Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

GCRs: Proxy for Space weather

Cosmic rays: a proxy to study
solar transient events
Arun Babu K. P.
iamarunbabu@gmail.com
arun@igeofisica.unam.mx

ICRR Seminars
22 January 2021
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

GCRs: Proxy for Space weather

OutlineIntroduction
Forbush Decrease Models
Relation of FD and Interplanetary MAgnetic field
Interplanetary Magnetic Flux-rope Observation by HAWC

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

GCRs: Proxy for Space weather

OutlineIntroduction
Forbush Decrease Models
Relation of FD and Interplanetary MAgnetic field
Interplanetary Magnetic Flux-rope Observation by HAWC

Arun Babu K.P.

22 January 2021

ICRR

1 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

GCRs: Proxy for Space weather

OutlineIntroduction
Forbush Decrease Models
Relation of FD and Interplanetary MAgnetic field
Interplanetary Magnetic Flux-rope Observation by HAWC

Arun Babu K.P.

22 January 2021

ICRR

1 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

GCRs: Proxy for Space weather

OutlineIntroduction
Forbush Decrease Models
Relation of FD and Interplanetary MAgnetic field
Interplanetary Magnetic Flux-rope Observation by HAWC

Arun Babu K.P.

22 January 2021

ICRR

1 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME
Coronal Mass Ejections (CMEs) are large blobs of (solar) coronal plasma

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME
Coronal Mass Ejections (CMEs) are large blobs of (solar) coronal plasma
CMEs are expelled (together with magnetic fields) and propagate through theinterplanetary medium.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME
Coronal Mass Ejections (CMEs) are large blobs of (solar) coronal plasma
CMEs are expelled (together with magnetic fields) and propagate through theinterplanetary medium.
Sometimes CMEs are directed towards Earth and cause geomagnetic storms.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME
Coronal Mass Ejections (CMEs) are large blobs of (solar) coronal plasma
CMEs are expelled (together with magnetic fields) and propagate through theinterplanetary medium.
Sometimes CMEs are directed towards Earth and cause geomagnetic storms.
We investigate the structure and effects of CMEs using Galactic cosmic rays
(GCRs) as a probe

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME
Coronal Mass Ejections (CMEs) are large blobs of (solar) coronal plasma
CMEs are expelled (together with magnetic fields) and propagate through theinterplanetary medium.
Sometimes CMEs are directed towards Earth and cause geomagnetic storms.
We investigate the structure and effects of CMEs using Galactic cosmic rays
(GCRs) as a probe

Arun Babu K.P.

22 January 2021

ICRR

2 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME, Shock & SheathArun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

CME, Shock & SheathArun Babu K.P.

22 January 2021

ICRR

3 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Sun-Earth connection

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cosmic rays and Solar activity

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cosmic rays and Solar activity

Being a charged particles, GCRs are profoundly affected by the magnetic fields
carried by the solar wind, specially by CME-shock-sheath system.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cosmic rays and Solar activity

Being a charged particles, GCRs are profoundly affected by the magnetic fields
carried by the solar wind, specially by CME-shock-sheath system.
Galactic cosmic rays (GCRs) are a good probe to study the Solar Transient
Events.
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease
Forbush decrease (FD) is a transient decrease in the observed galactic cosmic rayintensity at the Earth.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease
Forbush decrease (FD) is a transient decrease in the observed galactic cosmic rayintensity at the Earth.

Can be due to magnetic field compression of shock (like an umbrella), or low (cosmicray) density magnetic cloud behind it.

Arun Babu K.P.

22 January 2021

ICRR

6 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease
Forbush decrease (FD) is a transient decrease in the observed galactic cosmic rayintensity at the Earth.

Can be due to magnetic field compression of shock (like an umbrella), or low (cosmicray) density magnetic cloud behind it.
FD magnitude is estimated as the difference of GCR intensity at the pre-event time tothat at the minimum of the decrease.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease

Cane, 2000

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease

General (theoretical) view: Forbush decrease due
to propagating, diffusive barrier; i.e, CME-driven
shock”Two-step” Forbush decreases! second step due
to near-earth CME/magnetic cloud.
Some attribute entire Forbush decrease is due tothe magnetic cloud; i.e, it is a manifestation of
the low-density cavity(magnetic cloud) engulfing
the earth.

