## Sunday, November 4, 2012

### Halloween Hurricane Sandy

I'm sure everyone was inundated with media coverage of Hurricane Sandy this week, or was involved in it in some way.  Fortunately, I'm here to bring you the reason why Sandy was a strange and unique storm.  It formed during some very unique atmospheric conditions in the Atlantic, which caused Sandy to be funneled up the coast straight to New Jersey and New York City.  The combination of these systems also transformed Sandy from a hurricane to what is essentially a giant thunderstorm.

First of all, we should talk about storms. There are a few different types, but what matters here is that the type we see most often in our neck of the woods is an extratropical cyclone.  They form between 30° and 60° North or South of the Equator, and generally look something like this:

Note the hurricane-like rotation.

That magnificent specimen is a February 2007 blizzard. These storms are what drive the weather systems we're used to throughout the US and Europe, bringing wind, cloudy days and thunderstorms.  They are also known as "cold-core" systems. When you hear about a low pressure system on the news, it's generally one of these bad boys.  The main characteristic of this storm, the one that you should pay attention to, is that the wind and rain are spread out over a wide area.

Now, hurricanes are another type of storm, called a tropical cyclone.  They form in the tropics, or from 30° N to 30° S.  They have a unique shape, and also have a distinct eye.  These are our hurricanes (Atlantic) and typhoons (Pacific).  Tropical cyclones have a low pressure center with bands of thunderstorms radiating out from that.  In contrast to extratropical cyclones, most of the rain and wind is concentrated at the center of the storm, and they are known as "warm-core" systems.
This beauty is Hurricane Katrina, just after landfall.

Now that we know what those two types of storms look and act like, we'll take a look at Hurricane Sandy.  This particular storm started as a depression south of Jamaica, and due to favorable conditions, intensified to a Tropical Storm on October 22. It moved north across Jamaica, Cuba and the Bahamas over the next 4 days, intensifying to a Category 1 (or weakest class) hurricane on Oct 24.

As Sandy exited Cuba, it fell apart, and this is where it gets interesting. Conditions allowed the storm to maintain convection (drawing warm air up from the ocean) and kept it from dissolving completely. As it moved north, it formed an eye again and was upgraded to a hurricane once more.  At the same time over the continental US, a large trough was moving into the Eastern US and creating a situation that looked like this:

Credit goes to Dr. Chris Martucci at epawablogs.com

Normally, a trough that deep would block the hurricane and force it northeast, out into the Atlantic.  In the picture above, you can see that there's a high pressure system off the coast of Greenland, and a low pressure system to the south of that.  These two systems blocked Sandy's "escape route", so to speak, and with nowhere to go but northwest, it was captured by the trough and slammed right into New Jersey and New York City.  Here's a satellite photo to give some more idea of what this looked like:

In the top right, you can see the low pressure system swirling east of Canada, and Hurricane Sandy near Florida. That long band of clouds stretching from Texas through Canada is the trough that pulled Sandy in.

As Sandy moved north, it began to interact with this trough and lose some of its hurricane characteristics, becoming an extratropical storm.  As it moved in near New Jersey, it lost some convection but intensified due to the interaction between it and the low pressure system to the west.  At this point, Sandy's wind field was over 1800 km wide (or 1150 mi).  At landfall on Oct 29 it was declared post-tropical (which means it had transitioned to an extratropical storm).

via NASA Earth Observatory

So to recap: Sandy started as a hurricane, should have been pushed out to sea by a trough in the Eastern US, was blocked by weather systems in the Atlantic, which pushed Sandy back towards the trough, and then finally was intensified by interactions with the trough to become one of the costliest US hurricanes in recorded history.

Frankenstorm, indeed.

## Tuesday, October 23, 2012

### The Fibonacci Sequence

$1,\;1,\;2,\;3,\;5,\;8,\;13,\;21,\;34,\;55,\;89,\;144,\; \ldots.$

Looks like a bunch of random numbers, right?

