災(zāi)害天氣
Severe Weather

災(zāi)害天氣研究進展

1 災(zāi)害天氣監(jiān)測與資料應(yīng)用

1.1 雨滴譜數(shù)據(jù)在雙線偏振雷達雨滴譜反演及降水估測中的應(yīng)用

利用雙線偏振雷達在廣東鶴山（2014年5月1日至6月15日）參加華南前汛期暴雨外場觀測試驗，獲得大量的暴雨、大暴雨野外觀測資料，對資料進行了質(zhì)量控制。利用雨滴譜觀測數(shù)據(jù)分析了華南前汛期滴譜結(jié)構(gòu)，重新擬合偏振參量進行降水估測，提高了偏振雷達定量降水估測精度；利用雙線偏振雷達在西藏那曲（7月1日至8月31日）開展的第3次青藏高原科學(xué)考察野外觀測試驗數(shù)據(jù)，研究了高原對流云的宏、微觀特征。（胡志群）

1.2 C波段調(diào)頻連續(xù)波雷達降水云結(jié)構(gòu)研究及降水參數(shù)反演

C-FMCW雷達可以描述降水云的精細垂直結(jié)構(gòu)和快速演變特征。利用C-FMCW雷達參加江淮梅雨鋒降水觀測試驗、華南季風(fēng)強降水外場試驗和青藏高原那曲局地對流云的高原觀測試驗所獲得的資料，開展了降水云垂直結(jié)構(gòu)分析和降水參數(shù)反演研究?；夭ㄗV參數(shù)和譜分布的協(xié)同分析，有助于深入認識云中的水汽與動力過程，上升和下降運動的強烈變化在回波強度譜分布中的表現(xiàn)更加清晰，在弱回波強度區(qū)中發(fā)現(xiàn)了高空強的大氣下沉速度；反演的廣東陽江降水云中雨滴譜分布與地面雨滴譜儀觀測數(shù)據(jù)一致性較好（圖1～2）。（阮征）

1.3 聯(lián)合多種觀測設(shè)備在多個科研項目上開展外場試驗

完成行業(yè)專項“第3次青藏高原科學(xué)試驗——邊界層和對流層觀測”中的青藏高原云降水預(yù)觀測試驗、華南季風(fēng)強降水外場試驗和973項目“高原東移降水系統(tǒng)觀測”等外場試驗，獲取了云降水微物理結(jié)構(gòu)和動力結(jié)構(gòu)數(shù)據(jù)。主要創(chuàng)新點：在國內(nèi)首次利用云雷達、微降水雷達和水汽云探測激光雷達等云觀測設(shè)備，以及X波段相控陣天氣雷達和C波段雙線偏振雷達的強對流觀測設(shè)備，在青藏高原和高原東坡實現(xiàn)了云垂直結(jié)構(gòu)和對流系統(tǒng)中尺度結(jié)構(gòu)的觀測。以此為基礎(chǔ)，初步形成了多種遙感手段反演高原對流系統(tǒng)空氣上升速度和云水/云冰/雨水/雪水的垂直廓線的反演方法，驗證了國產(chǎn)新型探測設(shè)備在高原工作的能力，為青藏高原云和降水的研究提供了數(shù)據(jù)（圖3）。（劉黎平）

1.4 我國持續(xù)性強降水的動力預(yù)報理論與方法和可預(yù)報性研究

構(gòu)建了基于集合預(yù)報、全球海陸氣耦合模式和高分辨率區(qū)域模式嵌套的持續(xù)性強降水動力預(yù)報原型系統(tǒng)；開展了全球海陸氣耦合模式和同化系統(tǒng)研究，形成了全球海陸氣耦合預(yù)報與同化一體化系統(tǒng)，并進行了初步的數(shù)值試驗。結(jié)果顯示，對于20天內(nèi)預(yù)報，相對于使用FNL直接插值作為初值的確定性預(yù)報，使用CESM-DART預(yù)報同化系統(tǒng)的輸出作為初值的集合預(yù)報在北半球5天后的預(yù)報效果較好。開展了現(xiàn)有業(yè)務(wù)模式對持續(xù)性強降水預(yù)報能力的評估；研究了高分辨率區(qū)域模式的持續(xù)性強降水預(yù)報方法與技術(shù)，表明譜逼近方法對降水的量級、落區(qū)以及連續(xù)性都有較好的預(yù)報，2波及其以上波段的逼近效果更好，其中對降水TS評分的提高尤其體現(xiàn)在中雨及其以上量級的預(yù)報。（王東海）

