高層気象台彙報 第64号

収録内容

高層気象台彙報 第64号 2004年3月
題  目 著  者
まえがき 濱田忠昭
着氷が原因のレーウィンゾンデ強制降下事例 [要旨] 菊池康友
放射能ゾンデ観測値の経年変化考察のための試み [要旨] 井上聖吾・岩坪昇平・佐藤昌志・藤田建・武井保幸
ブリューワー分光光度計を利用した地面反射波長別紫外域日射観測装置の開発と観測 [要旨] 伊藤真人
ブリューワー分光光度計MKIIIの直射光監視観測-直射光オゾン・二酸化硫黄全量観測用常数の校正と観測結果- [要旨] 伊藤真人・宮川幸治
回折格子を利用した新型紫外域分光光度計の試験結果 [要旨] 伊藤真人
紫外域日射観測装置の入射角特性に関する観測値への補正の試み [要旨] 齋藤篤思
回折格子型サンフォトメータPGS - 100について(第二報) [要旨] 居島修
放射収支計CNR1の特性について(第二報) [要旨] 長井勝栄・長沼弘
散乱日射観測における低ゼロオフセット全天日射計の導入 [要旨] 長沼弘・長井勝栄

要旨一覧

題目
着氷が原因のレーウィンゾンデ強制降下事例
著者
菊池康友
要旨

レーウィンゾンデ観測時において上昇速度の低下が顕著な事例を集めて,強制降下の発生状況とその要因を調査した.その結果,全国の高層気象観測実施官署で1995年から2002年までの間に再観測を要した強制降下事例は26例が確認された.観測終了理由が着氷または降水による上昇速度低下とされた15例について着氷予測に用いられる-8D法で判定した結果,9例は着氷が関係し,その種類は雨氷や粗氷であると推定された.着氷と判定しなかった6例のうち,信号受信の途切れにより原因を推定できなかったものが1例,3例は着氷が関与しない降水によるもので,他2例は対流雲に伴う下降気流等が要因である可能性が示唆された.

題目
放射能ゾンデ観測値の経年変化考察のための試み
著者
井上聖吾・岩坪昇平・佐藤昌志・藤田建・武井保幸
要旨

放射能ゾンデ観測は,大気中にある人工放射性核種137Csから放射されるγ線の鉛直分布を直接観測するもので,1959年に業務として高層気象台に移管され,1年に3~4回観測を行っている.

今般,γ線計数値の経年変化を把握することを目的として,観測前に実施している飛揚前点検値から計数効率を求め観測値の補正を試みた.補正の結果は,補正後の値が補正前の値に比べバラツキが大きくなり,補正の有効性を確認できなかったが,飛揚前点検の方法について改善すべき点を明らかにすることができた.

題目
ブリューワー分光光度計を利用した地面反射波長別紫外域日射観測装置の開発と観測
著者
伊藤真人
要旨

A modified Brewer spectrophotometer and the calibration method for observing reflected spectral UVB on the ground surface were developed at the Aerological Observatory, Tsukuba. In this paper, the details of the Brewer modification for use at reverse position, the calibration procedure to ensure the instrument factors of modified Brewer at reverse position, and the results of spectral UVB reflectivity measurement of the ground under some typical surface conditions in winter season are presented. They are summarized as follows;

1) Brewer spectrophotometer MKII #059 was converted for accurate reflected spectral UVB measurement on the ground equipping with adjust foot #1 and #2, plates #1 and #2, level adjusters, and the cover. The spectrophotometer was carefully tuned by the tension adjustment of micrometer spring, the adjustment and fixing of mirror, the adjustments of zenith prism and iris of fore-optics, and full tightening of all screws in the instrument. The program of routine observation, skd.rtn, was modified for this purpose.

2) NIST lamp tests using the new calibration apparatus (Ito: 2002) showed that the difference between the calibration factors at the normal and the reverse position of modified #059 was within ±0.1%. The modified #059 at reverse position was proved to work normally in the tests of b2-ci, b1-ci, sl, hg, dt, rs, and others.

