Highest Educational Qualification:

Degrees Obtained:

Employment History:

Positions Held Outside India:

Post Doctoral Tenures:

Awards:

Awarded the Hari Om Ashram Prerit - Vikram Sarabhai Research Award in Space Sciences for the year 2003. The award comprising of a medal plus a cash prize of Rupees Fifty Thousand is given bi-annualy. Awarded the Alexander Von Humboldt Research Award in Astrophysics for the year 1996 by the Alexander Von Humboldt Foundation, Bonn, Germany. Was selected as a "Young Astronomer" in 1988 for the award of a Science Foundation (NSF, U.S.A.) grant to attend the Twentieth General Assembly of the International Astronomical Union at Baltimore, U.S.A. and to visit the Mullard Radio Astronomy Observatory in Cambridge, UK. Membership of Professional Organizations: Member of the International Astronomical Union (IAU)., Member of European Geophysical Society. Member American Astronomical Society (AAS) - Solar Physics Division Significant Research Contributions: Studies of the Solar Wind and the Interplanetary Medium Using IPS: In the past decade, the cause and solar sources of intense geomagnetic storms has been attributed, by different groups of research workers, to a variety of solar surface features ranging from solar flares and coronal holes to disappearing filaments and coronal mass ejection's (CME's). To understand this problem, I have made extensive interplanetary scintillation (IPS) observations with the Ooty Radio Telescope, India, and have monitored density enhancements and solar wind velocities in the directions of a large grid of compact extragalactic radio sources. I have developed a technique which first uses a theoretical model to predict the location in space of a flare generated shock and then uses the IPS sources as a movable picket fence in the sky to pinpoint and track, on a daily basis, the propagating shock front between 0.2 and 0.8 AU. The method was the first successful day-to-day tracking of interplanetary (IP) disturbances with the ORT and has had significant impact on the field by showing that large (X-class) flares are associated with IP shocks on a one-to-one basis. This has removed the generally accepted belief that all IP shocks are caused only by CME's. The method has also been successfully employed to study large-scale and global density anomalies in the IP medium that were earlier thought to have been caused by large-scale solar phenomenon like the solar polar field reversal that occur during every solar maximum. Extensive observations carried out, employing the above method, have shown that such phenomena are associated with large magnetic flux expansion factors (> 1000) and probably have their origins in either active region open fields located at central meridian or are outflows from small mid latitude or transient coronal holes that are appropriately located on the Sun so as to produce Earth directed flows. Developing this novel method of predicting and then tracking IP disturbances using IPS observations, involved carrying out and extensive IPS survey to first identify a grid of compact scintillating sources at 327 MHz. The IPS survey (1992-1996) was on a > 1.5 Jy complete sample of sources at 327 MHz and yielded a grid of 1000 strongly scintillating sources that can be used for space weather studies. A small subset of these sources were found to be ultra compact, with IPS estimated angular sizes of the scintillating component being < 100 milli arc sec. Due to the rarity of compact sources at meter wavelengths, this list of ultra compact sources is an important input to future space VLBI missions and large international projects like the low frequency array telescope and the Square Kilometer Array. Solar Wind Studies Very Close to the Sun and at High Latitudes: While IPS at meter wavelengths can be exploited to study the solar wind at distances beyond approximately 40 Rʘ spacecraft sounding data can be used to determine electron densities in the distance range < 40 Rʘ. Using dual-frequency Doppler sounding data from the Ulysses satellite's Solar Corona Experiment, I have developed a method of using the deep-space-network of telescopes to cross-correlate spacecraft sounding data across intercontinental baselines (for the first time) to derive solar wind velocities in this inaccessible region between 4-40 Rʘ. Since sounding data close to the Sun is heavily affected by solar noise, the method involved the developing of a digital filtering technique to extract cross-correlation amplitudes and time-lags that would otherwise be buried in the noise. Apart from yielding solar wind velocities and columnar electron densities at southern solar latitudes between the pole and the equator, (and in an otherwise inaccessible region of the IP medium), the method has been employed to identify various types of solar wind flows in the acceleration regime that depend on the nature and morphology of the underlying photospheric magnetic fields. The results thus have a significant impact on our understanding of the origin and nature of different types of solar wind flows in the low corona. Solar Studies Using the Giant Meterwave Radio Telescope (GMRT) and Very Large Array (VLA) Observations: The first successful solar imaging observations using the GMRT at 1060 MHz has led to the detailed analysis of a flare-CME event which took place on 17 November 2001. These GMRT imaging observations provided the first evidence in support of the so called breakout model of flare-CME initiation and has given valuable insights into such