Study Evaluates Surface Energy Balance Closure in Arid Environments
The exchange of energy and water vapor between the land surface and the atmosphere occurs mainly through turbulent fluxes and diffusion in the surface layer. This process plays a critical role in the hydrological cycle and boundary layer dynamics and hence in weather and climate.
High-resolution and long-term measurements are required to better understand the role of turbulent fluxes on land-atmosphere dynamics, and to subsequently improve existing model parameterization schemes. One of the most reliable ways to objectively evaluate turbulent flux measurements is through the surface energy balance closure (SEBC) using an Eddy Covariance (EC) instrument. Nevertheless, surface energy imbalances are a long-standing problem in EC studies and are one of the most frequently discussed concerns in micrometeorological research.
As the majority of work analyzing the reasons behind the surface energy imbalance in EC measurements have focused on vegetated regions, measurements for understudied arid and desert areas are crucial to better understand the SEBC in these regions.
Prof. Marouane Temimi, former Principal Investigator of the UAE Rain Enhancement Program (UAEREP) modeling integration project between Khalifa University (KU) and National Center of Meteorology (NCM) worked on a study investigating the diurnal and seasonal changes in micrometeorological parameters and surface fluxes and, consequently, the SEBC.
Titled ‘Micrometeorological measurements in an arid environment: Diurnal characteristics and surface energy balance closure’, the study aimed to assess the surface energy balance closure (SEBC) in an arid environment through a comprehensive analysis of surface radiation, heat fluxes, and other micrometeorological measurements.
These measurements were taken from a 2.3-m eddy covariance flux tower at Al Ain (24°16′26″ N, 55°37′03″ E) during the periods April – October 2017 and February 2018 – January 2019.
The analyses of the SEBC reveals that during daytime a three-way balance between the sensible heat, ground heat fluxes and the net surface radiative flux prevails, while at night the last two essentially balance each other.
The analyses of the micrometeorological measurements presented by the study provide a better understanding of the atmospheric thermodynamics in an arid site in the UAE. Complementing the evaluation of the predictions of numerical models, these measurements can be used to better estimate the actual values of surface properties such as roughness length, thermal conductivity, and soil thermal diffusivity.
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