Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

D. Arrazola · J.J. Blanco · J. Rodríguez-Pacheco · M.A. Hidalgo

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

OBJECTIVE

This study analyzes changes in the local HCS structure, mostly in terms of its local orientation, using multipoint spacecraft observations.

Our aim is to analyze the role of the solar wind and the magnetic connectivity among the observation points, trying to distinguish if these changes are due to the HCS local shape or to temporal variations.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

HCSHELIOSPHERIC CURRENT SHEET

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Data Analysis

Ascending phase of Cycle 23

ACE - Magnetic Field Experiment (1-s)

Solar Wind Electron, Proton and Alpha Monitor

Wind -

Magnetic Field Instrument (3-s)

Solar Wind Experiment

3D-Plasma and Energetic Particle

Minimum cycle (2007-08)

ACE -

Wind -

Magnetometer MAG (IMPACT) (1-s)

Solar Wind Data (PLASTIC)Twin STEREO

…

…

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Data Analysis. Criteria to identify HCS Crossings

1

2

3

4

Data Analysis. Criteria to identify HCS Crossings

Courtesy of S

olar Wind P

lasma E

lectron Analyzer (S

WE

A) -C

ES

R, U

C B

erkeley-and M

agnetometer (M

AG

) –GS

FC

-IM

PA

CT

Team

.

Courtesy of S

olar Wind E

lectron, Proton and A

lpha Monitor (S

WE

PA

M) –

Los Alam

os National S

ecurity.

Courtesy of S

olar Wind P

lasma E

lectron Analyzer (S

WE

A) -C

ES

R, U

C B

erkeley-and M

agnetometer (M

AG

) –GS

FC

-IM

PA

CT

Team

.

Courtesy of S

olar Wind E

lectron, Proton and A

lpha Monitor (S

WE

PA

M) –

Los Alam

os National S

ecurity.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

January 15, 2007. The change in Bx, By sign is clearly for whole spacecrafts. The electron pitch angle into the red boxes on the right panel. In this period, sunward IMF is connected to the northern solar magnetic hemisphere (Bx < 0 and By > 0) and the anti-sunward IMF to the southern hemisphere. Before crossing, IMF moves sunward in all spacecrafts.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Data Analysis.

HCS local orientation determination

• MVA presumes the one-dimensional nature of the current sheet and uses Gauss law to require that the projection of B along a to-be-determined direction n should be constant. Its purpose is to find an estimator of the normal direction (Sonnerup, 1998). This method is used to calculate the orientation of a discontinuity and consist in solve the real symmetric matrix of covariance.

• CVA technique uses (Scudder, 2005), like MVA, the covariance matrix, but unlike it, uses the maximum eigenvalue to find a normal vector to the coplanarity plane of the current sheet.

• HYTARO method is based on a local magnetic topology (Blanco et al., 2003). as a starting point that let us to apply only two consecutive rotations once the field orientation is defined from a constant initial magnetic field (B0). This method is going to be used to calculate time crossing of each event analyzed.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Data Analysis. Compare observations

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Data Analysis.

The evolution of the HCS local orientation and the magnetic connection among the different observation sites have been evaluated.

Elapsed time (tel) and expected time (tex) have been compared. The magnetic connection parameter (C) is a rough estimation of connection between two observation points.

ex

exel

t

ttC

Higher values of C parameter imply worse connections.

Relation between the LOCAL ORIENTATION and the MAGNETIC CONNECTION

The local orientation of the HCS will be similar from one to another satellite when the spacecraft are well connected

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

HCS crossing (15-01-2007 )The vertical lines marks the reversal times and the continuous lines represented the HYTARO results for the data interval used. The horizontal segments ended in arrows show the elapsed times.

On 15 January the HCS was observed by the four spacecraft before a SIR arrival. No large variations in the HCS local variation were observed. Poor magnetic connection from the observed elapsed and expected time a different HCS region was observed.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

HCS Crossings as observed by ACE and Wind

(Ascending phase of the Solar cycle)

Mean angle ranges: from 4º to 62ºMean angle shows a rising trend when the distance between spacecraft increases.

With the elapsed time, this trend is not so clear.

With magnetic connection (C), the same trend is observed.ex

exel

t

ttC

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

HCS Crossings as observed by ACE, Wind and Twin STEREO

(Solar minimum)

Mean angle shows a rising trend up to 5000RE. This trend changes at larger distances.

When the C parameter becomes worse, the angle shows a growing trend.

At distances larger than 5000 RE, the local HCS orientation has an evolution related to: • a continuous interaction with the solar wind• a worse magnetic connection.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

Conclusions

During the ascending solar cycle phase:

• The interaction between the HCS and the solar wind is very effective according to the observed poor magnetic connectivity.

During minimum solar cycle:

• Results show a growing trend between the variation of the HCS local inclination and spacecraft distances up to 5000 RE (<10 hours). For larger distances the results show a decreasing trend.

Summary:

• The spatial variation in the HCS local shape is in the range of hundreds of RE.

• The poor magnetic connection (C) observed is due to an effective interaction between the solar wind and the HCS.