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<br />-11- <br /> <br /> <br />o u 124 i <br /> <br />Of the four fluxes usually measured, only downward shortwave <br />radiation enjoys a geographic coverage that approaches what might be <br />termed a network, with measurements systematically taken, documented, <br />and published. The ,Weather Bureau operates this network (which includes <br />cooperating stations of several other organizations), processes the <br />strip charts, deposits them at the National Weather Records Center at <br />Asheville, N. C., and publishes daily sums in "Climatological Data, <br />National Summary." <br /> <br />There are some stations whose records are not published, commonly <br />because operation is tied to short-term experimental studies. However, <br />their records may fill gaps at a critical period in a hydrologic investi- <br />gation, and should be used after the station history is checked for <br />exposure of instruments, and in other pertinent respects. Many <br />allwave radiation instruments have been sold, and some may be in more or <br />less continuous operation, perhaps in conjunction with micrometeoro- <br />logical programs tied to some resource-management activity. Such stations <br />would be found by inquiry among local meteorologists and geophysicists. <br /> <br />Use of radiation data <br /> <br />Problems such as deterioration of an observational site, which have <br />been studied intensively in regard to precipitation, have scarcely been <br />touched for radiation. There is reason to believe that in cities like <br />Fresno, which is beginning to experience severe air pollution, radiation <br />has decreased significantly. If records so biased were used to estimate <br />radiation in adjacent wildland areas, the possibility of change in <br />relation should be considered. However, distances between stations are <br />so great that double-mass techniques cannot be applied confidently to <br />correlation of radiation records. <br /> <br />,The scarcity of radiation stations has led to a variety of mean for <br />extending coverage in space and time. Downward shortwave radiati,on has <br />been related to such consequences as soil temperature or daily maximum <br />temperature of the air (Landsberg, section 37), and to meteorological <br />factors such as 700-millibar height, (Miller, 1955), or cloud type and <br />cloud coverage (Haurwitz, 1945; Fritz and MacDonald, 1949). Sunshine <br />duration can be related to insolation; for example, see Hamon, Weiss and <br />Wilson (1954) for daily values. Clear-day shortwave radiation can be <br />estimated from astronomical data with consideration of absorption by <br />dust and water vapor in the atmosphere (Landsberg). The relationship <br />of upward longwave radiation to surface temperature is well known, as <br />is that of downward longwave radiation to vapor pressure and temperature <br />of the lower atmosphere (Brunt, 1941). There are also relationships <br />between downward shortwave radiation and the net allwave balance (Shaw, <br />1956). Many of these relationships are summarized by Landsberg and by <br />Budyko (1958, section 3). <br />