P K Manoharan

Professor and Head, RAC, Ooty
Radio Astronomy Centre
Tata Institute of Fundamental Research
Udhagamandalam - 643001,
Tamil Nadu, INDIA
Status: Retired

Main Research Areas: Multi-wavelength studies of Solar Eruptions; Solar activity; Acceleration of the Solar wind; The Interplanetary Medium.


P. K. Manoharan joined TIFR in 1975, immediately after his BSc (Special Physics) at American College, Madurai, and has been associated with the Ooty Radio Telescope ever since. He completed his doctoral studies in 1991 at TIFR, and then spent one year (1993) as a JSPS Fellow at the Solar-Terrestrial Environment Laboratory, Japan, more than a year (1995-96) as a Visiting Fellow at the Observatoire de Paris, Meudon, France, and nearly two years (2002-03) as a Visiting Scientist at the Goddard Space Flight Center, NASA and University of Maryland, USA.

Research description:

Manoharan is actively involved in research on solar and interplanetary physics. He developed a unique method to determine the speed and other physical properties of the solar wind using interplanetary scintillation (IPS) measurements from a single radio telescope. Based on IPS measurements from the Ooty Radio Telescope, several important studies leading to new results pertaining to the solar wind Space Weather processes in the inner heliosphere and their effects have been made by him. His single-station technique to estimate the solar wind speed is being used at several international observatories. Studies by Manoharan, in particular using the Ooty scintillation measurements, could explain the three-dimensional structure of solar wind density turbulence and its changes with solar cycles at the crucial heliocentric distance range above the solar wind acceleration region, for both low-speed and high-speed winds. A recent study, based on Ooty IPS measurements, showed a clear evidence for a steady decline in density turbulence (and hence, mass flux) of the solar wind from solar cycles 22 to 24, indicating that the Sun may be heading towards a deep minimum in the solar activity cycle. In one of his studies, Manoharan explained for the first time the formation of the twisted magnetic loop system (which was later named ‘sigmoid’) at the sites of flares or coronal mass ejections (CMEs), as observed at X-ray and radio wavelengths. Several studies by Manoharan and his co-workers, based on multi-wavelength solar and interplanetary observations, have been useful to understand fundamental issues regarding the physics of magnetic reconnection and the associated initiation of CMEs and particle acceleration processes in the low corona and in the near-Sun region. The propagation of CMEs (e.g., magnetic flux-rope structures) and their 3-D evolution have clarified the aero-dynamical drag experienced by CMEs in the inner heliosphere. Furthermore, shocks produced by fast CMEs have been identified in IPS images, suggesting the sources of solar energetic particles and their energy spectra, transport variability, and acceleration mechanism. These studies have also been extremely useful to pinpoint the arrival of CMEs, and to identified the interplanetary conditions that drive geomagnetic activities and storms at the near-Earth environment.
Upgrade of the Ooty Radio Telescope:
The Ooty Radio Telescope (ORT) is presently used for several important astrophysical studies, such as spectral line measurements, pulsar observations, space weather studies, etc. The front-end electronics of the ORT has been recently upgraded, with the installation of new digital front-end systems, each at a 2-m section of the ORT. The upgrade has been done in collaboration with the Raman Research Institute, Bangalore. The versatile upgraded system has provided a new lease of life to the ORT, with a wide field of view as well as a much improved sensitivity. It enables us to initiate various studies requiring high sensitivity, such as accurate pulsar observations, cosmological studies, spectral line studies, radio detection of transients, solar and space weather study observations, etc.

Selected publications:

1. Three-dimensional Evolution of Solar Wind during Solar Cycles 22-24 (P.K. Manoharan, 2012, ApJ, 751, 128)

2. Eruption of a plasma blob, associated M-class flare, and large-scale extreme-ultraviolet wave observed by SDO (P. Kumar & P.K. Manoharan, 2013, A & A, 553, A109)

3. Coronal Mass Ejections Propagation Time and Associated Internal Energy (P.K. Manoharan & A. Mujiber Rahman, 2011, Journal of Atmospheric and Solar Terrestrial Physics, 73, 671)

4. Ooty Interplanetary Scintillation -- Remote-sensing Observations and Analysis of Coronal Mass Ejections in the Heliosphere (P.K. Manoharan, 2010, Solar Physics, 265, 137)

5. Coronal Mass Ejections and Associated Phenomena (Chapter #11) and The Solar Wind (Chapter #12)  (P.K. Manoharan, in Physics of the Sun and its Atmosphere, World Scientific Publication, Singapore, 2008.)

6. Evolution of Coronal Mass Ejections in the Inner Heliosphere: A Study Using White-Light and Scintillation Images (P.K. Manoharan, 2006, Solar Physics, 235, 345)

7. Influence of coronal mass ejection interaction on propagation of interplanetary shocks (P.K. Manoharan, N. Gopalswamy,  S. Yashiro et al., 2004, Journal of Geophysical Research, 109, A06109)

8. Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection (P.K. Manoharan & M.R. Kundu, 2003, ApJ, 592, 597)

9. Coronal Mass Ejection of 2000 July 14 Flare Event: Imaging from Near-Sun to Earth Environment (P.K. Manoharan, M. Tokumaru, M. Pick, et al., 2001, ApJ, 559, 1180)

10. Evidence for Large-Scale Solar Magnetic Reconnection from Radio and X-Ray Measurements (P.K. Manoharan, L. van Driel-Gesztelyi, M. Pick & P. Demoulin, 1996, ApJ, 468, L73).