The Madden-Julian Oscillation and the diurnal cycle over the Maritime Continent: scale interactions and modelling

Peatman, Simon (2014) The Madden-Julian Oscillation and the diurnal cycle over the Maritime Continent: scale interactions and modelling. Doctoral thesis, University of East Anglia.

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Abstract

The Maritime Continent archipelago, situated on the equator at 95°–165°E,
has the strongest land-based precipitation on Earth. The latent heat release
associated with the rainfall affects the atmospheric circulation throughout the
tropics and into the extra-tropics.
The greatest source of variability in precipitation is the diurnal cycle.
The archipelago is within the convective region of the Madden-Julian
Oscillation (MJO), which provides the greatest variability on intra-seasonal
time scales: large-scale (�107 km2) active and suppressed convective envelopes
propagate slowly (�5 m s-1) eastwards between the Indian and Pacific Oceans.
High-resolution satellite data show that a strong diurnal cycle is triggered to the
east of the advancing MJO envelope, leading the active MJO by one-eighth of an
MJO cycle (�6 days). Where the diurnal cycle is strong its modulation accounts
for 81% of the variability in MJO precipitation. Over land this determines
the structure of the diagnosed MJO. This is consistent with the equatorial
wave dynamics in existing theories of MJO propagation. The MJO also affects
the speed of gravity waves propagating offshore from the Maritime Continent
islands. This is largely consistent with changes in static stability during the MJO
cycle.
The MJO and its interaction with the diurnal cycle are investigated in
HiGEM, a high-resolution coupled model. Unlike many models, HiGEM
represents the MJO well with eastward-propagating variability on intra-seasonal
time scales at the correct zonal wavenumber, although the inter-tropical
convergence zone’s precipitation peaks strongly at the wrong time, interrupting
the MJO’s spatial structure. However, the modelled diurnal cycle is too weak
and its phase is too early over land. The modulation of the diurnal amplitude
by the MJO is also too weak and accounts for only 51% of the variability in MJO
precipitation.
Implications for forecasting and possible causes of the model errors are
discussed, and further modelling studies are proposed.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Mathematics
Depositing User: Mia Reeves
Date Deposited: 13 Jun 2014 08:33
Last Modified: 13 Jun 2014 08:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/48786
DOI:

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