © NG Image Collection Water and the Hydrosphere The Hydrosphere • The small blue sphere represents the planet’s total water volume in proportion to the Earth’s size, demonstrating the limits on this critical resource © SPL/Photo Researchers Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere The Hydrologic Cycle Water moves among the ocean, atmosphere and land •Evaporation •Precipitation •Transpiration •Evapotranspiration •Runoff •Sinks into soil •Recharge of groundwater © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere Humidity • The amount of water vapor in the air • The maximum volume of water vapor, or humidity, of a mass of air increases sharply with rising temperature • Air at room temperature (20°C [68°F]) can hold about three times as much water vapor as freezing air (0°C [32°F]) Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Water and the Hydrosphere Humidity • The low humidity of Death Valley in California creates a warm but comfortable day for a trek across the sand • High-humidity conditions of a Florida wetland, the same temperature reading can be unbearably hot © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere Relative Humidity (RH) • Compares the amount of water vapor present to the maximum amount that the air can hold at that temperature • Expressed as a percentage • Air holding ½ its capacity has a RH of 50% • Can change in two ways: • Gain or lose moisture • Change in temperature Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere Specific Humidity • The actual amount of water vapor held by a parcel of air (g/kg) • When air cools, capacity is reduced • When air warms, capacity increases • Specific humidity and temperature values are high at low latitudes • Specific humidity values fall as temperature in high latitude regions Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere Specific Humidity © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Water and the Hydrosphere Dew Point • The temperature at which air with a given humidity will reach saturation when cooled without changing its pressure • Dew • Frost What happens as air is cooled below the dew-point temperature at temperatures above freezing? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Adiabatic Processes • As a parcel of air is lifted, atmospheric pressure becomes lower, and the parcel expands and cools • As air cools to the dew point, clouds form © John Wiley & Sons, Inc • As air descends, air is compressed and warms • Adiabatic processes = process in which the temperature of a parcel of air changes in responses to a change in atmospheric pressure Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Adiabatic Processes The Dry Adiabatic Lapse Rate •The rate at which rising air cools or descending air warms when no condensation is occurring •10°C per 1000 m •5.5°F per 1000 ft © A. N. Strahler Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Adiabatic Processes The Moist Adiabatic Lapse Rate • The rate at which rising air is cooled by expansion when condensation is occurring; ranges from: • 4 to 9°C per 1000 m • 2.2 to 4.9°F per 1000 ft Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © A. N. Strahler Adiabatic Processes Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © A. N. Strahler Adiabatic Processes © A. N. Strahler 1. Suppose the air parcel shown contained more water vapor. How would that affect the lifting condensation level? 2. What would be the effect if there were less water vapor in the air parcel? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Clouds consist of water droplets, ice crystals, or both Condensation nucleus = a tiny bit of solid matter (aerosol) in the atmosphere, on which water vapor condenses to form a tiny water droplet © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Clouds Classification by Height © A. N. Strahler Cloud Families: High clouds, middle clouds, low clouds, clouds of vertical development Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Cirrus Clouds © NG Image Collection Cirroform clouds = at the top of the troposphere, these clouds are high, thin, wispy clouds drawn out into streaks. They are composed of ice crystals and form when moisture is present high in the air Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Stratiform Clouds © NG Image Collection Stratiform clouds = are blanket-like layers that cover large areas. A common type is stratus clouds, which often cover the entire sky. In this photo, high cumulus clouds (left) grade into a high stratus layer (right). Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Cumulus Clouds © NG Image Collection Cumuliform clouds = globular masses of cloud that are associated with small to large parcels of moist rising air. In this photo, puffy, fair-weather cumulus clouds drift over a lake. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Cumulonimbus Clouds © NG Image Collection Nimbus clouds = are clouds of any of type that produce precipitation. An isolated cumulonimbus cell discharges its water volume as precipitation in this photo. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Clouds and Fog Fog •Radiation fog: formed when temperature of the air at ground level falls below dew point © NG Image Collection •Advection fog: forms when warm moist air moves over a cold surface • Common over oceans (“sea fog”) • West Coast of US and Canada Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © NG Image Collection © NG Image Collection Precipitation Types of Precipitation • Rain • Snow • Hail • Ice storm © NG Image Collection © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Annual rates of precipitation vary greatly around the world Tropical regions Deserts © NG Image Collection © NG Image Collection © John Wiley & Sons, Inc. Wet-dry regions Equatorial regions © NG Image Collection © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation • Globally, rainfall ranges from tropical to desert to polar • This profoundly influence landforms, the biosphere, and human activities • Most species have evolved to survive within narrow ranges of annual precipitation Tropical regions © NG Image Collection Deserts © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Precipitation forms in clouds by two different processes: •Warm Cloud = Collision Coalescence •Cold Cloud = Ice crystal process © John Wiley & Sons, Inc Warm cloud shown above = Formation of precipitation through coalescence of water droplets Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation © NG Image Collection © NG Image Collection © NG Image Collection Review Figure 4.10 and answer this question. Which type of cloud is represented in this figure? a. cirrus b. altostratus c. cumulonimbus d. cirrostratus © NG Image Collection © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Cold Cloud = Ice crystal process Precipitation forms as water vapor evaporates from super cooled liquid cloud drops. The water vapor is then deposited on ice crystals, forming snowflakes © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Types of Precipitation Courtesy NOAA • Rain and snow Courtesy NOAA • Freezing rain • Measuring Precipitation = U.S. National Weather Service’s NEXRAD (Next Generation Radar) Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Types of Precipitation • Hail can form during thunderstorms when there are strong updrafts © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Atmospheric Lifting • Air can move upward in four ways: through orographic, convective, frontal, or convergent lifting © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Atmospheric Lifting • Orographic precipitation = Precipitation that is induced when moist air is forced vertically over a mountain barrier • Convective precipitation = Precipitation that is induced when warm, moist air is heated at the ground surface, rises, cools, and condenses to form water droplets, raindrops, and eventually rainfall Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc Precipitation Orographic Lifting © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Convective Lifting © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Convective Lifting © John Wiley & Sons, Inc If the environmental lapse rate increased (that is, if it were cooler at higher altitudes), how would the lifting condensation level change? a. It would be higher. b. It would be lower. c. It would stay the same. d. It is impossible to determine. