and are associated with localized regions of anomalous vertical vorticity. Conceptual development Before the 1950s, the mechanism driving atmospheric Hadley cells—an air circulation that transports tropical heat and moisture poleward—was poorly understood. It was initially believed that the Hadley cell was fueled by the broad, diffuse, and gradual rise of warm and moist air near the equator. However calculations of Earth's energy budget using data from World War II showed that the mid-troposphere was an energy deficit region, indicating that the maintenance of the Hadley cell could not be explained by the broad ascent of air. The role of the tropical regions in the global climate system and the development of tropical disturbances were also poorly understood. The 1950s marked a pivotal decade that saw the advancement of tropical meteorology, including the creation of the U.S. National Hurricane Research Project in 1956. In 1958, Herbert Riehl and Joanne Simpson proposed that the release of latent heat caused by condensation within hot towers supplied the energy necessary to maintain Hadley cells and the trade winds; their hypothesis was initially based on aerial observations made by Simpson during her time at Woods Hole Oceanographic Institution. This mechanism required the existence of undilute cumulonimbus clouds that did not entrain the surrounding air, allowing for the efficient transfer of heat from the ocean surface into the upper troposphere. The existence of 1,500–2,500 of these clouds was required if they were to support the Hadley circulation. The researchers also argued that hot towers helped maintain the warmth present at the center of tropical cyclones and that the ascent of moist air within tropical cyclones was concentrated around the hot towers. In their original 1958 paper outlining the role of hot towers, Riehl and Simpson described these clouds as "narrow warm towers", but began terming the idea as the "hot tower hypothesis" by 1960. For the next two decades, hot towers dominated scientific discussion concerning the interaction between cumulus clouds and their larger-scale tropical environments. Aerial observations of Hurricane Daisy in 1958 suggested that convection within tropical cyclones was limited to a few areas of cumulonimbus clouds, dispelling the idea that rising air was distributed throughout the entire cyclone's envelope and lending support for the hot tower hypothesis. In the case of Hurricane Daisy, the convecting cumulonimbus clouds represented only about four percent of the total region of precipitation associated with the hurricane. A 1961 analysis