Dan's Wild Wild Science Journal

To me the most fascinating part of synoptic forecasting is Satellite Meteorology. I can still remember working in Tulsa at KJRH TV where we had a GOES Unifax machine. Every 15 minutes a high resolution image would spit out. During the day the resolution was 1 km on a visible image. This was good enough to see jet contrails at times.

Jet Contrails from the NASA Modis Satellite- It sees true colour. GOES does not. These contrails keep the nights warmer and days slightly cooler over much of America.

One afternoon a large contrail was visible across Northeast Oklahoma and I ran outside the station and there it was! I was looking at the bottom of it, the satellite was seeing the top from 36,000km away. This seems like no big deal now, but in 1978, it was a very big deal!

TV viewers have since grown very accustomed to seeing satellite images on TV weather reports and now even online. What the average person does not know is just how incredibly valuable these images are.

It was once said that if the GOES Satellites could see nothing but hurricanes in the ocean, they would be worth 100 times the money spent to build them and put them in orbit. I certainly agree.

They do however see MUCH more than just hurricanes. Read on learn some of the incredible ways these satellites are making accurate forecasts and early severe weather warnings possible.

First some misconceptions.

1. Satellite images are not in colour. TV Weather graphic equipment remaps the cloud images over colour maps. The next generation of weather satellites GOES R will be able to see almost true colour. It is really not that necessary to forecasting anyhow.

2. These satellites are VERY high. About 1/10th the way to the moon. The reason is that at 36k km they orbit the earth once a day, and since the Earth turns once a day, they appear to hover over the same spot. If one breaks, the Space Shuttle cannot even get one tenth of the way up to fix them.

3. They are called GOES for Geostationary Operational Environmental Satellite. We use two if them in the USA. Goes East and GOES West. They are in orbit over the Equator and cannot see well in the high latitudes because of the curve of the Earth. Alaska, and Northern Canada forecasters use the Polar Orbiting satellites, but only get a few pics a day. The current operational east satellite is GOES 12. GOES 13 and 14 are in orbit, but in storage until needed.

GOES Water Vapor IR imagery Image from July 4 05Z

4. They take mages every 15 minutes and can do an image over a small area every 7 minutes in rapid scan mode.

5. They do not have cameras per say. They have sensors that detect electromagnetic radiation. The visible light that your camera records when you take a picture is electromagnetic radiation. It’s light in the visible part of the spectrum.

X-rays and the radio waves from your favourite FM station are “light” as well. We humans just cannot see that light. So is infra-red radiation that “night goggles” use. You can buy video cameras now that see in the IR wavelengths.

The GOES imaging sensors actually see electromagnetic radiation in 5 different bands. One visible and 4 in the infra red. The GOES also has another sensor called the sounding radiometer. The sounder imager can actually detect temperatures and moisture at different levels in the atmosphere. Even under clear skies.

We can actually take a sounding without launching a weather balloon. (They cost you the tax payer about 100$ a pop too)

Even in daytime we get both the IR and visible images. At night we only get the IR of course. The visible channel can resolve objects bigger than about 1 km square. The IR imager is 4 km. One image you see rarely on TV is the Water Vapor IR images. These images look almost like an atmospheric X-ray and are very valuable to forecasters like me.

IR Image from GOES East Midnight 4 July 2009. See the storms in Kansas!

Using water vapor imagery we can see the outlines of troughs and even upper level low pressure centers called vorticity maximums. These “vort maxes” can kick off convection or intensify a low pressure system. Skies may clear suddenly behind them. Knowing their position also allows us to compare the real world with a forecast model. If the model has forecasted it well,then confidence in the models forecast is increased!

Since the amount of radiation an object gives off is related to it’s temperature, the IR images also can tell us the height of clouds and thunderstorms! The colder the cloud, the higher it is! High ice crystal cirrus clouds show up bright white on IR images, where ground fog is sometimes hard to see since it’s the same temp. as the ground.

