Summer heat waves in California’s Central Valley are almost always preceded by heavy rainfall over the tropical Indian and Pacific oceans, scientists at UC Davis and in South Korea determined in a recently published research effort.
Researchers identified 24 heat waves that took place in the Central Valley during summer months from 1979 to 2010, and compared those heat waves to a weather pattern called the Madden-Julian Oscillation (MJO) that brings heavy rain to the tropical Indian and Pacific oceans.
The study found a correlation involving each of those two dozen heat waves: each of them came between four and 16 days after an MJO system.
“Enhanced rainfall in the tropics preceded each heat wave in specific and relatively predictable patterns,” UC Davis said in a news release accompanying the research, which was performed in collaboration with the Asia-Pacific Economic Cooperation Climate Center.
“They also found that hot weather in the valley is most common after more intense MJO activity in the eastern Pacific Ocean, and next most common after strong MJO activity in the Indian Ocean.”
The study defines a heat wave as a stretch of three days in a row with temperatures exceeding 100 degrees.
Previous research efforts have shown a link between MJO activity and Central Valley weather in winter months, according to the research paper.
The research results were published online last Friday to the scientific journal Advances in Atmospheric Sciences.
“The more we know about such associations to large-scale weather patterns and remote links, the better we can assess climate model simulations and therefore better assess simulations of future climate scenarios,” UC Davis Professor Richard Grotjahn said in a statement.