Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Cooper, Harry J.; Smith, Eric A.; Gu, Jiujing; Shewchuk, S. R.

doi:10.1029/97jd00456

Cited by 10 publications

(6 citation statements)

References 23 publications

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“…3.3). Many studies exist, usually focused on the local scale, which have compared parameter aggregating to flux-aggregating techniques (see e.g., Avissar and Pielke 1989;Polcher et al 1996;Van den Hurk and Beljaars 1996;Cooper et al 1997;Molod and Salmun 2002;Essery et al 2003;Heinemann and Kerschgens 2005;Ament and Simmer 2006). These studies agree that by employing an aggregation of fluxes the representation of processes clearly improves compared to an aggregation of parameters.…”

Section: Introductionsupporting

confidence: 52%

On the Representation of Heterogeneity in Land-Surface–Atmosphere Coupling

Vrese

Schulz

Hagemann

2016

Boundary-Layer Meteorol

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A realistic representation of processes that are not resolved by the model grid is one of the key challenges in Earth-system modelling. In particular, the non-linear nature of processes involved makes a representation of the link between the atmosphere and the land surface difficult. This is especially so when the land surface is horizontally strongly heterogeneous. In the majority of present day Earth system models two strategies are pursued to couple the land surface and the atmosphere. In the first approach, surface heterogeneity is not explicitly accounted for, instead effective parameters are used to represent the entirety of the land surface in a model's grid box (parameter-aggregation). In the second approach, subgridscale variability at the surface is explicitly represented, but it is assumed that the blending height is located below the lowest atmospheric model level (simple flux-aggregation). Thus, in both approaches the state of the atmosphere is treated as being horizontally homogeneous within a given grid box. Based upon the blending height concept, an approach is proposed that allows for a land-surface-atmosphere coupling in which horizontal heterogeneity is considered not only at the surface, but also within the lowest layers of the atmosphere (the VERTEX scheme). Below the blending height, the scheme refines the turbulent mixing process with respect to atmospheric subgrid fractions, which correspond to different surface features. These subgrid fractions are not treated independently of each other, since an explicit horizontal component is integrated into the turbulent mixing process. The scheme was implemented into the JSBACH model, the land component of the Max Planck Institute for Meteorology's Earth-system model, when coupled to the atmospheric general circulation model ECHAM. The single-column version of the Earth system model is used in two example cases in order to demonstrate how the effects of surface heterogeneity are transferred into the atmosphere, influencing local stability and the turbulent mixing process. Furthermore, a simple flux-aggregation scheme was implemented into the JSBACH model. By comparing single-column simulations utilizing the VERTEX scheme and the simple flux-aggregation scheme, it can be shown that the horizontal disaggregation of the turbulent mixing process has a substantial impact on the simulated mean state of a grid box. Here, the differences between simulations with the two schemes may, in certain cases, be even larger than the differences between simulations with the simple flux-aggregation scheme and simulations in which surface heterogeneity is not explicitly accounted for (i.e., a parameter-aggregation scheme).

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Section: Introductionsupporting

confidence: 52%

On the Representation of Heterogeneity in Land-Surface–Atmosphere Coupling

Vrese

Schulz

Hagemann

2016

Boundary-Layer Meteorol

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“…A comparison of mosaic and mixture for a terrain type which is homogeneously covered by two vegetation types (savannah, where mixture is an accurate representation) was performed by Koster and Suarez [1992b], who showed that the resulting fluxes using the mosaic approach are quite close to the mixture results. Studies by Cooper et al [1997], van den Hurk and Beljaars [1996], Arola and Lettenmaier [1996], and Polcher et al [1996] all reported significant differences between mosaic and composite during the spring and summer at several different Northern Hemisphere locations. These studies find that the mosaic representation reduces the latent heat fluxes (and increases the sensible heat) and offers the more accurate estimates of surface fluxes.…”

Section: Introductionmentioning

confidence: 97%

A global assessment of the mosaic approach to modeling land surface heterogeneity

Molod¹

2002

J.‐Geophys.‐Res.

