Bottom mixing enhanced by tropical storm‐generated near‐inertial waves entering critical layers in the Straits of Florida

Near-Inertial Waves in Strongly Baroclinic Currents

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0132.1 ◽

2013 ◽

Vol 43 (4) ◽

pp. 706-725 ◽

Cited By ~ 62

Author(s):

Daniel B. Whitt ◽

Leif N. Thomas

Keyword(s):

Gulf Stream ◽

Velocity Vector ◽

Numerical Solutions ◽

Wave Theory ◽

Two Dimensional ◽

Inertial Waves ◽

Geostrophic Current ◽

Minimum Frequency ◽

Critical Layers ◽

Baroclinic Currents

Abstract An analysis and physical interpretation of near-inertial waves (NIWs) propagating perpendicular to a steady, two-dimensional, strongly baroclinic, geostrophic current are presented. The analysis is appropriate for geostrophic currents with order-one Richardson numbers such as those associated with fronts experiencing strong, wintertime atmospheric forcing. This work highlights the underlying physics behind the properties of the NIWs using parcel arguments and the principles of conservation of density and absolute momentum. Baroclinicity introduces lateral gradients in density and vertical gradients in absolute momentum that significantly modify the dispersion and polarization relations and propagation of NIWs relative to classical internal wave theory. In particular, oscillations at the minimum frequency are not horizontal but, instead, are slanted along isopycnals. Furthermore, the polarization of the horizontal velocity is not necessarily circular at the minimum frequency and the spiraling of the wave’s velocity vector with time and depth can be in the opposite direction from that predicted by classical theory. Ray tracing and numerical solutions illustrate the trapping and amplification of NIWs in regions of strong baroclinicity where the wave frequency is lower than the effective Coriolis frequency. The largest amplification is found at slantwise critical layers that align with the tilted isopycnals of the current. Such slantwise critical layers are seen in wintertime observations of the Gulf Stream and, consistent with the theory, coincide with regions of intensified ageostrophic shear characterized by a banded structure that is spatially coherent along isopycnals.

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Critical layers of hydromagnetic gravity inertial waves in the solar helmet streamers and magnetic sectors

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1987.0123 ◽

1987 ◽

Vol 413 (1845) ◽

pp. 415-427

Keyword(s):

Magnetic Fields ◽

Solar Corona ◽

Evanescent Waves ◽

Critical Layer ◽

Geometrical Configuration ◽

Inertial Waves ◽

Interplanetary Magnetic Fields ◽

Propagating Waves ◽

Key Factor ◽

Critical Layers

By using appropriate geometrical configuration and relevant frequency ranges it is shown that hydromagnetic gravity inertial waves propagating both in the helmet streamers and magnetic sectors of the solar corona exhibit critical layers. It is also pointed out that the absorption of propagating waves by the critical-layer mechanism provides a key factor in stabilizing the solar and interplanetary magnetic fields in counter-effect to over-reflection mechanism and critical-layer escalation of evanescent waves.

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