3) The daily responsivity trend of modified #059 in reflected UVB observation were traceable as accurately as in the normal operation of Brewers through regular external and internal lamp tests.

4) Global UVB irradiances by modified #059 at normal position and the Japanese standard #113 agreed within ±1%.

5) Spectral UVB reflectivity measurements on the ground were carried out by modified #059 at reverse position and #113 (temporarily replaced by #052) at normal position under some typical surface conditions. Both of the instruments were run by the time-controlled scan of uz.rtn which is a special routine prepared for instrument intercomparison. The results clarified (a), (b), and (c) as stated below;

(a) Dry concrete surface on the rooftop indicated the UVB reflectivity of about 0.07. It reduced to 0.05 when the surface was wet/pooled after rainfall. Linear wavelength-dependence of the spectral reflectivity was recognized, namely it showed higher values at longer wavelengths.

(b) The UVB reflectivity of dried grass in winter season was about 0.018 and 0.015 under clear/cloudy and rainy sky conditions, respectively. In these cases, no significant wavelength-dependence of spectral UVB reflectivity was observed for all weather conditions. Frost-covered grass surface in the morning showed the reflectivity of about 0.07.

(c) On the fresh snow surface, the maximum UVB reflectivity reached 0.94 under clear sky. The reflectivity decreased gradually as the snow melting proceeded, but it was kept above 0.60 until the grass surface appeared. Spectral UVB reflectivity on the snow surface showed no significant wavelength-dependence as a whole, but a weak declination at longer wavelength was shown during the time interval around the maximum reflectivity.

題目
ブリューワー分光光度計MKIIIの直射光監視観測-直射光オゾン・二酸化硫黄全量観測用常数の校正と観測結果-
著者
伊藤真人・宮川幸治
要旨

In atmospheric ozone monitoring careful data quality control plays an essential role for correct analysis and evaluation of the long-term ozone trend. In this connection the first WMO summary report on the comparison of total ozone measurements of Dobson and Brewer spectrophotometers (WMO:2003) says that the simultaneous operation of Dobson and Brewer instruments at the same station is highly recommended to improve the reliability of the total ozone measurements of the station. A problem in this measurement redundancy, however, is the present situation that no officially authorized calibration mechanism exists for Brewer, while Dobson is standardized in the solid calibration hierarchy established by the GAW/WMO.

As an approach to this problem in the Brewer MKIII UV observation network of the Japan Meteorological Agency (JMA), we have developed the calibration system for Brewer DS O3 measurement on the basis of the total ozone comparison between Dobson and Brewer performed under the most appropriate clear atmospheric conditions. For Brewer DS SO2 measurement, which is needed to evaluate the influence of SO2 on the Dobson total ozone measurement, a field Brewer MKIII traceable to one of the Brewer standards maintained by the Meteorological Service of Canada (MSC)/ Kipp & Zonen was used as the working calibration reference for other field Brewers.

The Japanese Brewer MKIII UV observation network is run concurrently with the Dobson ozone network comprised of Sapporo, Tsukuba, Kagoshima, Naha, and Syowa Antarctica. These overlapped networks continue to store quasi-simultaneous total ozone comparison data as well as SO2 since 2002. Long-range data accumulation into the future with these networks is expected to offer valuable data set to further enrich the understanding of the difference between Dobson and Brewer, which will lead to more accurate and sensitive ozone trend monitoring at these stations.

The summary of the calibration procedures and observation results in the latest few years are given below.

1) The instrument parameters of Brewer MKIII for DS O3 measurement were calibrated by comparing with any of the Dobson Asian standard D#116, field Dobson at local station, or traveling standard D#129. The calibration accuracy was shown to be within about ±1 per cent.

2) For Brewer DS SO2 measurement, calibration was done by comparing with Brewer MKII B#113 which was traceable to the Canadian Brewer MKIII B#158 via Brewer MKIII B#174. The SO2 calibration was difficult to carry out because the chance of having enough amount of SO2 for calibration was rather sporadic to happen.

3) On a daily basis the total ozone measurements by Dobson and Brewer sometimes indicated large discrepancies when ozone changed violently. This was due to the difference of the calculation method of daily value (Brewer: daily mean, Dobson: daily representative). On yearly time scale, both of the measurements agreed very well.

