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J-STAGE Advance published date: September 2, 2024
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1
2Simultaneous observation of near-inertial frequency

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gravity waves by a long-duration balloon and the

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PANSY radar in the Antarctic

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Yoshihiro Tomikawa1,2,3, Isao Murata4, Masashi Kohma5, andKaoru Sato5891National Institute of Polar Research, Tachikawa, Japan

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2The Graduate Institute for Advanced Studies, SOKENDAI, Tachikawa, Japan

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3Polar Environment Data Science Center, Research Organization of Information and

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Systems, Tachikawa, Japan13

4Tohoku University, Sendai, Japan

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5The University of Tokyo, Tokyo, Japan

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March 1, 2024

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-----------------------------------Corresponding author: Yoshihiro Tomikawa, Space & Upper Atmospheric Science Group
National Institute of Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan
Email: tomikawa@nipr.ac.jp
Tel: +81-42-512-0660

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Abstract

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Simultaneous observations using a long-duration balloon and the PANSY radar, a large-

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scale atmospheric radar, were performed at Syowa Station in the Antarctic, from January

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to February 2022. They captured near-inertial frequency gravity waves (NIGWs) in the36

lower stratosphere. The analysis using both datasets and the latest reanalysis ERA5

37

revealed that two NIGW packets with an upward group velocity and short vertical38

wavelengths of less than 3 km propagated northeastward and eastward above Syowa

39

Station. Although the NIGWs over Syowa Station were qualitatively represented by ERA5,

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their amplitudes were underestimated. In addition, the latter NIGW packet was observed

41

by the long-duration balloon, but not represented by ERA5. It could be because the42vertical wavelength of NIGW became shorter than the lower limit of vertical wavelength43

explicitly represented in ERA5 by entering the high static stability region around the44balloon, or due to explicit and implicit diffusion and/or misrepresentation of the position of45

the NIGW packet in the model. This result implies the difficulty to explicitly represent the46

behavior of NIGWs with short vertical wavelengths even in the high-resolution simulation.

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Keywords

gravity wave; Antarctic atmosphere; long-duration balloon; PANSY radar1

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1. Introduction

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In recent years, the horizontal and vertical resolution of operational analysis and52

reanalysis data has been increasing year by year, and it has become to resolve some gravity

53

waves. The spatial distribution of gravity wave activity in these data is qualitatively consistent54

with both satellite and balloon observations (Hoffmann et al., 2017; Jewtoukoff et al., 2015).

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The importance of these data in gravity wave research is increasing. On the other hand, it

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has been reported that the amplitude and momentum flux of gravity waves in these data are57

underestimated compared to observations (Hoffmann et al., 2017; Jewtoukoff et al., 2015;

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Wicker et al., 2023).

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The long-duration balloon (i.e., super-pressure balloon) has attracted attention as a60

means of observing gravity waves because it can resolve the entire frequency band of61

gravity waves and estimate their momentum flux (Alexander et al., 2010; Baldwin et al.,622019). The Vorcore/Concordiasi campaign, which was the long-duration balloon

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observations performed in 2005/2010 over Antarctica (Hertzog et al., 2007; Rabier et al.,642010), observed the horizontal distribution of momentum flux due to gravity waves and65

revealed that a small percentage of large-amplitude gravity waves are responsible for the66

large part of momentum transport (i.e., intermittency) (Hertzog et al., 2008, 2012).

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The PANSY radar, installed at Syowa Station in the Antarctic one year after the68

Concordiasi campaign, can resolve gravity waves in the entire frequency band and estimate

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their momentum flux (Sato et al., 2014), as well as the long-duration balloon. The PANSY
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radar started continuous observations in the troposphere and lower stratosphere since 201271

and revealed many facts, including the dominance of near-inertial frequency gravity waves

72(NIGWs), the generation of gravity waves with downward group velocity by the polar-night73

jet, that by spontaneous adjustment associated with the tropopause jet, and the difference74

in intermittency of gravity waves between the troposphere and stratosphere (Shibuya et al.,75

2015; Minamihara et al., 2016, 2018, 2020).

