Is the pressure greater than the standard atmospheric pressure when the weather is clear?

A, Torricelli experiment first measured the value of atmospheric pressure, which proved that the famous atmospheric pressure experiment was the Madeborg hemispheric experiment, so A was wrong;

B, helium balloon in the process of rising atmospheric pressure decreases, the pressure in the ball is greater than the external atmospheric pressure, so the balloon will expand, so b is correct;

C generally speaking, the atmospheric pressure will be higher when the weather is sunny and dry, so c is wrong;

D, atmospheric pressure is equal to the pressure generated by 760mm high mercury column, so D is wrong.

So choose B.