Study of Surface Energy Balance Closure over Hyper-arid Environment Using Eddy Covariance Measurements
Abstract
The evaluation of the predictions of high-resolution atmospheric models requires long-term micrometeorological measurements from flux towers covering varying land-surface and climate conditions. In this context, a 2.3-m eddy covariance (EC) flux tower was installed at Al Ain (24o16'26.5535'' N, 55o37'03.2196'' E; 243 m a.m.s.l.), and took micrometeorological measurements for the periods April - October 2017 and February 2018 - January 2019. In the present study, the quality of the EC measurements is assessed by investigating the Surface Energy Balance Closure (SEBC).
An analysis of the SEBC reveals that during daytime a three-way balance between the sensible heat flux, ground heat flux, and the net surface radiative flux prevails, while at night the last two essentially balance each other. The Energy Balance Ratio (EBR) during daytime is in the range 0.60 to 0.75, while at night it can be as low as 0.081. The mean residual flux (ΔE) during daytime (nighttime) is 30 W m-2 (-14 W m-2). Further analysis of the SEBC with respect to the prevailing wind direction revealed that the maximum closure is observed for north-northwesterly winds and the minimum for southerly winds. Secondary circulations and temperature advection may be more significant when the wind is blowing from the Rub Al' Khali desert, located to the south of the site. In addition, the presence of a building to the south of the EC tower and other heterogeneities may also explain the poorer SEBC for southerly wind directions. The SEBC is better for daytime and for periods when the friction velocity is higher.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A13N3137N
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3379 Turbulence;
- ATMOSPHERIC PROCESSES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES