Solar Astrophysics
Currently I am working with the
Ultraviolet Coronagraph Spectrometer (UVCS) group
connected with the
SOHO (Solar and Heliospheric Observatory) mission.
The overall goal of this project is to obtain an empirical description
of the extended solar corona and wind, which will lead to better
theoretical understanding of how the solar wind is accelerated.
There are many introductory WWW pages out
there that explain what we know about the Sun, and how it affects us
here on Earth.
To begin, I'll link to several of the best of these pages:
The objective of the UVCS investigation is to answer certain fundamental
questions concerning acceleration processes in the corona and their
relationship to solar wind properties near the earth.
These are some of the questions that UVCS is addressing (from the UVCS
Experiment
Handbook):
- What are the dominant
plasma heating and acceleration processes in the solar corona?
- What is the
role of MHD waves?
- What are the dissipation mechanisms?
- How are heavy ions
accelerated?
- How is the composition of the solar wind established and what
produces the abundance variations seen in the solar wind?
- Where is the slow
speed wind generated?
- Are coronal holes the only sources of non-transient
high speed wind?
- Why do some regions emit low speed wind and others high speed
wind?
- What are the roles of thermal pressure gradients, wave-particle
interactions and suprathermal particles in accelerating solar wind from
different types of regions?
- Why are the particle fluxes in high and low
speed winds similar?
- How does the coronal magnetic geometry affect the
outflow of the solar wind?
- What is the role of small-scale structures (polar
plumes, spicules) in generating high speed wind?
- What is the thermal state
of gas expelled during coronal mass ejections and what are the plasma
conditions in the associated shocks?
Since one of the primary topics of my Ph.D. thesis work was radiative
transfer, the first thing I did upon starting to work for the
UVCS group was to spend time understanding the actual diagnostics
(ultraviolet emission lines, white-light polarization, etc.) that are
used to infer things like density, velocity, and temperature in the corona.
I wrote several technical notes that contain bottom-up derivations of
how these diagnostics work (they are linked on my
miscellaneous and unpublished work
page).
I also spend a lot of time doing theoretical modeling
of the non-equilibrium plasma state of the extended corona.
We hope to understand the anisotropic ion temperatures and high outflow
velocities observed by UVCS in terms of detailed models of the
kinetic velocity distributions and wave fluctuation spectra.
More recently (post-2003), this work has taken a turn into the study
of magnetohydrodynamic turbulence . . .
(The left image is from
van Ballegooijen 1986;
the right image is from simulatations performed by the
Bartol group)
Other papers, presentations, and links:
-
See the
Four Steves
(left to right: Spangler, Suess, Cranmer, and Kahler)
that attended the 2000 UVCS Science Meeting.
The lobster was great!
-
2000 NEWS:
A summary of recent findings from UVCS/SOHO is provided as a
``lay-language paper'' from the virtual press-room of the
April 2000 meeting of the American Physical Society.
-
1999 NEWS:
Some of our UVCS/SOHO and UVCS/Spartan
research was reported in a NASA
NASA Space Science Update on 8 July 1999.
-
We were extensively involved with organizing the
SOHO-7
and
Solar Wind 9
meetings, that were successfully held in September and October 1998,
in Maine and on the island of Nantucket.
Proceedings for these meetings have been published.
-
There are several
PREPRINTS
of recent papers
submitted to and in press at various refereed journals, as well
as a more comprehensive
List of Publications
which also includes links to abstracts and proceedings where available.
-
Raid Suleiman and I have developed a set of
Tutorials
on how to use UVCS/SOHO data, and how to use a publically available
Fortran code which produces ``empirical models'' of an idealized
solar corona for comparison with actual data.
Many other online documents and news items are listed on the
UVCS Home Page.
- The
Spartan 201 Solar Physics Mission (see also NASA's overall
Spartan spacecraft
home page)
- The
NSSDC Space Physics Pages, providing links to
virtually every space physics mission with online data
- The
Space Physics Data Facility (SPDF) at Goddard, which hosts the
Sun Solar System Active Archive (S3CAA)
- The
Solar Data Analysis Center Home Page
- The Yohkoh SXT
Solar Web Guide
- The
LASCO/SOHO Handbook for Scientific Investigators
- The home page for the
Mirror Coronagraph for Argentina (MICA)
- The
American Geophysical Union (AGU) Home Page
- A
Space Physics Textbook from Oulu, Finland
- Zombeck's
Handbook of Space Astronomy and Astrophysics
- SAIC's MHD
Coronal Modeling and Prediction Page
- Bob Stein's Research on
Solar Convection, Chromospheres, etc.
-
Solar Oscillations (info and graphics from the BiSON Project)
- The Galileo Home Page (JPL)
- The TRACE
(Transition Region and Coronal Explorer) Home Page
- The Advanced
Composition Explorer (ACE) Home Page
- HAO's
Mauna Loa and
Skylab ATM Data Analysis and Archive Pages
- Online data from the
Wind magnetometer
- Home page for NASA's
Explorers Program
-
Miscellaneous solar and space physics colleagues with
interesting and informative WWW Pages:
Craig DeForest,
Lyndsay Fletcher,
S. Peter Gary,
Joe Hollweg,
Ildar Khabibrakhmanov,
Bob Leamon,
Bill Matthaeus (group),
Dave McKenzie,
M. V. Medvedev,
Valery Nakariakov,
Leon Ofman,
Sean Oughton,
Stefaan Poedts,
Eric Priest,
Bob Rosner,
Chuck Smith,
Steve Spangler,
Steve Suess,
Barbara Thompson,
and many others (to be added soon...)
GO BACK to
Steven Cranmer's
Home Page,
or to the
Harvard-Smithsonian CfA
Home Page.
Overview: The Solar Corona and Solar Wind