The diurnal cycle of precipitation over the Maritime Continent in a high‐resolution atmospheric model

Abstract

Climate models can exhibit systematic errors in their mean precipitation over the Maritime Continent of the Indonesian archipelago at the heart of the tropical warm pool. These can often be traced back to an erroneous simulation of the diurnal cycle, and can lead to errors in global climate, through planetary wave propagation. Here, we examine the simulation of the diurnal cycle over the Maritime Continent in a series of high-resolution integrations of the UK Met Office atmospheric model, with horizontal resolutions of 40 and 12 km (where the convection is parametrised) and 4 km (where the convection is explicitly resolved), as part of the Cascade project. In these models, the vertical heating profile over the islands changes from a convective profile with a mid-tropospheric maximum in the early afternoon to a more stratiform profile with upper-tropospheric heating and mid-tropospheric cooling later. The convective heating profile forces a first internal mode gravity wave that propagates rapidly offshore; the deep warm anomalies behind its downwelling wavefront suppress convection offshore during early afternoon. The stratiform heating profile forces a gravity wave with a higher-order vertical mode that propagates slowly offshore later in the afternoon. This mode has a negative, destabilising temperature anomaly in the mid-troposphere. Together with the convergence zone between the wave fronts of the two modes, favourable conditions are created for offshore convection. In the 4 km explicit convection model, the offshore convection responds strongly to this gravity wave forcing, in agreement with observations, supporting a gravity wave-convection paradigm for the diurnal cycle over the Maritime Continent. However, the convective response in the lower-resolution models is much less coherent, leading to errors in the diurnal cycle and mean precipitation.

Precipitation distributions for explicit versus parametrized convection in a large‐domain high‐resolution tropical case study

“…This is particularly true for the 12 km param model, which has an extremely regular diurnal cycle over the Maritime Continent land areas (Love et al, 2011).…”

“…Cascade seeks to better understand the interaction between tropical convection at the cloud-system scale and larger-scale processes including the MJO, the diurnal cycle of convection over land (Pearson et al, 2010;Love et al, 2011), easterly waves and equatorially trapped waves. To achieve this goal, Cascade employs high-resolution CSRM simulations of the UK Met Office Unified Model (UM) over very large tropical domains and compares them with high-resolution observations, operational analyses provided for the Year of Tropical Convection (YOTC: Waliser and Moncrieff, 2008) and simulations of the same model using parametrized convection.…”

Effects of the cold tongue in the South China Sea on the monsoon, diurnal cycle and rainfall in the Maritime Continent

“…Love et al (2011) showed that the upward motion over land from daytime propagates as a gravity wave offshore in nighttime. Figure 14 shows meridional sections of the diurnal deviation component of vertical circulation and hourly rainfall in the CTL and NCT runs as 2 h time slices from 0000 LST to 0800 LST.…”

Relationship between the direction of diurnal rainfall migration and the ambient wind over the Southern Sumatra Island

“…Accordingly, diurnal variations of rainfall over the MC have drawn great climatological interest for several decades [Hendon and Woodberry, 1993;Nitta and Sekine, 1994;Yang and Slingo, 2001;Kikuchi and Wang, 2008]. Many features of these variations have been well documented to date, e.g., the initiation of convection in a mountainous area in the afternoon, the peak of rainfall early in the night, and the movement of rain areas from the mountains to coast or offshore areas around midnight [Nitta and Sekine, 1994;Nesbitt and Zipser, 2003;Mori et al, 2004;Sakurai et al, 2005;Ichikawa and Yasunari, 2006;Love et al, 2011]. However, several fundamental issues still remain unexplained, such as the offshore shift mechanism, interactions with large-scale (longer-period) variations, and local orography effects, although they have been discussed by some previous studies [Ohsawa et al, 2001;Mapes et al, 2003;Ichikawa and Yasunari, 2008;Wu et al, 2009].…”

“…The relevant processes reported in previous studies include land breeze convergence [Houze et al, 1981], advection by background wind [Mori et al, 2004;Sakurai et al, 2009Sakurai et al, , 2011, self-replication of convective cells [Sakurai et al, 2009[Sakurai et al, , 2011, convergence of cold outflows produced by rainfall systems [Fujita et al, 2010], and gravity waves triggered by daytime heating of the mixed layer on land [Mapes et al, 2003] or convection on land [Love et al, 2011]. effects of seasonality on the diurnal propagation of precipitation systems.…”