Chapter 8 - Astronomical Control of Radiation

Question 1

What are solstices caused by?

Answer 1

changing position of the tilted Earth with respect to the sun, while maintaining a constant angle and direction of tilt. I.e. when it tilts directly towards or away from the sun

Question 2

Perihelion?

Answer 2

when Earth is closest to the Sun (January)

Question 3

Aphelion?

Answer 3

when Earth is farthest from the Sun (July)

Question 4

What are monthly seasonal insolation values dominated by?

Answer 4

Dominated by precession (modulated by eccentricity) at low and middle latitudes, with the effects of obliquity only at higher latitudes

Question 5

How does relative sense of phasing differ between obliquity and precession?

Answer 5

For precession, an insolation maximum (perihelion position) will be simultaneous everywhere. However, the result of tilt will have the opposite effect at each pole
Precessional changes also have an entire family of insolation curves for each month (because each month precesses into parts of the eccentric orbit that alternate at 23,000 year cycle)

Question 6

What is the use of time series analysis?

Answer 6

To simplify analyses of cyclic variations in climate change. They are records plotted against time which can be used to extract rhythmic cycles embedded in records

Question 7

Spectral analysis?

Answer 7

measures correlation between sine wave and climatic signals

Question 8

Power spectrum

Answer 8

spectral analysis which extracts 3 component orbital cycles. Height is related to the square of the amplitude of the cycle of that period

Question 9

Why do other powers besides the orbital cycles appear?

Answer 9

As orbital cycles are never perfect sine waves, always contain variation. Also due to errors in the records and random noise.

Question 10

Filtering?

Answer 10

extracts the shapes of individual cycles in specific time bands

Question 11

Aliasing?

Answer 11

false trends generated by under sampling
To avoid this:
- For confident identification of a cycle it must be repeated at least 4 times
For the shortest cycles, at least two samples per cycle are needed to verify the cycle

Question 12

Has earths spin slowed down?

Answer 12

Yes - corals from 440 mya show 11% more tidal cycles, suggesting the Earth spun 11% more times than today. This means there were 11% more days
Gradual slowing has occurred due to frictional effect of tides and sun/moon

Question 13

Why does Earth have seasons?

Answer 13

Seasons are due to the changing position of the tilted Earth with respect to the sun. Earth maintains constant angle and tilt direction as it revolved around the sun, thus when the NH/SH arrives at the position in orbit where it is tilted directly towards the sun, it received more radiation (summer)

Question 14

When is Earth closest to the Sun in its present orbit? How does this close pass position affect radiation?

Answer 14

During perihelion. The Earth receives more radiation and this will be simultaneous everywhere.

Question 15

Describe the concept of modulation of a cycle

Answer 15

Modulation has the effect of increasing the amplitude of variations in a given cycle, without disrupting the cycle itself. Precession is modulated by eccentricity.

Question 16

Earth’s tilt is slowly decreasing today. Are the polar regions receiving more or less radiation in summer and winter

Answer 16

Less radiation as they are at a less direct angle to the sun. This will decrease seasonal differences i.e. cooler summers and less harsh winters

Question 17

How is axial precession different to precession of the ellipse?

Answer 17

Axial precession refers to the wobbling of the Earth’s rotational axis (tracing out a cone shape), while precession of the ellipse is the slow movement of the Earth’s eccentric orbit around the sun

Question 18

How does eccentricity combine with precession to control a key aspect of the amount of insolation earth receives?

Answer 18

The combined effects cause the distance between the Earth and Sun to vary by season, thus altering insolation. High eccentricity produces high contrast while low eccentricity produces lowest contrast

Question 19

Does summer insolation maxima at both poles caused by obliquity occur at the same time?

Answer 19

No, occur at opposite times. When one pole is tilted directly towards the sun during its insolation maximum, the other pole is pointed away from the sun thus receiving an insolation minima

Question 20

Does summer insolation maxima in the tropics of both hemispheres caused by precession occur at the same time?

Answer 20

Precessional insolation maxima occur at the same time everywhere, so yes.