The Sunspot Drawing Collection of the National Solar Observatory at Sacramento Peak (1947–2004)

A complete dataset of sunspot drawings recorded at Sacramento Peak Observatory (SPO) from late 1947 till mid-2004 has been digitized. We present the history of the observations and describe the data included in the drawings. We compare the sunspot number index calculated from the SPO data and the International Sunspot Number (SNv2), and we find that both series exhibit a similar behavior. The ratio of two sunspot numbers is relatively constant at about 1.2 – 1.3 during 1955–1995, with larger variations present at the beginning of the time series. This work represents the first step for the publication of the SPO sunspot catalogue in digital format. More information, such as positions and areas of sunspots, will be included in the next versions in order to provide the space weather and climate community a more complete sunspot catalogue with good quality observations.