MM/DD 10:30--12:00 Name
Abstract
06/05 10:30--12:00 宮澤 淳次
火星は大気が希薄で乾燥した惑星である．しかし火星表面には水が流れた痕跡が あり,数十億年前は、現在よりはるかに高い気圧で暖かく湿った大気であったと 考えられている．大気が希薄になった理由の一つとして、宇宙空間への大気散逸 が考えられる．火星は地球より低重力であり、また固有磁場が存在しないので、 太陽風の影響を受けやすい．様々な大気散逸過程が考えらているが、その散逸過 程の詳細は明らかにされていない．そこで、衝突の効果を取り入れた大気散逸の モデリングを構築し、火星周辺での大気分布を求めた．本発表では、衝突の効果 を取り入れた、大気分布について報告する．
06/26 10:30--12:00 小林 縫
雷雲地上間放電に伴って発生するスプライトいついては、1989年の発見以来 さまざまな観測がおこなわれてきた。しかし, その発生条件や時間・空間発展 を決める要因については未解明な部分が多く, それを解明するための研究が 続いている。今回はその中でも, スプライトを発生させる親雷放電のパラメータ についての研究, シミュレーションによって求めた親雷放電による上空電場と ハイスピード画像の比較を行った研究, さらにスプライトストリーマの進展を シミュレーションで再現した研究などを紹介する。
07/03 10:30--12:00 今井 正尭
金星には, 大気が自転の60倍という速度で約4日の回転をするスーパーローテーションと呼ばれ る現象が存在し, 地球では見られないこの大気の高速循環の研究は, 惑星大気ダイナミクスを理解 する上で非常に重要である. Del Genio & Rossow (1982, 1990)は, 金星大気中に見られる ~1,000 kmスケールの明暗模様が 大気中の波動伝搬によって移動しており, 金星の紫外 (365 nm)の明るさがこれによって周期変動 することを明らかにした. 彼らは過去の衛星 Pioneer Venusによる測光観測から, 紫外模様の伝搬 速度と風速には対応関係をがあり, 明るさ変化の周期が時期や緯度によって約 4日-6日の間で変化 することを発見している. 本研究では, 金星紫外の明るさ時間変化を長期的にモニタリングし, 先行研究で明らかにされた周期 の移り変わる時間スケールを見積もることで, 金星大気波動現象とスーパーローテーションの関わ りを調査する。 我々は, 2012年に数度に渡って北海道大学の所有する惑星観測望遠鏡 "ピリカ望遠鏡"を用いた地上 から金星明るさのモニタリングを行った. また現行の金星観測衛星 Venus Express観測の紫外イメ ージを用い同時期の金星南半球での明るさ変化の様子も調査した. 本発表では, 地上と衛星両観測に よって可能となった金星両半球の明るさ変化の再現手法について紹介し, 将来の観測計画について 議論を行う.
07/17 10:30--12:00 三原 正大
雷放電に伴い、高度40-90kmにかけて発生する高高度発光現象(TLEs)は 1989年に初めて観測された[Franz., et al 1989]。これまでに地上観測 や数値計算を主軸に研究が行われ、基本的性質の解明がなされてきたが、 発生条件を何が決めるか、と言った本質的な問題は未だに解明されてい ない。その理由として、雷雲上空で発生するTLEsを地上から観測するに は多くの制約がつくこと、航空機から観測するには多大な費用がかかる ことが挙げられる。これらの問題を解決するのが宇宙空間からの観測で ある。本発表では、ISS(国際宇宙ステーション)からスプライトの観測 ミッションLSO(Lightning and Sprites observation)によって、2001年 10月から2002年12月までの間に得られたデータを扱った研究、2004年7 月から観測を続けている世界初のTLEs観測専用衛星、FORMOSAT-2搭載の ISUALによって得られたデータを扱った研究について紹介する。また、 2012年12月から定常運用が開始されたGLIMSについても簡単に述べる。
07/24 10:30--12:00 阪井 陸真
積乱雲1セルの水平スケールは5-10kmであり、既存のアメダスやレーダー網では雲内部 の対流活動の様子を把握する事は困難である。一方で、雲内の電荷は対流により分離、蓄 積されていくため、対流活動の指標になることが示唆されている。 大気電場観測では、雲内の電荷が蓄積、消失されることによる電場変化を捉えることがで きる。同時に、多地点での観測を行う事で、大気電場の変動を2次元で把握することがで きる。 過去の研究において、7地点以上での同時大気電場観測は、実行例が極めて少ない。こ の理由の一つに従来広く使われているフィールドミル型の大気電場観測器が非常に高価な ことが挙げられる。そのため、多地点での同時観測には、従来の高価な大気電場観測器に 代わる、安価でメンテナンスが容易な観測器を必要とする。 本研究の目的は、安価な観測装置を開発し、多地点大気電場ネットワークを構築し、積 乱雲接近時、多地点での大気電場をモニタリングすることで積乱雲内部の電荷分布を推定 し、対流活動との関係性を明らかにすることである。 2013年8月山梨県にて、時定数100msの大気電場計を7個、時定数7000sの電場計を1個設置 し、半径10kmの円内で同時多点観測キャンペーンを行う。異なる時定数を有する観測器を 用いることで、1フラッシュから積乱雲のライフタイム30分-60分間の電場の変動を捉える。 最低4点での観測によって、1フラッシュ毎の中和電荷量の位置と大きさを捉えることがで きる。また、種々の仮定を用いることにより、雲内放電による中和電荷量の位置と大き さ、積乱雲の発達に伴う内部電荷の蓄積過程を求める。 今回の発表では、8月の山梨県での観測キャンペーンにおける観測システム概要、解析 方法、期待される結果などを議論する。
07/31 10:30--12:00 堺 正太朗
2008 年に行われたカッシーニによるエンセラダスプリュームの観測では，電子 密度がイオン密度の 1% 未満であることが示された．これは電子がプリュームダ ストに付着し，負に帯電したダストが多く存在しているためである．これらの荷 電ダストは磁気圏プラズマと電磁気的に結合し，磁気圏に様々な影響を与えてい ると考えられている．今回我々は更に 5 つのエンセラダスフライバイのデータ 解析を行った．これらのフライバイではカッシーニはプリュームの様々な高度を 横切るような軌道を通った．これらのデータを用いて我々は，エンセラダスプ リュームのプラズマ密度，電子温度，イオン速度，ダストポテンシャルの高度依 存性について調査を行った．本発表ではこれらの高度依存性に加え，プリューム のスケールやダスト密度についても合わせて議論する．
08/21 10:30--12:00 古田 裕規
高度100-300kmの熱圏下部においては中性大気とプラズマが共存し, 運動量輸 送が相互に行われている. プラズマは, 中性大気に依存していると考えられてき たが, 近年の観測ではプラズマが中性大気に影響を与えていると思われる現象が いくつも発見されている. しかし, 大気重力波を含む熱圏大気観測や磁力線を介 した異なる領域間での大気・プラズマ結合の観測は十分行われていない. また, 電離圏ダイナモ, プラズマバブル, 伝搬性電離圏擾乱などの熱圏下部で 発生する中性大気-電離大気間の現象を解明する上で重要なパラメータが同時に 直接的に観測された例はほとんどない. この結合過程を解明するためにリチウムやTMAを用いたロケット実験を行っている. リチウム原子を気体状態にして熱圏大気中に放出すると, 日照状態では太陽光 のうち波長670.8 nm赤色単色光成分のみが効率的に励起され, 励起電子が基底状 態に戻る際に同波長の共鳴散乱光を発する. この現象を用いて, 高度100-200km の中性大気の観測をする. 2007年9月のS-520-23号機においては夕方の観測条件で, 2012年1月のS-520-26 号機においては明け方条件下での実験を実施し, 2013年1月のNASAワロップス実 験場でのTest Flight実験を実施し, 2013年5月のマーシャル諸島のKwajalein環 礁においてNASAが実施したEVEXロケット実験の2回の国際共同実験にて夕方条件 での実験を実施し, 2013年6月に米国NASAワロップス実験場での観測および, 2013年7月のS-320-42号機, S-520-27号機においては満月を光源とし、世界初と なる夜間リチウム共鳴散乱光を用いた実験に成功している. 今回は, 2013年5月のマーシャル諸島のKwajalein環礁においてNASAが実施した EVEXロケット実験と, 今後について発表する.