76

On the other hand, these two instruments, which can resolve the entire frequency band77

of gravity waves and estimate their momentum flux, have never been used in conjunction,78

not only in the Antarctic but also in any other regions. Therefore, we established the79

LODEWAVE (LOng-Duration balloon Experiment of gravity WAVE over Antarctica) project80

to collaboratively observe gravity waves in the Antarctic region using the long-duration81

balloon and PANSY radar (Tomikawa et al., 2023). We performed the first campaign

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observation using the long-duration balloon in January and February 2022 at Syowa Station,

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Antarctica. It successfully captured NIGWs simultaneously by the long-duration balloon and84

PANSY radar in the lower stratosphere at an altitude of 18-19 km. In this paper, the85characteristics of the captured NIGWs are clarified and compared with the latest reanalysis

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ERA5.

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The paper is organized as follows. The data used in this study are described in Section 2.

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Section 3 gives details of the NIGWs observed by the long-duration balloon and PANSY

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radar. Section 4 discusses why the NIGWs observed by the LODEWAVE balloon were not3For Peer Review

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represented in ERA5. Section 5 gives the conclusion.

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2. Data93

2.1 LODEWAVE observations

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Figure 1 shows the overall configuration of LODEWAVE observation system. The fully

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inflated super-pressure balloon (model: NPB02) used for this observation has a volume of96

183 m3, a height of 4.8 m, and a width of 8.1 m. To prevent the helium gas filled inside the97balloon from leaking and to ensure a long duration flight, the super-pressure balloon has a98

double-layer structure with a polyethylene balloon on the outside and a rubber balloon on99

the inside (Saito et al., 2020). Furthermore, by covering the balloon with a diamond-shaped

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net, high pressure resistance is achieved to withstand diurnal changes of differential

101pressure (Saito et al., 2014, 2021, 2023a). The observation instrument is equipped with a102

temperature sensor, three pressure sensors, and a GPS sensor to measure atmospheric103

temperature, pressure, and horizontal winds at the balloon's position every 30 seconds,

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respectively (Tomikawa et al., 2023). The measured data is transmitted to the ground every

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7.5 minutes via Iridium SBD (short burst data) (Kaho et al., 2022). The balloon's flight altitude106

was assumed to be 18-19 km (65-70 hPa), within the altitude range observable by the107

PANSY radar and with a low possibility of encountering other flying objects. The performed

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three flights are referred to as LODEWAVE 3, 2, and 1 in the order they were conducted

109(i.e., note that the numbers and the order are reversed) (Saito et al., 2023b).
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2.2 PANSY radar observations

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The PANSY radar is a mesosphere–stratosphere–troposphere (MST) radar installed at

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Syowa Station (69.0°S, 39.6°E) in 2011. It can observe three-dimensional winds in the113

troposphere and lower stratosphere with high temporal and vertical resolutions (Sato et al.,114

2014). Five beams are used in PANSY radar observations, which are pointing to the vertical

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and to the north, east, south, and west at the same zenith angle of 10°. Vertical winds are116

estimated directly from the vertical beam, and zonal and meridional winds are obtained from117

the line-of-sight velocity of the east–west and north–south beams, respectively. The

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accuracy of wind velocity is approximately 0.1 ms-1 for vertical winds and 0.5 ms-1 for zonal

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and meridional winds. The range resolution along the beam direction is 150 m. The original120

time resolution of tropospheric and stratospheric observations is approximately 200 s. In this121

study, we used 3-dimensional winds estimated from echo spectra incoherently integrated

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over 30 min since the 30-min integrated data can extend the upper limit of the observation

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altitude range by 3–5 km.

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2.3 ERA5 reanalysis

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ERA5 is the latest atmospheric reanalysis dataset provided by the European Centre for

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Medium-Range Weather Forecasts (ECMWF) (Hersbach et al., 2020). Hourly data are

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provided on 137 model levels vertically from the surface up to the pressure level of 0.01 hPa

128(~80 km altitude). The altitude interval in the lower stratosphere (from 15 to 20 km), which129

was the focus of this study, is 300-400 m. The latitude and longitude mesh is 0.25° × 0.25°.
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For comparison with the LODEWAVE data, the ERA5 data were linearly (i.e., linearly in the131

log pressure in the vertical) interpolated onto the balloon’s position and time. Data from the132

grid point (69.0°S, 39.5°E) closest to Syowa Station were used for comparison with the133

PANSY radar data.

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3. Results

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3.1 LODEWAVE campaign

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Three LODEWAVE balloons were released at Syowa Station in January and February

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2022. Their trajectories and altitudes are shown in Fig. 2. The release dates of LODEWAVE

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1, 2, and 3 were Feb. 6, Feb. 4, and Jan. 6, respectively. Their flight duration was 1-3 days.

