[Wrf-users] The meaning of "perturbation"

[Makoto Nakayoshi]

Hello

I am sorry for posting a silly question, but
could you please tell me the meaning of 'perturbation'?
I outputed 'P' (bottom grid) near Tokyo from wrfoutput,
and the value ranged approximately from 700 to 1000 [Pa].
I expected 'P' was just pressure, but Registory file says
'P' is perturbation pressure.
What is perturbation?
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Makoto Nakayoshi                      |  仲吉　信人
Master's course                       |　東京工業大学
Dept.of International Development Eng.|　国際開発工学専攻
Tokyo Institute of Technology         |　
O-okayama 2-12-1 Meguro-ku,Tokyo      |　東京都目黒区大岡山
152-8552 JAPAN                        |　　　　　　　2-12-1
Tel  +81-3-5734-2768                  |  Fax 03-5734-2768
FAX  +81-3-5734-2768                  |  Tel 03-5734-2768
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