Premium
Tidal and near‐inertial peak variations around the diurnal critical latitude
Author(s) -
van Haren Hans
Publication year - 2005
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2005gl024160
Subject(s) - latitude , atmospheric sciences , current meter , inertial wave , physics , geology , environmental science , geodesy , oceanography , wave propagation , optics , mechanical wave , longitudinal wave
Spectra from historic long‐term open‐ocean moored current meter data between latitudes 0° < ∣ϕ∣ < 45° reveal a significant drop in semidiurnal tidal band (D 2 ) energy by ∼50% at ∣ϕ∣ ≈ 25–27°, whilst the peak near the local inertial frequency f is increased by a factor of ∼10 up to the level of D 2 ‐energy at ∣ϕ∣ ≈ 28–30°, where f coincides with diurnal frequencies. The increase in f‐energy is accompanied by a red‐shift of the peak frequency to 0.97 ± 0.01f, or a poleward spreading of enhanced energy. This contrasts with more common blue‐shift. The enhancement may be the result of sub‐harmonic instability, as supported by sparse significant bicoherence at half‐D 2 , although i) systematic enhancement of diurnal tidal frequencies, notably M 1 , was not observed, ii) the latitudes of low D 2 ‐energy and high f‐energy do not coincide. This may be due to a mix of coupled and independent waves, whilst the poleward trapping of sub‐f energy suggests non‐traditional effects.