|Skew-T Plot of the temperature, dew point, and winds in the upper atmosphere on Nov 17,2001 at Yarmouth, N.S. (Yarmouth is the closest site providing upper atmosphere data). This is only the bottom section of the plot showing the stable inversion layer and has been annotated to explain the data presented.|
Only two gliders flew this day because it appeared that there was little of interest going on aloft except wind. There were no clouds at the time. It was felt that it was too much effort to rig the Ka7 (two seater) which was needed to check out two pilots who were not current. One other pilot could have flown but he was the only other winch driver. This whole day was a lesson in not being prepared. I flew because Dick was going to fly C-GUIL and I wanted to fly C-FVKA one more time this soaring season even if it were only a circuit flight. Normally, I put in my GPS and flight recorder and make a record of every flight but this day I had left them at home which I would regret along with other things.Wave Discovery
I was the first to be launched from runway 28 at 1:05 pm AST. My release height was 1400 ft which gave me time find a thermal to the west over a plowed field. Its strength was reassuringly strong if uneven while its size was small characteristic of most this time of the year. I did my tight turns and eventually centred it enough to climb slowly to about 3000 ft as I drifted southeast of the airfield. I eventually lost the lift in my thermal but UIL was now aloft and was circling in a thermal closer to the field. I flew overtop and joined that thermal. As I climbed, the thermal became suddenly turbulent with strong lift on one half the turn and as I gained height, I notice a wispy cloud forming below me slightly downwind. I flew back over the cloud and found no lift and was soon in sink. So I flew up wind and re-encountered the turbulent sink andlift. I turned in the lift then flew upwind with the idea that perhaps this was rotor and there may be wave lift. I flew into smooth lift. I couldn't believe it so I went downwind to find the turbulence then upwind to fly back into smooth lift. The rate of climb at this time was around 500 ft/min. I was elated and radioed Dick to tell him that there was definitely wave present.
I tacked back and forth perpendicular to the wind and climbed to 5000-6000 ft. Downwind and lower more wispy clouds were forming and in a short while I found myself difting past them into sink. This was definitely wave. Again I flew upwind to find the sweet spot of the wave lift and stayed there until I reached 9000 ft. By this time Dick had found the wave over Rt 101 which is upwind of the airport and my position. While climbing I noted that the only semi-permanent clouds in the sky were to the north over the North Mountain and it was time to explore.Exploring the Wave
Those clouds looked like they were associated with wave since they stretched along the mountain perpendicular to the wind direction. I had good height and the wave was still strong at my position downwind of the airport so I felt confident of heading upwind toward the cloud. I knew I would fly through heavy sink in the headwind but it would be easy to quickly return to the wave lift I had would be leaving.
As is usually the case, it took longer than expected to reach the next upwind wave lift but I did not reach it until I was well over the North Mountain. Usually the primary lift in wave is just downwind of the ridge generating it and at that time I thought the North Mountain was that ridge. I kept flying upwind and was rewarded with 500-600 ft/minute lift about 3 km from the Fundy coast but still behind and above the clouds. Dick had climbed quickly in the wave he had and had flown upwind also. I resumed my practice of tacking perpendicular to the wind to gain height but found that I drifted back if I flew only at 40 kts (a Ka6e's minimum sink speed). We judged that the windspeed was at least 45 kts at 10,000 ft. We continued to climb but I cut off my climb at 11,900 ft because I reach zero lift did not have the patience to find the sweet spot again and wanted to explore the wave eastward. (We could only go to 12,500 ft anyway because of airspace restrictions). While holding in the wave, we had flown west as far as Swindles Knob, a landmark at the edge of the Greenwood control zone. Dick did continued to climb and stopped at the bottom of the airspace with still 200 ft/min of lift.
Out over the Bay of Fundy, upwind of the clouds over the coast were a couple of wispy clouds that had the appearance of rotor cloud. Was there wave over the water? I now wish I had had the time and persistence to fly out there and sample the air. It leaves the question as to what was the real source of these wave oscillations in the atmosphere in which we were flying.
At 12,000 ft. the view of Nova Scotia is fantastic because the horizon is 200 km away. The North Mountain appeared as a low broadened ridge stretching off to the west and ending near St. Mary's Bay glistening in the sunlight 90 km away. Halifax Harbour and St. Margaret's Bay were plainly visible to the southwest. One could even see over the Tantramar marshes near Amherst to Prince Edward Island (pretty well on the horizon). I could easily see the Bluenose Soaring club's home airfield nestled in the woods at Stanley. It would have been easy to head downwind to land there.Physiological Effects of Cold Shortens the Flight:
The temperature at 12,000 ft this day was -6 C (I have an external reading thermometer on my glider - an inexpensive indoor-outdoor type). The climb up had been colder than that due to the inversion and I had measured -12 C at 4000 ft. I had not planned for a long flight and did not put on clothing for high altitude flying althougth I had dressed for the +2 C at the surface. I also had not put my relief system in the glider since I expected only a short flight. This was a disaster. When the body gets cold, ones blood vessels contract to keep from losing heat with too much blood flow. The fluid needed in the body is less, is removed by the kidneys and put in the bladder. My bladder had been full for the last hour.
