Meteorological OficeIGH-level clear-air turbulence and standing waves are often reported in the H same air stream. There are at least 17 occasions when they occurred within about 150 miles of each other and the average distance is much less than this. L. Larsson (I) has reported them 20 miles apart in Sweden, while glider pilots have often experienced waves and turbulence together, sometimes at high level. The possible connection between the two is supported by the frequent occurrence of strong upper winds or jet streams (2,3) and the great preponderance of stable air (4) with both phenomena. The relative infrequency of turbulence over the Atlantic (4) may also be significant.It is likely that sometimes the terrain determines which of the two effects, turbulence or waves, will occur : a second ridge, out of phase with an existing wave train, may make the flow become turbulent. One pilot, flying over the Midlands, reported each type of disturbance separately, while, on a day when marked waves were noted over Cheshire, on the Worcester Thum (a meteorological observing flight) the pilot reported turbulence only. Each effect, however, is known to be spasmodic, so the differences noted could be due to variations in time.Seasonalvariation (a marked minimum in summer in the incidence of waves) is absent, or much less marked in the case of turbulence. This suggests -Fig. I . Temperature and wind observations at Liverpool 25 January 1955 294