Engineering topics

Durran, D.

Publications and source records attributed to Durran, D..

2 records

NASA NTRS1993

Convectively generated stratospheric gravity waves - The role of mean wind shear

A two-dimensional numerical simulation of mid-latitude squall lines is used to study the properties of storm-induced stratospheric gravity waves. Owing to the tendency for convective cells to form at the forward edge of a squall line, and then propagate toward the rear, the simulated storms preferentially generate gravity waves that propagate toward the rear of the storm. This anisotropy in gravity wave generation leads to a net vertical transfer of momentum into the stratosphere. Cases with and without stratospheric mean wind shear are compared. In the latter case Doppler shifting of the waves to lower frequencies leads to wave breaking and enhanced wave - mean-flow interaction.

Holton, J. R.↗

NASA NTRS1992

Numerical simulations of convectively generated stratospheric gravity waves

A 2D model of a mesoscale convective flow is used to simulate the excitation and vertical propagation of gravity waves. Data obtained show that, in the absence of storm-relative mean winds in the stratosphere, the primary mode of excitation of gravity waves is by mechanical forcing owing to oscillatory updrafts. The stratospheric response consists of waves whose periods match the primary periods of the forcing. Due to the tendency of the oscillating updrafts to propagate toward the rear of the storm, gravity wave propagation is limited primarily to the rearward direction. Results suggest that squall-line-generated gravity waves arise from mechanical forcing rather than thermal effects.

Fovell, R.↗