HELMET STREAMER ANIMATION
THROUGH MAGNETOHYDRODYNAMICS
COMPUTER SIMULATION OUTPUT:
SPACE EARLY WARNING PRE-CURSOR
Bambang Setiahadi
Indonesian National Institute of Aeronautics and Space (LAPAN)
[email protected]
; [email protected]
INTRODUCTION
One of the most exciting phenomena on the solar surface is the formation of solar coronal helmet streamer. Many researches addressed to know physical processes and tried to relate directly or indirectly with the CHS formation. Including how the CHS attains equilibrium in highly dynamical solar corona. Other study is addressed to the impact in deep interplanetary space, planetary magnetosphere and planetary atmosphere.
Intuitive approach of the CHS formation relates the lower solar coronal activity, especially evolution of solar active region or SAR. The SAR is assumed as resulted from lower solar activity in photospheric level. In turn the photospheric activity is reflection of solar dynamo general energy transfer. The dynamo generates magnetic fields and global systematic plasma flow.
Computation all of the above aspects are of course difficult and timely tasks. Therefore we
assume a computational lower boundary is put on upper photospheric level. Evolution of active region is inferred by simulate magnetic fields penetration into lower boundary as a result of magnetic activity and energy transfer from lower SAR. The penetration is convey in relatively slow speed transfer to simulate slow energy build-up in SAR.
We hope this work may initiate interest in developing a research of how a CHS become unstable to initiate CME. This process probably might initiate the so-called solar storm and initiate solar early warning researcher to deal with. The loop-CME is important to study since it probably has huge plasma kinetic energy and magnetic energy. When interact the planetary boundary layer (PBL) it may change MHD balance to all basic physical parameter in PBL.
SAR EVOLUTION
radiative transfer modes until it reaches plasma opacities and the energy transfers change its modes to convective energy transfer. Solar upper layer which predominantly overwhelm with convective energy transfer is called solar convective layer. The photospheric layer is the upper most level of the convective layers.
The magnetic fields exposed on the photospheric level are viewed as result of general solar magnetohydrodynamo processes in the over-all convective layer from 20,000 km down below the photosphere, to upper photospheric surface (Setiahadi, 2008a, 2008b). Energy is flown gradually to upper layers in years time scale. The 11.0 years cycle show us that the energy releases escape periodically and hence number of CHS in the solar corona exhibit roughly the same period.
The photosphere is plasma pressure dominated region such that the magnetic fields evolution are controlled by plasma motion in convective layer and photosphere. In some phases the magnetic fields will occasionally gather in smaller region and become strong enough to slowdown random walk of free electrons and hydrogen atoms.
Temperature will decrease from 6,000 K to 4,000 K. Consequently the surface brightness will lower and we may be able to see darker small region. This is what is called the solar sunspot. SAR in sunspot may develop to more complex situations as a sunspot group grow larger and at the same time develop complex magnetic topology.
Figure 1: Sequence of solar coronal helmet streamer formation on both side of the sun on the coronal level observed by SOHO Very
observationally because very weak light.
MHD SIMULATION
The sunspot magnetic fields are very concentrated in relatively small region such that it induces the surrounding region. It may penetrated into chromosphere and into high solar corona. This situation works in the chromosphere and corona because these atmospheres very conductive to plasma and magnetic fields. It is very different with planetary cool and dense atmospheres. In cool atmosphere we have to take into account many non-ideal and complex processes.
As magnetic fields on the photosphere gather to form sunspot the magnetic fields will gradually induced upper solar level. In solar coronal level we may to begin observing a look-fuzzy structure streamer. As the sunspot attains strongest and stable magnetic fields we may observed a more highly-structure streamer that is the CHS. In very initial phase the structure is impossible to access observationally since it glow from coronal free electron through Thompson’s electron scattering processes.
A complete MHD simulation that computes all regions participated to lead the formation of a CHS is extremely difficult and need almost unlimited time work. Therefore we includes lower solar energy or magnetic transfers by assuming lower physical processes as lower physical boundary layers. The magnetic penetration from photospheric level is simulated to enter computational bottom boundary in relatively slow time scale comparable with general photospheric time scale.
At initial the solar corona above sunspot or SAR is filled with weak and disperse global solar magnetic fields and exponentially decreases low density coronal plasma. The magnetic fields topology lies horizontally parallel with the computational boundary.