Cane, 2000

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease

General (theoretical) view: Forbush decrease due
to propagating, diffusive barrier; i.e, CME-driven
shock”Two-step” Forbush decreases! second step due
to near-earth CME/magnetic cloud.
Some attribute entire Forbush decrease is due tothe magnetic cloud; i.e, it is a manifestation of
the low-density cavity(magnetic cloud) engulfing
the earth.

Cane, 2000

Arun Babu K.P.

22 January 2021

ICRR

7 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Forbush decrease

General (theoretical) view: Forbush decrease due
to propagating, diffusive barrier; i.e, CME-driven
shock”Two-step” Forbush decreases! second step due
to near-earth CME/magnetic cloud.
Some attribute entire Forbush decrease is due tothe magnetic cloud; i.e, it is a manifestation of
the low-density cavity(magnetic cloud) engulfing
the earth.

Cane, 2000

Arun Babu K.P.

22 January 2021

ICRR

7 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cut-off Rigidity
Rigidity Rg (volts) ≡ P c/Z e indicates how tightly a cosmic ray proton is tied
to the magnetic field.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cut-off Rigidity
Rigidity Rg (volts) ≡ P c/Z e indicates how tightly a cosmic ray proton is tied
to the magnetic field.
Protons below the cut-off rigidity don’t make it to the top of the atmosphere(to produce a muon shower); they are deflected by the geomagnetic field backinto space.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cut-off Rigidity
Rigidity Rg (volts) ≡ P c/Z e indicates how tightly a cosmic ray proton is tied
to the magnetic field.
Protons below the cut-off rigidity don’t make it to the top of the atmosphere(to produce a muon shower); they are deflected by the geomagnetic field backinto space.
The cut-off rigidity is very dependent on the B field geometry;

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME & Shock
Solar modulation
Forbush Decrease

GCRs: Proxy for Space weather

Cut-off Rigidity
Rigidity Rg (volts) ≡ P c/Z e indicates how tightly a cosmic ray proton is tied
to the magnetic field.
Protons below the cut-off rigidity don’t make it to the top of the atmosphere(to produce a muon shower); they are deflected by the geomagnetic field backinto space.
The cut-off rigidity is very dependent on the B field geometry;

Low (→ 0) for a nearly vertical field,
High (Maximum) for nearly horizontal
field;

i.e., its dependent on the viewing direction (different for East, West, North,South)

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

High-rigidity Forbush decreases: due to CMEs or shocks?
Cosmic ray Forbush decreases are a good proxy to understand the near-Earthstructure of the CME-shock system.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

High-rigidity Forbush decreases: due to CMEs or shocks?
Cosmic ray Forbush decreases are a good proxy to understand the near-Earthstructure of the CME-shock system.
The relative contributions of shocks and coronal mass ejections (CMEs) incausing FDs is a matter of debate.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

High-rigidity Forbush decreases: due to CMEs or shocks?
Cosmic ray Forbush decreases are a good proxy to understand the near-Earthstructure of the CME-shock system.
The relative contributions of shocks and coronal mass ejections (CMEs) incausing FDs is a matter of debate.
We studied the FD events by considering two independant models, and checked
the validity of these models using the FD-magnitude to rigidity spectrum fromGRAPES-3.
12

CME-only cumulative diffusion model
Shock-only model“High-rigidity Forbush decreases: due to CMEs or Shock?”, Arunbabu et al., 2013,
Astronomy & Astrophysics, 555, 139

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Located at Ooty, India

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Located at Ooty, India
11.4O N, 76.7O E, at an altitude of 2200 m.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Located at Ooty, India
11.4O N, 76.7O E, at an altitude of 2200 m.
3712 propotional counters in 4 muon stations each contain 4 modules

Arun Babu K.P.

22 January 2021

ICRR

10 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Located at Ooty, India
11.4O N, 76.7O E, at an altitude of 2200 m.
3712 propotional counters in 4 muon stations each contain 4 modules
Total area 560 m2 , (Now, expansion is doubling this area)

Arun Babu K.P.

22 January 2021

ICRR

10 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Located at Ooty, India
11.4O N, 76.7O E, at an altitude of 2200 m.
3712 propotional counters in 4 muon stations each contain 4 modules
Total area 560 m2 , (Now, expansion is doubling this area)
Cut-off rigidty 15-23.5 GV.
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Arun Babu K.P.

22 January 2021

ICRR

11 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

GRAPES-3 tracking muon telescope

Arun Babu K.P.

