Nighttime Net Radiation Research Articles

Estimating Daily and 24-Hour Net Radiation for All Sky Conditions through Remote Sensing and Climatic Data

Net radiation is a key variable in hydrological studies. However, measured net radiation data are rarely available and are often subject to error because of equipment calibration or failure. Additionally, point measurements of net radiation do not represent the diversity of the regional net radiation values, which are needed for many physical and biological processes such as climate monitoring and evapotranspiration mapping. The authors present a methodology to estimate daytime net radiation using a combination of remote sensing and climatic data. This paper expands on previous original research by extending the estimation of net radiation to 24 h under all sky conditions. The procedure estimates daytime and nighttime net radiation and combines the results to calculate the 24-h net radiation values. The methodology combines information from satellite and local weather stations to estimate net radiation values. The procedure can estimate net radiation under all sky conditions using measured or estimated solar radiation. Two different methods are presented to estimate net radiation. Comparisons between measured and predicted daytime and 24-h net radiation using the two methods resulted in an average ratio ranging from 0.98–1.0 and a standard error of estimate ranging from 0.83–1.62 MJ m−2 day−1. Satellite data were used for the calculation of leaf area index, albedo, and ground temperature. Although satellite data are scarce, the methodology is not limited to satellite imagery. One can easily use ground level measurements of leaf area index, albedo, and temperature to estimate daytime and 24-h net radiation using the proposed methodology.

Validation of remote sensing of bare soil ground heat flux

Ground heat flux is an important component of the energy balance in bare soils or sparsely vegetated areas. This study presents the results of a validation experiment of a remote sensing method for ground heat flux. A heat diffusion model, calibrated to local soil heat flux soil temperature profile measurements at an eddy covariance flux station in Spain, was used to validate the remote sensing method. The high energy balance closure of 93% at the site, the high correspondence of modelled temperature profile data to observations, and agreement of retrieved thermal properties with literature data gave confidence in the validation target. The remote sensing method makes use of retrieved radiometric temperatures and night-time net radiation. It was applied to field radiometry measurements over bare soil and to MSG-SEVERI data (10% of the pixel of the field site was covered by vegetation). Despite its simplicity, the remote sensing model applied to the field radiometry performed well (slope of the regression against the validation target: 1.00, r2=0.96). Good agreement was also found between the remote sensing method applied to field radiometry and to satellite data (slope of the regression: 0.79, r2=0.89).

Estimation of Biomass Heat Storage Using Thermal Infrared Imagery: Application to a Walnut Orchard

A new method to estimate tree biomass heat storage from thermal infrared (TIR) imaging of biomass surface temperature is presented. TIR images of the canopy are classified into trunk, branches, and leaves. The one-dimensional heat equation in cylindrical coordinates is forced with trunk and branch surface temperatures to simulate the temperature distribution and heat storage in tree trunks and branches. Assuming uniform leaf temperatures, heat storage in leaves is computed from the surface temperature of the leaves separately for the sunlit upper and shaded lower canopy. The sum of trunk, branches, leaf, and air heat storage gives the canopy heat storage. Measurements in a walnut orchard near Davis, California, in early June 2007 showed that biomass heat storage was of the same order as air heat storage and about 1% of daytime and 9% of nighttime net radiation.

Modeling Seasonal Changes in the Temperature Lapse Rate in a Northern Thailand Mountainous Area

AbstractTemperature data in the mountain forest regions are often extrapolated from temperature data recorded at base stations at lower elevation. Such extrapolation is often based on elevation differences between target regions and base stations at low elevation assuming a constant temperature lapse rate throughout the year. However, this assumption might be problematic where slope circulation is active and decoupled from the regional circulation. To model the seasonal change in the lapse rate, the authors compared daily maximum (Tmax) and minimum temperatures (Tmin) observed at a mountain forest site (Kog–Ma; 1300-m altitude) with those observed at the bottom of the basin (Chiang–Mai; 314-m altitude) in northern Thailand, where slope circulation is active and decoupled from the regional circulation. The difference in Tmax between Kog–Ma and Chiang–Mai (ΔTmax; Kog–Ma minus Chiang–Mai) was relatively unchanged throughout the year. However, the difference in Tmin between Kog–Ma and Chiang–Mai (ΔTmin) changed seasonally. Thus, assuming a constant lapse rate throughout the year could cause large errors in extrapolating Tmin data in mountainous areas in northern Thailand. The difference ΔTmin was related to nighttime net radiation (Rn), suggesting that nocturnal drainage flow affects the determination of ΔTmin. This relationship would be useful in formulating seasonal changes in the lapse rate for Tmin. As Rn data are generally unavailable for meteorological stations, an index that relates to the lapse rate for Tmin and is calculated from Tmax and Tmin data is proposed. This index might be useful for accurately estimating Tmin values in mountainous regions in northern Thailand.

