Astronomical Spring is here for those in the Northern hemisphere, and more “spring-like” weather is approaching. With the present Spring season kicking in comes an increase in the amount of solar radiation. This is because the Earth’s Northern hemisphere starts tilting more towards the sun on its axis bringing with it longer and warmer days. Since the land is getting warmer than the surrounding bodies of water, the differences in temperature can create localized pressure differences between them. Once this happens a phenomenon called a sea breeze can occur during the day, and a land breeze can occur during the evening. But what exactly is a sea and land breeze?
Sea and land breezes are thermally forced circulations that occur from Spring to Autumn driven by differential surface heating. This means that the temperature differences between the land and water create areas of low and high pressure, and since high pressure always flows toward lower pressure a circulation forms to create the breezy conditions. Ideally the temperature difference between the land and water should be around 6-10 degrees Fahrenheit. The land is able to heat up much faster than water during the day while the water is able to hold in its heat better than the land during the night due to specific heat differences between them.
Specific heat is defined as the amount of energy it takes to raise the temperature of 1 gram of water 1 degree Celsius. More simply, it takes water much more time to heat up than it does for the Earth’s surface. The specific heat of water is 1 calorie/gram degrees Celsius, or 4.186 Joules/gram degrees Celsius. This amount is roughly four times higher than the specific heat of land, which gives water this important characteristic and sets the stage for this thermally direct phenomenon.
Below is a simplified graphic showing the difference in pressures that can occur during the day and night:
Notice the “cold front” indicated in the image above. This merely represents the cooler breeze flowing from higher to lower pressure. The sea breeze is shown on the left while the land breeze is shown on the right.
This phenomenon does not only occur to oceans, but lake breezes also occur over smaller bodies of water such as the Great Lakes in the Northern part of the U.S. for example. However, these breezes can occur along nearly any coastal boundary around the world; a common location being the Florida peninsula. One of the main triggers of daily thunderstorm activity in coastal areas like this result from sea breezes that converge directly over the land. Having large temperature gradients such as these are often the main trigger to any convective development that can result from this mesoscale phenomenon.
Forecasting for these events requires knowledge of the local synoptic and mesoscale weather forcings that can initiate this, the orography of the area, and the general shape of the coastlines. Are there calm, synoptic conditions such as an area of high pressure that won’t disrupt the flow? Are there concave or convex qualities to the shape of the land that could enhance or diminish the circulation? Is there a significant temperature difference between the water and the land? These questions can be helpful in deciding whether or not this type of phenomenon could occur.
Sea and land breezes can have a large impact on local temperatures, making coastal areas or cities difficult to forecast for as these events are challenging to predict. During the day as the land heats up and a sea breeze is initiated, the temperature can be kept cool or significantly cooled as a result. The same goes for a land breeze. Once the sun goes down, the land cools off and the water is relatively warmer than the land initiating a land breeze. This can keep the air at a steadier temperature during the night and prevent the lake from warming the air onshore.
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@2019 Weather Forecaster Christine Gregory