1.5 東亞云水特征及其在參數(shù)化中的應(yīng)用

利用1980—1982年北方5?。ㄐ陆瑑?nèi)蒙古，陜西，寧夏，吉林）外場飛機觀測資料，探討了云中云水含量與云滴濃度的關(guān)系，并將該統(tǒng)計關(guān)系用于云微物理參數(shù)化方案中云滴數(shù)濃度的約束。利用2006—2011年CloudSat衛(wèi)星觀測數(shù)據(jù)統(tǒng)計分析了東亞地區(qū)云垂直結(jié)構(gòu)特征，并基于統(tǒng)計結(jié)果改進了Kessler型云雨自動轉(zhuǎn)換過程參數(shù)化的表達。利用CALIPSO-GOCCP數(shù)據(jù)統(tǒng)計分析了東亞地區(qū)3D云垂直結(jié)構(gòu)特征。（尹金方，王東海）

2 災(zāi)害天氣結(jié)構(gòu)與形成機理

2.1 第3次青藏高原大氣科學(xué)試驗

全面開展了2014年度觀測任務(wù)，進行了加密探空、邊界層和雷達觀測試驗數(shù)據(jù)的質(zhì)量控制。初步完成了雷達徑向風(fēng)和反射率、衛(wèi)星產(chǎn)品、風(fēng)廓線雷達資料、GPS/MET水汽資料的同化。研究了高原地區(qū)不同下墊面地氣能量交換特征、輻射收支和水熱交換變化特征，以及感熱、潛熱通量變化特征。研究了青藏高原地區(qū)云的時空變化特征，完善了混合相態(tài)的云微物理過程，改進了目前雙參數(shù)云物理方案中的氣溶膠活化方案；研究了青藏高原及周邊地區(qū)對流系統(tǒng)的變化特征，對比了青藏高原低渦的東移機制。分析了高原影響下中尺度氣旋在向淮河流域移動過程中引發(fā)暴雨過程的機制；揭示了青藏高原大氣加熱場異常變化對我國旱澇的影響，分析了年際尺度高原異常與我國西南地區(qū)5、6月降水的相關(guān)關(guān)系。（徐祥德）

2.2 青藏高原對梅雨區(qū)水分循環(huán)及降水變異的影響

進行了梅雨系統(tǒng)上游關(guān)鍵區(qū)青藏高原及東緣數(shù)據(jù)再分析與同化試驗研究；開展了青藏高原熱力特征變化及其對季風(fēng)梅雨區(qū)環(huán)流系統(tǒng)影響的診斷分析、青藏高原熱力特征變化對中低緯水汽交換及梅雨區(qū)大氣水分循環(huán)過程的影響研究、青藏高原熱力特征變化對梅雨帶異常及其旱澇災(zāi)害分布影響機理研究，以及青藏高原熱力特征變化對梅雨區(qū)大氣水分循環(huán)及降水異常影響的模擬試驗研究。（徐祥德）

2.3 不同天氣系統(tǒng)特征和變化規(guī)律及其對氣候變化的響應(yīng)

基于重污染天氣（重點霾天氣）時空變化特征，采用歷史相關(guān)各類氣象資料，剖析我國重污染天氣大范圍時空變化及其對氣候變化的年代際響應(yīng)，探討大地形對我國重污染天氣季節(jié)特征及其時空分布變化規(guī)律的影響，歸納出重污染天氣過程預(yù)警業(yè)務(wù)應(yīng)用的天氣背景各類模型。（徐祥德）

2.4 WMO/WWRP RDP“華南季風(fēng)降水試驗”（SCMREX）

2014年4月3—6日，進行了WMO/WWRP RDP“華南季風(fēng)降水試驗”（SCMREX）外場試驗儀器設(shè)備的選址工作。5月1日至6月15日，在業(yè)務(wù)觀測網(wǎng)基礎(chǔ)上開展了加密觀測，暴雨發(fā)生期間對移動觀測設(shè)備進行24 h監(jiān)控。探空加密觀測從2014年5月1日08：00開始，2014年6月15日08：00結(jié)束，華南3省的7個高空觀測站每站每日增加了14：00和02：00的觀測。觀測試驗之后，收集了移動設(shè)備觀測數(shù)據(jù)和華南地區(qū)業(yè)務(wù)數(shù)據(jù)，并進行了質(zhì)量控制，完成了項目網(wǎng)站與數(shù)據(jù)庫建設(shè)與維護，觀測資料已經(jīng)初步整理并在項目網(wǎng)站上進行共享。針對SCMREX 2014和2013年觀測試驗期間的暴雨過程，開展了多尺度機理研究以及資料同化影響、模式物理過程參數(shù)化方案等相關(guān)數(shù)值天氣預(yù)報試驗和研究，取得了初步的成果。2014年2次向WMO匯報SCMREX項目進展，得到肯定。（羅亞麗）

