Revised 26 October 1995 -- minor change in shape classification CATALOGUE OF CORONAL HOLES 1970-1991 by A. Sanchez-Ibarra Centro de Investigacion en Fisica, Universidad de Sonora Hermosillo, Sonora, Mexico and M. Barraza-Paredes Centro de Investigacion en Astronomia Solar, CIAS Hermosillo, Sonora, Mexico 1. INTRODUCTION Coronal Holes were first noted as "M" regions that produced periodic geomagnetic disturbances. These were first observed in 1970 by instruments on the Orbiting Solar Observatory (OSO) satellites, and also were noted with optical observations during the total solar eclipse of March 7, 1970. The Apollo Telescope Mount (ATM) on the Skylab manned mission observed in short wavelengths the real nature of Coronal Holes as regions of lower density and temperature than the rest of the solar corona. Three observational periods from Skylab produced substantial data on the development of Coronal Holes as well as their relationship with other types of solar activity. After Skylab, although Coronal Holes were later deduced from radio observations, the main data were obtained by observing the He I 10830A line at the Vacuum Solar Telescope at Kitt Peak National Observatory. These data, continuous from 1977 to date, were pub- lished in Solar-Geophysical Data (SGD) as Helium synoptic charts by Carrington Rotation or as Coronal Hole contours plotted on H-alpha synoptic charts. The Skylab observations of Coronal Holes were the subject of exhaustive examination. However, the main data source on Coronal Holes currently are the synoptic maps published in SGD. This catalogue was motivated by the lack of a global reference guide. It Intends to help many statistical researchers by making it easier to work with more organized information spanning a little more than one and a half solar cycles. Although this catalogue is based only on summary data for each Carrington Rotation, it presents interesting values and enough data to analyze several aspects of the evolution of Coronal Holes. 2. DATA SOURCES All the data used for this catalogue were taken from synoptic charts based on Carrington rotations. To determine the polarity of every Coronal Hole, and to identify it over several Carrington rotations, the contours of Coronal Holes were copied to H-alpha synoptic charts, although measurements were made on the original source. Magnetograms from Kitt Peak National Observatory were also used for this purpose. * For Carrington Rotation 1558, Coronal Holes were plotted on H- alpha synoptic charts based on spectroheliographic observations made from OSO-6, and also from observations made during the total solar eclipse of March 7, 1970 (Webb et al., 1984) * Data of Coronal Holes observed in Carrington Rotation 1568 are also based on observations from OSO-7 (Maran et al., 1973). * Coronal Hole data for Carrington Rotation 1601 to 1610 were obtained from contours plotted in H-Alpha synoptic charts, based on X-ray observations from Skylab (Hanson et al., 1980; Bohlin et al., 1978). * Data for Carrington Rotation 1623-27 and 1633-35, were provided by J. Harvey as synoptic maps taken from He I images. * Coronal Hole data for Carrington Rotation 1628-32, 1636-39, 1645- 47, and 1649, were taken from He I synoptic maps which appeared in SGD. * Data for Carrington Rotation 1650-1715 were published in SGD as synoptic maps. * From Carrington Rotation 1716 to 1828, Coronal Holes data were taken from contours plotted on H-alpha synoptic charts published in SGD (no data for Carrington Rotation 1807). * Synoptic maps for Carrington Rotation 1830-1849 were provided by J. Harvey of NSO (with no data for Carrington Rotation 1829, 1834, 1841, and 1845). All that data were contrasted with the Atlas of Stackplots Report UAG-101 (McIntosh, 1991), including data for several Carrington Rotation missed in the sources mentioned above. In summary, data of Coronal Holes were obtained for 234 Carrington rotations spanning 21 years of observations. Data for nine Carrington rotations were lost because of the time when ground- based observations started. See Table 1 on page 9. Table 2 on pages 10-13 lists the dates of commencement of Carrington rotations 1557- 1878 covering the years 1970-1991. 