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Solar-Heliospheric Event Ballistic Algorithm (SHEBA) The propagation model used in HELIO

Introduction

HELIO….the HELiophysics Integrated Observatory (HELIO; http://helio-vo.eu) propagation models complicated, but

The Solar-Heliospheric Event Ballistic Algorithm (SHEBA) is the first propagation model used in HELIO. This propagation model is based in a simple ballistic propagation applied to three different scenarios, providing expected time ranges of arrival for the different objects (planets and/or spacecraft). It also allows to back-propagate, i.e. obtain the starting time and location by giving the object and the time of impact of the event under study.

This document explains how this tool works, how to use it through the web interface, and, finally, how the model is implemented. It is important to know how the implementation is done, knowing so, the user will have a better understanding of the why certain results are different of expected.

How it works.

SHEBA is based on a simple 3D (radius, longitude and time) ballistic model, where it uses constant velocity for cells of matter that moves uniformaly on a radial direction. However, in order to time-delayes serched, each scenario requieres different approach.

SHEBA is able to model three different events, in both direction (forward and backward). They are coronal mass ejections (CMEs), solar energetic particles (SEP) and co-rotate interaction regions (CIR). Them all use the same principle, i.e. a simple ballistic propagation model, or also known as Parker’s spiral \citep{Parker1956}.

Coronal mass ejection

SHEBA considers the CMEs as blobs of plasma of infinitesimal radial width, that expands radially at a constant velocity, i.e. the longitudinal width is kept constant. SHEBA calculates an estimated time of arrival to each of the objects that are in the way of the CME, with SHEBA will provide a estimated time range of impact to the different objects in the heliosphere. In order to calculate this the user needs to input the starting position in the sun, the longitudinal width of the CME, and the speed at which it moves (with an error). SHEBA then will calculate whether any object is hit and when this would occur. Notice that dragging and solar wind effects are not taking into account. In the case of back propagation, the object chosen as hit is consider as being in the center of the CME. An example of how to use it is shown in the next section.

SEP

CIR

How to use it.

SHEBA does a simple balistic propagation which relies on what the user chooses. Some of the parameters can be taken from an observed event, others are completely free to the user to select the most appropriate. Some examples of how to choose the parameters after an observed event are shown below.

CME

CMEs are produced from flares, and there is many catalogues that show where and when they occurred. From these catalogues we can get the first two parameters asked: starting time and longitude (in heliographic coordinates). The other parameters are the speed and the longitudinal width. We can get some estimation of those from any of the CME catalogues available (LASCO CDAW, CaCTus). The user must know that those catalogues are made from plane of the sky observations, thus the speed provided is a projected velocity, but can be used as a first approximation. Finally, SHEBA needs a width to find the objects hit by the CME. This width is not provided anywhere, therefore is up to the user to choose one. Notice that the CME catalogues provide a PA_width. This width refers to the angular widht of the CME projected on the plane observed. Though it can be used as a first approximation, it is not the same. This will run the simple ballistic propagation and will provide the time range where the CME is expected to arrive for the different objects (planets and spacecraft) in the heliosphere. Those times intervals can be used then to find whether the CME has been detected by any in-situ instrument.

The backward propagation finds when and where a CME was originated if it has produced a direct hit with the planet (or spacecraft). Then the model proceed as before to run with those values as inputs of the forward model. In this case, the user could get the velocity and time of any of the in-situ instruments, this is enough to get the position of where the flare it happened, however, it also asks for a width to run the forward model as explained before. So, the user would be able to get, besides the origin, which other instruments, and when, the CME should be observed.

How it is implemented.

SHEBA is implemented in IDL, and it relies in some routing of sswidl, and of HELIO package in particular. On the following sections is described how the different routines work.

Charla SHEBA

charla de sheba explicando lo que detallo aqui

Charla de HFE =>

uso solo, in steps, why do we have a data cart, what we can pass

for the HFE:

CME

longitude: Heliographic longitude in degrees (e.g., the position of a flare) width: Longitudinal width of the CME in degrees speed: CME speed in km/s speed error:error in the speed in km/s

CME backward

width: Longitudinal width of the CME in degrees ( I would put this one as the last parameter) Object: This is fine speed: CME speed in km/s speed error:error in the speed in km/s

SW (or better CIR)

Longitude: Heliographic longitude in degrees (e.g., the most-west edge of a Coronal hole) Speed: The speed of the Solar Wind in km/s speed error:error in the speed of the solar wind in km/s

CIR backward

Object: As in CME Speed: The speed of the Solar Wind in km/s speed error:error in the speed of the solar wind in km/s

SEP

Longitude: Heliographic longitude in degrees (e.g., the position of a flare) Speed: Speed of the ambient solar wind in km/s speed error:error in the speed of the solar wind in km/s beta: fraction of lightspeed.

SEP backward

Object: As in CME speed: Speed of the ambient solar wind in km/s speed error:error in the speed of the solar wind in km/s beta: fraction of lightspeed.

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