Trackers in the Atmosphere

The search for clues begins whenever scientists and their measuring equipment come across unexpected signatures in the air. If the path taken by a parcel of air is traced back over a long enough period of time, information can be provided about the freight it carries. Did the air pass over areas that are burning; was it exposed to the smog of urban agglomerations or to emissions from forests? Did volcanic eruptions, desert dust storms, or leaks from gas pipelines or nuclear facilities leave traces?

In order to trace back the flight path of an air parcel (its trajectory), a concept is employed that has a long tradition in physics: the Lagrange description of a flow. For each air parcel and point in time, the position, velocity and direction is determined. Changes in air properties like temperature, density and material composition result on the one hand from the dynamics in the immediate vicinity of the air, and on the other hand from the movement of the air parcel into a new environment with other conditions. Physicists use the term “total differential” when they describe the changes in air parcel characteristics during a flight path. Similarly, if a hiker spends an entire day sitting at the top of the Zugspitze mountain and repeatedly measures the temperature, then he records the temperature range experienced over the course of the day. But if he instead hikes from there to Innsbruck on that day while he measures the temperature, his thermometer records not only the temperature changes over the course of the day, but also the changes he encounters on his route as he descends into valleys and climbs peaks.

Now, complex trajectories can be calculated online with a few clicks. After a brief computation period, the path of the arriving air parcel is shown for the desired location and point in time. A slider can be shifted to optimize the desired time period. FLEXTRA und FLEXPART codes (authors: A. Stohl et al., see link) are used. This tool is only one of many that have been developed in the context of the Virtual Alpine Observatory (VAO) for the “Alpine Environmental Data Analysis Center, AlpEnDAC”. DFD has a prominent role in developing AlpEnDAC. Other partners are the Leibniz Supercomputing Centre (LRZ), UFS GmbH, bifa GmbH and the Department of Physics at Augsburg University, which manages the project. AlpEnDAC makes it possible for scientists to carry out complex numeric simulations using a user friendly interface (“computing-on-demand”) even if they have no prior experience in the area of simulations.

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