We'll start with this picture of conditions along a sea coast.  At this point the air temperatures and pressures on both sides of the picture are the same.

A beach will often become much warmer than the nearby ocean during the day (the sand gets hot enough that it is painful to walk across in bare feet).  The warm air over the land will expand upward.  Note how the 900 mb level has moved upward in the picture.  We've left the temperature of the water the same as it was in the earlier picture and the 900 mb level above the ocean hasn't changed either.    So on the left side of the figure at the level where we find 910 mb we find 900 mb on right (see the top of the picture below).
Another way of figuring out the upper level pressure pattern is to recall that pressure decreases relatively slowly with increasing altitude in warm low density air.  There is only a 90 mb drop between the ground the green line on the left side of the picture above.  Pressure decreases more rapidly with altitude (a 100 mb drop) in the cooler higher density air on the right side.  We end up with the same upper level pressure pattern (910 mb on the left and 900 mb on the right).

These upper level pressure differences cause air above the ground to start to blow from left to right.

Once the air aloft begins to move it will change the surface pressure pattern.  The air leaving the top left side of the picture will lower the surface pressure (from 1000 mb to 990 mb).  Adding air at upper right side of the picture will increase the surface pressure (from 1000 mb to 1010 mb).  Now we have a pressure difference at the surface and the surface winds will begin to blow from right to left.

Sea breezes

You can complete the circulation loop by adding rising air above the surface low pressure at left and sinking air above the surface high at right.  The surface winds which blow from the ocean onto land are called a sea breeze (meteorologists specify where the wind is coming from).  Since this air is likely to be moist, cloud formation is likely when the air rises over the warm ground.  Rising air expands and cools.  If you cool moist air to its dew point, clouds form.

shortcut
It is pretty easy to figure the directions of the winds in a thermal circulation without going through a long-winded development like this.  Just remember that


Draw in a rising air arrow above the warm part of the picture, then complete the loop.

At night the ground cools more quickly than the ocean and becomes colder than the water.  Rising air is found over the warmer ocean water (sea below).  The thermal circulation pattern reverses direction.  Surface winds blow from the land out over the ocean.  This is referred to as a land breeze.

Land breezes

Country breeze
Here is an additional situation where a thermal circulation could develop.

Cities are often warmer than the surrounding countryside, especially at night.  This is referred to as the urban heat island effect.  This difference in temperature can create a "country breeze."  This will sometimes carry pollutants from a factory outside the city back into the city or odors from a sewer treatment plant outside of town back into town.

Global scale thermal circulation
We made use of this idea of a thermal circulation in class on Thursday when discussing the 1-cell model of the earth's global scale circulation.  Ordinarily you couldn't apply a small scale phenomena like a thermal circulation to the much larger global scale.  However because we assumed that the earth doesn't rotate or only rotates slowly, we could ignore the Coriolis force, and a thermal circulation could become established.


The temperature differences that would exist between the equator and the poles is shown above at left.  At right we've taken the country breeze figure and rotated it 90 degrees.  The two temperature patterns and the thermal circulations that would develop are similar.