Interplanetary Scintillation Observations of the Solar Wind Using SWIFT and Upgraded STEL

Multi-station System

M. Tokumaru, K. Fujiki, and T. Iju

(STEL, Nagoya University)

Interplanetary Scintillation Measurements of the Solar Wind

• Time Delay between IPS patterns at separated antennas → Solar wind speed V

• Strength of IPS → Density Fluctuations ΔNe (~Ne)

Time lag

Good Points of IPS Observations•Global coverage•Long-term monitoring

Interplanetary Scintillation; IPS

STEL Radiotelescope Array dedicated for IPS Observations

Kiso Sugadaira

Fuji

Toyokawa

Data•Solar Wind Speed•Scintillation level (g-value)

Frequency 327MHz Aperture Size = ~ 2000 　 or ~ 3400㎡

STEL IPS Antennas as Viewed in Google Earth

Fuji IPS TelescopeE-W 100m, N-S 20m

Solar Wind Imaging Facility Telescope; SWIFT (Toyokawa)N-S 106m, E-W 41m

Kiso IPS TelescopeE-W 75m, N-S 27m

A new system for observation control and data acquisition has been developed in 2010 to collect IPS data simultaneously at three stations. This system enables to determine the solar wind speed from the cross correlation analysis.

SWIFT-type low-noise amplifiers will be installed for Fuji and Kiso stations in this winter to improve sensitivity.

Development of SWIFT in 2006-2008. Highest Sensitivity among the array

Cross Correlation Analysis with Upgraded STEL IPS System

Solid lines: Cross CorrelationDashed/Dotted lines: Auto Correlation

Taking account of the baseline geometry, we determine the solar wind speed.For this case, we obtainV=522+/-3 km/s.Here, we assume the radial flow and the anisotropy.

Comparison between Spectrum Fitting and Cross Correlation Methods

Spectrum　Fitting　Method(Single-station　meas.)Speed　V1st.=459km/sAxial　Ratio=1.07Spectral　Index=3.8

3C273　2012/9/3

Cross Correlation Method(3-station meas.)Speed V3st.= 457±13 km/s

from IPS obs. for 3C273 in 2012

V3st. (km/s)

V1s

t. (

km/s

)

Correlation ~0.47

V1st/V3st=1.04±0.24

19912000

1996(Cycle 22/23 Minimum)

Blue=Fast windRed=Slow wind

(Cyclel 22 Maximum) (Cycle 23 Maximum)

Year-by-Year Variations in Source Surface Area of Fast, Slow and Intermediate Speed Winds during

1985-2012

AllLat.

HighLat.>70°

LowLat.<10°

from STEL IPS observations

SC23 SC24SC22

Excess of Fast Wind Particularly at Low Lat.

Deficit of Slow Wind

Peculiar dynamo

activity is going on.

Solar Maximum of Cycle 24:the smallest in last 100 years

SC24 max

Year-by-Year Variations of V (left) and ΔNe (right) Distribution on the Source Surface during 1997-

2012

AllLat.

HighLat.>70°

LowLat.<10°

Speed VSteady decrease (increase) in high (low) ΔNe area

Marked growth of low ΔNe region at low latitudes

Note that observation coverage is poor for 2010

SC23SC23 SC24SC24

Density fluctuations ΔNe(~Ne)

North-South Asymmetry of Solar Wind Speed Distribution over Poles (1985 ～

2012)

North Pole

South Pole

N-S Difference Blue = Fast wind, Red = Slow wind

Large N-S asymmetry in fast wind (blue) is observed in the declining phase of SC23 and SC24.

Summary• Global observations of the solar wind have been

carried out for more than 3 solar cycles using the multi-station IPS system of STEL.

• Some interesting aspects of the solar wind in the cycle 24 are revealed from STEL IPS observations. These are considered as manifestation of peculiar solar dynamo activity in this cycle, and also suggest that a drastic change of global heliosphere is in progress.

• We need to elucidate evolution of the solar wind during cycle 24 and beyond in detail.

327-MHz Radio Sky Observed by SWIFT

408MHz Radio Sky (Haslam et al., 1982)

Note: The system temperature increases at low elevation

41m(E-W)

106m (N-S)

Solar Wind Imaging Facility 　Telescope (SWIFT)

Frontend and signal combiners

Cylin

drica

l par

abol

ic re

flecto

r

Dipole antennas

7.2m

Upgrade of Fuji and Kiso IPS Systems• A new system for observation control and data acquisition

has been developed for the STEL IPS array.• The new systems enable to collect IPS data simultaneously

with the SWIFT and enable to determine the solar wind speed from the cross correlation analysis of 3-station data.

• New low-noise amplifiers will be installed for these stations in this winter.

Fuji IPS Telescope (FIT)E-W 100m, N-S 20m

Kiso IPS Telescope (KIT)E-W 75m, N-S 27m

Specifications of STEL IPS Radiotelescopes

Toyokawa(SWIFT)

Fuji(FIT)

Kiso(KIT)

Sugadaira

Tsys (K) 146 151 221 229

NF 0.72 0.87 1.61 0.75

Pre-amplifier HEMT Ga-As FET Transister Ga-As FET

Ae ( ㎡ ) 1970 (@zenith)

1500 1409 1120

Beam Cont. N-S

Electronical Mechanical Mechanical Mechanical

Beam Cont. E-W

(Fixed) Electronical Electronical Electronical

Physical Aperture

108 m NS× 40 m EW

20 m NS 　 × 100 m EW

27 m NS × 75 m EW

20 m NS 　 × 100 m EW

Comparison between New and Old IPS System Specifications

New Old

A/D Resolution 16 bits 13 bits

Sampling Period 20 ms (median mean of 10kHz sampling data)

50 ms

Start/End Time Resolution

Every 0 seconds Every 0 minutes

Observation Time JST (UT) Sidereal Time

Duration of IPS Obs ~2.7 min 7.5 – 15 min

1 Block for FFT Analysis 512 points 1024 points

Automatic Gain Cont. (H/W)

None Yes

High-Pass Filtering for IPS Data (H/W)

None Yes

PC Win-XP (samba/nfs) Win95/MS-DOS (nfs)

Strong Source Observations

IPS Power Spectra

Noise level