Flux Data
CIRA 1972, an empirical model of atmospheric temperature and densities as recommended by the Committee on Space Research (COSPAR), is also known as Jacchia 1971.
Jacchia-Bowman models require additional indices, which you can provide as described below.
Input method
Specify the method of input for solar and geomagnetic activity for both general and Jacchia-Bowman inputs. Select between Read from File and Static Values:
Read from file
This applies to general solar and geomagnetic activity inputs; Jacchia-Bowman files are discussed below. ODTK supports the following file formats:
- Space Weather flux file (.txt), is available at www.celestrak.com/SpaceData and sponsored by CSSI and AGI (default). Use the FluxData.InputFluxFile attribute to select this file.
- Flux (*.fxm) file.
- Schatten predict (*.dat) file.
If you decide to use an FXM file, the following types are available:
- stkFluxGeoMag.fxm
- stkFluxGeoMag.5yr.fxm
The two versions of the TXT and FXM files are updated daily on AGI's FTP site (https://ftp.agi.com/pub/DynamicEarthData), and you can download them using the Data Update Utility. They contain identical data, except that the TXT contains more historical data and therefore takes longer to read. These files contain sections of measured and predicted values. The measured data contains daily values for F10/F10bar and Ap and Kp values every three hours. The predicted data sections contain daily predictions for F10/F10bar and for Ap, which ODTK converts to Kp internally. The Space Weather TXT files also contain monthly predicts of F10/F10bar and Ap/Kp. The F10ObservedStartTime and F10ObservedStopTime fields (read only) display the F10/F10bar data time span (measured over observed data), while the ApObservedStartTime and ApObservedStopTime fields (read only) display the Ap/Kp data time span (measured over observed data) based on the selected file. The F10PredictStartTime and F10PredictStopTime fields (read only) display the F10/F10bar data time span (measured over daily and monthly predicted data) while the ApPredictStartTime and ApPredictStopTime fields (read only) display the Ap/Kp data time span (measured over daily and monthly predicted data) based on the selected file. ODTK processes that use the F10 or Ap data will use all data from the file (observed plus predicted).
The Monthly Fit section of the predictions is not included in the determination of the predict stop times mentioned above. However, ODTK will use data in this section if needed during processing.
Any satellite propagated in ODTK using drag will use the same interface to get F10, F10bar, and Kp. If you specify the file, all satellites will use values from that file.
Static values
This applies to general solar and geomagnetic activity inputs; Jacchia-Bowman files are discussed below. Instead of reading data from a file, you can input specific values for F10, F10bar, and either Ap or Kp. If you do, they will be the same for all satellites. If you enter a Kp value, ODTK recalculates the Ap value, and vice versa.
File span validation
If you set the boolean attribute ValidateFileSpan to true (the default), then, when you run the Filter, Simulator or Least Squares process, ODTK compares the time span of that process to the time span of the data in the space weather file. ODTK writes the results of the time span comparison to the message viewer for cases where the start and stop times of the process do not both lie within the observed data section of the space weather. ODTK displays informational messages for cases where start or stop time lies within the predict section of the space weather. ODTK dislays warning messages for cases where start or stop time lies outside of combined observed and predict sections of the space weather.
When you configure a Filter process with LastMeasurement as the Stop Mode, the span from filter start to filter start + WarnThreshold is used in the data span comparison described above. When running a Filter with a Stop mode that provides a definitive stop time, the actual filter stop time is checked, and the threshold is ignored. You can set the value of the WarnThreshold attribute; the default is 1 day, and days are the default unit.
