Storm Xaver held Germany spellbound. Optical satellite images show the storm front as a wide band of clouds. But satellite trace gas measurements reveal more. For example, HNO3 (nitric acid) functions like a contrast medium for identifying currents in the atmosphere. EOC scientists use such trace gas measurements as well as the 3D chemical transport model SACADA developed at DLR to analyze the activity of planetary waves. These waves play a decisive role in determining our weather.
If the horizontal temperature difference from south to north is especially large and exceeds six degrees per 1000 kilometres, then a wavy airstream forms in the atmosphere and encircles the entire planet. A so-called “planetary wave” arises. The jet stream, for example, in that case follows a wavy “super highway” on its journey around the earth. This results in a deviation of warm airstreams northward – and cold flows southward. These are associated with high- or low-pressure systems that are transported around the earth along with the wave.
These days the activity of planetary waves is especially noticeable. Planetary waves with zonal wave numbers 1-3 cause extreme denting and displacement of otherwise symmetric polar eddies. This is especially evident in the global distribution of HNO3. The relevant analyses are based on assimilations of atmospheric trace gas satellite measurements in the 3D chemical transport model SACADA. This "kneading" of the eddy has just now caused a large "trough" to form over Europe, through which masses of air continue to flow to us from polar latitudes as if they were rushing along a super highway. Our analyses using the Weather Research and Forecasting Model (WRF) show us how this situation develops and permit forecasting.
Prognose Orkan Xaver