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<br />OOB72 <br /> <br />Since the dOWlIWln'd fluxes of shortwave and longwave radiation <br />vary on a lllrge geographic scale, they may need to be measured at onJy <br />one place in a region of homogeneous cloudiness. The upward flux of <br />shortwave r!ldiation (if taken as albedo) and of longllave radiation <br />vary abruptly with changes in surface cover and in temperature, but <br />less abruptly with time than With distance. Thus, they may be amenable <br />to aerial observation. <br /> <br />Of the four fluxes usually measured, onJy downward shortwave <br />radiation enjoys a geographic coverage that approaches what might be <br />termed a network, with measurements systematically ta:ken, doc:umented, <br />and published. . The Weather BureaU operates this net'i{ork (which includes <br />cooperating stations of several other organizations), processes the strip <br />charts, deposits them at the National Weather Records Cente.r at AsheVille, <br />N. C., and publishes daily s:ums in Climatological ~, National SUlDlllary. <br /> <br />There are some stations whose records are not published, cOllllllonly <br />because operation is tied to experimental studies and may be interrupted. <br />However, their records may :fill gaps at a critical period in .a hydrologic <br />investigation,' and should be used after the station history is checked for <br />exposure and operation (including calibration). Many allwave radiation <br />instruments have been sold, and some may be in more or les$ continuous <br />operation, perhaps in conjunction With micrometeorological programs tied <br />to some operation function. Su.ch stations l(01l.ld be found by" inquiry among <br />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 t~ believe that in cities like <br />Fresno, "lIhiph 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 relation <br />shO'Uld be Cl)nsidered. However, distanCe::> between sta.tions are .so great <br />that it is not. certain that double-mass techniques can be appliedeol1:fi.dently <br />to radiation records. . <br /> <br />The sCllI'ci ty of radiation stations has led to Ii variety of means' for <br />extending chverage in space and time. Downward shortwave radiation has <br />been related to such consequences as soil temperatuI'e or daily maxi:n(:um <br />temperature of the air (Landsberg, section 37), and to meteorological <br />factors such as 700-millibar height, temperature of contour curvature <br />(Miller, 19p5), or cloud type and clOud coverage (Haurwitz, 1945; Fritz <br />and MacDonald, 1949) . Sunshine duration can be related to insolationJ <br />for example, Hamon, Weiss and Wilson (1954) for daily values. Clear-day <br />shortwave rildiation can be estimated from astronomical data with consideration <br />of absorptipn by dust and water vapor in the atmosphere (Landsberg). The <br />relationship of up"Ward longwave radiation to surface temperature is well <br />known, as is that of downward longwave radiation to vapor pressure and <br />temperature, of the lower atmosphere (Brunt, 1941). There are also relatiqn- <br />ships between dowmrard shortwave radiation and the net allwave balance <br />(Shaw, 1956). . Many of these relationships are sUlDlllsrizedby 1andsbergand <br />Qy Budyko (1958, section 3). <br /> <br /> <br />IV.5 <br />