Global Spectral UV in Recent 6 Years and Test Observation of Diffuse Spectral UV with Brewer Spectrophotometer at Rikubetsu, Central Hokkaido

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1 [Technical report] Global Spectral UV in Recent 6 s and Test Observation of Diffuse Spectral UV with Brewer Spectrophotometer at Rikubetsu, Central Hokkaido Mahito ITO *, Masaji ONO **, Noritsugu TSUDA ***, Toshinobu MACHIDA ****, Nobuyuki YOKOZEKI ***** and Yoshiyuki NOTO ****** Abstract The Aerological observatory has been implementing the checkup, adjustment, and calibration of Brewer spectrophotometer #57 (BR#57) of the National Institute for Environmental Studies Japan (NIES), at Rikubetsu station (43.45 N, E) in Central Hokkaido, every year since 25 as per the request of research cooperation from the afore mentioned institute. The calibration results of instrumental constants for UV observation, the observation results of global UV radiation in recent 6 years from Dec. 25 to Dec. 2 and the small test observation results of diffuse UV radiation at Rikubetsu are summarized as follows; () BR#57 has been maintained in good condition in recent 6 years by the maintenances included optical adjustment, NIST lamp calibration and comparison to the travelling standard Brewer every year. (2) The secular variation of the monthly means of the daily total global UV (GL UV ) at Rikubetsu in recent 6 years indicated the identical variation at Sapporo (43.6 N, 4.33 E), but differed from the one at Tsukuba (36.6 N, 4.3 E). Their irradiance ratios of the monthly means at Rikubetsu to Sapporo indicated the intensities from.8 to.4 and the average intensity was approx..98. On the other hand, the irradiance ratios at Rikubetsu to Tsukuba indicated the intensities from.3 to.3, and the average intensity was approx..75 to.85, which is remarkable seasonal variation, recognized every year. (3) Diffuse UV (DF UV ) was observed at Rikubetsu for 53 days during the winter season of Nov. 29 to Jan.. The average of daily diffusivity (RDF UV ) at Rikubetsu indicated approx..93 compared with approx..88 to.89 at Tsukuba during the period. This high value at Rikubetsu was presumed as due to the bad weather, including many of snowy days. As stated above, BR#57 at Rikubetsu has been maintained and controlled in good condition by the annual checkup and adjustment. The continuous global UV observation and the full-year diffuse UV observation by the Brewer are very important for the detailed clarification of the annual change and seasonal variation of the UV at Rikubetsu.. Introduction The Aerological observatory is implementing the technical assistance of Brewer MKII spectrophotometer #57 (BR#57) of the National Institute for Environmental Studies (NIES), at Rikubetsu station (43.45 N, E) in Hokkaido since 25 as per the request of research cooperation from the afore mentioned institute. BR#57 has been defined as a standard unit in the UV monitoring network (NIES: 25) of this institute and this standard unit measures global UV of GL UV, total ozone, and total sulfur oxide at the station in Photo.. Comparative observation and technical assistance of BR#57 was implemented at the Aerological Observatory, Tsukuba in 993, 995 and 999, but since 25, technical assistance, relating the checkup, adjustment, and calibration of BR#57 has been implemented every year as this unit is located at the nation s extremely cold environment. Moreover, highly accurate data can be acquired at Rikubetsu station, since the full-year monitoring assistance of BR#57 became possible. The preliminary result at Rikubetsu in 26 was reported in the last paper (Ito et al.: 27). As the observation data could be increased since 26, the observation results and the characteristics in recent 6 years from December 25 to December 2, and the small test results of diffuse UV observation at Rikubetsu from November 29 * Ozone and Radiation Division, Aerological Observatory, JMA. ** Center for Environmental Health Sciences, NIES. *** Global Environmental Forum. **** Center for Global Environmental Research, NIES. ***** Ginga Corporation (Rikubetsu Station). ****** Aerological Observations Division, Aerological Observatory, JMA. to January are described in this paper. Please refer McElroy et al. (28), Kipp & Zonen (996, 28a, 28b) and etc for all of the technical terms, used in this paper. 