Look closer.  Each number is the sum of the two that came before it. This set of numbers is called the Fibonacci sequence, after Leonardo of Pisa (not DaVinci) who was also known as Fibonacci.  He first discovered these numbers after traveling widely in the Arabic world as a boy, where he was exposed to the numbers we know now, Arabic numerals.  These proved to be much easier to do arithmetic with than Roman numerals, and he chose to study with Arabic masters.

Upon his return to Europe, he began work on his book, Liber Abaci or Book of Calculations.  Published in 1202, it detailed the efficiency and simplicity of Arabic-Hindu numbers, as well as introducing 0-9 and place values. He demonstrated the new system by using it in bookkeeping and interest problems, rendering it incredibly useful to the merchants of the day. It was widely read by educated Europeans.

But what about the Fibonacci sequence?  In Liber Abaci, Fibonacci presented a problem involving the growth of rabbit populations. In it, he assumed that two idealistic rabbits in a field can mate one month after birth and produce another pair of rabbits once a month thereafter.  The question is, if they mate once a month, how many rabbits will there be in one year?

We start off with one pair. In a month, they mate, but there's still only one pair.  This is the 1, 1 of the sequence. At 2 months, there are now 2 pairs of rabbits (1,1,2). At the end of 3 months, the original pair produces another pair, which makes 3 (1,1,2,3).  At the end of the fourth month, the original female and her daughter each produce a pair, which makes 5 pairs total (1,1,2,3,5).  This continues until the 12th month, when you have 144 pairs of rabbits.

Okay, so there's lots of story problems in modern math books too. What makes the Fibonacci sequence cool?

Maybe the fact that Fibonacci numbers occur in nature, and that this is probably where the sequence came from? Interestingly enough, Fibonacci number and their cousins, Lucas numbers, appear quite often in things like flowers and pinecones and cauliflower. Luckily, Vi Hart from Khan Academy explains it in this 3 part video that's fun and informative.

Isn't math neat?

Next week: Felix Baumgartner's jump from the "edge" of space.

## Tuesday, September 11, 2012

### Pluto: Planet?

Is it or isn't it?  Many people, comfortable and familiar with Pluto's status as the 9th rock from the Sun, have expressed dismay at the International Astronomical Union (IAU)'s ruling that Pluto would be demoted. The 2006 vote that determined what exactly constitutes a planet banished Pluto to the role of dwarf planet.

But what do we really know about our poor friend Pluto, other than that it's really far away?
(By the way, it is really far away: Pluto orbits between 30 and 49 astronomical units (AU), which is 30-49 times the distance between the Earth and the Sun!)

• Orbital period: 248 years
• Apehelion (farthest from the Sun): 48.871AU
• Perhelion (closest to the Sun): 29.657AU
• Size:
• Radius: 1153 +/- 10km (0.18 Earths)
• Mass: 1.305x10^22 kg (0.00218 Earths, 0.178 Moons)
• Temperature in Kelvin:
• Minimum: 33K (-400F)
• Maximum: 55K (-360F)
• Moons:
• Charon
• Nix
• Hydra
• P4
• P5

Pluto was discovered in 1929 by Clyde Tombaugh, an astronomer at the Lowell Observatory.  He was actually looking for the mysterious "Planet X", which was supposedly to blame for discrepancies in the orbits of Uranus and Neptune.  To do so, he would compare photographs of the night sky taken two weeks apart. To his surprise, after a year of comparisons he found movement in one of these pairs!  The discovery was big news, and the planet was named Pluto, after the Roman god of the underworld.

Over the next decades, further observations made it less and less likely that Pluto was Planet X.  For starters, they couldn't see a disk and the planet was faint, meaning it was probably small. Its albedo (or brightness) was calculated in 1976 and the researchers determined that with an albedo matching methane ice, Pluto could not be more than 1% the mass of Earth, When Pluto's moon Charon was discovered, they were able to calculate its mass and found that it was only 0.2% of the Earth's, which made it way too small to cause the gravitational disturbances of two gas giants.  When Voyager 2 passed by Neptune in 1989, scientists were able to revise the mass of the planet, which eliminated the discrepancies and nixed Planet X forever.

