The NASA Advanced Composition Explorer (ACE) satellite enables SWPC to give advance warning of geomagnetic storms. Geomagnetic storms are a natural hazard, like hurricanes and tsunamis, which the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) forecasts for the public's benefit. Geomagnetic storms impact the electric power grid, aircraft operations, GPS, manned spaceflight, and satellite operations, to name some of the most damaging. Severe geomagnetic storms can result in electric utility blackouts over a wide area.
The location of ACE at the L1 libration point between the Earth and the Sun, about 1,500,000 km forward of Earth, enables ACE to give up to one hour advance warning of the arrival of damaging space weather events at Earth. SWPC issues warnings of imminent geomagnetic storms using these data.
Ground tracking status for the ACE satellite is available here.
Plotted on this page is the real-time solar wind from the ACE satellite. Available plots include data from one or more of the four ACE instruments that are sent from the spacecraft in real-time.
The ACE satellite was launched in 1997 and has been providing real-time data for use in forecasting to NOAA since 1998. NOAA provided funds for the modification of the ACE transmitter to enable the broadcast of the real-time data and also funds to the instrument teams to provide the algorithms for processing the real-time data.
The four instruments for which data are available are:
- Electron, Proton, and Alpha Monitor (EPAM) of the Johns Hopkins University Applied Physics Laboratory
- Magnetic Field (MAG) of the University of Delaware Bartol Research Institute and subsequently University of New Hampshire
- Solar Isotope Spectrometer (SIS) of the California Institute of Technology
An inverse chronological list of ACE Real-Time Solar Wind Announcements
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October, 2012 New Pointing for the ACE Satellite to Improve SWEPAM data
The ACE satellite pointing is now being kept at larger angles with respect to the Sun in order to enable the SWEPAM instrument to expose more responsive channel electron multipliers (CEMs) to the solar wind. Prior to this time, the CEMs that had been exposed had done so for the life of the mission and they had degraded to where reliable solar wind parameters had become difficult to extract. The most significant impact will be improved, higher density values. In the weekly ACE reports that are available from the ACE Science the following description is available:
“The project has accepted the SWEPAM team proposal to keep the spacecraft at larger sun angles with weekly attitude maneuvers. The SWEPAM-Ion
instrument has a series of channel electron multipliers (CEMs) and larger sun angles allows more responsive CEMs to measure the solar wind.
The maximum sun angle follows the Sun-Earth-Vehicle angle (SEV). The SEV angle is determined by the size/shape of the orbit around L1. When the spacecraft antenna is pointed directly towards earth, the spacecraft's sun angle will be equal to the Sun-Earth-Vehicle angle. With weekly maneuvers, the average sun angle can be kept 4-8deg more than the SEV angle. This results in the spacecraft antenna aspect angle being kept between 5 and 9 degrees and never pointing directly back at earth. For reference, the SWEPAM team prefers sun angles above 13 degrees. With the current size of the L1 orbit, the sun angle will be above 13 degrees for ~45% of the time.”
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October 19, 2010 EPAM Energy Range Now Corrected on SWPC Website
Based on the advice of the ACE EPAM science team, the EPAM FP6p proton channel energy range shown in headers was corrected from 761-1220 keV to 795-1193 keV.
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June 1, 2006 ACE RTSW SWEPAM Data Improvement
The ACE RTSW SWEPAM data processing was updated at 0000 UTC June 1, 2006. This change will result in improved solar wind parameters (speed, density, and temperature) that more closely match ACE Science Center data.
ACE RTSW MAG, EPAM, and SIS data are unaffected.
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May 5, 2006 ACE RTSW SWEPAM Data Improvement
At 0000 UTC on June 1, 2006, the ACE RTSW SWEPAM data processing will be updated. This change will result in improved solar wind parameters (speed, density, and temperature) that more closely match ACE Science Center data. The most significant impact will be higher RTSW density values during low-speed, low-density solar wind conditions. ACE RTSW MAG, EPAM, and SIS data are unaffected.
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May 15, 2006 ACE RTSW Data Timing Problem Resolved
From 1300UT May 12 to 1300 UT May 13 there was a problem in the SEC ACE RTSW data. Values were correct but the associated time tags were about 15 minutes earlier than the actual reading.