4) Observation results in the latest two years showed that the difference between Brewer MKIII DS O3 and the total ozone by Dobson stayed within about ±1 per cent except for Syowa Antarctica. Excellent agreement was observed at Sapporo, Tsukuba, Kagoshima after 2003, and Naha where the total ozone variation is small through seasons.

5) The difference between Brewer DS O3 and the total ozone by Dobson showed similar seasonal variation as stated in the WMO summary report. The variation was small at Sapporo, Tsukuba, and Naha, and rather large at Kagoshima. The variation at Syowa Antarctica was the most distinctive.

6) Through Brewer DS SO2 measurement some characteristic behaviors of the SO2 at these stations were revealed. The SO2 at Sapporo kept nearly constant values of 2 to 3 m atm-cm through seasons. Whether it was caused by calibration error or urban background air pollution is still uncertain. Abrupt increase of SO2 was sometimes observed at Tsukuba. These phenomena could be the influence of Miyakejima volcano, about 220 km southwest of Tsukuba, but not yet confirmed. Sudden high level of SO2 lasting for few days often occurred at Kagoshima, which could be ascribable to the eruption of Sakurajima volcano located about 10 km from the station. The frequency of the sudden increase at Kagoshima seemed to have seasonal variation. The SO2 at Naha sometimes showed sudden but a small amount of increase. It was noticeable that the SO2 level over 5 m atm-cm was rarely observed even at Syowa Antarctica.

題目
回折格子を利用した新型紫外域分光光度計の試験結果
著者
伊藤真人
要旨

A new grating UV spectrophotometer is currently under development aiming to measure ultraviolet irradiance in the wavelength region from 200 to 400 nm. The new instrument has Si-CCD array detector and capable of measuring 960 channels simultaneously in the wavelength region. To evaluate the performance of the new spectrophotometer, some tests using spectrum lamps and NIST lamps were carried out. The summary of the results is shown below.

1) Scanning tests with spectrum lamps showed that the scanning accuracy was within 0.7 nm. The wavelength resolution was about 1.6 nm.

2) NIST lamp tests were repeated by changing the distance between the lamp and the detector surface to find the optimum distance for calibration. The result was that the calibration of this instrument could not be properly performed at the distance other than 50 cm due to stray light and dark counts. Even at the distance of 50 cm, the calibration in the wavelength region shorter than 280 nm proved to be extremely difficult because of dark counts. 3) Relative responsivity fluctuations during scans were about ±2% throughout the wavelength region from 200 to 400 nm.

4) Dark counts of the instrument increased as the irradiance level became higher by shortening the distance between the NIST lamp and the detector surface.

5) The lamp tests with and without the UV dome at the distance of 20, 30, and 50 cm clarified that the transmissivity of the dome was about 98%.

6) As practical operational modes for outdoor solar irradiance measurement with this instrument, the exposure time should be longer than 50 ms and the scanning over 50 times in each measurement. The UVA and UVB observations can be carried out every minute with this mode.

The problems caused by stray light and dark counts are expected to improve by furnishing with a cut-off filter and a thinner diffuser plate. Another improvement needed for practical use of this instrument may be the software to process and convert the raw data into user-friendly form depending on the purpose.

題目
紫外域日射観測装置の入射角特性に関する観測値への補正の試み
著者
齋藤篤思
要旨

高層気象台において2002年に開発された新型NISTランプ検定装置を用いて,紫外域日射観測装置(ブリューワー分光光度計)の特性試験を行った結果,詳細な入射角特性が明らかになった.本稿ではこの結果を基に,ブリューワー分光光度計MKIIIにより国内4官署(札幌,つくば,鹿児島,那覇)で観測された2002年以降のデータを見直し,その入射角特性に関する補正手法の開発を試みた.

入射角特性の補正において,(1)天頂角 θ>60°で測器感度が大きく変化するため,光の入射方向を考慮して補正すること,(2)日射環境や天気の状態を考慮して補正すること,(3)各測器の光学特性が異なるため,測器に応じた補正をすること,の3項目が重要である.

