大氣探測和雷電研究進(jìn)展

大氣探測與雷電防護(hù)
Atmospheric Sounding and Lightning Protection

大氣探測和雷電研究進(jìn)展

1 雷電觀測試驗和物理過程研究

1.1 雷電野外觀測試驗

2012年5月中旬至9月底，大氣探測研究所在廣州野外雷電試驗基地開展了第7年的廣東閃電綜合觀測試驗（GCOELD）。該試驗在人工引雷試驗場、從化市氣象局和廣東省氣象局3個觀測點實施。人工引雷試驗場主要圍繞人工引雷開展閃電光電磁綜合測量，通信基站、風(fēng)力發(fā)電機(jī)防護(hù)試驗，高壓輸電線感應(yīng)過電壓特征觀測以及閃電化學(xué)效應(yīng)的測量，同時兼顧對自然閃電的觀測；從化市氣象局觀測點主要對自然閃電開展綜合觀測，兼顧對人工引發(fā)雷電電磁輻射場的觀測；廣東省氣象局觀測點主要是針對高建筑物上雷電物理過程開展綜合觀測，以獲取自然閃電不同類型先導(dǎo)（特別是上行連接先導(dǎo)）的物理特征。

2012年廣東閃電綜合觀測試驗在數(shù)據(jù)質(zhì)量提高、觀測同步、應(yīng)用領(lǐng)域擴(kuò)展等方面獲得了較大進(jìn)展，近距離閃電電磁場探測技術(shù)、人工引發(fā)雷電電流測量精度得到進(jìn)一步發(fā)展和提高，不同站點的同步資料更加豐富，并且首次開展了閃電大氣化學(xué)效應(yīng)研究。

成功引發(fā)2次包含多次回?fù)舻睦纂姡捎诟倪M(jìn)了采集記錄方法，提高了采集記錄速度，改善了多站資料的匹配對應(yīng)問題，2次引發(fā)雷電3個測站的電磁場觀測資料收集齊全。

采用了更高性能的雷電電流采集記錄裝置，提高了電流數(shù)據(jù)的時間分辨率，獲得的數(shù)據(jù)在信號密集區(qū)時間分辨率高達(dá)10 ns，能夠展示更豐富的電流細(xì)節(jié)。同時，應(yīng)用混合采樣技術(shù)實現(xiàn)了較長時間的高精度電流信號的記錄。

針對近距離閃電電磁場探測的飽和問題，改進(jìn)了電磁場測量裝置，提高了量程，改進(jìn)后的電場慢變化測量裝置量程高達(dá)±110 kV/m，電場快變化測量裝置量程高達(dá)±30 kV/m。

設(shè)計實現(xiàn)了光輻射、寬帶輻射場、低頻電磁場綜合觀測系統(tǒng)，開展了自然閃電的寬帶綜合觀測試驗，獲取了閃電物理過程的寬帶同步觀測資料，為閃電物理過程的深入分析提供了豐富的數(shù)據(jù)。

開展了閃電化學(xué)效應(yīng)的觀測研究，成功記錄到了與閃電放電事件相伴隨的大氣化學(xué)成分的變化。初步的觀測研究結(jié)果表明，臭氧和氮氧化物的變化與閃電事件有直接相關(guān)性，但臭氧和氮氧化物的變化具有相反的趨勢。（張陽）

1.2 特殊閃電事件——袖珍云閃（CIDs）研究進(jìn)展

使用寬帶干涉儀首次獲取了袖珍云閃（CIDs）事件的時空發(fā)展圖像。對11次CIDs記錄的分析表明，CIDs通道主要在垂直方向上發(fā)展。CIDs通道的垂直方向尺度在0.4～1.9 km范圍。CIDs發(fā)展的視速度在(0.44～1.0)×108m/s范圍，平均值為0.61×108m/s。CIDs的時空發(fā)展呈現(xiàn)出震蕩特征，證實了之前研究工作中提出的CID通道中的電流在上下兩端出現(xiàn)反射的猜想。通道中的電流速度在（0.56～2.6）×108m/s范圍，平均速度為1.4×108m/s（圖1）。

基于自行研制的重慶VLF/LF閃電定位網(wǎng)獲得的大量2種極性的CIDs觀測資料，對+CIDs和-CIDs特征的差異進(jìn)行了討論。結(jié)果表明，-CID是一種更為特殊的放電。與+CID相比，-CID會引起更大的平均電場變化，而且更遠(yuǎn)離常規(guī)閃電孤立發(fā)生。

