Alert Information Transmitted by WWV & WWVH

Geophysical Alerts

The National Oceanic and Atmospheric Administration (NOAA) uses WWV and WWVH to broadcast geophysical alert messages that provide information about solar terrestrial conditions. Geophysical alerts are broadcast from WWV at 18 minutes after the hour and from WWVH at 45 minutes after the hour. The messages are less than 45 s in length and are updated every 3 hours (typically at 0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100 UTC). More frequent updates are made when necessary.

The geophysical alerts provide information about the current conditions for long distance HF radio communications. The alerts use a standardized format and terminology that requires some explanation. Before looking at a sample message, let’s define some of the terminology:

Solar flux is a measurement of the intensity of solar radio emissions with a wavelength of 10.7 cm (a frequency of about 2800 MHz). The daily solar flux measurement is recorded at 2000 UTC by the Dominion Radio Astrophysical Observatory of the Canadian National Research Council located at Penticton, British Columbia, Canada. The value broadcast is in solar flux units that range from a theoretical minimum of about 50 to numbers larger than 300. During the early part of the 11-year sunspot cycle, the flux numbers are low; but they rise and fall as the cycle proceeds. The numbers will remain high for extended periods around sunspot maximum.

The A and K indices are a measurement of the behavior of the magnetic field in and around the earth. The K index uses a scale from 0 to 9 to measure the change in the horizontal component of the geomagnetic field. A new K index is determined and added to the broadcast every 3 hours based on magnetometer measurements made at the Table Mountain Observatory, north of Boulder, Colorado, or an alternate middle latitude observatory. The A index is a daily value on a scale from 0 to 400 to express the range of disturbance of the geomagnetic field. It is obtained by converting and averaging the eight, 3-hour K index values. An estimate of the A index is first announced at 2100 UTC, based on 7 measurements and 1 estimated value. At 0000 UTC, the announced A index consists entirely of known measurements, and the word "estimated" is dropped from the announcement.

Space Weather describes the conditions in space that affect earth and its technological systems. Space weather is a consequence of the behavior of the sun, the nature of earth’s magnetic field and atmosphere, and our location in the solar system.

Space Weather storms observed and expected are characterized using the NOAA Space Weather scales. The abbreviated table below shows the levels of activity that are included in the announcements and the associated terminology. The descriptor used to identify observed or expected conditions is the maximum level reached or predicted. The NOAA Space Weather Scales are further described at the Space Environment Center’s web site.

NOAA Space Weather Scales

Geomagnetic Storms Solar Radiation Storms Radio Blackouts Descriptor
G5 S5 R5 Extreme
G4 S4 R4 Severe
G3 S3 R3 Strong
G2 S2 R2 Moderate
G1 S1 R1 Minor

Geomagnetic storm levels are determined by the estimated 3-hourly Planetary K-indices derived in real time from a network of western hemisphere ground-based magnetometers.

Geomagnetic Storm Levels

Planetary K indices Geomagnetic storm level
K = 5 G1
K = 6 G2
K = 7 G3
K = 8 G4
K= 9 G5

Solar Radiation storms levels are determined by the proton flux measurements made by NOAA’s primary Geostationary Operational Environmental Satellite (GOES).

Solar Radiation Storm Levels

Flux level of > 10 MeV particles Solar Radiation Storm level
10 S1
102 S2
103 S3
104 S4
105 S5

Radio Blackout levels are determined by the x-ray level measured by the primary GOES satellite.

Radio Blackouts

Peak x-ray level and flux Radio Blackout level
M1 and (10-5) R1
M5 and (5 x 10-5) R2
X1 and (10-4) R3
X10 and (10-3) R4
X20 and (2 x 10-3) R5

Every geophysical alert consists of three parts as shown in the two tables below. The first table describes the information contained in the geophysical alert. The second table provides example text from an actual message.

Information in Geophysical Alert Voice Message

Section Information in Voice Message
1 The solar-terrestrial indices for the day: specifically the solar flux, the A index, and the K index.
2 Space Weather storms observed during the previous 24 hours. Includes all observed geomagnetic storms, solar radiation storms (proton events) and Radio blackouts (class M1 and greater flares).
3 Space Weather expected during the following 24 hours.

Example Text from Actual Geophysical Alert Message

Section Example of Actual Geophysical Alert Message
1 Solar-terrestrial indices for 08 November follow.
Solar flux 173 and Mid-Latitude A-index 14
The Mid-latitude K-index at 1500 UTC on 08 November was 3.
2 Space Weather for the past 24 hours has been severe.
Solar radiation storm(s) reaching the S4 level is in progress.
Radio blackouts(s) reaching the R2 level occurred.
Alt. section 2

No Space Weather storms have been observed during the past 24 hours.


Space Weather for the next 24 hours is expected to be severe.
Solar radiation storms reaching the S4 level are expected to continue. Radio blackouts reaching the R2 level are expected.

Alt. section 3

No Space Weather storms are expected during the next 24 hours.

The announcements include the descriptor of the largest space weather event observed (2) or expected (3) in the first line of each section. The remaining lines give the type of events and the level observed for each one. In the example above, no geomagnetic storm information is included because none was observed or is expected during the period. In the case where none of the three types of events are observed or expected, the announcement would contain section 1, plus alternate section 2 and alternate section 3.

To hear the current geophysical alert message by telephone, dial (303) 497-3235. Inquiries regarding these messages should be addressed to:

Space Weather Operations
325 Broadway
Boulder, CO 80305-3328
(303) 497-3171

Marine Storm Warnings

Marine storm warnings are broadcast for the Atlantic and Pacific oceans and the Gulf of Mexico. The National Weather Service provides the storm warning information. Atlantic highseas warnings are broadcast by WWV at 8 and 9 minutes after the hour, and a Pacific highseas warning is broadcast at 10 minutes after the hour. WWVH broadcasts a Pacific highseas warning at 48, 49, 50 and 51 minutes after the hour. Additional segments (at 11 minutes after the hour on WWV and at 52 minutes after the hour on WWVH) are used if there are unusually widespread storm conditions. The brief voice messages warn mariners of storm threats present in their areas.

The storm warnings are based on the most recent forecasts. The forecasts are updated at 0500, 1100, 1700, and 2300 UTC for WWV; and at 0000, 0600, 1200, and 1800 UTC for WWVH. All marine forecasts rely heavily on the Voluntary Observing Ship (VOS) program for obtaining meteorological observations.

Here is the text of a typical storm warning announcement:

North Atlantic weather West of 35 West at 1700 UTC; Hurricane Donna, intensifying, 24 North, 60 West, mov­ing northwest, 20 knots, winds 75 knots; storm, 65 North, 35 West, mov­ing east, 10 knots; winds 50 knots, seas 15 feet.

For more information about marine storm warnings, write to: National Weather Service, NOAA, 1325 East West Highway, Silver Spring, MD 20910. Or, visit the National Weather Service web site.

Global Positioning System (GPS) Status Reports

The United States Coast Guard sponsors two voice announcements per hour on WWV and WWVH, giving current status information about the GPS satellites and related operations. The 40-s announce­ments begin at 14 and 15 after each hour on WWV and at 43 and 44 minutes after each hour on WWVH. The announcement can be heard by telephone by dialing (703) 313-5907. For further information, contact the U.S. Coast Guard Navigation Center, 7323 Telegraph Road, Alexandria, VA 22310, or call (703) 313-5900.

For more information on WWV/WWVH transmission formats:
NIST Time and Frequency Division Home Page