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Space Weather Alerts Description and Criteria

Space Weather Alert Service:

• Message format supports both readability and automatic decoding.
• Many alert service products correspond with the NOAA Space Weather Scales thresholds.
• SWPC's Alerts web pages provide extensive access to information and data related to the alerts service, including dynamic data displays (such as A-indices and K-indices charts, the Boulder-NOAA Magnetometer, and a 2-day Geomagnetic and Solar Indices table), an alert archive with related space weather data links, and this online help page.

Table of Space Weather Alerts Issued - Table of Alert Keywords

There are 4 types of Space Weather Alert Messages

• Watch messages, for Geomagnetic A-indices, are issued for long-lead geomagnetic activity predictions.
• Warning messages are issued when some condition is expected. The messages contain a warning period and other information of interest.
• Alert messages are issued when an event threshold is crossed and contain information that is available at the time of issue.
• Summary messages are issued after the event ends, and contain additional information available at the time of issue.

Space Weather Alerts are issued for these categories. Alerting criteria and descriptions are given below:

• X-ray Flux Alert and Event Summaries
• Radio Burst Alerts and Summary
• Geomagnetic Sudden Impulse Warning and Alert
• Geomagnetic K-index Warnings and Alerts
• Geomagnetic A-index Watches
• Electron Flux Alert
• Proton 10MeV and 100MeV Flux Warnings, Event Alerts and Summaries

X-ray Flux Alert and Event Summaries

• X-ray Flux ALERT: Issued in near-real-time, when flare x-ray flux exceeds the M5 (NOAA Scale R2 Moderate) level. Includes time of occurrence.

• X-ray Event SUMMARY: Issued for all flares exceeding M5, after decrease to half-peak flux level. Includes event begin, maximum, and end times, optical class, location, the peak flux level (M5, X1, X10, or X20) and the appropriate NOAA Space Weather Scale (R2-R5).

These products provide information on Major Flares (with peak X-ray flux above M5). An initial ALERT is issued in near-real-time when the flux exceeds the M5 level on the primary GOES satellite. After the flux has reached a confirmed maximum and decreased to a half-peak flux level, a SUMMARY is issued with details of the event. The SUMMARY is coded by maximum flux value, so individual summaries are available for M5, X1, X10, and X20 flares. The thresholds correspond to the NOAA Radio Blackout (R-Scale) for categories R2 through R5.

Radio Burst Alerts and Summaries

ALERTS are issued based on the confirmed onset of Type II and IV radio sweep observations.
SUMMARY will be issued for 10 cm Radio Bursts, upon receipt of a final observation report.

These products provide alerts and summaries of solar radio phenomena based on event begin time (and maximum and end times in the case of 10 cm). See the Sample Radio Alerts and Summaries for examples of these products.

Geomagnetic Sudden Impulse Warning and Summary

All SWPC Space Weather Alert Messages for geomagnetic phenomena are based primarily on real-time data from the Boulder-NOAA Magnetometer, which can be taken as a proxy for other mid-latitude locations, and as a general indicator of the trend in USAF "Planetary" values (based on a combined measure of several mid- and high-latitude magnetometer locations that are not available in real-time).

A Geomagnetic Sudden Impulse WARNING is issued based primarily on solar wind data available from the ACE satellite. These warnings are generally for short lead-time (30-60 minutes), high confidence indication of an expected Geomagnetic Sudden Impulse, and possible onset of subsequent geomagnetic storming. A Geomagnetic Sudden Impulse SUMMARY is issued upon its observation, and will generally be based on data from the primary Boulder-NOAA magnetometer, but may be based on a specified alternate magnetometer station if Boulder data is not available.

Geomagnetic K-index Warnings and Alerts

All SWPC Space Weather Alert Messages for geomagnetic phenomena are based primarily on real-time data from the Boulder-NOAA Magnetometer, which can be taken as a proxy for other mid-latitude locations, and as a general indicator of the trend in USAF "Planetary" values (based on a combined measure of several mid- and high-latitude magnetometer locations that are not available in real-time). Planetary K-index values of 5 through 9 correspond to the NOAA Geomagnetic Storm (G-Scale) for categories G1 through G5.

• WARNING: Issued and/or extended for any period with expected values of K= 4, 5, 6, or >= 7. Higher index warnings supersede lower ones.
• K4, K5 ALERT: Issued near-real-time, only for first occurrence in any period covered by K=4 or K=5 WARNINGS.
• K6, K7, K8, K9 ALERT: Issued near-realtime, for each occurrence within any 3-hr period, irrespective of WARNINGS.
• A 12-hour dynamic plot of the Boulder-NOAA Magnetometer and end-of-period Boulder K and estimated Planetary K indices are on the SWPC Website.
  

