OXYGEN ION ACCELERATION AND CONVECTION IN THE POLAR MAGNETOSPHERE

B. Klecker

for the CLUSTER Team at MPE

G. Paschmann, B. Klecker, M. Förster, H. Vaith, J. Bogdanova, E. Georgescu, S. Haaland, P. Puhl-Quinn

A. Blagau, A. Kis,H. Hasegawa, B. Sonnerup

Presentation at the Fachbeirat MPE 2002June 17 - 20, 2002

OUTLINE

• The CLUSTER Mission and Payload

• The Experiments EDI and CIS

• Ion Convection Measurements: a Tool

– to study spatial and temporal variations

– to study wave signatures

– to derive spatial scales from time series measurements

• Summary

CLUSTER: CORNERSTONE #1 (WITH SOHO) OF ESA‘S SCIENTIFIC PROGRAM AND PART OF ISTP

CLUSTER ORBIT IN FEBRUARY 2001

CLUSTER SEPARATION STRATEGY

Year Mission Phase Sep. (Km)

2001 nominal Cusp 600

2001 nominal Tail 2000

2002 Nominal Cusp 100

2002 Nominal Tail 3810

2003 Extended Cusp 5000

2003 Extended Tail 100-700

2004 Extended Cusp 100-700

2004 Extended Tail 10000

2005 Extended Cusp 10000-20000

2005 Extended Tail 20000

CLUSTER INSTRUMENTATION

CLUSTER OPERATION

THE ELECTRON DRIFT INSTRUMENT (EDI)

Scientific Objectives

Measurement of the ambient electric field by a novel technique developed over the last 20 years:

Emission and subsequent detection of tracer electrons by two sets of electron gun / detector units, positioned at 180° to each other.

THE ELECTRON DRIFT INSTRUMENT (EDI)

For any combination of magnetic field B and drift velocity V, only a single electron trajectory exists that connects each electron gun with the detector located on the opposite side of the S/C.

Technique:

Emission of an electron beam of 1 keV perpendicular to the local magnetic field.

Detection of the electrons with the detector on the opposite side of the S/C.

Measurement of the times-of-flight, T1 T2.

Computation of E from the drift step d, and B

d = Vd Tg ~ E / B2

T1,2 = Tg (1±Vd/Ve)

T1-T2 = 2 (d/Ve)

T1+T2 = 2 Tg = 4 me / e B

EDI: Triangulation and Time-of-Flight Technique

Triangulation Technique

By employing 2 beams and 2 detectors, the two unique directions can be monitored continuously and the displacement d obtained by a triangulation procedure.

Time-of-Flight Technique

When the magnetic field B becomes small, d ~ E/B2 becomes very large and cannot be determined accurately any more with the triangulation technique. Then d can be determined with higher precision from the time-of-flight differences.

T1-T2 = 2 (d/Ve)

EDI DATA PRODUCTS

• Electric field time series

• Vtime series

Time resolution: ≥100 msec, standard 1 sec

Limitations: magnetic field strength, typically B > 15 nTrapid time variations in E or Bsignal to background ratiodata from S/C-1, S/C-2, S/C-3

Note: EDI provides V without any additional assumptions

THE CLUSTER ION SPECTROMETRY INSTRUMENT (CIS)

Scientific Objectives / Instrument Requirements

Determination of the 3D Distribution function of ions in the energy range

~ 0 (S/C-potential) to 40 keV/e with 1 spin (4 sec) time resolution.

Identification of major ions in the near-Earth plasma environment, i.e. of H+, He2+, He+, and O+.

Technical solution to cover large dynamic range and to provide

redundancy: 2 sensors with 2 geometry factors each (factor ~100 )

CIS-1 (CODIF) Composition and Distribution Function Analyzer

On-board analysis provides H+, He2+, He+, and O+.

