A quick tutorial on millibars & stuff for those who keep asking:

[karlrschneider]

The measurement 'millibar' 1/1000 of a bar is simply a unit of atmospheric pressure...how much the air "weighs" over any given point.

"Standard" sea-level pressure is 1013.25 mb, or expressed another way, 29.92 inches of mercury, or about 14.7 pounds per square inch. (the STP or standard pressure & temp includes this figure as a worldwide average...the temperature is considered 59 deg. F)

As you go up the pressure generally decreases about an inch of Hg (mercury) per thousand feet, approximately. A bit less...the altitude at where the air pressure is HALF of standard is about 18,000 feet.

This info is easy to Google but we seem to have a lot of DUers who haven't figured it out...
:eyes:
I've taught meteorology for flight schools for about 40 years, feel free to ask me (PM or email [e-mail]) if you have more questions.
;-)

[Jacobin]

1. I've been trying to find some stuff on Hurricane Gilbert in 1988

It was enormous and had the lowest baromentric pressure ever...covered the entire gulf.

Fortunately it hit an area south of Texas that was not populated.

It had a double eye wall. I remember evacuating from that one, because it was headed for my town before it turned.

I'll google around some more. Incredible pictures

[highplainsdem]

16. Link to Hurricaneville's list of most powerful Atlantic hurricanes:

http://www.hurricaneville.com/all_time_storms.php


Gilbert at the top, with a minimum central pressure of 888 mb.

The list will have to be updated to add Katrina and Rita.

[Thtwudbeme]

2. What do you think this storm is going to do?

?

[karlrschneider]

5. All I know is it's gonna wreck a lot of stuff whereever it hits. 2 days

ago, I predicted landfall just east of the TX-LA border but it looks like that high pressure ridge didn't move northeast as fast as I expected so guess I mis-read the synoptic charts. I think it will come onshore very close to Houston as of right now. Not good no matter where, though.

[ChairmanAgnostic]

3. Damn. I kept thinking of hotel room bars.

seriously. what are some of the predictions of low pressure for Rita? and do you have some historical data about the heat sink known as the Gulf of Mexico? I thought I read that it was at an all time high recently, and that some meteorologists were seriously considering increasing the length of probable hurricanes this year.

[edbermac]

4. Tonight's forecast: Dark.

Continued mostly dark tonight, turning to widely scattered light in the morning, man...

This is Al Sleet saying...Remember, if you don't like the weather...MOVE!

[Fovea]

6. Forcast for the foreseeable future.

Residents of the area of the gulf are literally in hot water.

Water temp, and the difference between the vapor temperature, and the air temp aloft creates massive lift as the rising wet air hits the level where it starts to condense into clouds, releasing the latent heat of condensation, where it rises at the wet adiabatic rate.

Hotter water, more potential energy gets released at the point where it becomes a cloud, or for the poetic minded...

http://65.64.114.185/poetry/pages/RaininKansas.htm

[karlrschneider]

7. Adiabatic...cooling resulting only from pressure change with no

convection or other direct heat transfer.
:D
Often confused with but more or less the same thing as isentropic.

[Fovea]

14. thank you,

my wrong.

[ChairmanAgnostic]

8. Hey, karir, a question. please tell me if I am stupid.

It strikes me, as a layman, that there is a great deal of latent energy stored in the heat of the Gulf waters. Is it proper to view a hurricane as a release of that stored energy? In the form of wind, hydraulic action (rain/evaporation/rain/evaporation) and kinetic energy in the form of wave action? and the higher the temps, the more water is evaporated, then rained back onto the ocean?

If that is the case, every time we have a huge storm like Katrina or Rita, there is a release of the latent energy which turned into the storm's energy. If so, is there any perceptible cooling of the waters, once a Cat 5 storm hunkers down? if the release is too little, then, logically, we will have storm and storm after storm . . . ad abusrdum. Given our reliance on Gulf oil and natural gas, it may be outside forces that cause the US to change its energy policies. Like a total absence of Gulf energy supplies.

[karlrschneider]

10. Yes, there is a lot of 'latent' energy in the water. We call it enthalpy

The warmer the water is, the easier it is to evaporate and as it changes state from liquid to gas, it actually absorbs heat (about 500 calories per gram) which tends to lower the local temperature of the remaining water, but only a very tiny bit since there is a "hugh" reservoir of heat energy. The distinction between heat and temperature is important. You can have a cupful of water at the boiling point which is very "hot" but the amount of heat energy is very low compared with a bathtub full of water just a little 'hotter' than its surroundings (the ambient temperature.)

