Observing local and Remote Controls on Arctic Air mass evolution (ORCA2)

北极目前正以前所未有的速度变暖，伴随着海冰覆盖面积的急剧减少。这种加速变暖的现象被称为北极放大。虽然已知各种气候反馈过程发挥了作用，但最近的研究强调了北极气候系统和中纬度地区之间的气团交换同样重要。这包括南下的冷空气挤压，以及北上的暖湿空气侵入北极高地。特别是强湿气入侵事件可以通过相关的增强的经向热量和水汽输送而起到显著的作用。此外，嵌入在水汽侵入层中的低层液态云增强了地面向下的长波辐射通量，从而显著增加了地表热量收支，从而增强了海冰的融化。因此，近年来，对北极气团交换，特别是水汽入侵的确切性质进行了深入的研究。现在已经清楚的是，潮湿气团的演变是一系列过程的净效应，这些过程覆盖了令人难以置信的广泛范围，从微尺度的湍流和云物理一直延伸到全球罗斯比波。小尺度的过程就像是对气团的局部控制，而像下沉这样的大尺度的过程就像遥控器。最近对北极含云湍流混合层的大涡模拟研究突出了水汽入侵的两个方面：i)大范围下沉对气团演变的强烈控制，ii)湿度逆变在这一过程中可能发挥的重要作用。虽然这些新的见解代表着重要的进步，但仍然缺乏对这些建模结果的观察支持。为了达到这一目的，需要可靠地观测北极潮湿入侵期间的大规模下沉。该项目的目的是通过使用高空和远程研究飞机(HALO)在计划于2021年3-4月进行的HALO-(AC)3战役期间收集的数据来填补这一数据空白。Halo在这方面的一个明显好处是它的长期愤怒和高空速，使得能够有效和频繁地对北极偏远地区的移动气团进行拉格朗日采样。其次，使用了一种新的技术来测量大范围的发散，该技术依赖于在大圆周飞行模式中释放的下落探测仪，就像最近的NARVAL2活动中探索的那样。这些观测，再加上对混合相云、辐射和湿度倒置的额外独立测量，将与跟踪气团的拉格朗日高分辨率大涡模拟相结合。这种高分辨率拉格朗日模拟和水汽入侵观测的协同作用是一种新奇的东西，因此将为我们增加对气团转换的洞察创造新的机会。

The Arctic is currently warming at unprecedented rates, accompanied by dramatic loss in sea ice coverage. This accelerated warming is referred to as Arctic Amplification. While a variety of climate feedback processes is known to play a role, recent research has emphasized the similar importance of air mass exchanges between the Arctic climate system and the mid-latitudes. This involves southbound extrusions of cold air as well as northbound intrusions of warm and moist air into the high Arctic. Strong moisture intrusion events in particular can contribute significantly, through the associated enhanced meridional transport of heat and moisture. In addition, low level liquid clouds embedded in moisture intrusions enhance the downwelling long-wave radiative flux at the surface, which dramatically increases the surface heat budget and thus enhances the melt of the sea ice. Elucidating the exact nature of Arctic air mass exchanges, in particular moisture intrusions, has therefore been intensely researched in recent years. What has become clear is that the evolution of moist air masses is a net effect of a multitude of processes that covers an incredibly wide range of scales, stretching from micro-scale turbulence and cloud physics all the way to global Rossby waves. Smaller scale processes act like local controls on the air mass, while larger-scale processes like subsidence act like remote controls. Recent LES studies of cloud-bearing turbulent mixed-layers in the Arctic have highlighted two aspects of moisture intrusions; i) the strong control of large-scale subsidence on the air mass evolution, and ii) the potentially important role of humidity inversions in this process. While these new insights represent important progress, observational support for these modeling results is still lacking. What is needed to this purpose are reliable observations of large-scale subsidence during moisture intrusions in the Arctic. The aim of this project is to fill this data gap by using data collected by the High Altitude and LOng-range research aircraft (HALO) during the HALO-(AC)3 campaign, scheduled to take place in March-April 2021. A clear benefit of HALO in this respect are its long rage and high air speed, allowing the Lagrangian sampling of moving air masses in remote areas in the Arctic effectively and frequently. Second, use is made of a new technique for measuring large-scale divergence that relies on dropsondes released during large circular flight patterns, as explored during the recent NARVAL2 campaign. These observations, in combination with additional indepdendent measurements of mixed-phase clouds, radiation and humidity inversions, will be combined with Lagrangian high-resolution Large-Eddy Simulations that follow the air mass. This synergy of high-resolution Lagrangian simulation and observation of moisture intrusions is a novelty, and will thus create new opportunities for increasing our insight into air mass transformations.