Pukite QBO pressure-level explorer

The selected pressure level uses FU Berlin monthly mean zonal wind data. Three sideband constructions are available: a physical sample-and-hold mode for the stroboscopic annual input, an independent-control exploratory mode, and a Hilbert analytic variant of the independent mode. In physical mode the sideband strengths are not user-exposed; instead the square-wave-like hold is constructed only in physical mode on a finer internal time grid: the draconic signal is sampled at annual impulse times, held between events, damped by linear reversion to zero, and then averaged back to monthly values for display. For the analytic modes, the tropical and draconic factors are both carried explicitly in the forcing, following the tidal-constituent superposition idea in which close frequencies generate a natural beat envelope. No directly added continuous carrier is included in the displayed physical branch. A local fitting routine is also available to tune model parameters over the 1960–1975 training interval by maximizing correlation with a small RMSE penalty. The draconic and tropical amplitudes are now allowed to go negative so that phase reversals can be represented either by phase or by sign, which tends to raise the achievable correlation coefficient on the training interval. For the sample-and-hold differential equation, the initial state is also exposed and optimized as an explicit integration initial condition. The annual term is now a pure annual sinusoid with fitted amplitude and phase, in the same spirit as Chandler-plus-annual harmonic fits. The tropical 27.3216-day factor is now introduced alongside the 27.2122-day draconic factor in the forcing construction, so the 18.6-year nodal envelope arises naturally as a beat between the two factors rather than from a separately imposed modulation term.