22 January 2021

ICRR

11 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

The CME-only model: cumulative diffusion

High energy galactic (not of solar origin) cosmic rays progressively diffuse into
the expanding, propagating CME bubble, across the B fields bounding it.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

The CME-only model: cumulative diffusion

High energy galactic (not of solar origin) cosmic rays progressively diffuse into
the expanding, propagating CME bubble, across the B fields bounding it.
At the earth, the density contrast between the CME interior & outside (in highenergy CR protons) is manifested as the Forbush decrease.
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

The CME-only model: details
CME-only model
Flux of protons entering CME is
F (cm−2 s−1 ) = D⊥ (ρ , σ 2 )Arun Babu K.P.

22 January 2021

∂Na
∂r

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

The CME-only model: details
CME-only model
Flux of protons entering CME is
F (cm−2 s−1 ) = D⊥ (ρ , σ 2 )

∂Na
∂r

where
We used a TWO step velocity profile, first from observation in LASCO field ofview, second we assume that CME dynamics are governed exclusively by the
aerodynamic drag it experiences due to momentum coupling with the ambient
solar wind.
We assumed the density gradient, which are broadly consistent with observation, (De Simone et al., 2011)

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

CME-only Model: cumulative diffusion
FD magnitudeNa − NiδN≡NaNa
R T L(t)R(t)D⊥
2 0 κ(t)R 0.33 dt
L≡ 1−
R(T )2 L(T )M ≡Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

CME-only Model: cumulative diffusion
FD magnitudeNa − NiδN≡NaNa
R T L(t)R(t)D⊥
2 0 κ(t)R 0.33 dt
L≡ 1−
R(T )2 L(T )

M ≡

M
D⊥
R
L
RL

:
:
:
:
:

predicted FD magnitudediffusion coefficient ⊥ large scale B field
MC radius
MC length (into sky plane)
Larmor radius

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

The shock-only model (following Wibberenz et al 1998)

The Forbush decrease is due to the shock - a propagating, diffusive barrier. The B
field enhancement at the shock acts as an “umbrella” against galactic cosmic rays.

FD magnitude
M≡

Arun Babu K.P.

Ua − Ushock∆U
Vsw Lshock
=
=
Ua
Ua
D⊥ a

22 January 2021



D⊥ a
D⊥

ICRR


−
1
shock

15 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

24 November 2001

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

24 November 20012
σ 2 ≡ hBturb/B02 iFor CME-only (cumulative diffusion) model, σmc = 28 %,while for shock-only model, σshock = 400 %.
Typical quiet sun turbulence level: σ ≈ 6–15 % (Spangler 2002, Bavassano & Bruno 1995).

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

24 November 20012
σ 2 ≡ hBturb/B02 iFor CME-only (cumulative diffusion) model, σmc = 28 %,while for shock-only model, σshock = 400 %.
Typical quiet sun turbulence level: σ ≈ 6–15 % (Spangler 2002, Bavassano & Bruno 1995).
Forbush decrease due to cumulative diffusion of protons into the CME through the
turbulent sheath is a more reasonable picture
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

CME-only model
Shock only Model
Results

GCRs: Proxy for Space weather

Results

Event
11 April 2001
17 August 2001
24 November 2001
7 September 2002
20 November 2003
26 July 2004

CME-only model
σmc
9.4 %
13 %
28 %
13%
6.7 %
46 %

shock-only modelσshock
100 %
180 %
400 %
100%
400 %
200 %

FDs involving protons of rigidities ranging from 14 to 24 GV, the CME-only model is a
viable one, while the shock-only model is not.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

How are FDs related with IP mag-field enhancements?
Correlation between FD profile and interplanetary magnetic field enhancement:
understanding cross-field diffusion”How are Forbush decreases related with IP magnetic field enhancements ?”, K.P.
Arunbabu et. al., 2015, Astronomy & Astrophysics, 580, 41

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Forbush decrease & IP magnetic field
The shapes of FD profile and IP magnetic field compression are remarkably similar.

The FD looks like a lagged copy of the B field compression.

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

IP Magnetic fields

Btotal , scalar magnetic field

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

IP Magnetic fields

Btotal , scalar magnetic field
Bx , is the magnetic field in the Sun-Earth line in the ecliptic plane and pointing
towards Sun

Arun Babu K.P.

