Tag: weather

La Niña is dead – and good riddance

By Phil Plait | May 8, 2012 12:00 pm

I am very happy to see a very unwelcome visitor go away: La Niña is dead.

Over time, the pattern of ocean and atmospheric circulation changes. When cooler water in the eastern Pacific Ocean is brought to the surface at the Equator, it’s called La Niña, and when that water is warmer it’s El Niño. This changes the way winds blow and water evaporates, and during La Niña Australia gets torrential rains and floods, while the US gets drought conditions, especially in the southwest.

This year, the jet stream was also held up near the US/Canada border, so the winter was very mild, and many states suffered severely dry conditions. But finally, after two years, equatorial waters are warming up. As you can see in the image above, the water near the Equator was cooler (blue) in January 2012, and now a stream of warmer water (red) has appeared north of it. This means neutral conditions will take hold (and eventually lead to an El Niño).

All winter here in Boulder it’s been far warmer and drier than usual, and in my travels these past few months the story has been the same nearly everywhere. The mountains to my west have been nearly free of snow, something I haven’t seen since moving here. But literally, as I type this it’s raining steadily outside, again something I haven’t seen in many months.

It’s very welcome! Well, I’m rather hoping it doesn’t interfere with the talk and star party I’m doing in Boulder this coming Saturday, but in the meantime it’ll be nice to see the creeks rising, the snow pack increasing, and the trees looking a little bit peppier.

Image credit: NASA Earth Observatory/Jesse Allen and Kevin Ward, using JASON-2 data provided by Akiko Kayashi, NASA/JPL Ocean Topography Team.

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CATEGORIZED UNDER: Pretty pictures, Science
MORE ABOUT: El Nino, La Nina, weather

The pressure of living on a spinning planet

By Phil Plait | September 27, 2011 9:27 am

If you live on or near the East coast of the US and you’ve been wondering why it’s been so cloudy lately, here’s the reason:

That’s a low-pressure system that’s been squatting over the Great Lakes region for a few days, as seen by NASA’s Aqua Earth-observing satellite [click to centrifugenate]. It stretches clear across the country north-to-south; you can see the Gulf of Mexico at the bottom of the picture.

Why is it comma-shaped? Because the Earth rotates. Seriously.

The Earth spins once per day, and is about 40,000 km (24,000 miles) around at the Equator. That means someone standing there makes a circle that big once per day, moving at a velocity of about 1700 kph (1000 mph). But someone standing at the pole isn’t making a circle at all; they would just spin in place once a day. At an intermediate point, say a latitude of 45°, someone would be moving around in a circle at a velocity of about 1200 kph (700 mph).

Now imagine you’re standing on the Equator, moving east at 1700 kph. I suddenly magically transport you to 45° north latitude. What happens? Well, you’re still moving east at 1700 kph, but the ground is only moving east at 1200 kph. That means relative to the ground you’re moving faster to the east by 500 kph! To someone standing there, you’d pop out of thin air screaming eastward nearly as fast as an airplane. Better pack a parachute.

The opposite is true if you’re at the north pole, not moving at all, and I whisk you south to 45°: now the ground is moving east of you at 1200 kph. To someone already there, you’d appear moving west at that speed. It’s all relative.

Weird, isn’t it? But it’s a natural consequence of living on a rotating ball.

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CATEGORIZED UNDER: Cool stuff, Pretty pictures, Science

The fist of an angry cloud

By Phil Plait | July 16, 2011 7:00 am

I glanced out my office window the other day and saw what is clearly a sign that the weather is ticked off about something:

Go cloud! Punch that sky!

I was thinking at first the cloud was the result of a big convective updraft; warm air screaming upwards and forming a puffy column. A couple of weeks ago I saw this happen in a ginormous cumulonimbus storm cloud. There were several rapidly rising columns of air moving up so quickly they were forming pilei, which are caps of water vapor that look like little shock waves at the top of the cloud.

However, when I was looking at this fist cloud just a few minutes later as it blew east toward my house, I saw this was just a perspective effect, and it was just a normal puffy cloud.

Too bad. I was getting into it. Give it to the man! Fight the stratus quo!

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No, the "supermoon" didn't cause the Japanese earthquake

By Phil Plait | March 11, 2011 10:02 am

[UPDATE: I have posted an article with more info on the earthquake and where you can donate money toward the relief efforts.]

Japan suffered a massive earthquake last night, measuring nearly magnitude 9. This is one of the largest quakes in its history, causing widespread and severe damage. Before I say anything else, I’m greatly saddened by the loss of life in Japan, and I’ll be donating to disaster relief organizations to help them get in there and do what they can to give aid to those in need.

While there isn’t much I can do to directly help the situation in Japan, I do hope I can help mitigate the panic and worry that can happen due to people blaming this earthquake on the so-called "supermoon" — a date when the Moon is especially close to the Earth at the same time it’s full. So let me be extremely clear:

Despite what a lot of people are saying, there is no way this earthquake was caused by the Moon.

The idea of the Moon affecting us on Earth isn’t total nonsense, but it cannot be behind this earthquake, and almost certainly won’t have any actual, measurable effect on us on March 19, when the full Moon is at its closest.

So, how can I be so sure?

The gravity of the situation

Here’s the deal. The Moon orbits the Earth in an ellipse, so sometimes it’s closer to us and sometimes farther away. At perigee (closest point) it can be as close as 354,000 km (220,000 miles). At apogee, it can be as far as 410,000 km (254,000 miles). Since the Moon orbits the Earth every month or so, it goes between these two extremes every two weeks. So if, say, it’s at apogee on the first of the month, it’ll be at perigee in the middle of the month, two weeks later.

The strength of gravity depends on distance, so the gravitational effects of the Moon on the Earth are strongest at perigee.

However, the Moon is nowhere near perigee right now!

The Moon was at apogee on March 6, and will be at perigee on March 19. When the earthquake in Japan hit last night, the Moon was about 400,000 km (240,000 miles) away. So not only was it not at its closest point, it was actually farther away than it usually is on average.

So again, this earthquake in Japan had nothing to do with the Moon.

Time and tide

So why would people think this is due to the Moon?
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CATEGORIZED UNDER: Antiscience, Astronomy, Debunking

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