Transcript Intro-Giacalone

Welcome to the Third Joint Arizona/NSO Summer School
June 16-20, NSO Sac Peak Observatory, NM
6/16/08
UofA/NSO Summer School
List of Topics and Lecturers
• Solar Magnetic Fields: Observations
– Matt Penn, NSO, Tucson
• Solar Interior and Dynamo
– Tami Rogers, UofA, Tucson
• Helioseismology
– Irene Gonzalez-Hernandez, NSO, Tucson
• Solar Magnetohydrodynamics
– Gene Parker, Univ. of Chicago
• Solar Composition and “Dermatology”
– Aimee Norton, NSO, Tucson
6/16/08
UofA/NSO Summer School
List of Topics and Lecturers
• Solar Flares
– Sam Krucker, SSL, UC Berkeley
• Solar-Energetic Particles
– Randy Jokipii, UofA, Tucson
• Radiative Transfer
– Han Uitenbroek, NSO, Sac Peak
• Coronal Mass Ejections
– Spiro Antiochos, NASA/Goddard
• Solar Wind
– Chuck Smith, Univ., of New Hampshire
6/16/08
UofA/NSO Summer School
List of Activities
• Solar viewing through Hα telescope
– Outside of visitor center
• Student Presentations
• Monday – reception at the community center
• Tuesday – White Sands picnic
• Wednesday – Community BBQ
• Thursday – Pizza Night / evening lecture
• Tours of NSO/Apache Pt. Facilities
6/16/08
UofA/NSO Summer School
The Physics of the Sun
6/16/08
UofA/NSO Summer School
The largest flare
seen since the
National Oceanic
and Atmospheric
Administration
(NOAA) began
recording them in
1976
An x-ray image of the Sun (SoHO)
A Fact About Huge Solar Flares
(slightly smaller ones occur, on average,
about 3 times per day during solar max)
Artists depiction of a large
asteroid striking the Earth
(which occur, on average, about 1
every 100 million years)
Flare Energy ~ 5x1032 ergs
Asteroid Energy ~ 5x1030 ergs
100 times less than a flare!
Why Study the Sun ?
• Influence on Earth
• Important for
Astronomy/Planetary Sciences
– Only star that we can see closely
• The source of many interesting
and important physics problems
– Many interesting research projects
• For me?
– Many basic properties are a mystery
– Understanding the space radiation
environment, space weather,
acceleration of high-energy charged
particles
Inti, The Inca Sun God
6/16/08
UofA/NSO Summer School
Solar Structure:
The Standard Solar
Model
• Theoretical model used to determine
the physical properties of the Sun’s
interior
• Hydrostatic and thermal equilibrium
– A big ball of gas held together by
gravity + radiative diffusion
• Can add convection, but this is
difficult (simple approach – mixinglength theory)
• Nuclear reaction rates and opacities
are needed
• 6/16/08
Boundary conditions are tricky
– need
UofA/NSO Summer School
to use an iterative approach
Solar Oscillations
• Waves can propagate through
the Sun causing a variety of
vibrations
– Like sound waves
• These are used to infer
pressures, densities, chemical
compositions, and rotation
rates within the Sun
– Constraints on solar
models
• Helioseismology
6/16/08
UofA/NSO Summer School
• The tachocline is the interface between the rigidly-rotating radiative zone
and the differentially rotating convective zone
• The tachocline is suprisingly thin: only about 5% of the solar radius.
• Possibly the source of magnetic flux tubes which permeate the surface (i.e.
sunspots).
• Turbulent convective motions
cause overturning (bubbling)
motions inside the Sun.
– These are responsible for
the granulation pattern
seen on the Sun’s surface.
– Rayleigh-Bénard
convection
6/16/08
UofA/NSO Summer School
Recent Highresolution
Images of
granulation
6/16/08
UofA/NSO Summer School
The photosphere
• About 5700K
– Coolest region of
the Sun (coldest in
sunspots)
• Sunspots (usually in
pairs)
• Variety of convection
cells (granulation,
supergranulation, etc.)
6/16/08
UofA/NSO Summer School
• Limb Darkening
Sunspots
• Existence known
since 350 BC
(Greece), 28 BC
(China)
• Lower temperature
• Umbra and
penumbra
• Associated with
Intense magnetic
fields
– Zeeman effect
6/16/08
UofA/NSO Summer School
6/16/08
UofA/NSO Summer School
6/16/08
UofA/NSO Summer School
6/16/08
UofA/NSO Summer School
The Chromosphere
• Above the photosphere is a
layer of less dense but higher
temperature gases called the
chromosphere
“Color Sphere”
• characterized by spikes
of rising gas
• Spicules extend upward from
the photosphere into the
chromosphere along the
boundaries of supergranules
6/16/08
UofA/NSO Summer School
6/16/08
UofA/NSO Summer School
The Corona
• The outermost layer of the solar
atmosphere, the corona, is made of
very high-temperature gases at
extremely low density
• The solar corona blends into the solar
wind at great distances from the Sun
• Because the corona is very hot, it is
best viewed in the x-ray part of the
spectrum
• What heats the corona remains an
open question!
6/16/08
UofA/NSO Summer School
SOHO/EIT image at 195 Angstroms (FeXII)
6/16/08
UofA/NSO Summer School
SOHO/EIT movie of the “Halloween” Solar
Storms of 2003
SOLAR CORONA – SEEN DURING A TOTAL ECLIPSE
Magnetism is the Key to
Understanding the Sun !
The 11-year Sunspot Cycle
Number of Sunspots versus time – they come and go every 11 years
Number of Sunspots versus latitude – forms a “butterfly pattern”
6/16/08
UofA/NSO Summer School
The Babcock model and
Solar Dynamo
6/16/08
UofA/NSO Summer School
SOHO/LASCO (C3) movie of the “Halloween”
Solar Storms of 2003
Propagating Shocks
• Analogy with sonic booms
• Efficient particle
accelerators
• Radiation Environment
and Space Weather
6/16/08
UofA/NSO Summer School
In-Situ Particle Observations at 1AU of the
2004 Halloween Flares
Courtesy C. Cohen
ACE/SIS data
The solar wind carves out a cavern in the
local interstellar medium – the heliosphere
How does the Sun Influence Earth?
•
Provides the energy that creates life, warms
the planet, drives the dynamic atmosphere
and oceans
•
Sun-climate connection?
– What is the Sun’s role in global warming?
– 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
PTYS/ASTR 206
Solar Activity and Effect on Earth
4/1/08
The Sun is slightly dimmer during sunspot minimum as seen by
recent, highly sensitive (but not inter-calibrated!) measurements
Solar Energy arriving at Earth’s orbit
“The Solar Constant”
↑
Sunspot Minimum
↑
Sunspot Minimum
6/16/08
UofA/NSO Summer School
What are the consequences of a
geomagnetic storm?
•
disrupted communication
– Radio signals, telegraph wires, cell phones (?)
•
Overloaded power grids (induced ground currents)
•
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
Aurora in Tucson
6/16/08
UofA/NSO Summer School
To Finish
6/16/08
UofA/NSO Summer School