K-index WARNINGS are issued by SWPC under two conditions: Warning of expected ONSET of geomagnetic activity, and/or, warning of expected PERSISTENCE of geomagnetic activity.

K-index WARNINGS include a specific indication of what condition - Onset or Persistence - applies to the WARNING (or EXTENDED WARNING, when required). The WARNING period is expressed in terms of “Valid From” and “Valid To” times. EXTENDED WARNINGS always have the same “Valid From” time as the original WARNING, with a revised “Now Valid Until” time specified in the message. WARNINGS (and EXTENDED WARNINGS, when needed) are issued for K-index thresholds of 4, 5, 6, and 7 or greater. The appropriate NOAA Space Weather Scale is also appended to the warning.

K-index ALERTS for values of 4 through 9 are issued on a near-realtime criteria, based on thresholds of deflection from quiet-day curve values for geomagnetic field components over synoptic, 3-hour periods (the formal definition of a K-index is the maximum such deflection for the entire 3-hour period). K-index ALERTS are issued based on a near-realtime calculation of cumulative deflection values occurring within the current synoptic period. The message will also contain the magnetometer Station name which provided the data for the alert (in most cases this will be Boulder). End-of period values for Boulder (and estimated Planetary) K indices are available on the NOAA-SWPC Alerts Website

Lower-value K-index ALERTS (4 and 5) are only issued contingent on whether an active WARNING for that threshold is in effect. Given an active WARNING period for K = 4 or 5, only one such ALERT will be issued for the first occurrence within the valid WARNING time. Otherwise, K = 4 or 5 ALERTS will be issued once for each occurrence within a given synoptic period. To indicate the criteria in effect, K-index ALERT message formats include an Active Warning keyword (Yes/No), as well as a Synoptic Period keyword value for the period involved. See Sample K-index Alerts and Warnings.

In the case of higher value K-indices (deflections equaling a K-index of 6, 7, 8, or 9),one such ALERT will be issued for each and every synoptic period in which they occur, regardless of whether an active warning for those thresholds is presently in effect.

The diagrams below give an example of a severe geomagnetic storm period, indicating the K-index products that would likely be issued under these conditions. Also note the effect of active Warnings on the issuance of lower-value (K = 4 and 5) Alerts.

Sample Severe Geomagnetic Storm Period on Boulder-NOAA Magnetometer

Boulder-NOAA Magnetometer, H & D component trace data, from 2001 March 30 1200 UTC until 2001 April 1, 1200 UTC, with approximated Quiet Day Curve. Boulder K-indices were issued at the end of each 3-hour synoptic period (e.g. 0000 - 0300 UTC, etc.)

Magnetometer Data, showing cumulative value of nT deflections for each 3-hour period, and corresponding Alerts that would be issued. Note the effect of Active Warnings on K=4 and K=5 Alerts.

Geomagnetic A-Index Watches

All SWPC Space Weather Watches Messages for geomagnetic phenomena are based on Fredericksburg, Virginia (mid-latitude) magnetometer.

• A-Index WATCH: Daily Fredericksburg, Virginia A-index greater than 20, 30, 50, and 100 is predicted, with one day or greater lead time, in the daily forecasts issued by SWPC.
• Boulder A and estimated Planetary A indices are on the SWPC Website.
• End-of-period Boulder K and estimated Planetary K indices are on the SWPC Website.

A-index WATCHES are issued for valid times corresponding to entire calendar days, based upon the daily analyses and forecasts produced by SWPC. They serve as a long lead-time prediction of the expected trend in geomagnetic activity, within the limits of what the 24-hour A-index value can describe.

Geomagnetic activity WARNINGS and ALERTS are available only in terms of the K-index products (described above), however a running 24-hour value of the A-index (updated every 3 hours) is available on SWPC’s Alerts website.

Electron Flux Alert

Electron Events can persist for days, but the flux values observed at geosynchronous orbit follow a strong diurnal cycle due to the geometry of the Earth’s magnetic field. Maximum values generally occur near local noon locations on the daytime side of the Earth. ALERTS for Electron Events are therefore issued once per "satellite day" based on data from SWPC's primary GOES satellite, when electron fluxes have exceeded the event threshold (1000 pfu). The "satellite day" for GOES 12, SWPC's current primary satellite, is approximately 0500 to 0500 UTC; for GOES 11, the secondary GOES satellite, its approximately 0900 to 0900 UTC. On subsequent "days", an additional Electron ALERT is issued upon a new threshold crossing, and include the prior day's maximum flux time and value observed (if it occurred). No Electron ALERTS are issued on "days" when the threshold is not exceeded. As with any Electron Event, users should consider the locations of the satellite platforms of interest vs. the location of GOES, with regard to the specific timing of enhanced electron exposures that may occur. GOES 12 is at 75 degrees west longitude and GOES 11 is at 135 degrees west longitude. The satellite used in identified in the "Station" keyword, e.g. Station: GOES12