Ground analysis provides in addition O2+ and O2+

Energy range 0.020 - 40 keV/e + ~ 0 (S/C-potential) - 20 eV with RPA

CIS-2 (HIA) Hot Ion Analyzer

Ion energy range 0.005 - 32 keV/e

CIS-1: Principle of Operation

CIS DATA PRODUCTS

ON-BOARD ANALYSIS

• Moments (N, V, T, P) computed onboard every spin (4 sec) from 3D distributions for H+, He2+, He+, O+

• 3D Distributions of H+, He2+, He+, O+ for ≥ 1 spin -> telemetry

ANALYSIS ON GROUND

• 3D Distributions of H+, He2+, He+, O+ with max. 1 spin resolution.

• Moments (N, V, T, P) computed for selectable energy ranges.

Limitations: Counting statistics

Data from S/C-1, S/C-3, S/C-4

Plasma Drift / Convection: V derived from V and magnetic field B

PLASMA CONVECTION MEASUREMENTS

Measurements with the 4 CLUSTER S/C provide a tool for

the study of

• Spatial and temporal variations

• Spatial scales

• Wave signatures

OBSERVATIONS IN THE DAYSIDE POLAR CAP

SUN

• The velocity distribution of O+ shows a mono-energetic beam with systematic time dispersion.

• For Bz < 0 the energy is systematically decreasing with increasing latitude.

• The convection velocity inferred from the O+ velocity measurement and V as measured directly with EDI are in remarkably good agreement.

• The pole-ward convection is consistent with the 2-cell convection patterns as typically observed in the ionosphere for Bz < 0 .

Typical Signatures of O+ Beams in the CUSP and Polar Cap

Oxygen Beams in the Cusp and Polar Cap

Interpretation

Localized (in latitude) source of accelerated ionospheric ions with broad energy spectrum.

Velocity, V, from super-position of outward particle motion (VII) with pole-ward

convection (V)

This results in an apparently mono-energetic beam as observed on CLUSTER

MULTISPACERAFT OBSERVATIONSCLUSTER CONFIGURATION ON MARCH 4, 2001

MULTISPACECRAFT MEASUREMENTS

a) Energy-time spectrogram of O+.

b) Number density of O+ on S/C 1, 3, 4.

c) V|| of O+ on S/C 1, 3, 4.

d) V of O+ on S/C 1, 3, 4.

Note:

• For separation distances of ~ 600 km the convection velocities are essentially identical on all 3 S/C.

Check for time-lag between different S/C provides length-scale of coherence of convection.

CROSS - CORRELATION: CIS

CIS S/C-3 - S/C-4

Cross-correlation of V as

measured with CIS with 16 s resolution. Maximum correlation is obtained for zero time lag.

CROSS - CORRELATION: EDI

Cross-correlation of V as

measured with EDI with 1 s resolution. Maximum correlation is obtained for zero time lag.

SUMMARY-1

• The convection velocities derived from the O+ moments are in remarkable agreement with the drift velocity measured directly with the EDI experiment onboard CLUSTER. Thus, the combination of CIS and EDI measurements provide a full set of 4 S/C measurements with redundancy (2 x S/C-1, S/C-2, 2 x S/C-3, S/C-4)

• For separation distances of ~ 600 km the convection velocities are essentially identical on all spacecraft. This implies that the observed variations in V are temporal in nature, i.e. due to changes in the

convection pattern probably caused by substorm related activity.

Energy step structures of O+ and H+ ions in the cusp and polar capO+ distribution functions, S/C 1

• At 02:25:20 the O+ distribution function shows a beam-like behavior, at 02:35:40 the distribution function shows high perpendicular heating.

NEXT STEPS

Convected O+ Ions

• Correlate variations in convection velocity with substorm activity.

• Compare the O+ energy dispersion with model calculations (trajectory tracing). This method can be used, together with the information on the convection velocity, to infer the altitude distribution of ion injection and acceleration (e.g. Dubouloz et al., 2001, Bouhram et al., 2002).