08/23 10:30--12:00 仲本 純平
北海道大学では、北海道名寄市に設置した北大1.6 mピリカ望遠鏡に搭載するた めの惑星観測用大気ゆらぎ補償光学系を開発している。従来の天文用の補償光学 系では、参照光源として観測対象のごく近傍に点状光源(観測対象自身あるいは 近傍の恒星、もしくはレーザーガイド星)が必要であり、惑星のような面光源を 参照光源とすることができない問題がある。木星などの場合は、衛星を参照星と することが可能であるが、惑星と衛星の位置関係が都合の良い配置となるごく限 られた条件の場合(期間)のみに限られてしまう。 そこで本補償光学系では、惑星本体を波面測定の参照光源とするために、焦点面 に絞りを設置する方法を検討している。惑星像を焦点面絞りでマスクして擬似的 に点光源とすることで、波面測定の際に、像の広がりによって傾きの異なる波面 の情報が混ざりあうのを防ぐことができる。焦点面絞りを通すことで、波面全体 の傾き(ティップティルト)の情報は失われるが、代わりに惑星像の動きを別途測 定することでティップティルト情報を得ることができる。本研究の方法は、通常 の波面センサに焦点面絞りを追加するだけでよく、非常に簡便でコストも低い。 しかし、この方法はこれまでに例が無く具体的な性能は未知数である。焦点面絞 りのサイズは大きすぎると異なる波面情報の混ざり込みで測定精度を失い、逆に 回折限界程度にまで小さくすると高次の波面情報を失う。そこで、我々は、波面 センサに焦点面絞りを付けた場合の波面伝播について物理光学計算を行い、最適 ピンポールサイズと波面測定精度の見積もりを行っている。また、焦点面絞り付 き波面センサを試作し、実験室および1.6m望遠鏡に搭載しての実際の波面測定精 度の評価を進めている。 今回の発表では、物理光学計算の結果と実験室での波面測定精度の測定結果につ いて発表する。
08/28 10:00--11:00 古田 裕規
高度100-300kmの熱圏下部においては中性大気とプラズマが共存し, 運動量輸送が 相互に行われている. プラズマは, 中性大気に依存していると考えられてきたが, 近年の観測ではプラズマが中性大気に影響を与えていると思われる現象が いくつも発見されている. しかし, 大気重力波を含む熱圏大気観測や磁力線を介 した異なる領域間での大気・プラズマ結合の観測は十分行われていない. また, 電離圏ダイナモ, プラズマバブル, 伝搬性電離圏擾乱などの熱圏下部で 発生する中性大気-電離大気間の現象を解明する上で重要なパラメータが同時に 直接的に観測された例はほとんどない. この結合過程を解明するために, リチウムやTMAを用いたロケット実験を行っている. リチウム原子を気体状態にして熱圏大気中に放出すると, 日照状態では太陽光 のうち波長670.8 nm赤色単色光成分のみが効率的に励起され, 励起電子が基底状 態に戻る際に同波長の共鳴散乱光を発する. TMAは大気中の酸素と激しく反応し 白く発光する. この現象を用いて, 高度100-200kmの中性大気の観測をする. 2007年9月のS-520-23号機においては夕方の観測条件で, 2012年1月のS-520-26 号機においては明け方条件下での実験を実施し, 2013年1月のNASAワロップス実 験場でのTest Flight実験を実施し, 2013年5月のマーシャル諸島のKwajalein環 礁においてNASAが実施したEVEXロケット実験の2回の国際共同実験にて夕方条件 での実験を実施し, 2013年6月に米国NASAワロップス実験場での観測, そして 2013年7月のS-320-42号機,S-520-27号機においては満月を光源とし、 世界初となる夜間リチウム共鳴散乱光を用いた実験に成功している. 今回は, 各ロケット実験で観測された大気重力波と, 今後について発表する.
08/28 11:05--12:05 合田 周平
木星では赤道に平行ないくつもの帯を確認できる。帯ごとで風速の時間変化が確認されているが、 それらの原因はよく分かっていない。その原因として本研究では衛星との潮汐作用を考えている。 これを確認するためには時間分解能の高い緯度ごとの風速プロファイルを得ることで、帯ごとの 風速変化と衛星の公転周期との関係性を調べる必要がある。しかし現在の名寄の典型的なシーイング である1.8秒角では、緯度の空間分解能が4°程度であるため風速を観測することは厳しい。 そこで我々は0.4秒角のシーイングを達成して変化を見られるようにするために惑星用補償光学系 を開発中である。補償光学系には様々な種類があるが、その設計材料を得るためにMASS-DIMMを 使った大気擾乱プロファイルの測定を行う。 MASS-DIMMとは、MASSという装置とDIMMという装置を組み合わせた観測装置である。 MASSは高さに応じて地上での星像の揺らぎの空間スケールが大きくなることを利用して、 複数のサイズの異なる開口径でのフラックス変化から高度プロファイルを測定する。DIMMは2つの開口径で 同じ恒星から2つの星像を観測し、それぞれの星像の相対的な重心揺らぎからシーイングを推定する。 MASSは低空の感度が低く0.5kmより下の層（接地層）のプロファイルを作成することができない。 しかしDIMMで求められるシーイングサイズは、恒星光が装置に到達するまでに受ける擾乱の強度を 高度ごとに積分したものに関係している。よってMASSのデータとDIMMのデータを比較することで、 MASSでは測定できない接地層のプロファイルを得ることができる。 今回の発表ではMASS-DIMM装置の原理と解析手法について説明する。
09/04 11:00--12:00 合田 雄哉
木星極域には、成層圏ヘイズというエアロゾル粒子からなるもやが存在している。 これは主に深いメタンバンドである889nmや紫外線波長でみることができ、 このヘイズ領域の縁は波構造をしている。この波構造は特に南側で明るく見え、 67°Sで最も顕著になる。この波構造は数年にわ たって維持されており、 また過去の観測からこの波動現象が東向きのジェット気流のピーク中で西向きに伝搬しており、 ロスビー波としての可能性も示唆されている。本発表では過去に行われた木星極域に関しての 1994年から1999年のハッブル宇宙望遠鏡(HST)及び2000年の Cassini ISSによる観測、 そして名寄のピリカ望遠鏡を用いた2011, 2012年の木星の地上観測とそれらによる成果を紹介し、 その結果を踏まえてさらにまだ行われていない木星南極域における波構造の移動速度の 月単位での見積り及び鉛直方向の波構造の時間変化について、ピリカ望遠鏡を用いての 将来の観測計画についての議論を行う。
09/11 11:00--12:00 川原 健史
木星の北赤道領域(North Equatorial Belt:NEB)には、100-150 m/s ほどの強い東向き 風が吹いており、また、その速さが 1994-2011 年の間に 50 m/s も変化していることが 知られている。先行研究によって、これは NEB の南境界領域(NEBs)の dark projection (5μm hot spot (5μmの赤外線が強く放射されている場所)と一致する)と関連しており、 また、dark projection の動きの速度は、木星赤道領域のロスビー波と関連していることが 示唆されている。しかしながら、この木星赤道領域に発生するロスビー波の原因は、未だ 解明されていない。よって本研究では、この風速の変動を起こしているであろうロスビー 波の発生原因を解明したい。そのために、現在木星赤道域の風の数値シミュレーション という手段を検討している。 本発表では、ロスビー波の発生するメカニズムと、木星赤道領域におけるロスビー波に ついて紹介する。
09/18 10:30--12:00 渡部 重十
Electron temperature (Te) in the ionosphere is basically determined by the balance between the heating by photoelectrons, cooling through Coulomb collisions with ions and heat conduction along the magnetic field lines. Many studies have shown a negative correlation between the electron density (Ne) and Te during daytime because cooling through Coulomb collision increases with increase of Ne. On the other hand, we showed clear positive correlation when the daytime Ne is significantly high (>106 cm-3) using HINOTORI satellite observations [2011]. The correlation turns positive irrespective of latitude, longitude, season, solar flux levels, and geomagnetic activity levels. We will show additional evidences that