Fogageddon

PKatt sez: “Go to SF in the summer sometime its basically the same thing.” –My fist thought, exactly. The fog rolling over the first line of hills along that stretch of shore. This phenomenon is not suprising to locals of Bay area.

Somewhat related
http://nl.airliners.net/aviation-photos/photos/1/9/3/1229391.jpg

If there ever was a picture of the folly in charge in this kind of build-your-house-on-sand, this would be it. Weather can lull u into fuzzy fog feelings then flatten u like a bug on a windshield.

Clearly you are wrong because you forgot to factor in the radiative forcing of all that extra CO2 and in realith the mist is a result of the ocean boiling as the waves break.

Well there is more to it than that.
Don’t forget Bernoulli’s principle. The air in going around up, over, under an obstruction must speed up to maintain the flow, and so the pressure must drop in going through the venturi, so the air density lowers, and the dew point rises (in Temperature) so condensation occurs.
I see it quite often around automobiles driving along a roadway after a rainstorm in high humidity conditions. You think it is just water spray being kicked up by the tires off the wet road, yet you see it when there is virtually no water left on the road, and the fog forms ahead of the tires anyway.

I’m afraid this isn’t an orographic effect at all. You can see the fog along the shore where there are no high buildings to lift the air.
It will be warm saturated air from the ocean condensing as it travels over the cooler land, with perhaps a salt particle aerosol condensation effect.

this phenomenon is caused by changes in pressure, not temperature. and, as counterintuitive as it sound, the areas with the fog have a HIGHER static pressure than the other areas. the buildings cause a stagnation of the flow of the high humidity air flow oof of the water, raising the static pressure and creating the condensation
as eyesonu points out, a similar effect is seen on near super-sonic jets in high humidity as the expansion shock wave raises the static pressure (note that in this case the stagnation pressure actually goes down but thats another story)

@ur momisugly JPS February 12, 2012 at 6:53 pm
Thanks for the reply.
I want to understand every aspect of this phenomenon with regards to the ‘frisbee’ effect.
My theory was that a shock wave was continiously generated that was radiating outwards and the leading edge was traveling forward with the aircraft at the speed of sound ( say SOS) prior to the aircraft exceeding the SOS. Once the SOS was exceeded there would be a similar shock wave radiating outward but it would be generated ahead of the prior sub SOS wave and would collide thus creating the frisbee cloud. I was not certain if that collision resulting in condensation would have resulted in a point of higher pressure of the waves colliding or at a point of lower pressure just behind the point of the collision of the two waves. If this is correct, is the cloud actually formed in the high pressure point or immediately behind it at a lower pressure point?
A couple of questions:
1) At what speed does the shock wave travel creating the condensation (speed of sound ?).
2) If I read you correctly, then the condensation effect is caused directly as a result of high pressure.
3) Where could I find a very detailed explanation of this.
Inquiring minds need to know. I can then add it to my vast wealth of useless knowledge.

eyesonu-
i studied this type of thing for several years in grad school and still dont understand “every aspect” of it but I will give it a shot
first off, envision the plane without wings, so it is basically a cone- at the front edge (point) of the cone, a bow wave is formed, that, if you are going fast enough, becomes a shock wave. based on ideal gas theory (which is a usually good approximation in air), the actual value for this is the square root of–( gamma(ratio of specific heats)xR(ideal gas constant)xT (absolute temperature) )
if you get all the units right this comes out to about 350 m/s or 775mph at 25C.
on the front side of this shock wave the air is still, on the back side there has been a step change in fluid properties- the total pressure (static plus velocity component) has INCREASED, hence the term compression shock. however, the static pressure (the measured pressure) has gone down. now the air follows the cone politely until it encounters another change in direction, in this case where the fusilage of the plane begins to taper off- at that point there is another shock wave formed called an expansion shock- in this case the total pressure goes down, but the static pressure goes up. it is this change from a lower to a higher (a gradient) pressure that creates the condensation. it looks cool in this case because it occurs over a shock wave so it is basically a line in the sky.
incidentally, these two shock waves are what you hear (or used to hear) in when the space shuttle would land. two booms, the leading edge compression wave and the trailing edge expansion wave. you dont typically hear this on smaller planes that are closer to you because the two waves are right on top of each other
finally- the “bible” of compressible flow is considered to be two books by a guy named Ascher Shapiro in the 50’s

Have the climate models factored in this yet?