發(fā)展了一套基于電離層反射信號的CIDs定位方法，證實-CIDs確實發(fā)生在較高的高度；同時還分析了CIDs與對流強(qiáng)度的關(guān)系。在9個雷暴個例中，8次雷暴中-CIDs少于+CIDs, -CIDs所占的百分比似乎隨對流強(qiáng)度增長。盡管-CIDs相對少見,但它們出現(xiàn)得相當(dāng)集中,大部分-CIDs都是在很短的一段時間內(nèi)發(fā)生的。+CIDs也有這種特征,但沒有-CIDs顯著。

對廣州和重慶觀測到的大量CIDs事件發(fā)生高度的計算結(jié)果表明，大多數(shù)+CIDs發(fā)生高度在8～16 km，而大多數(shù)-CIDs發(fā)生高度在1619 km。很少有CIDs事件發(fā)生高度高于19 km或低于4 km。據(jù)此推斷，+CIDs發(fā)生在負(fù)電荷區(qū)和上部正電荷區(qū)之間，-CIDs發(fā)生在上部正電荷區(qū)與云頂負(fù)屏蔽電荷層之間（圖2）。

從2次雷暴中CIDs事件的高度變化情況來看，CIDs事件可以發(fā)生在任何2個相反極性電荷區(qū)之間。+CIDs的發(fā)生高度在-CIDs也發(fā)生的時段會相對較高。在一次雷暴的一段時間內(nèi)，-CIDs的發(fā)生高度總是高于+CIDs，并且指示出+CIDs與-CIDs間的電荷區(qū)（圖3）。（劉恒毅）

1.3 高建筑物上始發(fā)的上行未連接先導(dǎo)的特征研究

從2009年開始，在廣州開展了高建筑物上雷電物理過程的觀測試驗。在19次閃電過程中觀測到了45個上行未連接先導(dǎo)，這些上行先導(dǎo)均由閃電過程中開辟新接地點的下行梯級先導(dǎo)所誘發(fā)。利用高速攝像資料，統(tǒng)計了這些先導(dǎo)的一些特征，包括起始高度（范圍：40～503 m；樣本數(shù)：45）、起始時間（＜0.1～1.32 ms；38）、離接地點的距離（20 m～1.3 km；38）、起始時離最近下行先導(dǎo)頭部的2D距離（99～578 m；21）、2D長度（0.48～399 m；45）和2D平均速度（（5.79～33.8）×105 m/s；22）。統(tǒng)計分析表明：86%（19/22）的發(fā)展速度小于1.7×105m/s；起始時間提前回?fù)舫^0.5 ms的上行未連接先導(dǎo)，其起始高度均超過300 m；起始高度低于300 m的上行未連接先導(dǎo)的長度很少超過50 m，且只會被距離在600 m以內(nèi)的閃電所激發(fā)；而對于高度超過400 m的建筑物，其頂部的上行未連接先導(dǎo)甚至能夠被1 km以外的閃電所激發(fā)；對于起始高度分別在100～200 m、200～300 m和高于400 m的上行未連接先導(dǎo)，誘發(fā)上行先導(dǎo)發(fā)生的下行先導(dǎo)的最遠(yuǎn)距離分別大約為350 m、450 m和600 m（圖4）。（呂偉濤）

1.4 包含2次上行傳播過程的觸發(fā)閃電時間的光電觀測

分析研究了一個產(chǎn)生2次正極性上行傳播過程的反常人工觸發(fā)閃電，第1次出現(xiàn)在初始階段（即上行先導(dǎo)過程），第2次出現(xiàn)在一次負(fù)極性的下行企圖先導(dǎo)之后。此次觸發(fā)閃電沒有產(chǎn)生回?fù)簦|發(fā)時刻，試驗點上方的雷暴較弱，其內(nèi)的云閃放電都產(chǎn)生了正向的電場變化。初始階段的放電過程較弱，之后，直竄先導(dǎo)沿著由第1次上行先導(dǎo)建立的通道向下發(fā)展，并在距離地面約453 m的高度處停止，形成一次企圖先導(dǎo)過程。受下行企圖先導(dǎo)的影響，距離引流桿78 m處的地面電場在5.24 ms時間里穩(wěn)定下降了6.8 kV/m，隨后產(chǎn)生了一個新的上行通道發(fā)展（即第2次上行發(fā)展過程）。第2次上行發(fā)展過程顯然是由下行企圖先導(dǎo)觸發(fā)，其在下行企圖先導(dǎo)結(jié)束后4.1 ms起始，并沿著原有通道傳播，從電流記錄判斷共持續(xù)了2.95 ms。在第2次上行傳播過程的電流中，疊加了2個電流脈沖。第1個脈沖與該次上行先導(dǎo)的突然發(fā)展相聯(lián)系，表現(xiàn)出快速的上升和下降，其峰值電流也大于第2次脈沖。第2個脈沖對應(yīng)第2次上行發(fā)展的通道進(jìn)入到之前下行企圖先導(dǎo)發(fā)展的區(qū)域?？梢姷?次上行傳播過程包含了起始的類似先導(dǎo)過程和隨后的中和過程。該研究展現(xiàn)了一種新的先導(dǎo)觸發(fā)類型，即上行放電在原有的通道中被相同通道中出現(xiàn)的反極性、傳播方向相反的企圖先導(dǎo)觸發(fā)（圖5）。（鄭棟）

