Solar heating causes the periodic expansion and contraction of Earth’s atmosphere known as the atmospheric tide. This is observed at the surface as a semidiurnal pressure oscillation that appears to influence convection and rainfall. Roughly 0.5 to 1.0 billion years ago, when day length was roughly 21–22 hours, the tide would have been resonant, or close in frequency, with atmospheric Lamb waves of 10.5–11.0 hour periods. This ‘Lamb resonance’ would have amplified the pressure oscillation, perhaps strongly enough to affect the global or tropical climate. Here we run a general circulation model at different rotation rates to model the resonance and its impact on climate. The resonance exerts a dominant control on tropical cloud cover, convection and rainfall: sunrise and sunset are cloudy and rainy, whereas midday and midnight are clear and dry. Generally clear skies at noon lower the albedo, contributing 2–4 K warming in the global average, which would have helped counter the 10% fainter Sun. The hydrological cycle becomes more active, and the atmosphere moister. Our work highlights the role of tidally induced adiabatic expansion in controlling tropical precipitation, helping explain modern-day observations of a semidiurnal rainfall pattern.

太阳加热导致地球大气周期性膨胀和收缩，称为大气潮汐。这是在地表观察到的半日压力振荡，似乎影响对流和降雨。大约 0.5 至 10 亿年前，当白天长度约为 21 至 22 小时时，潮汐会与周期为 10.5 至 11.0 小时的大气兰姆波产生共振或频率接近。这种“兰姆共振”会放大压力振荡，其强度可能足以影响全球或热带气候。在这里，我们在不同的旋转速率下运行大气环流模型来模拟共振及其对气候的影响。共振对热带云量、对流和降雨具有主导控制作用：日出和日落多云多雨，而中午和午夜晴朗干燥。中午晴朗的天空会降低反照率，导致全球平均变暖 2-4 K，这有助于抵消 10% 的暗淡太阳。水文循环更加活跃，大气更加湿润。我们的工作强调了潮汐引起的绝热膨胀在控制热带降水中的作用，有助于解释现代对半日降雨模式的观测。