NEGIX: electron density gradient ionosphere index
Thematic areas: Space Weather, Ionosphere/Magnetosphere, Plasma measurements
Applicable missions: Swarm
Applicable spacecraft: Swarm-A, Swarm-C
NEGIX is the electron density (𝑁𝑒) gradient ionosphere index developed as part of the MIGRAS project to monitor mid-scale plasma density irregularities with horizontal spatial scales in the order of 100 km. This product benefits from the coordinated flight of Swarm satellites A and C that are orbiting the Earth from pole to pole, at a height of ca. 460 km. The distance between both satellites ranges from a few kilometres when they approach the poles and up to ca. 150 km at their equatorial pass. Therefore, plasma density measurements acquired with the Langmuir Probe instruments onboard of the Swarm satellites are ideal to monitor mid-scale density changes.
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(delivered separately)
| Name | Description | Type | Unit |
|---|---|---|---|
| Timestamp | Time in Universal Time | CDF_EPOCH | - |
| Longitude | Position of NEGIX (X, Y) in geocentric longitude. Averaged longitude position of central points (CPs) derived from the combination of Ne measurements of Swarm A and C. | CDF_DOUBLE | deg |
| Latitude | Position of NEGIX (X, Y) in geocentric latitude. Averaged latitude position of CPs derived from Ne measurements of Swarm A and C. | CDF_DOUBLE | deg |
| Distance | Averaged distance value from all dipoles used for the estimation of NEGIX values | CDF_DOUBLE | m |
| Azimuth | Averaged azimuth value from all dipoles used for the estimation of NEGIX values | CDF_DOUBLE | deg |
| Negix_X | Mean value of NEGIX for the West-East component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_X_Sigma | Standard deviation value of NEGIX for the West-East component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_X_P95 | 95-percentile value of NEGIX for the West-East component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_Y | Mean value of NEGIX for the South-North component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_Y_Sigma | Standard deviation value of NEGIX for the South-North component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_Y_P95 | 95-percentile value of NEGIX for the South-North component | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_Total | Total vector value of NEGIX, derived from the mean West-East and South-North components | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_Sigma | Vector value of the standard deviation of NEGIX, derived from the standard deviation values of West-East and South-North components | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| Negix_P95 | Vector value of the 95-percentile of NEGIX, derived from the 95-percentile values of West-East and South-North components | CDF_DOUBLE | e cm⁻³ m⁻¹ |
| N_Measurements | Number of elements for a data record from which NEGIX is determined | CDF_UINT2 | - |
| Flag_Negix | Flags characterising the dispersion of gradient values that are used to compute the total vector | CDF_UINT1 | - |
| Orbit_Label | Value defining whether the magnitude belongs to an ascending or descending orbit of the Swarm satellites | CDF_INT1 | - |
| Value of Flag_Negix | Pearson’s Coefficient Value | Description |
|---|---|---|
| 0 | -0.5 ≤ value ≤ 0.5 | The distribution of the sample of NEGIX total vectors within the given resolution is slightly skewed. |
| 1 | -1.5 ≤ value < -0.5, 0.5 < value ≤ 1.5 | The distribution of the sample of NEGIX total vectors within the given resolution is slightly skewed, with possible outliers in the sample. |
| 2 | value < -1.5, value > 1.5 | The distribution of the sample of NEGIX total vectors within the given resolution is strongly skewed, with a strong influence of outliers that may require more cautious investigation or removal. |
| Value of Orbit_Label | Description |
|---|---|
| 1 | Notation for measurements in an ascending orbit of the Swarm satellites. |
| -1 | Notation for measurements in a descending orbit of the Swarm satellites. |
| Product Identifier | NIX_TMS_2F |
|---|---|
| Definition | NEGIX is the electron density (𝑁𝑒) gradient ionosphere index developed as part of the MIGRAS project to monitor mid-scale plasma density irregularities with horizontal spatial scales in the order of 100 km. |
| Input Data | EFIA_LP_1B, EFIC_LP_1B |
| Input Time Span | 1 day |
| Spatial Representation | The spatial resolution for each dataset record is 0.5 degrees in latitude along the path of Swarm satellites A and C. Geocentric longitude and latitude coordinates for each dataset record are provided. In longitude, the spatial resolution is defined by the separation of the satellites, which is ca. 1.5 degrees (ca. 150 km) at the equator, reducing to a few kilometres in the polar regions. |
| Time Representation | The spatial resolution of 0.5 degrees represents about 8 seconds of records of Swarm satellites A and C. Therefore, a daily file product contains about 10,800 records. |
| Units | electron cm⁻³ m⁻¹ |
| Resolution | 1 electron cm⁻³ m⁻¹ |
| Uncertainty | The uncertainty is reflected in the flags. Higher values in flags indicate irregularities, potential measurement inconsistencies, or issues with geometries, especially in the polar regions. |
| Quality Indicator | The quality of the product depends on the quality of the L1b input for Swarm A and C. If any of the input files contains electron density flags (Flags_Ne) larger than 20 as reported in [RD-4], then the product quality indicator in the XML-header file is set to “001”. Otherwise, this value is “000”. This information is also reflected in the CDF global attributes individually for the input files. |
| Data Volume | 2 MB |
| Data Format | CDF |
| Output Time Span | 1 day |
| Update Rate | Daily |
| Latency | 5 minutes |
| Notes | - |
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