22 January 2021

ICRR

20 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

IP Magnetic fields

Btotal , scalar magnetic field
Bx , is the magnetic field in the Sun-Earth line in the ecliptic plane and pointing
towards Sun
Bz , is the magnetic field parallel to the ecliptic north pole

Arun Babu K.P.

22 January 2021

ICRR

20 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

IP Magnetic fields

Btotal , scalar magnetic field
Bx , is the magnetic field in the Sun-Earth line in the ecliptic plane and pointing
towards Sun
Bz , is the magnetic field parallel to the ecliptic north pole
By , is the magnetic field in the ecliptic plane pointing towards dusk (opposite
the Earth’s motion)
Arun Babu K.P.

22 January 2021

ICRR

20 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

IP Magnetic fields

Btotal , scalar magnetic field
Bx , is the magnetic field in the Sun-Earth line in the ecliptic plane and pointing
towards Sun
Bz , is the magnetic field parallel to the ecliptic north pole
By , is the magnetic field in the ecliptic plane pointing towards dusk (opposite
the Earth’s motion)B⊥ = (B2y + B2z )0.5 , perpendicular magnetic field.
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Correlation of FD magnitude with B

Dir
NW
N
NE
W
V
E
SW
S
SE
Arun Babu K.P.

Corr. with Btot
0.682874
0.692284
0.710686
0.687189
0.690613
0.677899
0.674214
0.662859
0.628104

22 January 2021

Corr. with B⊥
0.682926
0.689747
0.706913
0.684261
0.683616
0.672830
0.669421
0.656359
0.622673
ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

B-field compression and Turbulence
B-Field Compression

Arun Babu K.P.

22 January 2021

2
Turbulence Level σ 2 ≡ hBturb/B02 i

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

B-field compression and Turbulence
B-Field Compression

2
Turbulence Level σ 2 ≡ hBturb/B02 iEnhancement of magnetic field compression responsible for the FD is in fact theshock sheath: the region between the shock and the magnetic cloud.

Arun Babu K.P.

22 January 2021

ICRR

22 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

B-field compression and Turbulence
B-Field Compression

2
Turbulence Level σ 2 ≡ hBturb/B02 iEnhancement of magnetic field compression responsible for the FD is in fact theshock sheath: the region between the shock and the magnetic cloud.
The turbulence level is also enhanced in the shock sheath.

Arun Babu K.P.

22 January 2021

ICRR

22 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

The FD profile is very similar to the B field compression!

Arun Babu K.P.

22 January 2021

ICRR

23 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

The FD profile is very similar to the B field compression!

Arun Babu K.P.

22 January 2021

ICRR

23 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

The FD profile is very similar to the B field compression!

Arun Babu K.P.

22 January 2021

ICRR

23 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.

Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.
The lag between the IP mag. field compression and the FD profile can be
attributed to (turbulent) cross-field diffusion of protons through the B fieldcompression.

Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.
The lag between the IP mag. field compression and the FD profile can be
attributed to (turbulent) cross-field diffusion of protons through the B fieldcompression.
We calculated the No. of diff. required to address this lag

Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.
The lag between the IP mag. field compression and the FD profile can be
attributed to (turbulent) cross-field diffusion of protons through the B fieldcompression.
We calculated the No. of diff. required to address this lag

Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.
The lag between the IP mag. field compression and the FD profile can be
attributed to (turbulent) cross-field diffusion of protons through the B fieldcompression.
We calculated the No. of diff. required to address this lag

The FD profile correlates well with the IP magnetic field enhancement profile.

Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

Corr. FD mag with Bmax
Magnetic field compression
Corr. of FD profile with B

GCRs: Proxy for Space weather

Cross-field diffusion
We consider the (local) diffusion of high energy protons through the large scale
B field compression.
The lag between the IP mag. field compression and the FD profile can be
attributed to (turbulent) cross-field diffusion of protons through the B fieldcompression.
We calculated the No. of diff. required to address this lag

The FD profile correlates well with the IP magnetic field enhancement profile.
The observed lag between the FD and the IP magnetic field compression ≈ few
tens to few hundred diffusion times.
Arun Babu K.P.

22 January 2021

ICRR

24 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

MFR observation by HAWC
Identification of a magnetic flux-rope, first time using a ground based observatory”Interplanetary Magnetic Flux Rope Observed at Ground Level by HAWC”, S.
Akiyama et al., 2020 The Astrophysical Journal, 905, 73

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

HAWC

Located on a plateau between Sierra Negra & Pico de Orizaba volcanoes in
MexicoArun Babu K.P.