Here's a simple way to look at it: you can blow out a match and it will be several hundred degrees of 'hot' yet you can stick it on your palm without doing any serious damage...that's because even though the temp is high, it doesn't contain much thermal energy.

[muriel_volestrangler]

9. But just to add the "howevers" ...

That's the aviator's definition of 'standard temperature and pressure'. Chemists have a different one - see http://en.wikipedia.org/wiki/Standard_temperature_and_pressure.

For what it's worth, a millibar is the pressure of 100 Pascals, or 100 Newtons per square metre. A Newton being, very roughly (this is not the definition) the weight of an apple. :-)

[karlrschneider]

11. I figured somebody would bring this up. Haha

The 'chemists' operate with a slightly different set of physical parameters than we aviators and aerodynamicists do and it is mostly because they have more "completely" converted to SI units. Conversion factors and rounding errors have caused a lot of problems the last 40 years as they attempt to reconcile the usage of units in dimensional analysis. Some of this difficulty was manifested a few years ago when somebody forgot to convert feet to meters and screwed up a major scientific endeavor...I -think- it had something to do with the Hubble but I'm not sure on my memory there...maybe someone recalls it more clearly.

In any case, your Wiki link is most interesting and useful...thanks!
:D

[muriel_volestrangler]

12. Mars Climate Orbiter

http://edition.cnn.com/TECH/space/9909/30/mars.metric.02/

[karlrschneider]

15. Right! I couldn't recall the details, thanks.

:D

[JohnyCanuck]

17. Air Canada is lucky no one died in this screw up between kg and lb.

Air Canada's Gimli Glider (Air Canada 767 made a both engines out, dead stick landing in Gimli, Manitoba after running out of gas mid flight).

A Boeing 767 is normally fueled using a device known as the Fuel Quantity Information System Processor (FQIS), which operates all of the internal pumps and reports to the pilots on the status of the fuel load. However, Flight 143's FQIS was not working properly, a problem later traced to a bad solder joint in the capacitance gauges in the fuel tanks. Instead, the fuel load was measured with a dripstick, a dipstick for airplanes, as a means of determining the total volume of fuel in the tanks. The dripstick measure indicated 11,525 litres.

The error occurred when it came time to calculate how much fuel was needed for the flight from Montreal to Edmonton. The calculations were based weight instead of volume, which required a conversion in the measurements. The 767 measured fuel in kilograms, whereas all of the other manuals and planes in the Air Canada fleet used pounds. The pilots used an unit conversion factor of 1.77 lb/l. However, a fuel load measured in kilograms should have used the conversion factor of 0.8 kg/l. After using the 1.77 figure, the 20,400 figure was entered into the airplane's computer, attempting to tell it that they had 20,400 pounds on board. Instead, the computer interpreted the figure as 20,400 kilograms and indicated that there was enough fuel based on the erroneous input. However, the airplane only had 9,144 kg (20,160 lb) onboard, too little for the flight to Edmonton.

Both the pilots and the fueling crew had misgivings about the math and calculated the figures three times. After coming up with the same number the pilot, Captain Robert (Bob) Pearson, finally stated, "That's it, we're going." Flight 143 then flew the short distance from Montreal to Ottawa, where the fuel level was re-measured before the flight proceeded to Edmonton.


At 41,000 feet over Red Lake, Ontario, the cockpit warning system chimed four times and indicated a fuel pressure problem on the left side. The pilots thought a fuel pump had failed and turned it off; the tanks are above the engines so gravity will feed them without the pumps. The computer said that there was still plenty of fuel, but this was based on calculations using the assumption that the plane had started with 20,400 kg of fuel. A few moments later a second fuel pressure alarm sounded, and the pilots decided to divert to Winnipeg. Within seconds the left engine failed and they prepared for a one-engine landing.

While they attempted to re-start the engine and communicate with controllers in Winnipeg for an emergency landing, the warning system sounded again, this time with a long "bong" that no one present could recall ever hearing before. The sound was the "all engines out" sound, an event that was never simulated during training. Seconds later the right side engine stopped and the 767 lost all power leaving the cockpit suddenly silent and allowing the cockpit voice recorder to easily pick out the words "Oh, fuck!".

http://en.wikipedia.org/wiki/Gimli_Glider

[Ilsa]

13. Thanks. The refresher from my high school sophmore

chemistry class was worthwhile. That was over thirty-two years ago, but worth reviewing. :thumbsup: