Abstract Expressionism is the term applied to new forms of abstract art developed in the 1940s and 1950s by a group of American painters, primarily in New York. It is often characterized by large scale, gestural brush strokes, and the impression of spontaneity. Painters associated with Abstract Expressionism include Arshile Gorky, Helen Frankenthaler, Clyfford Still, Jackson Pollock, Mark Rothko, Robert Motherwell, Sam Francis, Lee Krasner, Willem de Kooning, Joan Mitchell, and Franz Kline. See also: action painting. Web resource here.
Joan Mitchell. To the Harbormaster. Oil on canvas. 1957. Private collection.