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IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
The GRAPES-3 cosmic ray instrument: a space
weather tool
Prasad Subramanian
Indian Institute of Science Education and Research (IISER), Punehttp://www.iiserpune.ac.in
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Introduction
The GRAPES-3 cosmic ray instrument at Ooty (PI: Sunil
Gupta) is a versatile cosmic ray instrument operated by theTIFR
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Introduction
The GRAPES-3 cosmic ray instrument at Ooty (PI: Sunil
Gupta) is a versatile cosmic ray instrument operated by theTIFR
It builds upon the long tradition of TIFR in cosmic rayresearch, and addresses science ranging from cosmic rayacceleration/knee studies and cosmic ray composition todetecting radioactivity in rain water
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Introduction
The GRAPES-3 cosmic ray instrument at Ooty (PI: Sunil
Gupta) is a versatile cosmic ray instrument operated by theTIFR
It builds upon the long tradition of TIFR in cosmic rayresearch, and addresses science ranging from cosmic rayacceleration/knee studies and cosmic ray composition todetecting radioactivity in rain water
The large (560 m2) muon detector makes it among the most
sensitive detectors in the world, capable of detecting changesin cosmic ray proton intensity of ∼ 0.1%
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Introduction
The GRAPES-3 cosmic ray instrument at Ooty (PI: Sunil
Gupta) is a versatile cosmic ray instrument operated by theTIFR
It builds upon the long tradition of TIFR in cosmic rayresearch, and addresses science ranging from cosmic rayacceleration/knee studies and cosmic ray composition todetecting radioactivity in rain water
The large (560 m2) muon detector makes it among the most
sensitive detectors in the world, capable of detecting changesin cosmic ray proton intensity of ∼ 0.1%
This makes it a sensitive space weather instrument
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Overview
It has been recognized for a while (≈ 1930) that solartransients cause changes in the galactic cosmic ray intensitydetected at the Earth
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Overview
It has been recognized for a while (≈ 1930) that solartransients cause changes in the galactic cosmic ray intensitydetected at the Earth
Specifically, magnetic clouds/near-Earth CME manifestationsand their associated shocks are known to cause Forbushdecreases in the galactic cosmic ray intensity.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Overview
It has been recognized for a while (≈ 1930) that solartransients cause changes in the galactic cosmic ray intensitydetected at the Earth
Specifically, magnetic clouds/near-Earth CME manifestationsand their associated shocks are known to cause Forbushdecreases in the galactic cosmic ray intensity.
More interestingly, precursors to Forbush decreases in galacticcosmic rays at the Earth provide advance information aboutparameters of the CME-associated shock, and hence theimpending geomagnetic storm
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FDs are due to near-Earth CME/shock
Shock (magnetic “umbrella” against cosmic rays) + CME (lowdensity cavity)
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Forbush decrease: GRAPES-3 data
Decrease in galactic cosmic ray intensity@Earth (due to largeICME/shock) on Oct 29 2003: data from GRAPES-3, Ooty
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
GRAPES-3 muon detector directional bins
GRAPES-3 can observe in 9 directions/rigidities/energies
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Forbush Decrease studies with GRAPES-3
Conventional wisdom has it that the shock (propagating,diffusive barrier) and the CME (magnetic “bottle”) are bothresponsible for the observed Forbush decrease
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Forbush Decrease studies with GRAPES-3
Conventional wisdom has it that the shock (propagating,diffusive barrier) and the CME (magnetic “bottle”) are bothresponsible for the observed Forbush decrease
At GRAPES-3 energies (≈ 14 – 42 GeV) we have shown(Subramanian et al 2009; Arun Babu, PhD thesis) that therelatively empty magnetic bottle (the CME) is the primarycause of the Forbush decrease.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Forbush Decrease studies with GRAPES-3
Conventional wisdom has it that the shock (propagating,diffusive barrier) and the CME (magnetic “bottle”) are bothresponsible for the observed Forbush decrease
At GRAPES-3 energies (≈ 14 – 42 GeV) we have shown(Subramanian et al 2009; Arun Babu, PhD thesis) that therelatively empty magnetic bottle (the CME) is the primarycause of the Forbush decrease.
We have derived tight constraints on the turbulence level(amplitude) in the vicinity of the CME (sheath region),especially with multi-rigidity data (Arun Babu, PhD thesis).We are also elucidating the role of cross-field diffusion in thepresence of MHD turbulence.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Forbush decrease due to magnetic bottle
CME starts out almost empty (of cosmic rays). Cosmic rays(cross-field) diffuse into it, but its still a depleted (cosmic ray)cavity when it reaches the Earth → Forbush decrease
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: summary
We now propose to work on the precursors to these FDs.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: summary
We now propose to work on the precursors to these FDs.
Use GRAPES-3 data to identify precursor decreases
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: summary
We now propose to work on the precursors to these FDs.
