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| Titel |
Radiosonde observations of mid-latitude planetary waves in the lower atmosphere over America and China |
| VerfasserIn |
Rui Wang, Shaodong Zhang, Jinsong Ping |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046744
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| Zusammenfassung |
| Planetary waves (PWs) are important atmospheric oscillations with periods from several days
to several dozens of days, and their zonal wavelengths range from several thousand to ten
thousand kilometers with zonal wave numbers between 1 and 5 in general. Therefore, they
are called planetary waves, as their horizontal sizes are as large as global radius. PWs are
mainly excited in the troposphere by topography and by diabatic heating associated with land
and sea thermal contrast. In certain conditions, PWs will propagate to the middle
atmosphere and play an important role in regulating middle atmosphere circulation and
constituent distribution, such as ozone. PWs are usually observed with different
oscillation periods mainly around 2, 5, 10, and 16 days. Quasi 2-day wave is a
Rossby-gravity wave with period about 2-4 days, whereas quasi 5-, 10-, and 16-day
waves are all Rossby waves whose periods are 4.5-6.2, 7.5-12, and 11-20 days,
respectively.
The characteristics of mid-latitude PWs in the troposphere and lower stratosphere (TLS)
are studied by both statistical and case studies with the data from radiosonde observations at
three middle latitude stations (Miramar Nas, 32.9Ë N, 117.2Ë W; Santa Teresa, 31.9Ë
N, 106.7Ë W; Fort Worth, 32.8Ë N, 97.3Ë W) in America and Wuhan (30.5Ë N,
114.4Ë E) in China. It is found that mid-latitude PWs exist in two regions. One is in
the troposphere, and the other is in the stratosphere. The PW activities are rather
intermittent, and their lifetimes are not longer than two months. In the troposphere, among
three perturbation components in zonal and meridional winds and temperature, the
temperature disturbance amplitude is the smallest, and the amplitude for the zonal and
meridional wind components are comparable. The amplitudes of the mid-latitude PWs
reach maximum round the center of the subtropical jet stream in winter, which
indicates the subtropical jet stream may be one of the PW excitation sources. Around
the subtropical jet stream, quasi 5, 10, and 16 -day PW activities can be observed
simultaneously at three American stations. Among these PW components, the quasi
5-day and 10-day PW are the weakest and strongest, respectively. While at Wuhan
station in China, quasi 5-day PW are much weaker than quasi 10-day and 16-day
PWs.
However, in the stratosphere, the higher region, only quasi 10-day and 16-day PWs
remain in winter, with the zonal component strongest, which amplitudes are smaller than
those in the troposphere. By calculating the refractive index for PWs, it is found that there is a
persistent reflection layer near tropopause, which is thick in summer and becomes thin or
even disappears in winter, revealing that Low-frequency planetary waves are easier to
propagate into the stratosphere through this reflection layer, and PWs in the stratosphere can
only occur in winter.
PWs in the 2000/2001 winter at the four stations are analyzed in detail. It is found
that for the focused observation duration, strong quasi 16-day waves exist both in
the troposphere and stratosphere. The quasi 16-day wave in the troposphere is a
standing wave in the vertical direction, with vertical wavelength larger than 26
km in the meridional component. Moreover, the tropospheric quasi 16-day wave
propagates eastward with the zonal numbers between 5 and 8. Especially, the quasi
16-day wave in Wuhan around the subtropical jet stream is probable the same quasi
16-day wave at the three American stations, which steadily propagates around the
latitude.The quasi 16-day wave in the stratosphere is also a quasi-standing wave
in the vertical direction with vertical wavelength larger than 10 km in the zonal
component. But it propagated westward with the zonal numbers between 1 and 2. |
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