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Turbulence and gravity waves in the vicinity of a midtropospheric warm front: A case study using VHF echo‐intensity measurements and radiosonde data
Author(s) -
Muschinski Andreas
Publication year - 1997
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/97rs00054
Subject(s) - radiosonde , geology , cold front , amplitude , front (military) , intensity (physics) , troposphere , gravity wave , radar , altitude (triangle) , stratification (seeds) , warm front , meteorology , atmospheric sciences , geodesy , gravitational wave , physics , optics , geometry , astrophysics , seed dormancy , telecommunications , mathematics , germination , botany , dormancy , biology , computer science
It is well known that VHF echo‐intensity data obtained at nonvertical beam directions can be used to retrieve the refractive‐index structure parameter C 2 n and that vertical profiles of C 2 n can be used to identify and monitor frontal structures in the free troposphere. In a case study, VHF radar observations of C 2 n are compared with vertical profiles of M 2 g (the square of the vertical gradient of the generalized potential refractive index) obtained from the data of two radiosondes launched from 4 km east of the radar site. The experiment was carried out in the Harz Mountains, north Germany, on October 18, 1993, during a high‐pressure period under clear‐sky conditions. Well‐defined maxima of C 2 n and M 2 g are found at the surface of a warm front at altitudes slightly below 5 km. At altitudes in the immediate vicinity of the front, echo‐intensity oscillations are observed, which have an amplitude of up to 9 dB and a period of about 40 min and which are attributed to gravity wave‐induced vertical displacements of the frontal surface. Vertical profiles of the outer scale of turbulence, L 0 , are obtained from the profiles of C 2 n and M 2 g . In the stably stratified region below the front (at altitudes between 3 and 5 km), 5–20 m is typical, while in the less stably stratified altitude region between 5 and 7 km, 20–50 m is more representative. It is found that large values of L 0 are correlated with low static stability; a relationship between L 0 and the Richardson number (dynamic stability), however, was not observed. A continuous temporal increase of C 2 n at altitudes between 5 and 7 km was observed. It is attributed to a temporal increase of the vertical variability of the humidity above the front.