A study of clear sky closure study using high resolution far-IR spectra from the high arctic

地球的能量平衡是平衡的，也就是说，吸收和释放的能量是等量的。太阳是地球所有能量的来源，通过阳光加热地球，使表面变暖，这些能量以热量的形式释放回太空。一个简单的计算可以估计保持这种平衡所需的表面温度，大约是255K，或-18摄氏度。大气中吸收热量的气体（温室气体，如水蒸气和二氧化碳）的存在影响了这种基本平衡，这意味着它通常不是表面，而是在我们头顶上方一定距离的大气层中释放能量到太空；使地表温度比我们最初预期的要高，适合我们人类居住。一旦我们更详细地研究实际发生的事情，情况就会变得非常复杂。例如，表面是否被海洋、沙漠、森林或雪覆盖会产生很大的不同，通过大气深度和任何云的数量、高度和类型产生的温室气体浓度也会产生很大的不同。一般来说，在热带地区，吸收的能量比释放回太空的能量要多；风和海洋将这些多余的热量从北向南输送到两极。在另一个极端，北极地区吸收的阳光很少，向太空发射的能量比接收的要多。北极地区有反射性很强的冰雪，由于太冷，与低纬度地区相比，空气相对干燥。由于水蒸气是主要的温室气体之一，北极不像热带那样能很好地吸收热量。在某些地方和气象情况下，大气的部分热（红外）光谱变得透明，使表面直接冷却到太空，消除了大气的一些变暖效应。对于试图了解控制大气热量流失的微妙机制的科学家来说，这种情况的发生非常有趣。利用帝国理工学院高分辨率远红外光谱仪（TAFTS）和美国光谱仪（AERI-ER），我们在北极高海拔地区的一个地点测量了整个红外光谱，那里发生了这些罕见的情况。该地点是2007年春天位于阿拉斯加州巴罗的美国能源部大气辐射测量（ARM）地点。这些测量使我们能够透过这些透明的窗户，研究在这些干燥条件下温室气体和热辐射之间的相互作用。这些测量是由美国ARM计划资助的，初步分析表明数据质量良好，具有科学用途。我们现在希望分析这些数据，以便从中获得充分的科学效益和影响。除了光谱辐射的红外测量外，我们还有辅助数据，这些数据定义了大气的状态，包括整个大气的温度和水蒸气分布，以及缺乏云的证据等。利用这些数据集，我们的目标是能够更好地量化水蒸气吸收线的强度，以及被称为连续吸收的水蒸气的潜在吸收。我们还将利用我们的结果和模型来研究远红外线对太空的冷却。这项工作将提高我们对大气的理解，在全球气候模式的辐射成分中有许多应用，并有望提高大气模式的准确性。

The Earth's energy balance is in equilibrium, that is to say, an equal amount of energy is absorbed and emitted, The Sun is the source of all energy for the Earth, heating the planet via sunlight, warming the surface and this energy is emitted back into space as heat. A simple calculation can be made to estimate the surface temperature needed to preserve this equilibrium, and is about 255K, or -18degC. The presence of gases in the atmosphere that can absorb heat (greenhouse gases, such as water vapour and carbon dioxide), affects this basic equilibrium, meaning that it isn't generally the surface, but a layer of the atmosphere some distance above our heads that releases the energy to space; keeping the surface warmer than we would initially expect, and habitable for us humans. Once we look into what actually happens in more detail, this picture becomes very complicated. For instance, whether the surface is covered by ocean, desert, forests or snow makes a big difference, as does the concentration of greenhouse gases through the depth of the atmosphere and the amount, height and type of any cloud. Generally speaking, in the tropics more energy is absorbed than is emitted back to space; the winds and oceans transport this excess heat north and south towards the poles. At the other extreme, the Arctic region absorbs very little sunlight, and emits more energy to space than it receives. There is highly reflective snow and ice in the Arctic region and because it is so cold, the air is relatively dry compared to lower latitudes. With water vapour being one of the major greenhouse gases, the Arctic doesn't trap the heat as well as in the tropics. In some places and meteorological situations, parts of the heat (infra-red) spectrum of the atmosphere become transparent, allowing the surface to cool directly to space, removing some of the warming effect of the atmosphere. Where this happens is very interesting for scientists who try to understand the subtle mechanisms that control the loss of heat from the atmosphere. Using the Imperial College high resolution far infrared spectrometer (TAFTS), together with the US spectrometer (AERI-ER) we have taken measurements of the whole infrared spectrum from a site in the high arctic, where these rare conditions occur. The site was the United States Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) site in Barrow, Alaska, in the spring of 2007. These measurements allow us to look up through these transparent windows to study the interaction between the greenhouse gases and thermal radiation in these dry conditions. These measurements were funded by the US ARM program, with initial analysis having shown that the data is of good quality and of scientific use. We now wish to analyse this data to take the full scientific benefit and impact from it. In addition to the infrared measurements of spectral radiances, we have the auxiliary data, which defines the state of the atmosphere, both the temperature and water vapour profile throughout the atmosphere, evidence for the lack of clouds etc. Using these datasets we are aiming to be able to better quantify the strength of the water vapour absorption lines, and the underlying absorption by water vapour, known as the continuum absorption. We will also use our results and models to investigate the cooling to space in the far infrared. This work will improve our understanding of the atmosphere, with many applications in radiation components of global climate models, and is expected to give greater accuracy in atmospheric models.