processes. The breakout model is different from other models in that the reconnection process that initiates a mass ejection begins from the top of the coronal loop as opposed to models that initiate the process by reconnections occurring lower in the corona. Due to the fact that the GMRT operates at meter wavelengths, imaging observations can yield information at heights in the corona that correspond to the tops of coronal loops. The results are significant in that it is the first observational evidence that could favor such a scenario. An ongoing program of combining visibilities from the GMRT and the Nancay Radio Heliograph (NRH) has yielded composite snapshot images with dynamic ranges between 250 and 400. Such high dynamic range images have been achieved for the first time and will be useful in studying bright radio features like bursts that occur along with fainter phenomenon like CME's. Such observations would also lead to a better understanding the morphology of decimetric emission from solar flares. In the light of the discovery of fast Moreton waves and EIT waves in the solar corona, I have has analyzed P-band (333 MHz) VLA solar data from the VLA archives to search for very fast propagating coronal disturbances. Interesting results were obtained on a very rapid flare associated solar disturbance. Solar surface maps produced with high time resolution were used to detect motion associated with a solar flare at a speed of 26000 km s-1. The observations have a significant impact because the inferred velocity is larger than any previously inferred velocity of a disturbance in the solar atmosphere, with the exception of beams of freely streaming accelerated electrons. Cometary Studies: At Meter Wavelengths: I have exploited the phenomenon of IPS to study cometary ion tail plasma via occultation of one or more radio sources and scintillation of their electromagnetic emission as it passed through the tail of the comet. I was able to show that the rms electron density fluctuations in cometary ion tails is sufficient to cause scintillation at the Earth provided very specific conditions of occulting geometry are met during the occultation. I have thus used IPS at meter wavelengths to study cometary tail plasma at distances well downstream of the nucleus. The ion-tail-plasma of comets Halley and Austin were studied by this method at 103 MHz using the Thaltej Radio Telescope at PRL. These results led to other workers studying comets Halley at 327 MHz using the Ooty Telescope and comet Wilson at 408 MHz using the Parkes Telescope in Australia using the same method. At Centimeter Wavelengths: During its perihelion passage in March/April 1997, K-band radio observations of comet Hale-Bopp (C/1995 OI) were made at the 100-meter telescope of the Max-Planck-Institüt für Radioastronomie. Emission was firmly detected from the five lowest metastable (J=K) inversion transitions of ammonia. Assuming a thermal distribution for the metastable states of NH3, a rotational temperature of 104 ± 30 K was derived and an ammonia production rate at perihelion of 6.6 ±1.3×1028 s-1. The ammonia-to-water abundance ratio was found to be of the order of 1.0%. A marginal detection of the 616−523 transition line of water at λ  =  1.35 cm was also made. The results are significant in that ammonia has been discovered in only two other comets so far. The observations have also yielded an accurate estimate of the rotational temperature thereby yielding a probable kinetic temperature of the inner coma of comets. Studies of Interstellar Scattering Using IPS: Using estimates of the compact component sizes derived from 103 MHz IPS observations with the Thaltej Telescope and published data at 151.5 MHz, I have made a good estimate of the interstellar scatter broadening of compact radio sources at 103 MHz. A comparison of these observations with 151 MHz IPS measurements from Cambridge was used to estimate the contribution of interstellar scattering at 103 MHz and to show the enhanced scattering in the plane of our Galaxy. Very Long Baseline Interferometry (VLBI) and VLA Studies: I have identified a set of 59 ultra compact (θ  < 100 milli arc seconds) radio sources at meter wavelengths using his extensive 4000 radio sources IPS survey (1992-1996). Since IPS observations do not identify the nature of the compact components, imaging observations of these objects using the European VLBI Network (EVN) at 333 MHz were carried out in 1997 while dual frequency observations, on the same objects, using the Very Large Array at 3.5 and 20 cm were carried out in September 1999. I was the PI on the VLA observing proposal that was allotted time and a co-I on the EVN proposal. The analysis is ongoing and will be an important contribution for projects like LOFAR and SKA. Spectroscopic Studies at Optical Wavelengths: Apart from space weather related studies, I have carried out spectroscopic observations at optical wavelengths using a fiber linked grating spectrograph coupled to the 1.2 m, f/13 Mt. Abu telescope, a facility of the Physical Research Laboratory. The spectrograph, with a resolution of 10000 over the visible region (4000-7000 Å) has been used to make a study of the H α emission line profiles of a large number of Be stars. A good correlation has been obtained between the full widths of the line profiles and the stellar rotational velocity (vsini), indicating that kinematics is the dominant factor in line broadening in Be stars vis-a-vis other mechanisms like thermal broadening, and non-coherent scatter broadening.

