The Nature of Storms
Have you ever felt a refreshingly cool breeze against your cheek on a hot day at the beach? If so, you experienced a sea breeze. A sea breeze can lead to a type of air-mass thunderstorm called
a seabreeze thunderstorm. To understand how seabreeze thunderstorms form, it’s first necessary to understand how sea breezes form.
A sea breeze and its nighttime counterpart, a land breeze, occur where the land meets the water. They exist because land and water absorb heat at different rates. Land heats up and cools down more quickly
than water. During the day, solar radiation warms the air over land by conduction. The heated air becomes less dense and creates an imbalance of both temperature and pressure between the air over the
land and the air over the water. You might suspect that something will happen to relieve this imbalance, and you’re right. Recall that air moves from areas of high pressure to areas of low pressure, and
that cooler air tends to displace warmer air. The cool, dense air over the water moves inland, forcing up the warm, less-dense air over land. A convection current results. This is a sea breeze.
Land Breeze
At night, the convection current reverses. Air over land cools down more quickly than air over water. The cooler, denser air moves toward the sea, forcing the air over the water to rise. This is a
land breeze.
During a land breeze, the temperature difference between the air over the land and the air over the water is relatively small. During a sea breeze, however, the temperature of the air along the coast
might be as much as 20°C higher than the temperature of the air over the water. The extreme temperature gradients that accompany sea breezes often help spark seabreeze thunderstorms. As the leading edge
of the cool sea breeze moves inland, it forces the warm air to rise quickly. This can produce the necessary updrafts that transform a cumulus cloud into a thunderous cumulonimbus cloud.
LINK-UP: Find out more information about thunderstorms.
Unleashing Floods
All thunderstorms, regardless of how they form, can cause severe floods. Floods happen in a number of ways. Sometimes, rain falls over a large area and drains into a river system faster than the river
can move the water downstream. The river overflows its banks and floods low-lying areas surrounding it. Frequently, heavy rains fall over areas that do not easily drain into river basins. The water then
collects in low-lying areas and gets deeper and deeper, depending on the terrain. This is called ponding. Ponding is common in low portions of cities where vast areas of land are covered by concrete and
asphalt, neither of which allow rainwater to be easily absorbed into the ground.
Yet another type of flooding occurs when torrential rains cause a sudden overflow of a river bed, gully, or other water-drainage feature. This type of flooding is called a flash flood. It commonly occurs
when thunderstorms that produce heavy rainfall move slowly over hilly or mountainous terrain, causing intense water runoff down the steep slopes. Regardless of their origin, floods must be taken seriously.
They are the main cause of thunderstorm-related deaths in the United States each year.
Activity
Use gravel, clay, and sand to design an experiment that compares and contrasts how water is absorbed by different materials. If possible, conduct your experiment, then relate your results to the factors
that cause floods.