A new technique has been developed that subtracts one channel from another and makes it possible to see fog at night. We call it the “fog Product“. High clouds over a fog layer will usually keep it from dissipating as fast so seeing the different layers of clouds is very important.

Lines of building cumulus clouds can be seen long before radar echoes show up. Many times when the atmosphere is unstable, these building towers are the first clue that severe convection is imminent and a tornado watch may be issued.

Geostationary weather satellites are over Europe and Asia, along with the Middle East, So we can actually see every corner of the globe. Not the high latitudes though, we only get images of the poles a few times a day. Forecasters in these high latitudes get very good at interpreting the lower and higher resolution images from the polar orbiting satellites. If you have the money, you can download the images from these satellites as they pass overhead. Lots of people do it!

Temperature structure of the atmosphere near Huntsville AL. From GOES. Numbers on the right are indexes that tell the forecaster about instability etc.

There are other sensors on these satellites as well. If you crash in a remote island, your plane will have an ELT on it. This Emergency Locating Transmitter will be picked up by the GOES. Detection of solar storms is also made possible by GOES along with other satellites. Arctic Ice in shipping lanes is also monitored with GOES. If there were GOES in 1912, maybe the Titanic would have missed that berg.

Yes, it cost a lot of money to put these satellites up in space and even more to build them, however the images they provide are very nearly priceless.

When I hear a scientist, talking about some astronomical object, and they say something is (for example) 8 billion miles away, I cringe. No doubt, the reporter asked for the distance in miles, or kilometers, because that unit of distance is familiar to most people. Does it really tell you anything?

I say no.

Yes, it tells you it is very far away, but nothing much more than that.

To really understand these distances, you need to compare it to something! When I talk with school kids about weather and earth Science, I try to compare measurements to something they can relate to.

Here is a little project you can use to teach your kids about the solar system. We will use a unit of distance called an Astronomical Unit. (AU). An AU is simply the distance from the Sun to Earth. Earth is 1 AU away from the Sun!

Grab a tape measure, and a football (Americans: Read that as soccer ball). A couple of small marbles, and some crumbs from week old brownies. Tiny pieces of gravel will do. Small enough that 8 or 9 of them will fit on your thumbnail.

Now, Go outside and put the ball in an open area. Use the tape measure to mark 1 meter. Put a piece of tiny gravel down. A persimmon seed will work too. At 5 meters from the ball put down your large marble. (A jaw breaker works really well here) At 9.5 meters put down your second biggest marble. At 19 meters put down a small marble and then another one at 30 meters.
Almost done now.

At 39.5 meters put down a tiny grain. now measure all the way out to 84 meters away from the ball. drop your tiniest grain on a piece of paper.

Welcome to the solar system. You have just built a pretty darn good model that is correct in size and scale!

At one meter is the Earth. You can put down a seed at 1.5 meters for Mars, and another seed about earth size at 70 centimeters. That is Venus.

The big marble at 5 meters is Jupiter. The one at 9.5 meters is Saturn. Neptune is at 30 meters, and while not a planet, Pluto is at 39.5 meters. Step back to Earth and look at the ball. It should look about as big as the disk of the sun in the sky. Now walk out to Neptune. Notice how tiny the sun looks!

Lastly, walk out to your grain of dust at 84 meters. Look back at the sun. This is where Voyager One is now. It is the most distant man made object from Earth. Launched in 1977, it now so far from sun, that the stream of particles from our Sun (The Solar Wind) is nearly gone. It’s not as big as the grain you have, it’s as big as the cold virus on the grain!

The fastest anything can travel is light speed. Physics people refer to it as “c”. Now, I can tell you that this is 186,282 miles per second, but I would be guilty of doing just what this post is about!

Lets do it this way.

At light speed, you can go around the Earth 7 times in one second. In our scale model, it takes light, 8.15 minutes (489 seconds) to go from the ball, out to Earth at 1 meter. In other words, on our newly built solar system, light speed is one meter every 8 minutes. I will let you do the math to figure out how long it takes to send a message to Voyager One, by radio.

