Unusual vertical oscillations of a radiosonde

In summer 2023 in southern England, we observed several unusual balloon launches which descended for a few minutes before resuming ascent again. This unusual vertical oscillation was repeated several times in a “roller-coaster”-like pattern. In this article, the behaviour of the balloons is discussed, and we suggest that these events occurred as a result of snow or ice accumulation on the surface of the balloon and payload. In a typical radiosonde launch, such profiles would have been discarded, so we recommend that datalogging operations be adjusted permitting retention of such ascents to avoid loss of potentially valuable sounding data.