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| Titel |
Diurnal cycle of precipitation observed in the western coastal area of Sumatra Island, Indonesia: offshore preconditioning by gravity waves |
| VerfasserIn |
Satoru Yokoi, Shuichi Mori, Masaki Katsumata, Biao Geng, Kazuaki Yasunaga, Fadli Syamsudin, Nurhayati Nurhayati, Kunio Yoneyama |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140076
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| Publikation (Nr.) |
 EGU/EGU2017-3414.pdf |
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| Zusammenfassung |
| In November and December of 2015, we conducted a field campaign, named Pre-YMC
(Years of the Maritime Continent), in the western coastal area of Sumatra Island, during
which we performed weather radar observation, 3-hourly radiosonde observation, and so
forth, at the Research Vessel Mirai, deployed about 50 km off the coast, and at a
coastal city, Bengkulu. Diurnal cycle of precipitation observed during the campaign
period is found to have many similarities with statistical behavior of the diurnal
cycle as revealed by previous studies, such as afternoon precipitation peak over
land and nighttime offshore migration of precipitation zone. Composite analyses
of radiosonde data demonstrate that, over the vessel, the lower free troposphere
starts cooling in late afternoon, a couple of hours earlier than the boundary layer
does, making the lower troposphere thermally more unstable before the arrival of
the precipitation zone. As the nighttime offshore precipitation tends to be more
vigorous on days when this cooling is larger, the destabilization probably contributes to
the offshore migration of the precipitation zone via enhancement of convective
activity. We also find that this cooling is substantially due to vertical advection by an
ascent motion, which is possibly a component of shallow gravity waves. These
observational results support the idea that gravity waves excited by convective systems
over land play a significant role in the offshore migration of the precipitation zone. |
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