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Anomaly in the Alpine diurnal pressure signal: Observations and theory
Author(s) -
Frei Ch.,
Davies H. C.
Publication year - 1993
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.49711951403
Subject(s) - ridge , mesoscale meteorology , anomaly (physics) , climatology , geology , terrain , asymmetry , amplitude , diurnal cycle , oscillation (cell signaling) , geophysics , atmospheric sciences , physics , geography , paleontology , cartography , quantum mechanics , biology , genetics , condensed matter physics
An examination is undertaken of the diurnal surface‐pressure pattern across the main east‐west ridge of the European Alps. A case study for clear‐sky, quiescent synoptic conditions reveals a pronounced across‐ridge asymmetry—to the north the primary feature is an approximate 0.5 hPa semi‐diurnal oscillation whilst on the southern side there is an approximate 2.5 hPa diurnal oscillation. A one‐year statistical climatology and a two‐month synoptic climatology confirm the existence, and indicate the prevalence of this asymmetry. The across‐ridge variation in the amplitude of the solar‐diurnal (i.e S 1 ) component is about 1 hPa and it has a lateral scale of around 200 km. From a theoretical standpoint physical arguments and dynamical considerations are advanced to suggest that the S 1 anomaly is not readily attributable to purely in situ effects. In addition a heuristic model is deployed to examine the possible nature of the Alpine modification of the planetary diurnall tide. The model, comprising a cylindrical island embedded in ‘reduced‐gravity’ shallow water, reveals a terrain‐induced modification in the form of a mesoscale, terrain‐trapped Kelvin wave that interferes destructively (constructively) with the global S 1 signal to the north (south) of the terrain. The pattern's amplitude, phase and spatial structure are consistent with the main features of the observed signal.