Open magnetic field lines, those which extend from the solar photosphere to interplanetary space, are traced in the current‐free (potential field) approximation using measured photospheric fields as a boundary condition. It is found that (1) only a relatively small fraction of the photospheric area connects via open field lines to the interplanetary magnetic field; (2) those photospheric areas which do contribute open field lines lie beneath coronal holes and within the boundaries of the holes as projected onto the photosphere or else between loop systems of an active region; (3) the interplanetary magnetic field in the plane of the sun's equator, essentially the field in the ecliptic plane, may connect to photospheric regions of high latitude; and (4) the fastest solar wind streams are correlated with those magnetic flux tubes which expand least in cross‐sectional area over the distance between the photosphere and the coronal height where the solar wind begins.

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LABORATORY OPERATIONSThe Laboratory OperatIons of The Aerospace CorporatIon lS conductmg expenmental and theoretIcal mvestIgahons necessary for the evaluatIon and apphcatIon of sClentIftc advances to new mlhtary concepts and systems Versahhty and flexlblhty have been developed to a hlgh degree by the laboratory personnelln deahng With the many problems encountered ln the nahon's rapldly developlng space and mlsslle systems Experhse m the latest sClenhflC developments lS vltal to the accomphshment of tasks related to these problems The laboratorles that contrlbute to th,s research are AerophyslCS Laboratory Launch and reentry aerodynamlcs, heat transfer, reentry physlcs, chemlcal kmehcs, structural mechamcs, fhght dynarrllcB, atrrlOsphenc pollutlOn, and hlgh-power gas lasers.Chemlstry and PhYS1CS Laboratory Atmosphenc reactions and atmospherIc optics, chemical reactions In polluted atmospheres, chenucal reactIons of excIted speCIes In rocket plumes, chemIcal thermodynamIcs, plasma and laser-mduced reactions, laser chemlstry, propulslOn chemlstry, space vacuum and radlahon effects on materials, lubricabon and surface phenomena, photosensltIve materlals and sensors, hlgh preC1Slon laser rangmg, and the apphcahon of phYS1CS and chemlstry to problems of law enforcement and b,omed,c,ne ElectroniCS Research Laboratory Electromagnetic theory, devlces, andpropagatIon phenomena, mcludmg plasma electromagnetIcs, quantum electronlcs, lasers, and electro-optics, conununlcahon SCIences, apphed electronics, semIconductIng, superconductIng, and crystal devlce physlcs, optIcal and acoustical lmagmg, atmospherlc pollutIon, mllhmeter wave and far-mfrared technology Matenals SClences Laboratory Development of new materlals, metal matrIX composItes and new forms of carbon, test and evaluation of graphIte and ceramlCS ln reentry, spacecraft matenals and electromc components ln nuclear weapons enVlronment, apphcatton of fracture mechaniCS to stress carrOSlOn and fatIgue-lnduced fractures ln structural metals Space SClences Laboratory Atmosphenc and lonosphenc phYS1CS, rad,atIon from the atmosphere, denslty and compoBlhon of the atmosphere, aurorae and alrglow, magnetospherIC phYSICS, cosmIc rays, generatIon and propagatIon of plasma waves m the magnetosphere, solar phYSiCS, studies of solar magnetic f,elds, space astronomy, x-ray astronomy, the effects of nuclear exploslOns, magnetlc storms, and solar actIvlty on the earth's atmosphere, lOnosphere, and magnetosphere, the effects of optIcal, electromagnetIc, and partIculate radlatIons ln space on space systems ACKNOWLEDGMENTSWe would like to thank Dr. R. Munro for assistance in the interpretation of I~O Skylab coronagraph data.

Models of open magnetic structures on the Sun are presented for periods near solar minimum (CR 1626-1634) and near solar maximum (CR 1668-1678). Together with previous models of open magnetic structures during the declining phase (CR 1601-1611) these calculations provide clues to the relations between open structures,'coronal holes, and active regions at different times of the solar cycle. Near solar minimum the close relation between active regions and open structures does not exist. It is suggested that near solar minimum the systematic emergence of new flux with the proper polarity imbalance to maintain open magnetic structures may occur primarily at very small spatial scales. Near solar maximum the role of active regions in maintaining open structures and coronal holes is strong, with large active regions emerging in the proper location and orientation to maintain open structures longer than typical active region lifetimes.Although the use of He ~ 10830 & spectroheliograms as a coronal hole indicator is shown to be subject to significant ambiguity, the agreement between calculated open structures and coronal holes determined from He I 10830 ,~ spectroheliograms is very good. The rotation properties of calculated open structures near solar maximum strongly suggest two classes of features: one that rotates differentially similar to sunspots and active regions and a separate class that rotates more rigidly, as was the case for single large coronal holes during Skylab.