The up and down sides of rotors relative to ridges

Mulling over a wave flight from last October and realized that I'd gotten it into my head (perhaps erroneously) that the up (lift) side of rotor is usually closer to the upwind ridge than the down side (sink) of the rotor. So for example, if I persist in heading closer towards the slope/ridge while in the downside of rotor, that I have a good chance of hitting the up side (lift) of the rotor. In other words, the sink side of the rotor is farther away from the upwind ridge than the lift side.

Now I realize that this situation is chaotic, anything can happen, and that before AGL gets tight, I'd better turn away from the slope and use the tailwind to hastily penetrate the sink that I just flew through and try for the secondary rotor, downwind ridge lift, or land.

But what about my assumption that the lift side of the rotor is generally found between the sink side of the rotor and the upwind ridge? Or does this depend on the particular ridge and the particular day?

And what about a downwind ridge? I've got it into my head that the sink side of the rotor is between the lift side of the rotor and the downwind ridge. There may be a band of ridge lift between the sink side of the rotor and the downwind ridge. Are rules of thumb possible/useful or is this just my limited experience on my local ridges?

Let's play a game of imagination and visualization.

Start with the upwind ridge on the left side of a piece of paper.
Looking into the paper is like looking to the north. The ridge is on
the west side of the paper and the wind is blowing from left to right.
As the air flows over the ridge top it sinks and then rebounds upward as
the rising air of the primary wave. Visualize it as a sinusoid. The
rotor is under this wave. The left side of the rotor (west) is
generally up while the right side of the rotor (east) is generally
down. If you have the altitude AGL you can generally climb on the
upwind side of the rotor and will get into the smooth laminar lift.
Another ridge downwind can either boost or kill the wave further
downwind. It depends upon wavelength and wind speed.

Personally, I would not penetrate upwind towards the leeward side of a
ridge in high winds hoping to get into the up side of a rotor.

YMMV

On 4/7/2016 6:26 PM, son_of_flubber wrote:
Mulling over a wave flight from last October and realized that I'd gotten it into my head (perhaps erroneously) that the up (lift) side of rotor is usually closer to the upwind ridge than the down side (sink) of the rotor. So for example, if I persist in heading closer towards the slope/ridge while in the downside of rotor, that I have a good chance of hitting the up side (lift) of the rotor. In other words, the sink side of the rotor is farther away from the upwind ridge than the lift side.

Now I realize that this situation is chaotic, anything can happen, and that before AGL gets tight, I'd better turn away from the slope and use the tailwind to hastily penetrate the sink that I just flew through and try for the secondary rotor, downwind ridge lift, or land.

But what about my assumption that the lift side of the rotor is generally found between the sink side of the rotor and the upwind ridge? Or does this depend on the particular ridge and the particular day?

And what about a downwind ridge? I've got it into my head that the sink side of the rotor is between the lift side of the rotor and the downwind ridge. There may be a band of ridge lift between the sink side of the rotor and the downwind ridge. Are rules of thumb possible/useful or is this just my limited experience on my local ridges?


--
Dan, 5J

On 4/7/2016 6:26 PM, son_of_flubber wrote:
Mulling over a wave flight from last October and realized that I'd gotten
it into my head (perhaps erroneously) that the up (lift) side of rotor is
usually closer to the upwind ridge than the down side (sink) of the rotor.
So for example, if I persist in heading closer towards the slope/ridge
while in the downside of rotor, that I have a good chance of hitting the up
side (lift) of the rotor. In other words, the sink side of the rotor is
farther away from the upwind ridge than the lift side.

That's certainly true along the Front Range of the Rockies in the Boulder, CO,
area.

Atmospheric waves can only exist downwind of the obstruction generating
them...though (IMO) their relationship to geography beneath and downwind of
the generating obstruction doesn't lend itself to accurate, simple,
declarative statements. Atmospheric dynamics along "the Boulder part" of the
Front Range are such that only once did I ever attempt (unsuccessfully; my
wallet gave out) or even need to tow directly into a wave; every other time
has come via thermalling, sometimes in what seemed to be "aligned thermic lift
bands" paralleling the suspected/sometimes-visible wave, other times using
what was unarguably rotor.

Snip...
But what about my assumption that the lift side of the rotor is generally
found between the sink side of the rotor and the upwind ridge? Or does
this depend on the particular ridge and the particular day?

I'll be surprised (shocked?) if anyone can point to a rotor that ever lies
UPwind of the wave-generating geographic feature, if that's what you're
wondering about, though that's not to say "your wave" is the first along the
wind's streamlines. If there's genyoowine rotor upwind of "your wave
generating feature" it's coming from another, upstream, feature. FWIW, in the
absence of an upstream wave, don't assume the lower level winds on the upwind
side of the wave-generating feature will be "ridge-lift smooth"...reality
always rules!


And what about a downwind ridge? I've got it into my head that the sink
side of the rotor is between the lift side of the rotor and the downwind
ridge. There may be a band of ridge lift between the sink side of the rotor
and the downwind ridge. Are rules of thumb possible/useful or is this just
my limited experience on my local ridges?


I'm all ears on this question!

Bob W.

