We investigated the influence of seasonality and proximity to the forest canopy on nocturnal turbulence regimes in the roughness sublayer of a Central Amazon forest. Since convective systems of different scales are common in this region, we also analyzed the effect of extreme wind gusts (propagated from convective downdrafts) on the organization of the turbulence regimes, and their potential to cause the mortality of canopy trees. Our data include high-frequency winds, temperature and ozone concentration at different heights during the dry and wet seasons of 2014. In addition, we used critical wind-speed data derived from a tree-winching experiment and a modeling study conducted in the same study site. Two different turbulence regimes were identified at three heights above the canopy: a weakly stable (WS) and a very stable regime (VS). The threshold wind speeds that mark the transition between turbulence regimes were larger during the dry season and increased as a function of the height above the canopy. The turbulent fluxes of sensible heat and momentum during the WS accounted for 88% of the entire nighttime flux. Downdrafts occurred only in the WS and favored a fully coupled state of wind flow along the canopy profile. The destructive potential of winds was four times higher than on nights without downdrafts.

我们调查了季节性和靠近森林冠层对亚马逊中部粗糙子层夜间湍流机制的影响森林。由于不同规模的对流系统在该地区很常见，我们还分析了极端阵风（从对流下沉气流传播）对湍流机制的影响，以及它们导致冠层树木死亡的可能性。我们的数据包括 2014 年旱季和雨季不同高度的高频风、温度和臭氧浓度。此外，我们还使用了从绞树实验和同一研究中进行的模型研究中得出的关键风速数据地点。在树冠上方的三个高度确定了两种不同的湍流状态：弱稳定 (WS) 和非常稳定的状态 (VS)。标志着湍流状态之间过渡的阈值风速在旱季更大，并且随着树冠上方高度的增加而增加。WS期间感热和动量的湍流通量占整个夜间通量的88%。下沉气流仅发生在 WS 中，并且有利于沿冠层剖面的风流完全耦合状态。风的破坏力是没有下沉气流的夜晚的四倍。