AEROSOL OPTICAL DEPTH VS. DAY OF YEAR
Shown above is all of the data obtained for 1998-2000. Aerosol optical depth (AOD) shows a seasonal dependence that correlates well with mean relative humidity, with a minimum in winter and a summertime maximum. The annual average value of AOD = 0.065, which is relatively low compared to measurements at more humid, low elevation sites. Dashed curve is a simple polynomial fit to the data.
EXAMPLE OF DIURNAL DATA FOR AOD
Total optical depths are determined by the slope of a log-linear plot of F(340) vs. secant of solar zenith angle (SZA). Our global radiation measurements are multiplied by a SZA-dependent scaling factor (direct/(direct+diffuse)), obtained from model calculations, to infer the direct beam component.
Plotted above are 340-nm direct solar fluxes for Oct 5, 2000. The slope of these lines (-.6754 for morning, -.6951 for afternoon) provide a measure of the total extinction optical depth. Aerosol optical depths (AOD) are determined by subtracting the molecular scattering contribution (MOD=.606 at our elevation) from the total. Daily values of AOD are taken from the average of AM and PM data. Here, a value of AOD=.079 is obtained.
COMPARISON OF MICROTOPS AND GUV AOD
AOD was also measured using a Solar Light Microtops II handheld sunphotometer (obtained on loan from NASA Goddard) between September and December 2000. The Microtops generally shows larger day-to-day variability, but monthly averaged data agree quite well and show the same downward trend from fall to winter seasons. We'd like to thank Gordon Labow for his assistance in obtaining and using the Microtops instrument.
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This information is being made available by Ken Minschwaner at New Mexico Institute of Mining and Technology's Physics Department.