Antarctic UV Spectroradiometer Monitoring Program: Contrasts in UV Irradiance at the South Pole and Barrow, Alaska

T. MESTECHKINA, C. R. BOOTH, J. R. TUSSON IV, AND J. C. EHRAMJIAN

Biospherical Instruments Inc, San Diego, California 92110-2621

INTRODUCTION

The Antarctic Ultraviolet Spectroradiometer Monitoring Network was established by the U.S. National Science Foundation (NSF) in 1988 in response to predictions of increased ultraviolet (UV) radiation in the polar regions. The network consists of several automated, high-resolution spectroradiometers: five are placed in strategic locations in Antarctica and the Arctic, one is established in San Diego to collect data and serve as a training and testing facility (Table 1), and a portable system is used for instrument intercomparisons [Seckmeyer, et al., 1995]. The network makes measurements of UV spectral irradiance and provides a variety of biological dosage calculations of UV exposure. Biospherical Instruments Inc., under contract to Antarctica Support Associates (ASA), directed by NSF, is responsible for operating and maintaining the network and distributing data to the scientific community.

TABLE 1. Installation Sites

*CADIC: Centro Austral de Investigaciones Cientificas, Argentina

†Ukpeagvik Inupiat Corporation-National Arctic Research Laboratory
 

The spectroradiometers used in the system are Biospherical Instruments, Inc. Model SUV-100. Each instrument contains an irradiance diffuser, a double holographic grating mono-chromator, a photomultiplier tube (PMT), and calibration lamps. A vacuum-formed Teflon diffuser serves as an all-weather irradiance collector, and it is heated by the system to deter ice and snow accumulation. Tungsten-halogen and mercury vapor calibration lamps are used for automatic internal calibrations of both responsivity and wavelength that occur two to four times daily. All instrument functions, calibration activities, and data acquisitions are computer controlled. Further details on the spectroradiometers can be found in Booth et al., 1996.

The South Pole and Barrow, Alaska, installations of the network are in locations that also have CMDL installations. Therefore, the balance of this report will focus on these two sites. The South Pole site is located away from the influence of mountains in a region of almost constant albedo. Cloud cover is relatively infrequent and it is generally thin when it does occur. The very small hourly change in the solar zenith angle at the South Pole supports examination of changes in total column ozone (as estimated by UV irradiance) at hourly resolution [Booth and Madronich, 1993]. For example, in Figure 1a, a substantial decrease is seen in irradiance around the 300 nm in late November 1993. Meanwhile, Total Ozone Maping Spectrometer (TOMS) Nimbus-7 data report a substantial increase in the 300 nm irradiance between November 15 and November 20, 1993.

Fig. 1. Noontime integrated spectral irradiance at Barrow, Alaska, and at South Pole from January 1993 through December 1995. Panel a (left) shows the integrated irradiance around 300 nm (293.507-303.03 nm) and is contrasted with panel b (right) which illustrates the UV-A irradiance (320-400 nm). The higher irradiance values at Barrow are due to the higher sun elevation. Normally, irradiance at Barrow peaks in June, while irradiance at the South Pole peaks in December.
 

Barrow, Alaska, contrasts with the South Pole in that it is located where a significant change in surface albedo occurs due to both the springtime snowmelt [Dutton and Endres, 1991] and changes in sea-ice coverage. Also, Barrow experiences significant changes in incident irradiance due to Arctic storms. The contrast in irradiances between Barrow and the South Pole is seen in Figure 1b, which depicts the integrated noontime irradiances over the UV-A spectrum (320-400 nm) from January 1993 through December 1995.

The integral of spectral irradiance from 298.507 to 303.03 nm is one of the most sensitive to changes in total ozone (and solar angle). A strong correlation between the ozone concentration and UV irradiance is illustrated by the Barrow 1995 example in Figure 2. Figure 3 emphasizes that in 1994 high UV levels at South Pole were observed comparatively early in the season (at the end of October) with an early termination of influence of the "ozone hole."

Fig. 2. Comparison of the 298.507 - 303.03 nm integrated spectral irradiance and TOVS total ozone measurements made at Barrow during austral spring 1995. Note that the right axis are inverted to make the effect of decreasing ozone on increasing irradiance readily apparent.
 

Fig. 3. Integrated 298.507-303.03 nm spectral irradiance at South Pole. The thin lines represent historical (1991-1993) minimum and maximum observations, while 1994 data are expressed as diamonds.
 

Table 2 lists the maximum UV-B irradiances (290-320 nm) recorded at each site in 1990-1995. The maximum irradiance reported in San Diego happened to be elevated by cloud coverage (days of partial cloud coverage are sometimes observed to have higher irradiances than completely clear days due to reflections off of cloud surfaces). The Antarctic site measurements are enhanced by high albedo due to snow and ice coverage. During the Palmer maximum, ice coverage was heavy, increasing surface albedo.

TABLE 2. UV-B (290-320 nm) maxima (µW/cm²)

SUMMARY

High spectral resolution scanning UV spectro-radiometers have been established at six sites and are successfully providing multiyear data sets. Resulting data were used to test radiative transfer models [Lubin and Frederick, 1992; Smith et al., 1992], investigate radiation amplification [Booth and Madronich, 1993; Madronich, 1994], derive ozone concentrations [Stamnes et al., 1992], examine the biological impact of enhanced UV [Cullen et al., 1992; Anderson et al., 1993; Benavides et al., 1993; Holm-Hansen et al., 1993] and explore geographical differences in the UV [Booth et al., 1995; Diaz et al., 1994; McKenzie et al., 1994; Seckmeyer et al., 1995].

