Medically important solar ultraviolet A. Radiation measurements.

Area of Science:

• Atmospheric Science
• Environmental Science
• Solar Radiation Physics

Background:

• Solar ultraviolet A (UVA) radiation is a key environmental factor with implications for health and climate.
• Equatorial regions receive high solar irradiance, necessitating detailed measurement studies.
• Long-term data is crucial for understanding seasonal variations and the impact of atmospheric conditions like cloud cover.

Purpose of the Study:

• To present results from a comprehensive 6-year study of solar UVA radiation.
• To quantify diurnal and seasonal UVA flux at an equatorial location (Penang, 5 degrees N).
• To assess the impact of significant cloud cover on incident UVA radiation levels.

Main Methods:

• Continuous measurement of solar UVA radiation flux over a 6-year period.
• Data analysis focused on diurnal patterns, daily totals, and seasonal variations.
• Statistical analysis of radiation data under varying cloud cover conditions (average 83% cloud cover).

Main Results:

• High midday diurnal UVA flux recorded, reaching approximately 3.0 x 10(-2) KWHM-2 on clear days.
• Average daily total UVA flux measured at 1.6 x 10(-1) KWHM-2, showing minimal seasonal variation.
• Even with 83% cloud cover, UVA radiation was reduced by only about half, indicating substantial residual exposure.

Conclusions:

• Equatorial regions experience consistently high solar UVA radiation levels throughout the year.
• Cloud cover significantly attenuates UVA radiation but does not eliminate it, posing a continuous exposure risk.
• The measured UVA flux provides a baseline lower limit for incident radiation relevant to tropical and equatorial zones.