Wednesday, April 19, 2006

It's Not the Heat...

Greetings Squaddies! Welcome back!

Before we get into the science post, did anyone see Pearl Jam on SNL this past Saturday night? I stopped watching SNL some time ago, and now I only record it if the musical guest is of intersest. As Pearl Jam is my most favorite band in the universe, nay, the multiplex, I had to record it. Their new album drops on May 2nd and I am super excited, even more so after watching them Saturday night. The band looked like they were having a great time, the set was tight and Eddie grew his hair out again. Yay! Back in college when I was young, stupid and impressionable, I grew my hair out to just above shoulder length so that I could look like Eddie Vedder. You might be surprised to know that I was in no way successful in looking like a rock star. Eddie played guitar on Worldwide Suicide which still doesn't look right. I remember the first time I ever saw Eddie playing guitar was on SNL and I remember thinking that Eddie doesn't play guitar. I don't know why it looks so odd to me, but it does. Anyway, the band looked fantastic, and Mike McCready looked like he lost some weight, which hopefully is just a health-kick thing and not a side effect (Mike has Crohn's Disease). I've already preordered the CD, and you can too but I'll warn ye, it's a bit pricey. However you do get a live show from 1992 when they opened for Keith Richards. The set includes "Dirty Frank" which is a charming, and often hilarious, song about a cannabilistic killer. Those guys!

Enough musical blathering, let us get wit da science! This week's question, like last week's question, comes from Andy who took time out of his busy motorcycle riding schedule to plum the depths of his scientific curiosity. You too can have your questions answered by me, you need only drop me an email at suburbanjoe - at - gmail - dot - com or leave your questions in the comments. No question is too large or too small. Remember, there are no stupid questions, only stupid questioners. Here we go.

If humidity is the moisture content of the air, why is the west coast less humid than the eastern seaboard, considering they are both close to large water sources?
This is an excellent question, and one that factors into both mine and Andy's lives as we both live in the south (him in VA and me in GA) where summers are disgustingly humid, and both of us have entertained notions of living in San Diego which, weather-wise, is paradise on earth. The difference is that Andy has a chance of living in San Diego where my need to not share a one bedroom apartment with a wife and 2 kids rules the idea out completely.

The short answer is that it's California, so who the hell knows why they do anything? I'm sure they had more humidity and then the residents voted to recall it. Ha! A little political humor there. Right, moving on. The temperature and humidity of your little piece of the world has to do with mainly two things, the temperature of the surrounding geography and which way the wind is blowing. And, as Dylan said, you don't need a weathervane to know which way the wind blows.

For the purpose of determining why CA is less humid than GA, the surrounding geography we're most concerned with are the massive bodies of water on each state's doorstep, the Pacific for CA and the Southern Atlantic/Gulf of Mexico for GA. In the summer, the Pacific ocean is relatively cool, with an average water temperature of around 60 degrees. On the other side of the country, the average temperature of southern Atlantic coast and the Gulf of Mexico is in the mid 80's. To see where we're going with this, take an ice cube and put it in front of a fan so that the fan is blowing over the ice and onto your face. Nice cool air, huh? Now do the same with a cup of hot water. Not so cool now, is it? On a simple level, this is what's happening in the summer in the US. On the west coast, winds blow from the west, over nice, cool 60 degree water and in turn brings cooler air to our folks in CA. On the east coast, air blows up from the Gulf of Mexico and the southern Atlantic Coast, gets warmed up and then hits the eastern seaboard.

Why this makes a difference for humidity is that the air that is warmed or cooled by the prevailing winds contains a small amount of water vapor. I say small, because as a percentage of the atmosphere, water vapor accounts for very little. It may not seem that way when you walk 10 feet to your mailbox and you sweat so much that it looks like someone hit you with a hose, but trust me, it's true. If that water vapor is surrounded by hot air, the temperature of the water vapor increases. If the temp of the water vapor is high, the vapor's pressure is high. If the vapor's pressure is high, the air+vapor combo has a greater capacity to hold water vapor. In other, more simplistic terms, the warmer the air, the more water vapor it can hold, and the more humid it feels. Cool air blowing in from the Pacific can hold less water vapor than warm air blowing up from the Gulf. Hence a nice leisurely pancake breakfast on the sidewalks of San Diego in the summer, and a stank inducing sweatfest jaunt outside in Washington DC.

The temperature and wind combo also accounts for the heat waves that usually hit NYC every summer. The warm air blowing up from the Gulf covers pretty much the entire eastern seaboard, including the Big Apple. That, combined with the heat generated from millions of people crammed in a large city make for some especially warm, and fragrant times. This also explains the joy that is summer nights in upstate NY. Sleeping in coastal CA at night is a wonderful thing, the temps drop, you open the windows, maybe smell the ocean, or the wildfires, or the looting and you drift off into dreamland. Summer nights in upstate NY is like sleeping wrapped in a hot, wet towel. Because the air on the east coast contains more water vapor, the cooling process is slowed considerably, which means that you ain't opening your windows at night. I can remember one of the first apartments Linda and I lived in had brick on the outside, and no air conditioning. In the day, those bricks would bake in the sun and then all that heat would radiate from them at night and it was positively sweltering. Opening the windows did nothing becuase it was warm and humid outside. Her dad rigged up some air conditioner for us, but because it didn't vent out the window properly, it would only run for about 5 minutes before it would shut down. We'd get up in the middle of the night, turn it on, and stand in front of it for those blessed 5 minutes of cold air before it would shudder and shut off. Good times. In contrast, in CA, the dry air can cool much quicker, which leads to a greater temperature variation between day and night.

We've covered summer, so why are the winters in NY and the northeast so bad, if the air is coming from the Gulf? That would be because it isn't. In the winter, the west coast still has air blowing in over the Pacific and this air is significantly warmer than the frigid, earth shatteringly cold air that blows down from Canada into NY and all points north. Once again, it all comes down to wind. Those on the West coast can rest easy, content with the knowledge that the mighty Pacific keeps their weather nice and mellow, which will be helpful when the next Big One hits and California is cast off into the ocean. Good luck and bon voyage!


MadSci Network - Why does warm air hold more water than cold air? - What causes humidity? - Air masses bring variety of weather - Chad Palmer - Answers: Weather, climate of the U.S. West


k o w said...

Now that is what I'm talking about. Great question and answer.

Booster MPS said...

And don't forget our friend the Gulf Stream that is ultimately responsible for bringing that warm water from the tropics. This is what sets up the massive high pressure systems that sit over the central US during the summer. Also helps to think of the weather system as 3 dimensional systems that move around the globe. Kinda like a huge pressure gradient field. Nerd - Out!

Bones said...

Another great post. You need to start charging for this stuff.

Asphyxiate said...

Another great question! errr I mean post. No! Questioner! Wheeee!

Oh and Oblivion - I'm 100 hours in and havent touched main quest now. Ulp.