what's sea breeze and how does it develop at night and day?

Question

How is humidity defined and how does temperature affect the ability of air to hold water vapor? How does this relate to the way clouds form?

Answer 1

Due to it's molecular arrangement, water holds its temperature better than almost all other materials (this is known as specific heat). As the sun warms the earth each day, the land heats up very quickly, but the water does not. This is why beaches are so popular, and why you need to wear sandals on a hot day.

As the surface warms due to the sun, it warms the layer of air closest to the ground. As the air warms, the ideal gas law requires (at a constant pressure) that the density decrease. (P=rho*R*T). This is a fancy way of saying "hot air rises." (Fellow nerds, don't ding me on this, I know it's not really "rising", but being displaced.)

As the air over the land rises, it must be replaced by surrounding air. The only air that is not rising as fast is the air over the water. That air rushes onshore, causing the sea breeze.

The interesting thing is that the air over the water that rushes onshore has to be replaced. It is replaced by air above it, which sinks into place. This air, in term, must be replaced by other air. And it is, by the rising air that rose over the land and cooled. This creates a closed loop of air rising over the land and sinking over the water, with low level winds going onshore (towards land) and high-level winds going offshore. (Pilot's get a reverse sea breeze as a tail wind when traveling towards water).

I skipped a small bit about the rising air cooling. That is another application of the ideal gas law. The pressure in the atmosphere decreases with altitude. Pressure is in essence a measurement of the weight of the air above you. As you go up in altitude, there is less air above you, hence, less pressure.

The ideal gas law (Pressure = density * Temperature * a constant) comes into play because the density is mostly constant as the bubble (or parcel) of air rises. (The parcel's density will remain the same, but if the surrounding parcels are more dense, it will rise.) As the parcel rises, it will, however, expand to match the (lower) pressure of the surrounding air. The ideal gas law tells us that, as pressure decreases (if density is constant), temperature must decrease. Put another way, hot air cools as it expands.

This creates a cycle of air rising and sinking on the coast. (If you're standing with your left foot in the water, right foot on the beach, the cycle goes counterclockwise, rising over the beach, sinking over the water).

Clouds form when these parcels of air cool due to rising. As the parcel rises, it cools, but it does not loose any of its particles (it's oxygen, nitrogen and water vapor). But the amount of water vapor a given parcel of air can hold depends on its temperature. Hot air can hold more water vapor. Cold air can hold less.

As the parcel rises and cools, it may reach a point where the amount of water vapor it is holding is too much for its temperature. This is known as the saturation point. At this point, water vapor begins aggregating into droplets. Enough of these droplets together will form a cloud. (Cloud scattering is similar molecular scattering, but because the particles are so much bigger, they scatter red and blue light about equally. This is why clouds are white in color (an equal blend of all colors)). The more humid the air is over the ground, the more likely and larger the clouds will form once the air rises.

All of this combines to give you a nice, clean line of clouds along the shore on a humid day.

This is also why you can see your breath in winter. Your breath is about 98 degrees and almost 100% humid. When you breath out on a cold day, your breath cools quickly and water droplets form.

The sea breeze effect takes place in reverse at night and in winter as well. (If you've ever lived in Buffalo or Chicago, you know this as lake effect snow.) At night or in winter, the water is warmer than the surrounding land. This means that the it's the air over the water that is rising and the wind whips offshore. In winter, the clouds will form over the lake and be blown onshore (by the top part of the cycle). This causes many feet of snow to be dumped on unsuspecting homeowners.

Answer 2

During the day time,the land becomes warmer than the adjacent sea in a coastal station, for the same incident solar radiation.The hot air above the land becomes light and rises.At the same time, a pressure gradient is developed due to the unequal heating of the land and sea which acts normal to the coast resulting in the movement of cold air from the sea to replace the rising hot air over land.Thus a wind blows from the sea towards the land .This is called sea-breeze.It blows during late-forenoon or afternoon.
Relative Humidity is defined as the ratio of the amount of water vapour present in the air to the amount of water vapour required to saturate it at that temperature.This is expressed as a fraction or a percentage.In short,the relative humidity is known as the degree of saturation.It can be also told that the relative humidity is the percentage of moisture in the air.
Warm air can hold more water vapour than cold air.So, if the temperature of air increases,air can hold more water vapour.
If the air temperature at a particular level above the ground, reduces to the dew point temperature,it can no longer hold the the water vapour and condensation starts resulting in the formation of clouds .

Answer 3

First, absolute humidity is a measure of the quantity of water in a given amount of air. Relative humidity is a measure of how saturated the air is. Relative humidity equals the absolute humidity divided by the total amount of water the air can possibly hold. 100% relative humidity means that the air is fully saturated and cannot hold any more water. 0% humidity means that there is no water at all in the air. Cold air can hold very little water. Warm air can hold a lot of water. So you can have nearly 100% humidity in the Arctic with the same absolute humidity as you have in the tropics where there is 40% relative humidity.

Clouds form when the air is nearly saturated (high relative humidity).

As for the sea breeze, it is a wind. Winds are air moving from high pressure areas to low pressure areas (gotta equalize the pressure). During the day, the air warms over land. When the pressure is higher over land than over water, you'll get an offshore wind (think Southern California's Santa Ana winds). At night, the water will produce a high pressure zone, higher than that over land. So the winds shift to an onshore flow.

Answer 4

Water takes a long time to heat up and also to cool down. Sea Breezes are mainly caused due to the difference in the temperatures of land and sea, hence also called trade winds.

In the day the sun heats the land quicker, and hence the air near the land rises upward as it gets hot and light. So the cooler air from the sea rushes to the land to take place of the displaced wind. These are called land breezes.

The reverse phenomenon takes place at night, at night the land cools quicker but the sea water is still hot, so the air near the sea rises upward after getting hotter and lighter, so the air from the land rushes to take its place.

Here the sea breezes are the ones blowing during the day from the sea to the land.

Answer 5

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