The condition that inspired this discussion isn't meant to pertain to the entire face of a peak, but rather a very small area in the lee of an obstruction to laminar flow. Described by the climbers as an area of total calm, whilst 100mph winds rip by at the edges of the rock.
Interesting thread, and you have got me wondering again.
Although everyone here is talking about rather simplified models and analogies to aerodynamically designed surfaces, shouldn't this be talked about from the viewpoint of blunt body aerodynamics? e.g. I wonder if anyone could pose this question to someone more familiar with empirical results from wind tunnel testing on buildings, such as the work done at RWDI?
A few factors to consider, which might be insightful as to the nature of the pressure zone we were in:
1. It was completely calm where we were. There wasn't even any noticeable suction.
2. The area of stillness was large. It was not confined to the leeward side of the sub-summit, but extended across the entire summit plateau from Misery Hill to the higher summit and all the way up the higher summit, so the area of reduced pressure was very large, easily covering the size of several football fields (at least until the wind shifted direction at an unknown hour and blew between the two sub-summits. At that point the high winds were encountered lower down and the calm zones were more transverse to the direction the wind was blowing). Since even the area near Misery Hill was calm, we were likely being shielded by the sub-summit above the West Face/Casaval Ridge, which was quite a ways away.
3. The boundary between the still and fast moving air was extreme. I have been in sustained +60 mph winds on mountains where it was difficult to walk, and even when huddling behind bus-sized boulders, the turbulence swirling around was so bad that it was only mildly calmer on the leeward side. On the summit where the high winds were still skimming across the ground, conditions went from completely calm to barely being able to crawl just by stepping out from behind a rocky obstruction.
The critical issue that led to Tom's death was how quickly his HACE developed and the lack of symptoms warning us of him experiencing any altitude related problems. We could and would have taken a higher risk from exposure hazards and descended sooner had Tom developed noticeable AMS, as we had only agreed to stick around if neither of us felt sick from the altitude. Although I could only tell so much from urine output on ascent (frequent & clear), Tom's physical performance on ascent (strong & steady), and Tom's self-reporting from a passive state on the sub-summit, he exhibited no signs of AMS, which is highly unusual to not have before HACE. His first awareness of any symptoms did not occur until he stood up to descend. He didn't even feel nauseous and had a good appetite for breakfast.
So I wonder if the pressure differential had something to do with this possible skipping over AMS, perhaps by causing other mechanisms of HACE to take hold before the usual ones of AMS became evident? If pressure differentials from blunt body aerodynamics could have a noticeable effect, I would wonder whether the morning arrangement of pressures would have had a greater or lesser effect than the evening arrangement, as the wind did change by 90 degrees when we were on the summit, resulting in a very different morning wind pattern, with us essentially in a calm zone transverse to and within a trough with a large venturi effect occuring (wind speeds increased as I descended the sub-summit and approached the lowpoint between the two summits).