Early‐stage bedforms develop into mature dunes through complex interactions between wind, sand transport, and surface topography. Depending on varying environmental and wind conditions, the mechanisms driving dune formation and, ultimately, the shape of nascent dunes may differ markedly. In cases where sand availability is plentiful, the emergence and growth of dunes can be studied with a linear stability analysis of coupled transport and hydrodynamic equations. Until now, this analysis has only been applied using field evidence in unidirectional winds. However, in many areas of the world and on other planets, wind regimes are more often bimodal or multimodal. Here, we investigate field evidence of protodune formation under a bimodal wind regime by applying linear stability analysis to a developing protodune field. Employing recent development of the linear stability theory and experimental research, combined with in situ wind, sediment transport, and topographic measurements during a monthlong field campaign at Great Sand Dunes National Park, Colorado, USA, we predict the spatial characteristics (orientation and wavelength) and temporal evolution (growth rate and migration velocity) of a protodune field. We find that the theoretical predictions compare well with measured dunefield attributes as characterized by high‐resolution Digital Elevation Models measured using repeat terrestrial laser scanning. Our findings suggest that linear stability analysis is a quantitative predictor of protodune development on sandy surfaces with a bimodal wind regime. This result is significant as it offers critical validation of the linear stability analysis for explaining the initiation and development of dunes toward maturity in a complex natural environment.

中文翻译：

---

双峰风况下的沙丘萌生

早期的床形通过风，沙的输送和表面地形之间的复杂相互作用而发展为成熟的沙丘。根据变化的环境和风况，驱动沙丘形成的机制以及最终形成的沙丘的形状可能会显着不同。如果有充足的沙土可利用耦合的运输和水动力方程的线性稳定性分析来研究沙丘的出现和生长。到目前为止，这种分析仅在单向风中使用现场证据进行了应用。但是，在世界上许多地区和其他星球上，风态通常是双峰或多峰的。在这里，我们通过对正在开发的原型场进行线性稳定性分析，研究在双峰风况下原型形成的现场证据。利用线性稳定性理论和实验研究的最新进展，结合在美国科罗拉多州大沙丘国家公园进行的为期一个月的野战活动中的原位风，泥沙输送和地形测量，我们可以预测空间特征（方向和波长）原始场的时空演化（增长率和迁移速度）。我们发现，理论预测与由重复地面激光扫描测量的高分辨率数字高程模型所表征的测得的dunefield属性具有良好的对比。我们的发现表明，线性稳定性分析是双峰风况下沙质表面原形发育的定量预测指标。