Solar Variability and its Effect on Earth and its Inhabitants

AnnouncementsReading AssignmentChapters 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 cycleCurrently, we are near the minimum in the solar cycleHowever, 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 FlaresAbrupt 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 coronaThese storms can interact with the Earth and create huge geomagnetic stormsThey 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 1976Artists depiction of the asteroid that hit the Earth 65 million years ago creating Chicxulub craterx-ray image of the Sun (SoHO)Flare Energy ~ 5x1025 JoulesAsteroid 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 stormsAuroraPower-grid failures (Canada, 1989); Telecommunications failuresConfused homing pigeons?

High-energy solar particlescan destroy ozonelarge 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 variableThe Maunder Minimum was a period from 1645-1715 in which very few sunspots were recordedAbout 50 during this period compared to ~50,000 over a similar time interval in the 1900sDuring the Maunder minimum, there was a period of extremely cold winters in northern EuropeThe 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!) measurementsSunspot MinimumSunspot MinimumSolar Energy arriving at Earths orbit The Solar Constant

The Suns role in Global WarmingThe 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 Earths mean temperature

However, the largest contributor to global warming is the increase in anthropogenic (man-made) green house gasesThis is the scientific consensus and is not debated in the scientific community

Geomagnetic Storms and their consequencesdisrupted communicationRadio 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 spacecraftConfused 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#GeomagneticStormsA geomagnetic storm is global disturbance in Earths magnetic field caused by the interaction of Earth with the material associated with solar explosions

The Space Radiation and Particle EnvironmentSolar 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 cancerThe 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

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 orbitMewaldt 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)

DOSE (GY)Based on Wilson (1997), Townsend (2003), Kim et al. (2005), and Turner (2006)Shielding from Huge Solar Particle EventsThis as an enormous solar superstorm that occurred in 1859

It is essentially impossible to shield from Galactic Cosmic Rays not cost effectiveCannot launch such extreme payloadsWould require several return trips to space where the spacecraft would have to be assembledE.N. Parker, Scientific American, March 2006

On the Surface of MarsThe Martian atmosphere is very thin and probably does not provide adequate protection from cosmic raysIt may, in fact, be worse because of numerous cascading secondary particles

Pioneers would need to quickly build large underground sheltersE.N. Parker, Scientific American, March 2006

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 optionGalactic cosmic rays are reducedSolar-energetic particles are increased significantly, but we can probably shield astronauts from these.

Solar Minimum is probably a bit riskierMore galactic cosmic raysAs 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