Ultraviolet Radiation – 21 DISCUSSION Future Research on UVR in Crater Lake

Figure 15A. Crater Lake regression of photometer Kd,blue against inverse Secchi depth (units m-1; annual averages for only same-day measurements, 1968–1991). Equation: Kd,blue = 2.08/ZSD – 0.026 (r2=0.54, N=13 years).

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Figure 15B. Crater Lake time series of Kd,blue from direct photometer (gray circles) and radiometer (black circles) measurements and proxy using Secchi depth (open circles). The spike in 1995 follows heavy summer rain in June and July (see Figure 10A). Many of the comparison points are for measurements made on different days in the same month.

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Figure 16A. Crater Lake time series (1940–2002) of Kd,320 and Kd,380 using radiometer and photometer data from Figure 15B plus all valid Secchi disk data. Open symbols are from Secchi disk (triangles are Kd,320, squares are Kd,380); black symbols are direct from radiometer; light gray symbols are photometer data; dark gray triangles are Kd,320 derived from radiometer Kd,380. The spike in 1995 follows heavy rain in June and July.

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Figure 16. B. Crater Lake times series of Kd,320 using average of all sources of data. Sample frequency prior to 1978 is inadequate to characterize cycles but maximum and minimum values from 1896–1969 (0.07–0.12) fall within the same range as the more frequent measurements since 1978 (0.07–0.14, or 0.07–0.12 without including the rainy summer of 1995).

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