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Chapter 3 Energy Balance and Temperature. Absorption. Atmospheric gases, particulates, and droplets all reduce the intensity of solar radiation ( insolation ) by absorption , a process in which radiation is captured by a molecule. It is important to note that absorption represents an

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Chapter 3 energy balance and temperature

Chapter 3

Energy Balance and Temperature


Chapter 3 energy balance and temperature

Absorption

  • Atmospheric gases, particulates, and droplets all reduce the

  • intensity of solar radiation (insolation) by absorption,

  • a process in which radiation is captured by a molecule.

  • It is important to note that 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 the surface is reduced.


Chapter 3 energy balance and temperature

Scattering and reflection

The reflection of energy is a process whereby radiation

making contact with some material is simply redirected

away from the surface without being absorbed.

The percentage of visible light reflected by an object

or substance is called its albedo. When light strikes

a mirror, it is reflected back as a beam of equal intensity,

in a manner known as specular reflection.

When a beam is reflected from an object as a

larger number of weaker rays traveling in different

directions, it is called diffuse reflection, or scattering.


Chapter 3 energy balance and temperature

Direct and diffuse radiation

In addition to large solid surfaces, gas molecules, particulates, and small droplets scatter radiation.

Although much is scattered back to space,

much is also redirected forward to the surface.

The scattered energy reaching Earth’s surface

is thus diffuse radiation, which is in contrast to

unscattered direct radiation.


Chapter 3 energy balance and temperature

Air molecules: Rayleigh scattering

Scattering agents smaller than about one-tenth the

wavelength of incoming radiation disperse radiation

through Rayleigh scattering, which is particularly

effective for those colors with the shortest wavelengths.

Thus, blue light is more effectively scattered by

air molecules than is longer-wavelength red light.


Chapter 3 energy balance and temperature

Air molecules: Rayleigh scattering

Scattering agents smaller than about one-tenth the

wavelength of incoming radiation disperse radiation

through Rayleigh scattering, which is particularly

effective for those colors with the shortest wavelengths.

Thus, blue light is more effectively scattered by

air molecules than is longer-wavelength red light.

Efficiency:

Kλ = c λ-4


Chapter 3 energy balance and temperature

Aerosols: Mie scattering

Microscopic aerosol particles are considerably larger

than air molecules and scatter sunlight by a process

known as Mie scattering, which does not have nearly

the tendency to scatter shorter wavelength radiation

that Rayleigh scattering does. Mie scattering causes

sunrises and sunsets to be redder than they would due

to Rayleigh scattering alone, so episodes of heavy

air pollution often result in spectacular sunsets.


Chapter 3 energy balance and temperature

Blue sky

The sky appears blue because gases and particles in the atmosphere scatter some of the incoming solar radiation in all directions. Air molecules scatter shorter wavelengths most effectively. Thus, we perceive blue light, the shortest wavelength of the visible portion of the spectrum.


Chapter 3 energy balance and temperature

Red sunset

Sunrises and sunsets appear red because sunlight travels a longer path

through the atmosphere. This causes a high amount of scattering to remove

shorter wavelengths from the incoming beam radiation. The result is sunlight

consisting almost entirely of longer (e.g., red) wavelengths.


Chapter 3 energy balance and temperature

Clouds: nonselective scattering

The water droplets in clouds are considerably larger than

suspended particulates reflecting all wavelengths of

incoming radiation about equally, which is why clouds

appear white or gray. Because of the absence of

preference for any particular wavelength, scattering

by clouds is sometimes called nonselective scattering.


Chapter 3 energy balance and temperature

Shortwave radiation

Incoming solar radiation available is subject to a number of processes as it passes through the atmosphere. The clouds and gases of the atmosphere reflect 19 and 6 units, respectively, of insolation back to

space. The atmosphere absorbs another 25 units. Only half of the insolation available at the top of the atmosphere actually reaches

the surface, of which another 5 units are reflected back to space.

The net solar radiation absorbed by the surface is 45 units.