2 雷電業(yè)務(wù)相關(guān)研究

2.1 雷電臨近預(yù)警系統(tǒng)的推廣應(yīng)用

（1）雷電監(jiān)測預(yù)警預(yù)報示范應(yīng)用基地的建立。以業(yè)務(wù)化推廣為目的，2012年雷電臨近預(yù)警系統(tǒng)經(jīng)過進(jìn)一步的技術(shù)升級，在可視化界面以及相應(yīng)功能上都進(jìn)行了改進(jìn)和擴(kuò)展，更適用于雷電預(yù)警預(yù)報的業(yè)務(wù)化應(yīng)用。同時建立了北京市氣象臺、河北省氣象臺和武漢中心氣象臺3個雷電監(jiān)測預(yù)警預(yù)報示范應(yīng)用基地，開展了區(qū)域化雷電監(jiān)測預(yù)警的業(yè)務(wù)平臺運行試驗，按照業(yè)務(wù)產(chǎn)品要求，實現(xiàn)了雷電臨近預(yù)警預(yù)報服務(wù)產(chǎn)品的自動生成、數(shù)據(jù)共享及其網(wǎng)絡(luò)服務(wù)功能，為雷電預(yù)警的專項服務(wù)奠定了基礎(chǔ)。目前上述3個示范應(yīng)用基地已將雷電臨近預(yù)警系統(tǒng)應(yīng)用于各自的雷電預(yù)警預(yù)報業(yè)務(wù)中，顯著提高了雷電活動的臨近預(yù)警準(zhǔn)確率，尤其是在強(qiáng)對流天氣的預(yù)警信號發(fā)布方面起到了較大的輔助決策作用。

（2）雷電臨近預(yù)警系統(tǒng)在國家林業(yè)局森林防火預(yù)警監(jiān)測信息中心業(yè)務(wù)應(yīng)用。由于雷擊引發(fā)的森林火災(zāi)給國家財產(chǎn)造成了不可估量的損失，如何有效減少雷擊森林火災(zāi)的損失一直是林業(yè)部門和氣象部門十分重視的頭等大事。中國氣象科學(xué)研究院與國家林業(yè)局森林防火預(yù)警監(jiān)測信息中心合作，依據(jù)雷擊森林火災(zāi)的監(jiān)測、預(yù)警的具體業(yè)務(wù)需求和當(dāng)前的網(wǎng)絡(luò)基礎(chǔ)條件，研制專門服務(wù)于林區(qū)雷擊火監(jiān)測以及雷擊火臨近預(yù)警服務(wù)方法，進(jìn)行雷擊森林火災(zāi)監(jiān)測預(yù)警系統(tǒng)的開發(fā)。目前該系統(tǒng)在國家森林防火指揮辦公室和雷擊森林火災(zāi)多發(fā)的黑龍江省、內(nèi)蒙古自治區(qū)，大興安嶺防火辦等單位業(yè)務(wù)試運行，各單位均可通過互聯(lián)網(wǎng)實時獲取雷擊火災(zāi)的監(jiān)測和預(yù)警產(chǎn)品信息。試運行期間該系統(tǒng)監(jiān)測到多起初發(fā)的雷擊火災(zāi)，具有較好的使用價值，基本滿足了雷擊森林火災(zāi)監(jiān)測和預(yù)警的業(yè)務(wù)需要。（姚雯）

2.2 基于觸發(fā)閃電和自然閃電觀測的閃電定位系統(tǒng)效能評估

基于2007—2011年廣東從化市人工觸發(fā)閃電試驗和2009—2011年廣州高建筑物上自然閃電觀測試驗獲取的觀測資料，對廣東電網(wǎng)閃電定位系統(tǒng)效能進(jìn)行了評估。