その補正の結果,次のようなことが明らかになった.1) 時別値に対する補正率は,快晴日には太陽天頂角が大きい朝夕の時間帯に高く,曇天日には散乱成分に対する補正率と等しくなる(測器毎に異なり5.8~7.9%).ただし2) その補正量は快晴,曇天いずれの場合においても紫外域日射量の多い時間帯に大きく,特につくばの夏期,南中時には,UVB量で最大123.80 W/m2(2003年6月27日11JST)に達した.また3) 日別値(日積算値)に対する補正率は,太陽天頂角が大きい冬期に高く(極値は地点毎に異なり月平均で8.3~10.9%),4) 日積算値補正量は紫外域日射量の多い夏期に大きかった(月平均で0.83~1.90 kJ/m2).

題目
回折格子型サンフォトメータPGS - 100について(第二報)
著者
居島修
要旨

第一報では,干渉フィルター型サンフォトメータとの比較から,回折格子型サンフォトメータの精度を検討した結果,測器定数は2ヵ月半の比較期間において,ほとんど変化がないことが確認された.第二報では,波長ずれの経年変化を調査し,また,回折格子型の350nm~1050nmまでの出力を用いて,直達日射量および可降水量の推定を行った.その結果,波長ずれの調査では,約1年3ヶ月の期間において波長ずれが最大で約3nmあった.直達日射量の推定では,回折格子型サンフォトメータの測器定数と大気外放射照度を用いて,サンフォトメータの測定出力を太陽放射照度に換算し,換算した全測定波長の太陽放射照度を積算して直達日射量を求めた.直達日射計と比較した結果,推定した直達日射量日積算値は直達日射計の約0.7倍であった.また,レーウィンゾンデから求めた可降水量と水蒸気の光学的厚さとの関係を調べた結果,両者の相関は高く,光学的厚さから推定した可降水量は実用上問題ない精度であった.

題目
放射収支計CNR1の特性について(第二報)
著者
長井勝栄・長沼弘
要旨

放射収支計CNR1には,一度に放射収支量を測定するモード(NRM)と,4つのセンサ出力を個別に測定するモード(4SCM)の2種類の測定モードがある.第一報ではNRMでの特性を述べたが,第二報ではさらに精査するため個々のセンサ単独の特性を評価できる4SCMについて調査した.

CNR1のNRMで設定したセンサの感度は,個々のセンサの観測値として使える感度にはならず,4つのセンサの誤差バランスをとった感度となっている.この誤差は天候,風,気温などに影響を受け原因を特定しにくい.

4つのセンサ個別に感度を検定して収支量を求めると,NRMで感度を設定した時よりも誤差が大きくなる.これはCNR1の下向き長波長放射計のシリコン窓加熱,反射日射などの測器温度差の影響による上側と下側の測器の出力の差が影響している.NRM,4SCMのどちらも精度の良い測定をするためには,測器の全体の温度を一定にする必要があり,そのためには測器全体を覆う通風装置が必要である.

題目
散乱日射観測における低ゼロオフセット全天日射計の導入
著者
長沼弘・長井勝栄
要旨

散乱日射観測においては,測定に用いる全天日射計の測定誤差要因のうち,ゼロオフセットの問題が精度向上を目指す上で一番の課題である.これまで使用していた測器(CM21)は,通風ファンが弱いこともあってゼロオフセットが生じ易かった.

今回,散乱日射観測用の測器としてKipp & Zonen 社が最近開発した全天日射計CM22を新たに導入し,通風ファンを強化した.CM22は,センサーを保護しているガラスドームに光学石英を用い,ゼロオフセットの低減を図っているのが特徴である.

従来の測器(CM21)とゼロオフセットについての比較調査を行った結果,CM22のゼロオフセットは絶対値,変動ともに少なく,ゼロオフセットの原因となる正味放射の変化に対する影響は従来の半分以下であった.CM22の採用により,ゼロオフセットを補正する際に,従来の測器で正味放射の変動が大きい場合に1%程度見込まれた誤差が半分以下に低減することがわかった.