the positive correlations are detected in several satellites and incoherent scatter radars. The results indicate that additional heating mechanism exists in high Ne region or neutral temperature affects Te through ion temperature. Photoelectron heating rate is known to increase with the increase of ambient plasma density [Hoegy 1984]. The energy dissipation of photoelectrons is proportional to the integrated Ne along the magnetic field line [Nagy and Banks, 1970]. The heating rate of electrons is possibly high in the region where the integrated Ne is high. Other mechanisms may be neutral temperature increase with the increase of solar radiation flux and/or Joule heating of neutral atmosphere, because the fast neutral wind flows near geomagnetic equator and the velocity difference between neutral atmosphere and plasma is large in the low latitude thermosphere. This is one of the Ionosphere-Thermosphere Coupling processes.
09/25 09:00--10:30 工藤剛史
雷をモニタリングすることにより，積乱雲の発生や発達，つまり水蒸気や気流の分布 及び変化のインジケータとなることが示唆されている (例えば，[Soula and Chauzy, 2001]，[Deierling and Petersen, 2008])．これまでの研究では，雷の活動度を示すものとして， 落雷頻度が使用されてきたが，落雷規模を示すCharge Moment Change (CMC) [C km]など， 電気的な特徴を考慮されていない．落雷の中和電荷量には100倍以上の幅があることが 知られており，この電気的な特徴を考慮した落雷情報に，積乱雲の発達過程を示す要素が 含まれている可能性がある． 一般的にCMCは，ELF (Extremely Low Frequency)帯域の雷電磁波観測から推定される． この周波数帯域は，帰還雷撃後に数msから数100msにわたり継続する連続電流に強い感度 があるため，数100 Ckm以上の大規模な落雷観測に向いている．一方，日本の暖候期の落雷 の90%以上は負極性落雷(-CG)で，これらの約半数は連続電流を伴わない数10 Ckm以下の 小規模な落雷と考えられている．落雷の大半を占める小規模な落雷のCMCを推定するため には，数10μsから数100μsの時定数を持つ帰還雷撃に伴い発生するVLF (Very Low Frequency)帯域の電磁波観測が必要となる．日本国内にはいくつかの雷観測網があるが，落雷位置標定 やピーク電流の算出を目的としており，CMCを推定できる雷観測網は存在しない． 関東地方はAMeDAS観測網や気象レーダーが複数設置され，落雷情報と気象パラメータ と比較するのに最も適した場所の一つである．この地域で連続的にVLF帯電磁波データを取得する ことにより，VLF帯雷電磁波形からCMCを導出し，気象パラメータと落雷規模を含む落雷情報の 定量的な関係を明らかにすることを目指す． 本研究では，同一仕様の観測システムを関東地方3箇所に設置し，雷放電電磁波の到達時間 差法を用いて落雷位置標定を行う．2011年10月に千葉県大網白里市，2012年4月に山梨県 甲府市，2013年5月に群馬県前橋市に設置が完了し，現在連続観測を行っている． 観測システムは，東西および南北水平2成分の磁場ループアンテナと，鉛直1成分のダイポール 電場アンテナ，受信器，PC等から構成される．A/D変換器とGPS時計により，VLF帯電磁波波形 データを16bit，83.3 kHzサンプリングレート，時刻精度10μs以内で記録する．この観測網により， 位置標定誤差を雷雲水平スケールである10km以下，関東全域で検出率100%を目指す． CMCを推定するためには，落雷の電流モーメントの時間変化（ソース電流の時間変化×放電路 の長さ）を得る必要がある．観測した雷電磁波波形は，電流モーメントの時間微分であることから， 観測波形を積分することにより電流モーメントを求める．観測波形は観測装置が持つ周波数特性 の影響を受けているため，位相およびGainの補正を行った．補正した山梨VLFの電場波形を基に， 東北電力尾神岳中継所にて観測された2例の落雷電流波形と比較し，CMCの算出法とその結果 について検証をした．落雷電流波形から推測されるCMCと比較したところ，インパルス的な変化を 示す部分（数10μs以内）については，誤差30%程度で推定された． 今回の発表では，CMCの推定方法および結果，検証方法について議論し，3地点同時観測による 位置標定結果を紹介する．
09/25 10:35--12:05 中尾 光
活動銀河は銀河中心からその銀河全体に匹敵する莫大なエネルギーを放射している銀河であり、 その中心領域を活動銀河核(AGN)という。 AGNの構造は(Antonucci 1993)により銀河の見込み角と可視光光度、電波強度の３つのパラ メータによって統一的な解釈がなされてきたが、電波強度を決定する構造の違いは分かっていない。 近年、電波の強いAGNでは質量降着率が低い為に降着円盤の内側に放射不良降着円盤(以下 RIAF)が 形成されると考えられているが、電波強度との詳細な関係は、RIAFのサイズなどが観測でき ていないために未確定である。 RIAFは幾何学的に厚いため降着円盤外縁を照らし、そこからダブルピークのバルマー輝線 が放射されると考えられている。そのため、ダブルピーク成分のプロファイルはRIAFのサイ ズを、プロファイルの変化はRIAFの活動性を反映しているはずである。そこでRIAFのサイズ や活動性に制限を設けるために、X線観測からRIAFの存在が示唆されているダブルピーク天体 である、Arp102Bのモニター観測を実施した。 簡易解析では、B,Vバンドに日スケールの変動が見られたが、分光による6800Åの連続光に は変動が見られなかった。またHα輝線の変動は、ダブルピーク成分とBLR成分とで放射領域が 異なるにも関わらず同じ変動を示しており誤検出の可能性が高い。これは分光データの系統エ ラーが大きいことが原因と考えられる。現状では優位なダブルピーク成分の変動を検出するこ とはできなかった。
10/29 10:30--12:00 Yukihiro Takahashi
No measurement of atmospheric electric field and electromagnetic waves on the ground in Mars has been made, though it could contribute only to the understanding of the electric current research but also to the meteorology, solid planet and space physics. DC electric filed near surface is considered to play an important role in initiating dust devil. The electromagnetic wave measurement makes it possible to know the location and the quantitative strength of dust devils wind with few observation sites. Though only one observation site enables us to determine the discharging location, two or three sites improve the accuracy significantly. This measurement also contributes to the studies both on the crust and the upper atmosphere. In this seminar the importance of electro-magnetic measurement on the surface of Mars is reviewed and the possible observation and the preparation in the Earth are discussed.