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April 3, 2006 Termination of ACE Solar Wind Data
A comment period for the proposed NWS Termination of ACE Solar Wind Data was April 3 - May 18, 2006
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May 19, 2005 SIS DATA noise
There is currently noise in the SIS RTSW proton rates. The SIS team is investigating the cause and expects it to be corrected
in the next few days.
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August 24, 2004 ACE MAG Data Processing Change
ACE MAG data processing was updated at 0000 UTC on 24 August, 2004. This update should result in improved RTSW magnetic field values that
more closely match ACE Science Center data.
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February 4, 2004 EPAM Data Switched from LEMS30 to LEMS120
Real-time proton data from the EPAM LEMS30 instrument has been replaced with similar proton data from the LEMS120 sensor. The new proton channels cover the following energy ranges: 47-68 keV, 115-195 keV, 310-580 keV, and 1.06-1.9 MeV. Previous real-time electron (38-53, 175-315 keV) and proton (0.761-1.22 MeV) data from the EPAM CA60 telescope remain unchanged. Plots and Data Lists of 5-minute and 1-hour averaged data were backfilled to January 29, 2004.
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January 15, 2004 SEC Planning to Switch EPAM Sensors
SEC is proceeding to switch the ACE RTSW EPAM proton data processing to another sensor. The operational switch over to the new sensor data has been reschedule to February 4, 2004. It is anticipated that the following proton energy ranges will be available: 47-68 keV (P1'), 115-195 keV (P3'), 321-587 keV (P5'), and 1060-1900 keV (P7').
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November 12, 2003 EPAM Data Problems Continue
As a result of the last two weeks of high solar activity several of the RTSW EPAM proton channels have become abnormally high and have shown excessive noise. As a result the data from the 65-112 keV (P2), 112-187 keV (P3), and 310-50 keV (P5) energy channels have been removed from the real-time plots and lists. The 1060-1910 keV (P7) channel remains but has also begun to show noise. The 761-1220 (W1) proton channel and electron channels, being from another EPAM sensor, have been unaffected. SEC is investigating the switch to another EPAM proton sensor for its RTSW data stream.
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November 3, 2003 ACE EPAM Data Problems
On October 29 the ACE EPAM 65-112 keV (P2) and 112-187 keV (P3) energy channels became spuriously high following the onset of a large solar energetic particle event and have not returned to nominal values. In addition, the 310-580 keV (P5) channel became elevated and erratic on November 1 and 2 during a second solar energetic particle event. The P5 channel appears to have recovered; however, this does not preclude similar problems in the future. The EPAM instrument team and SEC are investigating the cause of these problems and a possible cure. Look for more information here as information becomes available.
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March 18, 2001 ACE EPAM Data Processing Changed
ACE EPAM data processing was updated. The visible change was replacing the noisy Proton 47 to 65 keV data with the 65 to 112 keV data in EPAM lists and plots.
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March 5, 2002 EPAM Data Processing Change
On March 18, 2002 EPAM data processing will be updated. On data lists, the header line changes to show the new energy range for the first Proton channel. On data plots, the legend changes.
EPAM data processing update:
In late November and early December 2001 the P1 channel (47 to 65 keV) data increased during an energetic particle event (small radiation storm) and never returned to nominal levels. The channel became "noisy" and after monitoring for a few weeks the decision was made to replace the P1 channel with the P2 channel (65 to 112 keV) data, the next higher energy channel within the same detector on EPAM.
During the later part of December 2001 the P5 channel (310 to 580 keV) showed anomalous periods of increased particle flux. The instrument PI from JHU/APL determined that when the detector was pointed in the general direction of the sun, the sector pointed toward the sun showed large increases in particle flux. This is believed to be due to solar contamination and only happens during limited times between each set ofspacecraft maneuvers. The decision was to change the processing of all channels from this detector to eliminate the solar noise problem. A third problem was induced by the solar noise problem: Whenever the P5 channel became noisy the P1 and P3 data would drop out. The cause of the drop out was a programming filter designed to eliminate "bad" data. Since not all of the data were "bad", only the sunward directed sector, a decision was made to eliminate all data from the sunward sector. Problems two and three were solved by the removal of the data from the sunward sectors for all channels. The only impact from removing the sunward sector data is larger fluctuations in the data when the flux is near background levels.