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The altitude of LODEWAVE 3 temporarily descended on Jan. 8 because the LODEWAVE 3

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balloon was in a zero-pressure state due to the decrease in internal helium gas and solar

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radiation. It then returned to a super-pressure state again as solar radiation increased, but

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began to descend again as solar radiation decreased, finally descending to the Antarctic

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continent (Saito et al., 2023b). In this paper, we used data from LODEWAVE 3, which had

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the longest flight duration and captured the NIGWs.

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The flight trajectory of LODEWAVE 3 (Fig. 2a) shows a counterclockwise trochoidal

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motion with an eastward drift. This suggests that the counterclockwise rotation is

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superimposed on the background westerly wind. Figure 3 shows the time variations of zonal

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and meridional winds observed by LODEWAVE 3. Only data above 18.2 km altitude, which
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was under the super-pressure state, are plotted. Both zonal and meridional winds oscillate151

with an amplitude of about 4 to 5 ms-1 and a period of 10-12 hours throughout almost the152

entire period. The phase of the zonal wind preceded that of the meridional wind by about 90

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degrees, resulting in a counterclockwise rotational motion. Such trochoidal flight trajectory154

has been observed in past long-duration balloon observations and is thought to be due to155

NIGWs or inertial oscillations (Hertzog et al., 2002; Conway et al., 2019).

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3.2 Simultaneous observation of NIGWs by the LODEWAVE balloon and PANSY radar

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Figure 4 shows the time variations of zonal and meridional winds obtained by LODEWAVE

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3 and PANSY radar at an altitude of 18.5 km. It is found that the amplitude and phase of the159

oscillation of both winds are in good agreement between LODEWAVE 3 and PANSY radar160

from 15:00 UT on Jan. 6 to 03:00 UT on Jan. 7, during which the oscillation period is 9-11

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hours. After that, although both of zonal and meridional winds from LODEWAVE 3 and162

PANSY radar exhibit similar oscillations, the phase rotation of wind fluctuations from the163

PANSY radar is faster in time, resulting in a wave period of 8-10 hours for the PANSY radar

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wind oscillation and that of 10-12 hours for the LODEWAVE 3 one. LODEWAVE 3 was165

located at 69.9°S and 44.9°E, about 230 km away from Syowa Station, at 03:00 UT on Jan.

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7.

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Next, we compared LODEWAVE 3 and PANSY radar observations, and reanalysis ERA5.

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Dashed lines in Fig. 3 show the time variations of zonal and meridional winds of ERA5

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interpolated onto the time and position of the LODEWAVE 3 balloon. Compared with
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LODEWAVE 3, the amplitude of the oscillation for ERA5 is about half of that, although they171

are nearly in phase from 15:00 UT on Jan. 6 to 00:00 UT on Jan. 7. After that, the phase of172

the oscillation in ERA5 slightly precedes that of LODEWAVE 3 until 12:00 UT on Jan. 7, but

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thereafter ERA5 hardly reproduces the oscillation observed by LODEWAVE 3.

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Figure 5 shows the time-height sections of zonal and meridional winds from the PANSY

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radar and ERA5. All the figures captured oscillations whose phase descends with time. The

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vertical wavelength of the oscillations estimated for the PANSY radar observations before

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03:00 UT on Jan. 7 is about 2.4 km (i.e., positive peaks are around 15.2 km and 17.6 km at

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00:00 UT on Jan. 7 in Fig. 5a). During the same period, the ERA5 shows the oscillations

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with a similar vertical wavelength, but their amplitude was about half that of PANSY radar

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observation. On the other hand, the vertical wavelength of the oscillation observed by the181

PANSY radar around 00:00 UT on Jan. 8 is about 2.8 km (i.e., positive peaks are around182

16.8 km and 19.6 km at 00:00 UT on Jan. 8 in Fig. 5b). The oscillations seen in ERA5 during

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the same period also had a vertical wavelength similar to that of the PANSY radar

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observation, but their amplitude is about half that of the PANSY radar observation.

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To clarify the characteristics of the observed oscillation, a hodograph is drawn using the186(unfiltered) PANSY radar data in Fig. 6a. Although the direction of major axis of the187

hodograph changes with time, it always shows a counterclockwise rotation with altitude. This

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suggests that the observed oscillations were inertia-gravity waves with an upward group189

velocity, but the direction of their horizontal wavenumber vector is not clearly determined.
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Although the wave period close to 12 hours reminds us of a semidiurnal tide, the short191

vertical wavelength of the observed oscillations negates that possibility.

