Investigating submeso motions with DTS

Turbulence in the atmosphere mixes air and it tends to even out inhomogeneities in tempera- ture and gas concentrations. Of particular relevance, it controls how things like heat and gases are transported near the surface of the earth. Normally during the day the atmosphere is warmer near the surface and cooler above. In this case, turbulence is strong and can easily move gases and heat vertically, away from the surface, since the warm air below is more buoy- ant than the air above it. We understand this type of turbulence fairly well. In contrast, during the night, over reflective surfaces like snow, and in the polar winter, turbulence is often not as strong. In these cases, the atmosphere is cooler nearer the surface and warmer up above. In this case, the air near the surface is less buoyant than the air above it, creating stable condi- tions. As a result during stable conditions, vertical motions are often, but not always, sup- pressed, causing turbulence to only weakly mix gases and transport heat. This type of turbu- lence strongly affects a range of systems including agriculture, hydrology, weather forecasts, fog formation, and air quality. The main issue is that turbulence during stable conditions is not well understood. During stable conditions atmospheric turbulence can suddenly strengthen and mix the atmosphere, other times no turbulent transport occurs, and sometimes it is in between. Theory does not represent these transitions. As a result, models of the atmosphere (like for weather forecasts) often strug- gle to represent the atmosphere during stable conditions. It is suspected that well-organized flows in the atmosphere, with the technical name submeso motions, cause turbulence to switch between these states. However, these motions are difficult to study using typical obser- vations and theory since they have a size between what we can observe with weather stations and what we can observe using techniques like satellites. To improve our understanding of the atmosphere we need a novel approach. We have pioneered a completely new way of studying the motions of the atmosphere and can reveal flow patterns that could only be guessed at previously. First, we will use a new technique called distributed temperature sensing (DTS), which allows us to observe the atmosphere con- tinuously along strands of fiber optic cables hung up in the air. Submeso motions, among other types of flows, become clearly visible when using DTS. While this technique is new, it has been used before. The main limitation is using the data from DTS since it generates thousands of ob- servations simultaneously along each fiber optic cable. In the second part of the research we will build a new mathematical framework that reveals these motions in DTS data in an objective way. Using these two techniques, we can identify and characterize any motions of the atmos- phere, including submeso motions, which should provide a technical breakthrough for geophys- ical studies more generally. With these results, we will be able to directly describe arbitrary submeso motions for the first time and infer how they are generated. This knowledge will help us write the next generation of turbulence theory and improve weather forecasts.