Chapter 3 energy balance and temperature

Short&long wave radiation

Net radiation is the end result of the absorption of insolation and the

absorption and radiation of longwave radiation. The surface has a net

radiation surplus of 29 units, while the atmosphere has a deficit of 29 units.


Chapter 3 energy balance and temperature

Heat transfer by conduction

Heat is transferred by conduction

between the ground and the atmosphere

When the ground is warmer (colder) than the air

heat is conducted

from (to) the ground to (from) the atmosphere


Chapter 3 energy balance and temperature

Heat transfer by convection

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.


Chapter 3 energy balance and temperature

Heat transfer by convection

Forced convection (also called mechanical turbulence) occurs when

a fluid breaks into disorganized swirling motions as it undergoes a

large-scale flow. Air is forced to mix vertically because of its

low viscosity and the deflection of wind by surface features.


Chapter 3 energy balance and temperature

Latent heat

Latent heat is the energy required to change the

phase of a substance (solid, liquid, or gas).

In meteorology we are concerned with the heat

involved in the phase changes of water.

In the case of melting ice, the energy is called

the latent heat of fusion. For the change of phase

from liquid to gas, the energy is called

the latent heat of evaporation.


Chapter 3 energy balance and temperature

Heat balance for the Earth: global and yearly avarage

Both the surface and atmosphere lose exactly as much energy as they gain. The surface has a surplus of 29 units of net radiation, which is offset by the transfer of sensible and latent heat to the atmosphere.

The atmosphere offsets its 29 units of radiation deficit by the

receipt of sensible and latent heat from the surface.


Chapter 3 energy balance and temperature

Greenhouse effect

The interactions that warm the atmosphere are often

collectively referred to as the greenhouse effect,

but the analogy to a greenhouse is not strictly accurate.

The greenhouse gases of the atmosphere do not impede

the transfer of latent and sensible heat. Thus, it

would be more accurate if the term “greenhouse effect”

were replaced by “atmospheric effect.”

The greenhouse effect keeps Earth

warmer by absorbing most of the longwave radiation

emitted by the surface, thereby warming the

lower atmosphere, which in turn emits radiation downward.


Chapter 3 energy balance and temperature

Geographical and seasonal varaibility in heat balance leads to (i) variability in temperatures and (ii) transport of heat in the atmosphere

One of the most immediate and obvious outcomes of radiation gain or loss

is a change in the air temperature. The map depicts differences between

mean temperatures in January and July through the use of isotherms,

which are lines that connect points of equal temperature.


Chapter 3 energy balance and temperature

Geographical and seasonal varaibility in heat balance leads to (i) variability in temperatures and (ii) transport of heat in the ocean

Weather in motion Ch3 (ed4)


Chapter 3 energy balance and temperature

Geographical and seasonal varaibility in heat balance leads to (i) variability in temperatures and (ii) transport of heat in the ocean

Certain geographical factors combine to influence temperature patterns across

the globe. These factors include latitude, altitude, atmospheric circulation patterns,

local conditions, continentality, (the effect of an inland location that favors greater

temperature extremes) and ocean current characteristics along coastal locations.


Chapter 3 energy balance and temperature

Temperature means and ranges to (i) variability in temperatures and (ii) transport of heat in the

The daily mean is defined as the average of the

maximum and minimum temperature for a day.

The daily temperature range is obtained by

subtracting the minimum temperature from the maximum.

The monthly mean temperature is found by

summing the daily means and dividing by

the number of days in the month.

The annual mean temperature is obtained by

summing the monthly means for a year and dividing by 12.

The annual range is obtained as the difference

between the highest and lowest monthly mean temperatures.


Chapter 3 energy balance and temperature

Thermodynamic diagram: to (i) variability in temperatures and (ii) transport of heat in the

Profiles of temperature and humidity

Thermodynamic diagrams (such as the Stuve above) depict the vertical profiles of temperature and humidity with height above the surface enabling forecasters to determine the height and thickness of existing clouds and the ease with which the air can be mixed vertically. The data on the charts are obtained from radiosondes that are carried aloft by weather balloons

twice a day at weather stations across the globe.