A Comparison of Surface Mulch Type on Patterns of Above- and Below-ground Temperature and Surface Net Radiation in a Drip-irrigated Desert Landscape

Mulches applied to landscape surfaces can moderate soil temperatures by changing the surface heat energy balance and conserve soil water by reducing evaporation rates. In the Southwest, decomposing granite is commonly used as landscape mulch. However, organic mulches, such as pine residue mulch and shredded tree trimmings, are becoming more available as industry by-products. Recent impetus toward water conservation and recycling forest and urban tree waste into urban landscapes has increased the need to better understand how such mulch types effect the temperature, moisture. and light quality of drip-irrigated landscapes typically found in the Southwest. We compared effects of three mulches, two organic (composted ponderosa pine residue and shredded urban tree trimmings) and one inorganic (Red Mountain Coral decomposing granite), turf grass, and bare soil applied to 14 drip-irrigated landscape research plots on below-ground soil temperatures at depths of 5 cm and 30 cm, temperatures at the mulch-soil interface, mulch surface temperatures, diel mulch surface net radiation, and albedo. Below-ground soil temperatures were more buffered by organic mulches, and mulch-soil interface temperatures were lower under organic mulch than inorganic mulches. Inorganic mulch daytime surface temperatures were lower than organic mulch surface temperatures. Nighttime net radiation values were less negative over organic mulches than inorganic mulches and albedo was significantly higher for the inorganic mulch and bare soil treatments. These results provide evidence to show that organic surface mulches have higher resistances to heat transfer than inorganic mulches, which could improve landscape plant water and nutrient use efficiencies by lowering high summer root zone temperatures.

Remote estimation of thermal inertia and soil heat flux for bare soil

A method is presented which allows thermal inertia (the soil heat capacity times the square root of the soil thermal diffusivity, C h D h ), to be estimated remotely from micrometeorological observations. The method uses the drop in surface temperature, T s, between sunset and sunrise, and the average night-time net radiation during that period, for clear, still nights. A Fourier series analysis was applied to analyse the time series of T s. The Fourier series constants, together with the remote estimate of thermal inertia, were used in an analytical expression to calculate diurnal estimates of the soil heat flux, G. These remote estimates of C h D h and G compared well with values derived from in situ sensors. The remote and in situ estimates of C h D h both correlated well with topsoil moisture content. This method potentially allows area-average estimates of thermal inertia and soil heat flux to be derived from remote sensing, e.g. METEOSAT Second Generation, where the area is determined by the sensor’s height and viewing angle.

Altering Rainfall Timing and Quantity in a Mesic Grassland Ecosystem: Design and Performance of Rainfall Manipulation Shelters

Global climate change is predicted to alter growing season rainfall patterns, potentially reducing total amounts of growing season precipitation and redistributing rainfall into fewer but larger individual events. Such changes may affect numerous soil, plant, and ecosystem properties in grasslands and ultimately impact their productivity and biological diversity. Rainout shelters are useful tools for experimental manipulations of rainfall patterns, and permanent fixed-location shelters were established in 1997 to conduct the Rainfall Manipulation Plot study in a mesic tallgrass prairie ecosystem in northeastern Kansas. Twelv e9x1 4 ‐mfixed-location rainfall manipulation shelters were constructed to impose factorial combinations of 30% reduced rainfall quantity and 50% greater interrainfall dry periods o n6x6 ‐mplots, to examine how altered rainfall regimes may affect plant species composition, nutrient cycling, and above- and belowground plant growth dynamics. The shelters provided complete control of growing season rainfall patterns, whereas effects on photosynthetic photon flux density, nighttime net radiation, and soil temperature generally were comparable to other similar shelter designs. Soil and plant responses to the first growing season of rainfall manipulations (1998) suggested that the interval between rainfall events may be a primary driver in grassland ecosystem responses to altered rainfall patterns. Aboveground net primary productivity, soil CO2 flux, and flowering duration were reduced by the increased interrainfall intervals and were mostly unaffected by reduced rainfall quantity. The timing of rainfall events and resulting temporal patterns of soil moisture relative to critical times for microbial activity, biomass accumulation, plant life histories, and other ecological properties may regulate longerterm responses to altered rainfall patterns.

