Analysis and Reduction of Systematic Errors through a Seamless Approach to Modeling Weather and Climate

Abstract

The reduction of systematic errors is a continuing challenge for model development. Feedbacks and compensating errors in climate models often make finding the source of a systematic error difficult. In this paper, it is shown how model development can benefit from the use of the same model across a range of temporal and spatial scales. Two particular systematic errors are examined: tropical circulation and precipitation distribution, and summer land surface temperature and moisture biases over Northern Hemisphere continental regions. Each of these errors affects the model performance on time scales ranging from a few days to several decades. In both cases, the characteristics of the long-time-scale errors are found to develop during the first few days of simulation, before any large-scale feedbacks have taken place. The ability to compare the model diagnostics from the first few days of a forecast, initialized from a realistic atmospheric state, directly with observations has allowed physical deficiencies in the physical parameterizations to be identified that, when corrected, lead to improvements across the full range of time scales. This study highlights the benefits of a seamless prediction system across a wide range of time scales.

Development and evaluation of an Earth-System model – HadGEM2

“…The physical model configuration is derived from the HadGEM1 climate model and references therein) with improvements as discussed in The HadGEM2 Development Team (2011) and Martin et al (2010), and is only described briefly here. The atmospheric component uses a horizontal resolution of 1.25 • × 1.875 • in latitude and longitude with 38 layers in the vertical extending to over 39 km in height.…”

“…Hence a focus for the development of the physical components of HadGEM2 was improving the surface climate, as well as other outstanding errors such as El Niño Southern Oscillation (ENSO) and tropical climate. Details of the major developments to the physical basis of the HadGEM2 model family are described in Martin et al (2010) and The HadGEM2 Development Team (2011).…”

Preferred response of the East Asian summer monsoon to local and non-local anthropogenic sulphur dioxide emissions

“…Convection tends to be favoured over these latter regions due to the large availability of moisture and heat over the equatorial Indian Ocean and the orographic forcing as the low-level monsoon flow hits the Himalayan foothills respectively. This excessive equatorial Indian Ocean rainfall appears to be an inherent feature of the Met Office Unified model, with preferential model convection over areas with large amounts of available heat and moisture (Martin et al 2010). This bias is also found in other versions of the Met Office Hadley Centre Global Environmental Model (Levine and Turner 2012;Guo et al 2013).…”

Entrainment processes in the diurnal cycle of deep convection over land

“…This is in part by design due to the auxiliary role of convection in ensuring numerical stability in models, and the consequent requirement of a closure that is linked to the removal of convective available potential energy (CAPE) rather than an intrinsic convective time-scale (e.g. Martin et al, 2010).…”