Concentric gravity waves in the mesosphere generated by deep convective plumes in the lower atmosphere near Fort Collins, Colorado

Abstract

[1] Gravity waves in the mesopause region (80-105 km) may induce perturbations in OH Meinal Band emissions at $87 km. These perturbations can be observed by ground-based OH airglow imagers. In this paper, we present observations of concentric gravity waves (CGW) by the all-sky OH imager at Yucca Ridge Field Station (40.7°N, 104.9°W) near Fort Collins, Colorado. We find that expanding rings of concentric gravity waves were observed on 9 out of 723 clear nights from 2003 to 2008. In particular, on 11 May 2004, concentric rings were observed for $1.5 h, with nearly perfect circular rings entirely in the field of view during the first 30 min. The centers of the concentric rings occurred at the geographic locations of two strong convective plumes which were active in the troposphere $1 h earlier. We measured the horizontal wavelengths and periods of these gravity waves as functions of both radius and time. These results agreed reasonably well with the internal Boussinesq gravity wave dispersion relation with an assumed zero background wind. Similarly, for the other 8 cases, strong convective plumes occurred prior to the CGW observations near the apparent center of each of the arcs or rings. For the 7 out of the 9 cases, radiosonde data were available up to z = 30-35 km. These data showed that the wind speeds from the tropopause to $30-35 km were smaller than $20-30 m/s. Because 8 of the 9 cases occurred when the total horizontal mean winds were weak and because the horizontal winds below $87 km were less than $20 m/s on 11 May 2004 (according to radiosonde and TIME-GCM model data), we postulate that weak background horizontal winds are likely a necessary condition for gravity waves excited from convective overshooting to be observed as concentric arcs or rings in the OH layer.

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.…”

“…Ionospheric studies have found evidence of D-layer heating due to thunderstorm quasi-electrostatic fields [Inan et al, 1996;Pasko et al, 1995], evidence of direct heating of the D-layer due to lightning electromagnetic pulses [Cheng and Cummer, 2005;Cheng et al, 2007], and evidence of atmospheric gravity wave (AGW) influence on the E-region ionosphere (100-150 km) [Davis and Johnson, 2005;Johnson and Davis, 2006]. Stratospheric AGW studies have shown neutral density fluctuations at altitudes of 60-90 km due to tropospheric thunderstorms activities [Taylor and Hapgood, 1988;Dewan et al, 1998;Sentman et al, 2003;Yue et al, 2009], and the electron density at this altitude is expected to fluctuate in a similar manner. However, because of low electron densities in the D-layer, it is difficult to continuously measure the electron density and its possible spatial and temporal fluctuations.…”

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

“…Note that concentric rings from convective storms, like those in Fig. 6, have been occasionally observed in the OH airglow layer from deep convection (Taylor and Hapgood, 1988;Dewan et al, 1998;Sentman et al, 2003;Suzuki et al, 2007;Yue et al, 2009). …”

“…The convective plume model, ray trace model, and reconstruction methods described in this paper have been recently applied to the modeling of an observed deep, convective plume near Fort Collins, Colorado, which produced nearly concentric rings in the OH airglow layer for ∼1.5 h (Yue et al, 2009). Using radar measurements and satellite imagery, we estimated that this plume had a width of D∼15 km, a depth of D z ∼10 km, a duration of σ t ∼10 min, and an updraft velocity of w pl =35 m s −1 .…”

Upper atmospheric gravity wave details revealed in nightglow satellite imagery

“…Thunderstorms trigger a broad spectrum of gravity waves via latent heat release and interactions with the mean flow (37). In the early spring and fall, when wind speeds and shear in the middle atmosphere are at a climatological minimum (38), the initial structure of the waves is preserved, resulting in concentric rings of nightglow (39). Fig.…”