Daily cycle simulations of thermally stratified flows over forests

M. Avila*, R. A. Chávez-Arroyo, J. Arnqvist, H. Olivares-Espinosa, Ebba Dellwik

*Corresponding author for this work

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Abstract

The aim of the present work is to obtain a better understanding of how to model the thermally stratified wind field over a forest during full diurnal cycles. The setup of the study assumes a horizontally homogeneous forest, with the objective of finding a simple and efficient way to model the canopy flow using time-dependent input data, obtained from measurements and mesoscale simulations. With this, new insights can be gained for future microscale modelling of complex forested terrains using mesoscale input data. In terrain without forest a diurnal cycle is commonly simulated by imposing time-dependent ground temperature. However, the presence of forests partially isolates the temperature at ground level from the flow above the canopy, making this common approach ineffective. This work proposes imposing the time-dependent net radiation at the forest canopy top to drive the thermal stratification changes along the diurnal cycle. To this end, several full days of simulation are driven by prescribing the net radiative heat flux balance measured on top of the canopy, together with a geostrophic pressure gradient. The advantage of the method is its simplicity and that the input data can be easily obtained from mesoscale modelling. When compared to the observations at the Swedish site Ryningsnas, the new method dramatically improves estimations of wind speed, wind direction and turbulent kinetic energy compared to simulations that only assume neutral stratification. Out of the variables studied, temperature and turbulent heat flux profiles were the ones that qualitatively followed the measurements the best, while wind speed and turbulent kinetic energy showed a larger disagreement.
Original languageEnglish
Title of host publicationProceedings of the Wake Conference 2019
Number of pages14
Volume1256
PublisherIOP Publishing
Publication date2019
Edition1
Article number012003
DOIs
Publication statusPublished - 2019
EventWake Conference 2019 - Uppsala University Campus Gotland, Visby, Sweden
Duration: 22 May 201924 May 2019
http://standupforwind.se/konferenser-och-moten/wake-conference-2019/

Conference

ConferenceWake Conference 2019
LocationUppsala University Campus Gotland
CountrySweden
CityVisby
Period22/05/201924/05/2019
Internet address
SeriesJournal of Physics: Conference Series
NumberConf. 1
Volume1256
ISSN1742-6596

Cite this

Avila, M., Chávez-Arroyo, R. A., Arnqvist, J., Olivares-Espinosa, H., & Dellwik, E. (2019). Daily cycle simulations of thermally stratified flows over forests. In Proceedings of the Wake Conference 2019 (1 ed., Vol. 1256). [012003] IOP Publishing. Journal of Physics: Conference Series, No. Conf. 1, Vol.. 1256 https://doi.org/10.1088/1742-6596/1256/1/012003
Avila, M. ; Chávez-Arroyo, R. A. ; Arnqvist, J. ; Olivares-Espinosa, H. ; Dellwik, Ebba. / Daily cycle simulations of thermally stratified flows over forests. Proceedings of the Wake Conference 2019. Vol. 1256 1. ed. IOP Publishing, 2019. (Journal of Physics: Conference Series; No. Conf. 1, Vol. 1256).
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Avila, M, Chávez-Arroyo, RA, Arnqvist, J, Olivares-Espinosa, H & Dellwik, E 2019, Daily cycle simulations of thermally stratified flows over forests. in Proceedings of the Wake Conference 2019. 1 edn, vol. 1256, 012003, IOP Publishing, Journal of Physics: Conference Series, no. Conf. 1, vol. 1256, Wake Conference 2019, Visby, Sweden, 22/05/2019. https://doi.org/10.1088/1742-6596/1256/1/012003

Daily cycle simulations of thermally stratified flows over forests. / Avila, M.; Chávez-Arroyo, R. A.; Arnqvist, J.; Olivares-Espinosa, H.; Dellwik, Ebba.

Proceedings of the Wake Conference 2019. Vol. 1256 1. ed. IOP Publishing, 2019. 012003 (Journal of Physics: Conference Series; No. Conf. 1, Vol. 1256).

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

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N2 - The aim of the present work is to obtain a better understanding of how to model the thermally stratified wind field over a forest during full diurnal cycles. The setup of the study assumes a horizontally homogeneous forest, with the objective of finding a simple and efficient way to model the canopy flow using time-dependent input data, obtained from measurements and mesoscale simulations. With this, new insights can be gained for future microscale modelling of complex forested terrains using mesoscale input data. In terrain without forest a diurnal cycle is commonly simulated by imposing time-dependent ground temperature. However, the presence of forests partially isolates the temperature at ground level from the flow above the canopy, making this common approach ineffective. This work proposes imposing the time-dependent net radiation at the forest canopy top to drive the thermal stratification changes along the diurnal cycle. To this end, several full days of simulation are driven by prescribing the net radiative heat flux balance measured on top of the canopy, together with a geostrophic pressure gradient. The advantage of the method is its simplicity and that the input data can be easily obtained from mesoscale modelling. When compared to the observations at the Swedish site Ryningsnas, the new method dramatically improves estimations of wind speed, wind direction and turbulent kinetic energy compared to simulations that only assume neutral stratification. Out of the variables studied, temperature and turbulent heat flux profiles were the ones that qualitatively followed the measurements the best, while wind speed and turbulent kinetic energy showed a larger disagreement.

AB - The aim of the present work is to obtain a better understanding of how to model the thermally stratified wind field over a forest during full diurnal cycles. The setup of the study assumes a horizontally homogeneous forest, with the objective of finding a simple and efficient way to model the canopy flow using time-dependent input data, obtained from measurements and mesoscale simulations. With this, new insights can be gained for future microscale modelling of complex forested terrains using mesoscale input data. In terrain without forest a diurnal cycle is commonly simulated by imposing time-dependent ground temperature. However, the presence of forests partially isolates the temperature at ground level from the flow above the canopy, making this common approach ineffective. This work proposes imposing the time-dependent net radiation at the forest canopy top to drive the thermal stratification changes along the diurnal cycle. To this end, several full days of simulation are driven by prescribing the net radiative heat flux balance measured on top of the canopy, together with a geostrophic pressure gradient. The advantage of the method is its simplicity and that the input data can be easily obtained from mesoscale modelling. When compared to the observations at the Swedish site Ryningsnas, the new method dramatically improves estimations of wind speed, wind direction and turbulent kinetic energy compared to simulations that only assume neutral stratification. Out of the variables studied, temperature and turbulent heat flux profiles were the ones that qualitatively followed the measurements the best, while wind speed and turbulent kinetic energy showed a larger disagreement.

U2 - 10.1088/1742-6596/1256/1/012003

DO - 10.1088/1742-6596/1256/1/012003

M3 - Article in proceedings

VL - 1256

T3 - Journal of Physics: Conference Series

BT - Proceedings of the Wake Conference 2019

PB - IOP Publishing

ER -

Avila M, Chávez-Arroyo RA, Arnqvist J, Olivares-Espinosa H, Dellwik E. Daily cycle simulations of thermally stratified flows over forests. In Proceedings of the Wake Conference 2019. 1 ed. Vol. 1256. IOP Publishing. 2019. 012003. (Journal of Physics: Conference Series; No. Conf. 1, Vol. 1256). https://doi.org/10.1088/1742-6596/1256/1/012003