2.5 華南暖區(qū)暴雨發(fā)生發(fā)展機制及關(guān)鍵預(yù)報技術(shù)研究

把具有一定區(qū)域意義的暖區(qū)暴雨的天氣形勢分為鋒面類、暖濕急流北上類和低渦東移動類3種類型。給出3種類型暖區(qū)暴雨的統(tǒng)計特征及其差異?；诰C合分析幾個華南暖區(qū)暴雨個例，給出暖區(qū)對流觸發(fā)與組織過程與冷池傳播、地形等的可能關(guān)系。推導(dǎo)出適合于華南暖區(qū)暴雨的不穩(wěn)定判據(jù)，修正了Richardson數(shù)和Brunt-Vaisala頻率。個例研究表明，修正后的Richardson數(shù)和Brunt-Vaisala頻率表征的不穩(wěn)定區(qū)較之以前的不穩(wěn)定參數(shù)與未來雨區(qū)有較好的對應(yīng)。（姜智娜）

2.6 基于EnKF資料同化方法的華南前汛期暖區(qū)暴雨集合數(shù)值模擬研究

華南前汛期暖區(qū)暴雨的定量降水預(yù)報（QPF）水平很低，應(yīng)用集合卡爾曼濾波（EnKF）資料同化技術(shù)可以改善模式初始條件，從而提高定量降水預(yù)報水平。利用WRF-EnKF系統(tǒng)開展集合預(yù)報的模擬試驗，研究同化地面資料、探空資料和多普勒雷達徑向風(fēng)資料對模式初值和模擬結(jié)果的影響；將集合模擬與實際觀測分析相結(jié)合，研究對流系統(tǒng)的結(jié)構(gòu)和生消演變機制，重點關(guān)注對流觸發(fā)和維持機制、對流系統(tǒng)的組織模態(tài)、熱力和動力特征及其與中尺度環(huán)境大氣的相互作用。個例研究表明，利用WRFEnKF系統(tǒng)同化常規(guī)探空資料，顯著改善了數(shù)值預(yù)報的初始場，減小了各物理量的預(yù)報偏差和預(yù)報均方根誤差，進而提高了暴雨過程的降水落區(qū)和強度的預(yù)報準確率。（寶興華）

2.7 高污染區(qū)大氣冰核活化參數(shù)化方法及對強降水的影響

利用華北（北京及周邊）地區(qū)1960—2013年的外場冰核觀測資料，分析冰核濃度和活化譜特征，結(jié)合當(dāng)前已有的多種冰核活化參數(shù)化方法，提出高濃度冰核背景條件下冰核的活化新方法。將新方法耦合到WRF-SBM分檔模式中，利用改進后的模式，以華北地區(qū)常規(guī)觀測、地基雷達觀測、A-Train系列衛(wèi)星探測、風(fēng)云（FY）衛(wèi)星觀測等資料的實例作為研究對象，進行精細模擬，定量分析強降水過程中不同相態(tài)水物質(zhì)之間相互轉(zhuǎn)換，揭示冰核對強降水粒子群的影響途徑和量級，以便改進數(shù)值模式中冰核活化的參數(shù)化描述方法，提高數(shù)值模式對高污染區(qū)強降水的預(yù)報能力。（尹金方，王東海）

2.8 我國陸面水體對臺風(fēng)殘渦維持及其降水的影響

內(nèi)陸水體與陸面其他種類特征差異顯著，其熱量通量分布不均性更加明顯，導(dǎo)致臺風(fēng)中尺度對流系統(tǒng)活動以及降水強度和落區(qū)差異。富含水汽的臺風(fēng)下墊面（鄱陽湖及其周圍濕地）具有較高的感熱和潛熱通量，可為臺風(fēng)維持提供水汽供應(yīng)，從而也有利于降水。敏感性試驗發(fā)現(xiàn)，陸面水體移除（擴大）時可產(chǎn)生正（負）氣壓擾動，升高（降低）臺風(fēng)海平面氣壓，即陸面水體對陸上臺風(fēng)殘渦維持有積極作用。寬廣水面表層摩擦較小，低層風(fēng)加大，從而改變低層風(fēng)場輻合的強度和位置，影響降水強度及其落區(qū)。水體在夜間作為一個熱源，比陸地土壤釋放更多的表層水熱通量，從而加熱加濕低層大氣，是降水的一個能量源。（李英）

2.9 孟加拉灣熱帶氣旋活動及其對我國天氣的影響

對中國降水與孟加拉灣風(fēng)暴活動的相關(guān)性進行了分析，并對風(fēng)暴活動期間的降水進行EOF分解。發(fā)現(xiàn)二者有較好的相關(guān)性，其通過0.01的相關(guān)顯著性檢驗的高相關(guān)系數(shù)區(qū)位于中國西南地區(qū)、西藏東南部、西北地區(qū)東南部和山西南部，長江下游地區(qū)和臺灣部分地區(qū)也有較小范圍的高相關(guān)系數(shù)區(qū)。降水量多少與風(fēng)暴活動日數(shù)有較好的對應(yīng)。風(fēng)暴活動主要并同時影響中國西南地區(qū)和長江下游地區(qū)降水，且對秋季降水的影響比春季更顯著。（李英）

