# What Makes the Wind Blow?

To understand how the wind blows we have to think back to how Earth heats up.  We know from earlier in the unit that Earth experiences uneven heating...some places heat up faster, some colder, some areas are always hot and some areas are always cold.

These differences in temperature create differences in pressure.

Areas with HIGH TEMPERATURE have LOW PRESSURE.

Areas with LOW TEMPERATURE have HIGH PRESSURE.

# Wind Direction

Direction is one simple measurement we can make to describe the wind.  If we know where different pressure centers are on a map we can easily tell the wind direction because:

# WIND ALWAYS BLOWS FROM HIGH PRESSURE TO LOW PRESSURE

For example, on the map to the right, the wind goes from high to low like always.  So in this map the wind is blowing to the Northwest!

We measure the wind direction using an instrument called a WIND VEIN.

WINDS ARE NAMED FOR THE DIRECTION THEY ARE COMING FROM.

### For example:

• a wind blowing from North to South would be called a Northerly wind.
• A wind blowing from East to West would be called an Easterly wind.

# Wind Speed

Since different areas have different temperatures pressures, there exists a pressure gradient between them.  A pressure gradient is no different from any other kind of gradient we have discussed this year.

PRESSURE GRADIENT = difference in pressure / distance

The gradient or difference in pressure provides causes the wind to blow!

The higher the pressure gradient is between two locations the stronger the wind will be, and the faster it will be moving.

THE WINDIEST AREA ON AN ISOBAR MAP IS ALWAYS THE PLACE WERE THE ISOBARS ARE CLOSE TOGETHER.

ANEMOMETER - INTSRUMENT USED TO MEASURE WIND SPEED