Winds from the east. Easterlies blow in low latitudes in both high and low tropospheres, and in high latitudes in the lower troposphere (Ichigawa and Yasunari (2006) J. Climate 19, 7). The downward propagation of easterly winds occurs throughout the equatorial zone; see Baldwin et al. (2001) Rev. Geophys. 39. Easterly waves are weak troughs of low pressure in tropical areas. See Fuller and Stensrud (2000) Monthly Weath. Rev. 128, 8 on easterly waves and the North American monsoon, and Ross and Krishnamurti (2007) Monthly Weath. Rev. 135, 12 on easterly waves and tropical cyclones.