2.10 西北太平洋高空冷渦對臺風(fēng)路徑突變影響的機理研究

統(tǒng)計分析發(fā)現(xiàn)，當(dāng)臺風(fēng)與冷渦中心距離小于5經(jīng)（緯）距時，其未來12 h移向轉(zhuǎn)角明顯大于氣候平均值，而且臺風(fēng)在冷渦影響下平均移速有所減緩，尤其是移向突變的臺風(fēng)。臺風(fēng)“莫蘭蒂”（2010年）即為在冷渦影響下發(fā)生突然北折現(xiàn)象的典型個例。診斷分析表明，高空冷渦自臺風(fēng)中心東側(cè)向西北方向移動過程中改變了“莫蘭蒂”的高空引導(dǎo)氣流的方向，是其路徑突變的一個重要原因（圖4）。（李英）

2.11 超強臺風(fēng)“丹娜絲”對2013年第23號強臺風(fēng)“菲特”極端降水的作用

利用地面觀測資料、臺風(fēng)定位資料、ECMWF全球再分析資料等，采用熱帶氣旋（TC）降水天氣圖客觀識別法（OSAT）、TC路徑相似面積指數(shù)（TSAI）和氣流軌跡模式HYSPLIT等方法，從2013年第23號強臺風(fēng)“菲特”在我國東南沿海引發(fā)臺風(fēng)暴雨的極端性分析及其成因診斷入手，揭示了雙臺風(fēng)作用對極端暴雨的增強作用。結(jié)果表明：首先，強臺風(fēng)“菲特”給浙江帶來了1958年以來單站日降水排名第2的極端降水，余姚和奉化日降水量均為395.6 mm；“菲特”降水過程有2個明顯的強降水階段；其次，秋季強臺風(fēng)“菲特”登陸后之所以出現(xiàn)如此強度且持續(xù)的臺風(fēng)暴雨，與超強臺風(fēng)“丹娜絲”的存在密不可分。在強降水第1階段，雙臺風(fēng)作用增強了降水的極端性，臺風(fēng)“丹娜絲”向降水區(qū)域輸送了約79%的水汽，對杭州灣南側(cè)的強降水過程有重要貢獻；在臺風(fēng)“菲特”強降水第2階段，“菲特”的環(huán)流已經(jīng)基本消散，超強臺風(fēng)“丹娜絲”與冷空氣的共同作用主導(dǎo)了這一階段強降水的發(fā)生。（任福民）

2.12 孟加拉灣和阿拉伯海熱帶氣旋活動雙峰型差異及可能成因

針對北印度洋熱帶氣旋（TC）研究中存在的TC資料對比不足和TC活動雙峰型特征的區(qū)域性差異分析不足的現(xiàn)狀，采用聯(lián)合臺風(fēng)警報中心（JTWC）TC資料和印度氣象局（IMD）TC資料開展了針對性的研究。結(jié)果如下：IMD資料的時段（1990—2012年）較短且資料記錄時刻規(guī)律性差；而JTWC資料自1977年突變之后時段仍明顯長于IMD資料且資料記錄時刻穩(wěn)定，故采用1977—2012年JTWC資料進行TC氣候特征分析。1977—2012年，孟加拉灣TC頻數(shù)呈下降趨勢，而阿拉伯海TC頻數(shù)呈顯著增多趨勢；二者多年平均TC頻數(shù)分別為3.6個和1.5個；兩海區(qū)TC頻數(shù)的季節(jié)變化都表現(xiàn)為雙峰型，但在雙峰型的峰值時間、強度以及雙峰的強弱配置上存在較大差異。研究表明，緯向風(fēng)垂直切變和相對渦度的季節(jié)變化可能分別是影響孟加拉灣和阿拉伯海TC活動雙峰型的關(guān)鍵因子；就整個北印度洋而言，南亞夏季風(fēng)開始前和結(jié)束后，風(fēng)垂直切變維持在10 m/s及以下、正的相對渦度、較高的海表溫度、較大的相對濕度都是TC生成的有利條件。（任福民）

2.13 熱帶氣旋初始結(jié)構(gòu)對快速加強速率的影響

利用多層嵌套、可壓縮、非靜力熱帶氣旋數(shù)值模式研究了不同的渦旋初始結(jié)構(gòu)對熱帶氣旋的快速加強過程的影響，渦旋的初始結(jié)構(gòu)主要包括通過設(shè)置不同大風(fēng)半徑來描述的渦旋的大小以及用不同初始最大風(fēng)速徑向衰減曲率來表示的渦旋的不同的眼墻寬度。試驗結(jié)果表明，當(dāng)初始渦旋切向風(fēng)自最大風(fēng)半徑沿徑向迅速衰減，同時向臺風(fēng)中心平緩衰減時，熱帶氣旋快速加強明顯。反之，當(dāng)初始渦旋切向風(fēng)自最大風(fēng)半徑沿徑向衰減緩慢時，同時向臺風(fēng)中心衰減迅速時，熱帶氣旋快速加強受到抑制。另外，初始渦旋尺度的敏感性試驗表明，初始渦旋尺度大不利于熱帶氣旋快速加強，而小的初始渦旋有利于熱帶氣旋的快速加強。（徐晶）

