to the delivery of science data productsto the PI teams. While a higher level of risk is assumed in such a scenario, we

conclude thatthe assumption of such risk is appropriate for a re-use mission. This effort isalready under way, and should be

complete before the end of FY98.

VII) Summary of Scientific Impact

Some of the most distinctive discoveries of SOHO are:

I)

Helioseismology

*The firstever image of the convection zone of a star showsthatconvective cellsin the Sun are shaped like pancakes,

not spheres as assumed in mixing-length theory

*Differential rotation continues in depth to the bottom of the convection zone.

*Below the convection zone the Sun rotates as a solid sphere.

*There is a narrow shear zone at the bottom of the convection zone where the interior is very turbulent -- this is the most

likely region for the generation of the solar dynamo.

II)Solar Atmosphere and Corona

*The spectral lines of heavy elements in the corona have wider profiles than those of Hygrogen lines. This could be due

to extremely broad velocity distributions along the line of sight; the most likely explanation for the higher velocities in

heavier ionsis the deposition of MHD wave energy in the coronaviathe ion cyclotron resonance process.

*Coronal mass ejection (CME) observations have a new dimension.We are often able to see the initiation in the lower

atmospherewith EIT and follow itsevolution outto 30 Rwiyh LASCO. We arealso seeing forthe firsttime how
globally such eventsaffectthe corona.With CELIAS, and^sun
the aid of other SECmissions, mostparticularly the other

ISTP missions, we can follow earthward-directed disturbances all the way to the magnetosphere.

*For the firsttime,we can tracetheslow speed solarwind nearthe equatorialcurrentsheet,and havebeenableto

measureboth speed and acceleration.

III)

Solar Wind

*The detection of elements and isotopes never seen before in the solar wind.The solar wind isotopic abundances should

be close to the primordial composition of the solar nebula, before the planets were formed, and are important for many

cosmochemical and astrophysical applications, including the study of the history of the solar system.

*Better timeresolution in solar wind composition than hasbeenpossible beforeindicatesapatchy structure ofthe

corona with length scales of some 10⁴km and reveals the survival of these structuresfroma few solar radii to 1 AU.

Thereisa wealth to be learned fromcontinuing our study of the Sun asitevolvesfromsolar minimumto solar maximum.

SOHO along with the rest of the Sun-Earth Connections missions will greatly enhance our understanding of the space environ-

ment.A SOHO Solar Maximum Science program will allow us to:

I)

Helioseismology

• Determine whether wecan probe the deepestinterior of the Sun withg-modesand low-lp-modes
• Observehow the interior and convective transportevolvewith the solar cycleand study the interaction between the
  
  magnetic cycle and the shear zone
• Understand whereand how the dynamo really works

II)Solar Atmosphere and Corona

• Determine how the known changes in the basic structure of coronalstreamers between solar minimum and maximum
  
  effects the acceleration of the solar wind?We will be able to observe this directly
• Discover whether there are more fundamental physical parameters underlying the known CME latitude and frequency
  
  distribution changesoverthe cycle
• Use SOHO's ability to observe magnetic fields and the upper atmosphere simultaneously, with no atmospheric distor-
  
  tion, to allow us better to understand the relationship between the emergence, submergence, and merging of magnetic
  
  fieldsand solar activity
• Determine whether we can detect high-frequency MHD wave deposition of energy in the corona

III)

Solar Wind,Solar Energetic,and Heliospheric Particles