Energy Balance and Temperature

Transcription

1 Chapter 3 Lecture Understanding Weather and Climate Seventh Edition Energy Balance and Temperature Frode Stordal, University of Oslo Redina L. Herman Western Illinois University

2 Quiz om stråling Hva er forskjellen på en gul genser og en gul flamme?

3 Quiz om stråling Hva er forskjellen på en gul genser og en gul flamme? Hvorfor er himmelen blå?

4 Quiz om stråling Hva er forskjellen på en gul genser og en gul flamme? Hvorfor er himmelen blå? Hvorfor kan solnedgangen være rød?

5 The Global Radiation Budget

6 Atmospheric Influences on Insolation Absorption Particular gases, liquids, and solids in the atmosphere reduce the intensity by absorption. Less energy is transferred to the surface. Atmospheric gases are overall poor absorbers of energy.

7 Atmospheric Influences on Insolation Reflection and Scattering Energy is redirected by objects through reflection without being absorbed. Albedo is the percentage of energy reflected by an object. Specular reflection is reflection of energy as an intense beam.

8 Atmospheric Influences on Insolation Reflection and Scattering Energy reflected as disperse energy into less intense beams is diffuse reflection, or scattering. Gases in the atmosphere scatter radiation. Energy that reaches the surface is scattered and different in intensity from direct radiation.

9 Atmospheric Influences on Insolation Reflection and Scattering Scattering of light by agents smaller than 1/10 the wavelength of incoming radiation is known as Rayleigh Scattering. Partial to shorter wavelength energy. Rayleigh Scattering results in our blues skies. It s why our skies are blue to the human eye.

10 Atmospheric Influences on Insolation Reflection and Scattering Mie scattering, scattering sunlight, is predominantly forward scattering, diverting relatively little energy backward to space. Mie scattering causes sunrises and sunsets to be more red, when pollution is present.

11 Atmospheric Influences on Insolation Transmission The fraction of energy transmitted through the atmosphere to the surface. Transmission is dependent upon the atmosphere s ability to absorb, scatter, and reflect. Transmission of energy varies from place to place.

12 The Global Radiation Budget

13 The Fate of Solar Radiation Atmospheric reflection averages 25 units, 19 of which are reflected to space by clouds and 6 units are back-scattered to space from atmospheric gases.

14 The Fate of Solar Radiation Five units are reflected back to space. These five units combined with the 25 scattered to space from the atmosphere (clouds, etc.) equate to a total albedo of 30 percent for Earth. The remaining 45 units of energy at the Earth s surface is absorbed and this heats the surface from the ground up. Earth processes and transfers this energy back to space.

15 The Fate of Solar Radiation

16 Energy Transfer Processes Surface Atmosphere Radiation Exchange Earth s surface and atmosphere radiate longwave energy. Longwave radiation emitted from the surface is largely absorbed by the atmosphere. This increases the temperature of the atmosphere, which causes it to radiate energy in all directions, including toward the surface. This causes additional surface heating, and the cycle repeats. To describe longwave energy, we begin with 116 units of radiation. 104 units are absorbed by the atmosphere.

17 Energy Transfer Processes Surface Atmosphere Radiation Exchange Water vapor and CO 2 are the primary absorbers of longwave radiation (greenhouse gases). The range of wavelengths, 8-15 μm, matches those radiated with greatest intensity by the Earth s surface. This range of wavelengths not absorbed is called the atmospheric window. Atmospheric window

18 Energy Transfer Processes Conduction As the surface warms, a temperature gradient develops in the upper few centimeters of the ground. Temperatures are greater at the surface than below. Surface warming also causes a temperature gradient within a very thin (a few millimeters) sliver of adjacent air called the laminar boundary layer.

19 Energy Transfer Processes Convection The temperature gradients in the laminar boundary layer induce energy transfer upward through convection. This occurs any time the surface temperature exceeds the air temperature, typically occurring in the middle of the day. At night, the surface cools more rapidly that air and energy is transferred downward. Convection can be generated by two processes in fluids. Free Convection Mixing related to buoyancy, warmer, less dense fluids rise Forced Convection Initiated by eddies and other disruptions to smooth, uniform flow

20 Energy Transfer Processes Free Convection Forced Convection

21 Energy Transfer Processes Sensible Heat When energy is added to a substance, an increase in temperature can occur. Eight units of energy are transferred from the surface to the atmosphere as sensible heat.

22 Energy Transfer Processes Latent Heat Energy required to induce a change of state in a substance. In the atmosphere, we relate this to water. Energy must be supplied in order to melt an ice cube, freeze water, evaporate water, or boil it to water vapor.

23 The Global Energy Budget

24 The Global Energy Budget

25 Energy Transfer Processes Net Radiation and Global Temperature Earth s radiation balance is a function of an incoming and outgoing radiation equilibrium. Balances occur on an annual global scale and diurnally over local spatial scales. (1-α) I = σ T 4 α albedo I solar constant / 4 T = [(1-α)I/σ] -4 T = -18 C

26 The Greenhouse Effect Terrestrial radiation is trapped by certain atmospheric gases, allowing solar radiation to enter but trap outgoing heat energy. Without atmospheric gases (H 2 O, CO 2, and CH 4 ) trapping outgoing terrestrial radiation, average Earth temperatures would be about -18 C. Very cold. Increases in greenhouse gas concentrations through human activities may lead to future climatic changes and potential warming.

27 Energy Transfer Processes

28 Influences on Temperature

29 Influences on Temperature Altitude and Elevation Temperatures in the troposphere decrease with altitude. Earth heats from the ground up. Temperatures at high altitudes remain fairly constant. Air at high elevations (but near a surface) is influenced more by rapid diurnal temperature fluxes than air at lower elevations.

30 Influences on Temperature Atmospheric Circulation Patterns Latitudinal temperature and pressure differences cause large-scale horizontal energy transport through advection. Also influences latitudinal moisture and cloud cover, which then impact temperatures.

31 Influences on Temperature Contrasts Between Land and Water Surface composition affects atmospheric heating. Water bodies heat slower than land. Continentality is the effect of inland location that favors greater temperature extremes. Maritime locations experience more moderate seasonal temperature extremes due to the presence of water bodies, which change temperature very slowly. The water acts like a temperature regulator. Water heats less due to higher specific heat, transparency, evaporative cooling, and horizontal and vertical mixing factors.

32 Influences on Temperature Local Conditions Small topographical features impact temperatures. Slopes facing toward the equator heat more quickly than slopes facing the poles. South-facing slopes are typically more vegetated than north-facing slopes.

33 Daily and Annual Temperature Patterns Daytime Heating and Nighttime Cooling Forest regions reduce surface insolation during the day and trap radiation at night leading to cooler daytime temperatures and warmer nighttime temperatures. Vegetation reduces surface radiation during the day and traps it at night.

34 Our Warming Planet In 2007, the Intergovernmental Panel on Climate Change (IPCC) issued a report that concludes a rapidly warming planet. There are many other reports and accounts since this report that conclude the Earth is warming. Global temperatures have increased during the 20th century. Extreme hot and cold events are also believed to be an indicator of climate change. Scientists use complex mathematical programs called general circulation models (GCMs) to examine how the atmosphere might respond to increasing greenhouse gas concentrations in the future.

35 Our Warming Planet

36 Our Warming Planet The IPCC paid close attention to volcanic eruptions, solar radiation variability, and other factors that could influence global climates but still identified human greenhouse gas emissions as the primary cause of warming. The effect of humans on climate is one of the foremost matters that societies will have to deal with for some considerable time to come.