Corey’s family had planned to go home through the Bahamas because Dad wanted to be in a warm place after Wellington in winter, and Mother wanted go right round the world, not back across the Pacific. Alas! As the day of departure drew near, it gradually became clear that there would be no trip through the Bahamas this year. A late-season storm was developing into a hurricane, and the Bahamas were off-route indefinitely; they would have to make new plans.
Corey looked at the pictures of the hurricane. They were beautiful in their way, heavy lines of cloud gracefully spiraling inwards, counter-clockwise.
Counterclockwise… To the left? “Hey, wait a minute,” Corey exclaimed. “Aren’t the Bahamas in the northern hemisphere? How come the winds are going left?” He brought the picture to his dad.
“Dad, why do the winds turn left when my arrows always turn right?” he asked.
Pete was building a model train with the Barkers’ wonderful set of cars and tracks, but he stood up for a minute and looked over Corey’s shoulder.
“They’re trying to,” he observed and then sat down again. Corey watched him for a second, frowning.
“Trying to what?” he asked.
“Go right,” answered Pete and then flipped the switch so the train gave a long, loud whistle. Corey covered his ears.
“How can winds try anything?” he shouted. Pete didn’t seem to be listening; he stood up to survey his train.
“How do you know what the winds are “trying” to do?” demanded Corey when it was quiet again.
“Look,” said Pete. He leaned over Corey’s picture and quickly drew two arrows on top of the storm image.
“Hey, don’t draw on it!” cried Corey, but Pete just shrugged; he was already back to his train.
Dad was quiet for a minute. “It is a left-turning spiral,” he began, “A counter-clockwise storm like all northern storms.” His finger traced the winds coming into the storm from each direction.
“But the wind is not an arrow,” he continued. “It’s just a word for moving air. Air is the arrow, and Pete is right. Each parcel of air seeks to go straight to the center of the storm, but it goes off to the right and then it keeps being corrected by the tug of the storm center.”
“Being corrected!” said Corey thoughtfully. “Being corrected is why it curves then. Gaspard says that a curve is a continuously corrected motion. So the air is like an arrow that always wants to go straight to the right, but a continuous correction pulls it to the left.”
“Yes,” agreed Dad. “As the wind comes closer to the center of the storm, always staying to the right, it goes faster and faster always to the right but it also receives a stronger and stronger correction to go left instead of straight. You notice the hole in the middle of the storm? It never does get there.” He winked at Pete, who had sneaked a look at him but now quickly turned away.
Corey was not quite satisfied.
“But why does the air go towards the storm anyway,” he had to know. “Why doesn’t it just stay where it is and leave the storm alone? I don’t get it. Nobody is shooting the air; the wind isn’t some kind of bowman, or blow-man or something…”
“Whoa! Whoa!” Dad shook his head and waited for Corey to settle down a little.
“In the center of the storm” he began, “there is a space of soft, thin air, called low-pressure air. If it were in a balloon, the balloon would deflate. Low pressure is like a valley in the field of the air, and, just as rivers run into a valley, air wants to run into the low pressure space. But it can’t get there because it keeps racing off to the right, past the storm. Then the valley pulls the air in again so the air changes direction; but it still heads straight off to the right and the valley has to pull it again. So to you, it seems to be spiraling left, but to itself, it’s just going straight and being pulled sideways all the time.” He drew more arrows.
Corey studied the pictures and the arrows for a while in silence.
“Then what if the storm begins at the equator,” he finally asked. There was a momentary silence.
“They don’t,” said Pete. (How did he know?)
“They don’t,” agreed Dad. “Very rarely, partly because the hottest latitude moves around a little between June and December, a strong storm can form in the South China Sea, but hurricanes and typhoons usually weaken anywhere near the equator. Our hurricanes never start there; and they don’t cross and go south.” He waited for Corey to catch up with this thought.
“And New Zealand’s rare hurricanes spin to the right,” he added. “Clockwise.”
Corey took a deep breath as he pondered this.
“Dad,” he said at last, with a sigh, “I didn’t know you knew so much.”
“I didn’t know Pete knew so much,” answered Dad. “Anyway, let’s go to France instead of the Bahamas. How about it, Marie?”
“I’d rather go to France than the Bahamas any day,” answered Mother. “Allons!”
(Which means, in French, “let’s go,” and that meant that she really wanted to be in France, not some steamy, stormy little island.)