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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