6/16/08UofA/NSO Summer School Welcome to the Third Joint Arizona/NSO Summer School June 16-20, NSO...

transcript

6/16/08 UofA/NSO Summer School

Welcome to the Third Joint Arizona/NSO Summer SchoolJune 16-20, NSO Sac Peak Observatory, NM

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

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

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

The Physics of the Sun

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)

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!

A Fact About Huge Solar Flares(slightly smaller ones occur, on average, about 3 times per day during solar max)

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

Solar Structure: The Standard Solar

• 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 – mixing-length theory)

• Nuclear reaction rates and opacities are needed

• Boundary conditions are tricky – need 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

• 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

Recent High-resolution Images of

granulation

The photosphere

• About 5700K

– Coolest region of the Sun (coldest in sunspots)

• Sunspots (usually in pairs)

• Variety of convection cells (granulation, supergranulation, etc.)

• Limb Darkening

Sunspots

• Existence known since 350 BC (Greece), 28 BC (China)

• Lower temperature

• Umbra and penumbra

• Associated with Intense magnetic fields– Zeeman effect

The Chromosphere

• Above the photosphere is a layer of less dense but higher temperature gases called the chromosphere

“Color Sphere”

• characterized by spikesof rising gas

• Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules

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!

SOHO/EIT image at 195 Angstroms (FeXII)

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”

The Babcock model andSolar Dynamo

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

In-Situ Particle Observations at 1AU of the 2004 Halloween Flares

Courtesy C. CohenACE/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)

PTYS/ASTR 206 Solar Activity and Effect on Earth4/1/08

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”

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

To Finish

6/16/08UofA/NSO Summer School Welcome to the Third Joint Arizona/NSO Summer School June 16-20, NSO...

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