A Statistical Study of Inertia Gravity Waves in the Lower Stratosphere Over the Arctic Region Based on Radiosonde Observations

Abstract

Relative to many investigations of inertial gravity waves (IGWs) in the Antarctic, IGW activity in the Arctic region was paid less attention to. We use radiosonde observations at the Ny‐Alesund station (78.9°N, 11.9°E) from April 2012 to June 2016 to study the IGW characteristics in the lower stratosphere over the Arctic. The observation reveals a prevailing eastward zonal background wind below 20 km and an obvious annual cycle of the background temperature from the troposphere to the lower stratosphere, which is different from the results in the middle and low latitudes. By combining Lomb‐Scargle spectrum and hodograph technique, case study demonstrates that the lower stratospheric IGWs exhibit a feature of freely propagating waves. Statistical analysis indicates that the IGWs have dominant horizontal (vertical) wavelength of 50–1,050 km (1–4 km) and ratio (1–2.5) of the intrinsic to inertia frequencies. Wave energy exhibits an annual oscillation with the maximum in winter and the minimum in summer. In winter, the downward propagating waves increase to about 20% due to polar stratospheric vortex. Because of the lower atmospheric filtering, the IGWs display a dominant direction of westward propagation, thus have a mean vertical flux of −0.647 mPa for the zonal momentum, which indicates that the IGWs can put a westward drag on the atmospheric wind field over the Arctic as they break and dissipate. All the vertical wavenumber spectra have spectral slopes from −2.23 to −2.99 close to the universal spectrum index of −3.

Statistical Characteristics of Inertial Gravity Waves Over a Tropical Station in the Western Pacific Based on High‐Resolution GPS Radiosonde Soundings

“…Whether in the troposphere or stratosphere, the disturbance components of the zonal wind and meridional wind rotate clockwise with height, representing the upward propagation of energy (the energy propagation direction is used to represent the vertical propagation direction of GWs). The horizontal wind and temperature disturbance rotate clockwise with the height, indicating that the actual propagation direction is consistent with the azimuth angle of the major axis (Huang, 2018). The horizontal propagation directions of GW in the troposphere (2–14 km) and stratosphere (18–28 km) are 58.8° and 49.5°, respectively.…”

Investigation on Spectral Characteristics of Gravity Waves in the MLT Using Lidar Observations at Andes

“…The IGWs in the MLT over Andes evidently exhibit the preferential propagation in the meridian direction relative to in the zonal direction. The anisotropy in the wave propagation direction is extensively reported at different latitudes (Hu et al., 2002; Huang et al., 2018; Moffat‐Griffin et al., 2011; Vincent & Alexander, 2000; Yamamori & Sato, 2006; Yoshiki et al., 2004), which is generally attributed to the wave excitation process and propagation effect.…”

“…The frequency spectra in the zonal and meridional winds have the PSD slope between −1.5 and −2.2 in radar (Hoffmann et al., 2010; Larsen et al., 1986; Y. Yamamoto et al., 1996) and lidar (Senft & Gardner, 1991; Yang et al., 2006) data. A lot of observations showed that the index ranges of frequency and vertical wavenumber spectra in the temperature fluctuations are approximately the same as those in the horizontal wind perturbations (Chen et al., 2016; Cot, 2001; Guharay & Sekar, 2011; Guo et al., 2017; Huang et al., 2018; Wu et al., 2006; Yang et al., 2010). It can be noted that the observed frequency (vertical wavenumber) spectrum slope exhibits a change around the canonical value of −5/3 (−3) derived from the spectral theories.…”

“…Wave kinetic ( E k ) and potential ( E p ) energies represent the magnitude of wave activity. The kinetic and potential energies per unit mass are expressed as (Huang et al., 2018; S. D. Zhang & Yi, 2007) where is the relative temperature perturbation, defined as the ratio of the temperature perturbation T ′( z ) to the mean temperature T 0 ( z ); g = 9.77 m s −2 is the gravitational acceleration; and the overbar denotes an average over the height range. In this way, the kinetic and potential energies of the IGW are E k = 82.8 J/kg and E p = 71.8 J/kg derived from Equations and , and their ratio is 1.15.…”

“…As a delicate method, hodograph technique is extensively utilized to extract the predominant inertia–gravity wave (IGW) from the observational profiles of radiosonde (Huang et al., 2018; Tsuda et al., 1994; Vincent & Alexander, 2000; Yamamori & Sato, 2006; S. D. Zhang & Yi, 2005; S. D. Zhang et al., 2012, 2017), radar (Gavrilov et al., 2000; Nicolls et al., 2010; Suzuki et al., 2013; M. Yamamoto et al., 1987; Zhou & Morton, 2006), and lidar (Cai et al., 2014; Chen et al., 2013, 2016; Collins et al., 1994; Hu et al., 2002; T. Li et al., 2007; Lu et al., 2015, 2017; Rajeev et al., 2003; Xu et al., 2006). Combined with Doppler shifting equation, this technique can estimate the temporal and spatial parameters of quasi‐monochromatic IGW, such as wave period, wavelength, and propagation direction.…”