Abstract
Abstract. The net storage heat flux (ΔQS) is important in the urban surface energy balance (SEB) but its determination remains a significant challenge. The hysteresis pattern of the diurnal relation between the ΔQS and net all-wave radiation (Q∗) has been captured in the Objective Hysteresis Model (OHM) parameterization of ΔQS. Although successfully used in urban areas, the limited availability of coefficients for OHM hampers its application. To facilitate use, and enhance physical interpretations of the OHM coefficients, an analytical solution of the one-dimensional advection–diffusion equation of coupled heat and liquid water transport in conjunction with the SEB is conducted, allowing development of AnOHM (Analytical Objective Hysteresis Model). A sensitivity test of AnOHM to surface properties and hydrometeorological forcing is presented using a stochastic approach (subset simulation). The sensitivity test suggests that the albedo, Bowen ratio and bulk transfer coefficient, solar radiation and wind speed are most critical. AnOHM, driven by local meteorological conditions at five sites with different land use, is shown to simulate the ΔQS flux well (RMSE values of ∼ 30 W m−2). The intra-annual dynamics of OHM coefficients are explored. AnOHM offers significant potential to enhance modelling of the surface energy balance over a wider range of conditions and land covers.
Highlights
The essential role of an integrated land surface model is to physically predict the land–atmosphere interactions by resolving the transfer of energy, water, and trace gases (Katul et al, 2012; Liang et al, 1994; Sellers et al, 1997). Such land– atmospheric interactions are strongly modulated by the partitioning of solar energy at the land surface (Chen and Dudhia, 2001; McCumber and Pielke, 1981; Yang and Wang, 2014) which can be considered through the surface energy balance (SEB) equation (Oke, 1988): Q∗ − QS = QH + QE, (1)
An offline evaluation of AnOHM’s performance for five sites with different land covers (Sect. 4) provides evidence that this is an alternative approach to obtain Objective Hysteresis Model (OHM) coefficients. Given that this allows applications across a much wider range of environments and meteorological conditions, we conclude that AnOHM has important implications for land surface modelling
; with T S, ATS, and γ denoting the daily mean value, amplitude, and initial phase of surface temperature, respectively, which need to be determined by the boundary conditions imposed by the SEB
Summary
The essential role of an integrated land surface model is to physically predict the land–atmosphere interactions by resolving the transfer of energy, water, and trace gases (Katul et al, 2012; Liang et al, 1994; Sellers et al, 1997). Where the a1, a2, and a3 coefficients are for individual facets determined by least-square regression between QS and Q∗ using results from observations (e.g. asphalt road (Anandakumar, 1999), wetlands (Souch et al, 1998), forests (Oliphant et al, 2004), or numerical modelling – e.g. urban canyons (Arnfield and Grimmond, 1998) and roofs (Meyn and Oke, 2009) These coefficients capture the net behaviour of a facet type in a typical setting, rather than being required to identify the component materials within a facet (e.g. multiple materials making up a roof, wall, with varying thermal connectivity and individual properties). Given that this allows applications across a much wider range of environments and meteorological conditions, we conclude that AnOHM has important implications for land surface modelling (urban and non-urban)
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