South Pole sounding

[Tim Vasquez]

I suppose one thing every enterprising forecaster should see at least once is a sounding from the South Pole. Here is the sounding from last night.

Some tidbits for beginners:

* The elevation of the station is 9300 ft MSL. That's why the sounding doesn't extend to the bottom of the diagram. It's amazing to think how much snow it took to create those two miles of ice.

* Note the radiational inversion from 670 to 640 mb. That's a depth of about 900 ft. It's a layer of cold air close to the ground where radiational cooling is strongest.

* The surface temperature (-54C or -65F) has the potential to be much colder, but the surface winds, when they blow, tend to mix up the air with warmer air just above the surface. However the layer of air near the surface (the boundary layer) still remains strongly decoupled from the free atmosphere.

* The tropopause is not very sharp here but is being reported as 240 mb, or 22,000 ft. That's only 13,000 ft above the ground.

* How does it compare with model data? (see next image) The 500 mb GFS analysis suggests winds blowing from the north-northwest. This agrees fairly well with the sounding. Note that at the poles, directions are always referenced to the prime meridian.

* The low-level winds at the South Pole blow from the north or northeast whenever cold air from the vast interior is draining into the Ross Ice Shelf area (one of the two large "gulfs" in Antarctica) near McMurdo Bay. This is the most common kind of pattern and is what is occurring here.

Tim

 

[Greg Stumpf]

* The low-level winds at the South Pole blow from the north or northeast whenever cold air from the vast interior is draining into the Ross Ice Shelf area (one of the two large "gulfs" in Antarctica) near McMurdo Bay. This is the most common kind of pattern and is what is occurring here.

Don't the winds at the South Pole always only blow from the north?

 

[Robert Dewey]

Don't the winds at the South Pole always only blow from the north?

Interesting... I wonder how they normalize that for the purpose of wind barbs and vectors.

 

[Skip Talbot]

Note that at the poles, directions are always referenced to the prime meridian.

One paragraph above...

 

[Robert Dewey]

One paragraph above...

Gotcha... I moved on when it said "see next image" LOL

 

[Tim Vasquez]

I can't remember the specifics but back around 1965-1970 they flew a Boeing 707 to the North Pole which was equipped with new inertial navigation system (INS) technology. It was partly a proving flight to make sure the INS system behaved properly, as of course trig gets weird (tangent approaches infinity, etc) when you get close to 90 degrees. A northbound heading from lat=90 could be programmed into the INS but supposedly they had to figure out what would really happen.

Tim

 

[cdcollura]

Good day all,

Direction wise, right at the south pole (if you are standing EXACTLY at 90 S 0' 0'') ... Any direction is "northward". But take a look at the weather graphic...

You see the south pole and wind flow pretty much ACROSS it. Relative to the S pole (looking down), a wind blowing across ot can only be from (or to) the north. But it's all relative to that "magical" 90 degrees S "point".

Technically, there really is no true direction (lat / lon) right AT the south / or north poles. Each direction, depending on which MERIDIAN you are pointing at, is to the north (from S pole) along that meridian.

So the "easterly wind" is simply by looking down at the map, and assuming "north" is up intuitively. ofcourse, north is radially outward from the center along the meridians that also radiate outward from there ... Assuming the true S "pole" is in the center of the map.

Basically, if you are facing the direction of Europe, along the 0 degrees E or W meridian (longitude), the international date line (180 degrees E / W) starts from your back and runs through the central / west Pacific! Your arms would be 90 and 270 degrees (running through the Americas and central Asia, respectively) ... But all directions along these lines is generally northward.

Interesting sounding by the way! It almost appears that the "troposphere" is not even existant. If it wasn't for that little inversion, its almost like the stratosphere extends nearly to the ground (temp always increases with height starting at -60 near the surface).

One little correction. I see 240 MB mentioned as 22,000 feet MSL. I think 240 MB is more like 32,000 feet (250 MB is 30,000)? Still, having the stratosphere 23,000 feet AGL is pretty interesting. Almost no mixing / thermal dynamics whatsoever in the lower troposphere (whatever troposphere there is).

Got a chuckle seeing all the convective parameters (CAPE especially) pegged at -9999.