Ne Gradient Ionosphere indeX (NEGIX)
The NEGIX measures the spatial Ne gradients in the topside ionosphere (Swarm up to GNSS orbit) using GNSS Precise Orbit Determination (POD) measurements using Swarm onboard Langmuir probe (LP) measurements (using 2 Hz data).
Sample Data
Global NEGIX
Product Specification
One data file in CDF format is produced per day since also daily input electron density files are used for the determination of NEGIX. A spatial resolution of 0.5 degrees in latitude has been adopted to combine measurements and estimate plasma density gradients. This translates to around 8 seconds of transit of the Swarm satellites. Therefore, the expected length of dataset records in one product file is about 10,800.
As follows, a description of the expected output variables is presented:
| Name | Description | Type | Column Key | Unit |
0 | Timestamp | Time in Universal Time | CDF_EPOCH | Timestamp | no unit |
1 | Longitude | Position of NEGIX (X, Y) in geocentric longitude. Averaged longitude position of the central points (CPs) derived from the combination of measurements of Swarm A and C. | CDF_DOUBLE | Longitude | deg |
2 | Latitude | Position of NEGIX (X, Y) in geocentric latitude. Averaged latitude position of the central points (CPs) derived from the combination of measurements of Swarm A and C. | CDF_DOUBLE | Latitude | deg |
| 3 | Distance | Averaged distance value from all dipoles used for the estimation of NEGIX values | CDF_DOUBLE | Distance | m |
| 4 | Azimuth | Averaged azimuth value from all dipoles used for the estimation of NEGIX values | CDF_DOUBLE | Azimuth | deg |
| 5 | NEGIX X | Mean value of NEGIX for the West-East component | CDF_DOUBLE | Negix_X | e cm-3 m-1 |
| 6 | NEGIX X Sigma | Standard deviation value of NEGIX for the West-East component | CDF_DOUBLE | Negix_X_Sigma | e cm-3 m-1 |
7 | NEGIX X P95 | 95-percentile value of NEGIX for the West-East component | CDF_DOUBLE | Negix_X_P95 | e cm-3 m-1 |
| 8 | NEGIX Y | Mean value of NEGIX for the South-North component | CDF_DOUBLE | Negix_Y | e cm-3 m-1 |
9 | NEGIX Y Sigma | Standard deviation value of NEGIX for the South-North component | CDF_DOUBLE | Negix_Y_Sigma | e cm-3 m-1 |
10 | NEGIX Y P95 | 95-percentile value of NEGIX for the South-North component | CDF_DOUBLE | Negix_Y_P95 | e cm-3 m-1 |
11 | NEGIX Total | Total vector value of NEGIX, derived from the mean West-East and South-North components | CDF_DOUBLE | Negix_Total | e cm-3 m-1 |
| 12 | 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 | Negix_Sigma | e cm-3 m-1 |
| 13 | 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 | Negix_P95 | e cm-3 m-1 |
| 14 | N measurements | Number of elements for a data record from which NEGIX is determined | CDF_UINT2 | N_Measurements | no unit |
| 15 | Flag NEGIX | Flags characterizing the dispersion of gradient values that are used to compute the total vector | CDF_UINT1 | Flag_Negix | no unit |
16 | Orbit label | Value defining whether the magnitude belongs to an ascending or descending orbit of the Swarm satellites | CDF_UINT1 | Orbit_Label | no unit |
Sample data can be found in the SWARM archive.