Cloud effect in the estimation of instantaneous downward longwave radiation

Sugita, Michiaki; Brutsaert, Wilfried

doi:10.1029/92wr02352

Cited by 96 publications

(99 citation statements)

References 18 publications

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“…The reflected apparent temperature value within the portion is best measured by pointing the camera at a piece of crumpled aluminum foil, whose infrared reflectivity is very high, about 0.97. Estimating by empirical methods (Sugita and Brutsaert, 1993) might be unreliable, because those methods were usually developed to estimate incoming atmospheric radiation over the entire infrared spectrum.…”

Section: Atmospheric Effectsmentioning

confidence: 99%

Use of a thermal imager for snow pit temperatures

2012

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Abstract. Weak snow of interest to avalanche forecasting often forms and changes as thin layers. Thermometers, the current field technology for measuring the temperature gradients across such layers -and for thus estimating the expected vapour flux and future type of crystal metamorphism -are difficult to use at distances shorter than 1 cm. In contrast, a thermal imager can provide thousands of simultaneous temperature measurements across small distances with better accuracy. However, a thermal imager only senses the exposed surface, complicating its methods for access and accuracy of buried temperatures. This paper presents methods for exposing buried layers on pit walls and using a thermal imager to measure temperatures on these walls, correct for lens effects with snow, adjust temperature gradients, adjust time exposed, and calculate temperature gradients over millimetre distances. We find lens error on temperature gradients to be on the order of 0.03 • C between image centre and corners. We find temperature gradient change over time to usually decrease -as expected with atmospheric equalization as a strong effect. Case studies including thermal images and visual macro photographs of crystals, collected during the 2010-2011 winter, demonstrate large temperature differences over millimetre-scale distances that are consistent with observed kinetic metamorphism. Further study is needed to use absolute temperatures independently of supporting gradient data.

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Section: Atmospheric Effectsmentioning

confidence: 99%

Use of a thermal imager for snow pit temperatures

2012

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“…Several models have been proposed to parameterize « a for clear-sky conditions (Idso and Jackson 1969;Brutsaert 1975;Idso 1981;Swinbank 1963;Prata 1996) and cloudy-sky conditions (Sugita and Brutsaert 1993;Crawford and Duchon 1999). However, all of these formulations involve the use of empirical constants, specific to the biogeographic regions where the data were collected.…”

Section: B Incoming Longwave Radiationmentioning

confidence: 99%

Validation of a Simple Steady-State Forecast of Minimum Nocturnal Temperatures

Kala

Lyons

Foster³

et al. 2009

Journal of Applied Meteorology and Climatology

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A two-layer steady-state resistance model is compared with routine meteorological data collected from the Western Australian wheat belt during 2000-06. Major difficulties in implementing such a model are the correct parameterization for the incoming longwave radiation and estimation of daily soil moisture, neither of which are routinely measured. These difficulties are addressed by testing parameterizations for incoming longwave radiation calibrated to local conditions and incorporating a soil-water balance model based on routine weather data. The modified model has RMSE and biases ranging from 2.48 to 3.18C and 20.28 to 0.88C, respectively, across the wheat belt when comparing all minimum nocturnal temperatures. The model is shown to predict frost events approximately 55% of the time and illustrates that frost damage to foliage may occur when screen temperatures are , 28C.

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“…In order to evaluate the relationship existing between ε a and cloudiness, the clearness index (CI) has been used, as in Sugita and Brutsaert (1993), and equivalent to ratio s in Crawford and Duchon (1999). CI is the ratio between the theoretical shortwave irradiance at the top of the atmosphere (extraterrestrial radiation) and the surface-measured solar radiation.…”

Section: Local 3-state Parameterization (3sparam) For Rp Stationmentioning

confidence: 99%

Parameterization of atmospheric longwave emissivity in a mountainous site for all sky conditions

Herrero

Polo

2012

Hydrol. Earth Syst. Sci.

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Abstract. Longwave radiation is an important component of the energy balance of the Earth's surface. The downward component, emitted by the clouds and aerosols in the atmosphere, is rarely measured, and is still not well understood. In mountainous areas, direct observations are even scarcer and the fitting of existing models is often subjected to local parameterization in order to surplus the particular physics of the atmospheric profiles. The influence of clouds makes it even harder to estimate for all sky conditions. This work presents a long-time continuous dataset of high-resolution longwave radiation measured in a weather station at a height of 2500 m a.s.l. in Sierra Nevada, Spain, together with the parameterization of the apparent atmospheric emissivity for clear and cloudy skies resulting from three different schemes. We evaluate the schemes of Brutsaert, and Crawford and Duchon with locally adjusted coefficients and compare them with a completely parametric expression adjusted for these data that takes into account three possible significant atmospheric states related to the cloud cover: clear, completely covered, and partly covered skies. All the parametric expressions are related to the screen-level values of temperature, relative humidity and solar radiation, which can be frequently found in standard weather stations. Unobserved cloudiness measurements needed for Brutsaert scheme for cloudy sky are also parameterized from screen-level measurements. The calibration performed for a 6-yr period at the study site resulted in satisfactory estimations of emissivity for all the analyzed schemes thanks to the local fitting of the parameterizations, with the best achievement found for the completely parametric expression. Further validation of the expressions in two alternative sites showed that the greater accuracy of the latter can also be found in very close sites, while a better performance of the Brutsaert scheme, with a more physical background and the successful parameterization of the clouds effect, is found in nearby sites outside the initial mountain range. The results show the feasibility for the local calibration of expressions to estimate instantaneous atmospheric emissivity for all sky conditions only using surface data, either with a completely parametric scheme if longwave data are available, or through obtaining of locally fitted coefficients for Brutsaert and derived schemes. Nevertheless, the best performance of the first approach would be at the expense of a reduced local applicability.

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Cloud effect in the estimation of instantaneous downward longwave radiation

Cited by 96 publications

References 18 publications

Use of a thermal imager for snow pit temperatures

Use of a thermal imager for snow pit temperatures

Validation of a Simple Steady-State Forecast of Minimum Nocturnal Temperatures

Parameterization of atmospheric longwave emissivity in a mountainous site for all sky conditions

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