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Bowen Ratio

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Esmaiel Malek – 1st expert on this subject based on the ideXlab platform

  • calibRation of the penman wind function using the Bowen Ratio energy balance method
    Journal of Hydrology, 1994
    Co-Authors: Esmaiel Malek

    Abstract:

    Abstract The Bowen Ratio energy balance (BREB) method was used to calibrate the wind function constants (Wf = aw + bwu2) in the aerodynamic term of the Penman equation for computation of the hourly and 24 h alfalfa-reference evapotranspiRation (Etr) at an irrigated semi-arid valley in northern Utah during the 1991–1992 growing season. Statistical analysis of the 28 non-rainy days (when the conditions of alfalfa-reference evapotranspiRation were met) showed that the hourly constants in the wind function were aw = 2.677 and bw = 0.127 (with u2 expressed in km h−1). The hourly relationship between the alfalfa-reference evapotranspiRation estimated by the BREB method (Etr(BREB)) and that computed by the Penman method (Etr(Penman)) is Etr(Penman) = 0.976Etr(BREB), with the correlation coefficient (R) equal to 0.974. The daily (24 h) constants were aw = 1.00 and bw = 0.014 (with u2 expressed in km day−1). The 24 h relationship is Etr(Penman) = 1.009Etr(BREB), with R = 0.988. The wind function constants found here can be applied for computation of hourly and 24 h alfalfa-reference evapotranspiRation and irrigation scheduling in this semi-arid valley.

  • comparison of the Bowen Ratio energy balance and the water balance methods for the measurement of evapotranspiRation
    Journal of Hydrology, 1993
    Co-Authors: Esmaiel Malek, Gail E Bingham

    Abstract:

    Abstract An experiment was conducted in a 36 ha alfalfa field in Logan, Utah, USA, during three growth-harvest cycles of alfalfa in April–July 1992. A Campbell Scientific (CS) Bowen Ratio System was used to measure continuously 20 min means of micrometeorological elements such as air and dew point temperatures at 1 and 2 m, solar and net radiation, wind speed and direction at 2 m, soil heat fluxes at 8 cm (two locations), and soil temperatures at 2 and 6 cm during the three consecutive growing cycles. The gravimetric method (for 0–10 cm) and the Campbell Pacific Nuclear (CPN) Hydroprobe (for 20–150cm) were used to measure soil moisture daily at 09:00 h. The 24 h evapotranspiRation (LE, using the Bowen Ratio-energy balance method) was computed by adding the 20 min mean LE values from 09:00 h until 09:00 h of the next day for comparison with the water balance method. EvapotranspiRation measured by the water balance method was 98% of that measured by the Bowen Ratio-energy balance method during the experimental period (r = 0.987).

  • comparison of the Bowen Ratio energy balance and stability corrected aerodynamic methods for measurement of evapotranspiRation
    Theoretical and Applied Climatology, 1993
    Co-Authors: Esmaiel Malek

    Abstract:

    The Bowen Ratio-energy balance (BREB) and the stability-corrected aerodynamic method were used to estimate turbulent fluxes of sensible and latent heat at an irrigated alfalfa site in a semi-arid valley in northern Utah, U.S.A., during August and September of 1991. Despite inclusion of a generalized stability factor, the aerodynamic method underestimated the daytime (sunrise-sunset) sensible and latent heat fluxes by approximately 30% in comparison with the BREB method. The sum of the aerodynamic estimates of sensible and latent heat seldom balanced the energy avaiable from net radiation and change in storage. Wind speed was low during the experiment (averaging 1.6 m s−1), and so a second analysis was run for data from daytime, non-rainy, turbulent conditions (wind > 1.5 m s−1). This showed that sensible and latent heat were still underestimated by approximately 30% in comparison with the BREB approach. This suggests that underestimation of sensible and latent heat fluxes by the aerodynamic method was not related to the wind speed conditions during the experiment. These results show that the stability-corrected aerodynamic model did not agree with the Bowen Ratio method in this experiment. It appears unlikely that the discrepancies resulted from measurement errors. Perhaps the theoretical foundation of the similarity parameters (stability functions) in the aerodynamic model are not sufficiently generalized. The discrepancies found here confirm the necessity of calibRation checks on the validity of aerodynamic estimates of the turbulent fluxes.

