data sets.

The second,isthatreliable inferencesaboutthe structureand rotation of the solar interiorfrominversionsof the

p-mode datarequiresfrequency accuracy of a few tensof nano-Hz.

Because ofthe fundamentalrelation between frequency

accuracy and measurement duration,years of observation are required. The region of the Solar interior that most needs a long

duration istheenergygenerating core.Thepresentlimitsof accuracy providetantalizinghintsof mixing.Other primary

objectivesneed continuous sequences of days to months.These include the goalsthat can be addressed by the new science of

LocalHelioseismology, which allows imaging of the motions in the interior of the star.

The key scientific issues of the interior and surfaceThe data from the helioseismolgy instruments address global properties of

the solarinterior,variationsofsolar luminosity, interior and surface flows,andmagneticfieldevolution.Theseareasare

obviously tightly coupled and a breakdown into categories is due largely to the experimental techniques used to study the topics.

In the following subsections, we givethe key goals of each major category, a brief overview of the rational for that task, and an

indication of key progressin the firstyear of observations.

Global Properties of the Solar Interior

Radial Stratification of the Solar Interior-Determine the spherically symmetric components of the mean radial structure of the

Sun in pressure, density, composition, and sound speed.The structure of the solar interior is nearly spherically symmetric, so it

is convenient to separate the radial stratification from any non-spherical effects.p-andg-mode seismology determine the spheri-

calaveragesofpressure,density, temperature,andchemicalcomposition asafunction ofdepth.Sincethedeterminations

dependon thephysicsofthe solar material-theequation of stateandthe opacity, interiormixing,and diffusion-accurate

agreementof observation and theory requiresaccurate understanding of the interiorproperties.Fortunately, thereisa rough

spatialseparation of effectsin the Sun.In the bulk of the convection zone opacityplaysa small role because the temperature

gradientis essentially adiabatic. Beneath, the convection zone the principal contributors to the equation of state (H and He) are

nearly fully ionized, causing the opacity partof the heavier elements to be the principal physical issue.

The firstlong seriesof medium-l p-mode data hasnow been analyzed.The spectralnoise ismuch lower than corresponding

groundbased data., which givesconfidencethatthe noise is of solar origin.The inversionsof thisdata shows a region of high

sound speed notpredicted by currentmodelsatthe base of the convection zone (see Figure 3).The observation isconsistent

with additional turbulence atthe bottom of the convection zone.

Core StructureIn order to be able to deter-

mine the mean physical parameters in the vi-

cinity of the solar coreitisnecessary to de-

tect and classify several low degreeg-modes.

Knowledgeofthebasicphysicalproperties

ofthecorewillestablishwhetherthesolar

neutrino problemisdue to propertiesofthe

solar core or requiresabetter understanding

of the particle physics.The corestructure is

dependentupon thedegreeofinternalmix-

ing duringthe solar evolution, which is of cru-

cialimportanceforunderstanding of stellar

evolution.

Because of the discovery nature of theg-mode

search,the probability of successisdifficult

to estimate.A theoreticalestimate of ampli-

tude given by Kumar,Quataertand Bahcall

(ApJ Letters, 458, L83-L85, 1996) is 0.03 cm/

sforthelowestordermodes.Atthistime

GOLFcan detectmodeswith anamplitude

of 0.4 cm/s. GOLF has a chance of approach-

and in a standard solar model (using the most recent information on nuclear

reaction rates,radiative opacity, and equation of state), inferred from two months

of MDI medium-l (l < 300) data. The horizontal bars show the spatial resolution,

and theverticalbarsareerrorestimates. Thepeakjustbelow 0.7r/R is

significant, but thedipnear thecoremaybedueto oneof several possible

systemmatic errors.

ingtheestimateofKumaretal.

Itisalso

possible that the amplitude estimate based on

thep-modes may not take into account all the

properties of turbulence that could put energy

Proposal forSOHO SolarMaximum Science Program-

7