Quiz 3 review questions: Answers


Q1:
The factors influencing the amount of solar radiation available for
absorption by the Earth/Atmosphere are:

1. the amount of solar radiation output by the sun.  Careful
measurements show that this changes by only 0.2% over the course of 11
years.

2. the distance between the sun and the Earth/Atmosphere.  The
concentration of radiation decreases with the square of the distance
from the emitting object.  The distance between the sun and Earth
varies by 3% over the course of a year (look at the handout).  This
translates into a change in the concentration of solar radiation
available for absorption by the Earth/Atmosphere of only 7% between the
time the Earth is closest to the sun (Jan.) and when it is furthest
from the sun (July).

3. The angle at which the sun's rays strike the Earth/Atmosphere
determine how much the rays are "spread" and how much they are
attenuated by the atmosphere.  The least amount of spreading and
attenuation occurs for rays that strike head on.  As the angle becomes
more oblique, the spreading increases as does the amount of attenuation
by the atmosphere.  The result is that less energy is available for
absorption by the Earth/Atmosphere.

4. The length of daylight tells how long the sun illuminates a point on
the Earth during a 24 hour period.  The more hours of daylight, the
more solar radiation that can be absorbed.

5. The albedo describes the fraction of energy that is reflected back
by an object.  The remainder is then absorbed.

Q2
The seasons refers to the variation in the solar radiation available
for absorption by a given point on the Earth.  This changes as the
Earth makes one complete orbit of the sun over the course of a year.
The available solar radiation change is dominated by the change in the
orientation of the Earth's rotational axis and the sun.  During the
year North portion of the rotational axis always points toward Polaris
(the North Star).  However, with respect to our closest star (the sun)
the axis is sometimes pointing toward the sun (most directly on June
21) and sometimes away (most directly away on Dec. 21) and other times
neither toward or away, but off to the side in the plane that divides
night from day (Sept. 21 and Mar. 21).  Thus it is the tilt of the
Earth's rotational axis with respect to the plane in which it orbits
the sun that is the most important.  For instance, if the Earth's
rotational axis was perpendicular to the orbital plane, then there
would be no change in the orientation of the rotational axis and the
sun over the year.  In this case the length of daylight would be the
same everywhere (12 hours) on the Earth and the same every day of the
year.  The sun would still be closer to the horizon in the polar
latitudes than in the tropics, so the energy available for absorption
would still be greater in the Tropics, but this would not change over
the course of the year.

Q4
Because the rotational axis it tilted from the vertical, Uranus would
also experience seasons just as we do on Earth.  And like the Earth,
the "North Pole" portion of the rotational axis is pointed toward the
sun during part of Uranus's orbit around the sun, pointed away from the
sun during part of the year.  The result would be the same for Earth in
that there would be 4 seasons, they would just be more extreme.

Q5
This too is the same as the Earth in that any given point on Uranus
would experience 1/2 a Uranus year of daylight and 1/2 of night.

Q6
The noon-time sun is directly overhead at any given point on the
equator just twice a year.  Those dates are the Sept. 21 and Mar. 21
when the rotational axis of the Earth lies in the plane that divides
day from night.  Again, see the hand-out.

Q7
The noontime sun is directly overhead at a point on the Tropic of
Cancer just once during the year.  This date is June 21.  At points
lying between latitudes 23.5 degrees North and 23.5 degrees South the
Noontime sun is directly overhead twice a year.  At 23.5 degrees North
(Tropic of Cancer) and 23.5 degrees South (Tropic of Capricorn) the
noon-time sun is directly overhead only once a year.  Outside the
tropics, the noon-time sun is never directly overhead.

Q8
Every point on the Earth can receive exactly 6 months of daylight and 6
months of night. However, on any individual day the length of daylight
is different from latitude to latitude, except upon the Equinoxes where
the length of daylight is 12 hours for all locations.

Q9
This relates to the angle of the sun relative to the local horizon.
Since the north-facing slope is tilted slightly away from the sun, the
angle the sun's rays make with the north-facing slope is closer to the
horizon, than the angle between the sun's rays and the south-facing
slope.

Q10
The terms:
a. perihelion - point in Earth's orbit around the sun at which the
Earth is closest to the sun.

b. aphelion - point in Earth's orbit around the sun at which the Earth
is further to the sun.

c. equinox - dates at which the noon-time sun is directly overhead at
the equator and the length of daylight is the same (equal) for all
points on the Earth.

Q11
All points on the Earth that receive sunlight on June 21 (remember that
latitudes south of 66.5 degrees South do not receive any sunlight on
this day) see the sun rise North of East.  This is a result of the
North Pole end of the rotational axis of the Earth being tilted
directly at the sun on this day.  Likewise on Dec. 21 (Northern
Hemisphere Winter Solstice) all points on the Earth that receive
sunlight (remember that latitudes north of 66.5 degrees North do not
receive any sunlight on this day) see the sun rise South of East.  This
time the North Pole end of the rotational axis is pointing directly
away from the sun.

Global distribution of energy budget

Q1
On a yearly basis, the largest amount of solar radiation is absorbed in
the tropics.  So, of the choices available 0-30 degrees North would
absorb the largest amount of solar radiation.  Another way of saying
this would be to state that the region 0-30 degrees North has the
lowest albedo for shortwave solar radiation.

Q2
On a yearly basis, the largest amount of longwave radiation emitted to
space done in the tropics.  So, of the choices available 0-30 degrees
North would emit the largest amount of radiation to space.