11/11 10:30--12:00 Masahiro Mihara
Sprites which are mainly caused by positive lightning discharges are transient discharge phenomena occurring in the mesosphere and lower thermosphere. Until now, fundamental properties of sprites have been studied by numerical simulation and optical observation from ground and airplanes. However, the occurrence conditions of sprites haven’t been revealed. Especially, the spatial distributions of sprites are the key parameters in order to clarify the occurrence condition. It has been suggested that in-cloud (IC) activity of sprites-producing +CG strokes cloud play a role in sprites formations.JEM-GLIMS mission which is nadir observations of lightning discharges and sprites from International Space Station (ISS) was started at December 20, 2012. The purpose of this research is to identify the relationship between the spatial distributions of sprites and IC activity using observation data of JEM-GLIMS. In this presentation, I will talk about the progress of analysis to identify spatial distributions of sprites using two CMOS cameras which were on-board JEM-GLIMS.
11/19 10:30--12:00 Kei Nakaoka
The langmuir Probe(LP) onboard the cassini spacecraft measured the ion mass distribution in the Titan's upper atmosphere(Wahland et al., 2005). The ion mass obtained from the LP is about 20-40 amu at altitudes from 1200km to 1800 km, and the ion mass exceeds 60amu neat 1200 km altitude (Wahland et al., 2005). However, the ion composition inth Titan's upper atmosphereby solving the momentum and the continuity equations including the photochemical processes. Based on the photochemical model by Krasnopolsky(2009), we calculated the ion andelectron densities in the titan'supper atmosphere, where the atmophere and the plasma temperatures were assumed to be constant for altitude during a day. We used the neutral atmosphere consisting of 29 species, which was obtained from the observation of the Ion Neutaral Mass Spectrameter(Waite et al., 2007, Vuitton et al., 2007) onboard the Cassini spacecraft. Our model includes 32 ion species.The calculation results show that HCNH+,C2H5+,HC3NH+ are main ions at altitudesfrom 800 km to 1200 km (ionoshere,Solar Zenith Angle=30) and the day time ion densities are about 1500/cm3 500cm/3 300cm/3 at the peak density, respectively. The light ions under 30 amu distribute mainly at altitudes from 1000 km to 1500km and the heavy ions 50amu such as HC3NH+, C6H7+,C9H11+ distribute at altitude 800-1200km. But under 800km and above 1400km atmosphere, density of electron is not consistent with Cassini's observation and Krasnopolsky's model. So in this presentaiton I will discuss this results with explaining process of ionization and effect of diffusion on Titan's atmosphere.
11/26 10:30--12:00 Nui Kobayashi
The occurrence conditions and the development mechanisms of sprite streamers still remain to be an unsolved problem after the discovery of sprites. Though the detailed three-dimensional spatial structures and the temporal evolution of sprite streamers are the key parameters to clarify them, these spatiotemporal characteristics are not so clear so far. For this purpose, we have conducted an optical observation campaign using high-speed cameras from two jet aircrafts in summer US. In this campaign, we succeeded to capture sprite images for 28 events by the high-speed cameras with a sampling rate over 8,000 fps at each aircraft simultaneously. Using these image data, we have performed triangulation analysis to estimate (1) the spatial distributions of clusters of sprite streamers produced by same parent CG and (2) the three-dimensional spatial structures of columniform sprites. (1) In the four out of eight events, it is identified that the longer the distance between sprite columns and the parent CG becomes, the higher the bottom altitude of columns becomes. Furthermore, in the 2 events of them, the longer the distance between sprite columns and the parent CG becomes, the slower the speed of downward streamer tips becomes. These results are the first clear observational evident showing the radial gradient of the quasi-electrostatic field produced by the parent CG discharge. One the other hand, in the remaining 4 events, there is no clear relationship between the distance from parent CG location derived from NLDN data and the bottom altitude of sprite columns. This result may imply that the location of return strokes is different from the center of the charge distribution. (2) We revealed the three-dimensional structure of the sprite streamer with upward streamers that emanate from the core. The upward streamers are out from sprite core radially and the horizontal distances are 1.0 – 2.8 km.