2.14 海南島海陸風(fēng)演變特征及其引發(fā)的中尺度對流天氣預(yù)報技術(shù)研究

統(tǒng)計分析了2013年海南島海陸風(fēng)演變規(guī)律的年變化、月變化和日變化特征及其與溫度場和降水場的關(guān)系。分析顯示海南島各個月份的海陸風(fēng)特征明顯，海風(fēng)一般發(fā)生在上午11：00至晚上20：00之間，11：00附近和20：00附近為海風(fēng)與陸風(fēng)的轉(zhuǎn)換階段，20：00以后至次日11：00前為陸風(fēng)明顯的階段。海陸風(fēng)演變造成的輻散關(guān)系與降水分布關(guān)系密切，海陸溫差分布特征是造成海陸風(fēng)演變的主要原因。海陸風(fēng)的輻合為降水提供了很好的抬升機制，但需要水汽配合方能發(fā)生明顯的降水過程，地面相對濕度很好地反映了水汽條件的狀況。（梁釗明，王東海）

2.15 我國東部小時降水的特征分析

利用中國區(qū)域1951—2013年6月1日至8月31日2420個站點逐小時降水資料，經(jīng)過質(zhì)量控制、無資料剔除等處理，建立了我國105°E以東區(qū)域內(nèi)1980—2012年6—8月無缺測記錄的1489個站點的逐小時降水資料序列。分析了夏季年平均小時降水頻次、雨強和小時極端強降水頻次、雨強的分布特征；夏季降水頻次的變化趨勢；夏季和夏季分月雨強的趨勢變化；夏季和各月極端強降水頻次的趨勢變化；夏季和各月極端強降水雨強的趨勢變化。結(jié)果表明，我國東部夏季小時降水頻次整體以減少趨勢為主，小時降水平均雨強以增加趨勢為主，小時極端強降水頻次整體呈減少趨勢，極端強降水雨強整體呈增加趨勢（圖5）。（趙琳娜）

3 數(shù)值天氣預(yù)報和模式關(guān)鍵技術(shù)

3.1 高分辨模式物理過程研發(fā)

分析檢驗了CAMS云微物理方案在青藏高原地區(qū)雨滴譜截距偏小導(dǎo)致雨滴偏大和雷達反射率偏大的問題；利用飛機觀測資料總結(jié)了云水物質(zhì)含量與云滴濃度的關(guān)系，并采用衛(wèi)星遙感資料分析了東亞地區(qū)云垂直結(jié)構(gòu)，改進了云雨自動轉(zhuǎn)化參數(shù)化過程，從而有效改進了CAMS云微物理方案對我國高原和華南地區(qū)降水的模擬效果。利用觀測資料，對半干旱區(qū)地表交換系數(shù)檢驗修正，改善了交換系數(shù)和地表冠層阻尼參數(shù)化，改善了地表熱通量計算（圖6）。（高文華，尹金方，張果）

3.2 GRAPES模式準均勻網(wǎng)格技術(shù)研究

采用Schwarz方法在陰陽網(wǎng)格第1類邊界條件強迫條件下首次成功實施了對陰陽網(wǎng)格非靜力大氣動力模式的半隱式半拉格朗日求解，實現(xiàn)了GRAPES陰陽網(wǎng)格模式動力框架的穩(wěn)定積分；采用ILU預(yù)條件處理提高了陰陽網(wǎng)格GCR法求解Helmholtz方程的效率，加速了數(shù)值解的收斂速度。成功確認了準均勻網(wǎng)格GRAPES模式的二階精度算法改進和長期積分試驗，3D動力框架在2個月時間積分中保持很好的穩(wěn)定性和計算精度，為下一代高分辨率GRAPES模式發(fā)展提供了一個解決方案（圖7）。（彭新東）

3.3 降水短期預(yù)報的客觀訂正

圖1 2013年8月24日安徽蚌埠SA雷達和定遠C-FMCW雷達探測產(chǎn)品(a：SA雷達回波強度；b：C-FMCW雷達譜參數(shù)時序圖；c：C-FMCW回波強度譜密度分布)Fig. 1 Images of SA radar in Bengbu and C-FMCW radar in Dingyuan on August 24, 2013 (a: ref ectivity of SA Radar; b: timeheight section of C-FMCW radar; c: spectral density of ref ectivity of C-FMCW radar)