22 January 2021

ICRR

26 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

HAWC

Located on a plateau between Sierra Negra & Pico de Orizaba volcanoes in
Mexico18O 590 41”N, 97O 180 30”W, at an altitude of 4100 m.

Arun Babu K.P.

22 January 2021

ICRR

26 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

HAWC

Located on a plateau between Sierra Negra & Pico de Orizaba volcanoes in
Mexico18O 590 41”N, 97O 180 30”W, at an altitude of 4100 m.
300 Water Cherenkov detectors, Each of them 7.3 m diamter and 4.5 m deep.

Arun Babu K.P.

22 January 2021

ICRR

26 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

HAWC

Located on a plateau between Sierra Negra & Pico de Orizaba volcanoes in
Mexico18O 590 41”N, 97O 180 30”W, at an altitude of 4100 m.
300 Water Cherenkov detectors, Each of them 7.3 m diamter and 4.5 m deep.
Span over 22000 m2 area.
Arun Babu K.P.

22 January 2021

ICRR

26 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC scaler system

4 PMTs, 10” PMT at center and 8” at equilateral triangle of side 3.2 m.

Arun Babu K.P.

22 January 2021

ICRR

27 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC scaler system

4 PMTs, 10” PMT at center and 8” at equilateral triangle of side 3.2 m.
TDC DAQ counts hits in a time window of 30 ns for each PMT

Arun Babu K.P.

22 January 2021

ICRR

27 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC scaler system

4 PMTs, 10” PMT at center and 8” at equilateral triangle of side 3.2 m.
TDC DAQ counts hits in a time window of 30 ns for each PMTSingle PMT rate and multiplicity M2, M3, M4 are recorded.

Arun Babu K.P.

22 January 2021

ICRR

27 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC scaler system

4 PMTs, 10” PMT at center and 8” at equilateral triangle of side 3.2 m.
TDC DAQ counts hits in a time window of 30 ns for each PMTSingle PMT rate and multiplicity M2, M3, M4 are recorded.
Cut-off rigidity 8GV and median rigidity 40-46 GV.

Arun Babu K.P.

22 January 2021

ICRR

27 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC scaler system

4 PMTs, 10” PMT at center and 8” at equilateral triangle of side 3.2 m.
TDC DAQ counts hits in a time window of 30 ns for each PMTSingle PMT rate and multiplicity M2, M3, M4 are recorded.
Cut-off rigidity 8GV and median rigidity 40-46 GV.
Can measure GCR intensity with accuracy < 0.01% for every minute.
Arun Babu K.P.

22 January 2021

ICRR

27 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Solar modulations

The GCR intensity can be considered to be in quasi-equilibrium, hence thesource term S and rate of change of the GCR density ∂ncan be ignored.
∂t

Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Solar modulations

The GCR intensity can be considered to be in quasi-equilibrium, hence thesource term S and rate of change of the GCR density ∂ncan be ignored.
∂t
By numerically solving the Fokker-Planck equation, it was shown that effect of
the adiabatic cooling becomes very small at rigidities > 10 GV . Thus, the∂nadiabatic term 31 (∇.VSW ) ∂ln
can also be ignored.
P

Arun Babu K.P.

22 January 2021

ICRR

28 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Solar modulations

The GCR intensity can be considered to be in quasi-equilibrium, hence thesource term S and rate of change of the GCR density ∂ncan be ignored.
∂t
By numerically solving the Fokker-Planck equation, it was shown that effect of
the adiabatic cooling becomes very small at rigidities > 10 GV . Thus, the∂nadiabatic term 31 (∇.VSW ) ∂ln
can also be ignored.
P
The lowest-order approximation of the transport equation is the
diffusion-convection framework.

Arun Babu K.P.

22 January 2021

ICRR

28 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Solar modulations

The GCR intensity can be considered to be in quasi-equilibrium, hence thesource term S and rate of change of the GCR density ∂ncan be ignored.
∂t
By numerically solving the Fokker-Planck equation, it was shown that effect of
the adiabatic cooling becomes very small at rigidities > 10 GV . Thus, the∂nadiabatic term 31 (∇.VSW ) ∂ln
can also be ignored.
P
The lowest-order approximation of the transport equation is the
diffusion-convection framework.
This inward diffusive flux is countered by an outward convective flux,
Vn - κ dn=0
dr

Arun Babu K.P.