2. Maintenance and responsivity of BR#57 2. Brief overview of maintenance The flowchart of the maintenance, the calibration and the comparisons for BR#57 at Rikubetsu every year is shown in Fig.. (a) Before the maintenance Within the period of approx. week, comparative observation of UV and dso3/so2 between BR#57 and the travelling standard BR#3 was implemented for the confirmations of the last instrumental constants and the instrumental responsivity. After the comparison, BR#57 was calibrated by the NIST lamp (some pieces of, W halogen lamps calibrated by the National Institute of Standard and Technology) calibrations and the final external lamp (5 pieces of 5 W halogen lamps) tests before the maintenance. Final instrumental responsivity for UV observation could be confirmed by those results. Under the normal condition, difference of the instrument responsivity between the result of NIST lamp calibration and the external lamp test was within ± %. Daily responsivities need to be corrected before the maintenance, in case any larger difference was recognized. (Notice: the daily instrumental responsivities for a year were produced by the external lamp tests every 7 or days using 3 to 5 lamps in Japan)

2 Journal of the Aerological Observatory No.7 22 Photo. Brewer spectrophotometer (BR#57) of National Institute for Environmental Studies at Rikubetsu, N, E, in the Rikubetsu Astronomical Observatory. Routine observation for UV and dso3/so2 Comparison to standard Brewer for UV and dso3/so2 over one weeks and NIST lamp calibration ) Overhaul by repairing, adjestment of optical system, sealing and etcs. 2) Setting up the constants of stepping motors. 3) Dispersion tests, spectral tests and UV laser test. NIST lamp calibration Comparison to standard Brewer for UV and dso3/so2 over one weeks and Routine observation for UV and dso3/so2 Outside in the room Outside Fig. Flowchart of the maintenance, the calibration and the comparisons for BR#57 at Rikubetsu every year. Photo. 2 NIST lamp calibration for BR#57 in the observation room at Rikubetsu, every year. Table UVR files of BR#57 for UV observation by the NIST lamp calibration. UVR File NIST lamp Calibration Unit Reference Lamp 25 UVR245 S-79 JMA S-38, S-55, S-9, S UVR3356 S-79 new IOS 27 UVR327 S-79 new IOS 28 UVR348 S-7 new IOS 29 UVR3259 S-7 new IOS UVR38 S-7 new IOS 2 UVR36 S-7 new IOS S-38, S-55, S-9, S-94 S-38, S-54, S-94, S-7, S-36 S-79, S-94, S-53, S-7 S-94, S-53, S-7 S-94, S-, S-94, S-, S-23 after the maintenance within the period of more than week, for the confirmations of new constants for UV observation and the calibration of constants for O3/SO2 observation. The routine observation schedule was started after the comparisons. 2.2 NIST lamp calibration The NIST lamp calibrations were carried out by using a few or several pieces of NIST lamps before and after the maintenance (Ito et al.: 27). New constant of UVR file for UV observation was selected as a best constant in the results. The history of UVR files and the secular variation of the responsivities by the calibrations from 25 to 2 were shown respectively in Table and Fig.2. (b) Maintenance This maintenance consists of the repair and light axis adjustment, including the optical parts replacement, power voltage adjustment, and the repair of sealing of the housing and connectors. After