## What makes Pluto different?

Pluto is slightly out of place compared to the 8 other planets. The biggest inconsistency is its orbit. While the other planets orbit on the same plane, Pluto's orbit is tilted so that it crosses the plane and orbits above and below it.
It also has an exaggerated elliptical orbit, compared to the almost-circular orbits of the dominant 8 planets.

Pluto seems to be made up of methane and water ice, with a possible rocky core, much like a comet.

However, it does have quite a bit in common with the other objects in its neighborhood, such as the highly inclined orbit, size and orbital period.

## Why can't it be a planet?

The IAU has 3 criteria that a body must meet to be considered a planet.
1. It must orbit the sun
2. It must be pulled into a spherical shape by gravity
3. It must clear the neighborhood around its orbit

Pluto meets the first two, as it does orbit the sun (however strangely) and is roughly spherical. However, the other planets have relatively clear orbits. Most of them have some small asteroids like Trojans or Centaurs that are scattered through their orbits, but the planet itself takes up the majority of the mass of its orbit.  Pluto, however, orbits through this cloud of rocky bodies called the Kuiper Belt  (pronounced like Piper).  You can see in the diagram below that Pluto (the outermost red ring) most definitely doesn't clear its orbit.  (Forgive the non-perfect orbits, paint can only do so much).

## What happens to Pluto now?

Never fear, our dwarf planet hasn't been forgotten. It actually holds the honor of being the first of the Plutoids, or Trans-Neptunian bodies (meaning they orbit beyond Neptune) that orbit the sun in a similar fashion to Pluto and are large enough to be rounded. This family has expanded in recent years to include not only Pluto, but Eris, Haumea, Makemake, Quaoar, Orcus and Sedna

It's estimated that hundreds of objects like Pluto are orbiting in the Kuiper Belt and beyond; however, their distance and size make them difficult to even find, let alone observe.

As for Pluto, I have exciting news! In 2015, the New Horizons mission will arrive at Pluto and perform a flyby, giving us our first actual images of that cold, dark world.  It will perform a number of experiments, such as determining the makeup of Pluto's surface, discovering if it has a thin atmosphere as theorized, and perhaps even finding that it has much in common with Triton, Neptune's largest moon and a possible capture from the Kuiper Belt.   It will then continue on through the debris that rings our Solar System to see if there are more bodies like the Plutoids out there, silently swinging through space around our Sun.

## Thursday, September 6, 2012

### Dawn and Vesta

On Wednesday (5 September 2012), the probe Dawn left the asteroid Vesta, a 525km (236 miles, for those who dislike metric) wide hunk of rock orbiting the sun between Mars and Jupiter in our main asteroid belt.  Vesta happens to be a very special asteroid, however. Besides being the 2nd most massive asteroid, it is a fossil of sorts, a link to how rocky planets like Earth may have formed.

Vesta is the last protoplanet with a differentiated interior. This means that if we were to take a chunk out of the asteroid, we'd see that it has a crust, mantle and core, just like Earth.

 Earth's interior
 Vesta's interior

This is very exciting and very important, because the Earth was most likely formed from a protoplanet similar to Vesta.  There are estimated to have been a few hundred bodies like Vesta, which eventually (over the course of 100 million years) collided due to perturbations in their orbits and formed the dominant 8 planets we know today. (Before you say "what about Pluto?!", hang on! I'll address our lonely little friend in my next post.)

The Dawn mission objective is to visit Vesta (done!) and Ceres, a dwarf planet in the asteroid belt.  These two bodies are useful because of some specific characteristics.
1. Vesta has highly magnetized rocks. These, along with a differentiated interior, could help explain what starts a planetary dynamo. This is the process that creates a magnetic field, which in turn helps shield a planet from solar winds.  (Earth has a very strong magnetic field, while Mars has a very weak one.)
2. Ceres is believed to have a layer of surface or sub surface water ice, as well as a thin but permanent atmosphere.
These two bodies present incredible insights into the formation of worlds like Earth. It could help us understand our own origins, and possibly predict what we'll encounter around stars similar to our own.

BBC News,
Wikipedia, "Protoplanet"