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<br /> <br />001438 <br /> <br />IV. RADIATIVE HEAT TRANSFERS <br /> <br />Introduction <br /> <br />Available information on the four fluxes of radiation near the <br />earth IS surfaoe (de>'llnWllrd shortwave, upward shortnve, dowtnlll.rd lOngwll.ve, <br />and upward longwave) sheds relatively little light on dependability of <br />the data, op: representativeness of observations, or even on instl'lllll.ent <br />accuracy. While radiation measurements long have been recog:rUllled as <br />important in m8D;1 geophysical processes, they have not been made in net- <br />works for very long. The older records are likely to be highly indiv1dua~ <br />in type of instl'lllll.ent and installation, being parts of agricultural studies <br />in which on\J.:y local readings were needed. Recently the Weather :Bureau's <br />observatiolllll network for downward shortwave radiation has expanded.; <br />energy-bala1tce approaches in exper:iJllental studies of snow melting, evapo- <br />ration, and, evapotranspiration have beCOMe liidely accepted; and the . <br />International Geophysical Year and satellite programs have grea~ <br />stimulated "interest in radiation. In most areas of hydrologic operationSj <br />radiation stations are still scarce, but it is to be hoped that in time <br />small networks liill be installed in the larger drainage basins of the West., <br />somewhat as, networks of precipitation-intensity stations were installed in <br />the thirties for operational plU"poses. <br /> <br />Effects of station location <br /> <br />Radiation stations are few in nURIber and there is a strong temptatio-, <br />to extend their records over areas !IlUch greater' than is warranted. ExpoS\U'e <br />and location of stations become important for this reason. <br /> <br />I <br /> <br />BecaUSe l.'adiation sensors =st be connected v.\.th instI'Ulllents to record <br />continuously a SlIIlIll electrical output, the recording equipment is nototqy <br />bulky, fralt.Lle, and expensive but also needs frequent checking and servicing. <br />This requi~ement tends to confine rlldiation measurements to stations ha'Vin!t <br />technical personnel; most of these are in lwlands or valleys. MdI1ntains. <br />are poorly isampled. For eXample, the present network for dOllnvard shortwave <br />radiation :l;ncludes stations at considerable altitudes (Albuquerque, El;r, 'jand <br />Grand Junction), but these are in Valleys, . <br /> <br />A few:md\1I1tain stations have operated over short periods, but none ill <br />noW functidning continuously. Some comparisons suggest that extrapolation <br />of lowland'records to mountains may be difficult except on a day-to-da;r " <br />basis, v.\.tl:l observations of cloudiness at both places. For example, Dav1l' <br />and Soda 3Ijrings, California, have entirely different regimes Of winter <br />radiation, ithE1 valley being filled liith fog for long periodsiibile the <br />mountains are surmy. The summer regimes differ oppositely, the mountains <br />being commonly cloudy. <br /> <br />Cloudiness regimes also may differ in other geographic sitlllltions, <br />which are J,ess distinotive topographically than mou:ntain and lowland. <br />Coastal and inland regions may have different amounts of cloud cover, and <br />their regirites of shortwave and longwave radiation are dif':ferent. Thus, <br />caution shOuld be taken in extrapolating radiation data over ally long <br />distance. <br /> <br />",-. <br /> <br />IV.l <br />