Why do Hurricanes spin the way they do?

Kids are curious and their questions matter. All day they are asking about what they observe, wondering how things work, and applying their curiosity to our world in exciting ways. For example, my six year old asked me yesterday on the way to school “ Why can’t you drive faster on the side streets”, which just was a beautiful observation that led to a interesting conversation on risk, safety, and noise pollution.  KSL Parents know that all of our classes that we teach start with an engaging question that is asked by a child, and only then do we experiment, discover, and use creative design to apply science principles to innovating things like chairs made of cups or night lights made of LED’s for our student population, starting at age 2.  Our parents have been asking us for years to blog on the same cool science that we do in class each week and provide a forum for our students to ask their questions. So here you go, some hopefully useful news to engage your own curiosity as parents and help you to engage your kids in the car with some discussion. Enjoy!

There has been a lot of news recently on Hurricanes, with Hurricanes Harvey, Irma, and Maria reeking havoc on in the U.S. South and coastal islands.  One child asked us “Why do hurricanes spin that way”? It is a really an interesting topic and fundamental question. Many people know that most hurricanes originate in warmer climates, and that they involve fast moving winds, so let’s start by just figuring out what the problem is?  The main problem is that the earth is constantly moving, and its environmental conditions are constantly changing and evolving. It is this movement and the changes in the environment that end up creating a basic weather phenomenon, wind. We can’t even talk about hurricanes without talking about wind. If we know that the earth has air, the question really starts with why that air starts to move in the first place. Air, like most other natural phenomenon, wants to be in the least disruptive place, so whenever there is high pressure, it moves away towards low pressure. It is this basic movement of air from high pressure zones to lower pressure zones that creates what we call wind.   So when you see a lot of wind, it usually means that a very high pressure zone has moved in and the air is running away from it to find the nearest low pressure zone (peace).  This of this like a letting a balloon go, the air shoots out because inside it is stuffed in (high pressure) and it is trying to get out to the low pressure.  

Anything requires force to move, so wind is simply air that is in motion, moving away from high pressure zones to low pressure zones. Imagine you were sitting at the top of a slide, but haven’t moved yet. Then some big kid comes along and pushes you, whether you like it or not, you are moving. The bigger and harder the push, the faster your body is going down the hill. This example if important, because gravity and the environmental conditions (wetness, heat, etc) are also big effects in producing lots of wind, just like being pushed down a slide. 

Phew! So now that we are all on the same page that wind is just the earth pushing air around us, because there are strong forces (differences in high and low pressure generates force), lets get to the real question that this kid is having. 

 

Why do Hurricanes Spin The Way that they do? 

Scientists will tell you the basic science that hurricanes in the Northern Hemisphere typically rotate counterclockwise and in the Southern Hemisphere they rotate clockwise. But why? Well, to a child, it is like watching anything that spins, the air around it is going to move in the direction of motion of the object spinning. Since the Earth moves or spins to the right, the strong winds that are experienced by a hurricane are typically moving in that same direction. Regardless of whether the hurricane is moving north or south, it is spinning to the right because the earth is pushing it that way. 

Spin.jpg

If wind is the basic motion of air from high pressure to low pressure that is happening all the time everywhere on the planet, then its motion is almost always curving to the right, because that is the direction of the earth. There is a technical name for this called the Coriolis Effect, but that is not necessary to talk about to kids, just put that in your pocket for your next cocktail party!  So when you are in the Southern Hemisphere (south of the equator), and traveling north, the earth is going to push the wind to the right as that is the direction of its spin, which creates a clockwise spin for any hurricanes moving north through the southern hemisphere. If however, you are in the northern hemisphere and traveling south, the earth is still pushing you to the right, however the motion that results is counterclockwise. To show this to your kids, just have them draw a line with an arrow pointing downward on a piece of paper and then slightly bend the arrow it to the right and see that it starts to move into a counterclockwise rotation. Now draw the opposite line with an arrow pointing upward and slightly bend it to the right to see that it starts to move into a clockwise rotation. If your child is drawing the line, just slightly push her finger to the right while she is drawing and the circular motion will start to look like a clock moving in the wrong direction if you keep pushing their finger. 

That, our friends, is what creates the basic motion of a Hurricane in each of the hemispheres. Typically, Southern originating hurricanes moving north are clockwise and Northern originating hurricanes are counterclockwise as shown below. 