Q3
The tropical regions both absorb the most shortwave solar radiation and
emit the most longwave radiation to space, but these amounts are not
equal.  The amount absorbed is greater than the amount emitted.  So,
the net amount of radiation (in-out) is greater than zero.  In the
polar regions the amount emitted to space exceeds the amount absorbed
from the sun.  So, here the net amount of radiation is less than zero.
The figure in chapter 2 shows that the net amount (in-out) is equal to
zero at a latitude of about 40 degrees from the equator.  Remember that
this is averaged over the year.

Q4
Although in the tropics the amount of solar radiation absorbed exceeds
the amount emitted to space, the temperature from one year to the next
is much the same.  This is a result of the fact that the surplus of
energy (in-out greater than zero) is transported from the tropics
toward the poles where the in-out is less than zero.  The transportation
of the energy is done via conduction and convection by the atmosphere
and oceans.  Roughly the atmosphere transports about 50% of the energy
required to balance the global energy budget and the ocean transport
the other 50%.

Global Temperature Distribution

Q3 & Q4
The largest difference between the winter and summer temperatures can be found in the center of large land masses.  This is a result of both the relatively low specific heat of land (soil) and the amount of mass heated (also relatively low).  Oceans on the other hand have a much smaller range between winter and summer temperatures due to the large specific heat and the large mass that is either warmed or cooled.

Q5
The specific heat of a substance is the amount of energy required to change the temperature of 1 grams of substance 1 degree Celsius.

Q6
The size of the temperature increase of an object is directly related
to the amount of energy input.  The temperature increase is inversely
related to the mass of the object.  The temperature increase is also
inversely related to the specific heat of the object.  In class we
wrote a formula that allows one to calculate the size of the
temperature change.  It was

Temperature increase = Energy input / (mass x specific heat)

Q7
Both the specific heat is larger and the mass of substance either
heated or cooled is larger for the oceans than for the land.

Daily Temperature

Q1
The diurnal temperature cycle is a result changes in the net energy input into the surface (in-out).  When the in is greater than the out, then the surface warms.  When the in is less than the out, the surface cools.  When the in is equal to the out, then the temperature remains constant.  The physical factors that affect this net energy balance are:

Amount of solar radiation - this is determined by the length of
daylight and the solar angle.  Longer daylight means more solar
radiation.  The closer the solar angle is to the horizon, the lower the
solar radiation for absorption due to the increased beam spreading and
the increased attenuation.

Presence of clouds - Cloud have a high shortwave albedo (absorb very
light shortwave radiation) so they would decrease the amount of solar
radiation that a surface could receive during the day.  Clouds are also
good emitters of longwave radiation.  So, at night they would provide
additional longwave radiation for the surface of the Earth to absorb
(that is in addition to what the atmosphere also emits). Thus the
night-time temperature would be higher in the presence of clouds.

Moisture content of the surface - Some of the energy that is absorbed
by the surface goes into changing the temperature of the surface, and
some goes into changing the phase of whatever water might be in the
surface.  The less moisture in the surface the less energy goes into
changing the phase of the water from liquid to vapor and more goes into
raising the temperature of the surface.  Thus dry surfaces heat more
than moist surfaces.  They (dry surfaces) also cooler more.

Moisture content of the atmosphere - Remember that the atmosphere also
emits longwave radiation that is absorbed at the surface.  This
longwave radiation is emitted mainly by just two different gases, H2O
and CO2.  Remember the discussion about the variability of the water
vapor.  So, when there is more water vapor in the atmosphere, more
longwave radiation is emitted.  So, there is more longwave radiation
for the surface to absorb and then change the temperature of the
surface.

Ability to transfer energy via conduction/convection - Most of the
energy transport is dominated by radiation, but conduction and
convection are still important.  During the day the surface generally
wants to transfer energy away in an effort to balance the in-out energy
budget.  In the early morning hours this ability is rather low, so the
in exceeds the out.  As the day goes on ability to transfer energy away
from the surface via conduction/convection increases as a larger and
larger layer of air is warmed and moves up and down.  Thermals are
often formed as a result of this conduction/convection energy transport
away from the surface to the atmosphere.  This idea of enhancing
conduction/convection to cool a surface is turned around when we put on
a jacket or a blanket on a bed.  In this case the aim is decrease the
amount of energy that is transferred away from our bodies via
conduction/convection.  We hope to create a "layer of warm air" that
stays near our body and is not transported away.

Q2
A radiation inversion occurs when the surface cools via radiation such
that the surface temperature is less than the temperature of the air
above it so that the temperature actually increases with altitude (the
temperature inversion).  As the surface cools via radiation the air in
direct contact with the surface cools also via conduction.  This
transfer of energy is most efficient near the surface and becomes less
efficient as one gets away from the surface.  So the air right next to
the surface cools the most and follows the temperature of the surface
while the air further from the surface doesn't cool as much. The result
is that the temperature increases as we go away from the surface.  At
some altitude the conduction/convection energy transport is unable to
change the temperature and the air temperature is much the same as it
was during the day.  Above this altitude the temperature will exhibit
the general characteristic of the atmosphere and decrease with
altitude.

Q3
Looking at Q1 we can see that the lowest minimum temperature would
occur on a day in which the surface has received very little solar
radiation (less daylight and solar angle closer to the horizon) and a
lower amount of longwave radiation (no clouds and little water vapor).
In addition, a dry surface (lower specific heat) would cause the surface
to cool more.  Finally, the ability to transfer energy via
conduction/convection is enhanced by the wind.  In the case of
night-time temperatures the surface if usually cooler than the
atmosphere, so to have the lowest minimum temperature we would want to
make the transfer of energy from the atmosphere to the surface as small
as possible.  So, we would desire to have no winds (calm conditions).