Proton 10MeV and 100 MeV Warnings, Event Alerts, and Event Summaries

• 10 MeV Warning: Issued when flux levels above 10 pfu are predicted. The predicted level of activity is given in the NOAA Space Weather Scale categories.
• 10 MeV ALERTS: Issued when flux level exceeding 10, 100, 1,000, 10,000, or 100,000 pfu confirmed.
• 10 MeV Flux CONTINUED ALERT:Confirms 10MeV Proton Event persistence for highest level(s) at 0100 UTC each day. Includes date/times for begin and maximum flux level and value observed through Continuation time.
• 10 MeV Proton Event SUMMARY: Issued when 10 MeV flux levels make a confirmed drop below S-Scale thresholds. Includes date/times for begin, maximum, end, and applicable flux data.
• The appropriate NOAA Space Weather Scale will be included on 10 MeV warning, alert and summary
  messages.

• 100 MeV Flux ALERT: Issued when flux level exceeding 1 pfu confirmed.
• 100 MeV Flux CONTINUED ALERT: Confirms 100 MeV proton event persistence at 0100 UTC each day. Includes date/times for begin and maximum flux level and value observed through Continuation time.
• 100 MeV Proton Event SUMMARY: Issued when 100 MeV flux level makes confirmed drop below 1 pfu threshold. Includes date/times for begin, maximum, end, and applicable flux data.

Proton Event products are issued for several thresholds. The 10 MeV products match the NOAA Solar Radiation Storm (S-scale) thresholds, based upon values observed on the primary GOES satellite.

Proton Event WARNINGS are issued by SWPC under two conditions: Warning of expected ONSET of a Proton Event, and/or, warning of expected PERSISTENCE of a Proton Event.

The 10 MeV Integral Flux WARNING (and EXTENDED WARNING, when required) is issued based upon the expectation of exceeding flux levels above 10 pfu. The same applies for the 100 MeV Integral Flux WARNING, though for a threshold of 1 pfu. Proton Event WARNINGS include a specific indication of what condition - Onset or Persistence - applies to the WARNING (or EXTENDED WARNING, when required). The WARNING period is expressed in terms of “Valid From” and “Valid To” times. EXTENDED WARNINGS always have the same “Valid From” time as the original WARNING, with a revised “Now Valid Until” time specified in the message. The 10 MeV Integral Flux WARNING includes the predicted level of activity based on the NOAA S-scale.

Proton Event ALERTS are issued upon confirmation of 10 Mev or 100 MeV Integral Flux exceeding certain thresholds. Initial ALERTS for 10 MeV and 100 MeV are issued for integral flux exceeding 10 pfu and 1 pfu, respectively. Higher threshold 10 MeV ALERTS are also issued for threshold exceedences of 100, 1,000, 10,000, and 100,000 pfu, matching the thresholds described in the NOAA S-scale.

Proton Events can persist for several days, and unlike Electron Events, they do not have an appreciable diurnal cycle in flux values observed at geosynchronous orbit. Therefore, daily CONTINUED ALERTS are routinely issued for Proton Events, shortly after 0000 UTC each day, so long as flux levels remain above the given thresholds. These CONTINUED ALERTS serve to update the ALERT condition, reiterating the start time of the event, and the maximum flux value and time yet observed for the current event. In the case of the multiple-threshold 10 MeV ALERTS, a single daily CONTINUED ALERT will only be issued for the highest 10 MeV condition currently in effect. 100 MeV CONTINUED ALERTS are issued if flux levels remain above the single threshold of 1 pfu on any subsequent day following the initial 100 MeV ALERT.

Once the Proton Flux has made a confirmed drop below a given threshold, a Proton Event SUMMARY is issued, specifying the start, maximum, end times, maximum flux observed for the event, and the corresponding NOAA S-scale. Because flux levels can drop slowly, the time of a "confirmed" drop below threshold can sometimes take several hours to determine. In the case of higher threshold 10MeV events, once a SUMMARY has been issued for a given threshold, the next lower threshold will be subject to the CONTINUED ALERT procedure described above, until it too has ended.

Higher threshold products for 100 MeV flux levels, such as 100 pfu, are being considered for future implementation.

Updated: October 1, 2007

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