1. Large‐Amplitude Inertia Gravity Waves Over Syowa Station: Comparison of PANSY Radar and ERA5 Reanalysis Data.
- Author
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Yoshida, L., Tomikawa, Y., Ejiri, M. K., Tsutsumi, M., Kohma, M., and Sato, K.
- Subjects
GRAVITY waves ,PHASE velocity ,POWER spectra ,WIND power ,ATMOSPHERIC models - Abstract
We examined large‐amplitude inertia gravity waves (GWs) over Syowa Station, Antarctica using the PANSY (Program of the Antarctic Syowa MST/IS) radar data and the latest reanalysis (ECMWF reanalysis v5; ERA5) from October 2015 to September 2016. Focusing on large‐amplitude events with large absolute momentum flux (AMF), hodograph analysis was applied to both data to estimate the wave parameters. It showed that the inertia GWs with a downward phase velocity becomes dominant in the stratosphere. Although their vertical wavelengths got shorter with altitude, their intrinsic periods and horizontal wavelengths got longer with altitude. In addition, their southward propagation was predominant in the stratosphere. Although height dependence of the estimated wave parameters is consistent with previous studies investigating inertia GWs over Syowa Station, some features specific to large‐amplitude inertia GWs were also observed. The GW features obtained from PANSY were mostly consistent with those from ERA5 except for their amplitudes. Comparison of AMF between PANSY and ERA5 indicated that ERA5 significantly underestimated the AMF by a factor of 5 between 5 and 12.5 km altitudes and more above 12.5 km. Difference of horizontal and vertical wind power spectra between PANSY and ERA5 is quantitatively consistent with the difference of AMF and its height dependence. It was found that underestimation of vertical wind spectra primarily contributed to the underestimation of AMF in ERA5. The greater underestimation of AMF in the stratosphere might be due to larger vertical grid spacing in ERA5 and the shorter vertical wavelengths of the dominant GWs in the stratosphere. Plain Language Summary: Gravity waves (GWs) are important waves that transport momentum and energy in the atmosphere but it is known that atmospheric reanalysis data cannot adequately represent them. In this study, we compared the PANSY (Program of the Antarctic Syowa MST/IS) radar, which can capture gravity waves over almost the entire frequency range above Syowa Station over Antarctica with the latest atmospheric reanalysis ERA5 (ECMWF Reanalysis v5), which has high spatiotemporal resolution to determine the extent to which ERA5 can represent gravity waves. The results showed that ERA5 reproduced the properties of gravity waves (i.e., wavelength and direction of propagation) fairly well but underestimated the momentum flux of gravity waves by a factor of about five in the troposphere and more than that in the stratosphere. Furthermore, a comparison of their spectra quantitatively revealed that the underestimation of momentum flux in ERA5 is mainly due to the underestimation of the vertical wind disturbances and high‐frequency components by ERA5. These results indicate that state‐of‐the‐art atmospheric reanalysis is a useful tool for understanding the nature of gravity waves and that further improvement of the resolution of the models used in atmospheric reanalysis is necessary for a quantitative understanding of gravity waves. Key Points: We investigate the large‐amplitude gravity wave events over Syowa Station, Antarctica using PANSY radar and ERA5 reanalysisThe absolute momentum flux from ERA5 is smaller than the observed one by a factor of 5 at 5–12.5 km altitudes and even smaller above thatUnderestimation of absolute momentum flux in ERA5 can be explained by the underestimation of the power spectra of horizontal and vertical winds [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
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