International Journal of Biometeorology

, Volume 58, Issue 7, pp 1615–1625 | Cite as

Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

Original Paper

Abstract

This study contributes to the knowledge about the capabilities of the popular “six-directional method” describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (Tmrt). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the Tmrt values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10–15-min long “blind spot” when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the Tmrt decrease on clear sunny days will occur in different times and will be different in extent.

Keywords

Mean radiant temperature Six-directional technique Clear sky Daytime relapse Lateral directions 

Supplementary material

484_2013_765_Fig7_ESM.jpg (1.3 mb)
Appendix 1

(a) series: Sun-path properties and the corresponding radiation conditions in Huwei on the four cardinal days of the year: (a.1) Spring Equinox, (a.2) Summer Solstice, (a.3) Autumn Equinox, (a.4) Winter Solstice; (b–d) series: absorbed short-wave flux densities on the same days from the two vertical (Kvert*), from the four lateral (Klat*), and from all the six perpendicular directions (K*) in the cases of spherical (sp.) and standing (st.) reference shapes, and with different orientations: (b) series: N–E–W–S (0° deviation), (c) series: NNE–ESE–SSW–WNW (22.5° deviation), (d) series: NE–SE–SW–NW (45° deviation) (JPEG 1327 kb)

484_2013_765_Fig8_ESM.jpg (1.4 mb)
Appendix 2

(a) series: Sun-path properties and the corresponding radiation conditions in Göteborg on the four cardinal days of the year: (a.1) Spring Equinox, (a.2) Summer Solstice, (a.3) Autumn Equinox, (a.4) Winter Solstice; (b–d) series: absorbed short-wave flux densities on the same days from the two vertical (Kvert*), from the four lateral (Klat*), and from all the six perpendicular directions (K*) in the cases of spherical (sp.) and standing (st.) reference shapes, and with different orientations: (b) series: N–E–W–S (0° deviation); (c) series: NNE–ESE–SSW–WNW (22.5° deviation); (d) series: NE–SE–SW–NW (45° deviation) (JPEG 1469 kb)

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Copyright information

© ISB 2013

Authors and Affiliations

  • Noémi Kántor
    • 1
  • Tzu-Ping Lin
    • 2
  • Andreas Matzarakis
    • 3
  1. 1.Program of Landscape and Recreation, Research Center for the Humanities and Social SciencesNational Chung Hsing UniversityTaichung CityRepublic of China
  2. 2.Department of ArchitectureNational Cheng Kung UniversityTainan 701Republic of China
  3. 3.Chair of Meteorology and ClimatologyAlberts-Ludwigs-University FreiburgFreiburgGermany

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