The Ap index quantifies the global daily average activity level of the geomagnetic field. The 27-day forecast of the Ap index is performed using the Auto-regressive Integrated Moving Average (ARIMA) method and it is based on the work of McPherron (1999) in their paper “Predicting the Ap index from past behavior and solar wind velocity” [doi:10.1016/S1464-1917(98)00006-3]. The Ap forecast is based on identifying recurring geomagnetic activity. Thus, it will not forecast transient activity. This will also affect the quality depending on the solar cycle, with best results in the declining phase, while almost random results otherwise.
We advice caution when interpreting the product. The prediction may be best understood as the longer-term smoothed level of the geomagnetic activity ‘climate’ around which the actual daily activity would fluctuate.
The figure shows daily values of Ap (blue line) for the last 7 days, together with the forecasted next 27-days (red line), also with daily values. The dotted gray line indicates the 50% confidence interval, while the dotted red line indicates the 95% confidence interval.
The figure is updated daily. All date and time values are given in UTC.
Ap numerical values used to produce the forecast are provided by German Research Centre for Geosciences (GFZ).
These results are very much based on projects that received funding from the ESA Space Situational Awareness Programme’s network of space weather service development activities under ESA contract number 4000113185/15/D/MRP.
All publications and presentations using data obtained from this site should acknowledge the Norwegian Centre for Space Weather at Tromsø Geophysical Observatory and the ESA Space Situational Awareness Programme.
Comparison with 27 days ago
This product is designed to be a one page, simple look at recently observed and a three day forecast of space weather conditions. A brief description of why conditions occurred or are forecast is also included for each category.
A plain language, single page forecast text product issued every 12 hours, at 0030 and 1230 UTC, with both forecast and observed criterion now broken down for each of the three NOAA Scale categories. Each section includes a brief forecaster written rationale.
3-Day GeoMag (NOAA)
A daily deterministic and probabilistic forecast, for next three days, of geomagnetic activity. Observed values of Ap and deterministic Ap forecasts are provided, folLowed by probabilistic forecasts for four categories of geomagnetic activity, and deterministic 3-hourly Kp forecasts for three days.
Three-day forecast of Ap, Kp, and Geomagnetic Storm levels
The 27-day Space Weather Outlook Table , issued Mondays by 1500 UTC, is a numerical forecast of three key solar-geophysical indices; the 10.7 cm solar radio flux, the planetary A index, and the largest daily K values. A complete summary of weekly activity and 27-day forecasts since 1997, plus an extensive descriptive, are online as The Weekly.
The Preliminary Report and Forecast of Solar Geophysical Data (referred to hereafter as the Weekly) is compiled and issued every Monday. This publication is produced in Boulder, Colorado, jointly by the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center, formerly the Space Environment Center, and the Air Force Weather Agency (AFWA). It is a continuation of the weekly reports that began in 1951 and were issued by the High Altitude Observatory and NOAA and/or its predecessors. The current series began with serial number PRF 001 on 09 September 1975. The contents of the Weekly have no copyright or other restrictions. Comments concerning the content or improvements to the Weekly are invited. More details are available about forecast products in the Users Guide.