• Use the multi-spacecraft measurements to infer the latitude and longitude distribution of ion injection (for larger separation distances).

Perpendicular Heating

• Detailed correlation with wave measurements onboard Cluster

CONVERSION OF TIME SERIES DATA INTO SPATIAL PROFILES AT THE MAGNETOPAUSE

• The 4 MP crossings provide the magnetopause orientation and velocity at discrete instances in time.

• Continuous sensing of the magnetopause velocity is possible with the measurement of the plasma drift velocity made with EDI and CIS. Panel 3: VN, the drift velocity along the MP normal (EDI and CIS).

• Integration of VN defines the distance from the MP to the S/C (Panel 4).

• This distance scale can then be used to convert the time series data into a spatial profile.

STANDIG ULF WAVES IN THE POLAR REGION

• Phase shift between B and V = 90°

STANDING WAVE

• Positive Pointing Flux

Energy Input into Ionosphere

SUN

C1,C2,C4C3

C4

C1

C3

C1

C3

C2

C4

From OVT 16 UT Tsy87, KP=3

XGSM

ZGSM

Ion

Ion

Ion

UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 66.20 73.00 79.90 85.80 89.50 86.30 83.70MLT 12.40 12.50 12.70 12.90 23.40 00.40 00.80

UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 66.80 72.70 78.80 84.30 88.80 88.10 85.10MLT 12.40 12.50 12.60 12.70 12.80 00.90 00.90

UT 15:00 15:30 16:00 16:30 17:00 17:30 18:00ILAT 61.80 64.90 70.70 77.40 83.50 88.40 87.70MLT 12.20 12.30 12.40 12.40 12.30 11.00 01.80

CUSTER-CIS Day 30 - 08 - 2001

STUDY OF TIME VARIATIONS

Cluster C3

Ion

15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)

IMF

SuperDarn

C3

Geotail + 10mn

VcCIS

12

MHD

Cluster C3

Ion

15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)

IMF Geotail + 10min

SuperDarn MHD

C3 12

Summary-2

• Double cusp observed when IMF turned from South to North and dominant IMF-By negative.

• Second cusp observed on CLUSTER-3 is the cusp for Bz>0 that moved poleward.

• CIS and EDI measurements of plasma convection in the polar region can be used to investigate in detail changes of the convection pattern in response to solar wind conditions.

C3 C4,C2,C1

Start of cusp at C4,C2,C1SuperDarnMHD simulation

C4

12 12

Cluster C3

Ion

15:00 15:30 16:00 16:30 17:00 17:30 18:00 Time UT (HH:MM)

IMF

C3

Geotail + 10min

SuperDarn

12

MHD

Cluster C3

Ion

15:00 15:30 16:00 16:30 17:00 17:30 18:00Time UT (HH:MM)

IMF

C3

Geotail + 10min

SuperDarn MHD

12

OBSERVATIONS

• The dayside cusp region of the Earth‘s magnetosphere is known as a major source of ionospheric ions (e.g. Lockwood et al., 1985).

• The study of these ions provides information on energization processes (e.g. transverse ion heating by electrostatic, electromagnetic waves, parallel acceleration by DC electric fields)

•

DMSP-F1516:12 UT

DMSP-F1517:52 UT

15:30

16:18

16:48

Sketch of cusp motion

Bz<0, By<0

Cluster 3CuspCleft/LLBL

Bz>0, By<0

ONOING STUDIES

Cusp:

Magnetopause

Tail

Energy step structures of O+ and H+ ions in the cusp and polar cap,Ions transverse heating mechanisms

The heating can be associated

with broadband extra low frequency (BBELF) wave fields,waves near the lower hybrid (LH) frequency, or electromagnetic ion cyclotron (EMIC) waves near 0.5 fH+. The heating can also be correlated with auroral electrons, suprathermal electron burst (STEBs), or precipitating H+ ions. Furthermore, types 1 and 2 are often associated with field-aligned currents.