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Convergent Lifting © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Precipitation Frontal Lifting © John Wiley & Sons, Inc Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Human Impacts on Clouds and Precipitation Acid Rain • Also called acid deposition • made up of raindrops that have been chemically acidified by industrial air pollutants such as sulfur dioxide (SO2) and nitric oxide (NO2) • Acids have a low pH value, less than that of distilled water (pH = 7) • The lower the pH value, the more acidic the liquid. © Illinois State Water Survey Acidity of rainwater in U.S., 2005 Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Human Impacts on Clouds and Precipitation Effects of Acid Rain • Acid streams and lakes affect aquatic life • Damage to forests • Damage to soils © Gerd Ludwig/INSTITUTE • Damage to buildings © NG Image Collection Consider the pattern of acid rain deposition in the northeastern United States. What is the implication for international relations? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Human Impacts on Clouds and Precipitation Cloud Cover, Precipitation, and Global Warming Any rise in sea-surface temperature will increase the rate of evaporation, and an increase in evaporation will raise the average atmospheric content of water vapor. What effect will this have on climate? •Clouds: Longwave warming or shortwave cooling? •Increased Precipitation? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © NASA Images
Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 5 Global Atmospheric and Oceanic Circulation © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Chapter Overview Atmospheric Pressure Wind Speed and Direction Global Wind and Pressure Patterns Local Winds Oceanic Circulation © NG Image Collection Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Atmospheric Pressure • Atmospheric pressure is pressure exerted by the atmosphere because of the force of gravity acting on the overlying column of air. Measuring Atmospheric Pressure • Units = inches of mercury (in. Hg) or millibars (mb). • Standard sea level pressure = 1013.2 mb. • Cold, clear night pressure > 1013.2 mb. • Center of a storm with rising warm air will have a pressure < 1013.2 mb. • Barometer is an instrument that measures atmospheric pressure. © John Wiley & Sons ,Inc Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Atmospheric Pressure Measuring Atmospheric Pressure • Radiosonde (balloon) is launched twice a day at key locations in United States • Radiosondes measure: • Pressure • Altitude • GPS location • Temperature • Relative humidity • Wind speed and direction © NG Image Collection Would one expect low or higher than standard sea level pressure in a hurricane? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Atmospheric Pressure Atmospheric Pressure and Altitude • Air density depends on pressure and temperature. • Atmospheric pressure decreases with altitude. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © John Wiley & Sons, Inc. Wind Speed and Direction Wind: • Horizontal movement of air • Renewable resource • Measured with an anemometer Wind direction: • Identified by the direction from which the wind comes • West wind blows from west to east • Measured with a wind vane Courtesy Taylor Instrument Company and Wards Natural Science Establishment Wind speed and direction are determined by three factors: pressure gradient, Coriolis effect, and friction. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Wind Speed and Direction Pressure Gradients • Change of atmospheric pressure measured along a line at right angles to the isobars. • Pressure gradient goes from high to low pressure. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction Pressure Gradients • Isobar = line on a map drawn through all points having the same atmospheric pressure • Widely spaced isobars → weak gradient and weaker winds. • Closely spaced isobars → strong PG and stronger winds. Where would you find the greatest pressure gradient on this map? a. Oklahoma City b. Southwestern Missouri c. Memphis d. Nashville © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction Pressure Gradients • Unequal heating of the Earth’s surface leads to a pressure gradient and causes wind. • Latitude, terrain differences, and land cover can cause uneven heating, pressure gradients and wind. 1 2 3 © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction Pressure Gradients If the island were in the Arctic and covered by glacial ice, would the pressure gradient be the same or different? © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction The Coriolis Effect (CE) • An effect of the Earth’s rotation that acts like a force to deflect a moving object on the Earth’s surface to the: • Right in the northern hemisphere • Left in the southern hemisphere Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Wind Speed and Direction The Coriolis Effect (CE) © John Wiley & Sons, Inc. • Due to Earth’s rotation, a path from the North Pole to Chicago along 74°W meridian would curve to the right, toward Chicago. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction Geostrophic wind is wind at high levels (upper levels) above the Earth’s surface moving parallel to the isobars, at a right angle to the pressure gradient. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Wind Speed and Direction The Frictional Force (FF) • Force exerted by the ground surface that is proportional to the wind speed • Always acts in the opposite direction to the direction of motion • Greatest closest to the surface Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Wind Speed and Direction The Frictional Force A cyclone is a center of low pressure where surface air converges into a spiral and is uplifted to the upper troposphere. • The PGF, CE, and FF cause the surface wind to spiral, converging inward toward the low-pressure center. © John Wiley & Sons, Inc. As the inward motion converges, it forces the air to rise (uplift) → cools adiabatically → clouds and precipitation Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Wind Speed and Direction The Frictional Force An anticyclone is a center of high pressure where upper troposphere winds spins downward (subsidence) and diverges outward at the surface. © John Wiley & Sons, Inc. • Air warms adiabatically as it sinks → inhibiting clouds and precipitation Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Global Wind and Pressure Patterns Global surface winds on an ideal Earth (see Figure 5.11): © John Wiley & Sons, Inc. •Surface winds are shown on the disk of the Earth, and the cross section at the right shows winds aloft. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Tropical Circulation • Warm air over the equator rises and forms low pressure resulting in the equatorial trough (wet weather). • Trade winds converge at the equator. • Air descends near 25 to 30o latitude forming a subtropical high pressure (dry weather) zone. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. © John Wiley & Sons, Inc. Global Wind and Pressure Patterns Tropical Circulation • Hadley cell = A lowlatitude atmospheric circulation cell with rising air over the equatorial trough and sinking air over the subtropical highpressure belts. © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Tropical Circulation Intertropical Convergence Zone (ITCZ): • A zone of convergence of air masses along the equatorial trough • Doldrums • ITCZ shifts with the seasons following the zone of highest insolation: © John Wiley & Sons, Inc. • Over the ocean it shifts a few degrees between January and July. • Over land, the zone shifts 20o to as much as 40o in Asia. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Global Wind and Pressure Patterns Tropical Circulation • Monsoon = seasonal reversal of the wind • January = north wind (dry) • July = warm, moist air (wet) © NG Image Collection © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Considering the direction of the winds compared to the isobars, which statement is most correct? a. Because this area is near the equator, the Coriolis effect has no influence on these winds. b. Because the pressure gradients are great, friction has no influence on these winds. © John Wiley & Sons, Inc. c. Because some of the winds are over the ocean, neither the Coriolis effect nor friction has an influence on these winds. d. Because the alignment of the wind direction is at 45°to the isobars, both the Coriolis effect and friction are important. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns North American monsoon © Ralph Lauer/Zuma Press/NewsCom Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Subtropical high-pressure cells • Area of high atmospheric pressure centered at about 30° N and 30° S • Stable and dry weather • Trade winds and westerlies • Hawaiian and Azores high • Shift with the seasons • East and west coast differences © A. N. Strahler Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Global Wind and Pressure Patterns In the days of sailing ships, which pattern of navigation made the most sense, considering prevailing wind directions? a. United States to Africa to England back to the United States b. United States to England to Africa back to the United States c. United States to England back to the United States d. United States to Africa back to the United States © A. N. Strahler Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Midlatitude Circulation • Westerlies • Between about 30° and 60° latitude • Polar front = boundary between cold polar air masses and warm subtropical air masses Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Global Wind and Pressure Patterns Midlatitude Circulation • Jet stream = high-speed airflow in a narrow band within the upper-air westerlies and along certain other global latitude zones at high altitudes: • Polar-front jet stream • Shifts equatorward in the winter • Subtropical jet stream Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Global Wind and Pressure Patterns What a Geographer Sees • Jet Streams and Air Travel Courtesy NASA © John Wiley & Sons, Inc. If an airplane flying in the center of this subtropical jet stream travels east at 1000 km/hr (621 mi/hr), how fast will the same airplane go, with the same fuel expenditure, when it travels west in the jet stream on its return flight? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Jet stream disturbances • Rossby waves • Baroclinic instability • Zonal flow (west to east) Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © John Wiley & Sons, Inc. Global Wind and Pressure Patterns Jet stream disturbances • Growth of disturbances in the jet stream © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns High-Latitude Circulation • January • July Courtesy John E. Oliver Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Global Circulation at Higher Altitudes © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Global surface winds on an ideal Earth (Review) © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Global Wind and Pressure Patterns Global air cells: Ferrel, Hadley, or Polar? (Review) © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Local Winds Daily Cycles of Winds • Daily reversal of the winds as a result of uneven heating • Sea breeze • Land breeze © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Local Winds Daily Cycles of Winds •Mountain breeze •Valley breeze © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Local Winds Other Topographic Winds • Chinook: a dry wind • Santa Ana winds For north–south mountain ranges in midlatitude regions (30° to 45° latitude), dry regions will be found on the ____ side in the northern hemisphere and on the ____ in the southern hemisphere. a. east; east b. west; west c. east; west d. west; east Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © A. N. Strahler © John Wiley & Sons, Inc. Local Winds Other Topographic Winds Santa Ana winds can create fire hazards. In this photo, wildfires have already begun in some areas, as is apparent from the smoke drifting off the Southern California coast. Courtesy NOAA Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Oceanic Circulation Ocean Currents • A persistent, dominantly horizontal flow of water controlled by wind patterns • Gyres: large circular ocean movements © John Wiley & Sons, Inc What relationship do you notice with the northern hemisphere ocean current and the pressure type typically located at 30o N? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Oceanic Circulation Ocean Currents Ocean circulation and energy transport: • Warm surface waters in the tropics move poleward. • Thermohaline circulation: Cold and dense waters in the N. Atlantic sink, flow equatorward, and eventually upwell to the surface at far distant locations to cool surrounding regions and complete the circuit. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. © NG Maps Oceanic Circulation Circulation and Energy Transfer • Energy surplus • Energy deficit • In order to maintain the Earth’s energy balance, absorbed solar energy is moved from regions of excess to regions of deficit, carried by ocean currents and atmospheric circulation © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Oceanic Circulation Cycles in Atmospheric and Oceanic Circulation • El Niño–Southern Oscillation (ENSO) • La Niña © NG Maps © NG Maps Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Oceanic Circulation Cycles in Atmospheric and Oceanic Circulation • Climate effects of El Niño events © John Wiley & Sons, Inc. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Oceanic Circulation Cycles in Atmospheric and Oceanic Circulation • North Atlantic Oscillation (NAO) • Pacific Decadal Oscillation (PDO) © NG Maps © NG Maps Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc.

