Entering the hangar with the HALO research aircraft always feels special, but even more so today: it's the first time I've been allowed to fly on a research flight!

The beginning is already known: We work through the switch-on checklist for the instrument together as usual, and I also know how to hangar the aircraft from previous campaigns. But when the door of the converted Gulfstream G550 closes, it's different: now I'm sitting inside, not watching the plane take off as usual. A quick calibration is carried out, then we taxi onto the runway and off we go towards the North Sea!

Three of the four other scientists are also flying on this test flight for the first time today. Of course, nobody wants to make a mistake here, so there is a concentrated silence over the roaring cabin interior, where we sit between buzzing instruments and eagerly follow the measurement data on the laptops in front of us.

We can communicate with the others via headsets and write to the ground via a data stream. The lectures on air pollution and measurement methods are also watching from time to time. Luckily, everything is going well while the situation starts to get exciting:

The forecast already said that a tropopause fold could be observed: A region in which sinking air from the otherwise higher stratosphere penetrates to lower altitudes. And indeed, shortly after the end of the ascent, the aircraft begins to jerk and there is slight turbulence, indicating that something is happening in the atmosphere. Almost simultaneously, the measured values begin to change: N2O decreases while ozone increases, an indication of more stratospheric air masses and thus a possible tropopause fold.

The feeling is difficult to describe, it feels almost magical: Nothing can be perceived from the outside, the air is transparent and a tropopause fold is not visible to the naked eye. But we in the plane feel how it jerks, notice how our instrument can perceive changes in the air composition of 0.0000001% and can thus make this invisible phenomenon visible. Theory becomes practice, and I will remember this day forever.

Jonas Blumenroth (IPA, JGU Mainz)

Gray clouds hang low over the airfield in Oberpfaffenhofen. A rumble is heard as the aircraft's engines start up. Then HALO emerges from behind a building, zips across the runway and takes off. After a few seconds, it disappears into the low-hanging clouds and our observation post on the roof platform falls silent.

Inside the aircraft, however, the technology is now being eagerly tested. After six weeks of installation and testing, all the scientific instruments have been installed in the aircraft and HALO is ready to take off. Today's EMI flight is the very first of the NAWDIC campaign. EMI stands for electromagnetic interference. Following a ground test two weeks earlier, the aim is to ensure that the aircraft electronics and the electronics of the scientific measuring instruments do not interfere with each other and that the aircraft still flies safely despite all the equipment. From Oberpfaffenhofen, HALO will fly to the TRA (Temporary Reserved Airspace) Allgäu and back.

Stephan is there for our team and has some time during the successful flight to take a picture of Forggensee with Füssen and Neuschwanstein Castle in front of the Allgäu Alps.

After three hours, there is another rumble of thunder in the clouds and shortly afterwards HALO taxis back onto the apron in front of the hangar. We quickly save the data and switch off our UMAQS device completely. Now everything is ready for the scientific test flight next week.

Isabel Kurth (IPA, JGU Mainz)