利用高分辨率降水分析資料和距平積分數(shù)值訂正（ANO）方法，對2013年7月四川暴雨中尺度模式環(huán)流預(yù)報場和高分辨降水模擬進行了訂正試驗。結(jié)果表明，訂正對高分辨大氣環(huán)流場有明顯的改進，明顯改善了近地層大氣的日周期環(huán)流特征預(yù)報，位勢高度、溫度和比濕分別在對流層中層550 hPa和低層750 hPa改進尤為顯著，同時確認了高分辨WRF中尺度模式的短期降水預(yù)報的改善（圖8）。（彭新東）

圖2 廣東陽江C-FMCW雷達反演(120 m)雨滴譜與地面雨滴譜分布比對(左圖：1 min平均；右圖：10 min平均)Fig. 2 Raindrop size distributions at 120 m retrieved from C-FMCW radar in comparison with Parsivel disdrometer on surface (Yangjiang, Guangdong Province, May 8, 2014. left: average_ 1 min; right: average_10 min )

圖3 青藏高原云降水外場試驗觀測主要設(shè)備Fig. 3 The main equipment used in the experiment in the Tibetan Plateau

圖4 臺風(fēng)移向12 h轉(zhuǎn)折角度(曲線)及臺風(fēng)頻數(shù)(柱狀)隨臺風(fēng)與冷渦中心相對距離的變化(a)、臺風(fēng)“莫蘭蒂”地面中心(空心圓)和高空冷渦(實心圓)的路徑(b)Fig. 4 (a) Variation of average 12 h directional change of TC movement (red solid line) and accumulative frequency (blue bar) with the relative distance between TC and UTCL (The red dash line indicates the western North Pacif c climatology). (b) The tracks of typhoon Meranti (empty circle) and UTCL (dot)

圖5 我國東部夏季及夏季各月極端強降水雨強的變化趨勢空間分布(單位：%/10a):(a)6月；(b)7月；(c)8月Fig. 5 The spatial distribution features of the extreme precipitation intensity in summer over the east of China (Unit: %/10a): (a) June; (b) July; (c) August

圖6 2013年5月8日TRMM/TMI觀測降水(中)和CAMS云微物理方案改進前(左)后(右)模擬降水Fig. 6 The observed (middle) and WRF-CAMS microphysics simulated (left, original; right, improved) 24 h accumulated precipitation during 00:00 to 24:00 (UTC) on 8 May 2013

圖7 Haurwitz-Rossby波傳播第14天位勢高度(a)、地面氣壓(b)、u風(fēng)分量(c)和v風(fēng)分量(d)Fig. 7 The Haurwitz-Rossby wave propagation on day 14: (a) geopotential height; (b) surface pressure; (c) u component; (d) v component

圖8 WRF模式預(yù)報(ORI)和ANO訂正后的暴雨(a)和大雨(b)預(yù)報的ETS評分Fig. 8 Torrential (a) and heavy (b) rainfall forecasting of the original WRF model prediction (ORI) and ANO correction

Advances in Research on Severe Weather

1 Severe weather monitoring technology and data application

1.1 Application of rain drop size distribution (DSD) data to DSD retrieval and precipitation estimation with a dual polarization radar

Heavy rain data were observed with the dual linear polarization radar and disdrometer from May 1 to June 15, 2014 in Heshan, Guangdong Province during pre-rainy season in South China. The dual polarization radar data were controlled in quality before usage. By using the data observed with the disdrometers, the drop size distribution (DSD) of the pre-rainy season in South China was analyzed, and the algorithm of radar quantitative precipitation estimation (QPE) by polarimetric parameters was ref tted to improve the accuracy of QPE. The DSD was also retrieved by a dual linear polarization radar in Naqu Tibet during the third Tibetan Plateau Atmospheric Science Experiment (from July 1 to August 31, 2014), which was compared with distrometers. (Hu Zhiqun)

1.2 Micro-physics parameters retrieving vertical structure in the precipitation cloud using a C-FMCW radar

The C-FMCW radar data were used in such experiments as the Meiyu seasonal precipitation in Changjiang-Huaihe River valley, the South China sea monsoon onset and the precipitation cloud structure at the main region of Tibetan Plateau. Data from other active and passive remote sensing systems were used to research the microphysical parameters. The rain parameters were used to retrieve detailed vertical structures and raindrop size distributions in precipitation cloud (Fig.1–2). (Ruan Zheng)

