SHORT-TERM VARIABILITY OF ATMOSPHERIC TURBIDITY AND OPTICAL TURBULENCE IN A DESERT ENVIRONMENT

Variability of atmospheric turbidity calculated from direct beam solar radiation measurements and the transverse coherence length, r(o), der ived from differential image motion of stellar sources show pronounced fluctuations on the order of a few minutes under convectively unstabl e conditions in a desert environment. The quiescent periods, ''neutral '' events, when local near surface adiabatic conditions occur show sub stantial reductions in the fluctuations of the same quantities. Image motion results for nighttime (stable) conditions display slowing varyi ng patterns with reduced short term (few minutes) variations. The meas urements were taken using a suite of instrumentation probing the same volume of atmosphere. The instrumentation used includes a pyrheliomete r, Atmospheric Turbulence Measurement and Observation System (ATMOS), a sodar, a scintillometer, and tower-mounted sensors. A time-height di splay of sodar data calibrated for the refractive index structure para meter, C-n(2), coupled with scintillometer measurements show the diurn al evolution of the boundary layer responding to the local healing-coo ling cycle and drainage flows from the surrounding mountains. Several atmospheric features are seen and discussed in these results as they a ffect the nature of the patterns of turbidity and r(o). Of particular interests are the development of convection, changes in the capping in version, thermal plume structures, neutral events, and wave-turbulence interactions. Sinusoidal oscillations, identified as internal gravity waves, are seen in the nighttime laminated structures.