Trapped and Vertically Propagating Wave

There are two divisions of mountain wave:  Trapped and vertically propagating.  Trapped wave assume the form of a series of waves running parallel to the ridge and can extend many miles downwind of the ridge.  They occur when the wind increases {and stability deceases} with altitude (figure 7.9).  The increasing wind traps the wave against the earth's surface.

With vertically propagating waves (figure 7.7) the energy is directed upwards instead downstream.  They occur when the wind speed is constant (does not increase) with altitude and the wavelength is shorter than the base of the mountain.   Wavelength is proportional to wind speed so, expect vertically propagated waves with low or moderate wind speeds (higher stability also gives shorter wavelengths). 

Trapped Wave

I had a couple interesting wave flights this season.  The first was on May 5th in a trapped wave.  I was able to climb to 15,000' right over Post Mills Airport and then travel up wind 4 wavelengths to the Sugarbush airport.  At Sugarbush I climbed to 18,000'.  From there I was able to cross the spine of the Green Mountains and climb back up to 18,000' over the flat Champlain Valley.  Pushing ahead 2 more wave crests put me over the middle of Lake Champlain.  From there I could see small cumulus clouds making wave crests all the way to Lake Placid.   The day had the ideal amount of clouds.  They marked the wave but did not interfere with navigation.  This was a trapped mountain wave.  The wave generated by Sugarbush (and Mt. Marcy near Lake Placid) was tapped close to the earths surface as it traveled downwind many cycles to Post Mills.  The characteristic wind profile for trapped wave is high winds and winds increasing with attitude.

May 5th Flight - Colored lines show the peak of each climb.

October 5th  Radiosonde data from Albany at 8:00 AM - Note the increasing winds from 5,000' to 30,000'.

Vertically Propagating Wave

The second interesting flight occurred on October 9 during the Mt. Washington Wave Camp in a vertically propagating wave.  The vertical wave allowed a climb to over 32,000'.   The wind profile showed relatively lighter winds (about 25 kts at 6,000') and the wind speed did not significantly increase from 5,000' to 50,000' (always below 50 kts).   Without the increasing wind (with altitude) forcing the wave along the surface it is free to oscillate up into the upper atmosphere.  The wave length was very short with the primary lift over the Auto Road parking lot.

October 9th Flight - Yellow line shows the peak of the climb over the Mt. Washington Auto Road parking lot.

October 9th  Radiosonde data from Albany at 8:00 AM - Note the light consistent winds from 5,000' to 50,000'.

The only other time I have experienced a vertically propagating wave was on October 10, 2011.  This was probably the best day in modern wave camp history.  There were many spectacular flights.  Rick Roelke had a triple diamond flight (the 3 legs of a diamond badge in one flight).  Evan went to 26,000' and then flew 440 km in 8 hours.  Jim David went over 29,000' (he flew all the way down to Mt. Ascutney but didn't find wave along the way because it was vertical wave day).   I think there were 5 new Lennies that day.  Below is my flight in PM on that day.  It shows the pattern of lift found in the lee of Mt. Washington that can be seen in all the flights from that day.  The red arrow shows the location of the top of climb in the primary.  It is right over the Auto Road parking lot (very short wavelength).  The primary only went to about 13,000'.  To go higher you had to drop back to the secondary over the top of Wildcat (green arrow).  In a vertically propagating wave the secondary can go much higher than the primary (see figure 7.7).  The wind profile from that day was very similar to October 9 of this year.

October 10, 2011 - Red arrows are the top of the primary wave.  Green arrows show the top of the secondary wave.

October 10, 2011 - Radiosonde data from Albany at 8:00 AM - Note the light, relatively consistent winds from 5,000' to 50,000'.

In conclusion we need a trapped wave to fly out of Post Mills. We are many wavelengths downwind of the Green Mountains.  We want high winds and we want the wind to increase with altitude.  The best days at Mt. Washington (long XC and high altitudes) are going to be those with rare vertically propagating wave.  We want lighter winds and we don't want the winds to increase with altitude.  The best lift may be in the secondary.

