IMPORTANCE OF FAST MEASUREMENTS OF SOLAR WIND

PARAMETERS AT THE IP SHOCK FRONT

Moscow, February 6-10, 2012

Z. Němeček, J. Šafránková, L. Přech, O. Goncharov, A. Komárek

Charles University, Prague, Czech Republic

G. N. ZastenkerSpace Research Institute, RAS, Moscow, Russia

OOutline Brief description of the BMSW device

A new solution of plasma parameter determination – discussion of (dis)advantages

Examples of measurements

Comparison with measurements of another spacecraft

Importance of fast measurements

Conclusion

BMSW in course of time

• Solar wind parameters: density, velocity,

and temperature – with a time resolution of 1-0.03 s

• Engineering model - 2005

• Flight model – 2008

• Flight spare model – 2009

• Launch – July 18, 2011

B

BMSW in vacuum chamber

BMSW – engineering model

BMSW – flight model BMSW on the platform

BMSW - principles6 FCs and each FC is equipped with four grids: grounded grids cover the windows in both diaphragms; a positive control grid is placed between outer and inner diaphragms; and a suppressor grid lies between the inner diaphragm and a collector.

FC characteristics with homogeneous electric field

Influence of finite grid spacing

Influence of finite FC dimensions

The dependences of the normalized collector current on the spacing between wires

Configuration of the electric field in the space between two control grids

Safrankova et al. (2008)

Characteristics for different velocities Solar wind bulk energy of 1 keV

BMSW modes

BMSW can measure in two working modes:

• Sweeping mode – ion distribution between 100-3 000 eV; time resolution 0.5 or 1 s

• Adaptive mode – only 3 points on the distribution; time resolution 31 ms

BMSW – Block Scheme

Example of first measurements Aug 12, 2011

BMSW in the sweeping mode; speed of measurements – 0.031 s

- a full set of solar wind parameters – 1 s- 3 directed FCs show a change of the speed and density- 3 declined FCs show a change of the solar wind direction - Details of distributions – protons and alphas

Protons

Alphas

Data rate and data compression

A full time resolution – 0.031 s – can be transmitted only for rather limited time intervals, a compression algorithm is needed

- data from 3 direct FCs are averaged (12 points) in adaptive mode- steep slopes are transmitted with a full resolution and the rest of the sweep is averaged in sweeping mode - 12-point averages are transmitted from 3 declined FCs

Steps on the HV voltage are a result of compression algorithm

Comparison – BMSW, Wind, ACE

A first comparison of joint measurements of three solar wind spacecraft on August 14, 2011

Spectr-R, ACE, Wind

Spectr-R

Wind

ACE

Interplanetary shock September 9, 2011

Interplanetary shock on September 9, 2011 was observed by SOHO, Wind, ACE and also by Spektr-R

BMSW in sweeping mode and compressed data

Changes of the density and velocity direction

Comparison of BMSW and WindComparison of BMSW and WindSeptember 9, 2011 - cont

IP shock on September 9, 2011 –preliminary computed parameters with a time resolution of 1 s

Still 3 times better than earlier

Moscow time

Wind

BMSW

Is this overshoot real?

Why the fast measurements are needed?

Changes of the density and velocity direction as short as 0.3 s

? Active experiment in the solar wind?

Why the fast measurements are needed? IP shock is usually considered as a rectangular step

First measurements of the plasma parameters with 30 Hz time resolution

Oscillations of the flow direction with a period of about 0.3 s

Such oscillations could not be observed earlier, the best time resolution prior to BMSW was 3 s

Detailed analysis impossible due to lack of magnetic field measurements

Plasma waves connected with the IP shock front

A detail of observations

The flow angle can be determined with the full resolution but the resolution of plasma moments is 3 s only

The upstream oscillations are linearly polarized

On the other hand, a clear circular polarization was observed in the downstream region

Further analysis requires magnetic field data

Comparison with WIND magnetic field

WIND magnetic field, 92 ms time resolution

HF waves upstream

Two types of oscillations downstream

The upstream oscillations are circularly polarized

Downstream LF waves exhibit a circular polarization

Polarization of the HF part of downstream waves is not clear

Adaptive mode – compressed data

An example of processing of the adaptive working mode. Data compression not only decreases time resolution but it introduces artificial noise

Full time resolution without compression

- our data reveal the real fine structure of the solar wind flow

- a weak IP shock that cannot be resolved with 1-minute resolution

- frequency spectra of density, speed, and temperature are different

20 minutes

30 seconds

Comparison with standard data, the same time interval

Data distributionData distribution Web page of the device - under construction

Daily (6 hours) plots of FC currents - ready

Preliminary processed plasma moments with the time resolution of 30 s (density, velocity, and temperature) – under preparation

Detailed data from a short time interval – on the request

Future plansFuture plans

Finishing of the data processing software

Determination of temporal evolution of photocurrents

Gathering of interesting intervals with full time resolution

Investigation of fast disturbances Thank you

for your attention

Investigation of solar wind turbulence at kinetic scales

Preparation of a new generation of the BMSW device for future missions