1. Sixth European Space Weather Week Conference Site Oud Sint-Jan, Bruges, Belgium 16-20 November 2009 Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links P. Tortora (1), A. Richie-Halford (2), L. Iess (3), J. Armstrong (4), S. Asmar (4), R. Woo (4), S. Habbal (5) & H. Morgan (5) 1 Università di Bologna, Forli, Italy 2 Los Angeles Air Force Base, El Segundo, CA, USA 3 Università La Sapienza, Rome, Italy 4 Jet Propulsion Laboratory, California Institute of Technology, CA, USA 5 University of Hawaii, HW, USA

2. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Outline Context: classical and “new” solar conjunction radio science Localization in 3 dimensions and time: the basic idea Determining thickness of a scattering region A relatively simple example: 2001 DOY 149 A more complicated example: 2002 DOY 160 Solar Context: from ~2 w of the LASCO/SOHO C2 coronagraph observations Conclusions

3. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan What is a Solar Conjunction SUN Cassini Earth For missions in the ecliptic plane the S/C is nearly occulted by the Sun (as seen from the Earth)

4. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Cassini trajectory wrt the Sun (SCE1, 2002)

5. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Classical Solar Conjunction Radio Science Radiowave scintillation, using spacecraft and natural radio sources, has successfully probed the solar wind in and out of the ecliptic and very close to sun (in regions which will never be accessible to in situ spacecraft measurements) Traditional observable quantities include: –Density spectrum (from phase and amplitude scintillation) as function of position, wavenumber, and time –Time-resolved near-sun plasma variability (“space weather”) –Speed (ccf of multiple-station intensity scintillation) –Electric field statistics (mostly for engineering & comm applications) –Higher moments (e.g. bispectrum) –Total electron content (ranging) –Faraday rotation –Others

6. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan A “New” Aspect of Solar Conjunction Radio Science: Localization of Plasma Disturbances in Three Dimensions Uses transfer functions of plasma irregularities to Doppler fluctuations to localize disturbances along line-of-sight (in addition to plane of sky and time) “New” is in quotes because this is the first time it has been applied to the near-sun solar wind; technique’s roots are in papers from the 1970s –Localization technique is implicit in transfer function approach for precision Doppler (Estabrook and Wahlquist 1975; Estabrook 1978) –Transfer functions were used explicitly in noise budget & spectral analysis for Cassini’s GWE and SCE –Localization of near-earth plasma in the anti-solar direction (using a variation on this method) was done in Armstrong (2006) Potential payoff: localization has implications for origin and near- sun evolution of the solar wind

7. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan The Basic Idea*: Transfer Functions of Up- and Downlinks Can Locate Disturbances Along Line-of-Sight Space-time diagram of Cassini radio tracking: space plotted vertically; time horizontally -- ground station (DSS 25) and Cassini continuously exchange radio waves (a few shown as dashed lines) Wave passing through a blob shifts phase of both up- and downlinks Separation in time of Doppler disturbance in up- and downlinks -- measured as a function of time by windowed cross correlation of the data -- determines where the blob is in space (“x”) and time Before KAT failure, 5-link Cassini system produced up- and downlink plasma separately – the SCE data (Bertotti, Iess, Tortora 2003) were used in this pilot study * Due originally to Estabrook & Wahlquist (1975) and Estabrook (1978), in the context of noise transfer functions for Doppler tracking gravitational wave experiments

8. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Decorrelation From Unity Gives Thickness of Screen If screen is geometrically thin, the up- and downlink radio waves pass though a blob at the same point in space-time; in this case the uplink and downlink Doppler times series are offset exact copies of each other and the cross-correlation is unity at the correct lag T 2 – 2 x/c As thickness of screen increases, the up- and downlinks now sense different blobs in space- time – Doppler time series are no longer exact offset copies of each other If light time across screen is small compared with the width of Doppler temporal autocorrelation function (set by the temporal filtering), then decorrelation from unity is a sensitive measure of screen thickness Simulation (left) shows, e.g., that >0.97 correlation  full width screen thickness < 0.02 AU This works because excellent SNR of the Cassini radio links allows confident normalization of ccf (to fraction of 1%)

9. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Up- and Downlink Plasma Time Series for 2001/149 Five link system isolates uplink (red) and downlink (blue) plasma contributions separately (Iess et al. 2003; Tortora et al. 2004) (RMS plasma signal)/(RMS estimation error noise) in these data is > 300; even smallest variation seen in the plots is real plasma signal Note obvious counterparts (only a few of which are marked) separated by ≈ T 2 – 2 AU/c The time-separation (itself in principle a function of time) can be used to localize where the scattering is occurring along the LOS As shown in previous slide: model computation of decorrelation from unity also bounds thickness of the scattering region

10. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan How the CCF-As-A-Function-of-Time Was Computed This is a movie made during the analysis Upper panel: Plasma uplink time series; middle panel: plasma downlink time series Vertical bars show windowing of each time series Bottom panel: normalized cross-correlation function of the windowed data as a function of lag (in hours) for for fiducial time, t (= center of downlink window) Window is advanced to get ccf as a function of time and time lag -- time lag converted to distance by  (t) = T 2 – 2 x(t)/c

11. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Space-Time CCF of Up- and Downlink Doppler: 2001/149 Note high degree of correlation (red means > 0.9; orange 0.8-0.9, etc.) over most of the pass and particularly at the end of track (> 0.97) High coherence (Jenkins & Watts 1969) between up- and downlink Doppler --> excellent localization; in this case the centroid of scattering region at end of track is localized to a few thousandths of an AU High correlation also gives upper bound on width: scattering region must be < 0.02 AU thick This has relevance for the source, evolution, and spatial intermittency of the near-sun solar wind -- long standing problems

12. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Solar Context: Projected Position of Cassini-Determined Scattering Region. On 2001/149 it is Close to Computed Position of Heliospheric Current Sheet This is a tomographic reconstruction of density very near the sun using ~2 weeks of data near the time of the observation (2001 DOY 149) Important point for this presentation is the dashed line, which is the estimated location of the heliospheric current sheet (HCS = surface in the interplanetary medium separating regions of opposite magnetic polarity) Diamond is position of Cassini- determined scattering region, mapped to the sun In 2001 DOY 149 we are seeing a thin ( 1AU line- integrated phase scintillation.

13. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Space-Time CCF of Up- and Downlink Doppler: 2002/160 More complicated situations than that of 2001 DOY 149 occur too Solar activity, as determined from white light pictures, more pronounced in 2002 – figure to left is 2002 DOY 160 Note low correlation compared with 2001 DOY 149 --> absence of good localization over most of this pass Screen at start of track is at ‘wrong’ distance (not 1AU*cos(elongation)) In process: compare with high time resolution white light for short-term solar context & combine days to identify possible co-rotating spatial features

14. November 20, 2009Space-time Localization of Inner Heliospheric Plasma Turbulence Using Multiple Spacecraft Radio Links Cassini-Huygens Mission to Saturn and Titan Conclusions and Future Work We have shown a proof-of-concept demonstration of a technique to localize inner heliospheric plasma disturbances in space and time The method is based on the differing transfer functions of plasma scintillation to one- and two-way radio links between the earth and a distant spacecraft In the technique’s simplest form, discussed here, the up- and downlink plasma time series are compared to localize dominant plasma irregularities in time and along the line-of-sight Examples were shown for a situation where the scattering is dominated by a thin screen at well-defined location (2001/149) and a situation where the scattering is more extended (2002/160) When combined with other remote sensing observations such as white light images (and other simultaneous radio observations--e.g. intensity scintillation), this method has application in studies of inhomogeneity, nonstationarity, and other manifestations of inner heliospheric plasma variability.