3. TYPES, IDENTIFICATION AND CLASSIFICATION CRITERIA 3.1 Types Data spanning 21 years made it possible for us to recognize some of the Coronal Holes behavior, and allowed us to classify and identify them. Coronal Holes are almost permanently visible on solar poles, except at the time of the maximum of solar cycle, when po- larity inversion occurs. It is very common that coronal holes on solar poles expand to lower solar latitudes, following a sector of equal polarity. Moreover, isolated coronal holes appear at several latitudes at any time, connecting or disconnecting with holes prolongated from the pole. We classified coronal holes by two types: those which are an extension from the Coronal Holes at the poles (Polar Coronal Holes), and those which are isolated at any latitudes (Equatorial Coronal Holes). Polar Coronal Holes were identified as such when they were extended below +60 degrees of heliographic latitude. Exceptions were made when the global polar coronal hole passed below +60 degrees of latitude but did not produce a well-developed extension of the hole. Equatorial Coronal Holes were recognized as such when they were not connected with any Polar Coronal Holes and were present at any latitude. Even during the polarity inversion at the maximum of the cycle, Equatorial Coronal Holes were visible at very high latitudes. Connections and disconnections between both kinds of Coronal Holes are noted in the catalogue. Based on this selection, the catalogue was divided in two parts, one for Polar Coronal Holes and another for Equatorial Coronal Holes. 3.2 Identification Both kinds of Coronal Holes were identified by a consecutive number following the chronological order of apparition, and from higher to lower value of Carrington Longitude (from 360 to 00 degrees), independent of their heliographic latitude. When two Coronal Holes coincided in the Carrington longitude, we first classified the Coronal Hole visible in the Northern Hemisphere, and then the one in the Southern Hemisphere. The identification given to the Coronal Holes observed by Skylab (Bohlin and Sheeley, 1978) are noted in the remarks. The identification of the hole when it persisted for two or more Carrington Rotations was more complex. The main criteria to recognize the same Coronal Hole as such was the displacement of photospheric sectors of the main polarity. This also let us identify Coronal Holes when they had a strong drift both in heliographic latitude or longitude. So, the evolution of photospheric polarity sectors was also analyzed on each Carrington rotation. However, sometimes the identification was not very easy. Doubts about this parameter are noted in the remarks. Sometimes, two or more Coronal Holes of both or different types could have some relation to each other during the rotation (their positions may relate), although this is not necessarily a connection or disconnection. In these cases, a possible relation is noted for both holes involved. On the other hand, a hole was considered connecting or disconnecting with another one depending on the persistence of itself. Usually in these phenomena implying a Polar Coronal Hole and an Equatorial Coronal Hole, we denote for the Polar Coronal Hole only its relation with the Equatorial Coronal Hole, and the Equatorial Coronal Hole is noted as the hole that connects or disconnects to the Polar Coronal Hole. For each type of Coronal Hole, the catalogue is divided into a general list and a particular list. The general list presents all the Coronal Holes (see List 1 and List 2). Coordinates and extension values are average values for those Coronal Holes that were visible for more than one Carrington Rotation The particular list presents only the Coronal Holes visible for more than one Carrington Rotation with their specific values of coordinates and extension for each Carrington Rotation (see List 3 and List 4). 