Gail E Bingham – 2nd expert on this subject based on the ideXlab platform

  • comparison of the Bowen Ratio energy balance and the water balance methods for the measurement of evapotranspiRation
    Journal of Hydrology, 1993
    Co-Authors: Esmaiel Malek, Gail E Bingham

    Abstract:

    Abstract An experiment was conducted in a 36 ha alfalfa field in Logan, Utah, USA, during three growth-harvest cycles of alfalfa in April–July 1992. A Campbell Scientific (CS) Bowen Ratio System was used to measure continuously 20 min means of micrometeorological elements such as air and dew point temperatures at 1 and 2 m, solar and net radiation, wind speed and direction at 2 m, soil heat fluxes at 8 cm (two locations), and soil temperatures at 2 and 6 cm during the three consecutive growing cycles. The gravimetric method (for 0–10 cm) and the Campbell Pacific Nuclear (CPN) Hydroprobe (for 20–150cm) were used to measure soil moisture daily at 09:00 h. The 24 h evapotranspiRation (LE, using the Bowen Ratio-energy balance method) was computed by adding the 20 min mean LE values from 09:00 h until 09:00 h of the next day for comparison with the water balance method. EvapotranspiRation measured by the water balance method was 98% of that measured by the Bowen Ratio-energy balance method during the experimental period (r = 0.987).

  • continuous measurement of aerodynamic and alfalfa canopy resistances using the Bowen Ratio energy balance and penman monteith methods
    Boundary-Layer Meteorology, 1992
    Co-Authors: Esmaiel Malek, Gail E Bingham, Greg D Mccurdy

    Abstract:

    To investigate the alfalfa crop response to environmental factors, a Bowen Ratio-energy balance method was used to evaluate short-term alfalfa canopy resistance. Continuous evapotranspiRation (ET
    a
    ) and the aerodynamic resistance (r

    a
    ) for an alfalfa crop in each 20-min interval were calculated. Using the calculated ET
    a
    and r

    a
    and the Penman-Monteith approach, the bulk stomatal or actual canopy resistance (r

    c
    ) was evaluated. The continuous 20-min resistances were computed for clear and partially cloudy sky conditions, and different average crop heights. The results show that this technique can satisfactorily be used to study the manner in which the aerodynamic and canopy resistances respond to short-term variations in weather elements such as photosynthetically active radiation (PAR), wind speed and atmospheric satuRation vapor deficit.

Lu Zhang – 3rd expert on this subject based on the ideXlab platform

  • comparison of three evapotranspiRation models to Bowen Ratio energy balance method for a vineyard in an arid desert region of northwest china
    Agricultural and Forest Meteorology, 2008
    Co-Authors: Baozhong Zhang, Shaozhong Kang, Fusheng Li, Lu Zhang

    Abstract:

    The accurate determination of vineyard evapotranspiRation (ET) in the arid desert region of northwest China is important for allocating irrigation water and improving water use efficiency. Taken a vineyard at the Shiyang river basin of the Hexi corridor of Gansu Province as an example, this study evaluated the applicability of the Bowen Ratio-energy balance (BREB) method in the arid desert region of northwest China, simulated the variation of vineyard ET by Penman-Monteith (P-M), Shuttle-Wallace (S-W) and Clumping (C) models in this region and compared the estimated ET by the three models with the measured ET by the BREB. Results indicated that the BREB could provide the accurate measurement of vineyard ET from the arid desert region when the Bowen Ratio instrument with higher accuracy was correctly installed. Generally, the variation of the estimated ET from P-M, S-W and C models were similar to that of the measured ET by the BREB method. However, the P-M model overestimated the ET significantly; the estimated ET from the S-W and C models, especially from the C model was approximately equal to the measured ET by the BREB. After a rainfall, the performances of the S-W and C models were also good. Therefore, among the three models, the C model was the optimal model in simulating the vineyard ET in the arid region of northwest China. However, after a frost, the C model significantly overestimated the evapotranspiRation because the canopy resistance did not fully reflect the dramatic decrease of grapevine transpiRation.

  • estimation of seasonal crop water consumption in a vineyard using Bowen Ratio energy balance method
    Hydrological Processes, 2007
    Co-Authors: Baozhong Zhang, Shaozhong Kang, Lu Zhang, Taisheng Du, Sien Li, X Y Yang

    Abstract:

    Information about seasonal crop water consumption is useful to develop the appropriate irrigation scheme. Measurements of energy balance components using the Bowen Ratio method were made for a complete growing season at a vineyard in the arid region of northwest China. Vine in the experiment was furrow-irrigated using a trellis system. The measured evapotranspiRation was compared with estimates using the soil water balance method. It is shown that the Bowen Ratio method provided accurate estimates of evapotranspiRation from the vineyard and this requires that the Bowen Ratio system is appropriately installed. The energy balance components showed typical diurnal pattern with peaks that occurred around the midday, except for the ground heat flux which delayed its peak by 2–3 h. The sensible heat flux was greater than the latent heat flux and followed the net radiation closely. The Ratio of the latent heat flux to net radiation was low in the early growing season and increased over time. Under the limited irrigation experienced in the vineyard, the latent heat flux was controlled by available soil moisture and the total evapotranspiRation in the growing season was 253 mm. The seasonal progression of the crop coefficient is similar to that reported in the literature, with the maximum occurring during the month of September. The crop coefficient can be estimated as a non-linear function of day of year (DOY) and used to estimate evapotranspiRation from vineyards in the region. Copyright © 2007 John Wiley & Sons, Ltd.