References:

Figure 7.7 and 7.9 are from Dieter Etling:  Atmospheric Gravity Waves and Soaring Flight - Physical principles and practical applications  available for free at: https://www.schwerewelle.de/

Last flight out

Tim took these pictures on his way into and out of Gorham, to retrieve the PW-6 yesterday.

Altitude Record

It isn't official yet, but it seems that Tim Chow has broken the 49-year-old New Hampshire altitude record!

On October 9, Tim (BU) took off from Gorham and released over Mount Hayes at 2200 feet AGL.  He found some weak lift that took him up to Berlin where he got to 8000 feet MSL.  From there he transitioned to the Mount Washington primary (in the vicinity of the Wildcat ski area) and started climbing at about 8 knots on the averager.  He moved forward as he got higher and eventually topped out at 33031 feet MSL, which exceeds the old record by a little more than 1000 feet.  His high point was remarkably far upwind, about halfway between Route 16 and the summit of Mount Washington.

Tim's low release allowed him to claim the altitude gain record of 30046 feet.  The previous record (26271 feet) has been held by Evan since 2015.

Paradoxically, it was a warm day.  The sounding shows a very deep stable layer and ideal winds.

Congratulations, Tim!

Name that club member

Transition to Wave at PM

Here is the log of my flight last Saturday where I transitioned to wave a few miles north of PM airport.  I transitioned from thermals to wave at about 6,000' (cloud base) and then climbed in wave to about 9,000'.

The wind was out of the west (left) and I was flying directly downwind.  I was able to climb a little in 2 broken thermals (thermals are typically broken up by the rotor).  The third thermal was particularly strong (8 kts) and took me to cloud base.  I then pushed forward and continued to climb while I "ridge soared" the front of the clouds.  As is often the case the clouds drifted downwind.  Often more clouds will form up wind and you should push forward to get up wind of the new clouds.  In this case it looks like a jump downwind to another wave peak.

I was able to go to Franconia in wave without losing much altitude but I fell out of the wave (I thought for sure I would find better wave there) and had to thermal back to PM.

Here is the entire flight log:

Here is the Skew-t for the day:

The satellite image shows cloud streets (parallel to the wind) and not the usually wave bands (perpendicular to the wind):

Another first

Here's a picture of Chris taking off without the loquacious guy in the back seat:

Congratulations, Chris, on your first solo in a winged aircraft!

#505

Dog Days

It was so hot today that we didn't mind the impromptu shower occasioned by David's first solo.  Congratulations David!!

Briefing Room

Who's the confused-looking guy in the lower right corner?

Release

Which aircraft has the greater bank angle?

Summertime, and the living is easy

Happy Solstice!

Today is the longest day of the year, but it isn't the day with the latest sunset.  That day will be Wednesday, June 27.  The sunset will occur on that day at 8:36pm, almost two minutes later than today.  Tonight will last only 8 hours and 32 minutes.

And Happy Birthday to the Solstice Babies: Lane, Andy, Tony, and Sherry!

Mt. Washington Wave Flight

Dan (EA) and I (BU) had surprisingly good wave flights last Saturday.  The forecast was for strong northwest winds but the boundary layer (top of thermals) was forecasted to go up to about 7,500 ft.  The top of the boundary layer is the dividing line between unstable and stable air.   For wave you normally want stable air at the top of the mountains so we were not sure if we would find any.

Thermaling and ridge soaring to get to Mt. Washington was fairly straight forward.  Then Dan dropped back to the Carters and found wave over the Wildcat parking lot so I followed.  We enjoyed nice strong lift sometimes over 6 kts up to Class A airspace (18,000').

Dan at 17,742' still climbing at 2.7 kts

You would think from 18,000' the trip home would be a piece-of-cake but with the strong headwind and abundant sink Dan just squeaked it into PM.  I stopped to pick up extra altitude at the Mt. Lafayette wave.