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Recent Changes in Solar Irradiance in Antarctica*

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Recent Changes in Solar Irradiance in Antarctica* 2078 JOURNAL OF CLIMATE VOLUME 10 Recent Changes in Solar Irradiance in Antarctica* G. STANHILL AND S. COHEN Institute of Soils and Water, ARO, Bet Dagan, Israel (Manuscript received 13 May 1996, in ®nal form 8 January 1997) ABSTRACT A signi®cant decrease in the annual sums of global irradiance reaching the surface in Antarctica, averaging 20.28 W m22 yr21, was derived from an analysis of all complete years of measurement available from 12 pyranometer stations, 10 of which were on the coast. The decrease was greater than could be attributed to the nonhomogeneous nature of the database, the estimated errors of measurement, or changes in the amount of cloud cover. The smaller database of radiation balance measurements available showed no statistically signi®cant change. Possible causes of these results are discussed, as is the implication that the recent surface warming in Antarctica is not due to radiative forcing. 1. Introduction welling longwave radiation from the atmosphere L↓ should result in a more positive net radiation balance The importance of surface warming in Antarctica ex- at polar surfaces Q . However, an analysis of long-term tends beyond its signi®cance for the continent's fragile * series of Q* measurements from the Arctic showed that ecosystems because of the many important, complex, a small decrease has occurred; this was attributed to the and interacting feedback mechanisms linking the sur- accompanying much larger and statistically highly sig- faces of the polar regions with the global climate system ni®cant decrease in shortwave global irradiance K↓ that (Kellog 1975). was observed (Stanhill 1995). Analysis of surface temperature records from 15 coast- The seasonal and spatial distribution of this decrease, al stations in Antarctica (Jacka and Budd 1992) has as well as its magnitude, suggested that its cause was shown that a rapid and widespread warming took place the Arctic hazeÐtrapped incursions of polluted air 21, between 1959 and 1988, which averaged 0.0288Cyr reaching the Arctic from the industrial regions of the three times the mean rate observed for the earth as a Northern Hemisphere (Stonehouse 1986, Sturges 1991). whole during the same period (Jones and Briffa 1992). Reductions in K↓ caused by the Arctic haze could, by Other studies showing rapid surface warming in Antarc- balancing the increase in L↓, explain the absence of tica this century have been published by Jones (1990), surface warming in the Arctic that has been noted in a Limpert (1974), Raper et al. (1984), Sansum (1989), number of studies of climate change (Kelley et al. 1982; Braeten and Dresckhoff (1992), and King (1994). In con- Kukla and Robinson 1981; Lamb 1982; Tsuchiya 1991; trast, analysis of the South Pole records shows no increase Jaworowski et al. 1992; Jones and Briffa 1992; Kahl et in surface temperature (Hana 1989; Dutton et al. 1991). al. 1993; Walsh 1993). Enhanced warming due to increased concentrations The contrast between surface heating in the North of CO and other radiatively active gases in the atmo- 2 and South Polar regions is also evident in an analysis sphere, predicted for the polar regions 100 yr ago (Ar- of the radiosonde records taken from 1958 to 1992 (An- rhenius 1896), has recently been con®rmed for Antarc- gell 1994). tica by simulation studies using general circulation mod- As the concentration of pollutants and aerosols in els in the equilibrium but not in the transient mode Antarctica is much lower than that in the Arctic (Hansen (Houghton et al. 1992). et al. 1988; Heintzenberg 1989; Kane 1994; Radianov Surface warming caused by an increase in the down- 1994), changes in global irradiance in the South Polar regions should be correspondingly smaller. By contrast, the much higher rates of surface warming reported from * Agricultural Research Organization Contribution Number 1885-E. Antarctica, if caused by radiative forcing, should be re¯ected in an increase in the surface radiation balance. This paper presents a summary of irradiance mea- Corresponding author address: Dr. Gerald Stanhill, Institute of Soils and Water, Agricultural Research Organization, Bet Dagan surements made in Antarctica during the last 40 yr and 50-250, Israel. analyzes the changes found in light of the above hy- E-mail: [email protected] potheses. q1997 American Meteorological Society Unauthenticated | Downloaded 09/23/21 01:12 PM UTC AUGUST 1997 STANHILL AND COHEN 2079 FIG. 1. Positions of measurement sites in Antarctica. The isometric view is orientated as if light source were situated at the base of the map; the true viewpoint looking southward is 1358E. Reproduced from AntarcticaÐA Topographic Database [BAS (Misc) 7 sheet map] by permission of director, British Antarctic Survey. 