PTYS/ASTR 206Solar Activity and Effect on Earth 3/6/07 Solar Variability and its Effect on Earth and...

PTYS/ASTR 206 Solar Activity and Effect on Earth3/6/07

Solar Variability and its Effect on Earth and

its Inhabitants


Announcements

• Reading Assignment– Chapters 10 and 11

• 4th homework due March 20

• Next study-group session is tomorrow, from 10:30AM-12:00Noon – in room 330.


• We know that the number of sunspots on the Sun goes up and down with a fairly regular 11-year cycle called “the solar cycle”– Currently, we are near the minimum in the solar cycle– However, the number of sunspots at the peak is not

always the same (there were more in 1957, compared to 1812, for example)

Number of Sunspots versus time – they come and go every 11 years


These variations result from the way magnetic fields are generated within the interior of the Sun: The Solar Dynamo


The Buildup of magnetic field energy must be released – how?

• Coronal Mass Ejections and Flares

– Abrupt and unpredictable releases an enormous amount of energy

– A solar flare is a brief eruption of hot, ionized gases from a sunspot group

– A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona

• These storms can interact with the Earth and create huge geomagnetic storms

• They also accelerate particles to very high energies


SOHO/LASCO (C3) movie of the “Halloween” Solar Storms of 2003


SOHO/EIT movie of the “Halloween” Solar Storms of 2003


The largest flare seen since the National Oceanic and Atmospheric Administration (NOAA) began recording them in 1976

Artists depiction of the asteroid that hit the Earth 65 million years ago creating Chicxulub crater

x-ray image of the Sun (SoHO)

Flare Energy ~ 5x1025 Joules

Asteroid Energy ~ 5x1023 Joules

100 times less than a flare!

The amount of energy involved in a solar flare and coronal mass ejection is enormous


How does the Sun Influence Earth?

• Provides the energy that creates life, warms the planet, drives the dynamic atmosphere and oceans

• Sun-climate connection?– 11-year cycles in mammal populations?

• Geomagnetic storms– Aurora– Power-grid failures (Canada, 1989);

Telecommunications failures– Confused homing pigeons?

• High-energy solar particles– can destroy ozone– large radiation dosages for astronauts

and passengers/pilots on polar air-travel routes


The number of sunspots at the peak in the 11-year cycle is variable

• The Maunder Minimum was a period from 1645-1715 in which very few sunspots were recorded– About 50 during this period

compared to ~50,000 over a similar time interval in the 1900’s

• During the Maunder minimum, there was a period of extremely cold winters in northern Europe– The “Little Ice Age”

• Other cycles and climatic changes have been recorded using proxy records (tree rings, ice cores, riverbed sediments)


The River Thames (in London) froze over during a period within the “Little Ice Age” as depicted in this painting by Abraham Hondius


The Sun is slightly dimmer during sunspot minimum as seen by recent, highly sensitive (but not inter-calibrated!) measurements

↑↑Sunspot Minimum Sunspot Minimum

Solar Energy arriving at Earth’s orbit The Solar “Constant”


The Sun’s role in Global Warming

• The Sun is more active now than it has been for quite some time (we are in a period of time called the “modern maximum”)– This increased activity does

contribute to the overall increase in Earth’s mean temperature

• However, the largest contributor to global warming is the increase in anthropogenic (man-made) green house gases– This is the scientific

consensus and is not debated in the scientific community


Geomagnetic Storms and their consequences

• disrupted communication– Radio signals, telegraph wires, cell phones (?)

• Overloaded power grids (induced ground currents)– A huge and costly outage occurred in Canada in 1989.

• Oil pipeline corrosion (induced ground currents)• Dangerous intensities of energetic particles and space

radiation • Extended atmosphere that can cause drag on low-orbiting

spacecraft• Confused homing pigeons, sperm-whale strandings,

mammal population cycles?

