With local baselines, the H-alpha excess-to-continuum ratio falls between two intervals before the predicted 2024 December 16 transit of TOI-3884 b

We measure the H-alpha line excess and nearby continuum excess in public JWST/NIRISS spectra of TOI-3884. The test uses two parts of the known flare sequence before the predicted 2024 December 16 transit. We use a locally scaled quiet spectrum and linear quiet baselines. An interval with 18 integrations gives a flare excess equivalent width of 16.73 nm. One later integration gives 6.62 nm. Their ratio is 2.53, with a conditional 95% paired block-noise interval of 2.09–3.12. The line excess increases by a factor of 1.71 while the continuum excess increases by 4.32. We test 120 choices of bands, baselines, continuum methods, time windows, and line pixels. The earlier/later equivalent-width ratio ranges from 2.03 to 2.69 in these tests. Under the published circular transit geometry, every primary exposure ends before ingress. One scaled H-alpha profile cannot describe both local excess signals in the tested intervals. The result does not identify a heating mechanism. The intervals were selected after inspection. The uncertainty holds the spectral template fixed and assumes that quiet residuals describe flare errors. The package preserves spectral arrays for two visits, source hashes, code, results, figures, and offline reproduction checks. It does not include an independent reduction from detector data.

TOI-3884 · stellar flares · JWST · NIRISS · H-alpha · stellar contamination · time-resolved spectroscopy