3.3 Shape Classification To make the identification of each Coronal Hole in the synoptic charts easier, and also to explore a possible evolution of it, a shape classification is introduced in the catalogue (see Figure 1). * Polar Coronal Hole shapes are divided into conic (C), booted (B), ramified (R), sharp pointed (P), irregular (I), elongated (E), dumbbell (D), and square (S). * Equatorial Coronal Hole shapes are divided into almost circular (C), elongated (E), ramified (R), irregular (I), and elliptical (D). A Classification for each Coronal Hole was made for every Carrington Rotation. 4 CHARACTERIZATION 4.1 Identification -- Coronal Hole Number For both parts of the catalogue (polar and equatorial), every Coronal Hole received a consecutive number in chronological order from higher to lower Carrington longitude for each Carrington rotation. 4.2 Time observed -- Carrington Rotation Carrington rotation(s) where the Coronal Hole was visible. 4.3 First observation -- Year Year of the first Carrington rotation when the Coronal Hole was observed. Fig. 1. We show the five Shape Classifications of the Equatorial Coronal Holes and the eight Shape Classifications of the Polar Coronal Holes. 4.4 Heliographic latitude -- Heliographic Latitude Heliographic latitude of the hole measured at the middle point between its northern and southern limits. 4.5 Carrington longitude -- Carrington Longitude Carrington longitudes of the hole measured at the middle point between its eastern and western limits. 4.6 Extension in heliographic latitude -- Extent in Latitude Extension measured in degrees on the northern and southern limits of the hole. 4.7 Extension in Carrington Longitude -- Extent in Longitude Extension measured in degrees on the eastern and western limits of the hole. 4.8 Polarity -- Polarity Magnetic polarity of the hole, based on the dominant polarity of the polar hole (if it is a Polar Coronal Hole) or in the polarity of the sector (if it is an Equatorial Coronal Hole). 4.9 Shape -- Shape Shape classification of the hole. See page 4 or Figure 1 on page 5. 4.10 Remarks -- Remarks The remarks are spelled out here. However, these data are available in digital form from WDC-A for STP or from the author. Remarks are compressed with the following definitions: 1(...) Related to...(hole identification). 2(...) Connected to...(hole identification). 3(...) Disconnected from...(hole identification). 4(...) Reapparition of...(hole identification). 5 Uncertainty in position. 6 The hole drifted to the next Carrington rotation, based on its longitude and latitude. 7 The hole drifted to one Carrington rotation before. It is labeled based on its longitude. 8 Uncertainty in drawing, mostly when photographic synoptic charts were used for identification. 9 Deduced -- When the Coronal Hole was identified based on the drift of the photospheric sector deduced by the evolution of the magnetic sector. 10(...) Strong development (hole identification). 11 Only Carrington Longitude drifted to next Carrington rotation. 12 No data. 5. COMPUTED PARAMETERS Measurements of Coronal Holes were made on the position and the extension over boundaries marked in the synoptic charts. Both heliographic latitude and Carrington longitude of each hole were measured in the middle points of their north-south and east-west boundaries. Extensions or ramifications of the holes that represented less than 1/6 of their size both in latitude or longitude were not taken into account as an edge of the boundary. Latitudes N60 and S60 were always at the highest limits for measurements for heliographic lati- tude and extensions of Polar Coronal Holes. The precision of the measurements is about +1 degree. When boundaries were uncertain, it was noted. Extensions in both heliographic latitude and longitude were based on the same limits. There are plans to extend this catalogue every two years on the same basis. 