I had a very similar experience about 1/4 mile from the touchdown zone at
Narita, Japan. I wanted to get pictures of 747's landing.  It was too windy
after they passed. Wing Vortices are serious.

Jack Webb

Subject: [LML] Re: Wing pressure

Posted for "Skip Slater" <skipslater@earthlink.net>:

  "Has anyone experienced a downward blast from a landing aircraft?"Boy have
I ever!
  
  I took the attached photo on Diego Garcia during an Indian Ocean
deployment with the Navy back in 1981.  I was bored one day so I climbed up
on the ----- to keep from being blown off of it.  It was like being in a
vertical hurricane for a couple of seconds and then it just stopped.  Pretty
powerful demonstration.
  
  Skip Slater
  N540ES