That's Zulu not Sulu! (but live long and prosper anyhow)

My wife always laughs when someone asks me the time because I will tend to give the unsuspecting questioner the response...WHERE?
Time depends on where you are. (It also depends on how fast you are moving but let's leave the relativity stuff for another blog)

I'm also asked what the "Z" means on radar images and satellite images we show.


The answer is GMT.

Z stands for Greenwich Mean Time. The official time of science.

Science must have a single reference for time that everyone agrees upon. By world wide agreement that reference is GMT.


GMT is the time in Greenwich, England at Longitude zero. Why Greenwich, and why is it at longitude zero??

Well that is a great story...Read on!

If your at sea on a ship, finding your latitude above the equator is not too difficult. Just look at the North Star (Polaris). At the North pole, Polaris is 90° degrees overhead. At the equator, it is on the horizon. If you go out at night here and measure the angle of Polaris above the horizon you will get 35° degrees. Our latitude here in Huntsville.

You can also do the same with the sun at local noon... as long as you know the date. Mariners have done this for several centuries now!

The difficult thing for ship captains of the past, was not latitude but Longitude. It was nearly impossible to find out accurately how far East or West of "home" they were. Many times the error in position was only found when a ship ran into an Island or continent at night and promptly sunk!

In the early 1700's, when British sea power ruled the waves, A prize was offered to anyone who could solve the problem of longitude. Enter James Harrison. He solved it and then had to fight for years to get his prize. (An appeal, directly to the King himself was at last successful!) & (A&E screened a film a few years ago based on these events called "Longitude".

Harrison realized a key fact. If you divide the spherical earth into 360° degrees and it takes 24 hours for the earth to rotate, then the sun moves 15° degrees per hour.

Say for instance, we are in the Atlantic ocean. 15° degrees longitude west of Greenwich. The sun will reach it high point at noon precisely 1 hour later than it does back in England.

It would be a simple thing to produce a table of exactly when local noon was in Greenwich. This was already known in the 1700's very precisely. Harrison knew he could solve the longitude problem simply by inventing an accuarate clock!

Easier said then done. Clocks of the day used pendulums and they did not swing to well on a ship riding out a storm on the North Atlantic. Even if they could keep it running, the accuaracy would not be good.

To get an accuarate reading of longitude, a clock was needed that would only be off a few seconds in a year. If the clock ran fast or slow at a certain rate, that would be ok! The correction could be added in.

Harrison built 4 clocks. He called them Chronometers. The famous explorer James Cook took one with him around the world inthe 1770's and it was found to be very accuarate.

Cook would mark the time when the sun was at noon wherever he was. He would then look at the chronometer to see what time it was in Greenwich. A few calculations and BINGO...he knew where he was on the planet.

In an age of great inventions, Harrison's Chronometer was one of the greatest.

As Chronometers came into wide use, a single reference point for time was needed. That reference was already there. Greenwich England. Home of the Royal Observatory for the past 400 years!

It is still today the world standard for time. Now they have an atomic clock though!
I visited Greenwich a few years ago and stood on the zero longitude line! Harrison's clocks are on display there as well!

Gosh it is 0948GMT! I gotta get to bed!

Later,
Dan

Hydro ID off of ARMOR

I showed some of our first echo id data on air at 10pm Thursday.(See the last blog)
Using ARMOR and it's dual polarimetric capability, a computer program can be run to analyze the radar echoes using different variables like differential reflectivity and specific differential phase etc. (I have a link at the end that will explain these)

This program can then estimate whether the echo is rain..sleet hail etc. Truly the future of weather radar technology and I just bet I am the first person to ever show it on tv! (Something I care about and no one else!)

Missed it? Here it is (It will make sense when you look at it!)
HYDRO ID

A great web site on how dual polarimetric radar works is at this NSSL web site.

Our next goal is to be able to have this data in real time during severe storms.

Later,
Dan

ARMOR Update

It is pretty neat stuff coming to work every day with the most advanced weather radar at any TV station in the world. Our relationship with the UAH atmospheric Sciences Department and the National Space Science Technology Center, is allowing us to do some fabulous things. Research is already underway with ARMOR. We have a working algorythm now for hydro id as well. Read on and look for a neat link at the bottom...

Before you get lost in acronyms, let me explain some of them. ARMOR stands for Advanced Radar for Operations and Research. It is a dual Polarimetric radar. One of only a handful in the country. The others are at universities and govt. Research facilities. Looking at radar echoes in a horizontal AND vertical polarization has distinct advantages. The NEXRAD radars used by the weather service are going to be upgraded to dual. pol. in a few years.

We have already gotten a feed of ARMOR out to the NWS office here in Huntsville, making it one of the few NWS forecast offices with real time dual Pole Doppler data.

I mentioned Hydro id above.

Using ARMOR we can make a determination of what kind of echo the radar is seeing. Rain, snow, hail, sleet or wet snow..etc. You will see on air in a few weeks (I hope!) a color coded image showing what the radar is seeing. That will be a first!

The best thing about all of this is what we in the WHNT weather department are learning from the researchers at UAH. Very few Meteorologists working in TV or commercial work have this opportunity.

Ok, for those of you who read this far, the UAH folks have got a great web site up with armor data. Now the radar image is on our web site already but this is much much more data at higher resolution. Do me a favor, keep it to yourself. If the server melts we will have to make it private, but I want those of you who read these blogs and are really interested to have the link!
ARMOR LIVE

Later,
Dan

Geo Doom

First off,many thanks to those of you who filled out the survey for Andrew Pennell.

Andrew is doing a thesis on how people in the USA prepare for severe weather. He told me the other night that the city of Abilene, Texas has done away with their weather sirens and told folks to go out and buy a NOAA weather radio. (see my blog on screaming sirens).

Well some huge news in the Geological world. It seems a new tectonic plate has been found. Guess where? Tokyo! This is probably bad news for the world's most earthquake prone megalopolis. Tokyo has a 90% chance of a massive earthquake within 50 years. The last big one in the 1920's killed 140,000 people.

Tectonic plates are portions of the earth's crust that "sit" on the mantle rocks below and these tectonic plates slowly move. Here, in the Tennessee Valley, we are on the North American plate. It is moving W at about 1-4 cm per year. About as fast as your finger nails grow. Still in the ten years I have lived in Huntville my house has moved westward about a foot! (so has your's!)

Plate tectonics is really fascianting and even more amazing is the fact that it was only accepted as a working theory by Geologists around 1960! I mean really! Look at a global map and you can see that South America and Africa were once connected... right???

If you want to see what the world map looked like over the last 200 million years, then check out this web site.

Another bit of Geo doom for you. The La Palma Volcano, in the Azores, is in danger of losing it's side into the Atlantic. Some UK researchers made big news last year with calculations that this would cause a huge tsunami that would affect the East coast of the North America.

Other Geologists have pointed out that the collapse will probably not happen all at once and thus a mega tsunami is very unlikely.

Still if I am on the beach in North Carolina some Summer and I hear something on the radio about the Azores and a volcano...I'm gonna run like Speedy Gonzales to high ground.

Later,
Dan