The diurnal cycle of precipitation over the Maritime Continent

Mustafa, Jack Michael (2024) The diurnal cycle of precipitation over the Maritime Continent. Doctoral thesis, University of East Anglia.

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The archipelago straddling the equator between the Indian and Pacific Oceans, known as the Maritime Continent (MC), is a broad region experiencing very high mean precipitation rate. Powerful global circulation cells are driven by the significant latent heat released over the MC. As such, variability of precipitation over the MC has widespread implications for global weather.

The dominant source of precipitation variability over the MC is the diurnal cycle (DC). As the spatio-temporal resolution of satellite-derived precipitation data products continues to improve it is becoming possible to characterise the DC in increasing detail. The first diurnal harmonic (FDH) waveform becomes an increasingly insufficient approximation of the 24-hour variability as complex DC characteristics are increasingly resolved. In order to characterise rapid changes in precipitation rate within the DC, such as the rapid intensification typical over land in the afternoon, the characterisation of the DC with waveforms more complex than the FDH is explored. The amplitudes of the complex waveforms are shown to be a more reliable indicator of the magnitude of diurnal variability than the amplitude of the FDH, and the phases of the complex waveforms offer a more reliable indication of the time of peak precipitation. These new parameters offer a more detailed framework with which a modelled DC may be assessed.

The simulated DC of precipitation in convection-parametrised (MC12) and convection-permitting (MC2) configurations of the Met Office Unified Model are analysed in the newly-developed characterisation framework. The nature of the DC is generally accurate in MC2, however the DC phase is several hours too early in MC12, as in many convection-parametrised models. These results demonstrate the capacity for skillful simulation of diurnal variability in a convection-permitting model without significant influence of boundary forcing.

The DC is shown to strengthen and weaken, slightly ahead of large-scale precipitation variability associated with the Madden-Julian Oscillation (MJO), an intra-seasonal mode of variability featuring eastward propagation of a large-scale convective envelope across the Indian and Pacific Oceans. Systematic shifts in the phase of the DC of up to four hours are observed in some locations, with westward (eastward) propagation of precipitation favoured before (after) the passage of the MJO over the MC. A resultant west–east phase regime divide is identified over the large islands and certain seas.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Nicola Veasy
Date Deposited: 08 Jul 2024 13:56
Last Modified: 08 Jul 2024 13:56


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