In recent evenings, some distant sounds have appeared closer, a phenomenon linked to atmospheric conditions. As autumn begins with the equinox, regions such as Brittany are experiencing cool mornings followed by still summer afternoons. These temperature differences indicate the return of calm and clear nights, ideal for a phenomenon that affects sound perception. On clear, calm, and windless nights, temperature inversions trap cold air near the ground under a layer of warmer air, making distant sounds seem closer and louder. This same phenomenon also promotes the formation of morning fogs and cloud seas, as well as the accumulation of pollutants near the ground. These temperature inversions, frequent during anticyclonic episodes, will recur regularly throughout the autumn and winter of 2026-2027. Clear skies, no wind, and almost still air create conditions common during autumn anticyclonic episodes, which are accompanied by a more stable atmosphere with limited vertical movements. Cold and humid air remains trapped near the ground instead of dispersing. During these calm nights, without clouds to retain heat, distant sounds begin to seem abnormally close and powerful. This phenomenon has been observed in mid-September in several mountain valleys, where strong morning temperature inversions have caused temperatures to drop near the ground. During a clear night, the ground cools rapidly through infrared radiation. The air just above becomes colder than the layers above it, sometimes with a difference of more than 10°C over only a few hundred meters of altitude. This is called a temperature inversion, the most common being the surface inversion, or radiation inversion, typical of largely clear autumn and winter nights. This unusual configuration, with cold air below and warmer air above, modifies the propagation of sound waves. The Midwestern Regional Climate Center, affiliated with Purdue University and the NOAA, explicitly cites this effect among the consequences of temperature inversions: sound waves travel farther and seem stronger. This is a possible explanation for these nighttime noises that appear to emerge from nowhere, when in reality they come from a source much farther away than the ear might suggest. This same temperature inversion that deceives our ears also promotes the formation of morning fogs and cloud seas in valley backgrounds, a classic sight in the mountains where cold, denser air accumulates in low areas while the peaks remain sunny and mild. The ceiling of this layer of cold air varies by region, generally between several hundred meters and a bit more than a thousand meters in the Alpine massifs, and it can sometimes rise up to 800 to 1,500 meters in Haute-Savoie. This same vertical blocking of air also has less poetic consequences: by preventing mixing, it promotes the accumulation of pollutants near the ground, which explains many pollution peaks in autumn and winter. Another effect to know is that dew forms almost systematically during these inversions, a detail that increases the risk of disease for crops sensitive to humidity. This type of weather situation, favored by atmospheric calm and the absence of wind, will recur regularly throughout the autumn and winter of 2026-2027, with each new anticyclonic episode.