We’ve been having a lot of wind this past week. What happens to make the wind speed faster than normal?

Question answered by Jason Rich
Meteorologist, NOAA ARL Field Research Division

Convection Currents

Spring is typically windy as we transition from the cool season to the warm season. Uneven heating of the Earth’s surface creates differences in atmospheric pressure across the globe. When differences in the pressure exist, winds flow from the high pressure to the low pressure. The strength of the winds is determined by the pressure difference (or gradient) between the high and low pressure systems: the bigger or tighter the pressure difference, the stronger the winds will be. With the increasing sun angle causing more areas of uneven heating of the Earth’s surface across the northern hemisphere during this Spring transition period, we will continue to see windy conditions as the low and high pressure systems pass through Idaho.

Isobars

Atmospheric pressure is the pressure of air on the Earth’s surface. It’s lower in areas with warmer air and higher in areas with colder air. Points with the same atmospheric pressure on a weather map are connected with lines called isobars.

Air tends to move to a lower pressure area pretty much the same way air comes out of an inflated balloon when it isn’t sealed–from higher pressure (in the balloon) to lower pressure (outside the balloon). The higher the pressure difference between two areas is, the higher the wind speed is. That’s why isobars that are close to one another mean high wind speed.

Convection

Convection is the transfer of heat by the movement of heated particles into an area of cooler particles. You experience convection when you light a candle. The air directly above the lit candle is always hotter than the air below the flame.

The difference in temperature around the flame is caused by the effect of heat on the density of air. Hot air is less dense than cool air and will rise. As the air cools, it becomes more dense and the air will sink. This pattern of air is called a convection current. Both air and water transfer heat through convection currents.

Materials: lightweight paper plate, pencil, scissors, crayons, needle and thread, desk lamp or table lamp

  1. Draw an oval shape in the center of the paper plate, then draw a spiral line around and around 4-5 times until it reaches the edge of the plate.
  2. Use scissors to cut along the spiral line from the outside edge to the center oval. Draw eyes to make the center oval of the plate into a snake’s head.
  3. Poke a small hole into the center of the snake’s head. Pull a piece of thread through the hold from the top and tie a big knot in it so the thread can’t pull through.
  4. Hang or hold the snake by the thread above the lamp.
  5. Turn on the lamp, remove the shade and direct the light towards the ceiling. (Remember: light bulbs get hot, so take care not to burn yourself.)
  6. What did you snake do?

Heat from the heat source caused air to rise up toward your snake. As the air molecules bumped into your spiral-shaped snake, they caused it to spin around.

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