6. ACKNOWLEDGMENTS We gratefully acknowledge Dr. J. Harvey who provided us with several synoptic maps including those that were unpublished when he started identifying Coronal Holes on Helium images. The National Solar Observatory of NOAO kindly permitted us access to their files. Also we acknowledge the revisions and assistance of P. Navarro, A. Cruz, M. Ayala, M.A. Norzagaray, M. Pedroza, C. Calcaneo, and M. Ruiz. 7. REFERENCES BOHLIN, J.D. and 1975 "Synoptic Maps of Solar Coronal Hole Boundaries D.M. RUBENSTEIN derived from He II 304 A Spectroheliograms from the Manned Skylab Missions", Report UAG-51, NOAA, World Data Center A for Solar-Terrestrial Physics, NOAA, Boulder, Colorado, USA 80303- 3328, 21 pp. BOHLIN, J.D. 1977 "Extreme-Ultraviolet Observations of Coronal Holes, Solar Phys, 51, 377-398. BOHLIN, J.D. and 1978 "Extreme-Ultraviolet Observations of Coronal Holes" N.R. SHEELEY, JR. Solar Phys., 56, 125-151. HANSON, J.M., 1980 "Solar Observations During Skylab (April 1973 - E.C. ROELOF, and February 1974)", Report UAG-79, NOAA, World R.E. GOLD Data Center A for Solar-Terrestrial Physics, Boulder, Colorado, USA 80303-3328, 43 pp. HARVEY, J., 1980 "Synoptic Solar Magnetic Field Maps for the Interval J.B. GILLIESPE, including Carrington Rotations 1601-1680 (May 5, P. MIEDANER, and 1973-April 26, 1979)", Report UAG-77, NOAA, CC. C. SLAUGHTER World Data Center A for Solar-Terrestrial Physics, Boulder, Colorado, USA 80303-3328, 66 pp. MARAN, S.P. and 1973 "The OSO-7 Year of Discovery", The New R.J. THOMAS Astronomy and Space Science Reader, J.C. Brandt and S.P. Maran, Editors, W.H. Freeman and Company, San Francisco, USA, pp. 295-301. McINTOSH, P.S. 1975 "H-Alpha Synoptic Charts of Solar Activity for the Period of Skylab Observations (May 1973-March 1974)", Report UAG-40, NOAA, World Data Center A for Solar-Terrestrial Physics, Boulder, Colorado 80303-3328, USA, 32 pp. McINTOSH, P.S. 1979 "Annotated Atlas of H-Alpha Synoptic Charts for Solar Cycle 20 (1964-1974)", Report UAG-70, NOAA, World Data Center A for Solar-Terrestrial Physics, Boulder, Colorado, USA 80303, 327 pp. McINTOSH, P.S. 1991 "Atlas of Stackplots", Report UAG-101, NOAA World Data Center A for Solar-Terrestrial Physics, Boulder, Colorado, USA, 80303-3328, 188 pp. SANCHEZ-IBARRA, A. 1990 "Longitudinal and Temporal Variations of Sunspot Regions and Coronal Holes During Cycle 21", Solar Phys., 125. Solar-Geophysical Data 1970-91 NOAA, World Data Center-A for Solar-Terrestrial Physics, NGDC, Boulder, Colorado, USA, 80803. SPEICH, D.M., 1978 "Solar Activity during Skylab -- Its Distribution and J.B. SMITH, JR., Relation to Coronal Holes", NASA Technical R.M. WILSON, and Memorandum 78166, Marshall Space Flight Center, P.S. McINTOSH Alabama, USA. TIMOTHY, A.F. and 1975 "The Structure and Evolution of Coronal Holes", A.S. KRIEGER Solar Phys., 42, 135-156. WEBB, D.F., 1984 "Observations of the Reappearance of Polar J.M. DAVIS, and Coronal Holes and the Reversal of the Polar P.S. McINTOSH Magnetic Field", Solar Phys., 92, 109-132. Table 1. DATA SOURCES ======================================================================================== Carrington Rotation SOURCE ======================================================================================== 1658 Webb, Davis, and McIntosh, 1984; Maran and Thomas, 1973; SGD 1601-1610 Roelof and Gold, 1980; Bohlin and Sheeley, 1978; McIntosh, 1991; SGD 1623-1628 Harvey, NSO; SGD 1629-1632 McIntosh, 1991; SGD 1633 Harvey, NSO 1634-1635 Harvey, NSO; McIntosh, 1991; SGD 1636-37 McIntosh, 1991; SGD 1638 Harvey, NSO 1639 McIntosh, 1991 1640-1641 No data 1642 McIntosh, 1991 1643-1644 No data 1645-1647 McIntosh, 1991; SGD 1648 No data 1649-1796 McIntosh, 1991; SGD 1797-1805 SGD 1806 Harvey, NSO 1807 No data 1808-1828 SGD 1829 No data 1830 Harvey, NSO 1831 SGD 1832-33, 1835-40 Harvey, NSO, (No data for 1834) 1841 Harvey, NSO; SGD 1843-44, 1846-49 Harvey, NSO, (No data for 1845) __________________________________________________________________________________________