solar wind source michigan solar wind model cassini saturn mission

There are two types of mSWiM files: Full resolution and Hourly. Both are described below.

Full Resolution Files


Basic Properties

Full resolution files come directly from the solar wind simulations. They contain ASCII data for approximately 1 year centered on the apparent opposition date. The file is not exactly one year due to the rotations to and from the inertial line on which we make the propagations. Doing the propagations ± 6months around apparent opposition is the most accurate way to make the calculation.

Filenames

Object_yyyyDddd-yyyyDddd.dat

The naming convention for files includes the object to which we are propagating (a planet or spacecraft) and the year and day of year (separated by "D") for the start and end dates of the data in the file.

File Header

name:   Jupiter 
start date (yr mo dy hr mn sc ms):  1994 12 16 0  0  0  0
grid spacing: 3.37500E+08
it  t  dt  yy  doy  mon  day  hr  min  sec  ms  r  rho  vr  vt  vn  T  br  bt  bn

Each file contains the above 4 line header which indicates the object, the start date of the simulation (not the same as the first entry in the file due to the rotations to and from the inertial line), the spacing between grid points in km and a list of the variables on each line of the file.

Time in Files

it   t   dt   yy   doy   mon   day   hr   min   sec   ms

Each line of the file contains the time in the above format with each item as a fixed width column. The first three variables are related to the code: the iteration number, the time (in seconds) since the start of the run, and the time step (also in seconds).

The columns which follow are the year, day of year, month, day, hour, minute, seconds and milliseconds of the data each as and integer.

Cadence

The MHD model uses a time step based on the solar wind conditions. Therefore the time step between data points is not a constant.

Hourly Resolution Files


Basic Properties of Files

Hourly resolution files are generated from the full resolution files. Each file contains ASCII data for 1 calendar year. This means that multiple full resolution files are combined together to make this product. The file merge happens at the time when the object (a planet or spacectraft) and Earth are separated by 180 degrees in helioecliptic longitude. At this point the rotation angle of the boundary conditions reverses that is instead of rotating the boundary conditions backward from Earth to the simulation longitude, we rotate the boundary conditions forward with the Sun from this time on in order to get the best estimate of boundary conditions at the simulation longitude. The reversal of the rotation angle introduces an artifitial discontinuity in the predicted solar wind data. Therefore solar wind predictions in the date range ± one month of the 180-degree longitudinal separation (dΦ) should not be used for correlative studies.

Filenames

Object_yyyy_h.dat

The naming convention for files includes the object to which we are propagating (a planet or spacecraft) and the year. The "h" indicates the fact there are hour resultion files.

File Header

Name: Jupiter
Opposition (DOY): 124.60
Apparent opposition (DOY): 139.89
Recurrence index: 0.62
Input solar wind data coverage: 99.4
yy   doy   mon   day   hr   dphi   r   rho   vr   vt   vn   T   br   bt   bn

Each file contains the above 6-line header which indicates the object, the opposition date in the given calendar year (if there is one), the apparent opposition (if there is one), the recurrence index for the solar wind for this year, the solar wind data coverage for this year and a list of the variables on each line of the file. See the method and validation description for definitions of these terms.

Time in Files

yy doy mon day hr

Each line of the file contains the time in the above format with each item as a fixed width column. The columns include the year, day of year, month, day, hour of the data each as and integer.

Cadence

These files have hourly data linearly interpolated between adjacent data points in the full resolution files closest to the hour.

Additional Variable in the Hourly Resolution Data Files

dΦ (denoted as dphi in the header), the longitudinal separation between the object and Earth ranging from -180 to 180 degrees, is included in the hourly resolution files as an additional variable. This could be used as a quality factor of the solar wind prediction. dΦ=0 marks the time of opposition when the actual boundary conditions can be used in the simulation, and dΦ=180 or -180 marks the time when the boundary conditions have to be rotated from the other side of the Sun to the simulation longitude. See the method and validation description for details on the prediction efficiency as a function of dΦ.

Formats Common to Both Files


Data Quantities and Units

r   rho   vr  vt   vn   T   br   bt   bn

Each line of the file contains the above quantities as fixed width columns of real numbers: r (spacecraft range), rho (number density), vr, vt, vn (velocity in RTN coordinates), T (plasma temperature) and br, bt, bn (magnetic field in RTN coordinates). Units are r(km), rho(#/cm^3), v(km/s), T(K), b(nT).

Coordinate system: RTN

Velocity and magnetic field coordinates are in RTN (Radial-Tangential-Normal) coordinates defined as:

  • R points radially away from Sun toward the object.
  • T points toward the cross product of the solar rotation vector and R.
  • N points toward the cross product of R and T.

In this coordinate system, R is therefore similar to the –X axis in many magnetospheric coordinate systems (GSM, KSM), T is nearest to, but not equivalent with, the –Y axis and N is closest to, but not equivalent with, the +Z axis


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