Referees:

1. Dr. Murray Dryer

National Oceanic and Atmospheric Administration

Space Environment Laboratory/ ERL/NOAA

Boulder CO. 80303

U.S.A.

Email : Murray.Dryer AT noaa.gov

                               murraydryer AT msn.com

Phone :1-303-798-1440

Fax     : 1-303-497-3645

2. Prof. Mukul Kundu

University of Maryland,

Department of Astronomy

College Park,

Maryland 20742-2421; MD

USA

Email : kundu AT astro.umd.edu

Phone :1-301-405-1524

Fax     :1-301-314-9067

3. Dr. M. K. Bird

Radioastronomisches Institüt

AIfA - Abteilung Radioastronomie

Universitüt Bonn

Auf dem Hügel 71

53121 Bonn

GERMANY

Email : mbird AT astro.uni-bonn.de

Phone: (+49) (0) 228 73-3651

Fax     :(+49) (0) 228 73-1775

Refereed Research Publications (1989  − Present):

Quasar Enhanced. Alurkar, S.K., Sharma, A.K., Janardhan, P ., and Bhonsle, R.V. (1989). Nature , 338, 211−212. Three-Site Solar Wind Observatory. Alurkar, S.K.,Bobra, A.D., Nirman, N.S., Venat, P., and Janardhan, P. (1989). Indian Journal of Pure and Applied Physics, 27, 322−330. Interplanetary Scintillation Network for 3-Dimensional Space Exploration in India. Bhonsle, R.V., Alurkar, S.K., Bobra, A.D., Lali, K.S., Nirman, N.S., Venat, P., Sharma, A.K. and Janardhan, P. (1990). Acta Astronautica, 21, No. 3, 189. Estimation of electron density in the ion-tail of comet Halley using 103 MHz IPS observations. Sharma, A. K., Alurkar, S. K. and Janardhan, P. (1991). Bull. Astr. Soc. India, 19, 82. Enhanced scintillation of radio source 2204+29 by comet Austin (1989c1) at 103 MHz. Janardhan, P., Alurkar, S. K., Bobra, A. D., Slee, O. B. (1991). Bull. Astr. Soc. India, 19, 204. Enhanced Radio Source Scintillation Due to Comet Austin(1989 c1). Janardhan, P., Alurkar, S.K.,Bobra, A.D. and Slee, O.B. (1991). Aust. J. of Phys., 44, No. 5, 565. Power Spectral Analysis of Enhanced Scintillation of Quasar 3C459 Due to Comet Halley. Janardhan, P., Alurkar, S.K.,Bobra, A.D., Slee, O.B. and Waldron, D. (1992). Aust. J. of Phys., 45, No. 1, 115. Possible Contribution of a Solar Transient to Enhanced Scintillation Due to a Quasar. Janardhan, P. and Alurkar, S.K. (1992). Earth, Moon, and Planets, 58, 31−38. Comparison of Single-Site Interplanetary Scintillation Solar Wind Speed Structure With Coronal Features. Alurkar, S.K., Janardhan, P. and Vats, H.O. (1993). Sol. Phys., 144, No.2, 385−397. Angular Source Size Measurements and Interstellar Scattering at 103 MHz Using Interplanetary Scintillation. Janardhan, P. and Alurkar, S.K. (1993). Astronomy & Astrophys ., 269, 119−127. Measurements of Compact Radio Source Size and Structure of Cometary Ion Tails Using Interplanetary Scintillation at 103 MHz. Janardhan, P. (1993). Bull. Astr. Soc. India, 21, 381. IPS Survey at 327 MHz for Detection of