Dai Matsushima

A Proper Method for Estimating Sensible Heat Flux above a Horizontal-Homogeneous Vegetation Canopy Using Radiometric Surface Observations

Abstract A multilayer energy budget model for a horizontal-homogeneous vegetation canopy and a simple radiometric canopy model are developed to estimate sensible heat flux with use of the observed directional radiometric temperature of the canopy surface. Field experiments were carried out in an almost horizontal-homogeneous rice paddy under various canopy conditions to obtain boundary conditions and data to test the models. A proper method for estimating sensible heat flux is proposed, which is based on model simulations and the observational results. Key parameters required for the estimation of the flux are the aerodynamic conductance and the optimum viewing angle, which are investigated in detail using a rice paddy model. The aerodynamic conductance is a function of three parameters, namely, the leaf-area index (LAI), wind speed, and virtual temperature difference between the canopy and the surface layer. The optimum viewing angle for sensible heat is found to be between 50° and 70° of the nadir angle...

Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Received 4 May 2008; revised 9 June 2008; accepted 18 June 2008; published 23 July 2008. [1] Dual-Doppler lidar and heliborne sensors were used to investigate the three-dimensional (3D) structure of the wind field over Sendai Airport in June 2007. The 3D structures of several-hundred-meter-scale horizontal convective rolls (HCRs) in the sea-breeze layer were observed by the dual-Doppler lidar. The scale of the HCRs determined by the heliborne sensors roughly agreed with that determined by the dual-Doppler lidar. Analysis of the dual-Doppler lidar data showed that the region of upward flow in the HCRs originated in near-surface low-speed streaks. This structure is consistent with the results of large-eddy simulations of the atmospheric boundary layer. The aspect ratios of the HCRs were close to those predicted by linear theories. Citation: Iwai, H., et al. (2008), Dual-Doppler lidar observation of horizontal convective rolls and near-surface streaks, Geophys. Res. Lett., 35, L14808, doi:10.1029/ 2008GL034571.

An Estimation of the Bulk Transfer Coefficients for a Bare Soil Surface Using a Linear Model

Abstract A linear heat budget model is developed to estimate the daytime means of the bulk transfer coefficients for heat and evaporation efficiency using the daily variation of observational data. The daily variation of shortwave radiation, ground-level air temperature, surface temperature, wind speed, and daily mean ground-level specific humidity are required to obtain the bulk coefficients. The relationship between the atmospheric resistance and the wind speed is also required. The daily variation of heat flux (1-h average) with respect to the surface heat budget can be reproduced using the same model and the presently estimated bulk coefficients within an error of 41 W m−2 for the sensible heat flux and within an error of 53 W m−2 for the latent heat. Sensitivity tests were performed under six different conditions. It was found that a systematic error of ±1°C in the surface temperature will lead to erroneous estimates of the bulk coefficients.

Soil Moisture Estimation Using Thermal Inertia: Potential and Sensitivity to Data Conditions

AbstractThermal inertia retrieval using a thermal infrared remote sensing technique has been examined as a possible method for estimating soil moisture. This method is an application of the theory that thermal inertia highly correlates with soil water content. This study shows a method for retrieving thermal inertia from a heat budget model of the earth’s surface using radiative surface temperatures, insolation, and meteorological data observed in field experiments. In bare to sparsely vegetated areas, this method has the potential to estimate subsurface soil moisture with a precision of ±3%–4% of the daily volumetric soil moisture content at a significance level of 5%, which is enough to roughly classify thermal inertia estimates into a few levels of soil moisture (e.g., wet, middle, and dry). The analysis also includes an examination of the practical performance of the thermal inertia estimation according to the temporal resolution of the data, assuming the use of satellite and routine meteorological da...

FIELD MEASUREMENTS ON THE COOLING EFFECT OF THE IMPERIAL PALACE AND ITS THERMAL INFLUENCE ON THE SURROUNDING BUILT UP AREA

In this paper, results are shown from micro-climatological observations performed in and around a largest green space in central Tokyo, “Imperial Palace”, during summer. Its area is 230ha, and it was once the Edo-Castle, then surrounded by a moat.In a clear calm night, the cool air flows out from the Imperial Palace to the surrounding city area gravitationally. Different from the daytime advection by prevailing wind, the turbulent mixing is very weak in nighttime seeping phenomena because of the stable atmospheric condition. In the west side, the cool air flows over the valley of moat (20m depth) and spreads out into the built-up area. In the east side, cool air front sometimes penetrates the adjacent CBD area and reach near the Tokyo Station. The wide streets have a larger effect on cool air seeping than the moat dose even though water temperature is higher than ambient air temperature.

A simple parameterization of longwave radiative cooling with application to the atmospheric boundary layer for clear sky conditions

A simple parameterization is proposed to obtain longwave radiative cooling rates, which can be used for atmospheric boundary-layer simulations on clear days in mid-latitudes. The net flux difference which is set to zero at the surface, can be parameterized with the use of three variables: the surface temperature, the lowest level (1.5 m) air temperature, and the total amount of water vapor. If these three elements, along with the water vapor profile are known, it is possible to estimate the cooling rate due to longwave radiation. The results of this parameterization are in good agreement with those of a precise scheme (Roach and Slingo, 1979), within a range of ± 1°C/day of diurnal change for boundary-layer simulations.

Thermal inertia approach using a heat budget model to estimate the spatial distribution of surface soil moisture over a semi-arid grassland in Central Mongolia

AbstractThermal inertia is a physical parameter that evaluates soil thermal properties with an emphasis on the stability of the temperature when the soil is affected by heating/cooling. Thermal inertia can be retrieved from a heat budget formulation as a parameter when the time series of Earth surface temperature and forcing variables, such as insolation and air temperature, are given. In this study, a two-layer, linearized heat budget model was employed for the retrieval of thermal inertia over a grassland in a semiarid region. Application of different formulations to the aerodynamic conductance with respect to atmospheric stability significantly improved the accuracy of the thermal inertia retrieval. The retrieved values of thermal inertia were well correlated with in situ surface soil moisture at multiple ground stations. The daily time series of thermal inertia–derived soil moisture qualitatively agreed well with in situ soil moisture after antecedent rainfalls, which was found after fitting the time ...

Regional distribution of sensible and latent heat fluxes over rice paddies using satellite infrared temperature and a heat-budget model

This study aims at evaluating regional distribution and diurnal variation of surface sensible and latent heat fluxes over vegetation using limited number of satellite IR images, meteorological data, and a numerical heat budget simulation together. Data used in this study are as follows: NOAA-AVHRR thermal IR image for retrieving surface temperature, surface and upper meteorological data, time series of solar radiation, and leaf area index for determining surface aerodynamic conditions. To evaluate sensible heat flux, retrieving the surface effective temperature of sensible heat flux is required. This temperature is different from IR temperature in general, even an original IR temperatures is atmospherically corrected and a correction of emissivity is performed.