SWEPAM Level 2 Data Documentation

Sensor		Full Name		Measured Species		Measured Quantities		Typical Energy (KeV)		Measurement Technique
SWEPAM		Solar Wind Electron, Proton & Alpha Monitor		H, He, e^-		E/Q distributions		0.26 - 36 (ions) 0.001 - 1.35 (e^-)		E/Q

The SWEPAM Instrument on ACE

Important note: 2021-02-09: SWEPAM Level 2 data from 2013 onwards have been reprocessed to account for changes in CEM detector gains over time. See the Release notes for SWEPAM level 2 data for details.

The Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) measures the solar wind plasma electron and ion fluxes (rates of particle flow) as functions of direction and energy. These data provide detailed knowledge of the solar wind conditions and internal state every minute. SWEPAM also provides real-time solar wind observations which are continiously telemetered to the ground for space weather purposes.

Electron and ion measurements are made with separate sensors. The ion sensor measures particle energies between about 0.26 and 36 KeV, and the electron sensor's energy range is between 1 and 1350 eV. Both sensors use electrostatic analyzers with fan-shaped fields-of-view. The electrostatic analyzers measure the energy per charge of each particle by bending their flight paths through the system. The fields-of-view are swept across all solar wind directions by the rotation of the spacecraft.

For more information about the SWEPAM instrument, visit the SWEPAM Home Page, at Los Alamos National Labs.

Oct 23, 2012: SWEPAM data status update
The SWEPAM observations, in particular the proton density and to lesser extent the temperature, became increasing sparse starting in 2010 as the primary channel electron multiplier (CEM) detectors have aged. Now, many years past the original planned mission lifetime, these Ulysses spare detectors do not provide adequate gain to make good measurements. In response, the ACE science team has developed and implemented, starting Oct 23 2012, an innovative mission operations concept that more frequently repoints the ACE spacecraft's spin axis further away from the Sun. This allows other, stronger CEMs that have received significantly less total fluence to measure the solar wind; this operational improvement has significantly increased the frequency of good quality SWEPAM observations, back to levels not seen in several years.
For more details, please read this analysis by the SWEPAM team of The Effect of ACE Spacecraft Repointing on SWEPAM Calculated Moments

Release notes for SWEPAM level 2 data - provided by the SWEPAM instrument team. All users of SWEPAM data should read these notes.

SWEPAM Data Description

Time Data
All level 2 data records for all ACE instruments contain timing information in the same format. The format of the timing information is described here.

Solar Wind Data
SWEPAM level 2 data is organized into 27-day time periods (Bartels Rotations - roughly one solar rotation period). For each Bartels Rotation, the level 2 data contains time averages of solar wind parameters over the following time periods:

64 seconds (ion data only)
128 seconds (electron data only)
hourly (all data)
daily (all data)
27 days (1 Bartels rotation) (all data)

SWEPAM level 2 data consists of the following data items:

Ion data
- Proton Density (n_p in cm ^-3)
- Radial Component of the Proton Temperature (T_P,rr in ^o Kelvin)
- Ratio of Alpha Density to proton Density (n_He/n_P)
- Proton Speed (V_P in km/s)
- Proton Velocity Vector in GSE coordinates (in km/s)
- Proton Velocity Vector in RTN coordinates (in km/s)
- Proton Velocity Vector in GSM coordinates (in km/s)

Electron data
- Electron Temperature (in ^o Kelvin)
  While the SWEPAM team does routinely calculate electron temperatures, it was agreed very early in the mission that because of reduced funding SWEPAM would focus on validation of the ion moments, and that the electron moments would not be validated or made available through the ASC. Again, these parameters are automatically calculated, and the SWEPAM team is happy to work with researchers who need them for specific studies, but the team has never had the resources required for scientific validation.

In addition, the ACE spacecraft position is provided, in the GSE coordinate system (float32) and in the GSM coordinate system (float32):

pos_gse_x,y,z - The x,y,z-components of the spacecraft position, in GSE, in km.
pos_gsm_x,y,z - The x,y,z-components of the spacecraft position, in GSM, in km.

Release notes for SWEPAM level 2 data - provided by the SWEPAM instrument team. All users of SWEPAM data should read these notes.

A data value of -9999.9 indicates bad or missing data for the given time period.

Download SWEPAM level 2 data

Last Updated: 7 November, 2007

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