Energy balance comparison of sorghum and sunflower

An understanding of the energy exchange processes at the surface of the earth is necessary for studies of global climate change. If the climate becomes drier, as is predicted for northern mid-latitudes, it is important to know how major agricultural crops will play a role in the budget of heat and moisture. Thus, the energy balance components of sorghum [Sorghum bicolor (L.) Moench.] and sunflower (Helianthus annuus L.), two drought-resistant crops grown in the areas where summertime drying is forecasted, were compared. Soil water content and evapotranspiration (ET) rates also were determined. Net radiation was measured with net radiometers. Soil heat flux was analyzed with heat flux plates and thermocouples. The Bowen ratio method was used to determine sensible and latent heat fluxes. Sunflower had a higher evapotranspiration rate and depleted more water from the soil than sorghum. Soil heat flux into the soil during the daytime was greater for sorghum than sunflower, which was probably the result of the more erect leaves of sorghum. Nocturnal net radiation loss from the sorghum crop was greater than that from the sunflower crop, perhaps because more heat was stored in the soil under the sorghum crop. But daytime net radiation values were similar for the two crops. The data indicated that models of climate change must differentiate nighttime net radiation of agricultural crops. Sensible heat flux was not always less (or greater) for sorghum compared to sunflower. Sunflower had greater daytime values for latent heat flux, reflecting its greater depletion of water from the soil. Evapotranspiration rates determined by the energy balance method agreed relatively well with those found by the water balance method. For example, on 8 July (43 days after planting), the ET rates found by the energy-balance and water-balance methods were 4.6 vs. 5.5 mm/day for sunflower, respectively; for sorghum, these values were 4.0 vs. 3.5 mm/day, respectively. If the climate does become drier, the lower soil water use and lower latent heat flux of sorghum compared to sunflower suggest that sorghum will be better adapted to the climate change.

Frost risk mapping for landscape planning: A methodology

Minimum air temperatures were measured during three winters with a network of stations in open, undulating terrain. It was observed that the change in minimum air temperature with elevation could be predicted from mean nighttime windspeed, total nighttime net radiation loss and a hill-top reference minimum temperature. It was also found that the deviation of temperatures at individual sites could be predicted from a local terrain parameter which reflects the extent of cold air accumulations. Thus a methodology for frost risk mapping has been developed which is based on regional weather dataand local terrain analysis. This paper describes the model and illustrates the regional weather and terrain effects with three-dimensional block diagrams.

Solar net radiation over a bare wet field at Giza, estimated on the basis of its close relationship with global radiation

A comparison was made between daytime, night-time and daily net radiation measured in different seasons over a bare wet field at Giza, and the corresponding values of net radiation over irrigated short vegetation and global radiation. Close linear relationships were obtained in all cases. The relations with daytime and daily global radiation were applied to monthly averages of daily global radiation for a 10-year period, to obtain monthly averages of daily and daytime net radiation over the bare wet field. The annual variations of these variables, together with night-time net radiation obtained as the difference between these values, are described. Seasonal and annual values of these parameters, together with monthly, seasonal and annual values of the ratios of net radiation over the wet field to global radiation, and of net radiation over the same field to net radiation over irrigated short vegetation were also given. The corresponding values of the ratio daytime/daily net radiation over the wet field were also obtained to give an idea of the diurnal variation of net radiation in the different seasons. Brief information was also given about the highest and lowest values of net radiation during the day, and their times of occurence.

Spatial Distribution of Soil Heat Flux Under a Sour Cherry Tree

AbstractThis paper presents data on the spatial variability of surface soil heat flux in an orchard (Prunus cerasus L.), evaluates the error involved in estimating the surface soil heat flux, and develops a method by which a spatial average may be taken. Surface soil heat flux was calculated from measurements of the heat flux at the approximately 5‐cm depth and of the heat stored above the heat flux plate. The heat flux plate calibrations were corrected for the thermal conductivity of the soil as measured in situ. Measurements were made at six sites both under an orchard tree and in the open between trees. Results showed that the nighttime flux under the tree was occasionally < 50% of the values measured in the open. In contrast, the daytime spatial and temporal variability was very high and occasionally a small upward flux was recorded under the trees while a near maximum downward flux was being recorded in the open or under the tree a short time earlier or later. A spatial average was calculated by weighting the soil heat flux values by the area of the orchard they represented using an integration procedure. The spatial averages showed that 50–80% of the nighttime net radiation loss from the orchard was derived from the soil.