Influence of Subseasonal Variability on the Diurnal Cycle of Precipitation on a Mountainous Island: The Case of New Caledonia

Abstract

The relationship between the large-scale intraseasonal variability, synoptic wind regimes, and the local daily variability of precipitation over the main island of New Caledonia (southwest tropical Pacific) is investigated with a focus on the austral summer wet season (November–April). The average diurnal cycle of precipitation over the island is characterized by a sharp afternoon maximum around 1600 local time, with significant differences between the windward east coast, the leeward west coast, and the mountain range. The afternoon peak is related to the afternoon sea-breeze circulation and to the diurnal cycle of convection over land. In general, its magnitude follows the same evolution as the daily mean. In agreement with past studies, a clear modulation of the Madden–Julian oscillation (MJO) on both the diurnal cycle of precipitation and the probability of occurrence of four robust wind regimes can be identified in the New Caledonia region during the wet season. From the evidence that there is a qualitative correspondence between the effects of both the MJO phases and the wind regimes on features in the diurnal cycle of precipitation, a simple model is proposed to inspect the MJO forcing mediated by wind regimes on the diurnal variability of rain. The complete decomposition of the MJO impact shows that the modulation of diurnal cycle by the MJO relies on complex interactions between the MJO and synoptic winds that involve both large-scale MJO convective anomalies and MJO-induced modification of wind patterns.

Fine-scale rainfall over New Caledonia under climate change

“…A classification of the warm season weather regimes yielded four dominant weather regimes that are consistent with previous studies (Leroy 2006;Lefèvre et al 2010;Specq et al 2019). Regime 3, which corresponds to a strong trade winds regime, accounted for 83% of the NDJFMA precipitation decrease but without changes in wind direction, suggesting a dominance of changes in the synoptic circulation associated to large-scale moisture convergence rather that of local effects induced by orography.…”

“…The 'NbClust' function in the factoextra R package allows comparing the results from 26 different methods (Charrad et al 2014). The 4 clusters presented here correspond to a consensus between these 26 methods (16 methods suggest 3 or 4 clusters, with 4 being the most common result, not shown), in agreement with the studies of Lefèvre et al (2010), Leroy (2006) and Specq et al (2019). We then produced precipitation composites for each regime.…”

Active and weakening MJO events in the Maritime Continent

“…In addition to horizontal differences in the structure and amplitude of OLR, and horizontal and vertical differences in specific humidity, differences in the diurnal cycle of specific humidity in the lower troposphere between active and weakening MJO were examined in hourly values of specific humidity from ERA5. It is important to note here that while many MJO studies have examined the diurnal cycle of precipitation, particularly comparing over-land to over-water convection (e.g., Tian et al 2006;Rauniyar and Walsh 2011;Oh et al 2012Oh et al , 2013Virts et al 2013;Peatman et al 2015;Hagos et al 2016;Tan et al 2018Tan et al , 2021Specq et al 2020), here we examined the diurnal cycle of specific humidity in the lower troposphere (1000-700 hPa) over the MC (10° S-10° N, 100°-150° E; see the boxed region in Fig. 5a).…”

Characterization of south central Pacific Ocean wind regimes in present and future climate for pearl farming application

“…As they characterize robust yet simplified wind patterns, they have been used for example to study typical fish larval dispersion in the New Caledonian lagoon (Cuif et al, 2014). In addition, three recent studies (Hopuare et al, 2019;Lorrey and Fauchereau, 2018;Specq et al, 2019) have characterized regional WRs in the South Pacific, and studied how the large-scale signals of the Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO) modulate the frequency of occurrence of these WRs. These three studies each considered a different spatial domain, but none of them covered all of the atolls of French Polynesia and Cook Islands.…”

“…In the present study, we use a methodology similar to Hopuare et al, (2019) and Specq et al, (2019) to calculate WRs, but we considered all the South-central Pacific, and projected the presentday WRs into future conditions. To that end, regional atmospheric simulations are performed with the Weather Research and Forecast (WRF) model for present day, and for the end of the 21 st century under RCP.8.5 scenario.…”