Representing the Australian Heat Low in a GCM Using Different Surface and Cloud Schemes

Matthew M Allcock,Duncan Ackerley

doi:10.1155/2016/9702607

Matthew M Allcock, Duncan Ackerley

Open Access

https://doi.org/10.1155/2016/9702607

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Abstract

The high insolation during the Southern Hemisphere summer leads to the development of a heat low over north-west Australia, which is a significant feature of the monsoon circulation. It is therefore important that General Circulation Models (GCMs) are able to represent this feature well in order to adequately represent the Australian Monsoon. Given that there are many different configurations of GCMs used globally (such as those used as part of the Coupled Model Intercomparison Project), it is difficult to assess the underlying causes of the differences in circulation between such GCMs. In order to address this problem, the work presented here makes use of three different configurations of the Australian Community Climate and Earth System Simulator (ACCESS). The configurations incorporate changes to the surface parameterization, cloud parameterization, and both together (surface and cloud) while keeping all other parameterized processes unchanged. The work finds that the surface scheme has a larger impact on the heat low than the cloud scheme, which is caused by differences in the soil thermal inertia. This study also finds that the differences in the circulation caused by changing the cloud and surface schemes together are the linear sum of the individual perturbations (i.e., no nonlinear interaction).

Highlights

The high insolation and surface heating of the Australian land surface in summer (December, January, and February (DJF)) create a strong diurnal cycle in temperature and circulation [1,2,3,4]
Given that the CMIP5 models assessed in Ackerley et al [16] use many different combinations of parameterizations, this study presents an opportunity to identify whether the surface scheme, cloud scheme, or both together play the dominant role in governing the Australian heat low structure
The main difference in the diurnal cycle between A1.1 and A1.0 is that the low-level atmosphere over the heat low is cooler during the day and warmer overnight in A1.1 compared with A1.0

Summary

Introduction

The high insolation and surface heating of the Australian land surface in summer (December, January, and February (DJF)) create a strong diurnal cycle in temperature and circulation [1,2,3,4]. Solar heating of the land surface acts to warm the air in the low-level atmosphere, which rises, lowering the surface pressure. This area of low pressure is known as a heat low. As the surface cools at night, a stable nocturnal boundary layer forms, allowing the development of a low-level jet and convergence over the heat low [5]. The boundary layer becomes unstable in the morning (following surface heating), which initiates convection and a reduction in surface pressure as described above. Heat lows occur in other semiarid areas of the world, for example, the Iberian Peninsula [6,7,8,9] and West Africa [10,11,12,13]

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