15:45 〜 16:00
[PEM15-14] An analysis of wind fields in the mesosphere at high latitude in the Southern Hemisphere based on the long-term PANSY radar observations
キーワード：中間圏、南極、大型大気レーダー
1. Introduction
In the mesosphere, it is known that there is a residual mean circulation that is upwelling at high latitudes in the summer hemisphere, moving toward the winter hemisphere, and downwelling at high latitudes in the winter hemisphere (Plumb, 2002). This meridional circulation is mainly driven by forcing due to absorption at critical levels and breaking of gravity waves (McIntyre, 1989). Atmospheric tides are also known to contribute significantly to wind variations (e.g. Andrews et al., 1987).
Meteor radar and MF radar observations are useful for the analysis of mean winds because they can provide continuous wind data for long periods in the mesosphere including studies at high latitudes (e.g. Vincent, 1994; Dowby et al., 2007).
In this study, we analyzed wind fields based on the long-term continuous observations by the PANSY radar at the Syowa Station (69°S, 40°E) (Sato et al., 2014), which is the first and only large-scale atmospheric radar in the Antarctic, to reveal the seasonal variation of wind fields in the mesosphere at high latitudes in the Southern Hemisphere.
2. Data and Methodology
The PANSY radar provides winds estimated from turbulence echo such as the polar mesospheric summer echoes (PMSE) and polar mesospheric winter echoes (PMWE) and from meteor echo simultaneously. The turbulence echo observations provide 3-dimensional winds and the meteor echo observations provide horizontal winds. In this study, we used data based on turbulence echo observations from October 2015 to May 2023 and meteor echo observations from March 2021 to June 2023. In addition, we obtained the climatology of 3-dimensional winds from the long-term JAGUAR-DAS (Koshin et al., 2020; Koshin et al., 2022a) reanalysis data for the whole middle atmosphere from October 2015 to May 2023 and compared it with the observations. In this presentation, the months from November to February are described as summer and the remaining period as winter.
3. Results
The meteor echo observations show that the zonal wind is westward (eastward) in summer (winter) below approximately z=97 km. The zonal wind changes from westward to eastward as the 0 m/s line gradually descends from z=95 km in summer. A vertical change in the zonal wind direction is also observed in winter near z=97 km. The meridional wind is northward in summer with a maximum at z=90–95 km in December. In winter, it is generally southward, but weaker than the northward wind in summer, with some periods of northward wind.
Zonal wind characteristics from turbulence echo observations are in good agreement with those from the meteor echo observations. The maximum of the eastward wind in winter is below z=70 km. The meridional wind is southward in winter below approximately z=65 km. The height of the 0 m/s line is near z=80 km except in March, April, September, and October. The vertical wind is downward below z=70 km from April to November, but interestingly it is upward in the range of z=75–85 km from March to November. The vertical wind is negative in the range of z=80–95 km in summer, which may be due to the downwelling of polar mesospheric clouds (PMC) structure.
We also show the JAGUAR-DAS result compared to the observations in the presentation.
In the mesosphere, it is known that there is a residual mean circulation that is upwelling at high latitudes in the summer hemisphere, moving toward the winter hemisphere, and downwelling at high latitudes in the winter hemisphere (Plumb, 2002). This meridional circulation is mainly driven by forcing due to absorption at critical levels and breaking of gravity waves (McIntyre, 1989). Atmospheric tides are also known to contribute significantly to wind variations (e.g. Andrews et al., 1987).
Meteor radar and MF radar observations are useful for the analysis of mean winds because they can provide continuous wind data for long periods in the mesosphere including studies at high latitudes (e.g. Vincent, 1994; Dowby et al., 2007).
In this study, we analyzed wind fields based on the long-term continuous observations by the PANSY radar at the Syowa Station (69°S, 40°E) (Sato et al., 2014), which is the first and only large-scale atmospheric radar in the Antarctic, to reveal the seasonal variation of wind fields in the mesosphere at high latitudes in the Southern Hemisphere.
2. Data and Methodology
The PANSY radar provides winds estimated from turbulence echo such as the polar mesospheric summer echoes (PMSE) and polar mesospheric winter echoes (PMWE) and from meteor echo simultaneously. The turbulence echo observations provide 3-dimensional winds and the meteor echo observations provide horizontal winds. In this study, we used data based on turbulence echo observations from October 2015 to May 2023 and meteor echo observations from March 2021 to June 2023. In addition, we obtained the climatology of 3-dimensional winds from the long-term JAGUAR-DAS (Koshin et al., 2020; Koshin et al., 2022a) reanalysis data for the whole middle atmosphere from October 2015 to May 2023 and compared it with the observations. In this presentation, the months from November to February are described as summer and the remaining period as winter.
3. Results
The meteor echo observations show that the zonal wind is westward (eastward) in summer (winter) below approximately z=97 km. The zonal wind changes from westward to eastward as the 0 m/s line gradually descends from z=95 km in summer. A vertical change in the zonal wind direction is also observed in winter near z=97 km. The meridional wind is northward in summer with a maximum at z=90–95 km in December. In winter, it is generally southward, but weaker than the northward wind in summer, with some periods of northward wind.
Zonal wind characteristics from turbulence echo observations are in good agreement with those from the meteor echo observations. The maximum of the eastward wind in winter is below z=70 km. The meridional wind is southward in winter below approximately z=65 km. The height of the 0 m/s line is near z=80 km except in March, April, September, and October. The vertical wind is downward below z=70 km from April to November, but interestingly it is upward in the range of z=75–85 km from March to November. The vertical wind is negative in the range of z=80–95 km in summer, which may be due to the downwelling of polar mesospheric clouds (PMC) structure.
We also show the JAGUAR-DAS result compared to the observations in the presentation.