Using real-time solar wind observations to display solar wind / magnetosphere interactions
This web page displays dynamic modeling of the Earth's bow shock and magnetopause.
Real time data from the upstream spacecraft (top two panels) are used to predict the shape and location of these boundaries at the present time and into the near future.
In the figure to the right, the Earth is in the center, and is illuminated from the left by the Sun (not shown). In this view, we are looking down upon the North pole; thus the figure represents the equatorial plane. The solar wind emanating from the Sun is super-magnetosonic with respect to the Earth, so that a shock wave is formed. As the solar wind flows through the shock it is slowed down, and the pressure of the solar wind is balanced by the pressure from the Earth’s magnetic field. The boundary at which this pressure balance is achieved is called the magnetopause.
The upstream spacecraft monitors the solar wind from a position about 200 Earth radii (RE) sunward of the Earth. The real time solar wind data from this spacecraft allows us to predict what will happen at the Earth many minutes before the solar wind actually reaches us. Important solar wind values obtained from the upstream observations include the z-component of the interplanetary magnetic field (Bz) measured in units of nano-Tesla, and the dynamic pressure (also called the momentum flux) of the solar wind, measured in units of nano-Pascal.
Geosynchronous orbit (where many weather and communication satellites orbit) is depicted by the green dashed circle.
This movie is updated every five minutes
(unless there is an extended data gap in the upstream observations).
MORE DETAILS
Coordinate System
The coordinate system shown is Geocentric Solar Magnetospheric. In this coordinate system, the Earth is at the origin. The X-axis is positive towards the Sun. The Z-axis is 90 degrees from the X-axis, and is within the plane containing the X-axis and the dipole axis of the Earth's magnetic field. The Z-axis is positive towards the North Pole. The Y-axis is at right angles to the X and Z-axes.
Solar Wind Parameters
The solar wind parameters are from the upstream spacecraft, obtained in real-time, at a temporal resolution of one-minute. As such, these values are provisional, and are subject to corrections. The data used include the position of the upstream spacecraft, the measured interplanetary (solar wind) magnetic field (IMF), the solar wind ion density, bulk flow speed, and ion temperature. Linear interpolation is used to interpolate over small intervals of bad or missing data. From these values, the solar wind dynamic pressure and the magnetosonic Mach number are calculated. Small data gaps in the solar wind are seen in the display as constant values (last known values). An extended period of time with bad or missing solar wind values will cause the movie to not be updated, until new solar wind data are taken.
Dynamic Pressure
The dynamic pressure of the solar wind is calculated as the square of the solar wind bulk speed times the mass density (number density times its mass) of ions. The ions are assumed to be 96 percent protons and 4 percent He++ by number.
Magnetosonic Mach Number
The solar wind magnetosonic Mach number is calculated from the solar wind magnetic field intensity and plasma parameters. An electron temperature of 1.5×105K and a polytropic index of 5/3 is assumed.
Solar Wind Flow Angles
The flow angles of the solar wind are not available in the real-time data sets. Though the programs used for this web site are equipped to handle varying flow angles. Instead, an average value of 4 degrees is used, which accounts for the motion of the Earth around the Sun and the nominal solar wind speed (aberration).
Convection Time
The convection time of the solar wind is simply estimated as the distance of the upstream spacecraft from the Earth (or other place) along the (aberrated) Sun-Earth line, divided by the solar wind speed.
Magnetopause Model
The magnetopause shown in the movie is based upon the empirical model of Petrinec and Russell [J. Geophys. Res., 101, 137-152, 1996]. This model depends upon the solar wind dynamic pressure and IMF Bz.
Bow Shock Model
The bow shock shown in the movie is based upon the empirical model of Farris and Russell [J. Geophys. Res., 99, 17681-17689, 1994]. This model depends upon the standoff distance, and ‘bluntness’ of the magnetopause, as well as the solar wind magnetosonic Mach number.
Interpolation Scheme
Basically, at each moment in time, many solar wind ‘front’ positions are calculated. For simplicity, all ‘fronts’ are perpendicular planes to the (aberrated) Sun-Earth line. Then for each ‘front’, entire 3D surfaces of the magnetopause and bow shock are calculated, using the average steady-state empirical models. This means that for a given time step (e.g., 01:00 UT at Earth), several magnetopause surfaces and bow shock surfaces are determined. The 3D surfaces are then cut along a single plane (in the case of the movie, the GSM equatorial plane). The ‘fronts’ then determine the locations where each of the shapes are most appropriate. At present, if one ‘front’ overtakes another, then the boundary shapes pertaining to the overtaken ‘front’ are dropped from the procedure (this may be changed in the future). A linear interpolation between each shape is then performed and displayed. This process is repeated at each subsequent time step, and the resulting images are merged together. In this way, variations observed in the solar wind are manifested as ‘waves’ along the bow shock and magnetopause.
Programs Used
The primary program used is Python.