Hoping to clarify, my upwind Ridge A generates the primary. My downwind ridge Ridge B is downwind of Ridge A (and lower in altitude). Secondary wave lift and rotor forms upwind of Ridge B. Oftentimes, ridge lift between the rotor and the ridge.

On Thursday, April 7, 2016 at 8:56:48 PM UTC-4, BobW wrote:
On 4/7/2016 6:26 PM, son_of_flubber wrote:
....
But what about my assumption that the lift side of the rotor is generally
found between the sink side of the rotor and the upwind ridge? Or does
this depend on the particular ridge and the particular day?

I'll be surprised (shocked?) if anyone can point to a rotor that ever lies
UPwind of the wave-generating geographic feature, if that's what you're
wondering about,...

No. I'm only talking about rotor that is formed downwind of the wave-generating topographic feature (aka Ridge A).

My thinking is that for a wind blowing towards the east, the top of the rotor is also blowing east and the bottom of the rotor is blowing west, so the lift side of the rotor is to the west of the sink side. This is idealized because if the feature causing the wave is convoluted and irregular, all sorts of chaotic interactions can result in unpredictable patterns.

S of F, as for other locations I can't comment but for the sierra generated orimary wave, yes your assumptions hold true. As a starving college student who wanted to fly wave as much as possible, I could not affort high tows into the wave so on numerous occasions I would "thermal" the "upwind" rising side of rotor to work my wave into wave. After succeeding a few times I got pretty good at working rotor into wave in the minden nv system.

It always made for an incredably rough ride. The rising portion of the rotor was very small and there were many times what I gained in the few moments of lift, was cancelled out by associated sink. I can remember one time working for more than an hour barely gaining on each gust untill I finaly worked high enough to contact laminar flow. But a poor boy will always find a way. I hope this helps.
Dan

On 4/7/2016 7:54 PM, son_of_flubber wrote:
On Thursday, April 7, 2016 at 8:56:48 PM UTC-4, BobW wrote:
On 4/7/2016 6:26 PM, son_of_flubber wrote:
...
But what about my assumption that the lift side of the rotor is
generally found between the sink side of the rotor and the upwind
ridge? Or does this depend on the particular ridge and the particular
day?

I'll be surprised (shocked?) if anyone can point to a rotor that ever
lies UPwind of the wave-generating geographic feature, if that's what
you're wondering about,...

No. I'm only talking about rotor that is formed downwind of the
wave-generating topographic feature (aka Ridge A).

My thinking is that for a wind blowing towards the east, the top of the
rotor is also blowing east and the bottom of the rotor is blowing west, so
the lift side of the rotor is to the west of the sink side. This is
idealized because if the feature causing the wave is convoluted and
irregular, all sorts of chaotic interactions can result in unpredictable
patterns.


I may still not be fully understanding what you're puzzling over, but...yes,
rotors revolve with their "top" moving in the same direction of the overall
prevailing stream flow, their "bottom" moving against the large-scale stream
flow, their "back edge" (relative to the prevailing stream flow) moving down
toward the ground, and their "front edge" (relative to the prevailing stream
flow) moving up. Rotor "organization" in my experience is useful more as a
mental concept than as PIC-reality, though - situation/geography permitting -
if you believe yourself in rotor and averaging the wrong direction (i.e.
toward the ground below), moving upwind, against the overall stream flow is
often a useful tactic in striving to change "averagely down" to "averagely
up." In the Boulder, CO, region, some days that was a practical proposition,
others "surely you jest!"

Bob W.

At 00:56 08 April 2016, BobW wrote:
If there's genyoowine rotor upwind of "your wave
generating feature" it's coming from another, upstream, feature.

If you sail close in to a headland in tidal waters you could well find
eddies in front of the headland. Sort of 'under' the general flow.

Flying a ridge over a quarry filled with water in high winds I have seen
'cats paws' banging on the water. This is surely a rotor effect upwind of
the ridge just like the eddies seen above. I would not, however want to try
to soar on them!

Jim

The downwind ridge can generate a wave of its own. What I tried to say
earlier is that this second wave (not to be confused with a secondary
peak off of the first wave) can either reinforce or cancel the upwind
wave with the result being either much stronger downwind of the second
ridge or little to nothing at all. There have been books written on
this. A good example is Mark Palmer's "Practical Wave Flying".

On 4/7/2016 7:39 PM, son_of_flubber wrote:
Hoping to clarify, my upwind Ridge A generates the primary. My downwind ridge Ridge B is downwind of Ridge A (and lower in altitude). Secondary wave lift and rotor forms upwind of Ridge B. Oftentimes, ridge lift between the rotor and the ridge.

--
Dan, 5J

My thinking is that for a wind blowing towards the east, the top of the
rotor is also blowing east and the bottom of the rotor is blowing west,
so the lift side of the rotor is to the west of the sink side. This is
idealized because if the feature causing the wave is convoluted and
irregular, all sorts of chaotic interactions can result in unpredictable
patterns.
That's right, and I don't think it can be predicted, hence my original
position that I would not penetrate upwind looking for the up side of
the rotor unless I had plenty of altitude AGL and a place to bail out
(figuratively). I have personally worked rotor up into wave an several
occasions, but I've always had at least 5K' AGL when I did it. This is
the nature of western flying.
--
Dan, 5J