Despite my discomfort, I continued to explore. If the wave was associated with the North Mountain there should lift all along the mountain. I headed eastly trying to stay over the mountain but drifted out into the Valley over the town of Canning. There was no strong sink and I lost only 1500 ft in flying 30 km. I flew north against the wind and did find lift in the wave again. At these heights Cape Split and Parrsboro to the north seemed very close. I contemplated gaining more height and flying out over the Split but gave up the idea since it was up wind and I was not physically comfortable.
Dick was afflicted by the same physiological problems and considering the hour we decided it best to head back to the airport.More exploration:
I headed directly to the Waterville Airport over the Valley then further downwind in order to come at the airport from the south. Over the Valley, I encountered two more lift areas in the wave (These are marked on the map as areas D and E ) and three sink lift areas . The 3rd sink area was over southern upland. The time was about 4 - 4:30 pm and the lift was still 500-600 ft/min. In the down part of the wave the sink was even more extreme at up to 1000 ft/min which makes a great down-elevator. The downwind lift areas were fairly narrow but that is probably because one's ground speed is increased dramatically when going in that directions. (flying at 50 kts with a 40 knot tailwind produces a 90 knot ground speed). The upwind lift was encountered going against the wind which makes it seem wide (flying 50 kts with a 40 kt head wind gives a 10 kt ground speed). On the map the three lift regions are approximately equidistant apart (~7.3 kilometres).
On the flight back to the airport from Canning, I encountered a group of medium sized birds (gulls?) at about 8000 ftg oing in the opposite direction. This was definitely in wave lift area (secondary). It is interesting to observe that the birds use this lift to move about (migration?).Reflection:
The day's flight was one of the most exciting of the soaring year for me. From the ground, I had seen wave-type clouds over the Valley many times and had always wanted to prove that this type of lift existed here. I had no idea that the wave would be so high and wide spread. This was not my first wave flight and I had been up to 18,000 ft in wave at Sugarbush, VT almost exactly a month earlier. My excitement was due to (1) the fact that this existed in my own backyard and (2) the delight of thermalling to the bottom of the wave and transitioning relatively gently into wave lift.
Now that I am sure wave occurs here, I want to be able to fly in it again. This requires that I recognize what the special conditions were to produce the high wave. Tom Bradbury in his book " Meteorology and Flight" identifies four conditions for formation of wave down wind of a ridge.These Conditions are:
Did the meteorological situation on November 17 have these conditions? The diagram at the bottom of the page summarizes the wave situation as determined by data from the flight and the skew-T plot from the balloon sampling of the atmosphere at Yarmouth.On November 17, we had:
It appears that the conditions were ideal for wave conditions on November 17. One important question has not been answered by this flight "By what ridge were they generated?" We saw what may have been rotor clouds up wind of the north mountain and over the Bay of Fundy. We did investigation those clouds but the next time it happens, I shall try. My present thinking is that the wave was generated from the hills on the shore of the Bay of Fundy in New Brunswick. (See discussion below)
The diagram below shows the scale of the Annapolis Valley wave. The heights and distances are on the same scale. The wave amplitude was calulated from the wavelength, wind speeds, and lift. The temperatures and wind speeds are from those measured with the electronic thermometer and altimeter in the sailplane which in general agree with the skew-T plot above.
Atmospheric waves such as the ones we flew in need to be touched off by a topographic feature. The larger the feature, the more likely that wave will develop. The map below shows the relative positions and sizes of significant ridges that might initiate wave over the Valley.
The best candidates are the Fundy Uplands just west of Fundy National Park. This wide upland stays high right to the Bay of Fundy shore then drops 700-800 feet to the water's edge. The cliffs of the uplands are 65 km upwind of the Kings County airport. This is almost exactly 9 wavelengths of the wave on Nov 17. The uplands are fairly long and might create a wave 50-60 km wide. The other candidate is the Chignecto Peninsula of Nova Scotia. This point of land is 700 ft high and protrudes into the Bay of Fundy.The downwind side (NW wind) drops steeply into the Advocate Bay. This structure is 37.5 km north-west of the airport which is equivalent to 5 wavelengths of the atmospheric wave. This structure is only 5 km long and would not produce a very wide wave.
Created Nov 29, 2001