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A hodograph with time obtained by LODEWAVE 3 is also shown in Fig. 6b. A lowpass

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filter with a cutoff period of 6 hours is applied to LODEWAVE 3 data to remove the short-194

period fluctuations. A linear wave theory indicates that inertia-gravity waves in the southern

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hemisphere show a counterclockwise rotation with time in the hodograph regardless of the196

direction of the vertical group velocity. This is actually the case. On the other hand, the shape197of the hodograph is longer in the meridional direction before 06:00 UT on Jan. 7, but

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becomes almost circular after that. Thus, it is inferred that the propagation direction of

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inertia-gravity waves varied during the observation period.

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Next, polar projection maps of zonal winds at an altitude of about 18.4 km obtained from201

ERA5 are shown in Fig. 7. A bandpass filter with a cutoff wave period of 6-24 hours is applied202

to the data to extract the near-inertia frequency gravity waves. Red and blue solid lines in

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Fig. 7 indicate positive and negative phases of the zonal wind anomalies around Syowa

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Station, respectively. A negative zonal wind anomaly over Syowa Station at 15:00 UT on

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Jan. 6 (Fig. 7a) was spread from northwest to southeast and moved northeastward with time206

as shown by blue solid lines (Figs. 7b-c). Its horizontal wavelength is estimated to be about

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1000 km. On the other hand, a negative zonal wind anomaly over Syowa Station at 00:00

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UT on Jan. 8 (Fig. 7e) moved eastward with time (Figs. 7f-g). Since the areas of positive209

and negative anomalies over Syowa Station extend about 1000 km in the zonal direction in
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Figs. 7f and 7h, respectively, its horizontal wavelength is estimated to be about 2000 km.

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Therefore, the near-inertial frequency oscillations over Syowa Station observed by the212

PANSY radar from Jan. 6 to 8 were probably caused by two inertia-gravity wave packets

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with different horizontal wavelengths and different propagation directions.

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4. Discussion

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The results of Section 3 suggest that the simultaneous observation using the long-duration

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balloon and PANSY radar captured the same wave packet of NIGWs until 03:00 UT on Jan.

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7. On the other hand, while the NIGWs observed over Syowa Station after 12:00 UT on Jan.

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7 did not appear to reach the position of LODEWAVE 3 in the ERA5 data, the LODEWAVE

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3 data captured near-inertial frequency oscillations. In this section, we discuss why the latter

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NIGW packet represented by ERA5 near Syowa Station was no longer represented by

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ERA5 at the position of LODEWAVE 3.

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Figure 8 shows the longitude-time section of ERA5 zonal wind at an approximate altitude

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of 18.4 km and the time variation of LODEWAVE 3 zonal wind. The ERA5 zonal wind225

disturbance at the longitude of LODEWAVE 3 (solid black line in the left panel of Fig. 8) after

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03:00 UT on Jan. 7 is not consistent with that of LODEWAVE 3 as shown in Fig. 3. However,227

it would be in good agreement with the phase of LODEWAVE 3 zonal wind when the positive

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and negative phases of ERA5 zonal wind were extended eastward. Therefore, it is10For Peer Review

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considered that the real NIGWs had a large amplitude up to the longitude region where

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LODEWAVE 3 was located, but it was not represented in ERA5.

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Figure 9 shows the filtered Brunt-Väisälä frequency squared and zonal wind in the same232

section as the left panel of Fig. 8. The Brunt-Väisälä frequency squared and zonal wind are

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filtered by a lowpass filter with a cutoff period of 24 hours and a bandpass filter with a cutoff

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period of 6-24 hours, respectively. It can be seen that the zonal wind anomaly over Syowa

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Station is extended eastward and does not enter the region where the Brunt-Väisälä

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frequency squared exceeds about 4.5×10-4 s-2. The dispersion relation for hydrostatic

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inertia-gravity waves with vertical wavelengths sufficiently shorter than the scale height is238

given by

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𝒎𝟐 =

𝑵𝟐𝒌𝟐
(𝟏)
𝝎𝟐 ― 𝒇𝟐

240(e.g., Fritts and Alexander, 2003) where 𝒌 and 𝒎 are the horizontal and vertical241

wavenumbers, respectively, and 𝑵, 𝒇, and 𝝎 are Brunt-Väisälä, inertial, and intrinsic

242

frequencies, respectively. From Eq. (1), it is considered that the vertical wavelength is243

shorter in the region with large Brunt-Väisälä frequency. In general, the wavelength of gravity

244

waves that can be resolved by the model is about 6-8 times the grid spacing, both245

horizontally and vertically (Skamarock, 2004; Skamarock et al., 2019; Klaver et al., 2020).