Compact Radio Sources. Balasubramanian, V., Janardhan, P ., Ananthakrishnan, S., and Manoharan, P.K. (1993). Bull. Astr. Soc. India, 21, 469−471. Observations of PSR 0950+08 at 103 MHz. Deshpande, M.R., Vats, H.O., Janardhan, P ., and Bobra, A.D. (1993). Bull. Astr. Soc. India, 21, 613−614. Terrestrial Effects of PSR 0950+08. Vats, H.O., Deshpande, M.R., Janardhan, P ., Harish, C., and Vyas, G.D. (1993). Bull. Astr. Soc. India , 21, 615−617. Radio and X-ray burst from PSR 0950+08. Deshpande, M.R., Vats, H.O., Chandra Harish, Janardhan, P., Bobra, A.D. and, Vyas, G.D. (1994). Astrophys. Space Sci., 218, No.2, 249−265. Latitudinal Variation of Solar Wind Velocity. Ananthakrishnan, S., Balasubramanian, V., and Janardhan, P. (1995). Space Sci. Rev ., 72, 229−232. A 327-MHZ Interplanetary Scintillation Survey Of Radio Sources Over 6-Steradian. Balasubramanian, V., Janardhan, P . and Ananthakrishnan, S. (1995). Jou. Astrophys. & Astron., 16, 298. Unique Observations of PSR 0950+08 and Possible Terrestrial Effects. M.R. Deshpande, H.O. Vats, P. Janardhan, A.D. Bobra, Harish Chandra, and G.D.Vyas. (1995). Jou. Astrophys. & Astron ., 16, 253. Simultaneous Observations of Large Enhancement In the Flux of PSR 0950+08 Over a 200 KM Baseline at 103 MHz. Bobra, A. D., Chandra, H., Vats, H. O., Janardhan, P., Vyas, G. D., Deshpande, M. R., (1996). Proc. of the 160th Colloquium of the IAU−−ASP Conf. Series.,  S. Johnston, M.A. Walker, & M. Bailes Eds. pp. 477−448. On the Nature of Compact Components of Radio Sources at 327 MHz. Balasubramanian, V., Janardhan, P., Ananthakrishnan, S. and Srivatsan, R. (1996). Bull. Astr. Soc. India, 24, 829. IPS Observations of the Solar Wind at 327 MHz - A Comparison with Ulysses Observations. Janardhan, P ., Balasubramanian, V., Ananthakrishnan, S. and Srivatsan, R. (1996). Bull. Astr. Soc. India , 24, 645. Travelling Interplanetary Disturbances Detected Using Interplanetary Scintillation at 327 MHz. Janardhan, P., Balasubramanian, V., Ananthakrishnan, S., Dryer, M., Bhatnagar, A. and McIntosh, P.S. (1996). Sol. Phys., 166, 379−401. Tracking Interplanetary Disturbances Using Interplanetary Scintillation. Janardhan, P., Balasubramanian, V. and Ananthakrishnan, S. (1997). Proc. 31st. ESLAB Symp., ESA SP−415 , pp. 177−181. Radio Detection of Ammonia in Comet Hale−Bopp. Bird, M. K., Huchtmeier, W., Gensheimer, P., Wilson, T. L., Janardhan, P. and Lemme, C. (1997). Astronomy & Astrophys Lett., 325, L5−L8. Ammonia in Comet Hale-Bopp. Wilson, T. L., Huchtmeier, W. K., Bird, M. K., Janardhan, P., Gensheimer, P. and Lemme, C., (1997). Bulletin of the American Astronomical Soc., 29, 1259. Detection and Tracking of IPS Disturbances Using Interplanetary Scintillation. Balasubramanian, V., Srivatsan, R., Janardhan, P., and