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Abstract A novel methodology is developed to extract accurate skeletal reaction models for nuclear combustion. Local sensitivities of isotope mass fractions with respect to reaction rates are modeled based on the forced optimally time-dependent (f-OTD) scheme. These sensitivities are then analyzed temporally to generate skeletal models. The methodology is demonstrated by conducting skeletal reduction of constant density and temperature burning of carbon and oxygen relevant to Type Ia supernovae (SNe Ia). The 495-isotopes Torch model is chosen as the detailed reaction network. A map of maximum production of⁵⁶Ni in SNe Ia is produced for different temperatures, densities, and proton-to-neutron ratios. The f-OTD simulations and the sensitivity analyses are then performed with initial conditions from this map. A series of skeletal models are derived and their performances are assessed by comparison against currently existing skeletal models. Previous models have been constructed intuitively by assuming the dominance ofα-chain reactions. The comparison of the newly generated skeletal models against previous models is based on the predicted energy release and⁴⁴Ti and⁵⁶Ni abundances by each model. The consequences ofy_e≠ 0.5 in the initial composition are also explored wherey_eis the electron fraction. The simulated results show that⁵⁶Ni production decreases by decreasingy_eas expected, and that the⁴³Sc is a key isotope in proton and neutron channels toward⁵⁶Ni production. It is shown that an f-OTD skeletal model with 150 isotopes can accurately predict the⁵⁶Ni abundance in SNe Ia fory_e≲ 0.5 initial conditions. 

We propose that the upcoming Decadal Survey on Solar and Space Physics describe prominent contributions of lightning and its impacts beyond the troposphere, particularly within the NASA Heliophysics portfolio. We present a brief review of several topics highly relevant to NSF and NASA. We opt to unify these topics into one white paper, with longer reviews/references included.