the afore mentioned maintenance, adjustments of stepper motors, the dispersion test, the spectral check test using spectral lamps and the UV laser test were carried out. After that, a new constant of UVR file by the NIST lamp calibration (Photo.2) and a standard instrumental responsivity by 5 external lamp tests were calibrated as a final procedure. (c) After the maintenance Same as the one before the maintenance, comparative observation between BR#57 and the travelling standard BR#3 was implemented 2.3 Daily instrumental responsivities for UV observation were carried out by the external lamp tests by using 5 pieces of 5 W halogen lamps and the test unit every 7 or days. First responsivity was determined on the same day of first NIST lamp calibration, and daily responsivities till the next NIST lamp calibration were determined by those tests. The daily responsivities of BR#57 could be highly accurate, because of the annual maintenance and the annual NIST lamp calibration. 3. UV radiation at Rikubetsu from 25 to 2 UV radiation by BR#57 at Rikubetsu was derived by the compute method for MKII (Method of Noto and Ito (2)). However,

3 Global Spectral UV in Recent 6 s and Test Observation of Diffuse Spectral UV with Brewer Spectrophotometer at Rikubetsu, Central Hokkaido Difference Sci Kipp S-877 S-935 S-38 S-54 S-55 S-79 Gosei S-9 S-94 S-7 S-53 S-7 S- S-23R Trend Table 2 Annual means of the UV irradiance ratios, Rikubetsu/ Sapporo and Rikubetsu/Tsukuba, from 26 to 2. Rikubetsu/Sapporo Rikubetsu/Tsukuba AVG Fig. 2 Secular variation of the responsivity ratios of BR#57 from 25 to 2 by NIST lamp calibrations at Rikubetsu. same as last report (Ito et al.: 27), coefficient of BR#52, (which is most close to the stray light characteristics) was used for this calculation, since the coefficient for the correction of stray light was not derived. The UV radiation from December 25 to December 2 was shown as (total UV from 28 to 325 nm), (total UV from 28 to 35 nm), (erythema UV) and (damaging UV), respectively in Fig.3, Fig.4- and Fig.4-2. In those figures, same UV radiation at Sapporo (43.6 N, 4.33 E) and Tsukuba (36.6 N, 4.3 E) were added for the purpose of comparison. Fig.3 (a-) and (a-2) indicate the secular variation of monthly means of daily total UV radiation. The monthly means at Rikubetsu indicated high intensities from May to August and low intensities from November to January. Maximum monthly means were recognized in June or July, except for in May, 29, and the minimum was recognized in December of every year. Every year, their degrees (level) of annual change at Rikubetsu were very close to Sapporo. Fig.3 (b) and Table 2 indicate the irradiance ratios of the monthly means and the annual means at Rikubetsu against to Sapporo and Tsukuba, respectively. The ratios of the monthly means to Sapporo indicated the intensities from.8 to.4, and these averages of annual means in 6 years, as,, and, became the intensities of approx..98. Therefore, the UV radiation at Rikubetsu is similar irradiance as Sapporo. The seasonal variation of the ratio to Sapporo, the high ratio (Rikubetsu > Sapporo) in winter season and the low ratio (Rikubetsu < Sapporo) in summer season, had been recognized in 26 and 27. But after 28, the seasonal variation has not been clarified and some small fluctuations of the difference have recognized every few months. The ratios of the monthly means to Tsukuba indicated the intensities from.3 to.3, and the seasonal variation had been markedly recognized every year. The ratio showed the high intensity in June to July, and the low intensity in December. These averages of annual means in 6 years showed the intensities of approx..75 () to.85 (), the UV radiation at Rikubetsu indicated lower intensities of -25 to -5 % against to Tsukuba. Ratios between Rikubetsu and Tsukuba were smaller in the UVs