Ananthakrishnan, S. (1998). Bull. Astr. Soc. India, 26, 225−229. Radio Observations of Transient Solar Wind Flows. Balasubramanian, V., Janardhan, P., Srivatsan, R. and Ananthakrishnan, S. (1998). Proc. of the 3rd. SOLTIP Symposium, Feng, X.S., Wei, F.S., and Dryer, M. Eds. pp. 319. Coronal Velocity Measurements with Ulysses: Multi−link Correlation Studies During two Superior Conjunctions. Janardhan, P., Bird, M K., Edenhofer, P, Plettemeier, D., Wohlmuth, R., Asmar, S W., Patzölt, M. and Karl, J. (1999). Sol. Phys., 184, 157−172. K−Band Detection of Ammonia and (Possibly) Water in Comet Hale−Bopp. Bird, M. K., Janardhan, P., Wilson, T. L., Huchtmeier, W., Gensheimer, P., and Lemme, C. (1997). Earth Moon and Planets, 78, 21−28. Study of Solar Wind Transients Using IPS. Ananthakrishnan, S., Kojima, M., Tokumaru, M., Balasubramanian, V., Janardhan, P., Manoharan, P.K., and Dryer, M. (1999). Proc. of Solar Wind 9 Conference, S.R. Habbal, eds, AIP, New York. pp 321. Anisotropic Structure of the Solar Wind in its Region of Acceleration. Efimov, A.I., Rudash, V.K., Bird, M.K., Janardhan, P., Patzölt, M., Karl, J., Edenhofer, P. and Wohlmuth, R. (2000). Advances in Space Res., 26, 785−788. Radio Detection of a Rapid Disturbance Launched by a Solar Flare. White, S.M., Janardhan, P. and Kundu, M.R. (2000). ApJ Lett., 533 , L167−L170. Observations of Interplanetary Scintillation During the 1998 Whole Sun Month: A Comparison between EISCAT, ORT and Nagoya Data. Moran, P.J., Breen, A.R., Canals, A., Markkanen, J., Janardhan, P., Tokumaru, M. and Williams, P.J.S. (2000). Annales Geophysica, 18, 1003. H−alpha Observations of Be Stars. Banerjee, D.P.K., Rawat, S.D. and Janardhan, P. (2000). A&A Suppl., 147, 229. Near Infra−red and Optical Spectroscopy of Delta Scorpii. Banerjee, D.P.K., Janardhan, P. and Ashok, N.M. (2001). A&A Lett., 380, L13. Flow Sources and Formation Laws of Solar Wind Streams. Lotova, N.A., Obridko, V.N., Vladimirskii, K.V., Bird, M.K. and Janardhan, P. (2002). Sol. Phys., 205, 149. Fine Structure of the Solar Wind Turbulence Inferred from Simultaneous Radio Occultation Observations at Widely−Spaced Ground Stations. Bird, M.K., Janardhan, P., Efimov, A.I., Samoznaev, L.N., Andreev, V.E., Chashei, I.V., Edenhofer, P., Plettemeier, D., and Wohlmuth, R. (2003). Proc. Solar Wind 10., 679, 465−468. IPS Observations of the Solar Wind Disappearance Event of May 1999. Balasubramanian, V., Janardhan, P., Srinivasan, S., and Ananthakrishnan, S. (2003). Jou. Geophys. Res. 108, A3, 1121. Giant Meter Wave Radio telescope Observations of an M2.8 Flare: Insights into the Initiation of a Flare−Coronal Mass Ejection Event. Prasad Subramanian, Ananthakrishnan, S., Janardhan, P. , Kundu, M.R., White, S.M., Garaimov, V.I. (2003). Sol. Phys. 