2. Measurements of global irradiance and diation Balance Data (The World Network), published radiation balance since 1964 by the Voeikov Main Geophysical Obser- Continuous measurements of irradiance in Antarctica vatory in St. Petersburg, Russia. made with calibrated thermoelectric pyranometers and The position of these measurement sites is shown in pyrradiometers started in 1956, with preparations for Fig. 1; their coordinates, together with details of the the International Geophysical Year 1957±58. Since then, periods for which data are available, are presented in 203 yearly global irradiance values have been published Table 1, along with the mean annual totals of K↓, their for 12 sites by various authorities, either directly or coef®cients of variation (standard error as a fraction of through the monthly bulletin Solar Radiation and Ra- mean), and their fractions of extraterrestrial irradiance. TABLE 1. Global irradiance measurements in Antarctica. Mean annual values Period of K↓ CV Data a 22 b c Site Coordinates measurement (GJ m ) FE (%) sources South Pole, United States 908009S 08009 2800 m 1957±92 (2) 4.061 0.73 Ð A Vostok, Russia 788279S 1068529E 3488 m 1958±87 (18) 4.765 0.82 3.5 B Scott, New Zealand 778519S 1668459E 16 m 1957±94 (36) 3.455 0.59 6.1 C Halley, United Kingdom 758319S 268459W 29 m 1956±82 (22) 3.491 0.58 3.0 AD Novolazerevskaya, Russia 708469S 118509E 98 m 1964±87 (24) 4.027 0.63 4.3 B Sanae, South Africa 708399S 28219W 56 m 1975±85 (7) 4.563 0.72 9.9 E Neumayer, Germany 708379S 88229E 1982±94 (11) 3.707 0.58 6.4 F Syowa, Japan 698009S 398359E 21 m 1966±94 (28) 4.026 0.66 4.0 G Mawson, Australia 678369S 628539E 15 m 1975±78 (2) 3.946 0.60 Ð H Mirny, Russia 668339S 938009E 39 m 1956±87 (27) 4.334 0.64 5.6 BI Casey, Australia 668179S 1108329E 15 m 1974±76 (3) 3.606 0.53 Ð H Faraday, United Kingdom 658159S648169W 11 m 1963±82 (20) 3.153 0.46 5.8 D a Figure in brackets is the number of complete years. b FE is the fraction of the extraterrestrial. c AÐWMO (1960); Dutton et al. (1989); Climate Monitoring and Diagnostics Laboratory NOAA; E. G. Dutton (1994, personal communication. BÐMonthly bulletins; Solar Radiation and Radiation Balance Data (The World Network); Voeikov Main Geophysical Observatory, St. Petersburg, Russia. CÐThompson and McDonald (1962); National Institute of Water and Atmosphere Research, Wellington, New Zealand; S. Nichol (1994, personal communication); S. Nichol (1996, personal communication). DÐWMO (1960), Gardiner and Shanklin (1989). EÐWeather Bureau, Pretoria, South Africa; M. Laing (1994, personal communication). FÐSchmidt and Konig-Langlo (1994); Alfred-Wegener-Institute fuÈr Polar und Meeresforschung, Bremerhaven, Germany; G. Konig-Langlo (1995, personal communication). GÐJARE Data Reports (Meteorology), National Institute for Polar Research, Tokyo, Japan; Japan Meteorological Agency, Tokyo, Japan; M. Saiki (1996, personal communication). HÐBureau of Meteorology, Melbourne, Australia; N. A. Streten (1994, personal communication). IÐRusin (1964). Unauthenticated | Downloaded 09/23/21 01:12 PM UTC 2080 JOURNAL OF CLIMATE VOLUME 10 TABLE 2. Radiation balance measurements in Antarctica. Mean annual values Period of Q* CV Data a b 22 c d Site measurement (GJ m ) QE (%) source Vostok, Russia 1966±87 (4) 20.076 20.016 Ð B Halley, United Kingdom 1959±82 (21) 20.303 20.09 24.7 D Novolazerevskaya, Russia 1964±87 (21) 1.177 0.29 10.9 B Neumayer, Germany 1983±94 (11) 20.189 20.05 50.5 F Mirny, Russia 1957±84 (6) 20.201 20.04 Ð B Faraday, United Kingdom 1963±82 (20) 20.151 20.05 71.1 D a Site coordinates as in Table 1. b Bracketed ®gures are the numbers of complete years. c Here, QE is the fraction of global irradiance. d For data sources, see Table 1. The references to data sources tabulated in nearly all over a 1-yr period is similar to the accuracy of daily cases give details of the pyranometers and pyrradiome- values, largely because of the limiting accuracy of cal- ters used, as well as their exposure and calibration. In- ibration possible with pyranometers suitable for contin- formation on instrument exposure at the three Russian uous measurements in the ®eld (WMO 1983). stations is given on pages 91±92 of supplement II, 1968 The accuracy of radiation balance measurements is of the monthly bulletin Solar Radiation and Radiation less than that of global irradiance (Halldin and Lindroth Balance Data (The World Network) cited above. 1992); the WMO guide previously cited suggests a 50% It can be seen from Fig. 1 that all but two of the greater uncertainty in the precision of measurements of measurement sites were situated on the coast between Q* made with pyrradiometers compared with the cor- 668W and 1678E. The two inland sites at which K↓ was responding classes of pyranometers used to measure K↓. measured were Amundson±Scott at the South Pole, at The irradiance measurements available for Antarctica an elevation of 2800 m, and Vostok, 3488 m above mean do not form a homogeneous dataset; rather, they rep- sea level near the Pole of Inaccessibility of the contig- resent a collection of individual measurement series us- uous continent.
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