GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 14, PAGES 1841-1844, JULY 15, 1995 Coronal streamers and fine scale structures of the low latitude corona as detected with Spartan 201-01 white light coronagraph Madhulika Guhathakurta I and Richard R. Fisher NASA Goddard Space Flight Center, Code 682, Greenbelt, MD 20771 Abstract. The solar corona was observedwith an externally oc- culted White Light Coronagraph carried on the SPAR- TAN 201-01 spacecraft for a 47 hour period beginning on April 11, 1993. At this phase of the descending solar magnetic activity cycle there were well developed coro- nal helmet streamers located over both the east and west limbs of the sun. Of additional interest in the SPARTAN data are the finer scale streamer structures observed in the low latitude coronawhich are partially resolvedby the SP201-01 instrument. The purpose of this investigation was to determine the physical and morphological characteristics of the streamers and the fine scale ray structures observed in the region between streamers. A comparison of theselow latitude rays with the polar rays observedin the north and south polar holes during the same flight suggest that they havesim- ilar morphology and physicalcharacteristics. Introduction The SPARTAN 201-01 Mission had as its scientific goalthe investigation of the physical conditions of the solar coronaand the coronal-heliospheric interface. The large-scale features of this part of the sun's atmosphere include both helmet streamer structures and coronal holes. Coronal holes with low density and open mag- netic field regionare associated with the generation of highspeed streams of material found in the solar wind. low speed solar wind on the other hand is speculated to come from high density regions as those observed in the quiet sun regionwhich surround the active regions and the helmet streamer type structures. In this investigation we presentfine scalestructure analysis of the streamers on the east limb and the re- gion between these streamers, utilizing the space-based SPARTAN 201-01 whitelight coronagraph (WLC) and theground based Mk-III K-coronameter polarized bright- ness (pB)observations, and present their morphological and physical characteristics. Fromhereon we referto thisregion asstreamer/inter-streamer region. With pB 1Also at PhysicsDepartment, The Catholic University of America, D.C. known, it is possible to obtain model dependent distri- butions of the coronal electron density and the gradi- ent of electron density, also known as the density scale- height parameter [Fisher and Guhathakurta, 199d]. White Light Coronagraph The WLC is an externally occulted coronagraph, third in the series of the HAO orbital instruments, which incorporatesa polarimeter is sensitive to the state of linear polarization. This instrument has three fea- tures which differfrom the two previous (SkyLab ATM and Solar Maximum Mission)devices. The detector usedis an RCA charge coupled device (CCD) which has anoperational bandpass of 500 ]k FWHM centered on4800 ]k.Thefirst external occulting disk is notcir- cular but is serrated in an effort to control diffraction effectsat this point in the instrument. Finally, the po- larimeter is constructed such that the rotating analyzer is locatedat an imageof the objective rather than adja- cent to the final imageplane. The result is a decrease in optical noise dueto retarder (analyzer) inhomogeneity. The SP201 WLC usesa flight spare doublet objective lense3.5 cm in clear aperture which was fabricated for the SMM Coronagraph/Polarimeter instrument. The WLC instrument is approximately 3 m in length and fits into half of the 42 cm diameter instrument carrier module provided by the SPARTAN 201 spacecraft. The WLC has an optical configuration which off sets the occulting disk in the field of view and allowsabout 180 degrees of position angle to be viewedout to an al- titude of 3 Re above the limb (Figure1). The extreme fieldof view extends to 6 R© opposite the occulting disk stem,and the occulting diskdiameter is 1.25 R©. This is different from the previous ATM and SMM instru- ments which had occulting diskswhich were somewhat larger and restricted the inner limit of the field of view to approximately 2/i•©. The CCD format was256 x 320 pixels each of which subtended 22.5 arc seconds in the final image plane(Figure1). Details of Mauna Loa K coronameter data are provided in Fisher et al., [1981]. Observations Copyright 1995 by the American Geophysical Union. Papernumber 95GL01603 0094-8534/95/95GL-01603503.00 Four images were selected, each, from Mk-III, and WLC aboard SPARTAN 201, on 11th of April, 1993, to reduce systematic errors in the photometric reduction of data. A typical display of these images is presented 1841