Investigating the impact of IR surface emissivity knowledge & uncertainties on climate & weather-forecasting timescales

人类引起的气候变化的规模和速度预计将在高纬度(极地)地区达到最大。地表和大气之间的辐射相互作用是理解气候变化的关键，在极地地区，冰冻层和开阔海洋之间的相互作用加强了这种相互作用，在中至远红外中，冰冻层和开阔海洋的大气异常透明。全球许多表面类型的表面反射/发射率已经在可见光和近红外光谱中得到了广泛的研究。然而，最近的气候模型模拟表明，迄今尚未被认识到的反馈过程可能会通过红外相互作用显著加快北极地区的变暖速度。这一过程被称为“冰发射率”反馈，假定依赖于来自积雪和海洋表面的远红外辐射(波长在15微米到100微米之间)的差异表面发射(Feldman等人，2014年)。在FIR中，对表面发射率的理论估计表明，海洋的发射率低于上覆的冰层和雪层，因此，当雪/冰融化时，额外的热量可能被困在上层海洋中，加速冰的融化，导致近地表和表面进一步变暖。现有的研究表明，有必要改进目前对全红外光谱中表面发射率的估计。这些研究还表明，雪和冰表面的发射率光谱确实与完美的黑体发射体的发射率光谱有很大不同(这是目前大多数天气和气候预测模型所做的假设)。帝国理工学院空间和大气物理小组最近开展的工作首次通过空中观测对FIR表面发射率进行了现场估计(Bellisario等人，2017年)。我们目前还在开发通过专门设计的便携式地面系统测量穿过红外线的表面发射率的能力。目前的建模工作主要集中在极地地区对红外表面发射率的长期响应上，但它对较短的“天气”时间尺度的未研究影响以及它为月度尺度预测增加的大量不确定性来源不应被估计。因此，在这个项目中，您将：(1)进一步利用北极飞行活动数据来评估我们初始结果的稳健性，并对理论雪/冰表面发射率估计值进行额外评估。(2)利用我们的新的地面干涉仪系统，在一系列不同的表面和条件下获得跨越中红外和远红外的红外发射率的现场估计，最初侧重于雪/冰覆盖的高纬度地区。(3)与合作主管机构合作，评估新的稳健的红外表面反射率/发射率测量对EOCAL/VAL、气候研究和数值天气预报应用领域的影响。

The magnitude and pace of human-induced climate change is projected to be at its largest in high-latitude (polar) regions. The radiative interaction between the surface & atmosphere is key to understanding climate change, enhanced in Polar Regions by the interplay between the cryosphere & open ocean under an exceptionally transparent atmosphere in the mid- to far-IR. Surface reflection/emissivity has been studied extensively throughout the visible and NIR for many surface types across the globe. However, recent climate model simulations have highlighted that a hitherto unrecognised feedback process may significantly accelerate the rate of warming in arctic areas through IR interactions. Termed the 'ice-emissivity' feedback, the process is postulated to rely on differential surface emission of far infrared (FIR) radiation (wavelengths between ~ 15 and 100 microns) from snow covered and ocean surfaces (Feldman et al., 2014). In the FIR, theoretical estimates of surface emissivity suggest that the ocean is less emissive than overlying ice and snow layers, hence as snow/ice melts additional heat can be trapped within the upper ocean, accelerating ice melt and leading to further near surface and surface warming. Existing studies evidence a need for improvements in current estimates of the surface emissivity across the full infrared spectrum. These studies also indicate that snow and ice surfaces do indeed have an emissivity spectrum that is significantly different from that of a perfect, blackbody emitter (an assumption made in most current weather and climate prediction models). Very recent work within Imperial College's Space and Atmospheric Physics group has delivered the first ever in-situ estimates of FIR surface emissivity from airborne observations (Bellisario et al., 2017). We are also currently developing the capability to make measurements of surface emissivity extending across the infrared via a purpose designed portable ground-based system. Current modelling efforts have focused on the long-term response of the polar regions to infrared surface emissivity, but its unstudied impact on shorter 'weather' time-scales and the large source of uncertainty it adds to monthly-scale predictions should not be estimated. In this project you will thus: (1) Further exploit arctic flight campaign data to assess the robustness of our initial results and perform additional evaluation of theoretical snow/ice surface emissivity estimates.(2) Utilise our new ground-based interferometer system to obtain in-situ estimates of infrared emissivity spanning the mid- and far infrared for a range of different surfaces and conditions, focusing initially on snow/ice covered high latitudes.(3) Work with the co-supervisor institutions to assess the impact of new robust IR surface reflectance/emissivity measurements on EO cal/val, climate studies & numerical weather prediction application areas.