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Since the vertical spacing in the lower stratosphere of the model used in ERA5 is 300-400

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247m, the NIGWs with vertical wavelengths of 2.8 km over Syowa Station was probably near248

the limit of what could be resolved in ERA5. Since the Brunt-Väisälä frequency squared249

increased from 4.3×10-4 s-2 over Syowa Station to 4.5×10-4 s-2, the decrease of vertical250

wavelength is only about 100 m. However, it cannot be ruled out that the shortening of the251

vertical wavelength in the high Brunt-Väisälä frequency region may have prevented this252

inertia-gravity wave from being represented explicitly in ERA5. In addition, explicit and253

implicit diffusion in the model may have caused NIGWs with short vertical wavelengths to254

decay faster than in the real atmosphere (Polichtchouk et al., 2023). Another possibility,

255

although difficult to verify with the present data because of no observation in the vertical at256

the balloon’s position, is that the coarse vertical resolution overestimates the vertical257

wavelength of the NIGW (cf. Yoshida et al., under review), resulting in a faster upward group258

velocity of the NIGW and propagation of the wave packet above the balloon altitude.

259

It should also be noted about the effect of data assimilation. Although the PANSY radar

260

data was not assimilated into ERA5, radiosonde data twice a day at Syowa Station were261

assimilated. Therefore, it is possible that the NIGWs were reproduced only over Syowa

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Station due to data assimilation. On the other hand, Yamashita et al. (2010) compared263

satellite observations to operational analysis data with approximately the same resolution

264

and data assimilation system as ERA5 and reported that the effect of data assimilation on

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gravity waves was small. In addition, since this inertia-gravity wave packet has already266

appeared upstream (i.e., west) of Syowa Station (Fig. 8), it is unlikely that this inertia-gravity
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wave is reproduced by the data assimilation.

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5. Concluding remarks

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The first campaign observation of the LODEWAVE project, which aims to observe gravity

271

waves in the Antarctic region using long-duration balloons, was performed at Syowa Station

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from January to February 2022. Three balloons were released and one of them captured

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NIGWs at an altitude of around 18.5 km. Simultaneous PANSY radar observations also274

captured the same NIGW packets. Analysis of the NIGWs using LODEWAVE and PANSY

275

radar observations, and the latest reanalysis ERA5 datasets revealed that the two different

276

NIGW packets with an upward group velocity and vertical wavelengths of 2.4 and 2.8 km

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passed over Syowa Station and propagated northeastward and eastward, respectively,

278

during the observation period.

279

Comparison of the LODEWAVE and PANSY radar data with ERA5 showed that although

280

ERA5 was able to represent the NIGWs over Syowa Station qualitatively, it underestimated281

their amplitudes. In addition, ERA5 could not capture the latter NIGW packet at the position282

of LODEWAVE balloon. It could be because its vertical wavelength became shorter in the283high Brunt-Väisälä frequency region and was below the lower limit of vertical wavelengths

284that can be represented by ERA5, or due to explicit and implicit diffusion and/or

285

misrepresentation of the position of the NIGW packet in the model.

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In recent years, the range of resolved gravity waves has expanded as models have13Page 15 of 33

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287

become higher resolution. Although it is expected that this will avoid problems associated288with gravity wave drag parameterization (Plougonven et al., 2020), this study showed that289

even the vertical resolution of the latest reanalysis ERA5 is not always enough to explicitly290

represent NIGWs with short vertical wavelengths and their propagation in this observed

291

event. Although such NIGWs are generally observed near their critical level, an infinitesimal292

vertical resolution is theoretically required to explicitly represent them near the critical level

293(Wicker et al., 2023). In the real atmosphere, some kind of damping process will eliminate294

the need to resolve scales smaller than a certain vertical scale, but its scale has not yet been295

clarified by observations. In other words, even if much higher vertical resolution is achieved296

in the future, it will not be easy to explicitly represent the dissipation and momentum

297

deposition of gravity waves near the critical level. It will cause the momentum deposition298

and drive the meridional circulation at a different place from the real atmosphere. Therefore,299

both gravity wave drag parameterization and explicit representation of gravity waves will300

continue to be required.

