Quantifying Surface Heat Exchange over Heterogeneous Land Surfaces at Ultra-High Spatio-Temporal Resolution

The lateral transport of heat above abrupt (sub-)metre-scale steps in land surface temperature influences the local surface energy balance. We present a novel experimental method to investigate the stratification and dynamics of the near-surface atmospheric layer over a heterogeneous land surface. Using a high resolution thermal infrared camera pointing at synthetic screens, a 30Hz sequence of frames is recorded. The screens are deployed upright and horizontally aligned with the prevailing wind direction. The screen’s surface temperature serves as a proxy for the local air temperature. We developed a method to estimate near-surface two-dimensional wind fields at centimetre resolution from tracking the air temperature pattern on the screens. Wind field estimations are validated with near-surface three-dimensional short-path ultrasonic data. To demonstrate the capabilities of the screen method, we present results from a comprehensive field campaign at an alpine research site during patchy snow cover conditions. The measurements reveal an extremely heterogeneous near-surface atmospheric layer. Vertical profiles of horizontal and vertical wind speed reflect multiple layers of different static stability within 2m above the surface. A dynamic, thin stable internal boundary layer (SIBL) develops above the leading edge of snow patches protecting the snow surface from warmer air above. During pronounced gusts the warm air from aloft entrains into the SIBL and reaches down to the snow surface adding energy to the snow pack. Measured vertical turbulent sensible heat fluxes are shown to be consistent with air temperature and wind speed profiles obtained using the screen method and confirm its capabilities to investigate complex in situ near-surface heat exchange processes. Here you find the data and the documented code used to create the plots in the publication.地表温度存在突变的（亚）米级台阶时，其上方的横向热输送会对局地地表能量平衡产生影响。我们提出了一种新颖的实验方法，用以研究非均匀下垫面上方近地表大气层的层结特征与动力学过程。 本研究采用一台指向合成屏的高分辨率热红外相机，记录了帧率为30Hz的帧序列。这些合成屏垂直架设，并与盛行风向水平对齐，其表面温度可作为局地气温的替代观测指标。我们开发了一套方法，通过追踪合成屏上的气温分布特征，估算厘米级空间分辨率的近地表二维风场。随后，我们利用近地表三维短程超声观测数据对风场估算结果进行了验证。 为展示该合成屏方法的性能，我们给出了在高山研究站点开展的综合野外观测试验结果，试验工况为斑块状积雪覆盖环境。观测结果揭示了极强非均匀的近地表大气层结构：在地表以上2米范围内，水平与垂直风速的垂直廓线呈现出多层不同静力稳定度的特征。在积雪斑块的前缘上方，会形成一层动态薄型稳定内部边界层（Stable Internal Boundary Layer，SIBL），该边界层可阻挡上方暖空气与雪面接触。当出现显著阵风时，高空暖空气会卷入该稳定内部边界层并下传至雪面，为雪层补充能量。实测的垂直湍流感热通量与通过合成屏方法得到的气温、风速廓线结果一致，验证了该方法可用于研究复杂的原位近地表热交换过程。 本研究附带有该论文发表中用于生成各类绘图的原始数据与带注释代码。