She has researched hot towers, hurricanes, the trade winds, air-sea interactions, and helped develop the Tropical Rainfall Measuring Mission (TRMM).

In 1958, Simpson (then Malkus) collaborated with Herbert Riehl and calculated the average moist static energy and how it varied vertically throughout the atmosphere.

By 1966, Simpson became the director of Project Stormfury while chief of the Experimental Meteorology Branch of the Environment Satellite Services Administration's Institute for Atmospheric Sciences.

In 1948, she married her second husband, physics instructor Willem Van Rensselaer Malkus, who would go on to be a professor of applied mathematics at MIT.

Yet, poignantly, in an article published in the Annals of the New York Academy of Sciences, she was quoted as saying, "I am not convinced that either the position, rewards or achievements have been worth the cost.