對于28次包含回?fù)暨^程的觸發(fā)閃電，廣東電網(wǎng)閃電定位系統(tǒng)的閃電事件探測效率為89%（25/28），回?fù)籼綔y效率為46%（37/81）。當(dāng)有2個以上探測子站參與定位計算時，平均定位誤差的算術(shù)平均值和中值分別為759 m和649 m（基于33個經(jīng)典觸發(fā)閃電回?fù)魳颖荆?，而空中觸發(fā)閃電回?fù)舳ㄎ唤Y(jié)果與火箭發(fā)射架之間距離的算術(shù)平均值和中值分別為675 m和646 m（13個樣本）。當(dāng)觸發(fā)閃電回?fù)綦娏鞣逯担?5 kA 時，回?fù)籼綔y效率為100%（15 個樣本）；當(dāng)觸發(fā)閃電回?fù)綦娏鞣逯担?5 kA時，回?fù)籼綔y效率降為50%（7/14）；對于電流峰值＜10 kA的回?fù)?，閃電定位系統(tǒng)的探測效率僅為33%（1/3）?；?fù)綦娏鞣逯抵苯訙y量結(jié)果與閃電定位系統(tǒng)反演結(jié)果呈現(xiàn)高度線性相關(guān)，相關(guān)系數(shù)達(dá)到0.92（21個樣本）。

對于34次擊中高建筑物的自然閃電，廣東電網(wǎng)閃電定位系統(tǒng)的閃電事件探測效率為97%（33/34），對這些閃電所包含的81次回?fù)舻奶綔y效率為74%（60/81）。當(dāng)有2個以上探測子站參與定位計算時，平均定位誤差的算術(shù)平均值和中值分別為633 m和453 m（54個樣本）（圖6）。

總體上，廣東電網(wǎng)閃電定位系統(tǒng)的閃電事件探測效率為94%（58/62），回?fù)籼綔y效率為60%（97/162）；當(dāng)有2個以上探測子站參與定位計算時，平均定位誤差的算術(shù)平均值和中值分別為710 m和489 m（87個樣本）；當(dāng)剔除1個最大異常值時，回?fù)綦娏鞣迪鄬μ綔y誤差在0.4%～42%之間，算術(shù)平均值和中值分別為 16.3%和19.1%（21個樣本）（圖7）。（張義軍）

2.3 1997—2009年全國雷電災(zāi)害特征統(tǒng)計

利用全國雷電災(zāi)害數(shù)據(jù)庫資料，分析了1997—2009年我國雷電災(zāi)害在人員傷亡、財產(chǎn)損失等方面的統(tǒng)計特征。1997—2009年，我國共發(fā)生雷電災(zāi)害61614起，發(fā)生雷擊人員死亡事故5033起，雷擊人員受傷事故4670起。在空間分布上，我國雷電災(zāi)害發(fā)生頻率呈現(xiàn)出東部沿海和南部地區(qū)高于西部地區(qū)的特點。在時間分布上，雷電災(zāi)害主要發(fā)生在夏季的7—9月，而冬季的10月至次年3月雷電災(zāi)害相對較少。雷電災(zāi)害的時空分布特征與我國閃電頻次的時空分布相一致。雷電災(zāi)害和人員傷亡事故在1997—2007年呈現(xiàn)逐年上升趨勢，2008年開始有所下降。我國每年每百萬人口的雷擊死亡率和受傷率分別為0.31和0.28。農(nóng)村人口占雷擊死亡和雷擊受傷人數(shù)的51%和29%，農(nóng)民是雷電災(zāi)害的主要受害者。雷擊損失行業(yè)和雷擊環(huán)境的分析表明，民用行業(yè)在雷災(zāi)事故受損行業(yè)中占有較大比重，農(nóng)田是雷擊傷亡事故的主要發(fā)生地（圖8）。（張文娟）

3 地基云自動化觀測技術(shù)和方法研究

地基全天空云觀測系統(tǒng)的穩(wěn)定性有了較大提升。引入PLC模塊實現(xiàn)了觀測系統(tǒng)中各種機(jī)械運動的控制和設(shè)備內(nèi)部溫濕度的監(jiān)測，采用光纖轉(zhuǎn)換模塊解決了觀測設(shè)備和中央控制系統(tǒng)之間的遠(yuǎn)距離傳輸問題。

重新設(shè)計開發(fā)了地基全天空云觀測系統(tǒng)的軟件，新版觀測軟件界面友好，功能豐富，增加了天頂方向云底高度、太陽位置信息、日出日落時間和日照時數(shù)等的計算和顯示（圖9）。