Kp subsampling ratio
Select one of the following options for the KpUpdate attribute:
| Kp Subsampling Options | |
|---|---|
| Option | Description |
| 3-Hourly | When you select this option, the subfield KPSubSamplingRatio does not show. This means that when ODTK requires a Kp/ap value in a particular three-hour window, it will be derived from a stored three-hour Kp/ap constant, where each pair of adjacent three-hour constants has a discontinuity at the interior three-hour boundary. |
| 3-Hourly Cubic Spline | This updates by interpolating the three-hourly data using natural cubic splines. |
| 3-Hourly Interpolated | When you select this option, the subfield KPSubSamplingRatio displays. The integer 1 (recommended) will select one third-order interpolating polynomial spline per three-hour Kp/ap window. The integer 2 will select two third-order interpolating polynomial splines per three-hour Kp/ap window. The integer n will select n third-order interpolating polynomial splines per three-hour Kp/apP window. |
| Daily | When you select this option, ODTK derives a Kp/ap value from a stored daily Kp/ap constant, where each pair of adjacent daily constants has a discontinuity at the interior daily boundary. |
Jacchia-Bowman models
Jacchia-Bowman atmospheric density models — ODTK supports the 2008 model — require additional indicators of solar and geomagnetic activity. You can obtain the required indices at sol.spacenvironment.net/~JB2008/indices.html.
Read from file
Solar and geomagnetic data are provided in separate files at sol.spacenvironment.net/~JB2008/indices.html. ODTK reads these files in their respective provided formats.
The solar flux indices F10 and F10bar are included in both the Jacchia-Bowman files and the general solar and magnetic indices file described above, though the reference time of day for the daily-provided value may be different. When you select the Jacchia-Bowman 2008 atmospheric density model, ODTK uses the F10 and F10bar values from the Jacchia-Bowman specific files.
Static values
Instead of reading data from a file, you can provide specific values for F10, F10bar, M10, M10bar, S10, S10bar, Y10, Y10bar, and DstDTc. If you use these static values, they will be the same for all satellites.
Background on flux data
Here are some useful descriptions of solar flux (F10):
NorthWest Research Associates Space Weather Services: The F10.7 index is a measure of the noise level generated by the sun at a wavelength of 10.7 cm at the earth's orbit. The global daily value of this index is measured at local noon at the Penticton Radio Observatory in Canada.
Australian Space Weather Services: The radio emission from the sun at a wavelength of 10.7 centimetres (often called "the 10 cm flux") has been found to correlate well with the sunspot number. Sunspot number is defined from counts of the number of individual sunspots as well as the number of sunspot groups and must be reduced to a standard scale taking into account the differences in equipment and techniques between observatories. On the other hand, the radio flux at 10.7 centimetres can be measured relatively easily and quickly and has replaced the sunspot number as an index of solar activity for many purposes.
As used in ODTK, F10bar, or average F10, is the statistical mean of the F10 values over 81 days, which is approximately three solar rotations, or 3 * ~27 days. The Sun rotates once every ~27 days. According to NASA's Marshall Space Flight Center:
Since the Sun is a ball of gas, it does not have to rotate rigidly like the solid planets and moons do. In fact, the Sun's equatorial regions rotate faster (taking only about 24 days) than the polar regions (which rotate once in more than 30 days).
The mean value of F10 for a given day is centered on that day, with the span of the average starting 40 days prior and ending 40 days following the given day.
The following are technical descriptions of Kp and Ap. For further information see the National Geodetic Data Center site.
The "p" in "Kp" and "Ap" stands for "planetary."
Three-hour range index K
K indices isolate solar particle effects on the Earth's magnetic field. Over a three-hour period, they classify, into disturbance levels, the range of variation of the more unsettled horizontal field component. Each activity level relates almost logarithmically to its corresponding disturbance amplitude. Three-hour indices discriminate conservatively between true magnetic field perturbations and the quiet-day variations produced by ionospheric currents. K indices range in 28 steps from 0 (quiet) to 9 (greatly disturbed), with fractional parts expressed in thirds of a unit. A K-value equal to 27, for example, means 2 and 2/3 or 3-; a K-value equal to 30 means 3 and 0/3 or 3 exactly; and a K-value equal to 33 means 3 and 1/3 or 3+. The arithmetic mean of the K values scaled at 13 selected observatories gives Kp.
Amplitude
The A-index ranges from 0 to 400 and represents a K value converted to a linear scale in gammas (nanoTeslas), a scale that measures equivalent disturbance amplitude of a station at which K=9 has a lower limit of 400 gammas.
In summary, Kp and Ap indices are used to quantify solar particle effects on the Earth's magnetic field. The Kp index is one of the input parameters to the atmospheric density model for drag calculations.