HR: 0830h
AN: SA51A-0498    [PDF]
TI: Breaking of Thunderstorm-Generated Gravity Waves as a Source of Short-Period Ducted Waves Observed at Mesopause Altitudes
AU: * Snively, J B
EM: jbs231@psu.edu
AF: CSSL Laboratory, Penn State University, 204 EE East, University Park, PA 16802 United States
AU: Pasko, V P
EM: vpasko@psu.edu
AF: CSSL Laboratory, Penn State University, 204 EE East, University Park, PA 16802 United States
AB: Atmospheric gravity waves with periods of 5 to 8 minutes have been observed at airglow altitudes [Taylor et al., GRL, 22, 2849, 1995; Walterscheid et al., JASTP, 61, 461, 1999; Hecht et al., JGR, 106, 5181, 2001; and references cited therein]. These waves are believed to propagate as thermally-ducted wave modes, trapped in the Brunt-V\"{a}is\"{a}l\"{a} frequency minimum of the upper mesosphere and lower thermosphere [e.g., Walterscheid et al., 1999]. Many of these recently observed waves have been traced to thunderstorm activity located hundreds of kilometers from the point of observation. However, these gravity waves would be evanescent in most regions of atmosphere, where their frequency exceeds the local Brunt-V\"{a}is\"{a}l\"{a} frequency. It is therefore improbable that the observed waves with short periods ($\tau$$\simeq$$5$ min) would be able to propagate freely from a tropospheric convective source to the lower thermosphere. Thunderstorms are known radiators of gravity waves, with typical forcing periods of 10 to 16 minutes (approximately equal to the Brunt-V\"{a}is\"{a}l\"{a} period of the upper troposphere) [e.g., Pierce and Coroniti, Nature, 210(5042), 1209, 1966]. Recent numerical studies have demonstrated that the breaking of low frequency gravity waves can excite harmonic secondary waves, with frequencies and horizontal wavenumbers approximately twice that of the primary waves [e.g., Franke and Robinson, J. Atmos. Sci., 56, 3010, 1999, Zhou et al., JGR, 107(D7), doi:10.1029/2001JD001204, 2002]. It has also been proposed that these radiated secondary waves may be subject to ducting near the breaking region [Vadas et al., J. Atmos. Sci., 60, 194, 2003]. It can thus be predicted that if thunderstorm-generated gravity waves, with periods of 10 to 16 minutes, were to break near mesopause, they may excite secondary waves with short periods of 5 to 8 minutes. These waves would be trapped in the lower thermospheric duct. Using a high-resolution, two-dimensional, nonlinear numerical model, we examine this process in a thermally-realistic atmosphere for a tropospheric oscillatory source modeling the effects of convection. Simulated results demonstrate that breaking thunderstorm-generated gravity waves may be able to excite quasi-monochromatic, short-period, thermally ducted wave modes at airglow altitudes. These results will be compared with linear mechanisms (such as ``kissing" modes [e.g., Walterscheid et al. JGR, 106, 31825, 2001]); the applicability and limitations of the different mechanisms will be discussed.
DE: 3314 Convective processes
DE: 3332 Mesospheric dynamics
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 3369 Thermospheric dynamics (0358)
DE: 3384 Waves and tides
SC: SPA - Aeronomy [SA]
MN: 2003 Fall Meeting