Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    We will mail you new results for this query: keywords==sensible heat flux
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Sensible heating as a potential mechanism for enhanced cloud formation over temperate forest
Bosman, Peter J.M. ; Heerwaarden, Chiel C. van; Teuling, Adriaan J. - \ 2019
Quarterly Journal of the Royal Meteorological Society 145 (2019)719. - ISSN 0035-9009 - p. 450 - 468.
cloud formation - flux partitioning - forest cloud cover - large-eddy simulation - sensible heat flux - sensible heating - surface heat fluxes

It has been recently shown for two forests in France (Les Landes and Sologne) that summer cloud cover over the forest is increased relative to its surroundings. This study aims to contribute to the elucidation of the physical mechanisms responsible for this increased cloud cover, focusing on surface flux partitioning. This was done by performing a case study for a heatwave day on which enhanced cloud cover over the forest of Les Landes was observed. Two numerical experiments (large-eddy simulations) with a homogeneous forest cover were performed, one in which the sensible heat flux was increased by approximately 5% of the total available energy and another one in which the same amount of energy was added to the latent heat flux. The addition of energy to the sensible heat flux led to a stronger increase in cloud cover than the same addition to the latent heat flux. The mean relative humidity at the boundary layer top showed only small differences, indicating it was not a sufficient indicator for cloud formation in this case. Important information, which immediately underlines the need for large-eddy simulations, is contained in modifications of the shape of the probability density functions of temperature and humidity. With enhanced sensible heating, the higher peak values of relative humidity contribute to an increased cloud cover. A crucial reason for the differences in cloud cover between the experiments is conjectured to be a decrease in the required amount of energy for air parcels to reach the lifting condensation level, indirectly caused by the boundary layer and near-surface warming associated with the stronger sensible heat flux. As forests in the region do have a higher sensible heat flux than their surroundings, we highlight one potential mechanism for enhanced cloud cover.

Coupling between radiative flux divergence and turbulence near the surface
Gentine, Pierre ; Steeneveld, Gert Jan ; Heusinkveld, Bert G. ; Holtslag, Albert A.M. - \ 2018
Quarterly Journal of the Royal Meteorological Society 144 (2018)717. - ISSN 0035-9009 - p. 2491 - 2507.
flux-gradient relationship - radiation divergence - sensible heat flux - turbulent kinetic energy - turbulent potential energy

Near-surface turbulent flux and radiation divergence field observations are analysed over a grass-covered surface located at the Wageningen observatory, the Netherlands. Net radiative flux divergence appears to be a large component of the energy budget near the surface, accounting for a cooling rate of several tens of degrees per day. Long-wave radiation divergence dominates this radiation divergence flux. We show here that long-wave flux divergence near the surface is strongly coupled to sensible heat flux, except in high relative humidity (>90%) and foggy conditions. The net long-wave radiative flux divergence exhibits a sharp gradient within the first 20 m above the surface. This flux divergence is itself strongly coupled to sensible heat flux through adjustments in surface-layer profiles. Nonetheless, no systematic effect of radiation is witnessed on the turbulent temperature spectrum so that the main effect of near-surface radiation is on the mean heat budget. As typical flux-gradient relationships are derived based on observations taken in the near-surface boundary-layer region where sharp long-wave divergence is present, we suspect that those relationships implicitly represent some of the long-wave divergence term. A modification of Monin–Obukhov Similarity Theory to include the effect of radiative divergence is proposed and discussed. This calls for independent measurements of turbulent fluxes and radiative flux divergence near the surface to re-derive turbulent flux-gradient relationships independently of radiative effects.

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