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January 25, 2002 EPAM P1 Channel Data Update
EPAM lowest energy channel (P1) 47-65 keV data are suspect since late November. This channel will be replaced by late February. Possible cures are being investigated by the instrument team and SEC.
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December 20, 2001 ACE EPAM P1 Channel Data Suspect
Data from the ACE EPAM lowest energy channel (P1) 47-65 keV are suspect since late November, following the large proton event that ended on the 24th. The cause and possible cure are being investigated by the instrument team and SEC. Look for further messages here as more information becomes available.
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July 26, 2000 ACE EPAM Data Lists Header Line Changes
The ACE EPAM 5-min data lists, had incorrect Differential Proton Flux ranges. The header lines were changed beginning 26 July 2000.
CORRECTED:
# -- Differential Flux --------------------------
# UT Date Time ------------------ Protons keV ----------------
# YR MO DA HHMM 47-65 112-187 310-580 761-1220 1060-1910
INCORRECT:
# -- Differential Flux --------------------------
# UT Date Time ------------------ Protons keV ----------------
# YR MO DA HHMM 56-78 130-214 337-594 761-1220 1073-1802
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July 30, 1998 ACE Hourly Averaged data
SEC creates monthly files of hourly averaged data from each of the ACE instruments. The files are updated every 3 hours beginning at 0010UT. The current month's files are recreated at each run. The previous month's files is created for the last time on the first day of the new month.
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July 28, 1998 EPAM Algorithm Updated
The EPAM 761-1220 MeV Proton algorithm was adjusted at 7/28 1600UT. There was factor of 3 decrease which matches expected values.
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April 3, 1998 Update on Quality of ACE RTSW Data Sets
MAG: All data nominal
SWEPAM: All data nominal. When the velocity of the solar wind falls to low values the current algorithm will often set a flag indicating a problem exists. SEC flags the data in the data base and does not plot the data on the web site. The end result is a number of missing data at the one minute cadence.
EPAM: All differential flux channels nominal, except for W1. This channel is impacted by above normal temperatures on ACE. APL is looking at this issue. The only impact is the anisotropy index is not valid. The energy range of this channel is covered by the other existing channels.
SIS: Both integral channels nominal. Integral flux is at background until a large event is detected
Update on tracking:
RAL, NASA, and AFSCN are fully operational. CRL is down for antenna repair and is expected up in two months. AFSCN has added extra tracking coverage during the time period normally covered by CRL. Occasionally short dropouts occur during a tracking pass, usually due to data transmission problems. Bad data records are received during some tracking passes. Software eliminates most of the problem data, but not all problem data.
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2/9/98 - A software solution to the SWEPAM instrument problem was installed on Feb 5. Density, Bulk Speed and Ion Temperature data now appear nominal.
2/2/98 - The Spacecraft Location files will not be available until March.
2/2/98 - The Magnetometer data is still in spacecraft coordinates (RTN). Will not be switched to GSM coordinates in March.
2/2/98 - Lists of hourly average will not be available until March.
2/2/98 - The limits shown below for Mag component magnitude, SWEPAM bulk speed, SWEPAM X vector velocity, and Xgse location were corrected 2/2/98.
1/21/98 - Operational ACE data lists began running.
There is no official archive of the ACE 'real-time' data as displayed on these web pages. However, most of the data are available from either NOAA or solarsoft.
ACE 1-minute and 5-minute averaged real-time data can be retrieved from the SWPC Data Service and for the past 30 days from the SWPC ftp service ACE directory and for historical data back to August, 2001 from solarsoft.
ACE 1-hour averaged real-time data and historical data can be retrieved from the SWPC ftp service ACE2 directory and for historical data back to August, 2000 from solarsoft.
ACE science data and many other related products are archived at the ACE Science Center(link is external).
The GSM coordinates theta (GSM latitude) and phi (GSM longitude) are defined at the ACE Science Center (https://izw1.caltech.edu/ACE/ASC/browse/browse_info.html#mag) and are repeated here:
B_gsm_theta (GSM Latitude) - The angle in degrees with 0 at Bx/By plane and + toward Bz (-90 to +90 degrees)
B_gsm_phi (GSM Longitude) - The angle in degrees with 0 at Bx and + toward By (0 to 360 degrees)
Anyone with questions about these data should contact SWPC.