12/03 09:00--10:30 Takeshi Kudo
Early studies have suggested that there exists good relationship between atmospheric parameters,such as precipitation, radar reflectivity, and updraft of cumulonimbus and occurrence frequency of lightning. The lightning data is effective in investigating Cumulonimbus, because a space-time resolution of Meteorological radar which is typically used to research Cumulonimbus is not enough to investigate Cumulonimbus by its rapidly development and convective structure. However, early studies used only the information of lightning occurrence frequency in spite of different electrical characteristics, such as charge moment change (CMC, i.e., neutralized charge amount times vertical discharge length). In fact, relationship between life cycle of Cumulonimbus and lightning magnitude is not understood. CMC is typically estimated by observing electromagnetic wave radiated by cloud to ground (CG) lightning at the range of the Extremely Low Frequency (ELF, 3-3000 Hz) band. The observation of ELF band has strong sensitivity in the lightning continuing current which flow continuously from a few millisecond to a few hundreds of millisecond after the lightning return stroke. Therefore, the observation of ELF band is suitable for estimating a huge CG lightning with more than a few hundreds of C km. The negative CG lightning (-CG) account for 90 % or more of CG in warm season in Japan. It is believed that most of –CG is small charge moment change, since approximately half of –CG do not accompany the continuing current. In order to estimate the small charge moment change, observation of the Very Low Frequency (VLF, 3-30 kHz) radiated by portion of the return stroke which has the time constant from a few tens of microsecond to a few hundreds of microsecond is required. In addition, in order to link short-term meteorological forecast in the future, simple method of estimation of CMC is important. However, by the current lightning detection systems operated in Japan, which measure higher frequency than VLF range, only the information of peak current of the stroke is estimated and the CMC cannot be derived. The purpose of this study is to establish the methods of analysis to estimate small CMC of –CG and to clarify the relationship between developing process of cumulonimbus and lightning information including CMC. This study focuses on three subject: 1) development of a new VLF observation system in Kanto region, Japan and its continuous operation, 2) establishment of the methods of analysis to estimate small CMC of –CG and peak current from VLF sferics, 3) relationship between atmospheric parameter and lightning magnitude. Firstly, We developed a new VLF observation system have carried out continuous monitoring of 1-40 kHz waveform at three station in Kanto region, Japan, for the first time. Kanto region is the one of the best location in the world because of existing the dense meteorological observation and a good terrain condition. We have operated the observation system at Oami site since October 2011, Yamanashi site since April 2012, and Maebashi site since May, 2013. Many important results of this study have been obtained from the data observed at Yamanashi site for the period from May 2013 to August 2013. Secondly, we established of the simple methods of analysis to estimate impulsive CMC (iCMC) calculated for a period of time within 1 ms and the duration time of electric field. The peak current is estimated by comparison of Japan Lightning Detection Network (JLDN) peak current with normalized amplitude of electric field waveform. We analyzed 10,606 VLF sferic events obtained at Yamanashi site at the distance from 50 to 200 km, we obtained the number of estimated iCMC of –CG and +CG are 7418 and 57 ,respectively. The detectability of iCMC estimation of –CG is about 70-80 %. iCMC of –CG and +CG are -6.9 C km and +12.9 C km on average. This result is a reasonable value by comparison of neutralized charge amount of CG reported by Schoene et al. [2010]. We examined relationship between peak current, iCMC and duration time of electric field waveform. iCMC is correlated with peak current intensity (R2=0.72), but in the case of –CG, iCMC less than -20 C km is weak correlated with peak current intensity. There exists weak relationship between iCMC and duration time of electric field waveform (-CG: R2=0.12, +CG: R2=0.31). The peak current intensities have little association with duration time of electric field waveform (-CG: R2=0.03, +CG: R2=0.05). This results suggest that iCMC is affected by peak current intensity, but iCMC, cannot be determined by just peak current because of little association between duration time of electric field and peak current intensity. Finally, by using the estimated iCMC, peak current and duration time of electric field waveform, we examined relationship between a time variation of rain volume, area of radar echo top (nearly cloud top) more than 12 km and lightning parameters to the 3 cases. The rain volume and area of echo top were calculated using the Japan Meteorological Agency (JMA) rain radar data every 10 min. It is found that the absolute value of iCMC of -CG increases with increasing occurrence frequency of –CG, area of the radar echo top more than 12 km and rain volume (i.e., with the development of Cumulonimbus). It seems that time variation of peak current and duration time of electric field indicates a similar tendency in spite of little relationship between peak current and duration time of electric field. It is found that occurrence frequency of –CG rapidly and temporarily decrease preceding a downburst while the area of radar echo top more than 12 km is increasing. This result agree with U. S. thunderstorm reported by Metzger [2010]. In addition, it seems that small iCMC (less than 5 Ckm of its absolute value) of -CG dominate at occurrence time of a downburst. In the present study, we can estimate lightning magnitude for any CG lightning at the distance from 50-200 km. Then, by comparing estimated lightning magnitude and meteorological radar data, we exemplified the electrical characteristic change of CG in the life cycle of Cumulonimbus for the first time.
12/03 10:30--12:00 Shotaro Sakai
The Enceladus' cryovolcanos near the south pole form the plume which is composed of the water vapor and ice dust [e.g., Porco et al., 2006; Spahn et al., 2006; Waite et al., 2006]. The dust and the neutral gases expelled from Enceladus are considered as a main source of the E ring and the Enceladus torus [Horányi et al., 2004; Kurth et al., 2006; Kempf et al., 2008], and after the ionization by the solar EUV and the charge exchanges theybecome a plasma source of the Saturn's magnetosphere [Smith et al., 2010]. An interesting feature is that the dust grains of the plume are negatively charged [e.g., Horányi et al., 2004] and their kinetics is electromagnetically coupled to the ambient plasma [Wahlund et al., 2009; Farrell et al., 2009; Shafiq et al., 2011; Morooka et al., 2011]. A large amount of the electrons are attached to the small grains and the dust plays an important role in plasma as a negative charge carrier. The situation is so called "the dusty plasma" [e.g., Fortov et al., 2005] and possibly affects the electrodynamics of the extended plasma disk of the Kronian magnetosphere [Holmberg et al., 2012]. As mentioned above, they suggested the dust-plasma interaction in Saturn's inner magnetosphere from the observation of cold plasma characteristics. However, it is difficult to clarify the dust-plasma interaction with only observations. I tried to clarify the dust-plasma interaction in the inner magnetosphere from the analyses of the cold plasma data in the Enceladus plume and the numerical model in the inner magnetosphere and ionosphere. First, I'll present the in-situ observations of the Enceladus' plasma environment obtained by the Cassini Langmuir Probe. Previous results from E03 to E06 flybys showed that the electron densities were less than 1% of the ion densities up to 7 RE above the south pole. This is since the plume dust of nano- to micro- meter sized are negatively charged and electrically coupled to the background magnetospheric plasma. Here we used five flybys, where Cassini passed across the plume of different altitudes, to determine the altitudinal profile of the plasma densities, electron temperatures, ion speeds, and the spacecraft potential as a proxy to the electrical potential of dust grains. Combining all the results from the five flybys, the diameter of the plume was ~1.6 RE at Z = -1.3 RE, and ~7.1 RE at Z = -11 RE. The plume was broader in the downstream at high altitudes. The electron density was lower than the ion densities in the plume region, which was similar to previous observations near the E ring and Enceladus. The ion density and the density ratio of the electron to the ion were ~104 cm-3 and < 1% at the low altitude of Z = -1.3 RE while they became ~102 cm-3 and 50% at the high altitude of Z = -7.3 RE. The plume signature was identified at least at Z = -12 RE. The spacecraft potentials were overall negative, however, we found a few cases of the positive potential just above the south pole. This can be due to that the charging of dust doesn't achieve a static state since dust has just been released from Enceladus. The estimated negative charged dust density was ~100 cm-3 at the low altitude and decreased to 0.3 cm-3 at the high altitudes. Secondly, we calculated the ion speeds by using multi-component fluid equations, taking into account dust interactions to investigate the effects of ion–dust coulomb collision, mass loading, as well as taking into account magnetosphere–ionosphere coupling to investigate the effect of the magnetospheric electric field. The results show that the ion speeds can be significantly reduced by the electric fields generated by the ion-dust collisions when the dust density is high and the thickness of dust distribution is large. We also show that the ion speeds from our model are consistent with the LP observations when the maximum density of dust is larger than ~10^5 m-3. However, we gave the constant ionospheric conductivity in this study. Finally, we have developed a plasma density-temperature model of Saturn's mid-latitude ionosphere to investigate the effect of the ionospheric conductivity to the dust-plasma interaction. We used the magnetospheric plasma density and temperature as outer boundary conditions. The ion density is about 10^4 cm-3 at the altitude of 1200 km. It is similar to the densities from radio occultations. On the other hand, temperature is 1000 K or higher at the altitude of 1200 km. The higher temperature is necessary if the density is about 50 cm-3 at the altitude of 10000 km. The ionospheric Pedersen conductivity is about 1 S at 5 RS.
