It's Been Sounding Like Last Summer In Anchorage

I noticed we had planes flying over our house again last week.  Lots of them.  Last summer was the

From my backyard today

second summer of widening the North-South runway at the Anchorage Airport.  Thus all the planes took off to the east - over probably half the population of Anchorage.  But that was supposed to leave us with quiet summers.

Yesterday I talked to Terri Tibbe, Operations Airport Operations Manager.  There are two basic reasons for the noise:

• Seasonal Maintenance 
• Every year there is some maintenance of the runways - repainting, striping.  And that was happening yesterday.
• Winds Aloft
• She described these as winds above ground level but low enough to affect planes taking off.  The pattern recently has dictated planes taking off to the east.  

In addition, she pointed out that 6-8 weeks ago there has been an increase in cargo flights and they are bigger and heavier than passenger planes and make more noise as they take off.

The airport controls the maintenance, but FAA makes decisions about wind affecting take-off direction.

I did google 'winds aloft' because I didn't quite catch what Terri said.   So, for instance, I found this map of winds aloft 200 MB for Alaska for June 17.

But what does this mean?  There were several other charts available at different MB levels.

"'bar' is the unit by which we measure pressure."

The lower the millibars the lower the pressure and the higher the altitude.  So the 200 MB is at a much higher altitude than the 850 MB chart, which is the lowest they show.    Here's the same location, same time, but for the 850 MB

"Constant Pressure Charts: 850 mb
This pressure level is near an elevation of 5,000 feet though it ranges from 3,800 feet (1,170 meters) to 5,200 feet (1,590 meters). As with all other constant pressure charts the heights are in meters with the last digit (zero) truncated. So, a height value of 132 represents 1,320 meters."

So the wind directions and speeds vary significantly at different altitudes.


And here's a bit more to help understand symbols on the maps above.

Wind Speed

When the height contours (lines) are close to each other, it means there is a more rapid change in altitude of the constant pressure level, and indication of a large temperature gradient.

As the temperature gradient increases (more rapid change) so does the pressure gradient. Wind is created when there is a pressure gradient, and the stronger the gradient the stronger the wind.

Wind speeds on weather maps are in knots (kt) where one knot equals 1.15 mph and 1.85 km/h. Toggle the "Wind Barbs" check box to display the speed and direction of the wind across the map.

The wind barbs indicate wind direction and wind speed (rounded to the nearest 5 knots). The longest line (shaft) points in the direction FROM which that wind is blowing.

The shorter lines, called barbs, indicate the wind speed in knots (kt). The speed of the wind is determined by the barbs.

Each long barb represents 10 kt with short barbs representing 5 kt. A pennant is used to represent each 50 kt. Total the barbs and pennants to provide the wind speed at that location.

When lines of equal wind speed are drawn (called isotachs) the regions of greater and less wind speed stand out. Isotachs are typically drawn for every 20 kt.

I've gotten myself further into this than I ever intended, but not far enough to understand clearly why the planes are taking off over midtown and whether the wind patterns are going to change soon.  And I know enough to realize that a little knowledge can be a dangerous things.  But it is also the first steps to more knowledge.  But if you go to this page at the Weather Service you can start exploring.  They even have some cool lessons.