NDMC – at the Border to Outer SpaceDFD Hosts Symposium
Some 50 scientists from 10 countries have been invited by DFD to meet in Grainau, at the base of the Zugspitze mountain, from 20 to 22 May to share information about the status of their research and to discuss open questions.
The scientists are part of the international “NDMC – Network for the Detection of Mesospheric Change” programme. The mesosphere, that part of the atmosphere between about 50 and 100 kilometres altitude, is a region not readily accessible to measurement. Aircraft and balloons, for example, do not reach this height. So this slice of Earth’s atmosphere is one of the least researched parts of our planet – similar to the deepest parts of our oceans.
In 2007, from all over the world scientists with access to measurement instruments suitable for observing these distant heights joined forces. The instruments include spectrometers, radiometers and lasers capable of measuring over a wide range of the visible and infrared electromagnetic spectrum. The signals they collect can be read like fingerprints and permit deductions about temperature, wind and trace substances. At present about 50 groups of scientists from 20 nations participate in NDMC.
Why is this altitude range so interesting?
One of the major issues is the subject of climate variability. Quite different from the situation at the surface, an increase in the concentration of carbon dioxide at this altitude leads to cooling. The interesting point is that this cooling seems to be far greater — by about one order of magnitude — than the warming at the surface. This suggests that the temperature trend in the mesosphere could almost serve as an early indicator of climate change. Because the changes are so large there, trends could be reliably identified much faster than with measurements made only at the surface of the earth
Because of the relatively low density in this part of the atmosphere – air pressure at 100 kilometres altitude is only about one millionth that on the surface of the earth – it is much easier to study many fundamental physical processes there than at lower levels of the atmosphere.
One example is atmospheric waves. Waves can form in the atmosphere similar to the way they form on a water surface. They are generated, for instance, by airflow over land-ocean transitions, mountain ranges and from warm regions. Once generated, these waves travel large distances through the atmosphere, simultaneously transporting energy and momentum. Like a courier, so to speak, they connect various parts of the atmosphere. This aspect must definitely be taken into account when formulating computer-driven climate models so that forecast accuracy can be improved. Because air density decreases with altitude these waves are much more pronounced in the mesosphere than at lower atmospheric levels; the mesosphere functions, so to speak, like a “magnifying glass” for observing atmospheric waves. We can use the mesosphere like a kind of laboratory to explore fundamental physical issues.
What is DFD’s scientific interest in NDMC?
Various chemical and photochemical reactions produce a bright, planet-spanning layer of air called airglow at altitudes between about 80 and 100 kilometres (the so-called mesopause – more or less the border to outer space). It is caused by hydroxyl molecules (OH), which enter an excited state when they form. The introduced energy is released in the form of light in the visible and infrared spectral range.
This light can be recorded with the ground-based infrared spectrometer GRIPS and conclusions can be drawn from the data about the temperature at this high altitude. These measurements are made in cooperation with the Atmospheric Remote Sensing group of the Department of Physics at Augsburg University. They are routinely collected on the Zugspitze mountain at the Environmental Research Station (UFS), which is supported by the Bavarian Ministry of Environmental Affairs and Consumer Protection, BayStMUV. (DLR is a partner in the UFS consortium).
Long-term monitoring of the temperature in the mesopause region contributes to increased understanding of the processes involved and to the early detection of temperature trends.
Other aspects of research based on this airglow data are addressed in cooperation with Augsburg University:
- Reduction in the number of false tsunami alerts:
At present, every strong seaquake generates a tsunami alert. But these quakes are often not associated with a vertical lifting of the sea floor so no masses of water are raised vertically and no tsunami is initiated. When a water surface is raised vertically, analogous to a loudspeaker membrane infrasound is induced in the atmosphere. It travels at the speed of sound and after about five minutes reaches an altitude of 90 kilometres. This sound is a longitudinal wave which leaves a trace in the form of airglow shimmer that can be detected by GRIPS. If no airglow shimmer is detected over the epicentre after about five minutes then no tsunami will be generated and no alert need be given. - Improvements in the accuracy of forecasting the lifetime, intensity and path of powerful storm systems (particularly so-called Genoa lows or Vb weather conditions, which regularly lead to heavy rain and flooding in southern Germany):
Strong cyclones generate waves in the atmosphere, similar in effect to rotating helicopter blades. In this case they are infrasound waves (producing low frequency sounds inaudible to the human ear) and so-called gravity waves (vertically oscillating air packets). The stronger the waves the stronger must be the cyclone that generates them. A methodology was developed to continuously record these waves over a cyclone using the above-mentioned GRIPS technology on a satellite. From this data conclusions can be drawn about the state of the cyclone itself, and this information can be directly incorporated in the forecast model.
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- NDMC (240.6 KB)