PROGRAM TITLE:	Solar Studies/Global Change
ACTIVITY STREAM:	Observation
SCIENCE ELEMENT:	Solar Influences

 SMITHSONIAN INSTITUTION
SMITHSONIAN ASTROPHYSICAL OBSERVATORY (SAO)

SCIENTIFIC MERIT:  The influence of the sun and its inputs to the terrestrial 
atmosphere both in particle deposition and  solar radiation are critical 
elements in the overall understanding of global change.  The near constancy 
of  solar output in the visible region of the spectrum provides the earth with 
the steady source of radiative  input required to create the stable weather 
conditions which have permitted terrestrial life to flourish.  There is 
suggestive evidence of a direct link between long-term changes in solar 
irradience and global warming/cooling.  The solar shortwave radiative 
output  (far ultraviolet, extreme ultraviolet (EUV), x-ray, gamma ray 
radiations) and solar particle output (solar  wind, high-energy accelerated 
particles from flares) is highly variable and depends on solar activity.  The 
EUV, for instance, drives the chemical reactions, controls the energy balance, 
and powers the dynamical processes in the upper atmosphere, and through 
physical, chemical, and electromagnetic couplings, influences the chemistry 
and dynamics of other atmospheric regions.  However, direct measurements 
of the solar EUV flux have been very limited.

There is a need for more empirical and theoretical work on the behavior of 
the solar activity cycle and the  relationship between solar activity and 
changes in solar irradience in order to establish or refute connections between 
solar activity/irradience and global change.  In addition, as part of an overall 
program of solar irradience monitoring, an instrument must be developed to 
carry out in-orbit, regular, accurately calibrated measurements of the solar 
EUV flux over a long time period.

In order to understand the causes of solar variability and improve our 
capabilities in making solar predictions, we need to investigate the basic 
physical  processes responsible for solar activity.  Solar theorists are needed 
who can explore the detailed interactions between solar magnetic fields and 
plasmas.  In order to study the relationship between the solar activity cycle 
and luminosity (irradience) variations,  measurements of stellar activity 
cycles for solar-like  stars will be carried out.  We propose to continue and  to 
strengthen our program in observing stellar activity  cycles using existing 
equipment and our new robotic  Automatic Photoelectric Telescopes.  Because 
the radiometric sensitivity of an EUV spectrometer changes  during its use, it 
is necessary to develop an instrument which can make accurate long-term, 
calibrated, spectrally-resolved irradience measurements.  Two methods of 
achieving radiometric accuracy in the EUV are being studied:  (1) use of 
absolute detectors, and (2) use of "standard" sources.

STAKEHOLDERS:  Nearly all the solar research at SAO addresses the basic 
physics behind the variations in the solar output  of radiation and particles.  
SAO scientists are studying chromospheric and coronal heating, the heating  
and accelerations of the solar wind, solar activity, the structure of the solar 
atmosphere, and the role of the solar magnetic field in these phenomena.  
SAO has two instruments under development for empirically studying the 
origins of the solar wind, and for probing  the solar interior by seismology 
techniques.  Funded by  NASA and AFOSR, laboratory activities are 
underway to develop an absolute extreme-ultraviolet solar spectral irradience 
monitor which can be recalibrated reliably in-orbit.

POLICY RELEVANCE:  A knowledge of the spectral distribution of solar 
radiation reaching the earth's surface depends on the irradience emitted by 
the sun -- as outlined in the  STIB Core Project of the IGBP.  The scientific 
objectives of the above research program also respond to a number of key 
milestones in section 2(c) -- Global  Water, Energy Cycles, and Sea Level 
Change (Atmospheric  Radiation, Clouds and Precipitation) of the USGRCP 
Implementation Plan, including Solar forecasting improved, Solar-climate 
hypotheses tested, Solar  influences quantified, and Solar particle interaction 
with global atmosphere defined.  The need for improved  solar EUV flux 
measurements has also been called for in a number of reports that urge a 
national effort to provide accurate solar EUV flux data on a regular basis.  
Representative examples of such reports are:  (1) The National Research 
Council Report "Long-Term Solar-Terrestrial Observations" (1988); (2) The 
"Report of the [NASA] Working Group on Predictions of Solar  Activity and 
the Atmospheric Response" (1989); (3) The  RISE (Radiative Inputs of the Sun 
to Earth) Report, a  "Research Plan for the 1990's on Solar Irradience 
Variation", prepared for the Division of Atmospheric Sciences of the 
National Science Foundation (1990).

PROGRAM CONTACTS:

SI SGCR Representative:	Ted A. Maxwell
		NASM MRC 315
		Smithsonian Institution
		Washington, D.C.  20560
		202 357 1424
		FAX:  202 786 2566
		Email: tmaxwell@ceps.nasm.edu
	
Bureau Representative:	Kate Kirby
		Smithsonian Astrophysical Observatory
		60 Garden St.  MS-14
		Cambridge, MA  02138
		617 495 7237 or 9524
		FAX: 617 495 5970