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| Titel |
Moist convection and its upscale effects in simulations of the Indian summer monsoon with explicit and parametrised convection |
| VerfasserIn |
Peter Willetts, John Marsham, Cathryn Birch, Doug Parker, Stuart Webster, Jon Petch |
| 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 |
250149991
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| Publikation (Nr.) |
 EGU/EGU2017-14407.pdf |
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| Zusammenfassung |
| In common with many global models, the Met Offce Unified Model
(MetUM) climate simulations show large errors in Indian summer monsoon
rainfall, with a wet bias over the equatorial Indian Ocean, a dry bias over
India, and with too weak low-level flow into India. The representation of
moist convection is a dominant source of error in global models, where
convection must be parametrised, with the errors growing quickly enough
to affect both weather and climate simulations. Here we use the first multi-
week continental-scale MetUM simulations over India, with grid-spacings
that allow explicit convection, to examine how convective parametrisation
contributes to model biases in the region.
Some biases are improved in the convection-permitting simulations with
more intense rainfall over India, a later peak in the diurnal cycle of
convective rainfall over land, and a reduced positive rainfall bias over the
Indian Ocean. The simulations suggest that the reduced rainfall over the
Indian Ocean leads to an enhanced monsoon circulation and transport of
moisture into India. Increases in latent heating associated with increased
convection over land deepen the monsoon trough and enhance water vapour
transport into the continent. In addition, delayed continental convection
allows greater surface insolation and, along with the same rain falling in
more intense bursts, generates a drier land surface. This increases land-sea
temperature contrasts, and further enhances onshore flow. Changes in the
low-level water vapour advection into India are dominated by these changes
to the flow, rather than to the moisture content in the flow. The results
demonstrate the need to improve the representations of convection over
both land and oceans to improve simulations of the monsoon. |
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