W&C Chapter 3

Describe the fate of incoming solar radiation as it is affected by the atmosphere.

Absorption, scattering, and transmission affect the distribution of temperature throughout the atmosphere and a number of atmospheric phenomena. Solar radiation does not pass unimpeded through the atmosphere, but rather is attenuated by a variety of processes. The atmosphere absorbs some radiation directly and thereby gains heat. Another portion of radiation disperses as weaker rays going out in many different directions through a process we call scattering. Some of the scattered radiation is directed back to space; the remainder is scattered forward as the light we see from the portion of the sky away from the solar disk. In either case, the energy that is scattered is not absorbed by the atmosphere and therefore does not contribute to its heating. The remaining insolation is neither absorbed nor scattered—it passes through the atmosphere without modification, reaching the surface as direct radiation. But not all the energy reaching the surface is absorbed. Instead, a fraction is scattered back to space and, like the radiation scattered by the atmosphere, it does not contribute to the heating of the planet. Solar energy passing through the atmosphere is subject to absorption and scattering, while a certain amount is able to be transmitted to the surface. Scattering reduces the intensity of the direct radiation reaching the surface but at the same time creates blue skies, red sunsets, and white clouds. About a quarter of incoming solar radiation is absorbed by the atmosphere with about an equal amount scattered back to space. Thus, about half the energy reaches the surface, with some of that likewise reflected back to space.

Describe the diurnal temperature curve. When is the warmest time of the day? Why?

As the Sun emerges above the horizon, the incoming energy does not effectively heat the surface due to the beam spreading and atmospheric depletion associated with the low solar angle. At sunrise and for some time period afterward, the receipt of solar radiation does not offset the loss of longwave radiation at the ground, leading to steady or slowly decreasing temperatures. As the morning proceeds, the Sun sweeps a path from where it rose over the eastern sky toward the south (or north in the Southern Hemisphere), while at the same time rising upward from the horizon. Thus, as the outgoing longwave radiation remains roughly constant, the incoming solar radiation increases. At some point the Sun rises far enough above the horizon for its energy to offset the loss of longwave radiation, and warming occurs. above Daytime Warming: - Air at the ground warms faster than air immediately above - Warmest in the late-afternoon • Nighttime Cooling: - Air at the ground cools faster than the air immediately above - Coolest time is right before sunrise on normal occasions

What influence do clouds have on the diurnal temperature curve?

During the day the cloud cover can greatly reduce the daytime input of solar radiation and likewise reduce the magnitude of the net longwave radiation loss over the entire 24-hour period (Figure 3-23b). The overall effect is to lower the daytime maximum temperature while keeping nighttime temperatures somewhat higher than they would be on a clear night. Overall, the temperature difference over the 24-hour period is much less They reduce the minimum and maximum temperature as well as the absorbed solar radiation

(a) Convection is a heat transfer mechanism involving the mixing of a fluid. In free convection, local heating can cause a parcel of air to rise and be replaced by adjacent air. (b) Free convection can create updrafts able to keep a hawk airborne without it having to flap its wings.

Figure 3.11

At latitudes between about 38° north and south, a radiant energy surplus exists. Poleward of these latitudes, the atmosphere and surface lose more radiant energy than is gained.

Figure 3.15

Currents that are moving warm water are depicted by red arrows, those moving cold water by blue arrows.

Figure 3.16

The air inside a greenhouse is warmer than that outside because glass allows solar radiation to enter but is opaque to outgoing longwave radiation. It also precludes the movement of heat away from the surface by convection. This latter effect makes the action of a greenhouse different from that of the atmosphere. Therefore, the term "greenhouse effect" is not completely appropriate when applied to the atmosphere.

Figure 3.17

Distribution of mean January (a) and July (b) surface air temperatures. The difference in temperature between the two months is shown in (c).

Figure 3.18

During the day (a) lower elevation sites (a) undergo more rapid warming than area farther from the surface (B) or at higher surface elevations (c). At night (b) higher elevation locations (C) have more rapid cooling than do lower elevations (A) or the air at the same altitude above sea level but farther from the surface (B).