12/10 10:30--12:00 Junji Miyazawa
Martian atmosphere is thin and dry [McKay and Stoker, 1989; Kerr, 2000; Baker, 2001]. However, it is considered on the surface of Mars has evidence of water flows, several billion years ago, the atmosphere was warm and moist in the anticyclone [Carr, 1987 1999]. One of the reasons that has become thin atmosphere of Mars is the outflow of air to the space [Chassefière and Leblanc, 2004]. Affected by the solar wind, Mars is a low gravity than Earth, because there is no intrinsic magnetic field [Acuña et al., 1998]. Although the thought process from various atmospheric outflow, the details of the runoff process have not been clarified [Chassefière and Leblanc, 2004]. The questions are what the composition of the Mars atmosphere escaping, What the mechanism of the Mars atmosphere escaping and how much the Mars atmosphere escaping. Then, I constructed a model of atmospheric escape incorporating the effect of the collision. we obtain the distribution of the atmosphere around Mars. In this presentation, I report the density distribution and the distribution of the three-dimensional average flux of non-thremal oxygen obtained from the model.
12/17 10:30--12:00 Rikuma Sakai
Horizontal scale of one cell cumulonimbus is a 5-10km, knowing the state of the convective activity of the cloud portion is difficult to radar network and AMeDAS existing.The other hand, since the charge of the clouds are separated by convection, and is accumulated, be a index of convective activity has been suggested. The purpose of this study is the following two points. ・I have developed an inexpensive electrostatic field and charge of precipitation observation devices, to build a multi-point observation network. ・I make an estimate of the space charge structure of internal cumulonimbus, and coupled with convective activity. This presentation, from the results of Storm Chase campaign that was carried out in Yamanashi in August 2013, to announce topics of the following two involved in the estimation of the charge structure of the cumulonimbus. (1)Observation of the electrostatic field change By observing multi-point electrostatic field change caused by lightning, it is possible to determine the spatial position and the absolute value of the charge that is neutralized in the cloud. The electrostatic field changes observed in past studies, field mill or slow antenna have been used (Jacobson and Krider, 1976; Krehbiel et al, 1979). However, there is a problem that field mill is expensive, slow antenna is poor time resolution(RC> 1s). In the latest study (Bitzer ea al, 2013), by using (RC = 100ms, sample rate = 1MHz) the electric field observation devices of plate type, this paper determine position of the charge from the arrival time difference. However, it is not possible to determine the absolute value of the charge by using raw data. This is because change sensitivity due to the fact that the state of the ground changes. Therefore, the simultaneous observation of a multi-point, alternative to expensive electrostatic field observation device of conventional, maintenance and production of easy device at a low cost, the derivation of the sensitivity that takes into account the state of the ground is required . In this study, we established seven points at 4km intervals in the range of 7km × 7km (RC = 100ms, sample rate = 100Hz) the plate type field observation devices. To announce the results of performing the estimation of the position and the amount of charge in one stroke, the derivation of the sensitivity that takes into account the state of the earth. (2)Observation of precipitation charge By directly observed charged precipitation particles, it is possible to clarify the rough charge structure in the horizontal direction of the cloud. The radiosonde is the mainstream charge measurement of precipitation particles(Takahashi, 1973). It is a useful observation is to reveal the fine structure of the charge cloud, but for clouds occurring sudden, simultaneous observations at multiple points is very difficult. In this study, we ground multi-point observed using the observation device of the plate type used in the electrostatic field change observation. By paying attention to precipitation polarity , charge amount,the number per unit time, we discuss the horizontal distribution of cloud charge compared to the JMA C-band radar and AMeDAS. In addition, to announce that the potential as a rain gauge,we were also successfully able to record a slight precipitation that can not be captured by AMeDAS rain gauge.
12/24 10:30--12:00 Yuuki Furuta
As WIND-2 Campaign, S-520-26 sounding rocket was launched from ISAS/Kagoshima Space Center (131.08E, 31.25N) at 05:51 on January 12, 2012. The rocket installed Lithium Ejection System (LES), which releases the lithium atom in the lower thermosphere. Lithium atoms scattered sunlight by resonance scattering with the wavelength of 670.8nm. We observed at Uchinoura, Sukumo and Muroto using bandpass filter of passing the Lithium emission. From the diffusion of lithium clouds, we estimated neutral density and temperature in the thermosphere. I give a simple neutral wind, was to reproduce the neutral wind. Then, by comparing the image of observation, we inferred the neutral wind of the lower thermosphere.
01/07 09:30--10:30 Nui Kobayashi
Sprites are high-altitude optical emissions produced by a subset of cloud-to-ground (CG) lightning discharges. Sprites occur between 40 and 90 km above thunderstorms as a result of conventional electric breakdown in upper atmosphere [Pasko et al., 1997b]. Most sprites consist of multiple elements that appear simultaneously. Optical observations show that sprites are often displaced from the ground location of parent strokes, and the horizontal offset can vary from zero to as much as 100 km [Lyons, 1996; Wescott et al., 2000]. These experimental results suggest that the charges removed by CG are away from the ground location of parent strokes because of in-cloud activity of sprite-producing +CG strokes [Ohkubo et al., 2005; Lu et al., 2013]. However, the positions of the charge centers that produce sprites have never been identified, even though it is very important to clarify the occurrence conditions of sprites streamers. The purpose of this study is to identify the charge center and the horizontal distribution of sprite-producing electric field by specify the spatial distributions of sprite columns. In 2011 summer US, we have conducted the optical observation campaign using high-speed cameras from two jet aircrafts. Using these image data, I have performed triangulation analysis for 8 events to estimate the spatial distributions of the bottoms of columns. In the results, 4 of 8 events show the relationship that the longer the distance between sprite columns and ground locations of parent strokes becomes, the higher the bottom altitude of columns becomes. The result suggested that, in these events, the charge centers give close agreement with the ground locations of parent strokes and the distribution of columns show the horizontal spatial gradient of the quasi-electrostatic field produced by the parent CG discharge. On the other hand, 4 of 8 events have no clear relationship between displacements from ground locations of parent strokes and the bottom altitude of columns. The result suggested that, in these events, the charge centers are away from the ground location of parent strokes. Then, I searched for the locations that fulfilled the condition that the longer the distance between sprite columns, the higher the bottom altitude of columns becomes. These locations are considered as the charge centers that produce sprites.
