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Despite being the most prominent emission line in the solar spectrum, therehas been a notable lack of studies devoted to variations in Ly$\alpha$ emissionduring solar flares in recent years. However, the few examples that do existhave shown Ly$\alpha$ emission to be a substantial radiator of the total energybudget of solar flares (on the order of 10%). It is also a known driver offluctuations in earth's ionosphere. The EUV Variability Experiment (EVE)onboard the Solar Dynamics Observatory now provides broadband, photometricLy$\alpha$ data at 10 s cadence with its Multiple EUV GratingSpectrograph-Photometer (MEGS-P) component, and has observed scores of solarflares in the 5 years since it was launched. However, the MEGS-P time profilesappear to display a rise time of tens of minutes around the time of the flareonset. This is in stark contrast to the rapid, impulsive increase observed inother intrinsically chromospheric features (H$\alpha$, Ly$\beta$, LyC, C III,etc.). Furthermore, the emission detected by MEGS-P peaks around the time ofthe peak of thermal soft X-ray emission, rather than during the impulsive phasewhen energy deposition in the chromosphere - often assumed to be in the form ofnonthermal electrons - is greatest. Given that spectrally-resolved Ly$\alpha$observations during flares from SORCE/SOLSTICE peak during the impulsive phaseas expected, this suggests that the atypical behaviour of MEGS-P data is amanifestation of the broadband nature of the observations. This could implythat other lines and/or continuum emission that becomes enhanced during flarescould be contributing to the passband. Users are hereby urged to exercisecaution when interpreting broadband Ly$\alpha$ observations of solar flares.Comparisons have also been made with other broadband Ly$\alpha$ photometerssuch as PROBA2/LYRA and GOES/EUVS-E.

The Anomalous Temporal Behaviour of Broadband Ly$\alpha$ Emission During Solar Flares From SDO/EVE