Mary, Mary, How does your dewpoint vary?

Today we are modifying the old nursery rhyme which inquires about Mary's garden  to consider typical fluctuations in dewpoint temperature.  Since the dewpoint depends on the total atmospheric pressure, and that changes from day-to-day, the dewpoint will change (for a given amount of moisture in the air) as the barometric pressure changes. We'll also look at how dewpoint might change with altitude.

Moisture and the Speed of Sound

Many of us first learned about the speed of sound as children when we were taught that counting the seconds between the flash of lightning and the sound of the thunder provided an estimate of the distance to the lightning strike (around 5 seconds per mile).  Later, perhaps, we learned that the speed of sound is calculated by sqrt(k*R*T) where k is the specific heat ratio, R is the gas constant for a particular gas, and T is the temperature.  Obviously, the speed of sound varies with the temperature, but it also varies with the makeup of the air (through k and R).  So, does humidity have a significant effect on the speed of sound?  We’ll explore that question today.