NEW: The Estimated ISN
Maybe you noticed: the daily ursigrams and geoalert have changed a little! From today onwards, we provide an estimation of the International Sunspot Number, in short: the Estimated ISN.
Nederlandstalige versie /Version franaise posted on Dec 20, 2005

The first of every month, the provisional daily International Sunspot Number is calculated for the previous month. Many observatories provide at the end of every month their daily Wolf numbers. They do this as soon as possible. Recently, a new web interface has been developed through which observers can enter their observations. This can be done on a daily basis. Thanks to this effort done by some observers and the daily received USSPS (SunSPotS) messages, we are able to calculate the Estimated ISN.

The Wolf numbers which reach us before the daily forecast is done (typically around 12:30UT), are used to make an estimation of the provisional daily International Sunspot Number. We multiply the Wolf number with the K-reduction coefficient of that particular station. The Estimated ISN is the mean of all these numbers. Outliers, i.e. sunspot numbers that fall outside a permitted interval, are not used.

Up till now, daily observations are received on a regular basis from 8 stations:

  • Catania Astrophysical Observatory, Italy
  • Dubois F., Belgium
  • Holloman Air Base, USA
  • Learmonth Solar Observatory, Australia
  • Meeus L., Belgium
  • Ondrejov Observatory, Czech-republic
  • SOON station, San Vito, Italy
  • Royal Observatory of Belgium, Belgium

Typically 3 to 4 observations reach us on time to calculate the Estimated ISN. Thanks to all!