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ESTIMATION OF TURBULENT HEAT FLUXES VIA THE SYNERGISTIC ASSIMILATION OF LAND SURFACE TEMPERATURE, AIR TEMPERATURE AND SPECIFIC HUMIDITY INTO A VARIATIONAL DATA ASSIMILATION MODEL

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Title:ESTIMATION OF TURBULENT HEAT FLUXES VIA THE SYNERGISTIC ASSIMILATION OF LAND SURFACE TEMPERATURE, AIR TEMPERATURE AND SPECIFIC HUMIDITY INTO A VARIATIONAL DATA ASSIMILATION MODEL
Authors:Tajfar, Elahe
Contributors:Bateni, Sayed M. (advisor)
Civil Engineering (department)
Keywords:Civil engineering
Water resources management
Environmental engineering
air temperature
land surface temperature
show 3 morespecific humidity
Turbulent heat fluxes
variational data assimilation model
show less
Date Issued:2019
Publisher:University of Hawai'i at Manoa
Abstract:The balance of energy at the Earth's surface is linked to the overlying atmospheric boundary layer (ABL). The sensible (H) and latent (LE) heat fluxes are important components of Earth’s radiation budget and its climate system, which directly influence the properties of the boundary layer and characterize exchange of heat and moisture between the land surface and its overlying atmosphere. Therefore, their accurate estimation is of crucial importance for a better understanding of land surface-atmosphere exchange processes and obtaining the heat and moisture budgets. Different approaches have been developed to estimate turbulent heat fluxes (i.e., H and LE). A number of studies used time-series of air temperature and specific humidity observations to estimate turbulent heat fluxes. These works require the specification of surface roughness lengths for heat and momentum and/or ground heat flux, which are often unavailable. This study estimates turbulent heat fluxes and the atmospheric boundary layer (ABL) height, potential temperature, and humidity by assimilating sequences of air temperature and specific humidity into an atmospheric boundary layer model within a new variational data assimilation (VDA) framework. The unknown parameters of the VDA system are neutral bulk heat transfer coefficient (CHN) and evaporative fraction (EF). It needs neither the surface roughness parameterization nor ground heat flux measurements. The performance of the developed VDA approach is tested over the First International Satellite Land Surface Climatology Project Field Experiment (FIFE) site for the summer of 1987 and 1988. The results show that the developed VDA framework is capable of estimating the unknown parameters (i.e., EF and CHN) reasonably well. The developed VDA model can predict the turbulent heat fluxes fairly accurately at the FIFE site. In addition, the ABL height, specific humidity, and potential temperature estimates from the VDA system are reasonably close to those inferred from the radiosondes both in terms of magnitude and diurnal trend. The introduced VDA framework is advanced by the synergistic assimilation of LST, air temperature and specific humidity into a coupled land surface-ABL model. The augmented VDA system is also validated at the FIFE sites. It outperforms the previous study in which air temperature and specific humidity were assimilated. Finally, both developed VDA approaches are tested at five sites (namely, Desert, Audubon, Bondville, Brookings, and Willow Creek) with contrasting climatic and vegetative conditions. The results show that the first VDA system (that assimilates reference-level air temperature and specific humidity) performs well at wet/densely vegetated sites (e.g., Willow Creek), but its performance degrades at dry/slightly vegetated sites (e.g., Desert). These outcomes show that the sequences of reference-level air temperature and specific humidity have more information on the partitioning of available energy between the sensible and latent heat fluxes in wet and/or densely vegetated sites than the dry and/or slightly vegetated sites. The second VDA approach (that assimilates LST, reference-level air temperature and specific humidity) outperforms the first approach that assimilated only the state variables of atmosphere (i.e., reference-level air temperature and humidity), and can accurately estimate turbulent heat fluxes over a wide variety of environmental conditions.
Pages/Duration:211 pages
URI:http://hdl.handle.net/10125/63483
Appears in Collections: Ph.D. - Civil Engineering


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