Radiative properties of rock types in the Harquahala Plains area, Arizona, and possible meteorological implications

Abstract

Radiation from the ground surface into the overlying atmosphere during summertime in Southern Arizona constitutes a major reason for convectional overturn of the moist, unstable air occurring over the state at this time. Radiation = f (T) and for a given rock type in the field, T=g (Q(s), α, κ) where Q(s) = incident solar radiation, α=albedo, κ=thermal diffusivity. The relative quantities of visible energy absorbed by each of the six main rock types occurring in the Harquahala Plains area was measured coincident with measurements of temperature change versus time atl inch depth for a day over each of the rock types in question. This data allowed computations of the temperature variation with time in each of the rock types assuming an average daily insolation value for July. Outgoing radiation, (I(1)), from each of the rock types was computed from the relationship: I(1)= σT^4 where T=absolute temperature, σ=Stefan’s constant. The greater the magnitude of I(1), then the greater the probability for convectional rainfall to occur. Thus, the relative values of I(1) throughout the Plain area establish a possible ordered preference for convective rainfall. These values were then compared with rainfall/unit area measured over each of the rock types by radar for one summer rainy season and the results obtained seemed to indicate that for those rock types constituting a significant portion of the total area, a relationship between radiation and rainfall/unit area does exist in that the regions of larger I(1) experienced greater rainfall totals per unit area.