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Mesoscale observations of upstream blocking
Author(s) -
Manins P. C.,
Sawford B. L.
Publication year - 1982
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710845608
Subject(s) - froude number , mesoscale meteorology , ridge , geology , blocking (statistics) , wind speed , meteorology , acceleration , atmospheric sciences , geomorphology , flow (mathematics) , mechanics , physics , climatology , oceanography , paleontology , statistics , mathematics , classical mechanics
Analysis of detailed tethered balloon soundings simultaneously undertaken at two sites in a valley shows that blocked (i.e. near stagnant) flow upwind of the ridges is characterized by a critical internal Froude number, Fr = u a H −1 (gγa/θ r ) −1/2 of approximately 1.6. For Fr above this value the air in the valley is swept out by ambient wind. Otherwise blocking to near ridge height is observed. Here u a is ambient wind speed measured above ridge height H , g is acceleration due to gravity, θ r a reference potential virtual temperature and γ a the ambient vertical gradient of this quantity.