22 January 2021

ICRR

28 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Solar modulations

The GCR intensity can be considered to be in quasi-equilibrium, hence thesource term S and rate of change of the GCR density ∂ncan be ignored.
∂t
By numerically solving the Fokker-Planck equation, it was shown that effect of
the adiabatic cooling becomes very small at rigidities > 10 GV . Thus, the∂nadiabatic term 31 (∇.VSW ) ∂ln
can also be ignored.
P
The lowest-order approximation of the transport equation is the
diffusion-convection framework.
This inward diffusive flux is countered by an outward convective flux,
Vn - κ dn=0dr
where κ depends on magnetic field B, turbulence level and rigidity of particle.
Our observations will have modulation effects, due to variation in velocity V andmagnetic field B
Arun Babu K.P.

22 January 2021

ICRR

28 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC Scaler Rate

Arun Babu K.P.

22 January 2021

ICRR

29 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

TDC Scaler Rate-Local

Arun Babu K.P.

22 January 2021

ICRR

30 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Significance of Event in HAWC observation

Arun Babu K.P.

22 January 2021

ICRR

31 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Significance of Event in HAWC observation

TDC-Scaler
R1
M2
M3
M4
Arun Babu K.P.

σ(%)
9.18 × 10−03
1.46 × 10−02
1.60 × 10−02
2.72 × 10−02

Magnitude of Peak 1(%)
in terms of σ
0.712277.6
0.756251.8
0.723545.2
0.669024.6

22 January 2021

Magnitude of Peak 2(%)
in terms of σ
0.776184.6
0.784353.7
0.794049.7
0.757027.8

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

First thought

But this event was not due to these analogy

Arun Babu K.P.

22 January 2021

ICRR

31 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

CME transport
Using a 2D hydrodynamic code we are able to reproduce the speed and density SW
profiles observed at 1AU before, during and after the passage of the ICMEIn this particular event the CME/magnetic-cloud/flux-rope was not perturbed by other
SW structures in the interplanetary medium
Arun Babu K.P.

22 January 2021

ICRR

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Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Effects on magnetosphere

Arun Babu K.P.

22 January 2021

ICRR

33 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Effects on magnetosphere

Also time of event was not correlating with the magnetosphere disturbances.
Arun Babu K.P.

22 January 2021

ICRR

33 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

What can be the cause?

Arun Babu K.P.

22 January 2021

ICRR

34 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Flux-rope

We fitted the fluxrope model in circular cylindrical coordinate system(Nieves-Chinchilla et al. 2019)

Arun Babu K.P.

22 January 2021

ICRR

35 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Flux-rope

We fitted the fluxrope model in circular cylindrical coordinate system(Nieves-Chinchilla et al. 2019)
h
2 i
B0
Br = 0,
By = By0 1 − Rr,
Bφ = −H |C y | Rr ,10

Arun Babu K.P.

22 January 2021

ICRR

35 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Flux-rope

We fitted the fluxrope model in circular cylindrical coordinate system(Nieves-Chinchilla et al. 2019)
h
2 i
B0
Br = 0,
By = By0 1 − Rr,
Bφ = −H |C y | Rr ,10

MFR was having an axis orientation of longitude φ = 99O and latitude
θ = −21O .
Arun Babu K.P.

22 January 2021

ICRR

35 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Flux-rope

We fitted the fluxrope model in circular cylindrical coordinate system(Nieves-Chinchilla et al. 2019)
h
2 i
B0
Br = 0,
By = By0 1 − Rr,
Bφ = −H |C y | Rr ,10

MFR was having an axis orientation of longitude φ = 99O and latitude
θ = −21O .
Radius of fluxrope were 0.146 AU.
Arun Babu K.P.

22 January 2021

ICRR

35 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Validating GCR guiding

Arun Babu K.P.

22 January 2021

ICRR

36 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Validating GCR guiding

Low turbulene level make it feasible for Lorentz acceleration.

Arun Babu K.P.

22 January 2021

ICRR

36 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Validating GCR guiding

Low turbulene level make it feasible for Lorentz acceleration.
Larmor radius and diffusion length are << than size of MFR

Arun Babu K.P.

22 January 2021

ICRR

36 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.
Accelerations were estimated using Lorentz force

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.
Accelerations were estimated using Lorentz force
Relativistic converson were used into particle frame.

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.
Accelerations were estimated using Lorentz force
Relativistic converson were used into particle frame.
Inside MFR its position and velocity were estimated in every 100 m travel.