To anticipate big variations on magnetic fields penetrating speed and plasma flow entering the computational domain we computed basic MHD physical parameters in flow-following concept of magneto-fluid dynamics for solar coronal environment. These lead to expression of basic MHD time dependent partial differential equations as below:
(
)
ρFor practical reasons and computational stability of the code, we express the basic
physical parameters as
ρ
,ρ
VX ,ρ
VY,ρ
VZ,X
B , BY, BZ,
P
, The physical constants todetermine the rate of change in non-ideal processes and inter-conversion among the physical parameters are α, ν, η, and κ. The thermodynamic structure is expressed by usual standard symbol γ. Other symbols are having their usual meaning as magnetic fields (B), plasma density (ρ), pressure (P), velocity (V), and gravitation (G).
Magnetic penetration from SAR is simulated by introducing magnetic boundary time-growth for all magnetic components. The z-component is set constant to mimic electric current moves along neutral sunspot region on photospheric surface parallel to z-component. The equation is equally well with magnetic growth in general sunspot formation. The x- and y-component includes implicitly the sunspot magnetic flux tube geometry.
⎟⎟
Where τ is penetration time-scale from the photospheric level through computational bottom boundary. Careful must be taken to choose computational time-step not larger than
τ.
Figure 3: A sketch interpreted from MHD simulation or animation. The CHS is a consequence sunspot magnetic system in solar active region in coronal level, since the corona is very conductive to the process.
DISCUSSION
From animation it is shown that after magnetic fields penetrates the computational region then in several minutes the CHS will attain dynamical equilibrium. This feature will maintain its equilibrium no matter we prolong computational cycle (Setiahadi, 2009c).
The CHS seems to move other dynamical phase if we introduce essential perturbation along the CHS bottom boundary condition and we enter the next phase that is evolution from CHS to loop-CME (Setiahadi, 2009b). The last phenomenon has severe impact to interplanetary space and warning of the impact is important to consider (Setiahadi, 2009d).
Suggestion to next research is careful investigations on MHD physical processes from CHS which has strong and predominant loop magnetic topology at initial before eruption as the loop-CME. This loop-type CME has great impact on planetary magnetosphere and subsequence atmospheric induced electric fields. The loop structure may be observed indirectly by solar radiograph at Nobeyama Solar Radio Observatory.
REFERENCES
[1]. Setiahadi, B. 2008a, Research on Sunspot Migration due to Global Solar Meridional Plasma Flow, p. 132, Prosiding Seminar Nasional
Sistem & Teknologi Informasi
(SNASTI) 2008, Sekolah Tinggi
Manajemen Informatika & Teknik Komputer Surabaya, Surabaya, 22 Oktober 2008, ISBN: 978-979-89683-31-0
[2]. Setiahadi, B. 2008b, Existence of Solar Dynamo Waves by Mean-Fields
Magnetohydrodynamics, p. 221,
Prosiding Seminar Nasional Matematika, Vol 3 th 2008, Univ
Katolik Parahyangan, Bandung, 6
September 2008, ISSN: 1907-3909 [3]. Setiahadi, B. 2009a, The MHD Equilibrium
Onset of Solar Coronal Helmet
Streamer: Warning of the
Coronal Mass Ejection, p. 116,
Prosiding Seminar Nasional Matematika & Pendidikan
Matematika Tahun 2009,
Universitas Negeri Surabaya (UNESA), Surabaya, 8 Agustus 2009, ISBN: 978-979-028-071-7
[4]. Setiahadi, B. 2009b, Coronal Magnetic Arcade Dis-Equilibrium as the Cause of Solar Coronal Mass Ejection, p. 118, Prosiding Seminar Nasional Matematika, Vol 4 th 2009, Univ
Katolik Parahyangan, Bandung, 5
September 2009, ISSN: 1907-3909 [5]. Setiahadi, B. 2009c, Numerical Scheme for
Non-Linear and Non-LTE MHD Solar Physics and Astrophysics Developed at
LAPAN Watukosek 2009, p. 189,
Prosiding Seminar Nasional Sains dan Pendidikan Sains IV, Univ Kristen Satya Wacana, Salatiga, 13 Juni 2009, ISBN: 978-979-1098-63-9
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