Seat-of-the-Pants Climatology

A week ago, I took a 10,000 mile journey from New York to Sydney.

It’s still mind-boggling to me that we can travel to the (almost) opposite side of the world in just 25 hours.  Granted, 25 hours is plenty of time to get bored.  Looking outside over the nighttime Pacific, you’d see no difference if somebody taped black construction paper over the windows.  My biggest source of entertainment on flights is looking out the windows.  Deprived of that option, I slept.

A few hours later, turbulence rattled me awake.  I’d be worried about crashing if I weren’t too sleepy to care.  But, since I was awake, I might as well check our location on the seatback TV map.  We were right near the equator.  Maybe a hundred miles north.

Turbulence?  Near the equator?  Is that a coincidence?

Nope.  It’s the Intertropical Convergence Zone!  I felt the ITCZ!

Let’s backpedal a bit.  In general, the warmest air on Earth is found near the equator, which receives the most sunlight.  The sun heats this air, which then rises, carrying moisture from the ocean into the upper troposphere.  That air then moves away from the equator, bringing warmth and moisture towards higher latitudes.  It’s a lot like heating water over a stove.

Of course, all that air has to be replenished somehow.  The trade winds from the Northern and Southern Hemispheres accomplish this, converging near the equator to resupply rising air.  Hence the “Intertropical Convergence Zone,” or ITCZ for short.

A very simplified model of the ITCZ.  Sun-warmed air rises at the equator, then moves poleward.  This creates a low pressure belt that draws low-lying cool air toward the equator.  Note that 1) there are more convection cells than shown here, and 2) this model doesn’t show the effects of a spinning Earth (the Coriolis Effect). (Introduction to Tropical Meteorology)

That warm, rising, moisture-laden air produces a lot of storms.  Those storms are so frequent that you can actually see the ITCZ in satellite images as a band of clouds near the equator.  Storms create turbulence, so the ITCZ is infamous for jostling planes around.

The ITCZ is visible as a band of clouds near the equatorial Pacific. (NOAA-NASA GOES Project) You can explore the most recent satellite video here.

So, if you ever fly over the equator, pay attention: one of Earth’s largest climate phenomena might be shaking your seat.

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