Data, referenced to both beginning- and end-of-season calibration constants are distributed on CD-ROM and are available to any interested researcher. For more information, please contact: Biospherical Instruments Inc., 5340 Riley Street, San Diego, CA 92110-2621 (Fax: (619) 686-1887, Internet: uvgroup@biospherical.com, www:http://www.biospherical.com).

Acknowledgments. This research and monitoring activity was funded by contract SCK-M18914-02 from Antarctic Support Associates under the direction of Polly Penhale at the National Science Foundation, Office of Polar Programs. B. Mendonca of CMDL assisted in providing operators and support for the installations at Barrow. R. McPeters of NASA/GSFC provided TOMS Total Ozone data for comparison purposes. A TOMS update CD-ROM is available from the National Space Science Data Center (NSSDC), Goddard Space Flight Center. Barrow operators include D. Norton (Arctic Sivumnun Ilisagvik College), D. Endres and M. Gaylord (CMDL). The Ukpeagvik Inupiat Corporation of Barrow provided installation assistance. Operators at Palmer, the South Pole, and McMurdo were provided by ASA.

REFERENCES

Anderson, S., J. Hoffman, G. Wild, I. Bosch, and D. Karentz, Cytogenetic, cellular, and developmental responses in antarctic sea urchins (Sterechinus neumayeri) following laboratory ultraviolet-B and ambient solar radiation exposures, Ant. J. U. S., 1993 Review, 28(5), 115-116, 1993.

Benavides, H., L. Prado, S. Díaz, and J.I. Carreto. An exceptional bloom of Alexandrium catenella in the Beagle Channel, Argentina, Proceedings of the 6th International Conference on Toxic Marine Phytoplankton; Nantes, October 18-22, 1993.

Booth, C.R., T.B. Lucas, T. Mestechkina, J. Shmidt, and J. Tusson, High resolution UV spectral irradiance monitoring program - contrasts in UV exposure in Antarctica and the Americas, Ant. J. U. S., in press, 1996a.

Booth, C.R., T.B. Lucas, T. Mestechkina, J.R.Tusson IV, J.P. Schmidt, D.A. Neuschuler, and J.H. Morrow, NSF Polar Programs UV Spectroradiometer Network 1994-1995 Operations Report, 182 pp., Biospherical Instruments Inc., San Diego, CA, 1996b.

Booth, C.R., and S. Madronich, Radiation amplification factors: Improved formulation accounts for large increases in ultraviolet radiation associated with Antarctic ozone depletion, in Antarctic Research Series, edited by C.S. Weiler and P.A. Penhale, 62, pp. 39-42, 1993.

Cullen, J.C., P.J. Neale, and M.P. Lesser, Biological weighting function for the inhibition of phytoplankton photosynthesis by ultraviolet radiation, Science, 258, 646-650, 1992.

Diaz, S.B., Frederick, I. Smolskaia, W. Esposito, T.B. Lucas, and C.R. Booth, Ultraviolet solar radiation in the high latitudes of South America, Photochem. Photobio., 60(4), 356-362, 1994.

Dutton, E.G., and D.J. Endres, Date of snowmelt at Barrow, Alaska, U.S.A., Arctic Alpine Res., 23(1), 115-119, 1991.

Holm-Hansen, O., D. Lubin, and E.W. Helbling, Ultraviolet radiation and its effects on organisms in aquatic environments, in Environmental UR Photobiology, edited by A.R. Young et al; pp. 379-425, Plenum Press, New York, 1993.

Lubin, D., and J.E. Frederick, Observations of ozone and cloud properties from NSF ultraviolet monitor measurements at Palmer Station, Antarctica, Ant. J. U. S., 1989 Review, 25(5), 241-242, 1992.

Madronich, S. Increases in biologically damaging UV-B radiation due to stratospheric ozone reductions: A brief review, Arch. Hydrobiol. Beih: Ergebn. Limnol., 43, 17-30, 1994.

McKenzie, R.L., M. Blumthaler, C.R. Booth, S.B. Diaz, J.E. Frederick, T. Ito, S. Madronich, and G. Seckmeyer, Surface Ultraviolet Radiation, in Scientific Assessment of Ozone Depletion: 1994, World Meteorological Organization Global Ozone Research Monitoring Project, 37, pp. 9.1-9.22, WMO, Geneva, Switzerland, 1994.

Seckmeyer, G., B. Mayer, G. Bernard, R.L. McKenzie, P.V. Johnston, M. Kotkamp, C.R. Booth, T.B. Lucas, T. Mestechkina, C.R. Roy, H.P. Gies, and D. Tomlinson. Geographical differences in the UV measured by intercompared spectroradiometers, Geophys. Res. Lett., 22(14), 1889-1892, 1995.

Smith, R.C., Z. Wan, and K.S. Baker, Ozone depletion in Antarctica: Modeling its effect under clear-sky conditions, J. of Geophys. Res., 97, 7383-7397, 1992.

Stamnes, K., Z. Jin, J. Slusser, C.R. Booth, and T.B. Lucas, Several-fold enhancement of biologically effective ultraviolet radiation levels at McMurdo Station, Antarctica, during the 1990 ozone hole, Geophys. Res. Lett., 19, 1013-1017. 1992. 

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