CHANGES IN SOLAR IRRADIANCE AND ATMOSPHERIC TURBIDITY IN COSTA-RICA DURING THE TOTAL SOLAR ECLIPSE OF JULY 11, 1991

Solar global radiation was measured in several places in Costa Rica du ring the total solar eclipse that occurred on July 11, 1991. In two of these places, Puntarenas and Santa Cruz, measurements in the ultravio let range (295-385 nm) were also taken. In Santa Cruz, a normal incide nce pyrheliometer with Schott filters OG530 and RG630 was used to meas ure direct solar radiation in its whole range, and in the 530-2800 nm and 630-2800 wavebands respectively. Global radiation, and consequentl y direct, diffuse and irradiance in any of the wavebands considered, d ecreased gradually as the sun was being eclipsed and reached zero duri ng the totality. then increased to their normal values. Data registere d in Santa Cruz were used to determine Angstrom's atmospheric turbidit y parameters alpha and beta. Computations show that between 13:00 and 14:30 LT (local time), alpha decreased and beta increased significantl y. This indicates that atmospheric turbidity was high and large partic les were more abundant than small ones. The size of hygroscopic partic les increased during the eclipse when temperature decreased and relati ve humidity increased in a comparatively short time.