2012年8月起，在廣東從化市氣象局和西藏自治區(qū)日喀則氣象局各架設(shè)了一套地基全天空云觀測系統(tǒng)開展對比觀測試驗，并實現(xiàn)了系統(tǒng)的遠(yuǎn)程控制和數(shù)據(jù)傳輸。

研究了兩種卷云檢測算法，通過引入數(shù)學(xué)形態(tài)學(xué)和Markov隨機(jī)場模型較大地改進(jìn)了全天空圖像中卷云檢測的精度。在云狀識別方面，研究了一種新的器測云圖分類方案，先將云分成積狀云、層狀云和卷云，通過模式識別方法先將這3類云分開，再結(jié)合激光云高儀獲取的云底高度信息，根據(jù)云底高度將云分成低云、中云和高云3族，則可得到較具體的云圖分類結(jié)果。（楊俊）

圖1 一次-CIDs事件VHF輻射源的二維方位角-仰角定位結(jié)果隨時間的變化Fig1 Azimuth and elevation mapping of VHF radiation sources versus time for a -CIDs event

圖2 廣東和重慶觀測到的致密云閃高度分布(廣東：1318+CIDs，625-CIDs；重慶：5489+CIDs，1400-CIDs)Fig2 Distributions of discharge heights of CIDs observed in Guangzhou (a) and Chongqing (b)

圖3 重慶一次雷暴過程中致密云閃高度隨時間的分布特征(藍(lán)色和綠色的三角形分別代表每15個連續(xù)的+CIDs或-CIDs的平均高度，矩形陰影區(qū)域表示沒有-CIDs 發(fā)生的時間段，幾乎將+CIDs和-CIDs分開的黑色曲線表示上部正電荷區(qū)的可能位置)Fig3 CID discharge heights in a thunderstorm in Chongqing. (Blue and green triangles represent average heights for each 15 successive positive CIDs and negative CIDs, respectively. Shaded rectangles indicate the periods when no negative CID is produced. Black curve represents the possible location of the upper positive charge layer, dividing almost all positive CIDs and negative CIDs into two sides)

圖4 2010年6月21日廣州高建筑物上一次閃電的高速攝像記錄（在此個例中觀測到4個上行未連接先導(dǎo)，UUL09～UUL12）Fig4 The high-speed images of a lightning fash striking a tall structure in Guangzhou on 21 June 2010. (Four unconnected upward leaders, UUL09—UUL12, are observed in this case)

圖5 下行負(fù)極性企圖先導(dǎo)((a)～(h))和隨后的第2次上行正極性傳播過程((i)～(l))((i)和(h)間隔4.1 ms）Fig5 Negative downward aborted leader ((a)-(h)) and the subsequent second positive upward propagation ((i)-(l)) (There is a 4.1-ms interval between (i) and (h))

圖6 閃電定位系統(tǒng)對54次擊中高建筑物的回?fù)舻亩ㄎ黄頕ig6 The location errors of LLS reports for 54 return strokes on tall structures. The origin corresponds to the ground strike point

圖7 觸發(fā)閃電回?fù)綦娏鞣逯档闹苯訙y量結(jié)果與定位系統(tǒng)反演結(jié)果的對比Fig7 LLS-reported vs directly measured peak currents in the triggered lightning experiment

圖8 我國雷擊人員傷亡事故排序Fig8 The rank of each province in the rate of lightningrelated casualties in mainland China

圖9 新版地基全天空云觀測系統(tǒng)軟件界面Fig9 The interface of the new CAMS_TCI software

Progress in Atmospheric Sounding and Lightning Research

1 Lightning feld experiment and physics process research

1.1 Lightning feld experiment

Guangdong Comprehensive Observation Experiment on Lightning Discharge (GCOELD) has been conducted by the Institute of Atmospheric Sounding (IAS) at the feld experiment site for lightning research and testing in Guangdong Province from 15 May to 20 September 2012. The observations were carried out at the test site of triggered lightning, Conghua Municipal Meteorological Bureau, and Guangdong Provincical Meteorological Bureau. In the test site of triggered lightning, the main experiments include the comprehensive observation of optical radiation and electromagnetic feld, the protection of communication base station andwind generators, the observation of induction overvoltage for high voltage transmission, and the observation of lighting chemical effect. At the Meteorological Bureau of Conghua, natural lightning and triggered lightning are observed. At the Meteorological Bureau of Guangdong Province, the comprehensive observation of lightning striking on tall structures is conducted in order to obtain the physical characteristics of different leaders (especially the upward connecting leader) in natural lighting fashes.

