Heat and Weather Patterns( pg 92-93)
Convection currents in the atmosphere are
responsible for most of the Earth’s weather patterns.
During the day, the land mass heats more quickly. This
causes the air above it to warm, become less dense, and
rise. This becomes a sea breeze that moves from the
water to the land. Once the heated air rises and moves
away from the land, it cools and begins to sink. But the
only place it can go is out over the water into the space
left by the air that moved inward.
Questions:
1. Explain a thermal.
2. How do thermals help birds?
3. Explain the expression “hot air rises”.
4. Are thermals most likely to be set up in winter or
summer? Explain.
5. Are thermals most likely to be set up on cloudy days
or sunny? Explain.
Answers:
1. A thermal is convection current. It can occur on
clear day, when energy from the sun warms the land
and the air near it. The warmer air rises (expands)
and becomes less dense, as the warm air expands it
rises and is replaced by cooler, dense air.
2. Thermals help birds glide in the air for hours,
searching for prey. As the warm air rises, the birds
can ride it higher by gliding in circles within the
thermals.
3. The expression “hot air rises” means that when air
is heated, the particles gain energy, move more
quickly, and spread out. This air is less dense then
the surrounding air, so it rises.
4. Thermals are most likely to be set up in the summer
because light (energy) from the sun is more direct
and heats up the land more quickly than in winter.
5. Thermals are more likely to be set up on sunny day
because the sun’s light can more easily heat up the
land than on a cloudy day.