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| Titel |
Long-term behavior of the Kelvin waves revealed by CHAMP/GPS RO measurements and their effects on the tropopause structure |
| VerfasserIn |
M. Venkat Ratnam, T. Tsuda, T. Kozu, S. Mori |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 24, no. 5 ; Nr. 24, no. 5 (2006-07-03), S.1355-1366 |
| Datensatznummer |
250015552
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| Publikation (Nr.) |
 copernicus.org/angeo-24-1355-2006.pdf |
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| Zusammenfassung |
| The vertical and temporal variations of Kelvin waves and the associated
effects on the tropical tropopause were studied using long-term (from May
2001 to October 2005) CHAMP/GPS (CHAllenging Mini satellite Payload/Global
Positioning System) radio occultation (RO) measurements. The periods of
these waves were found to be varying in between 10 and 15 days, with vertical
wavelengths 5–8 km. These variations clearly show eastward phase propagation
in the time-longitude section and eastward phase tilts with height in
altitude-longitude, displaying the characteristics of Kelvin waves. The peak
variance in the temperature is found over the Indian Ocean and into the
western Pacific within the broad region of the equator. Kelvin wave
amplitudes were found significantly enhanced in the eastward shear of
the quasi-biennial oscillation (QBO) and are confined in and around the tropopause
during westward phase of QBO, where it extends between 17 and 25 km during
the eastward phase of QBO and is damped away above, consistent with earlier
reported results. The amplitudes are increasing during the months of
Northern Hemisphere winter and sometimes they are highly sporadic in nature.
Seasonal and inter-annual variations in the Kelvin wave amplitudes near
the tropical tropopause coincide exactly with the tropopause height and
temperature, with a sharp tropopause during maximum Kelvin wave activity. A
clear annual oscillation, along with a month-to-month coincidence is evident
most of the time in both the tropopause height and Kelvin wave activity, with
maximum and minimum Kelvin wave amplitudes during the Northern Hemisphere winter
and summer, respectively. In addition, a signature of quasi-biennial
oscillation (QBO) in the tropopause structure is also seen in long-term
tropopause variations, although the amplitudes are less when compared to
the annual oscillation. In the westward phase of QBO (during strong Kelvin wave
activity) at 20km (in 2001–2002 winter and 2003–2004 winter), the
tropopause height was slightly larger with a sharp tropopause and low
temperature. The process behind these observed features has been discussed. |
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