GGR100H1 Lecture Notes - Milky Way, Shortwave Radiation, Solar Wind

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Published on 16 Oct 2011
School
UTSG
Department
Geography
Course
GGR100H1
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of 3
Solar Radiation//Christopherson, Chp.2
Goals to learn this lecture:
-What is electromagnetic radiation?
-What are the patterns of receipt of solar radiation on Earth?
-What are seasons and why do we have them?
Why it’s important: solar radiation drives physical systems and the biosphere
abbreviations used in document: ‘sorad’ = solar radiation; ‘bill.’ = ‘billion’; ‘amnt’ =
‘amount. Others should be self-explanatory I hope.
Earth-Sun relationships are critical to how Earth systems behave
-Revolution and Rotation = 2 very distinct characteristic of Earth
>Revolution: Earth orbits annually around sun in an ellipse (1 complete revolution/year)
>Rotation: Earth rotates eastwards daily on own axis, which gives day and night
aphelion and perihelion: related to certain distances of Earth from Sun at diff. times
aphelion. = July 4th/Summer: Earth at its farthest from Sun at this point in revolution
perihelion. = January 3rd/Winter: Earth at its closest to Sun at this point in revolution
>Aphelion and perihelion raise questions against misconceptions about proximity to
Sun equitable with seasonality, since further we are, it’s summer, whereas closer we
are, it’s winter.
The Sun
-typical of one of several 100 bill. stars in Milky Way Galaxy
-6000K @ surface
-Enormous mass @ high temp. & pressure nuclear fusion
-Sun emits charged particles which give phenomena such as solar wind, short-wave
radiation
>emits , at surface, high energy radiation travelling at speed of light
Radiation
-energy transmitted as waves of electric and magnetic oscillations
-ELECTROMAGNETIC RADIATION is emitted by all matter with a temp. above absolute 0/
0K
-radiation intensity emitted depends on the temp. of the object: Stefan-Boltzmann law
Q proportional to T^4
-Wavelength of radiation inversely related to surface temp (hotter = shorter
wavelengths)
>wavelength is distance ‘twixt two adjacent peaks.
Why human beings dont glow...
-comfy human skin temp ~ 33Cs
-Avg. Human surface area ~ 1.8m^2
-895 watts emitted (1 watt = 1 joule/s)PWR = energy emitted per unit time. Watt= unit
of PWR.
-This is similar to 9 household light bulbs
-Radiation is in the thermal infrared part of the spectrum (heat) not visible light; which
is why human beings don’t glow
Solar Radiation//Christopherson, Chp.2
Some Def’ns
Ozone layer: contains ozone (O3) which absorbs much sorad (UV and X-ray). Else we’d
die rightquick.
Thermopause: outer boundary of Earth’s energy system
Solar constant: Avg. Insolation received at thermopause when Earth is at its avg.
Distance from Sun
Watt: standard unit of PWR [energy (Joules) per unit time (seconds)]
Absorption of diff. wavelengths by gases in the atmosphere
How much insolation does Earth intercept?
-Incoming short wave radiation at the top of the atmosphere = 1372W/m^2 (solar
constant)
-Sub-solar point: where sun is directly overhead; most intense, maximum receipt of
sorad.
>varies with the seasons
>more diffuse as you move away
Avrg. Daily latitudinal energy imbalance @ top of atmosphere is spatial variation
Net R : total amnt of radiation @ given point in atmosphere in watts/m^2
- isolines connect points of equal sorad receipt
-Earth’s “heat engines” distribute energy (wind, ocean currents and weather)
>Earth’s many irregularities make ‘imbalance’ in terms of equator isn’t necessarily
hottest at isolines
Seasonal changes in insolation are called temporal variation
-Changes in Sun’s position above horizon and in day length
-Declination = latitude of sub-solar point
>where Sun is in terms of sub-solar pt. Determines seasons
Declination of Sun: Where Sun is above horizon
Revolution
-Revolution around Sun: length of seasons
-Difference between aphelion and perihelion not significant
-Eccentricity (epsilon): degree of departure from perfectly circular orbit
>varies from 0-1
>Earth’s epsilon = 0.0167 (thus nearly circular)
>Eccentricity aren’t too significant for determining Earth’s seasons
Rotation and orbital position
-Rotation around Earth’s axis: day length
-Equator: day length = 12 hrs year round
Tilt: Earth’s axial tilt is major factor in explaining seasons
>Earth axis is at 23.5 degree tilt from plane of ecliptic
>axis always points to Polaris (North Star), regardless of time of year = “axial
Solar Radiation//Christopherson, Chp.2
parallelism”
Annual march of the seasons
Equinoxes: circle of illumination passes through both poles, Day length = 12 hrs.
everywhere

Document Summary

Why it"s important: solar radiation drives physical systems and the biosphere abbreviations used in document: sorad" = solar radiation; bill. " = billion"; amnt" = Earth-sun relationships are critical to how earth systems behave. Revolution and rotation = 2 very distinct characteristic of earth. >revolution: earth orbits annually around sun in an ellipse (1 complete revolution/year) >rotation: earth rotates eastwards daily on own axis, which gives day and night aphelion and perihelion: related to certain distances of earth from sun at diff. times aphelion. = july 4th/summer: earth at its farthest from sun at this point in revolution perihelion. = january 3rd/winter: earth at its closest to sun at this point in revolution. >aphelion and perihelion raise questions against misconceptions about proximity to. Sun equitable with seasonality, since further we are, it"s summer, whereas closer we are, it"s winter. Typical of one of several 100 bill. stars in milky way galaxy.