Weathering a storm in LUNA

Instruments deployed on the surface of the Moon have to brave very challenging conditions, for example caused by the lack of an atmosphere and an internal magnetic field. These include huge temperature swings between more than +120° C during day time to below -200° C during night, and the impact of solar and cosmic radiation which is damaging to electronics. In the seismic data collected during the Apollo missions, the large temperature changes on the lunar surface resulted in high-amplitude spurious signals observed specifically during sunrise or sunset. Here in LUNA, the Earth’s atmosphere provides us with another kind of environmental signal that can be registered with the continuously recording seismometer in the regolith hall – one which is related to weather.

After a few unusually hot days near the end of May, the first big thunderstorm of the summer hit Cologne and surroundings in the evening of May, 29^th. The onset of high winds related to this storm stands out prominently in the seismic data from LUNA as a sudden increase in long-period motion on the horizontal seismogram components (marked by the red line in the graphs). These signals correspond to tilt generated by coupling of wind pressure into the ground. The correct identification of the signal can be confirmed by comparison to weather data provided by Deutscher Wetterdienst (DWD) for a station at CGN airport, next to LUNA. Here, wind gusts actually reached hurricane force in the 10 minutes surrounding 5:55 pm, with a maximum wind speed corresponding to Beaufort 12 (exceeding 118 km/h). The higher temporal resolution of the seismic data suggests a more accurate timing of 5:53 pm for this event. A later wind event, starting at about 6:50 pm UTC as identified in the weather data, is also visible seismically. Signals on the vertical seismogram component are characterized by significantly higher frequencies and most probably related to the impact of raindrops and hail on the ground and the roof of LUNA, rather than to wind.

While the storm fortunately did not cause any problems for LUNA, it shows that phenomena other than earthquakes also have a visible seismic impact and can be monitored by very sensitive seismometers like the one in LUNA. In fact, data from the InSight Mars seismometer has already been used to infer wind speeds on Mars when the associated wind sensor was not operational.