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.
Accelerations were estimated using Lorentz force
Relativistic converson were used into particle frame.
Inside MFR its position and velocity were estimated in every 100 m travel.
We chose only particle that travel significant distance along axial direction

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Simulation of Particle Trajectory
We used Cordinate system with origin at MFR center.
It can be obtained from GSE by rotation RZ by θ and RY by φ.
Then assumed the MFR have cylindrical crosssection
Field inside MFR were modelled using observations at 1 AU.
Accelerations were estimated using Lorentz force
Relativistic converson were used into particle frame.
Inside MFR its position and velocity were estimated in every 100 m travel.
We chose only particle that travel significant distance along axial direction

Arun Babu K.P.

22 January 2021

ICRR

37 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

GCR guiding

Arun Babu K.P.

22 January 2021

ICRR

38 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

GCR guiding- Crossection view

Arun Babu K.P.

22 January 2021

ICRR

39 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Coupling to HAWC direction
Assymtotic direction of HAWC, Estimated using IGRF12, and backtracing method.
Spacecraft paths on Oct 13 2016
80
80 N
70
60 N

60

50

20 N

0

40

ACOA-HAWC
20 S

40 S

60 S

30

AATB
PTFM
ATHN
TSMB
CALM
MXCO
HAWC

GOES-15
THEM-E
MMS-1
THEM-C

Rigidity [GV] for ACOA-HAWC

40 N

20

10
80 S
0
150 W

100 W

50 W

Arun Babu K.P.

0

50 E

100 E

150 E

22 January 2021

ICRR

40 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Coupling to HAWC direction
Assymtotic direction of HAWC, Estimated using IGRF12, and backtracing method.
Spacecraft paths on Oct 13 2016
80
80 N
70
60 N

60

50

20 N

0

40

ACOA-HAWC
20 S

40 S

60 S

30

AATB
PTFM
ATHN
TSMB
CALM
MXCO
HAWC

GOES-15
THEM-E
MMS-1
THEM-C

Rigidity [GV] for ACOA-HAWC

40 N

20

10
80 S
0
150 W

100 W

50 W

0

50 E

100 E

150 E

cos(Λ) =~N̂ · B.
|B|

Λ is the angle between assymtotic direction and the interplanetary magnetic field.

Arun Babu K.P.

22 January 2021

ICRR

40 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Other observations
Time difference as a function of geo-longitude of the observed decrease of rates

HAWC rate is scaled down by a factor of 30
Arun Babu K.P.

22 January 2021

ICRR

41 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.
The MFR was with perfect magnetic topology and low density cavity, because ofwhich the ram-pressure was lower than ambient solar wind.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.
The MFR was with perfect magnetic topology and low density cavity, because ofwhich the ram-pressure was lower than ambient solar wind.
The GCRs of low GeV energy were trapped inside the MFR and guided throughthe axis.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.
The MFR was with perfect magnetic topology and low density cavity, because ofwhich the ram-pressure was lower than ambient solar wind.
The GCRs of low GeV energy were trapped inside the MFR and guided throughthe axis.
These particle were allowed to enter in to Earth’s atmosphere while it was
passing through MFR.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.
The MFR was with perfect magnetic topology and low density cavity, because ofwhich the ram-pressure was lower than ambient solar wind.
The GCRs of low GeV energy were trapped inside the MFR and guided throughthe axis.
These particle were allowed to enter in to Earth’s atmosphere while it was
passing through MFR.
The first enhancement observed in HAWC was dues to 14-30 GeV protons,
where as second peak was due to 8-12 GeV protons.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

Introduction
Forbush decrease Models
FD & IP mag. field relation
MFR observed by HAWC

HAWC observation
CME & its effects
GCR guiding

GCRs: Proxy for Space weather

Results

The CME was associated with a very weak shock, which does not shield away
the GCRs from getting into the fluxrope.
The MFR was with perfect magnetic topology and low density cavity, because ofwhich the ram-pressure was lower than ambient solar wind.
The GCRs of low GeV energy were trapped inside the MFR and guided throughthe axis.
These particle were allowed to enter in to Earth’s atmosphere while it was
passing through MFR.
The first enhancement observed in HAWC was dues to 14-30 GeV protons,
where as second peak was due to 8-12 GeV protons.
First evidence of particle guiding inside a fluxrope.

Arun Babu K.P.

22 January 2021

ICRR

42 / 43

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