NOAA has a list of “severity scales” on their website http://www.sec.noaa.gov/NOAAscales/index.html#GeomagneticStorms

A geomagnetic storm is global disturbance in Earth’s magnetic field caused by the interaction of Earth with the material associated with solar explosions


The Space Radiation and Particle Environment

Solar Photons (x-rays, UV)

Particles trapped in the Van-Allen radiation belts (atomic nuclei)

Solar-Energetic Particles (atomic nuclei)

Cosmic Rays (atomic nuclei) Most of these particles originate from shock waves associated with supernovae remnants


Galactic Cosmic Rays and the Solar Cycle


Are cosmic rays dangerous?• Yes (if you are unprotected) !!!

– When a cosmic ray strikes skin, it will creates a cascade if secondary particles in your body (like an air-shower in the atmosphere)

– It can damage DNA and may cause cancer

The precise effect of cosmic rays on humans (cosmic-ray intensity vs. radiation dosage, how rapidly DNA can repair itself, etc.) is under study.


NASA limits on human radiation exposure are designed to lead to a <3% increase in lifetime fatal cancer risk and to ensure that astronauts do not suffer short-term radiation effects

• Dose Equivalent is measured in units of Sieverts (or REM).

– 1 Sv = 100 REM– 0.01 REM per routine

chest x-ray image– 4 REM for a CAT scan

• BFO = Blood-forming organs

10,000 chest x-rays

20,000 chest x-rays


E.N. Parker, Scientific American, March 2006


The solar minimum intensity of Galactic cosmic rays (for a 9-month journey to Mars) is enough to exceed the current radiation limits for astronauts in low Earth orbit

Mewaldt et al. 2006


But – new data indicate that another big threat is from solar-energetic particles (SEPs). This plot shows how much SEPs vary from one “event” to the next (the one with the dark green arrow is a 1 million –fold increase in the intensity)

Solar Energetic Particles (SEPs)

Galactic cosmic rays (GCRs)

↓


DO

SE

(G

Y)

Based on Wilson (1997), Townsend (2003), Kim et al. (2005), and Turner (2006)

Shielding from Huge Solar Particle Events

This as an enormous solar superstorm that occurred in 1859←


It is essentially impossible to shield from Galactic Cosmic Rays – not cost effective


• Cannot launch such extreme payloads• Would require several return trips to space where the spacecraft would have to

be assembled


On the Surface of Mars

• The Martian atmosphere is very thin and probably does not provide adequate protection from cosmic rays– It may, in fact, be worse

because of numerous cascading secondary particles

• Pioneers would need to quickly build large underground shelters



So when would be the best time to send humans on an

18-month round trip to Mars and back?

• Solar Maximum might be the best option– Galactic cosmic rays are reduced– Solar-energetic particles are increased significantly,

but we can probably shield astronauts from these.

• Solar Minimum is probably a bit riskier– More galactic cosmic rays– As we saw today, huge flares can occur, even during

solar minimum (see spaceweather.com)


Astronauts will spend ~20% of their time on EVA


Fortuitous timing of Apollo missions


What would happen during a big event such as that which occurred in Aug. 1972 (between Apollo 16 and 17)?

• It takes about 20 minutes for the earliest arriving particles to reach Earth

• It takes about 8 minutes for light to travel to Earth, which would be the earliest warning sign

• It will take at least 5-10 minutes to decide what to do

• This leaves very little time to actually do something

A huge (X28) flare that occurred during the “Halloween” solar storms period


What would happen during a big event such as that which occurred in Aug. 1972 (between Apollo 16 and 17)?

• What would you do?– Hide in a crater wall (assuming

that you are near one)?• Not a good idea

– Get back into the LM or a pre-dug underground shelter?

• Best option – better hurry, though!

– Bury yourself in the lunar soil?• Not possible to get deep

enough, and, in fact, may worsen the issue because of the cascading secondary particles produced

PTYS/ASTR 206Solar Activity and Effect on Earth 3/6/07 Solar Variability and its Effect on Earth and...

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