Use GRAPES-3 data to identify precursor decreases
Theoretical understanding of FD precursors in terms of losscone decreases
A thorough understanding of FD precursors will result inpredictive capability (∼ 3 - 4 hours) wrt the strengthof/turbulence level near the shock that is due to hit theEarth’s magnetosphere
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: general understanding
The B field compression near the shock is like a magnetic mirror.Since v⊥ ↑ with B ↑, v‖ can → 0 at the mirror point for energy tobe conserved.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
If v‖/v⊥ ≫ 1 (low pitch angle), the mirror effect is minimal, andthese particles can “leak” through the mirror. This “loss cone” ofparticles can propagate (at speeds ≈ c) ahead of the shock,forming a FD precursor.Cartoon: Nelson Schuch, Brazil
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: physics
Cosmic ray particles undergo resonant pitch angle scatteringwith turbulent irregularities near the shock. This alters theloss cone/precursor characteristics (Ruffolo et al 1999; 2003)
∂F
∂t= −
∂
∂z
[
µ v+
(
1−µ2 v2
c2
)
u
]
F+∂
∂µ
[
φ
2
∂
∂µ
(
1−µu v
c2
)
F
]
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: physics
Cosmic ray particles undergo resonant pitch angle scatteringwith turbulent irregularities near the shock. This alters theloss cone/precursor characteristics (Ruffolo et al 1999; 2003)
∂F
∂t= −
∂
∂z
[
µ v+
(
1−µ2 v2
c2
)
u
]
F+∂
∂µ
[
φ
2
∂
∂µ
(
1−µu v
c2
)
F
]
F : particle distribution function, z : distance from shock, µ:(cosine) pitch angle. So we have pitch angle diffusion due toresonance with turbulent eddies (embodied in the term φ:crucial!)
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: physics
Cosmic ray particles undergo resonant pitch angle scatteringwith turbulent irregularities near the shock. This alters theloss cone/precursor characteristics (Ruffolo et al 1999; 2003)
∂F
∂t= −
∂
∂z
[
µ v+
(
1−µ2 v2
c2
)
u
]
F+∂
∂µ
[
φ
2
∂
∂µ
(
1−µu v
c2
)
F
]
F : particle distribution function, z : distance from shock, µ:(cosine) pitch angle. So we have pitch angle diffusion due toresonance with turbulent eddies (embodied in the term φ:crucial!)
Characteristics of loss cone precursors will yield information onφ → turbulence amplitude, strength of shock
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: lead times
Net effect 1: Loss cone precursors for higher energy cosmicrays generally precede the FD by a longer time (complication:it also depends upon the geometry of the large-scale magneticfield/Parker spiral connecting the observer with the shock)
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: lead times
Net effect 1: Loss cone precursors for higher energy cosmicrays generally precede the FD by a longer time (complication:it also depends upon the geometry of the large-scale magneticfield/Parker spiral connecting the observer with the shock)
Net effect 2: Precursor lead time can also provide informationabout turbulence level near the shock/strength of shock(important!)
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: data analysis
There has been some work in the past on FD precursors(Nagashima et al) and a flurry of recent work from the globalmuon detector network (e.g., Munakata et al 2000; Fushishitaet al 2010; Rockenbach et al 2011)
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: data analysis
There has been some work in the past on FD precursors(Nagashima et al) and a flurry of recent work from the globalmuon detector network (e.g., Munakata et al 2000; Fushishitaet al 2010; Rockenbach et al 2011)
Precursor decreases are generally rather weak; the largecollecting area/unprecedented sensitivity and directionalresolution of the GRAPES-3 muon telescope offers a distinctadvantage.
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: data analysis
There has been some work in the past on FD precursors(Nagashima et al) and a flurry of recent work from the globalmuon detector network (e.g., Munakata et al 2000; Fushishitaet al 2010; Rockenbach et al 2011)
Precursor decreases are generally rather weak; the largecollecting area/unprecedented sensitivity and directionalresolution of the GRAPES-3 muon telescope offers a distinctadvantage.
A first step would be to come up with a robust statisticalidentification of precusors in the existing GRAPES-3 Forbushdecrease database. Non-trivial, for the search involvesdifferent rigidities/energies and directions
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
FD precursors: data analysis
There has been some work in the past on FD precursors(Nagashima et al) and a flurry of recent work from the globalmuon detector network (e.g., Munakata et al 2000; Fushishitaet al 2010; Rockenbach et al 2011)
Precursor decreases are generally rather weak; the largecollecting area/unprecedented sensitivity and directionalresolution of the GRAPES-3 muon telescope offers a distinctadvantage.
A first step would be to come up with a robust statisticalidentification of precusors in the existing GRAPES-3 Forbushdecrease database. Non-trivial, for the search involvesdifferent rigidities/energies and directions
This could enable prediction of impending shock strengths
Subramanian FD precursors
IntroductionOverview
Forbush decreasesForbush Decrease (FD) precursors
FD precursors
Conclusion: FD precursors with GRAPES-3
Forbush decrease precursor data from GRAPES-3 thus offerssignificant promise for diagnostics of turbulence levels nearshocks/shock strengths with lead times of at least a few hours.
The (very) interesting physics apart, it could serve as a effectivespace weather tool.
Thank you for your attention!
Subramanian FD precursors
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