Tutor Answer

brilliantmind
School: New York University

Attached.

Topic: Module 2: HUMIDITY
Section 1: Understanding Humidity

Section 2: Using the Saturation Curve Graph
Section 3: Measuring Relative Humidity with a Sling Psychrometer
Section 4: Practice Exercises Using Given Sling Psychrometer Values
Section 5: Relative Humidity Measurements


SAINT MARY’S UNIVERSITY

GEOG 1200

DEPARTMENT OF GEOGRAPHY

FUNDAMENTALS OF PHYSICAL GEOGRAPHY

Module 2: HUMIDITY

Objectives
1.

To study the concept of humidity.

2.

To understand use of the saturation curve graph.

3.

Learn about how relative humidity is measured using a sling psychrometer.

Section 1: Understanding Humidity

Terminology
Air can hold up to a certain amount of water vapour (water in a gaseous state) but the amount varies depending on the
temperature. Humidity is a general term that refers to the amount of moisture in air. Some other important terms to
know when dealing with moisture in the atmosphere are:

Specific Humidity (SH): the actual quantity of water vapour in the air, in grams per kilogram (g/kg).
Maximum Specific Humidity (MSH): the maximum quantity of water vapour that could be held in the air at a given
temperature (g/kg). If the air is unsaturated, the SH is less than the MSH.

Relative Humidity (RH): the ratio of SH to MSH, expressed as a percentage:
Equation 1:

Specific Humidity
RH (%) = ----------------------------------Maximum Specific Humidity

x

100

Dew-Point Temperature (DT): the temperature at which air saturation and condensation occur for a given value of
specific humidity. Condensation is the change of water from a gaseous state to a liquid state.

Saturation Curve: a graph (on a separate sheet) showing the relationship between air saturation and temperature.
Once the saturation point is reached, the RH is 100% and no more water vapour can be evaporated into the air.

Example
For reference, an example using the Saturation Curve ...

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