The word undulate has appeared in 10 New York Times articles in the past year, including on Sept. 24 in "The Sun That Did Not Roar" by Kenneth Chang:

• For scientists trying to understand the dynamics in the interior of the Sun, it has been a humbling experience enlightening them about how much they do not know. "If there's anyone who has figured it out, I haven't heard, that's for sure," said Douglas Biesecker, a physicist at the Space Weather Prediction Center and the chairman of a panel that had issued predictions about the solar cycle.
• They do have a basic understanding. Inside the Sun, flows of electrons and protons generate magnetic fields that undulate on roughly an 11-year schedule. The roiling of the fields create regions that are cooler and darker - sunspots. The twisting magnetic fields within sunspots periodically snap, releasing enormous amounts of energy in solar flares and coronal mass ejections.