Saturday, August 2, 2008

Hot & Dry Weekend

It was a hot and dry start to the weekend with widespread 90s and 100s from the Rocky Mountains to the deep south.

Denver set a new record high of 104 degrees on Friday. Wichita Falls, TX tied their record high of 108 degrees. North Little Rock, AR (where I was born) tied their record high of 103 degrees.

I am writing this blog at 3pm on Saturday and we have set another record here in Denver at 102 degrees today.

But get this....we had a heat index of 95 when it was 102 degrees. The dewpoint was 27 and the relative humidity was 7%.

Jacksonville, AR (just down the road from N. Little Rock) was 102 degrees with a heat index of 113 degrees. The dewpoint was 73 degrees with a relative humidity of 40%.

I am SO glad I am not back home today.

The hot air is spreading east and north over the next few days, so places like Chicago and Minneapolis can expect a warm up.

Today's Lesson

We're ready to talk about density of the air. This is determined by the masses of all atoms and molecules and the amount of space between them.

In other words, density tells us how much matter is in a given space. (that is volume)

Mathematically, it looks like this.

Density = (mass ÷ volume)

There are considerably more molecules within the same size volume of air near the Earth's surface than at higher levels.

Air density decreases with height, rapidly at first, then more slowly the higher you go in the atmosphere.

Air molecules are always in motion. They bounce around off people, objects, even your plants and trees.

Each time an air molecule hits something, it gives a tiny push.

This small force (push) divided by the area on which it pushes is called pressure.

Pressure = (force ÷ area)

I bet by now you are thinking so how in the heck do you measure air?

Well luckily there is a standard to go by.

If you took a column of air (1 square inch in size) that extended from the ocean surface to the top of the atmosphere, it would weigh about 14.7 pounds.

Therefore, normal atmospheric air pressure near sea level is close to 14.7 pounds per square inch.

If more molecules were packed into that column, it'd become more dense or heavier, and since the air would weigh more pressure would go up. (high pressure)

The opposite would be low pressure if there were fewer molecules of air in that 1 square inch column.

Now in weather we don't typically measure air pressure in pounds per square inch. The most common unit used to measure air pressure is the millibar.

The hectopascal (hPa) is also widely used in science as is mercury (Hg) on television and in weather reports that go out to the public.

Here are the conversions for standard sea level pressure. All 4 of the following are equal.

  • 14.7 pounds per square inch is standard sea level pressure
  • which converts to 1013.25 mb
  • or 1013.25 hPa
  • or 29.92 in. Hg

    Tomorrow we'll dive a little deeper into air pressure.
  • 1 comment:

    1. HI CHRIS,I'M BETTER KNOWN AS GA-FT-11.YOU REMEMBER,THAT NUT DOWN IN GEORGIA THAT RECORDED 5.69 INCHES OF RAIN AND MADE NO COMMENT.
      WELL,THIS IS WHAT I CAN TELL YOU ABOUT THAT READING.
      I PURCHASE THE RECOMMENDED RAIN GAUGE FROM "WEATHER YOUR WAY" AND MOUNTED IT ON A POST IN MY BACK YARD.YOU MAY VIEW THE LOCATION ON GOOGLE EARTH.319 RIVERTOWN RD FAIRBURN,GA.[33* 34'16.60"N,84*35'28.34"W]
      IT BEGAN TO RAIN AT 7:05PM[1905HRS.]
      AND WAS STILL RAINING HEAVILY AT 10:30PM WHEN I RETIRED FOR THE NIGHT.WHEN I CHECKED THE GAUGE SHORTLY AFTER 7:00AM 8/1/2008 I WAS AMAZED AT THE AMOUNT OF RAIN WHICH HAD BEEN COLLECTED.
      I TOOK THE GAUGE INTO MY HOUSE TO SHOW MY WIFE.THERE I EMPTIED THE INNER TUBE AND REFILLED IT FROM THE
      LARGER CONTAINER TO OVERFLOWING FOUR
      TIMES.THAT'S FIVE INCHES.THE FIFTH TIME THE GAUGE HELD ".69INCHES".
      I HAVE TWO ONE HUNDRED LBS.RODESIAN
      RIDGEBACK DOGS IN MY BACKYARD AND IT VERY UNLIKELY THAT ANYONE WENT INTO MY YARD AND TAMPERED WITH THE GAUGE.
      NO ONE KNEW ABOUT IT OTHER THAN MY WIFE.
      YES 5.69 INCHES OF RAIN FELL AT MY LOCATION WHICH CAUSED LINE CREEK AND
      BEAR CREEK TO OVERFLOW THEIR BANKS.
      I UNDERSTAND WHY SOMEONE WOULD QUESTION THIS PHENOMENON{1. a fact, occurrence, or circumstance observed or observable: to study the phenomena of nature.
      2. something that is impressive or extraordinary.
      3. a remarkable or exceptional person; prodigy; wonder.
      4. Philosophy. a. an appearance or immediate object of awareness in experience.
      b. Kantianism. a thing as it appears to and is constructed by the mind, as distinguished from a noumenon, or thing-in-itself.}
      THANK YOU FOR YOUR INTEREST,
      HENRY

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