30 October 2012

## Hurricane Sandy’s Rainfall in Perspective

Posted by Ryan Anderson

So. This is happening:

Screenshot of hurricane Sandy as seen on the amazing real-time USA wind map. Click to see the original in action.

With all the breathless reporting about how hurricane Sandy (a.k.a. Frankenstorm) is such a massive weather event, I was curious what the quantity of rainfall from Sandy looks like in comparison to, say, the amount of water in the martian atmosphere.

To find out the volume of rainfall estimated from Sandy, I turned to the twitter hive mind (of course). Fellow martian Caleb Fasset provided me with a link to a site that gives the amount of rainfall for an average hurricane as 2.1×10^16 cubic centimeters of water per day. That number is based on a storm with a radius of 665 km. In contrast, Sandy was sporting tropical storm-force winds out to a radius of 780 km. That means that Sandy covers an area around 1.4 times larger, so if the rainfall scales up by the same amount, then a very rough ballpark number would be 2.9×10^16 cubic centimeters per day. Convert that to cubic kilometers and you get a whopping 29 cubic kilometers of water falling from the sky per day!

So, how does that compare to water on Mars? Well, the amount of water vapor in the Martian atmosphere is usually expressed as “precipitable microns” per square centimeter. That is, how many microns of water would you get if you condensed all the water out of the whole column of atmosphere over a one square centimeter area? This value varies from around 10 to around 60 precipitable microns. A micron is equal to one millionth of a meter. Let’s take 30 precipitable microns as an approximate average for Mars. The surface area of Mars is 144,798,500 square kilometers. If I’m doing my math right (feel free to check me!), that works out to 4.35 cubic kilometers. In other words, one day’s worth of rain from hurricane Sandy (29 cubic km) is equal to around 6.67 times as much as all of the water in the martian atmosphere.

In other words: Mars is very dry, and Earth is very wet. Particularly the northeastern United States at the moment.

Stay safe and dry everyone!