Figure 3.19

In the process of scattering, a beam of radiation is broken down into many weaker rays redirected in other directions.

Figure 3.2

(a) Dense vegetation cover lowers daytime temperatures because of its shadowing effect on incoming solar radiation. (b) At night the forest canopy retards the loss of longwave radiation to space, resulting in higher nighttime temperatures than in the open.

Figure 3.22

Surface temperature increases whenever the energy gains exceed energy losses. (a) On clear days the availability of solar radiation in the middle of the day produces a large surplus that persists into the afternoon, but at night the longwave radiation loss results in substantial cooling. (b) Overcast conditions suppress the diurnal change in temperature mainly by reducing the incoming solar radiation gain during the day and by supplying more downward longwave radiation from the atmosphere at night.

Figure 3.23

The sky appears blue because the gases and particles in the atmosphere scatter some of the incoming solar radiation in all directions. Air molecules scatter shorter wavelengths most effectively. Someone at the surface looking skyward perceives blue light, the shortest wavelength of the visible portion of the spectrum.

Figure 3.3

Sunrises and sunsets appear red because sunlight travels a longer path through the atmosphere when the Sun is low on the horizon. In (a) the sun contains a wide variety of wavelengths. As it passes part way through the atmosphere (b) some of the shorter wavelengths have been scattered out of the direct beam. By the time it reaches the surface (c) the approaching light contains little of the original short wavelengths.

Figure 3.5

A number of processes affect solar radiation as it passes through the atmosphere. The clouds and gases of the atmosphere reflect 17 and 6 units, respectively, of insolation back to space. The atmosphere absorbs another 23 units. Only 54 percent of the insolation available at the top of the atmosphere actually reaches the surface, where another 7 units are reflected back to space. The net solar radiation absorbed by the surface is 47 units.

Figure 3.8

What is the urban heat island all about? Relate to an urban area you are familiar with or interested in.

Highest temperatures found within the city core • Large city parks typically cooler

What factors influence temperature, pick two and describe how they work and how you observe them on the Earth

Land and Water Because the atmosphere is heated primarily from below, it should be no surprise that the type of surface influences air temperature. The greatest influence arises because of contrasts between land and water. Water bodies are far more conservative than land surfaces with regard to their temperature, meaning that they take longer to warm and cool when subjected to comparable energy gains and losses. Four reasons cause water bodies to be more conservative than landmasses with regard to temperature: 1. The specific heat of water is about five times as great as that of land. 2. Radiation received at the surface of a water body can penetrate to several tens of meters deep and distribute its energy throughout a very large mass. In contrast, the insolation absorbed by land heats only a very thin, opaque surface layer. 3. The warming of a water surface can be reduced considerably because of the vast supply of water available for evaporation. Because much energy is used in the evaporative process, less warming occurs. 4. Unlike solid land surfaces, water can be easily mixed both vertically and horizontally, allowing energy surpluses from one area to flow to regions of lower temperature.

Latitude

Less total sunlight at high latitudes => colder poleward

Greenhouse effect

The interactions that warm the atmosphere

Energy Balance

as much energy goes into the Earth surface-atmosphere system as goes out of it. A balance between incoming solar radiation and outgoing terrestrial radiation

Isotherm

connects points of equal temperature.

Advection

energy surplus at low latitudes is offset by the horizontal movement,

Altitude

height above mean sea level

Latent Heat

is the energy required to change the phase of a substance (that is, its state as a solid, liquid, or gas).

Reflection

process where light bounces back from an object at the same angle and intensity

Scattering

produces a larger number of weaker rays (diffused light), traveling in different directions

Absorption

represents an energy transfer to the absorber. This transfer has two effects: The absorber gains energy and warms, while the amount of energy delivered to Earth's surface is reduced.

Continentality

the effect of an inland location that favors greater temperature extremes

Albedo

the percentage of insolation reflected by an object or substance Fraction reflected Light-colored surfaces (e.g., snow, light roofs) reflect more light Dark-colored surfaces (e.g., forests, dark roofs) absorb more light