Days of unrelenting high temperatures are the most deadly weather phenomenon on Earth, but like other extreme weather events, they are difficult to predict.
Across Europe in 2003, heat waves were blamed for 50,000 deaths. Six hundred lives were lost in California in 2006 because of the scorching temperatures.
Now scientists have identified a weather pattern in the atmosphere that may help meteorologists predict heat waves and, as a result, save lives.
Heat wave precursor
While prior studies have focused on land or sea surface conditions to try to identify patterns that precede heat waves, climate scientist Haiyan Teng turned her attention to the atmosphere.
She and colleagues at the National Center for Atmospheric Research in Boulder, Colorado, ran a 12,000-year computer simulation over the northern hemisphere.
"Instead of just 20 or 30 from the last 50 years of observations, we’ve got 6,000 extreme heat wave events," she said. "This gives us enough samples to study the precursor circulation patterns for these heat waves.”
Teng says the computer model identified a pattern that showed up before the temperature rose. It is characterized by a sequence of alternating high and low pressure systems - five of each - circling the northern latitudes.
“It’s high above the atmosphere in the upper troposphere and this pattern [precedes] the U.S. heat waves by two weeks,” she said.
Making the connection
While the pattern is well documented in the historic record, this is the first time it has been connected to extreme heat waves. When the scientists reviewed real heat waves in the United States dating back to 1948, a similar pattern often emerged.
“We think, ok, this pattern is a pattern in nature, and it is useful for the heat wave probability forecast. It is an estimate of the probability, not exactly how warm the temperature is going to be," Teng said.
The wave pattern Teng describes in the journal Nature Geoscience is global in scale and has implications beyond the Northern Hemisphere.
While more research needs to be done to confirm the findings, Teng says her team will continue their search for other circulation and environmental factors that foreshadow extreme weather.