Wind direction and fir wave motion

Abstract

The direction of travel for each of 11 fir waves in the White Mountains of New Hampshire was determined from their positions on aerial photographs taken in 1978, 1966, and 1943–1944. The direction toward which trees within each wave were flagged was determined in the field and used to infer the direction of prevailing winds. Flagging and fir wave directions are found to be closely related. Most wave velocities fall within the range 1–3 m year−1, as found in earlier studies. Wave direction generally parallels the fall line, but in cases where the flagging direction crosses the fall line, the wave follows the flagging direction. The flagging observed in fir waves appears to be caused by rime ice damage. It indicates that a narrow range of mean annual wind velocities are present where waves occur. The close relationship between flagging and fir wave directions suggests that wind and rime ice buildup are important factors in advancing the dieback zone of fir waves.