01/07 10:30--12:00 Masataka Imai
The superrotation, which is a phenomenon that Venusian atmosphere moves westward at a velocity 60 times faster than the solid planet rotation, is a unique atmospheric system of Venus. When we observe the Venusian atmosphere in UV range (especially 365 nm), the planetary scale dark pattern like Y-feature can be seen. Yamamoto & Tanaka (1997) suggest that atmospheric waves (Kelvin wave in equator and Rossby wave in mid-latitude) propagating at an altitude of 70 km or higher play an important role in the formation of the Y-feature and would be related to the superrotation. From the Pioneer Venus spacecraft observation, it was revealed that Venus has several time scale variabilities in UV brightness caused by the propagation and distribution of UV features [Del Genio & Rossow (1982, 1990)], however the correspondence between these time scales and dynamic states in Venus atmosphere has not been established. A few weeks and ~2-month fluctuations seems to have grate association with Kelvin and Rossby waves, but further observation from the Pioneer Venus mission has not revealed this. In this study, we need to observe the Venusian UV brightness variation as a function of latitude and time. Venus Monitoring Camera (VMC) onboard the Venus Express ongoing spacecraft can provide very precious information, but observation of VMC is mainly limited in the southern hemisphere. In order to realize the long-term Venus monitoring in both hemisphere, we have carried out the ground-based simultaneous observations with Multi-Spectral Imager (MSI) onboard the Pirka telescope. The Pirka 1.6 m telescope, owned and operated by the graduate school of science in Hokkaido University, is primarily dedicated to the observations of solar planets. Using this system, we can carry out daytime observation and monitor the planetary scale UV-features (~ 5,000 km) over 8 hours in 1 day. In 2013, we carried out total ~2 months observation from mid-Aug. to mid-Nov. From the VMC data analysis, we could deduce the absolute brightness variation in southern hemisphere, and we found that the Venusian UV brightness variation can be categorized into two types; one is a phase showing strong periodicity, and the other is a phase when the strong periodicity can not be confirmed. The time interval between these two phases is under investigation. From the MSI data, we could not estimate the absolute brightness variation because of extinction of Earth's atmosphere. But the time variation of the normalized brightness in each latitudinal band by 70N-70S area brightness from the MSI data in Jul. 2012, had good correlation with the VMC data. By using this normalizing technique, we consider to be able to reconstruct the UV brightness variation from the MSI data. In this presentation, we will show the latest observation results from MSI's 2013 data.
01/14 10:00--10:45 Shuhei Goda
We are developing the Adaptive optics for observing planets to be carried 1.6-m Pirika telescope of the Hokkaido University, which is located at the Nayoro Observatory of the Faculty of Science, the Hokkaido University. For this adaptive optics, we consider the configuration of MCAO (Multi-Conjugate Adaptive optics) or GLAO (Ground-layer Adaptive Optics) system which is expected to provide a seeing improvement over a wide-field. We need to know the atmospheric turbulence profile to evaluate the performance of AO system. I measured the atmospheric turbulence profile at Nayoro site using MASS-DIMM (Multi-Aperture Scintillation Sensor with Differential Image Motion Monitor; Kornilov et al. 2007) for that. The MASS has four apertures and measures stellar scintillation. The measure of scintillation gives turbulence profile at altitudes of 0.5, 1, 2, 4, 8, 16km.In DIMM, the turbulence integrals as seeing is estimated from the variance of the differential image motion in two small apertures, cut out in the entrance pupil of telescope by a mask. To MASS and DIMM work on the same optical path, two instruments combine as MASS-DIMM. The measured seeing in DIMM is equal to turbulence integrals of all altitudes. So, if the DIMM seeing is subtracted from the MASS seeing, the GL seeing is calculated. I borrow the MASS-DIMM, which NAO requested to Cerro Tororo Observatory. And that instrument is modified to use by Celestron C11, which is Schmidt-Cassegrain telescope and suitable for MASS-DIMM. I measured turbulence profile for 18 days of September 2013 through December 2013. I will present results of atmospheric turbulence profile at Nayoro site.
01/14 11:00--11:45 Takeshi Kawahara
At 7°N of jupiter, the the southern extremity of North Equatorial Belt (NEB), there are the thermal emission regions at 5μm wavelength called 5μm hotspots. They are also called Dark Projections because they are the dark regions at visible wavelength. N. Barrado-Izagirre et al. (2013) suggest that the numbers of these hotspots are correlated with variation of speed of a jet about 100 - 150 m/s at 7°N, and drift speed of hotspots are correlated with equatorial Rossby wave. A. P. Showman et al. The example of numelical simulation is A. P. Showman et al. (2000). They simulate these hotspots by adding local regions of high pressure. However, it haven't been proved how and by which hotspots is formed yet. So I want to prove what is the cause of forming these hotspots. In order to prove it, I use DCPAM, which is the General Circulation Model (GCM) produced by GFD-Dennou Club (http://www.gfd-dennou.org/), and be tring to simulate the formation of these hotspots. In this presentation, I introduce the previous observations and numerical simulations about 5μm hotspots, the methods of DCPAM, the result of the test simulation as the first step of my study, and problem of my simulation.
01/21 09:30--10:15 Yuya Goda
A wave structure of haze in Jupiter’s south pole and observation by ground-based telescope. abstract: In Jupiter’s polar areas, there is stratospheric haze formed by aerosol particles. Using deep methane band filter at 889 nm, the stratospheric haze can be measured as it shows cup structures covering the polar region and as the edge of bright caps shows a wavy structure spreading in longitudinal direction. This structure can be clearly seen in the Jupiter’s south pole than the north pole, and contrast of wave is clearly at 67S latitude in particular -[Sánchez-Lavega, 2008). Jupiter’s polar areas have been observed by the Hubble Space Telescope (HST) from 1994 to 1999, by the Cassini ISS in 2000. This wavy structure has been seen for several years in the Jupiter’s both polar regions. And previous studies suggested that this wavy structure is caused by a planetary Rossby waves because this wavy structure lasts for a longer period and moves westward relative to the background flow. However, detailed origin and generation mechanism of this wavy structure is not clear so far and the structure shows unknown behavior (e.g. the vertical structure of the wave, change of the propagation velocity of the wave in the short time scale) because the observations of the wavy structure are not enough performed. Thus, we have carried out the telescopic observations of Jupiter in the period from 2011 to 2013 by using the Pirka telescope. In this seminar, I will introduce the results derived from previous studies of the Jupiter’s polar regions and wave structure. I will present observational results of the wavy structure in Jupiter’s polar region, which was measured in 2011 to 2013, and I will discuss the behavior of the wavy structure.
01/21 10:30--12:00 Jumpei Nakamoto
We are developing a adaptive optic system for use in observing of the Solar system planets to install on 1.6-m Pirka telescope which is located at the Nayoro Observatory of the Faculty of Science, the Hokkaido University. The adaptive optics system for astronomical conventional, point-like light source is required in close proximity to the observation target as reference light source, there is a problem that can not be used as a reference source to a surface light source, such as a planet. If the planet, such as Jupiter, has satellites one can use it for reference. However, it can only when suitable positional relation between the planet and the satellites. So, one can observe for a limited time only. So, we deliberate adaptive optics that use a focal-plane mask for make a pseudo point source. This method has only to add a focal-plane mask, such as pinhole, to the usual wave front sensor, and it is very simple, easy, and cost is low. But, this method no example ever, specific performance is unknown. Therefore I perform a physical optics calculation about the propagation of the light wave and estimate the most suitable parameter. In addition, I produce a wave front sensor experimentally and evaluate the actual wave front measurement installed in the 1.6-m Pirka telescope. I will present the result of physical optics calculation and the measurement in the the 1.6-m Pirka telescope.
