Had observed a 747 on the tarmac in damp weather and there was a large vortex extending from the front of the engine to the pavement like an inverted tornado. My first thought was, what a good job it was doing cleaning the ramp, but then I got to wondering why the funnel mouth had settled onto the pavement. I know that the swirling air created a venturi and thereby caused the interior to have a lower pressure, but does this phenomenon result in the funnel being heavier than the surrounding air, making it sink down?

Might have something to do with effect of the constrained space between the underside of the engine cowling and ground (and maybe between the ground and the wing) biasing the airflow pattern. A constraint like that would lower the local pressure between the (constraints) as air is moving (Bernoulli effect). Just speculation, frankly... but in any case you do not have a symmetrical system so some biase one way or the other should not be a surprise.

Yeah, now that you mention it the airflow interaction might be creating a lower net air pressure near the ground. Thanks, ken.