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302

Data Availability Statement

303

The LODEWAVE data are available from the corresponding author on reasonable request.

304

The PANSY radar data are available from https://pansy-data.nipr.ac.jp/pansyda/home

305(accessed on 14 February 2024) upon request. The ERA5 reanalysis data on model levels

306

were provided by the European Centre for Medium-range Weather Forecasts and were14

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available at the Climate Data Store. It is not available now because of the migration of CDS

308

to a new infrastructure (accessed on 1 March 2024).

309
310

Acknowledgments

311

The LODEWAVE and PANSY radar observations at Syowa Station were conducted by312

the 63rd Japanese Antarctic Research Expedition (JARE63). It was supported by National

313

Institute of Polar Research under MEXT. This work was supported by JSPS KAKENHI Grant

314

Number 18H01276 and 21H01160. Figures were drawn using Dennou Club Library (DCL).

315
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wave momentum flux in the stratosphere. J. Atmos. Sci., 69, 3433–3448.
Hoffmann, L., R. Spang, A. Orr, M. J. Alexander, L. A. Holt, and O. Stein, 2017: A decadal

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satellite record of gravity wave activity in the lower stratosphere to study polar

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stratospheric cloud formation. Atmos. Chem. Phys., 17, 2901–2920.

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Kaho, T., Y. Saito, and Y. Tomikawa,2022: Communication Experiment of Iridium Satellite

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and Super Pressure Balloon over Antarctica. 2022 Asia-Pacific Microwave Conference

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Klaver, R., R. Haarsma, P. L. Vidale, and W. Hazeleger, 2020: Effective resolution in high361

resolution global atmospheric models for climate studies. Atmos. Sci. Lett., 21, e952,362

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Minamihara, Y., K. Sato, N. Kohma, and M. Tsutsumi, 2016: Characteristics of vertical364

wind fluctuations in the lower troposphere at Syowa Station in the Antarctic revealed by365

the PANSY radar. SOLA, 12, 116–120.

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Minamihara, Y., K. Sato, M. Tsutsumi, and T. Sato, 2018: Statistical Characteristics of17For Peer Review

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gravity waves with near-inertial frequencies in the Antarctic troposphere and lower

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stratosphere observed by the PANSY radar. J. Geophys. Res. Atmos., 123, 8993–9010.

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Minamihara, Y., K. Sato, and M. Tsutsumi, 2020: Intermittency of gravity waves in the370

Antarctic troposphere and lower stratosphere revealed by the PANSY radar observation.

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Plougonven, R., A. de la Cámara, A. Hertzog, and F. Lott, 2020: How does knowledge of373

atmospheric gravity waves guide their parameterizations?. Quart. J. Roy. Meteorol.

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Polichtchouk, I., A. van Niekerk, and N. Wedi, 2023: Resolved Gravity Waves in the376

Extratropical Stratosphere: Effect of Horizontal Resolution Increase from O(10) to O(1)377

km. J. Atmos. Sci., 80, 473–486, https://doi.org/10.1175/JAS-D-22-0138.1.

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Rabier, F., A. Bouchard, E. Brun, A. Doerenbecher, S. Guedj, V. Guidard, F. Karbou, V.

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Peuch, L. El Amraoui, D. Puech, C. Genthon, G. Picard, M. Town, A. Hertzog, F. Vial, P.

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ERA5 Reanalysis Data, J. Geophys. Res. Atmos., under review.

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List of Figures

427
428
429

Fig. 1

Overall configuration of LODEWAVE observation system.

Fig. 2(a) Trajectories and (b) time variations of altitude of LODEWAVE 1, 2, and 3. The

430
431
432

bottom axis in (b) represents the elapsed day since the date of balloon release.

433
434

Fig. 3Time variations of zonal (black) and meridional (red) winds along trajectories of

435

LODEWAVE 3. Solid and dashed lines represent LODEWAVE and ERA5 data,

436

respectively.

437
438
439

Fig. 4Same as Fig. 3 except that dashed lines represent the PANSY radar data at analtitude of 18.5 km.

440
441
442

Fig. 5Time-height sections of zonal (a, c) and meridional (b, d) winds from the PANSY

radar (a, b) and ERA5 (c, d).