involved many UV irradiances at short wavelength, as " > > > ". These differences are due to the difference of the seasonal variation of total ozone between Rikubetsu and Tsukuba (Ito et al.: 27). Fig.4- (a-) to (c-2) indicate the daily total UV radiation, " and " in the left side figures and " and " in the right side figures, at Rikubetsu (upper figures), Sapporo (middle figures) and Tsukuba (lower figures), respectively. The degrees of the daily total UV radiations at Rikubetsu were closely resemble as the degrees at Sapporo, and their annual peaks at Rikubetsu in a year were appeared at the midsummer time of highest solar angle. On the other hand, the annual peaks at Tsukuba were not appeared because the rainy season was in the midsummer time, but the peaks were recognized in and 2. Contrary, the peaks were not recognized at Sapporo in and 2. Fig.4-2 (a) and (b) indicate the ratios of the daily total UV radiation, ",, and ", at Rikubetsu against to Sapporo in the left figure and Tsukuba in the right figure, respectively. The curves in the figures indicated the seven-days running means. The seasonal variation of the ratio to Sapporo, the high ratio (Rikubetsu > Sapporo) in winter season and the low ratio (Rikubetsu < Sapporo) in summer season, had been recognized in 26 and 27. But after 28, the seasonal variation has not been clarified. On the other hand, the ratio to Tsukuba had been kept generally in low intensities, and the seasonal variation, the high ratio (Rikubetsu > Tsukuba) in summer season and the low ratio (Rikubetsu < Tsukuba) in winter season, had been recognized very clearly in recent 6 years. 4. Test observation of diffuse UV radiation The diffuse UV, DF UV, was observed by using uv.rtn (scanning wavelength: 29 to 325 nm per.5 nm) at Rikubetsu for 53 days in the winter season from November 23 (327JD) 29 to January 4 (4JD). DF UV observation was scheduled by the automated shadow unit (Ito: 26) every 9±4 minutes, as shown in Photo.3. On the other hand, the routine GL UV observation was implemented every ±4 and 3±4 minutes. (a-), (a-2), (b-), (b-2) and (c) in Fig.5 indicate the daily total GL UV ( and ), GL UV ( and ), DF UV ( and ) and the daily diffusivity of RDF UV (,, and ) at Rikubetsu, respectively. For the purpose of comparison, (d-), (d-2), (e-), (e-2) and (f) in Fig.5 indicate the same GL UV, DF UV and RDF UV at Tsukuba. The daily total GL UV and DF UV at Rikubetsu have been indicating continuous low intensities of almost half degree to Tsukuba. Their daily totals indicated most low intensities in a year, now that the solar angle was lowest around 35 JD in the periods

4 Journal of the Aerological Observatory No.7 22 and (a-) Rikubetsu Rikubetsu Sapporo Tsukuba 8 Rikubetsu Sapporo 6 Sapporo 4 Tsukuba 2 Tsukuba 25 (a-2) Sapporo Tsukuba and Rikubetsu Rikubetsu Rikubetsu 3 Sapporo 2 Sapporo Tsukuba Tsukuba 25 (b) UV Ratio 2. vs Sappro vs Sapporo Irradiance Ratio vs Sapporo.5 vs Sapporo vs Sapporo. vs Tsukuba vs Tsukuba.5 vs Tsukuba vs Tsukuba vs Tsukuba ) Fig. 3 Monthly means of daily total UV irradiance (J/m Tsukuba from 25 to and irradiance ratios of the monthly means at Rikubetsu, Sapporo and (a-) and (a-2): Monthly means of daily total UV irradiance,,, and, at Rikubetsu with BR#57, at Sapporo with BR#69 and at Tsukuba with BR#73(#74). (b): Irradiance ratios of the monthly means at Rikubetsu to Sapporo and Tsukuba. GL uv at Rikubetsu (a-2) 5 (a-) (b-) GL at Rikubetsu (c-2) (c-) GL at Sapporo (b-2) GL uv at Sapporo Fig. 4- Daily total UV irradiance (J/m2) and irradiance ratios of daily total irradiance, at Rikubetsu, Sapporo and Tsukuba from 25 to 2. (a-) and (a-2): Daily total UV irradiances as " and " and " and " with BR#57 at Rikubetsu, (b-) and (b-2): with BR#69 at Sapporo and (c-) and (c-2): with BR#73 (#74) at Tsukuba

