Boundary Layer Late Afternoon and Sunset Turbulence

BLLAST is a research programme aimed at exploring the late afternoon transition of the atmospheric boundary layer. The late afternoon period of the diurnal cycle of the boundary layer is poorly understood. This is yet an important transition period that impacts the transport and dillution of water vapour and trace species. The main questions adressed by the project are: - How the turbulence activity fades when heating by the surface decreases? - What is the impact on the transport of chemical species? - How relevant processes can be represented in numerical models? To answer all these questions, a field campaign was carried out during the summer of 2011 (from June 14 to July 8). Many observation systems were then deployed and operated by research teams coming from France and abroad. They were spanning a large spectrum of space and time scales in order to achieve a comprehensive description of the boundary layer processes. The observation strategy consisted in intensifying the operations in the late afternoon with tethered balloons, resarch aircrafts and UAVs.

BLLAST是一项旨在探究大气边界层傍晚过渡期的研究计划。边界层日循环的傍晚时段，其理解尚显不足，然而这却是一个至关重要的过渡期，对水汽和痕量物种的传输与稀释产生显著影响。该项目主要解决的问题包括：当地表加热减弱时，湍流活动如何逐渐衰减？化学物种的传输受到何种影响？何种相关过程可以在数值模型中得到有效表征？为解答上述所有问题，于2011年夏季（6月14日至7月8日）开展了一次实地考察。众多观测系统由来自法国及海外的科研团队部署并运行，涵盖了广泛的空间和时间尺度，以实现对边界层过程的全面描述。观测策略在于通过系留气球、研究飞机和无人机等手段，在傍晚时段加强观测活动。