Ooty Solar Wind Studies - Indian Institute of Astrophysics

Interplanetary ScintillationRadio sourceL-O-SSunEarth

IPS temporal spectrum provides• spatial spectrum of density turbulence• radio source size (size cut-off)• solar wind speedscintillationI(t)Time

Solar wind Density Spectrum and Speed• For a radio source of known size(q source = 2πf/V and Φ(q) ~ q -α )– source-size cutoff on the temporal spectrumprovides the solar wind speed– Power - Frequency distribution gives shape ofthe spatial spectrum of density turbulence

Solar wind Density Turbulence(also spectrum)Density Turbulence* Scintillation index, m, is a measure of level of turbulence* Normalized Scintillation index, g = m(R) / * Quasi-stationary and transient/disturbed solar wind• g > 1 → enhancement in δNe• g ≈ 1 → ambient level of δNe• g < 1 → rarefaction in δNeScintillation enhancement w.r.t. theambient wind identifies the presenceof the CME along the line-of-sightdirection to the radio source

Scintillation Temporal Spectrum

f -apower @ large-scalepower @ small-scalespeed

power @ large-scalepower @ small-scalespeed

PKS1445-161power @ large-scalepower @ small-scalef -aspeed

Solar Wind Speed and Density Fluctuations (10 – 50 R )• Acceleration of speed is observed up to ~30 R • Acceleration profile of high-speed wind: shows quick risewithin ~20 R ; it is different from the low-speed wind;• Scale size of irregularities a >100 km dominates at R < 20 R • Scale size a 20 R • Spectrum of spatial density turbulence becomes steeper withdistance from the Sun– Radial evolution of the spectrum (or dissipation of energy)is important to understand the solar wind acceleration– Useful to constrain solar wind acceleration model

Solar Wind Density Turbulence and Speed (3 days)

δn e mapCR 2041

Solar wind speed synoptic mapCR 2041

Ooty IPS measurements: Density Turbulence and Speedof the Solar Wind in the Inner heliosphereCR2027February 25 –March 25, 2005

1Solar Cycle 23

Solar Cycle 23 – Solar Wind Density DistributionAp

Radial Evolution of CIRs75 solar radii100 solar radiiexpansion150 solar radii

Solar Cycle 23 – Solar wind Speed Distribution

Latitudinal Structure of CIRs• With heliocentric distance, interaction becomes stronger.• The interaction observed at latitudes away from the solarequator is caused by the tilt of the solar magnetic dipolerelative to the solar rotation axis.• The wind outflow from the Sun is structured as a function ofsolar magnetic latitude [e.g., Pizzo 1994].• With increasing heliocentric distance, the interaction regionsexpand in the directions transverse to the interfaces.

Coronal Mass Ejections Largest phenomenon associated with the dissipation ofmagnetic flux at and above the surface of the Sun Travel outward at range of speeds, 10 -- 2500 km/s Mass involved in each ejection is ~10 14 –10 15 g Main cause of large geo-magnetic storms CMEs appear to be an important factor of space weather,which has multiple geospheric, biospheric, and technologicaleffects. A great interest in understanding the propagation and arrivalof Earth-directed CMEs, which cause major storms at theEarth’s magnetosphere. However, there are many open questions concerning CMEsorigin, evolution, structure/extent in the interplanetary space To progress in understanding the effects of CMEs requiresdetail 3-D data on them from Sun to Earth

IPS Imaging of interplanetary disturbances (CIRs and CMEs)Radio SourceShockSunCMEEarth

Radial Evolution of CMEs– LASCO and IPS measurements between Sunand 1 AU– Halo and Partial Halo CMEs– ICME at 1 AU (Wind and ACE data)– Initial Speeds in the range 250 – 2600 km/s

June 25, 1992West Limb CME on June 25, 1992* X3.9 Flare, X-ray LDEType-IVManoharan et al. ApJ., 2000

Some example of November 2003 CMES

Fast CME on April 2, 2001: Ooty Images

CME in the interplanetary mediumLASCO Images

CME Propagation Speed (from Sun to Earth)Height – Time plotRadial Evolution of SpeedK.E. lost/dissipated within 100 R

LASCOGopalswamy et al. 2005A fast CME EventJanuary 20, 2005

Speed Profiles: V CME(R)V CME(R) of 30 CMEs• IPS & LASCO provide sky-plane speeds• Include constant speed, accelerating anddecelerating events•V CME(R) can be represented by power-lawforms:V CME(R) ~ R -βR < 50 R (Manoharan 2006)decelerationconstant speedaccelerationV CME(R) ~ R -α• 2-step effective accelerationR ~ 100 - 200 R • Transition around 70 – 80 R • at R < 70 R : -0.3 < β < +0.06• at R > 70 R : -0.76 < α < 0.58• slope > 0 : acceleration• slope < 0 : deceleration• index ‘β’ shows no significant dependenceon the initial speed of the CME• index ‘α’ shows dependence on the initialspeed

CME Initial Speed vs Acceleration Slope at R > 70 R deceleration zoneV = 380 km/sα = 0.2-6.4×10 -4 V+1.1×10 -7 V 2acceleration zone‘zero’ acceleration lineAerodynamic drag force:Interaction between the CME cloudand the ambient solar wind plays animportant role in the propagation ofCMEsK.E. utilized/gained times α against the“drag force” imposed by the ambientsolar wind [~ (V CME–V AMB) 2 ] showsgood linear correlation (~97%)

Initial Speed – Arrival Time at 1 AUT CME = 109 - 0.5 × 10 -1 V CME + 1.1 × 10 -5 V 2 CME hoursV CME = 400 km/s, T CME = 90 hours (considerable assistance by CME expansion)V CME = 2000 km/s, T CME dominated by interactionIncludes energy provided by CME Expansion + SW interaction

Axial ratio, AR, greater than 1.25 is indicated by ellipse.The ratio of major to minor axes indicates the anisotropy.Axial ratio is large at regions where the CME interactswith preceding CME(s)

Three-dimensional view of CME

CME Propagation - summary• CME Speed profile, V(R), shows dependence on initial speed• CME goes through continuous changes, which depend on CMEinteraction with the surrounding solar wind• Arrival time and Speed of the CME at 1 AU predicted by the speedprofile are in good agreement with measured values• Mean travel time curve for different initial speeds suggests that upto a distance of ~80 Rsun, the internal energy of the CME (or itsexpansion) dominates and however, at larger distances, the CME'sinteraction with the solar wind appears to control the propagation• Most of the CMEs tend to attain the speed of the ambient flow at1 AU or further out.• These results are useful to quantify the ‘drag force’ imposed on theCME by the interaction with the surrounding solar wind and it isessential in modeling the CME propagation.• Present study also indicates, Size of CME, a CME ~ R 1.0• Large anisotropy seems to be associated with the turbulence caused bythe CME-CME interaction.

Thank you

Spectra associated with ambientlow- and high-speed solar wind flowsSolar windDensity turbulence spectrumDensity turbulence spectrum associatedwith propagating CMEcut-off (inertial) scale = V A /ω P= N –1/2V A Alfven speedω P Proton cyclotron frequencyN Plasma density