Catholic University of America
"In our obscurity - in all this vastness - there is no hint that help will come from elsewhere to save us from ourselves.
It is up to us."
- Carl Sagan
The inherent human ability to wonder about the universe is invaluable. This same sense of wonder has led me to pursue science, and begin my decade-long journey into space physics. From tiny charged particles whizzing around in space, to large magnificent displays of aurora, I have been fortunate to explore this world's hidden enchantments. And hence I wish for a future where humans can continue to enjoy the beauty of this universe.
However, technological advancements that have bestowed us with unforeseen benefits have also made existential threats a reality. It would be a shame if all this beauty, and our ability to marvel at it, were sacrificed at the altar of human folly. Thus, currently I am looking for projects where I can leverage my skills to understand how we might mitigate the existential threats that we face from ourselves. [More]
Started work at NASA Goddard Space Flight Center through the Catholic University of America.
Defended my Ph.D. in Electrical Engineering successfully at Boston University (Aug 2020)
Summer Research Fellow at Future of Humanity Institute, Oxford. (Jul 2020)
Our work gets highlighted by NASA.
[NASA Highlight, 27 Aug 2019][Link] New
ECE PhD Student Receives Prestigious NASA Fellowship
[BU College of Engineering, Spotlight, 2018][Link]
Features in aurora mark the outer extent of the radiation belt. It can potentially be used to constrain magnetic field models, and identify real-time extent of the belts.
Simultaneous measurements of substorm-related electron energization in the ionosphere and the plasma sheet
Intense aurora is sometimes accompanied by energetic electrons. Using multiple instruments we identified the source of the electrons (~ 300 keV) to be beyond 60,000 km (9 RE) in the plasma sheet.
[Nithin Sivadas, Josh Semeter, Toshi Nishimura, Antti Kero. Journal of Geophysical Research: Space Physics, 2017][Link]
Remote sensing of energetic electron precipitation [Ph.D. Dissertation]
Here I explore the source and effects of energetic electrons in the polar regions using sensors from ground and space, far away from the auroral altitudes. [Nithin Sivadas, Boston University, 2020] [Link] [Plain-language summary]
Coincidental TID production by tropospheric weather during the August 2017 total solar eclipse
During the total solar eclipse across the United States in 2017, observation of "bow waves" induced by the moon's shadow racing across the Earth's ionosphere were reported. We show that this is unlikely the case, and that the wave-like features are likely caused by a tropospheric thunderstorm in the eclipse path.
[Sebastijan Mrak, Josh Semeter, Toshi Nishimura, Michael Hirsch, Nithin Sivadas. Geophysical Research Letters, 2018][Link]
Prediction and understanding of soft proton contamination in XMM-Newton: a machine learning approach
Space-based X-ray telescopes that probe astronomical objects are plagued by background noise from soft (~10-100 keV) protons, leading to a loss of telescope observing time. Using previous data we develop a machine learning model to predict the background contamination. We conclude that future missions should choose orbits that minimize time spent during high solar wind speeds and dusk flank regions in the southern hemisphere to reduce the contamination.
E. A. Kronberg, F. Gastaldello, S. Haaland, A. Smirnov, M. Berrendorf, S. Ghizzardi, K. D. Kuntz, N. Sivadas, R. C. Allen, A. Tiengo, R. Ilie, Y. Huang, and L. Kistler [The Astrophysical Journal, 2020][Link]
Spacecraft & Instrumentation
A nano-satellite mission to study charged particle precipitation from the Van Allen radiation belts caused due to Seismo-Electromagnetic emissions
Describes the mission and science goals of the IIT Madras Nano Satellite (iitmsat), which carries a high energy particle detector that can measure electrons (1-15 MeV) and protons (1-100 MeV) precipitating from the Van Allen radiation belts.
[Nithin Sivadas and others. The 5th Nano Satellite Symposium, 2014.][Link]
IITMSAT, an efficient nano-satellite bus design for a large payload
Describes the design of an efficient nano-satellite bus design, that can house a large science instrument.
[Akshay Gulati, Nithin Sivadas, and others. The 5th Nano Satellite Symposium, 2014][PDF]
Extreme Magnetosphere‐Ionosphere‐Thermosphere Responses to the 5 April 2010 Supersubstorm
During an extreme substorm event, auroral intensification in the poleward boundary of the auroral oval followed by an auroral streamer was associated with relativistic electron precipitation. The results suggest that localized magnetic reconnection might lead to the release of substantial energy resulting in large effects in the ionosphere.
Y. Nishimura, L. R. Lyons, C. Gabrielse, N. Sivadas, E. F. Donovan, R. H. Varney, V. Angelopoulos, J. M. Weygand, M. G. Conde, S. R. Zhang [The Astrophysical Journal, 2020][Link]
How frequently do we see auroral signatures of radiation belts?
The radiation belt outer boundary seem to be correlated to structured diffuse aurora during growth phase of a substorm. I am trying to find out how frequent these signatures are in aurora.
Optical signature of the radiation belt boundary observed at Poker Flat, Alaska using the Digital All-Sky Camera from the Geophysical Institute. (From Sivadas et al., 2019)
How much does
the Earth's magnetotail stretch?
Solar wind interactions with the Earth's magnetic field results in the stretching of the Earth's magnetotail and a series of processes. It shifts the equilibrium of the complex magnetosphere-ionosphere system to the edge of an instability - the onset of a magnetic substorm - the most visible features of which are the intense auroral displays in the polar regions. With Anton Artemyev, we are trying to understand the extent of the stretching, and the strength of the current that deforms the magnetic fields.
Magnetic field configuration with a stretched magnetotail, calculated using the Tsyganenko 96 magnetic model. (From Sivadas et al., 2019)
Contribution of energetic electrons to ionospheric conductance
Ionospheric conductance is an essential parameter that affects Magnetosphere-Ionosphere coupling. However, most quantitative estimates of ionospheric conductance takes into account only those caused by precipitation of electrons <30 keV, due to sparse data. Estimating the conductance of the D-region ionosphere due to energetic precipitation also remains a challenge. Can we estimate quantitatively the contribution of energetic electrons > 30 keV to the ionospheric conductance? We try to answer this using measurements from the AMISR system operated by Roger Varney and his team at SRI International.
Altitude profile of electron density measured by Poker Flat Incoherent Scatter Radar in Alaska, showing the extent of D- and E-region ionospheres. The conductivity is proportional to the electron density and is a function of the ion chemistry. (From Sivadas et al., 2017)