Quoted from: https://ccmc.gsfc.nasa.gov/models/modelinfo.php?model=DBM

Model Description
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.

Model Input

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, r_Sun) is the distance of CME tip in coronagraph image on today's date or arbitrary selected date. Valid values are: 1  r_Sun ≤  R₀ ≤ 214 r_Sun.
• 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°.
• φ_CME (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° < φ_CME < 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 R_target (in astronomical units, AU) and the Earth-target heliocentric angular separation φ_target (in deg). Valid values are: R₀ ≤ R_target ≤ 50 AU and -180° < φ_target < 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 R_target (in astronomical units, AU) and the Earth-target heliocentric angular separation φ_target (in deg). Valid values are: R₀ ≤ R_target ≤ 50 AU and -180° < φ_target < 180°.

Model Output

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 φ_CME 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.

References and relevant publications

• P. J. Cargill. On the Aerodynamic Drag Force Acting on Interplanetary Coronal Mass Ejections. Solar Phys., 221:135-149, May 2004.
• J. A. Davies, R. A. Harrison, C. H. Perry, C. Möstl, N. Lugaz, T. Rollett, C. J. Davis, S. R. Crothers, M. Temmer, C. J. Eyles, and N. P. Savani. A Self-similar Expansion Model for Use in Solar Wind Transient Propagation Studies. Astrophys. J., 750:23, May 2012.
• N. Gopalswamy, A. Lara, R. P. Lepping, M. L. Kaiser, D. Berdichevsky, and O. C. St. Cyr. Interplanetary acceleration of coronal mass ejections. Geophys. Res. Lett., 27:145-148, 2000.
• Y. Leblanc, G. A. Dulk, and J.-L. Bougeret. Tracing the Electron Density from the Corona to 1 au. Solar Phys., 183:165-180, 1998. ISSN 0038-0938.
• N. Lugaz, J. N. Hernandez-Charpak, I. I. Roussev, C. J. Davis, A. Vourlidas, and J. A. Davies. Determining the Azimuthal Properties of Coronal Mass Ejections from Multi-Spacecraft Remote-Sensing Observations with STEREO SECCHI. Astrophys. J., 715:493-499, May 2010.
• C. Möstl and J. A. Davies. Speeds and Arrival Times of Solar Transients Approximated by Self-similar Expanding Circular Fronts. Solar Phys., page 77, April 2012.
• R. Schwenn, A. dal Lago, E. Huttunen, and W. D. Gonzalez. The association of coronal mass ejections with their effects near the Earth. Ann. Geophys., 23:1033-1059, March 2005.
• B. Vršnak. Deceleration of Coronal Mass Ejections. Solar Phys., 202:173-189, August 2001
• B. Vršnak and T. Žic. Transit times of interplanetary coronal mass ejections and the solar wind speed. Astron. Astrophys., 472:937-943, September 2007.
• B. Vršnak, T. Žic, T. V. Falkenberg, C. Möstl, S. Vennerstrom, and D. Vrbanec. The role of aerodynamic drag in propagation of interplanetary coronal mass ejections. Astron. Astrophys., 512:A43, March 2010.
• B. Vršnak, T. Žic, D. Vrbanec, M. Temmer, T. Rollett, C. Möstl, A. Veronig, J. Čalogović, M. Dumbović, S. Lulić, Y.-J. Moon, and A. Shanmugaraju. Propagation of Interplanetary Coronal Mass Ejections: The Drag-Based Model. Solar Phys., 285:295-315, July 2013.
• 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.

Relevant links
Development Site: http://www.geof.unizg.hr/~tzic/dbm.html

Official site: http://oh.geof.unizg.hr/DBM/dbm.php

CCMC Contact(s)
Leila Mays
301-286-1999

Developer Contact(s)
Tomislav Žic