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[1] Modeling the impact of small-scale land surface heterogeneities on scales resolved by general circulation models (GCMs) has long been a challenging problem. We present here a global offline comparison between two approaches to account for the heterogeneities. These approaches are mosaic, which computes separate energy budgets for each surface type within a grid box, and dominant, which assumes that a grid box can be completely described by the dominant vegetation. The experiments are all conducted using the turbulence parameterization of the Goddard Earth Observing System (GEOS) GCM, coupled to the Koster-Suarez Land Surface Model. The results show a large impact in the high-and middle-latitude Northern Hemisphere climates. At high latitudes the warming of the surface after the spring snowmelt is more rapid for dominant. At midlatitudes, where the surface is potentially under moisture stress, the mosaic approach results in a drier, warmer climate. This impact is determined to a large extent by the influence of bare soil areas on the grid-scale climate. The impact of the choice of approach is less important over more homogeneous terrains, such as deserts, as can be expected in the offline framework. These results support the need for a mosaic-type approach to properly model the coupling at the land surface interface.

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“…Sampaio et al, 2007;da Silva et al, 2008), and modelling studies using the tile approach (e.g. Arola and Lettenmaier, 1996;Polcher et al, 1996;van den Hurk and Beljaars, 1996;Cooper et al, 1997). These differences indicate a reduction in evaporation and net radiation, and an increase in skin temperature, sensible heat flux, surface albedo, and near-surface winds.…”

Section: Discussionmentioning

confidence: 99%

“…These aggregation methods are widely used in landsurface modelling and have shown satisfactory results in the representation of surface processes (e.g. Arola and Lettenmaier, 1996;Polcher et al, 1996;van den Hurk and Beljaars, 1996;Cooper et al, 1997;Molod and Salmun, 2002;Manrique-Suñén et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Effects of the surface heterogeneities on the local climate of a fragmented landscape in Amazonia using a tile approach in the Eta/Noah‐MP model

Pilotto

Chou

Tomasella

et al. 2017

Quart J Royal Meteoro Soc

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This study evaluates the use of tiles to estimate the effects of surface heterogeneities in simulations of local climate in a landscape‐fragmented region of Amazonia. Three experiments using the Eta/Noah‐MP model were designed as follows: two experiments with a spatial resolution of 5 km with and without the use of the tile approach. The third experiment used a finer spatial resolution of 2 km without the use of the tile approach (high‐resolution experiment). Simulations were carried out for the rainy and dry seasons, which correspond to the months of March and September 2003, respectively. In general, the magnitude of surface fluxes is significantly affected by the introduction of tiles. In the dry season, the use of tiles in the simulation increases the magnitude of precipitation (about 7 mm day−1), skin temperature (about 4 °C), sensible heat flux (about 80 W m−2) and surface albedo (about 0.7). It reduces the latent heat flux (about 30 W m−2) and net radiation (about 40 W m−2). On the other hand, in the rainy season, the model produces excessive precipitation. This may have partly masked the signs of the land fragmentation impact. The tile experiment generates a warmer and drier boundary layer during the dry season. The impact of the surface heterogeneity representation is higher in the dry season than in the rainy season. The results suggest that the degree of impact of the subgrid process representation on the local climate is related to the spatial scale of the fragmentation. The use of the tile approach improves the representation of the effects of landscape heterogeneity on the spatial distribution of surface flux variability in fragmented areas. Comparison against measured data from flux towers in the region show that the model can simulate diurnal and seasonal variations in the local fluxes, despite the biases.

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Modeling the impact of averaging on aggregation of surface fluxes over BOREAS

Cited by 10 publications

References 23 publications

On the Representation of Heterogeneity in Land-Surface–Atmosphere Coupling

On the Representation of Heterogeneity in Land-Surface–Atmosphere Coupling

A global assessment of the mosaic approach to modeling land surface heterogeneity

Effects of the surface heterogeneities on the local climate of a fragmented landscape in Amazonia using a tile approach in the Eta/Noah‐MP model

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