5 Global Spectral UV in Recent 6 s and Test Observation of Diffuse Spectral UV with Brewer Spectrophotometer at Rikubetsu, Central Hokkaido (a) I rra d ia n c e R a t io (b) GL uv ratio (Rikubetsu/Sappro) 2 I rra d ia n c e R a t io GL uv ratio (Rikubetsu/Tsukuba) Fig. 4-2 Daily irradiance ratios of daily total UV irradiances, ",, and ". (a): Rikubetsu to Sapporo. (b): Rikubetsu to Tsukuba. GL uv at Rikubetsu (b-) 5. DF uv at Rikubetsu 29.8 (b-2) (e-). DF uv at Tsukuba DF uv at Tsukuba (f) Diffusivity (DFuv/GLuv) at Rikubetsu (e-2) 29.9 (c) Diffusivity Diffusivity DF uv at Rikubetsu (d-2) 5 Irradiance(J/m2) (d-) GL uv at Rikubetsu 5 (a-) (a-2). Diffusivity (DFuv/GLuv) at Tsukuba Fig. 5 Daily total GLUV (global UV), daily total DFUV (diffuse UV) and daily diffusivity (RDFUV: DFUV/GLUV) at Rikubetsu and Tsukuba from November in 29 to January in. The data of DFUV at Rikubetsu were produced for 53 days from 327 JD in 29 to 4 JD in. (a-), (a-2), (d-) and (d-2): Daily total GLUV, " and " and " and ", with BR#57 at Rikubetsu and BR#73 at Tsukuba, respectively. (b-), (b-2), (e-) and (e-2): Daily total DFUV as the same mentioned above. (c) and (f): Daily diffusivity at Rikubetsu and Tsukuba. Photo. 3 Diffuse UV observation with BR#57 using the automated shadow unit at Rikubetsu for the observation period, from 327 JD in 29 to 4 JD in. Table 3 Average of the diffusivity (DFUV/GLUV) at Rikubetsu and Tsukuba for 53 days, from 327 JD in 29 to 4 JD in. Rikubetsu Tsukuba AVG MIN RDFUV indicates the intensity of "." under the cloudy condition, and the intensity of the lower limits line of RDFUV indicates the regional characteristics. The lower limits line indicated the intensity of approx..88 at Rikubetsu compared with approx..8 at Tsukuba. The RDFUV at Rikubetsu is high intensity of approx. 8 % to Tsukuba. The average and the minimum value of daily RDFUV of ",, and " at Rikubetsu and Tsukuba for the observation periods of 53 days are summarized in Table 3. The averages of RDFUV at Rikubetsu were indicated the higher intensities of approx..93 compared with approx..88 to.89 at Tsukuba. Although Rikubetsu station is known as a station in the clear atmospheric environment of low intensities of turbidity and aerosol, data at Rikubetsu indicated higher intensities. Weather condition at Rikubetsu has been constantly under bad condition (many of snowy days and cloudy days), during the observation period of 53 days. Compare to Tsukuba, Rikubetsu had 9 snowy days, while Tsukuba had day with snow fall. On the premise that a day with more than 7 hours of sunshine duration is the day with clear sky, Rikubetsu had 2 days with clear sky, while Tsukuba had 27 days with clear sky

6 Journal of the Aerological Observatory No.7 22 Therefore, same diffuse UV observation shall be carried out in the other season, in order to clarify the level of the secular variation of RDFuv at Rikubetsu. 5. Conclusion Calibrations of instrumental constants for UV observation, the maintenance methods for instrument, the observation results of global UV radiation in recent 6 years from December 25 to December 2 and the small test observation results of diffuse UV radiation with Brewer spectrophotometer #57 of the National Institute for Environmental Studies, Japan (NIES), at Rikubetsu station were described as follows; BR#57 has been maintained in good condition in recent 6 years by the maintenances included optical adjustment, NIST lamp calibration, dispersion test, spectral tests and comparison to the travelling standard Brewer every year. The secular variation of the monthly means of the daily total global UV (GL UV ), as,, and, at Rikubetsu in 6 years indicated closely resemble to the variation at Sapporo, but differed from the variation at Tsukuba. Their irradiance ratios of the monthly means at Rikubetsu against to Sapporo indicated the intensities from.8 to.4 and the average was the