218, 247−259. The Solar Wind and Interplanetary Disturbances. Janardhan, P., (2003). Solar Terrestrial Environment − Space Weather R.P. Singh, Rajesh Singh and Ashok Kumar Eds., Allied Publishers, New Delhi., pp. 42−56. Radio Observations of Rapid Acceleration in a Slow Filament Eruption/Fast CME Event. Kundu, M.R., Garaimov, V.I., White, S.M., Manoharan, P.K., Subramanian, S., Ananthakrishnan, S., and Janardhan, P. (2004). ApJ. 607, 530−539. Resolving the Enigmatic Solar Wind Disappearance Event of 11 May 1999. Janardhan, P. , Fujiki, K., Kojima, M., Tokumaru, M., and Hakamada, K. (2005). Jou. Geophys. Res.110, A08101. Combining visibilities from the Giant Meterwave Radio Telescope and the Nancay Radio Heliograph. Mercier, C., Prasad Subramanian, Kerdraon, A., Pick, M., Ananthakrishnan, S. and Janardhan, P. (2006). A&A. 447, 1189−1201. The Morphology of Decimetric Emission from Solar Flares: GMRT Observations. Kundu, M.R., White, S.M., Garaimov, V.I., Subramanian, S., Ananthakrishnan, S., and Janardhan, P. (2006). Sol. Phys. 236, 369−387. Enigmatic solar wind disappearance events: Do we understand them?. Janardhan, P., (2006). Jou. Astrophys. Astron. 27, 1−7. Locating the solar source of the extremely low−density, low−velocity solar wind flows of 11 May 1999. Janardhan, P., Fujiki, K., Kojima, M. and Tokumaru, M. (2007). Proc. of the ILWS Workshop 2006, ISBN: 81−87099−40−2, p.132−138. Insights gained from Ground and Space Based Studies of Long Lasting Low Density Anomalies at 1 AU. Janardhan, P. , Ananthakrishnan, S., Balasubramanian, V., (2007). Asian Journal of Physics, 16, 209−232. Eds.:  Janardhan, P., Vats, H.O., Iyer, K.N., & Anandarao, B.G. Prospects for GMRT to Observe Radio Waves from UHE Particles Interacting with the Moon. Sukanta P., Mohanty, S., Janardhan, P. , and Oscar, S., (2007). JCAP., 11, 022−038. The Source Regions of Solar Wind Disappearance Events. Janardhan, P. , Fujiki, K., Sawant, H.S., Kojima, M., Hakamada, K. and Krishnan, R., (2008). Jou. Geophys. Res. 113, A03102. The Solar Wind Disappearance Event of 11 May 1999: Source Region Evolution. Janardhan, P., Tripathi, D., Mason, H.E., (2008). A & A Lett., 488, L1−L4. When the Solar Wind Vanishes: Causes on the Sun, Effects at the Earth. Janardhan, P. (2009).  Bull. Astr. Soc. India  (In Press).    IAU Telegrams : PSR 0950+08. Janardhan, P., Deshpande, M. R., Bobra, A. D., Venat, P., Nirman, N. S. and Lali, K. S. (1992). IAU Circular No. 5575. Jupiter and Comet Shoemaker−Levy. O. P. N. Calla, V. Sukumaran, B. M. Darji, M. R. Deshpande, H. O. Vats, Janardhan, P., and N. M. Vadher., (1994). IAU Circular No. 6088. Comet C/1995 O1 (Hale−Bopp). Bird, M. K., Janardhan, P., Gensheimer, P., Huchtmeier, W. and Wilson, T. L., (1997). IAU Circular No. 6607.