1.3 Various kinds of equipment were employed in f eld observation experiments for many scientif c projects

The Third Tibetan Plateau Atmospheric Science Experiment, heavy rainfall experiment in Huanan for RDP project and precipitation system observation from Tibetan Plateau in 973 Project were carried out and comprehensive measurements of water vapor, clouds, and precipitation were conducted. The most advanced radars in China, such as Ka-Band millimeter-wave cloud, Ku-Band micro-rain, C-Band continuous-wave and lidar, and microwave radiometer and disdrometer were deployed to observe high spatial-temporal resolution vertical structures of clouds and precipitation. Based on the radar measurements in this experiment, the air vertical draft and content prof les for water cloud, ice cloud, rain and snow were retrieved. The observation capabilities of equipment made in China were verif ed. The above measurements and preliminary analyses provide a basis for further in-depth study of cloud physics and precipitation processes in the Tibetan Plateau (Fig.3). (Liu Liping)

1.4 Forecasting theory and method and predictability of persistent extreme precipitation events in China

A dynamic prototype forecast system for persistent extreme precipitation is constructed based on the ensemble forecast technique, globally coupled oceanic-land-atmospheric model and nested high-resolution regional model. An integrated system composed of globally coupled forecast and global assimilation is developed and used to perform preliminary numerical experiments. The results show that for 20-day forecast, compared with deterministic forecasts, which use the interpolated FNL analysis as initial conditions, the ensemble forecasts, which use the output of the CESM-DART forecast-assimilation system as initial conditions, exhibit better forcast skills after 5 days for Northern Hemisphere. The prediction ability of the operational model for persistent extreme precipitation is verified. The forecasting theory and method of persistent extreme precipitation events by using the high-resolution regional model are studied. The results show that the numerical simulations by using the spectral nudging and filtering methods have improved obviously precipitation forecasting for magnitude, rain band and continuity, the better nudging effect ref ects above 2-wave bands, and, the TS scores also display an improvement in the precipitation rate categories above light rain. (Wang Donghai)

1.5 The cloud-precipitation characteristics and their application in cloud microphysical parameterization

A statistical analysis of cloud microphysical properties was performed based on the in-situ observations from the North China Cloud Physics Detection Project (NCCPDP) during the period from 1980 to 1982. From the statistical results, the relationship between liquid water content (LWC) and cloud number concentration (NC) was investigated. The vertical distributions of LWC in precipitating and non-precipitating clouds were analyzed based on a large number of CloudSat observations over Asian land areas between June 2006 and April 2011. The results of this analysis were used to propose a new def nition of the threshold value for Kesslertype parameterization of warm cloud autoconversion. The spatial distribution of clouds and their seasonal variations, and the three-dimensional (3D) cloud structures over East Asia were analyzed with the CALIPSOGOCCP data during the period from 2007 to 2012. (Yin Jinfang, Wang Donghai)

2 Structures and mechanisms of severe weather

2.1 The 3rd Tibetan Plateau Atmospheric Science Experiment (TIPEX III)

During the period of TIPEX III in 2014, all the following actions were conducted: (1) the observation was executed comprehensively, in which the quality control for intensive sounding, boundary layer and radar observation data was carried out, and the assimilation of observations from radar radial velocity and ref ectivity, satellite products, wind prof ler radar data, GPS/MET water vapor was completed initially; (2) the exchange characteristics between the ground and the atmosphere, the change in radiation budget and waterheat exchange, and f ux change in sensible and latent heats underlying surface on the plateau were researched; (3) the spatial and temporal variation of the cloud in the Tibetan Plateau was investigated, in which the cloud’s microphysical processes in mixed phases were refined, and the aerosol activation scheme in existing dualparameter cloud’s physical processes was improved; (4) the change characteristics of a convective system over the Tibetan Plateau and its neighboring areas were studied, in which the mechanism of eastward movement of low vortex in Tibetan Plateau was detected, and the mechanism of storms triggered by the mesoscale cyclones when moving eastward to Huaihe River Basin was analyzed; (5) the inf uence of abnormal atmospheric heating f eld in Tibetan Plateau on f ood and drought in China was revealed, in which the relationship between the interannual-scale anomalies in plateau and precipitation in May and June in Southwest China was analyzed. (Xu Xiangde)

2.2 The effect of Qinghai-Xizang Plateau on water cycle and precipitation variation in Plum Rain region

We have made a reanalysis and assimilation experiment for the data of the Qinghai-Xizang Plateau and its eastern margin, the key upstream areas for the Plum Rain system, a diagnostic analysis of the thermodynamic variation characteristics in the Qinghai-Xizang Plateau region and a study of its impact on the circulation system in the monsoon and Plum Rain region, a study of the influence of the thermodynamic variation in the Qinghai-Xizang Plateau on the water vapor exchange between low and middle latitude areas, as well as atmospheric water circulation processes in the Plum Rain area, a study of the mechanism on the influence of the thermodynamic variation in the Qinghai-Xizang Plateau on the anomalies of the Plum Rain zone and the distribution of flood and drought disasters, and a simulated experimental study of the influence of the thermodynamic variation in the Qinghai-Xizang Plateau on the anomalies of atmospheric water cycle and precipitation in the Plum Rain area. (Xu Xiangde)