The nearest star to our Sun is 272,021 Astronomical units away. Since we used 1 meter as an AU in our solar system, we can put it on our scale. Get a rubber ball 5 centimeters wide, and drive 272 kilometers away. Set it down, and write Proxima Centauri on it! It will take a radio signal moving at 1 meter every 8 minutes, over 4 years to get there.

That should give you an idea of the size of the solar system! Cool ay?

Dan

Looking at the satellite imagery this evening is a scary prospect. Hannah is now a hurricane east of the Bahamas. The numerical weather prediction (NWP) guidance brings it into Savannah or S. Carolina as a minimal hurricane by Friday afternoon.

A new tropical storm has formed in the middle of the Tropical Atlantic. This system looks very healthy, and is now named Tropical Storm Ike. I suspect it will become a hurricane and approach the Bahamas and perhaps the USA in 7-10 days.

Looks like a busy September, with a lot of tropical troubles….

Later,
Dan

I have a screencast update on Hurricane Gustav. It was recorded at 12:30 am (0530Z). I’m still getting used to this software, and it will get better.

This is a chance for you to get an in depth look at what I am seeing in the maps as I go through the forecast process.

Video is here: GUSTAV UPDATE

On the brighter side of things. Meteorological Summer ended at midnight!!

Dan

ps: You will need the Quicktime movie player to view it. It will play much fast if you are on a mac. I recorded it on my Imac at home. If you are on Windows PC, download the file to your desktop before playing. File is 23 megbytes, so broadband is needed.

Admit it.

Sometime in the past you have complained that it always seems to rain on the weekend. In the back of your mind though, you told yourself that it really doesn’t rain more on any one day of the week.

Right???

WRONG! (If your in the Southeast U.S. anyway.)

Seems that a group of scientists decided to test a theory that it should rain more during the latter half of the work week than on the weekend. This makes sense because rain drops form on aerosols. (Aerosols include dust, sea salt, and soot etc. from air pollution.) More air pollution-more rain.

There was a famous paper (well in the geeky science world that I live in) about this affect about 30 years ago. The paper looked at rainfall downwind from St. Louis, and found that rain amounts were noticeably higher in Illinois to the East. Something the farmers there have for some reason decided not to complain too much about!

Along comes the TRMM satellite. The Tropical Rainfall Measuring Mission satellite was the first time we put a good old fashioned weather radar on a rocket and blasted it into low Earth orbit. There has been a ton of science coming out of this radar. Including a study by NASA using our ARMOR Dual Polarimetric Radar.

Thomas Bell of Nasa Goddard, and several other scientists have written a paper about using the TRMM satellite to track rainfall variations by day of the week. They found that indeed there is a signal. Wednesday and Thursday are wetter than Saturday and Sunday over the Southeast. Not only that. The opposite is true in the Atlantic Ocean, to the east of the S.E. USA.

This makes sense for two reasons. First, the air pollution will get pushed eastward by the prevailing westerlies. So the weekend will have more aerosols in the air over the Atlantic.More aerosols-more weekend rainfall.

Secondly, (A bit more complex) is the atmosphere must maintain hydrostatic balance. In other words if air rises up into thunderstorms over the southeast, it has to sink back down somewhere else to compensate. Therefore, the Western Atlantic should be drier if we are wetter. This phenomenon is very noticeable around hurricanes. You usually see very litte airmass thunderstorm activity outside the circulation of a tropical storm.

So yes, all that junk we spew into the atmosphere not only reduces the visibility, it makes it rain more. (Visibilities in the Great Smokey’s are less than half what they were 50 years ago!) Look on the bright side. The weekend is ever so slightly drier and sunnier!

I found the paper in pdf form on Doctor Bell’s website:

http://climate.gsfc.nasa.gov/publications/fulltext/Bell-etal_JGR_2008.pdf

NASA has a summary here: http://www.nasa.gov/centers/goddard/news/topstory/2008/midweek_rainfall.html

If Math scares you, use the second link.

Later,

Dan