02/04 09:00--10:30 Nguyen Thi Thao
Along with various advanced satellite onboard sensors, an important place in the near future will belong to hyperspectral instruments, considered as suitable for different scientific, commercial and military missions. As was demonstrated over the last decade, hyperspectral Earth observations can be provided by small satellites at considerably lower costs and shorter timescales, even though with some limitations on resolution, spectral response, and data rate. In this work the requirements on small satellites with imaging hyperspectral sensors are studied. Physical and technological limitations of hyperspectral imagers are considered. A mathematical model of a small satellite with a hyperspectral imaging spectrometer system is developed. The ability of the small satellites of different subclasses (micro- and mini-) to obtain hyperspectral images with a given resolution and quality is examined. As a result of the feasibility analysis, the constraints on the main technical parameters of hyperspectral instruments suitable for application onboard the small satellites are outlined. Comparison of the data for designed and planned instruments with simulation results validates the presented approach to the estimation of the small satellite size limitations. Presented analysis was carried out for sensors with conventional filled aperture optics.
02/04 10:30--12:00 To Anh Duc
Small satellites for remote sensing—how is a small satellite characterized, what is the basis for it,what are the trends, and what the application areas. The requirements concerning spatial, spectral and time resolution for the manifold application areas indicate the wide range of potential application for small satellites. Most of them can be covered using small satellites because of their already proven high performance capabilities in terms of spatial and spectral resolution. In my presentation, I will talk about remote sensing and it's progress in Vietnam.
02/18 09:00--10:30 Mitsuteru Sato
Since the successful launch and installation at the exposed facility of ISS/JEM in 2012, JEM-GLIMS carries out continuous measurements of lighting and lighting-associated transient luminous events (TLEs). So far, totally 3,130 transient optical events related to lightning flashes and/or TLE emissions were detected by the JEM-GLIMS optical instruments. JEM-GLIMS has to observe these phenomena in the nadir direction from ISS, it is naturally difficult to distinguish relatively weak TLE emission from strong lightning flashes. Our group has developed an analysis method to identify TLEs using JEM-GLIMS optical data and ground-based ELF observation data. At the presentation, the analysis method will be presented in detail and TLEs identified by this technique will be presented. In addition to this, recent results derived from JEM-GLIMS electromagnetic wave observations will be presented.
02/18 10:30--12:00 Hikaru Nakao
Active galactic nuclei (AGN) are the most energetic persistent objects in the Universe. The broad-line AGNs showing two peakes in the emission originating in an accretion disk. The most studied double-peaked emitter is the active nucleus of Arp 102B. For this object, a study by Chen & halpern (1989) has shown that the double-peaked Balmer lines cannot be driven by local viscous dissipation in the line-emitting part of the disk, as the Hα luminosity is of the order or even exceeds the energy locally available to power the line. This conclusion suggested that the lines are powered by illumination from an external source. The ionizing source could be a geometrically thick accretion flow, located within the inner radius of the line-emitting portion of the disk. In the case of Arp102B Eracleous et al. (2003) found that the spectral energy distribution (SED) of the nucleus is indeed well described by such a structure, a radiatively inefficient accretion flow (RIAF). This has led to the conclusion that an inner RIAF is the ionizing source of the accretion disk in Arp102B. We aim to make an accretion disk and RIAF model to fit observed profiles to size and luminosity of RIAF. In this seminar, I will introduce the previous studies of accretion disk of Arp 102B, and compare previous accretion disk model with observed data.
02/24 10:30--12:00 Tetsuya Fukuhara
The Japanese Venus Climate Orbiter called Akatsuki, which has failed to enter the Venusian orbit and now is orbiting around the sun, has obtained photometry data of day-side Venus between February and March 2011 at a distance of 1.2-1.7×10^7 km. One of potential cameras onboard akatsuki called the Longwave Infrared Camera (LIR) with an uncooled micro-bolometer array, which detects wavelength of 8–12 micron, acquired successfully 52 photometry data during the observation. The spatial resolution of LIR and an apparent diameter of Venus being almost equivalent, Venus' disk in the image extends to several pixels that include both Venus and the background radiation. All brightness pixels that included Venus were summarized and the background radiation component were removed from them to estimate a Venus' brightness component. Furthermore, the brightness has been converted to the brightness temperature by using calibration data acquired in the laboratory before the launch. Since the variation of brightness temperature has irregular time gaps, the Lomb-Scargle periodgram has been applied for getting a spectrum instead of the Fast Fourier Transform. The result shows spectrum peaks at 5-day and 8-day period. The 5-day period may be caused by the super rotation, and the 8-day period may be a planetary-scale wave that has the phase velocity of ~50 m/s.
03/04 10:40--11:10 Junichi Kurihara
New types of remote-sensing sensors for 50-kg class microsatellites have been developed at Hokkaido University, a member of microsatellite projects promoted by the Japanese government. In those sensors, a liquid crystal tunable filter (LCTF) was applied for the first time in the world to a space-borne multispectral sensor onboard the RISING-2 microsatellite. The LCTF is a kind of optical band pass filter with the center wavelength electrically controlled at 1 nm intervals in the visible (420-700 nm) and near infrared (650-1050 nm) regions. Compared to conventional multispectral sensors using a rotating filter wheel with (normally less than 20) selected spectral bands, the advanced sensor using the LCTF has the great advantage of enabling multispectral observations with hundreds of bands. The LCTF can also reduce size, weight, and power consumption of multispectral sensors and the advanced sensors using the LCTF are suitable for small and dynamically unstable platforms such as UAVs and microsatellites. In this presentation, applications of the advanced sensor using the LCTF to the Earth observations by UAVs and microsatellites are introduced.
03/11 10:30--12:00 Makoto Watanabe
The polarimetric observing mode was newly developed for the Infrared Camera and Spectrograph (IRCS) on the 8-m Subaru telescope. It enables near-infrared high-angular resolution imaging polarimetry (Y,J,H,K bands) and spectro-polarimetry (0.95--2.5 micron) with the 188-element adaptive optics system (AO188) and laser guide star system (LGS). This mode is a dual beam system with a rotatable half-wave plate and a LiNbO3 Wollaston prism. The first-light observation of the polarimetric mode was done on October 2013 and the instrumental polarization and its dependency on the telescope pointing were measured. Also, the polarization efficiency and its dependency on the image rotator inside the AO188 module were measured. The primary scientific targets is type 2 active galactic nuclei to reveal their polarization mechanism and the spatial distribution of scattering and/or absorbing materials around nuclei. On November 2013, a type 2 Seyfert nuclei, Mark 348, was observed, and a small extended component (about 0.15 arcsec) elongated along east-west direction was detected around nuclei.
03/18 10:30--12:00 Koji Nakau
Wild fire is not only natural disaster, but also one of massive causes of deforestation or also source of greenhouse gases. Therefore, wildfire monitoring utilizing satellite through active wildfire location (HS) product is quite important for reduce such impacts as well as tactics of fire agencies. Research group including Hokkaido University will launch mid-high resolution thermal infrared sensors UNIFORM-1 on-board. Under collaboration with other new Japanese sensors, we can monitor fire locations almost every day within 500m accuracy. This means drastically change of the current fire monitoring with MODIS or VIIRS. Toward such change of use, Hokkaido University is developing wildfire monitoring system for Asian countries including fire information providing system as well as wildfire detection and fire danger index under collaboration with Asian countries.