Outer Precipitation Bands of Hurricanes Edna and Ione

Hurricanes Edna, 1954, and Ione, 1955 were observed by radar at South Truro, Massachusetts. Both storms are associated with convective shower bands near the northern extremities of their circulations. Shower characteristics in the two cases are virtually identical in most respects, but the bands which they comprise propagate in grossly dissimilar ways. The differences are attributed to the presence of a convergence line or zone (cold front) at the boundary between two large scale air streams in the case of Ione, and the absence of a corresponding feature in the case of Edna. The Ione observations are in general accord with the Bjerknes cold frontal model, as recently modified by Sanders, in which warm air is entrained into the frontal zone and converges and rises there and above it. While the showers thereby formed move with the warm air in which they are embedded, the convergence zone moves with the winds northwest of the wind shift line. The Edna showers develop in an almost horizontally homogeneous wind field, and there is some question as to the persistence of the small scale lines of convergence which produce them. This note also contains some brief discussion of banded structures associated with altostratus clouds and rain which occur in the outskirts of both Edna and Ione.