Inertio-Gravity Waves and Subtropical Multiple Tropopauses:
Vertical Wavenumber Spectra of Wind and Temperature Observed by
the MU Radar, Radiosondes and Operational Rawinsonde Network

Yoshiaki Shibagaki, Yasuyuki Maekawa
Osaka Electro-Communication University, Neyagawa, Osaka 572, Japan

Izuru Takayabu National Meteorological Center, NOAA, Washington DC 20233, USA

Journal of Atmospheric and Terrestrial Physics , Vol. 58 , No.6, pp.785-805

Extended from Paper GW-6 (Original title: Meteorological Processes and Troposphere-Stratosphere Interactions Revealed by MST Radar Techniques) presented at the Workshop on Dynamics and Coupling of Ionosphere, Middle and Lower Atmosphere in the 26th URSI General Assembly, Kyoto, Japan, 1 September 1993.
Submitted: January 31, 1994; Received: February 7, 1994;
First Revision: October 31, 1994; Second Revision: December 18, 1994;
Received: January 13, 1995; Accepted: January 20, 1995
Published: April, 1996

1. Introduction

2. Three-Week MU Radar Observation Campaign and Routine Rawinsonde Data

3. Mean Tropopause Gap and Multiple Tropopauses

4. Spectral and Monochromatic Analyses of Horizontal Wind Observed by the MU Radar

5. Temperature and Horizontal Wind Spectra Obtained from Radiosonde/Rawinsonde Data

6. Conclusion

Appendix: Quasi-Monochromatic Formulation of Wave Energy

• Fig. 1. Location of the MU radar observatory (MUR) in Shigaraki and five JMA stations providing rawinsonde data used in this study: Sapporo (47412), Akita (47582), Wajima (47600), Shionomisaki (47778) and Minamidaitojima (47945). `Meridional' cross-sections shown in this paper (Figs.\ 2,\ 6 and 7) are taken along the baseline $AA'$, which is the same as in Fukao {\it et al.}\ (1988,\ 1991), Larsen {\it et al.}\ (1991), Yamanaka (1992a) and Yamanaka and Fukao (1994b).
• Fig. 2 Mean meridional-vertical cross-sections of (a) zonal wind and (b) temperature fields, averaged for the whole observational period (17 June-8 July 1991). Data of the MU radar (30-min averaged) and radiosondes (every 12 hours) at Shigaraki and of rawinsondes (every 12 hours) at the five JMA stations shown in Fig.\ 1 were used. The altitude range (15-19 km) mainly analyzed in this study is hatched in the both panels.
• Fig. 3 Temporal-vertical cross-sections for zonal wind observed during 17 June-8 July 1991 by the MU radar at Shigaraki (30-min average of data taken every 3 min) and by rawinsondes at the five JMA stations (every 12 hours) shown in Fig.\ 1. The tropopause levels defined along the WMO guideline are also plotted by cross signs.
• Fig. 4 Same as Fig.\ 3 but for meridional wind.
• Fig. 5 Temporal-meridional cross-section for horizontal wind speed at an altitude of 12 km during the observational period (17 June-8 July 1991). Data shown in Figs.\ 3 and 4 were used. The latitude of Baiu front at 136\degr E is also plotted by a thick curve with dots.
• Fig. 6 Same as Fig.\ 3 but for equivalent potential temperature calculated from temperature and humidity data obtained by radiosondes (VAISALA RS80) at Shigaraki and by rawinsondes (Meisei RS2-80) at the five JMA stations.
• Fig. 7 Meridional-vertical cross-sections of pseudo-adiabats (thin solid contours; every 5 K), zonal isotachs (broken contours; every 10 m/s), tropopausal and frontal surfaces (thick solid curves) and other temperature significant levels (thick broken curves), based on the same database as used in Figs.\ 3-5. The analysis was done every 12 hours for the whole observational period, but here the results only for 09 LT (00 UT) everyday until 7 July are shown.
• Fig. 8 Profiles of vertically $\sim 2$ km band-passed data of zonal (thin solid) and meridional (dashed) winds observed by the MU radar and temperature (thick solid) observed by radiosondes simultaneously at Shigaraki. The first tropopause levels defined along the WMO guideline and the zonal velocity maximum levels are indicated by horizontal dashed and solid lines, respectively.
• Fig. 9 Vertical wavenumber spectra of zonal wind observed by the MU radar in 15-19 km altitude range. The analysis was done by calculating medians every 1 hour from 48 spectra (each analyzed from the same database as used for panels of Shigaraki in Figs.\ 3 and 4) obtained during $\pm 12$ hours before and after, but here the results only every 16 hours are shown. The `universal' $-3$ slope is indicated by dashed lines.
• Fig. 10 Same as Fig.\ 9 but for meridional wind.
• Fig. 11 Hodographs of horizontal wind velocity analyzed from 1-hour averaged MU radar data for 15-19 km altitude range. The analysis was done every 1 hour during the whole observational period, but here examples only for the first day (17 June) are shown.
• Fig. 12 Temporal variations of intrinsic frequency ($\hat{\omega}_{*}$) and vertical wavelength ($m_{*}$) for the dominant mode of inertio-gravity waves in the tropopause region (15-20 km altitudes), compared with the scalar kinetic energy ($E$) and the maximum horizontal wind speed ($U$) of the tropopausal westerly jet stream. Results obtained from the spectral and hodograph analyses (partly shown in Figs.\ 9-11) are 24-hour running-averaged.
• Fig. 13 Mean vertical wavenumber spectra of (a) zonal and (b) meridional winds and (c) temperature for 15-19 km altitude range, averaged for the whole observational period (17 June-8 July 1991). Data of the MU radar (30-min averaged) and radiosondes (every 12 hours) at Shigaraki and of rawinsondes (every 12 hours) at the five JMA stations shown in Fig.\ 1 were used without any modifications. A model given by $F = N^{2} / 6 m^{3}$ with $N = 1 / (5$ min) is also indicated by dashed-dotted lines.
• Fig. 14 Same as Figs.\ 13 (a) and (b), but multiplied a factor (see text) with rawinsonde data spectra in order to recover the attenuation due to a running-average in routine operations.

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