The Drag-Based Model (DBM) tool provides prediction of the interplanetary coronal mass ejection (ICME) expansion and its prediction of arrival at arbitrary location (or preselected planet or satellite) in the ecliptic plane. The calculation is based on the assumption that the dominant magnetohydrodynamical force exerted upon ICME in interplanetary space is equivalent to the aerodynamic drag (for details see Vršnak et al., 2013, and references therein). The model is based on the additional assumption that the background solar wind is approximately stationary and isotropic, where its speed w is always constant (Vršnak et al., 2007). In that case, immediately follows that the drag-parameter γ is constant as well. Finally, for a given set of input parameters the model provides the ICME Sun-"target" transit time, the arrival time, and the impact speed (Vršnak et al., 2007).
The web-tool is divided into the basic and advanced form. The purpose of the basic form is to predict the radial heliocentric ICME propagation, the arrival time at and the impact speed on preselected "target" in the ecliptic plane (the position R(t) and velocity v(t) in time plots are coupled together with the numeric results). Additionally, the advanced form of DBM produces the similar output for the selected target in the ecliptic plane, however the shape of ICME is taken into account and employed to, so-called, the cone-geometry (see example in Appendix of Žic et al., 2015).
In this option the CME geometry is preserved and the CME propagates in self-similar manner, i.e. the CME leading edge expands proportionally with the radial distance.
The basic form requires input values, such as (see the input list below): CME take-off date and time; value of the drag parameter, γ; value of the solar wind speed, w; the starting radial distance and speed of the CME (R0 and v0, respectively); the target (or manually entered distance of the target). The values of γ and w are kept constant during CME propagation.
The advanced form additionally requires (see italic rows in the input list below): the CME angular half-width, λ, and the source region central meridian distance, φ (i.e. the starting direction of the CME in ecliptic plane).
The complete input list consists of parameters:
- CME take-off date: The date of CME take-off (when CME tip is located at radial distance R0)
- CME take-off time: The time of CME take-off in UTC (when CME tip is located at radial distance R0).
- γ: The constant drag-parameter value γ (in ×10-7 km-1). The valid values for the drag parameter are in between: 0.1 ≤ γ ≤ 100.
- w: The constant solar wind speed w (in km/s) could be determined by expected solar wind speed at 1 AU. The valid values for solar wind speed are in between: 200 km/s ≤ w ≤ 800 km/s.
- R0: Starting radial distance of CME (in solar radii units, rSun) is the distance of CME tip in coronagraph image on today's date or arbitrary selected date. Valid values are: 1 rSun ≤ R0 ≤ 214 rSun.
- v0: The speed v0 = v(R0) in km/s is the speed of CME tip located at R0. Valid values are: 50 km/s ≤ v0 ≤ 5000 km/s.
- λ (advanced): CME's angular half-width λ (in deg) is based on coronagraphic observation. Valid values are: 0° < λ < 90°.
- φCME (advanced): Longitude of source region is CME propagation direction determined on observation of eruptive phenomena on the solar disc at low-heliographic latitudes (in deg). Valid values are: -180° < φCME < 180°.
- Target: The target can be selected from the given list (Mercury, Venus, Earth, Mars, STEREO-A or STEREO-B satellite) or target position could be entered manually, providing the distance Rtarget (in astronomical units, AU) and the Earth-target heliocentric angular separation φtarget (in deg). Valid values are: R0 ≤ Rtarget ≤ 50 AU and -180° < φtarget < 180° . The target can be selected from the given list (Mercury, Venus, Earth, Mars, STEREO-A or STEREO-B satellite) or target position could be entered manually, providing the distance Rtarget (in astronomical units, AU) and the Earth-target heliocentric angular separation φtarget (in deg). Valid values are: R0 ≤ Rtarget ≤ 50 AU and -180° < φtarget < 180°.
The general DBM tool is basically focused on the ICME arrival forecasting to Earth position (Žic et al., 2015, see Appendix), although it can be generally used for the estimation of the ICME propagation in the complete ecliptic plane. Therefore, from the input values the basic option calculates: the date and time of the CME arrival at preselected (or entered) target position, transit time (i.e. the ICME travel-time to target position) and the ICME impact speed on preselected target. Furthermore, the heliocentric R(t) and v(t) plots are created from the DBM calculation.
On the other hand, the advanced option, using additional λ and φCME parameters and the cone-geometry, estimates the same ICME impact parameters and the kinematic R(t) and v(t) plots as the basic option, however in addition animates the time-dependent ecliptic ICME expansion in the form of schematic movie.
Limitations and Caveats
Caveats: A constant drag parameter (γ) and constant solar wind speed (w) is used. Model is 2D (ecliptic plane). CME is symmetric.
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- T. Žic: Eruptive processes in the solar corona and their heliospheric propagation. PhD thesis, 2012. Faculty of Science, University of Zagreb. http://www.knjiznica.phy.pmf.unizg.hr/radovi/Download.ashx?file=2574.pdf.
- T. Žic, B. Vršnak, and M. Temmer. Heliospheric Propagation of Coronal Mass Ejections: Drag-Based Model Fitting. Astrophys. J. Supp. 218:32, 2015.
Development Site: http://www.geof.unizg.hr/~tzic/dbm.html
Official site: http://oh.geof.unizg.hr/DBM/dbm.php