intensity of approx..98. The seasonal variation of the irradiance ratio to Sapporo had been recognized in 26 and 27, but has been obscure after 28. On the other hand, the irradiance ratios at Rikubetsu to Tsukuba indicated the intensities from.3 to.3 and the average was the intensity of approx..75 to.85. The seasonal variation had been markedly recognized every year. The seasonal variations are due to the difference of total ozone between Rikubetsu and Tsukuba. The diffuse UV (DF UV ) was observed at Rikubetsu for 53 days in the winter season from November in 29 to January in. The average of daily diffusivity, RDF UV, at Rikubetsu indicated approx..93 compared with approx..88 to.89 at Tsukuba for the period. The high value at Rikubetsu to Tsukuba was due to the bad weather including many snowy days during the observation period at Rikubetsu. Now that the UV data of BR#57 at Rikubetsu has been maintained and controlled in good condition by the annual checkup, and adjustment. The continuous global UV observation and the full-year diffuse UV observation by the Brewer are very important for the detailed clarification of the annual change and seasonal variation of the UV at Rikubetsu. Wish that those data at Rikubetsu becomes useful for many studies in the future. Acknowledgment We would like to thank Dr. A. Takami, Mr. Y. Tarui, Mr. N. Sakagawa and Ms. M. Ohashi of the Center for Global Environmental Research of National Institute for Environmental Studies (NIES), the staffs of Rikubetsu Astronomical Observatory, and the staffs of Aerological Observatory, JMA. References Ito, M. (26):Diffuse spectral observation using Brewer spectrophotometer and new automated shadow unit. Jour. of the Aerological Observatory, 66, Ito, M., M. Ono and Y. Noto (27):Results of calibration and spectral UV/DS ozone observations using Brewer spectrophotometer at Rikubetsu. Jour. of Aerological Observatory, 67, Ito, M., T. Grajnar, M. Brohart, V. Savastiouk and K. Lamb (27): Intercomparison of Brewer Spectrophotometers between MSC and JMA at Toronto, Canada in 26 and accuracy of MSC, IOS and JMA systems for NIST lamp calibration. Jour. of Aerological Observatory, 67, Kipp & Zonen (996):Brewer MKIII Spectrophotometer Final Test Record, BR#74. Kipp & Zonen Inc., 75pp. Kipp & Zonen (28a):Brewer MKIII Spectrophotometer Operators Manual. Kipp & Zonen Inc., 32pp. Kipp & Zonen (28b):Brewer MKIII Spectrophotometer Service Manual. Kipp & Zonen Inc., 25pp. McElroy, C.T., V. Savastiouk and T. Grajnar (28):Standard operating procedures manual for the Brewer Spectrophotometer, Ver. D.. Environment Canada, 38pp. NIES (25):The activity report of the UV monitoring network. Center for Global Environmental Research, NIES, 6pp. Noto, Y and M. Ito (2):The new Brewer control programs of JMA version for Windows (II). Jour. of Aerological Observatory, 6, 陸別のブリューワー分光光度計による最近 6 年間の紫外線量の推移と散乱紫外線量観測の試み 伊藤真人 * 小野雅司 ** 津田憲次 *** 町田敏暢 **** 横関信之 ***** ****** 能登美之要旨高層気象台では, 国立環境研究所の研究協力依頼により同研究所陸別成層圏総合観測室 ( 北海道足寄郡陸別町, 観測地点 :43.45 N, E) におい て同地点のブリューワー分光光度計 BR#57 の点検 調整と常数校正を 25 年より実施してきた. 本稿では,25 年 月 ~2 年 2 月までの約 6 年間の測器常数の推移, 陸別における全天紫外線量の推移, さらに短期間ではあるが散乱紫外線量の観測結果についてまとめた. () 陸別の測器 BR#57 は, 過去 6 年間の毎年の点検 調整,NIST ランプ検定, 分光常数校正, スペクトル点検, 移動準器との比較観測等により, 良好な測器状態が維持されている.(2) 陸別における,,, としての月平均日積算全天紫外線量の 6 年間の推移は, 札幌 (43.6 N, 4.33 E) の推移と酷似しているが, つくば (36.6 N, 4.3 E) の推移とは異なっている. これらの陸別の札幌に対する月平均値の照度比は,.8~.4 で, 平均.98 となった. いっぽう, 陸別のつくばに対する月平均照度比は.3~.3 で, 平均.75~.85 となり, 季節変化が顕著に認められた.(3) 29 年 ~ 年にかけての冬季期間 (53 日間 ), 陸別において散乱紫外線量を観測した. 陸別における当期間の紫外線散乱率は平均約.93 を示し, つく ば ( 平均.88~.89) より高い値となった. この高い値は, 陸別の当期間における降雪を含む悪天候が原因と推定される. 以上のように, 陸別の測器は毎年の点検 調整により良好に維持 管理されている. 今後も連続した全天紫外線量の観測, 及び年間を通した散乱 紫外線量の観測が, 陸別の紫外線の年変化や季節変化を詳細に解明する上で重要である. * 高層気象台観測第三課 ** 国立環境研究所環境健康センター *** 地球 人間環境フォーラム **** 国立環境研究所地球環境研究センター ***** 銀河コーポレーション ( 国立環境研究所陸別成層圏総合観測室委託 ) ****** 高層気象台観測第二課