Intermittency of Gravity Waves in the Antarctic Troposphere and Lower Stratosphere Revealed by the PANSY Radar Observation

Abstract

The momentum fluxes associated with gravity waves (GWs) significantly vary both in time and space. It is important to qualify the intermittency of GWs because the intermittency largely affects the vertical profile of momentum flux convergences in the middle atmosphere. In this study, 1 year of continuous observation with high time/height resolution and accuracy was provided by the PANSY radar, a Mesosphere‐Stratosphere‐Troposphere (MST) radar at Syowa Station (69.01°S, 39.59°E) in the Antarctic. The PANSY radar is used to study the intermittency of GWs in the troposphere and lower stratosphere. In all seasons, the intermittency is large in the troposphere with Gini coefficients of 0.4–0.6 for absolute momentum fluxes ( ρo||u′w′true¯) and 0.4–0.7 for vertical wind variances multiplied by the density ( ρotruew′2¯). However, the intermittency is small in the lower stratosphere with Gini coefficients of 0.3–0.5 for ρo||u′w′true¯ and 0.2–0.4 for ρotruew′2¯. The seasonal characteristics in the lower stratosphere are different between ρo||u′w′true¯ and ρotruew′2¯: small Gini coefficients are observed in May–July for ρo||u′w′true¯ and in December–February for ρotruew′2¯. Simple model experiments with ideal distributions of GWs as a function of momentum flux magnitude and ground‐based phase velocity are performed. These results indicate that the vertical profiles of the Gini coefficient obtained by the PANSY radar are largely affected by orographic GWs with large amplitudes. The results also suggest that the generation and the partial reflection of GWs play an important role in determining the vertical profile of GW intermittency.

Role Of the Sun and the Middle atmosphere/thermosphere/ionosphere In Climate (ROSMIC): a retrospective and prospective view

“…The horizontal propagation and intermittency of gravity waves must be taken into account to improve the parameterization of gravity wave drag in climate models (Plougonven et al 2020;Senf and Achatz 2011), because they control the horizontal and vertical distribution of gravity wave drag. The horizontal propagation is mainly detected by satellite observations (Yamashita et al 2013;Fritts et al 2016), and the intermittency is characterized through balloon, radar, and lidar observations (Hertzog et al 2012;Minamihara et al 2020;Baumgarten et al 2018). Observational evidence for secondary GWs is also emerging through lidar and satellite observations (Bossert et al 2017;Song et al 2017;Kogure et al 2020).…”

Gravity‐Wave‐Driven Seasonal Variability of Temperature Differences Between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes

“…This enhanced intermittency of GW activity is caused by more frequent extreme GW events over mountainous regions compared to flat landscapes and ocean surfaces. The intermittency of GWs is important because the vertical profiles of GW momentum flux convergence determine the wave forcing of the mean wind, which is different for sporadic GWs with large amplitudes versus GWs with same mean momentum but smaller amplitudes (Minamihara et al, 2020). GW intermittency can be well quantified by the Gini coefficient (popular in economics) as in Plougonven et al (2013) for GW momentum flux…”

High‐Cadence Lidar Observations of Middle Atmospheric Temperature and Gravity Waves at the Southern Andes Hot Spot

“…In this context, the community speaks of GW intermittency, which describes the irregular occurrence of large‐energy bursts that interrupt the dynamics of a periodic system (Strogatz, 1996). One measure to estimate GW intermittency is the Gini coefficient (Alexander et al., 2016; Minamihara et al., 2020; Plougonven et al., 2013; Wright et al., 2013). GW intermittency is an important parameter because it indicates the extent to which the GW momentum flux deviates from a continuous mean flux.…”