443
444

Fig. 6

Hodographs (a) with height obtained by the PANSY radar and (b) with time at an

445

altitude of about 18.5 km obtained by LODEWAVE 3. LODEWAVE 3 data are filtered by446

a lowpass filter with a cutoff period of 6 hours. Solid circles represent initial height (a)21For Peer Review

Page 23 of 33447

and time (b).

448
449

Fig. 7

Polar projection maps of zonal wind, which is filtered by a bandpass filter with450

cutoff periods of 6 and 24 hours, at an approximate altitude of 18.4 km from ERA5 (a-d)

451from 15 UT on 6 Jan. to 00 UT on 7 Jan. and (e-h) from 00 UT to 09 UT on 8 Jan. 2022.

452

Black and red stars denote Syowa Station and LODEWAVE 3, respectively. Red and453

blue solid lines indicate positive and negative phases of the zonal wind anomalies454

around Syowa Station, respectively.

455
456

Fig. 8(Left) longitude-time section of zonal wind at 69.0°S and an approximate altitude of457

18.4 km from ERA5 and (right) time variation of zonal wind obtained by LODEWAVE 3.

458

Solid and dashed lines in the left panel represent the longitudes of LODEWAVE 3 and459

Syowa Station (39.6°E), respectively.

460
461

Fig. 9Filtered Brunt-Väisälä frequency squared (colors) and zonal wind (contours) from462

ERA5 in the same section as the left panel of Fig. 8. Brunt-Väisälä frequency squared463

and zonal wind are filtered by a lowpass filter with a cutoff period of 24 hours and a464

bandpass filter with a cutoff period of 6-24 hours, respectively. Contour intervals are 1465

ms-1. Contour of 0 ms-1 is omitted. Negative values are dashed.

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467
468

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Fig. 1

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470

Fig. 1

Overall configuration of LODEWAVE observation system.

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Fig. 2

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473
474

Fig. 2(a) Trajectories and (b) time variations of altitude of LODEWAVE 1, 2, and 3. The

bottom axis in (b) represents the elapsed day since the date of balloon release.

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Fig. 3476
477

Fig. 3Time variations of zonal (black) and meridional (red) winds along trajectories of478

LODEWAVE 3. Solid and dashed lines represent LODEWAVE and ERA5 data,479

respectively.

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Fig. 4

481
482
483

Fig. 4Same as Fig. 3 except that dashed lines represent the PANSY radar data at analtitude of 18.5 km.

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Fig. 5

485
486
487

Fig. 5Time-height sections of zonal (a, c) and meridional (b, d) winds from the PANSY

radar (a, b) and ERA5 (c, d).

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Fig. 6489
490

Fig. 6

Hodographs (a) with height obtained by the PANSY radar and (b) with time at an

491

altitude of about 18.5 km obtained by LODEWAVE 3. LODEWAVE 3 data are filtered by492

a lowpass filter with a cutoff period of 6 hours. Solid circles represent initial height (a)493

and time (b).

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Fig. 7495
496

Fig. 7

Polar projection maps of zonal wind, which is filtered by a bandpass filter with497

cutoff periods of 6 and 24 hours, at an approximate altitude of 18.4 km from ERA5 (a-d)

498from 15 UT on 6 Jan. to 00 UT on 7 Jan. and (e-h) from 00 UT to 09 UT on 8 Jan. 2022.

499

Black and red stars denote Syowa Station and LODEWAVE 3, respectively. Red and500

blue solid lines indicate positive and negative phases of the zonal wind anomalies

501

around Syowa Station, respectively.

502

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Fig. 8503
504

Fig. 8(Left) longitude-time section of zonal wind at 69.0°S and an approximate altitude of505

18.4 km from ERA5 and (right) time variation of zonal wind obtained by LODEWAVE 3.

506

Solid and dashed lines in the left panel represent the longitudes of LODEWAVE 3 and507

Syowa Station (39.6°E), respectively.

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Fig. 9509
510

Fig. 9Filtered Brunt-Väisälä frequency squared (colors) and zonal wind (contours) from511

ERA5 in the same section as the left panel of Fig. 8. Brunt-Väisälä frequency squared

512

and zonal wind are filtered by a lowpass filter with a cutoff period of 24 hours and a513

bandpass filter with a cutoff period of 6-24 hours, respectively. Contour intervals are 1514

ms-1. Contour of 0 ms-1 is omitted. Negative values are dashed.

515

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