Kerguelen/Heard Island Simulations

This page describes a suite of numerical simulations of gravity waves over Kerguelen and Heard Islands as observed by six different overpasses of the AWE instrument.

Computational Domain

The mesh in the horizontal direction is shown in the figure below.

surface


The mesh is clustered near both Kerguelen and Heard islands and then is gently stretched with increasing distance to the horizontal boundaries. The spacing in both x and y is 500 m near Kerguelen Island and is 800 m near Heard Island. The vertical grid spacing is 500 m from the surface to an altitude of 102 km, where it is then gently stretched to the upper boundary at 112 km. A sponge layer occupies the stretched region between 102 and 112 km. The (x,y) origin corresponds to (49.3° S, 69.2° E). Inviscid wall boundary conditions are used at the lower surface whereas characteristic (radiative) conditions are used in combination with a sponge layer at the lateral and top boundaries.

Forcing

In order to minimize starting transients, the mean winds are damped to zero between the surface and 30 km. Forcing terms are then used to increase the near-surface winds over a period of two hours. The forcing terms follow a hyperbolic tangent function in time, which results in very gentle accelerations near the beginning and end of the forcing period. The maximum forcing rate is equivalent to that of a linear ramp with a duration of a half hour.

Wind Profiles

The individual cases are differentiated by distinct wind and temperature profiles, corresponding to the date and time of the AWE overpass. In these preliminary runs, the wind and temperature profiles were held fixed in the horizontal directions and in time, at the point 49.5°S, 69.5°E. The profiles were gnerated by combining archived ERA5 and JAWARA data.

Cases

Orbit 3234 - June 17, 2024

Orbit 8735 - June 7, 2025

Orbit 8765 - June 9, 2025

Orbit 8842 - June 14, 2025

Orbit 8873 - June 16, 2025

Orbit 306 - December 11, 2023