GCOELD in 2012 has made great progress in the improvement of data quality, the synchronization of multi-station observation, and the extension of application area. The saturation problem during close electromagnetic detection and the measurement precision of current data have been improved, and the synchronous data in different observation sites have been enriched. In addition, triggered lightning as a tool has been applied to the research of atmospheric chemistry. Detailed results are shown as follows.

Two lighting fashes accompanied by many return strokes have been successfully triggered. Based on a new method of data acquisition, the speed of data acquisition has been improved. As a result, the synchronous data of three observation sites for two triggered lightning have been collected.

The time resolution of lightning current measurement has been improved by using the acquisition and recording equipment with higher performance. As a result, the time resolution is 10 ns for dense signals and more detailed information is obtained. At the same time, longer recording time can be achieved by application of a hybrid sampling method.

The detection system of electric feld range has been improved in order to resolve the saturation problem for close electromagnetic feld detection. The measurement range of slow electric feld change is ±110 kV/m, and the corresponding value is ±30 kV/m for the improved system of fast electric feld change.

The detection system of optical radiation, broadband radiation, and low frequency electromagnetic feld has been developed. During the broadband comprehensive observation, the synchronous data of lightning sunphysical process have been collected, which will beneft the further analysis of lightning process.

The observation of lighting chemical effect has been conducted. The chemical composition in ambient atmosphere varies when lightning flashes occur. The preliminary results show that there is a correlation between the concentration change of ozone and nitrogen oxide and the lightning event, but the change tendency of ozone concentration is opposite to that of nitrogen oxide. (Zhang Yang)

1.2 Progress in the research of compact intracloud discharges (CID)

The CID channel evolution images obtained by using VHF broadband interferometers are presented for the frst time. Analysis of 11 CIDs shows that the channels of CIDs develop mainly in the vertical direction. The vertical scale of CIDs is in the range of 0.4-1.9 km. The average apparent speed of CIDs is in the range of (0.44-1.0)×108m/s with a mean value of 0.61×108m/s. The temporal-spatial evolution of the radiation sources of the CID shows an oscillation pattern, confrming the previous prediction that there is an oscillating current being refected at the two ends of the CID channel. The estimated speed of the current wave in the CID channel is in the range of (0.56-2.6)×108m/s with a mean value of 1.4×108m/s (Fig1).

On the basis of a large number of CIDs of both polarities recorded by our VLF/LF lightning location network, characteristic differences between +CIDs and ?CIDs are discussed. The results reveal that ?CID is a more special type of discharge. Compared with +CIDs, ?CIDs produce larger electric feld changes on average, and they are more isolated from other discharge processes.

A locating method based on ionospheric refection pairs of CIDs is developed, which confrms that?CIDs do occur at higher altitudes. The relationship between CIDs and convective strength is also analyzed. Out of nine storms analyzed in this study, eight produce fewer ?CIDs than +CIDs. The percentage of ?CIDs seems to increase with the convective strength. Although ?CIDs are relatively rare, their occurrences are more temporally compact, that is, a large portion of ?CIDs are produced in a very short period. +CIDs also have this characteristic, but not as pronounced as that of ?CIDs.

Discharge heights of thousands of CIDs observed in Guangzhou and Chongqing of China are calculated. The result shows that most positive CIDs occur between 8 and 16 km while most negative CIDs occur between16 and 19 km. Very few negative CIDs are above 19 km or below 4 km. It is inferred that positive CIDs are produced between main negative charge layer and upper positive charge layer while negative CIDs are produced between upper positive charge layer and negative screening charge layer at the cloud top (Fig2).

Variations of CID discharge heights in two thunderstorms are analyzed. It seems that CIDs can be produced at any position between corresponding charge layers. Positive CIDs are generally higher in the periods when negative CIDs are also occurring. For a given short time period during a single thunderstorm, negative CIDs are always observed to occur at higher altitudes than positive CIDs, indicating a dividing charge layer between positive CIDs and negative CIDs. We believe CIDs are produced in vigorous convective surges that develop to the height comparable to the discharge height of CIDs (Fig3). (Liu Hengyi)

