地表熱通量與水氣通量模擬研究

Abstract

本論文研究地表熱通量與水氣通量的預估方法，分成兩章。第一章為利用淨輻射模擬地表熱通量之研究。地表熱通量在地表能量平衡中扮演著重要的一環，本章的目的為研究利用淨輻射及Objective hysteresis model (OHM)模擬地表熱通量的可行性，並與線性迴歸法做比較。本篇研究所使用的數據包含：住宅區屋頂-台中縣清水鎮、校園草地-台灣大學大氣系觀測坪、農業區草地-愛爾蘭Dripsey以及農業區沼澤溼地-愛爾蘭Glencar等四個地方，藉由儀器量測或是利用能量閉合來獲得地表熱通量。 本研究選取各實驗地的晴朗及乾燥天，利用二元線性迴歸得到實驗期間內各月份的OHM係數，發現各係數會隨月份而有所變動，並將OHM與線性迴歸法相比發現利用OHM預測地表熱通量的表現會比線性迴歸法來的好。 第二章為水氣通量之非參數化法研究。Liu等人在2012年研究出一非參數化方法(nonparametric method)來估計水氣及可感熱通量，此篇研究的主要目的在於驗證非參數化方法於潮濕區域的可行性以及與Equilibrium evaporation之間的優劣、關聯性。本研究使用數據的實驗地點位於愛爾蘭的Dripsey(濕潤草地)以及Glencar(沼澤地)，於兩地量測可感熱(H)及水氣通量(LE)、淨輻射(Rn)、土壤熱通量(G)、空氣溫度、蒸氣壓差等氣候數據。 研究結果顯示當量測值經過能量閉合(energy closure)修正後，以非參數化法及Equilibrium evaporation的表現最好且兩者表現十分接近。兩方法的誤差差值約在蒸發率(LE / (Rn-G))為0.6時最小，當蒸發率大於0.6時使用Equilibrium evaporation預估水氣通量較佳，反之當蒸發率小於0.6時則以非參數化法預估水氣通量較佳。影響非參數化法最大參數是空氣溫度及地表溫度。

In this study, we estimate ground heat flux and latent heat flux. This study is divided into two chapters. Ground heat flux plays an important role in surface energy balance. In this chapter we are going to evaluate the capability of using net radiation and objective hysteresis model (OHM) estimate ground heat flux and compare with the linear regression model. The experimental sites are including a suburban roof, a grassland in a city, a grassland pasture and a bog. Ground heat flux was measured directly or obtained with the surface energy balance. We choose clear and dry days and obtain OHM coefficients by binary linear regression in each month. We found coefficients would change in each month, and used OHM model estimating ground heat flux is better than linear regression model. In chapter two, we are going to estimate latent heat flux using a nonparametric method.Liu et al. proposed a nonparametric approach to estimating latent heat and sensible heat flux. In this chapter, we are going to evaluate the capability of the nonparametric approach and figure out the applicability and relationship with equilibrium evaporation equation. The experimental site are located in a grassland pasture (Dripsey) and a bog (Glencar). Latent heat flux, sensible heat flux, net radiant flux, air temperature, surface temperature and vapor pressure deficit were measured in two sites. Result showed that nonparametric approach and equilibrium evaporation are really close and they provide the best estimate after measured latent heat flux and sensible heat flux was corrected. Both methods have minimum error when evaporation fraction is 0.6. Equilibrium evaporation equation estimate latent heat flux is better than nonparametric approach when evaporation fraction is more than 0.6, on the contrary, nonparametric approach is better than equilibrium evaporation equation when evaporation fraction is less than 0.6. In all input parameters, air and surface temperature influence nonparametric approach most.