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Using ERA5 reanalysis data, precipitation data from GPM IMERG and automatic weather stations (AWS), RMCR radar composite reflectivity data, and the WRF model, this study investigates the hierarchical influence of multiscale topography on gravity waves (GWs). Furthermore, it examines the impact of GWs of different wavelengths, excited by multiscale topography, on mesoscale convective systems (MCSs) and rainstorms in the Sichuan Basin. Results elucidate the specific roles and synergistic effects of multiscale terrain. The broad windward slopes of the Yunnan-Guizhou Plateau (with a horizontal scale on the order of 1000 km) excite long-wavelength GWs (GW1), which propagate horizontally through the middle and upper troposphere via the wave duct effect. Superimposed local peaks and valleys on the Yunnan-Guizhou Plateau (with horizontal scales on the orders of 10 or 100 km) excite shorter-wavelength GWs (GW2), propagating through the lower and middle troposphere. Sensitivity experiments demonstrate that local topographic features serve as direct excitation sources for GW2, while simultaneously acting as a disruptive factor for GW1. Topographic disturbances induce complex airflow motions, generating densely distributed updrafts, downdrafts, and eddy currents, which collectively reduce the maintenance duration of GW1. Once excited, GW1 enhances updraft development in the upper troposphere downstream of its propagation path, thereby modulating the overall intensity of the MCS and influencing widespread precipitation. In contrast, GW2 propagates at lower altitudes and can directly affect updraft intensity within a specific region of the MCS, thereby expanding the spatial extent of heavy rainfall in the Sichuan Basin. This study demonstrates that the superposition of broad topographic forcing (order of 1000 km) and local topographic triggering (orders of 10 or 100 km) jointly controls the evolution of rainstorms.

We report observations of faint (10<SUP>−6</SUP>), concentric, planet-wide rings in the polarized flux of sunlight that is reflected by Venus, obtained during a serendipitous, 36-minute run in 2010, with the highly sensitive Extreme Polarimeter (ExPo) on the William Herschel Telescope. The rings appear to be centered slightly downwind of the subsolar point, are visible in different filters across the visible, and are not obvious in the simultaneous total flux observations. ExPo's dual-beam exchange and double-differencing design strongly suppresses first-order instrumental polarization, and we could not identify an instrumental cause of the observed pattern. Because ExPo was dismantled before the rings were identified in the data, this is the only set of observations of these rings. We are therefore careful in claiming the detection of a new atmospheric phenomenon on Venus. However, numerical radiative transfer simulations show that planet-wide rings in polarization can arise owing to density variations of 5%─10% in the gas above the clouds, consistent with a gravity wave. Our simulations also show that such density variations would not show up in total flux observations. By presenting our observations and numerical simulations, we hope to motivate new polarimetric observations of Venus that could confirm or refute the presence of such planet-wide waves.