1.3 Characteristics of unconnected upward leaders initiated from tall structures

To study the processes of lightning flashes striking on tall structures, a field experiment has been conducted in Guangzhou since 2009. 45 unconnected upward leaders (UULs) that occurred in 19 downward negative fashes are analyzed. Each observed UUL is initiated by a downward stepped leader before a new strike point is struck. For each UUL, several parameters are determined by using highspeed images∶ inception height, inception time prior to return stroke (RS), horizontal distance from the fash's strike point, two-dimensional (2D) distance between the nearest downward leader branch tip and the UUL’s inception point at its inception time, 2D length, and 2D average propagation velocity. Their corresponding values range from 40 to 503 m (number of samples∶ 45), ＜0.1 to 1.32 ms (38), 20 m to 1.3 km (38), 99 to 578 m (21), 0.48 to 399 m (45), and 5.79×105to 33.8×105m/s (22), respectively. Statistical analysis shows that 86% (19/22) of the velocities are smaller than 1.7×105m/s; no UUL with an inception time prior to RS greater than 0.5 ms is initiated from a structure lower than 300 m; those UULs with inception heights lower than 300 m seldom exhibit lengths longer than 50 m and can only be initiated by fashes within approximately 600 m, while those higher than 400 m can even reach several hundred meters and be initiated by fashes over 1 km away. The maximum distances for the downward leaders to attract the UULs with inception heights from 100 to 200 m, 200 to 300 m, and over 400 m are approximately 350 m, 450 m, and 600 m, respectively (Fig4). (Lü Weitao)

1.4 Optical and electrical observations of an abnormal triggered lightning event with two upward propagations

This study investigates an abnormal artificially triggered lightning that produced two times positive upward propagations∶ one during the initial stage (i.e., the upward leader (UL)) and the other after a negative downward aborted leader (DAL). The triggered lightning was performed in a weak thunderstorm over the experiment site and did not produce any return stroke process. All the intracloud lightning around the experiment site produced positive electric field changes. The initial stage was of weak discharge process. After that, a downward dart leader propagated along the original channel produced by the 1st UL and ended at a height of about 453 m, forming a DAL. Infuenced by the DAL, the electric feld at a point located 78 m from the rod showed a steady reduction by about 6.8 kV/m over 5.24 ms before the initiation of a new upward channel (i.e., the 2nd upward propagation (UP)). The 2nd UP, which started at about 4.1 ms after termination of the DAL and propagated along the original channel, was triggered by the DAL and sustained for about 2.95 ms according to the current record. Two current pulses were superimposed on the current of the 2nd UP. The frst pulse, related to the sudden initiation of the 2nd UP, showed a more rapid increase and decrease, and large peak value, than did the second pulse, related to the development of the 2nd UP into the area where the DAL had propagated. The 2nd UP contained the similar-to-leader process and the following neutralization process. This study represents a new type of triggering leader, in which a new upward discharge is triggered in an established channel by the aborted leader propagating along the same channel with opposite polarity and propagation direction (Fig5). (Zheng Dong)

2 Research related to lightning operational work

2.1 Promotion and application of the Lightning Nowcasting and Warning System (LNWS)

(1) Establishment of demonstration bases for lightning monitoring, warning, and forecasting. For the purpose of operational application, the LNWS conducted further technology upgrades in 2012. With improvement and expansion of visual interface, it is more suitable for the operational lightning warning forecast. Meanwhile, three demonstration bases for lightning monitoring, warning, and forecasting have been set up in the Beijing Meteorological Center, Hebei Meteorological Center, and Wuhan Meteorological Center, and running tests of these regional operational platforms have been carried out. In accordance with the requirements of operational products, the system automatically generates service products for lightning warning and forecasting and has the function of data sharing and network services. Presently, the above three demonstration bases have applied the LNWS to their own lightning warning operation and improved the nowcasting accuracy, especially in the early warning of severe convective weather.

(2) Operational application of the LNWS in Forest Fire Warning at the Monitoring Information Center of the State Forestry Administration. Considering the grave losses to state property by the lightning-ignited forest fres every year, how to effectively reduce the losses of forest fres caused by lightning has been a top priority concern for both forestry and meteorological administrations. Based on the specifc operational needs and current network infrastructure, the Chinese Academy of Meteorological Sciences in cooperation with the Forest Fire Warning and Monitoring Information Center of the State Forestry Administration, established a specialized service for monitoring and nowcasting lightning-ignited forest fres, and developed a Lightning-Ignited Forest Fire Monitoring and Warning System. The system has currently been put into operational use in the State Forest Fire Prevention Offce in Hei Longjiang Province, Inner Mongolia Autonomous Region, and the Daxing'anling Mountain Range. All the departments could obtain the lightning-ignited fre monitoring and warning products in real time via the Internet. During the test run period, the system captured several initial lightning-ignited fires, which demonstrates the good value of this system in monitoring and nowcasting of lightning-caused forest fres. (Yao Wen)

2.2 Performance evaluation for a lightning location system based on observations of artifcially triggered

lightning and natural lightning fashes

Performance evaluation for the lightning location system (LLS) of the power grid in Guangdong Province of China was conducted based on observational data of the triggered lightning fashes obtained in Conghua of Guangdong during 2007—2011 and natural lightning fashes over tall structures obtained in Guangzhou during 2009—2011.

