A model study of the effects of winds on concentric rings of gravity waves from a convective plume near Fort Collins on 11 May 2004

Abstract

[1] Using a convective plume model and a ray trace model, we investigate the effects of winds on concentric rings of gravity waves (GWs) excited from a convective plume on 11 May 2004, near Fort Collins, Colorado. We find that winds can shift the apparent center of the concentric rings at z = 87 km from the plume location. We also find that critical level filtering (for GWs with small phase speeds propagating in the same direction as the wind) and wave reflection (for high-frequency GWs with small horizontal wavelengths propagating in the opposite direction to the wind) prevent many GWs from reaching the OH airglow layer. Additionally, we find that strong winds disrupt the concentric ring patterns, causing distorted ''squashed'' ring and arc-like patterns instead. Using a zero wind profile and a representative April mean zonal wind profile, we compare our model results with observations of concentric rings at the Yucca Ridge Field Station (40.7°N, 104.9°W). We find that the model horizontal wavelengths and periods agree reasonably well with the observed data. We also compare the model temperature perturbations with the temperature perturbations calculated from the intensity perturbations. Because the observations show less critical level filtering than from the April wind profile and more critical level filtering than from the zero wind profile, we conclude that the winds on 11 May were likely somewhat smaller than the April zonal wind profile assumed here.

High temporal and spatial-resolution detection of D-layer fluctuations by using time-domain lightning waveforms

“…A wider angular-range analysis further indicates that the fluctuations propagate away from the storm. The fluctuation periods, possible propagation speed, and inferred propagation direction are consistent with recent observations and model studies of atmospheric gravity waves (AGW) at the D-layer altitude that are originated from convective thunderstorm activity overshooting the tropopause [Alexander et al, 1995;Vadas and Fritts, 2004;Vadas et al, 2009;Yue et al, 2009]. From LASA's own observations of some intracloud discharges (e.g., NBEs), it was noticed that several intermittent clusters of events elevated to 15 km or higher in this storm, suggesting that corresponding convection cells overshot the local tropopause.…”

Reconstruction of the gravity wave field from convective plumes via ray tracing

“…Via intercomparision between the ray trace and FL solutions, we determined the normalization constant needed to convert the spectral, ray traced momentum fluxes to the real-space momentum fluxes. Because the ray trace model is generalizable to non-isothermal temperatures and non-zero winds, the formalism developed in this paper allows for the determination of GW effects in the MLT and TI for more realistic atmospheric environments (see Vadas et al, 2009b).…”

“…Fourier analysis has shown that energy transfer cannot occur between waves of different frequencies for a set of linear equations when the coefficients do not depend explicitly on time (Lighthill, 1978). For all of the simulations in this paper, in Fritts and Vadas (2008), and in Vadas et al (2009b), the background parameters are constant in time; therefore, ω r is constant in time for each GW. However, for the reverse and forward ray trace simulations performed for this SpreadFEx campaign in Vadas et al (2009a), we assume that the background temperatures and winds vary slowlyenough to approximate that ω r is constant in time.…”

“…(63). It was found that the concentric rings became "squashed" or arc-like if the intervening winds were strong, and that the apparent center of the concentric rings shifted with respect to the convective plume if the average horizontal wind between the tropopause and the OH layer was large (Vadas et al, 2009b). It was also found that the model results agreed reasonably well with the amplitudes, phases, horizontal wavelengths, and periods of the observed waves, and that a disappearance of part of the concentric GW rings after an hour could be explained by the reflection of high-frequency GWs propagating opposite to the direction of the background, horizontal wind.…”

“…This inter-comparison allows for the normalization of the GW spectral amplitudes, so that the amplitudes of GWs can be determined via ray tracing. It also allows for studies involving ray tracing through varying temperature and wind profiles (Vadas et al, 2009b). Note that Fritts and Vadas (2008) employ the GW amplitudes and spectra determined in this paper to anticipate general GW propagation, filtering, and amplitude growth accompanying various thermospheric temperature and wind profiles.…”