Wind stress curl, including negative variations, is a well-established physical meteorological and oceanographic phenomenon used extensively to model ocean circulation, Ekman pumping, and upwelling.
The claim states that negative wind stress curl is a physically defined meteorological phenomenon. Multiple peer-reviewed studies across meteorology and oceanography routinely compute, model, and analyze wind stress curl (including negative values) to explain phenomena like Ekman pumping, upwelling, and Sverdrup transport. There is unanimous support in the literature for its physical definition and utility.