Hemisphere.jpg

Now that we understand that wind is just the resulting motion of air from high pressure to low pressure, and that hurricanes spin clockwise or counterclockwise almost entirely based on their origin and the rotation of the earth (Coriolis Effect), we can begin to talk to our kids about environmental conditions. A Hurricane needs food to grow big and strong, and the food that hurricanes love the most are water, warmth, and strong differences in pressure. When the wind starts to move over water, it is called a Tropical Depression, which is basically strong enough to feel (up to 38mph), but doesn’t cause major damage most of the time. When the wind feeds on water that is evaporating, warmth, and pressure difference, the wind gets stronger and can build into a Tropical Storm (winds 39-73mph).  A tropical storm causes damage, but it not nearly as bad as what happens next, which is a Tropical Hurricane (winds > 74mph). 

A basic hurricane has a low pressure center (peaceful in the middle), with ridiculously strong winds immediately boring this low pressure EYE and winds that decrease in strength as you move further away from the eye of the hurricane.  There are hundreds of tropical storms a year, and only some of them have the right mix of wind and pressure conditions that they develop into Hurricanes (Category 1 - Category 5). Hurricanes, Typhoons, and Cyclones are all the same thing, they just originate in different zones. 

When discussing with kids, there is a basic experiments that can do to demonstrate their power at home.  The first is to grab an empty two liter bottle and fill it with water. Put a tiny bit glitter or cinnamon (colorful spice) into the bottle and fill it up. Then, just turn it over and watch the water flow out, as you observe it, the glitter or cinnamon won’t do anything.  Next, repeat the experiment, but as you turn the 2 liter upside down, give it a tiny circular spinning motion, which will start a vortex (higher speeds of motion) and the kids will see that the glitter is now moving violently in a circular motion and the water will pour it twice as fast. This helps kids see that circular motion effects an increase the rate of water being dumped and simulate the naturally occurring rotation effects on wind as the earth moves.  If you happen to have small solid object that will fit into the water, it makes for a really interesting observation as the spinning vortex will whip that object around the 2 liter as the vortex pushes everything down! 

Ok, so wind is simply motion of air that is caused by differences in pressure, the earth spins to the right, hurricanes develop over time under the right conditions of warmth, water, and pressure, that are sustained, and if you know the hurricane develops in the south or the north, you can reasonably predict whether it will be spinning clockwise (destination Northern Hemisphere from Southern Hemisphere). That’s cool. So what is all this recent media business on whether Hurricanes are getting worse. Well, it turns out, that climate change suggests that our climate is getting warmer. The basic principle is that since the oceans are getting warmer, then the evaporative movement of water will be forming more storm clouds, which will experience higher pressure differences, which will create faster movement of wind, which will increase wind speeds with circulation motion, which will result in stronger hurricanes. :) A Category 5 Hurricane can raise water levels up to 20 feet, which is why there is so much flooding during a hurricane. Water is literally being pushed by the wind over long distances and it piles up onto the shore or in other instances leaves beaches with dry ocean beds.

We could talk about this topic forever, but we will start with some basic problem solving. We can’t really control mother nature, so Hurricanes and Storms will happen. However, if you look at how you theoretically stop them, there are three basic methods:

  • Cool The Air
  • Remove the Water
  • Disrupt the flow of Air with large objects/deflectors (friction is the force that slows things down as we are learning over the next two weeks at Kids Science Labs)

When speaking to kids, we can’t really talk about complexity, as they just are not that interested in that deep level of detail. The basic reason that Hurricanes Spin the way that they do, is that the earth is spinning to the right, and all hurricanes have wind that is being pushed to the right. It just matters whether the hurricane is traveling to the South or traveling to the North, that causes the hurricane to be Clockwise (Destination Northern Hemisphere) or CounterClockwise (Destination Southern Hemisphere). Some of your kids may want to know more, and if so, just bring them to Kids Science Labs because we do this stuff all day. We are the place to bring the curious child to be engaged and learn about how the world works! 

 

If your child has a question that involves science, please let us know and we will address it on Facebook or via a new feature of “I Have A Question”, a regularly occurring blog explaining basic science to kids around the world. Just email your question to “questions@kidssciencelabs.com” and our team of passionate teachers, engineers, and parents will gladly get back to you.