π€ AI Summary
This study investigates whether intraday volatility dynamics are entirely driven by deterministic diurnal patterns. To this end, the authors propose a nonparametric approach that extends pre-averaged bipower variation to high-frequency data featuring jumps and market microstructure noise within a general ItΓ΄ semimartingale framework, yielding a robust estimator of the diurnal scaling factor. A test statistic is constructed based on seasonally adjusted returns, and an improved bootstrap procedure is introduced to enhance finite-sample inference. Empirical results show that while the diurnal pattern accounts for a substantial portion of intraday volatility, significant residual heteroskedasticity remains, indicating the presence of additional time-varying sources of volatility beyond the deterministic seasonal component.