For 28 artificially triggered lightning flashes (each of them contains one or more return strokes), the LLS’s flash detection efficiency and stroke detection efficiency are approximately 89% (25/28) and 46% (37/81), respectively. The location accuracy of LLS reports is analyzed based on those location retrieval results using more than two sensors. For 33 return strokes occurring in classical triggered lightning fashes, the arithmetic mean and median values of the LLS’s location error are estimated to be approximately 759 and 649 m, respectively; and for 13 return strokes occurring in altitude triggered lightning fashes, the arithmetic mean and median values of the distances between the LLS’s records and the rocket launcher are approximately 675 and 646 m, respectively. When the absolute peak current of a return stroke was greater than 15 kA, the detection effciency was 100% (15/15), but it decreased to 50% (7/14) when the peak current was less than 15 kA, and only 33% (1/3) in cases where the peak current was less than 10 kA. There is a strong positive linear relationship between the directly and LLS estimated and directly measured peak currents, with the correlation coeffcient being 0.92 (for 21 samples).

For 34 natural lightning fashes over tall structures in Guangzhou, the LLS’s fash detection effciency is approximately 97% (33/34). For the 81 return strokes included in these fashes, the LLS’s stroke detectionefficiency is approximately 74% (60/81). If more than two reporting sensors are involved in the location retrieval, the arithmetic mean and median values for location error are estimated to be approximately 633 and 453 m, respectively (for 54 samples) (Fig6).

Totally, the LLS’s fash detection effciency and stroke detection effciency are approximately 94% (58/62) and 60% (97/162), respectively. The arithmetic mean and median values for location error are estimated to be approximately 710 and 489 m, respectively, when more than two reporting sensors are involved in the location retrieval (for 87 samples). After eliminating one obviously abnormal sample, the absolute percentage errors of peak current estimation are within 0.4%-42%, with arithmetic mean and median values of approximately 16.3% and 19.1%, respectively (for 21 samples) (Fig7). (Zhang Yijun)

2.3 Lightning casualties and damages in China from 1997 to 2009

The lightning-related fatalities, injuries, and property damages reported in China from 1997 to 2009 are summarized by using the National Lightning Hazards Database. The characteristics of the incidents including 5033 deaths, 4670 injuries, and 61614 damage reports are analyzed. For the spatial distribution of lightning disasters in China, the eastern costal and southern areas have more frequent lightning disasters than the western areas. Lightning disasters mainly occur in summer months from July to September while fewer damages occur in winter months from October to March, which correlate signifcantly with the temporal variability of lightning frequency in China. Lightning-related casualties and damages in China have increased for the period of 1997—2007, and then began to decrease since 2008. The national fatalities and injuries per million people per year are 0.31 and 0.28, respectively. Rural people accounts for 51% and 29% of all lightning fatalities and injuries, which makes residents in agricultural and rural area the major lightning victims. Characteristics of lightning disasters and correlative factors are also studied, including hazard affected industries and locations. The results show that civil industry has the worst property loss and farmland is the largest category in lightning-caused casualty locations (Fig8). (Zhang Wenjuan)

3 Progress in research on ground-based cloud automatic observation

The stability of the ground-based Total-sky Cloud Imager (CAMS_TCI) has been greatly improved after accomplishing the monitor and control of mechanical motion and internal temperature and humidity by using PLC module. The problem of long-distance transmission between the observation equipment and the central control system has been solved by adopting fber optic conversion module.

The software of the CAMS_TCI has been re-designed. The new observation software interface is friendly and feature-rich, with added information such as the height of the cloud base, the position of the sun, sunrise and sunset time, sunshine, and so on.

Since August 2012, two sets of CAMS_TCI have been installed at the Conghua Meteorological Bureau and Shigatse Meteorological Bureau to carry out a comparative observation experiment, respectively. A remote control and data transmission technique between the client and the host were used in the experiments.

By introducing mathematical morphology and Markov random field model, two cirrus detection algorithms have been proposed, which have improved the cirrus cloud detection accuracy of the total-sky image greatly. In the cloud type recognition, a new instrumental classifcation scheme has been put forward, which classifies the cloud into cumuliform cloud, stratiform cloud, and cirrus cloud. The three types of clouds were identifed through pattern recognition, then combined with the cloud base height from the laser ceilometer, which could divide the cloud into low cloud, middle cloud, and high cloud. Specifc cloud type classifcation results could thus be obtained (Fig9). (Yang Jun)