New numerical model of mesospheric bores: Observational implications
Abstract
Mesospheric bores are space-time varying frontal structures that may play a role in transport and coupling between horizontally separated regions. We examine the observational implications of a new numerical model of the generation and propagation of mesospheric bores. The bores develop as long-wave excitations in mesospheric wave ducts, formed by the temperature and wind structure, in much the same way as they do in the tropospheric boundary-layer duct. However, while the boundary-layer duct has a clamped ground boundary (zero vertical displacement), the embedded mesospheric duct has two free boundaries, which results in some differences in behavior. With a separability assumption valid in the long-wave limit, the fluid equations separate into a product of solutions of the Taylor-Goldstein equation describing the vertical dependence of the mode function and of the Benjamin-Davis-Ono (BDO) equation describing the horizontal and time behavior. We compare results of the numerical model with the analytic model of Dewan and Picard (1998) that is based on Lighthill's channel-bore solutions. The numerical model leads to predictions of new or as-yet-unobserved phenomena, including (1) the conceivable existence of bores in Doppler ducts, (2) the existence of a fast sinuous-mode bore with no channel-bore analogue having phase speeds of 150-180 m/s, and (3) the possibility of foaming or turbulent (non-undular) bores. Following Christie (1989), we model the turbulent dissipation processes in the latter case by including a Burgers-type term in the BDO equation. We also discuss the response of emitted radiance to bores and compare model predictions with recent bore observations accompanied by simultaneous lidar data [Smith et al., 2001; She et al., 2004].
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.3674P