2011-Aug-11/AOGS 2011

Global Observations of the Solar Wind with STEL IPS Array

M. Tokumaru, K. Fujiki, T. Iju, M. Hirota, M. Noda, and M. Kojima

(STEL, Nagoya University)

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㎡

41m(E-W)

106m (N-S)

Solar Wind Imaging Facility (SWIFT)

Frontend and signal combiners

Cylin

drica

l par

abol

ic re

flecto

r

Dipole antennas

7.2m

Solar Wind Speed Synoptic Maps for 1996 (upper) and 2008 (lower)

• In the previous minimum (1996), the structure was stable.

• In the current minimum (2008), the structure shows rapid variability.

11 Carrington Rotations versus Heliographic Latitude(Note that the Carrington rotation number increases from right left)

327-MHz Radio Sky Observed by SWIFT

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

Note: The system temperature increases at low elevation

Model Fitting Analysis of IPS Power Spectrum

Speed=379km/sAxial　Ratio=0.99Spectral　Index=3.17

Speed=499km/sAxial　Ratio=0.51Spectral　Index=4.34

3C48　2009/4/6 3C49　2009/4/6

Upgrade of Fuji and Kiso IPS Systems• A new IPS system was developed for Fuji and Kiso stations.• The new system enables to determine the solar wind speed

from the cross correlation analysis of 3-station data.• The new system also improves quality and reliability of IPS

data.

Fuji IPS Telescope (FIT) Kiso IPS Telescope (KIT)

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.

19912000

1996(Cycle 22/23 Minimum)

Blue=Fast windRed=Slow wind

(Cyclel 22 Maximum) (Cycle 23 Maximum)

Solar Cycle Change in Source Surface Area of Different Speed Components during 1985-2009

AllLat.

HighLat.

LowLat.

Dominance of fast

winds at high

latitudes except for the solar maxima

Prevalence of slow

winds at low

latitudes

from STEL IPS observations

(Tokumaru et al., 2010)

Solar Wind Speed Synoptic Maps for 1996 (upper) and 2008 (lower)

• In the previous minimum (1996), the structure was stable.

• In the current minimum (2008), the structure shows rapid variability.

11 Carrington Rotations versus Heliographic Latitude(Note that the Carrington rotation number increases from right left)

Solar Wind Speed Maps for 2009 and 2011

Summary and Future Subjects• The STEL IPS system has been upgraded

recently. Three-station measurements of the solar wind speed have been conducted with the upgraded system.

• Some interesting aspects of the solar wind in the cycle 24 are revealed from our IPS observations.

• We need to elucidate evolution of the solar wind during the cycle 24 in detail.– Further improvement of the IPS system is needed.

STEL IPS Antennas as Viewed in Google Earth

Fuji IPS Telescope (FIT) Kiso IPS Telescope (KIT)

Toyokawa Observatory

SWIFT

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)

•Large-Aperture Parabolic Reflector88m×39m×η=3432×η ㎡Efficiency ηobs~0.65

•192-Elements Phased Array in N-S Direction

Single Beam with a Steerable Range of 60 deg S-30 deg N1 Element = Combination of East and West λ/2-dipolesDelay Correction

・ Low-Noise Receiver327MHz ±5MHz maxFront-end: NF <1dB 、 VSWR <1.5Loop-Method Calibration System

•RFI ReductionSmall Height of Focal Points Shielding Fence at North and South Ends

North

South

Solar Wind Imaging Facility (SWIFT)