Ashok Ambastha

Senior Professor
Udaipur Solar Observatory
Physical Research Laboratory

E-mail: ambastha[at]
Telephone: +91-294-2457207

My current research interests include:

We have been studying large flares and their photospheric, chromospheric and helioseismic responses. We have carried out research on solar oscillations and local helioseismology for probing the sub-surface weather of quiet and active regions (using ring diagram and inversion techniques). We have obtained statistically significant amplification of p-mode power in association with large flares. We found that power in low-l modes are stochastic in nature, and there is a poor correlation of with disk-integrated flare index and CME-counts for the period of May 1995--October 2005.

We have continued the studies pertaining to observations and modeling of solar active regions and energetic transients using high spatial and temporal resolution data obtained from ground-based and space-borne instruments. These include magnetic and velocity field evolution in solar active regions, energy storage and release in flares/CMEs, magnetic helicity injection due to motion and emergence/submergence of fluxes, spectral line profile characteristics and their changes during transient solar activities, stability and eruption of prominences, coronal structure and polarization using total solar eclipse observations.

I have led USO-PRL expeditions for coronal structure and polarization studies during total solar eclipses of 1995 (Kalpi, India), 1999 (Isfahan, Iran), 2001 (Lusaka, Zambia), 2006 (Manavgat-Antalya, Turkey), and 2009(Anji, China).

Future research will include, apart from the above topics, studies using the proposed MAST facility to become available at USO; zonal and meridional velocities in deeper layers underneath solar active regions; superflaring and flare-quiet active regions; flare associated variations in magnetic, doppler and helioseismic parameters; and the stability of prominences. Solar helioseismological data now available for over one complete solar cycle will be studied to relate the flare and CME indices with p-mode parameters.

Selected Publications :

On the injection of helicity by shearing motion of fluxes in relation to Flares and CMEs

P. Vemareddy, A. Ambastha, R. A. Maurya and J. -C. Chae (2012). Astrophys.J., 761, id 86, 18 pp.


Filament Eruption in NOAA 11093 Leading to a Two-Ribbon M1 Class Flare and CME

P. Vemareddy, R.A. Maurya, A. Ambastha. (2011). Solar Phys., doi: 10.1007/s11207-011-9903-6.


Sub-surface Meridional Flow, Vorticity and the Lifetime of Solar Active Regions

R. A. Maurya and A. Ambastha. (2010). Astrophys.J., .714, L196-L201.


Variations in p-Mode Parameters with Changing Onset Time of a Large Flare
R. A. Maurya, and A. Ambastha (2009).
Astrophys.J., 706, L235-L239.


Possibility of Excitation of Low-l P-modes by Energetic Solar Transients
A. Ambastha,
H. M. Antia (2006).
Solar Phys., 238, 219-230.

Solar P-mode Characteristics Associated with Superactive-Regions Observed during Oct-Nov 2003
A. Ambastha,
S. Basu, H.M. Antia, and R.S. Bogart (2004). ESA SP-559, 293.


Flare-Induced Excitation of Solar p-modes
A. Ambastha,
S. Basu, and H.M. Antia (2003).
Solar Phys., 218, 151.


Emerging Flux and X-Class flares in NOAA 6555
Debi Prasad, A. Ambastha, and Guoxiang Ai (1998). Solar Phys., 179, 133-140.


The Magnetic Evolution of AR6555 which led to Two Impulsive,  Relatively Compact, X-Type Flares
J. M. Fontenla, A. Ambastha, B. Kalman, and Gy. Csepura (1995). Astrophys. Jnl., 440, 894-906.


Evolutionary and Flare Associated Magnetic Shear Variations Observed in a Complex, Flare-Productive Active Region
, M.J. Hagyard, and E.A. West (1993). Solar Phys., 148, 277-299.


Non-Adiabatic Motion of Charged Particles in Axisymmetric Mirror Magnetic Fields
and R.K. Varma (1988).
Plasma Phys. and Controlled Fusion. 30, 1279-1296.


On the Global Density Waves in Self-Gravitating Flat Disks
A.Ambastha and R.K. Varma (1983).
Astrophys. Jnl., 264, 413-426.



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