2.3 Characteristics and evolution of different weather systems and their response to climate change

Building on the spatial and temporal characteristics of the seriously-polluted weather (particularly the haze) derived from all kinds of historical meteorological data associated, we described the large-scale temporal and spatial variation of seriously-polluted weather and its decadal response to the climate change in China, and explored the effects of large scale topography on the seasonal evolution of seriously-polluted weather and its spatial and temporal distribution. At last, we established diverse synoptic background models for warning application during the formation of seriously-polluted events. (Xu Xiangde)

2.4 WMO/WWRP RDP South China Monsoon Rainfall Experiment (SCMREX)

During 3–6 April 2014, the site selection of the field experiment instruments and equipment was completed. Based on the conventional observation network, intensive observations were made during May 1–June 15. The mobile observation equipment was under the 24-hour monitoring during periods of heavy rainfall. Intensive sounding observations started at 8 BST on May 1, 2014 and ended at 8 BST on June 15, 2014. 7 upper-air stations in the three South China provinces made additional observations at 14 BST and 02 BST per day. After the observation experiment, not only the conventional observation data but also the mobile equipment observation data were collected and controlled in quality. Also, the development and maintenance of the project website and database were achieved. After being primarily processed, the observation data were shared on the project website. Focusing on these heavy rainfall cases during 2013–2014 SCMREX experiment, we studied the multiple scales mechanism, the impact of data assimilation, and the difference of various model physics Parameterization Schemes, with initial results achieved. We reported SCMREX progress twice in 2014, which was recognized by WMO. (Luo Yali)

2.5 Mechanism and forecast skill of warm sector heavy rainfall in South China

According to weather regimes, warm sector rainfall is divided into three types: (1) Frontal rainfall, (2) Northward motion of warm and moisture jet, (3) Eastward motion of low vortex. The above three types of warm-sector rainfall are analyzed and compared. A case study pointed out that the triggered convection in a warm sector may be closely related to its organization process, the cold cell spreading and the terrain. Besides, the instability criterion f t for the warm-sector rainfall is derived, e.g. the modif ed Richardson number and Brunt-Vaisala frequency. The study shows that the instable region revealed by the modif ed Richardson number and Brunt-Vaisala frequency can well represent the future rainfall region. (Jiang Zhina)

2.6 On the warm-sector heavy rainfall during the early summer rainy season over South China: An EnKF data assimilation based simulation study

The Quantitative precipitation forecast (QPF) skill for the warm-sector heavy rainfall over South China during the early summer rainy season is very low. The application of the Ensemble Kalman Filter (EnKF) data assimilation technique can potentially improve the initial conditions of simulation and thus improve the QPF skill. On the one hand, ensemble simulation experiments will be conducted using the WRF-EnKF system. Impacts of a variety of observational data, including not only the surface and sounding observations but also the Doppler radar velocity, on the initial conditions and the simulation results will be investigated. On the other hand, combining the ensemble simulation experiments with the observational analysis, we will study internal structures and organizational modes of the rainy storm, and inf uencing factors for the convective interactions between the rainy storm and its mesoscale environments. One case study results show that, compared to no data assimilation experiment (NODA), not only the initial conditions of EnKF data assimilation experiment (DA) are much closer to the observed f elds, but also the DA predicted physical parameters are improved in terms of both biases and root-mean-square errors, which leads to a more accurate prediction of the location and magnitude of precipitation from DA. (Bao Xinghua)

2.7 Study of the ice nuclei activation parameterization and its influence on severe precipitation under the conditions of high pollution

An attempt was made to delineate the characteristics of ice nuclei (IN) over the eastern central China using the ground-based measurement data over 1960–2013. Based on the statistical results, a new parameterization was proposed for ice nuclei activation within high ice nuclei conditions. Based on the ice nuclei field observational data over the last five decades and the widely used ice nuclei activation parameterizations in numerical models, the new scheme will be coupled into the WRF model with Spectral Bin Microphysics (WRF-SBM). Based on the improved model, we will focus on the conversion among the hydrometeors (vapor, cloud water, rain water, cloud ice, snow, graupel, and hail) in a severe precipitation event which has been captured by ground-based radars, and satellites of A-train (mainly including CloudSat and CALIPSO) and Fengyun (FY). The results will be used to identify the effects of high ice nuclei concentration on the development and formation of a severe precipitation. Based on the results, the parameterization for ice nuclei activation will be improved to improve severe precipitation forecasting within polluted conditions by a numerical model. (Yin Jinfang, Wang Donghai)

2.8 The impact of land surface water on the inland behavior of landfalling typhoon

Inland water surface has remarkable differences in heat property and roughness from other land surface covers. It could lead to the uneven distribution of surface f ux, which inf uences the mesoscale systems and rainfall of landfalling typhoon significantly. That is, inland water surface (such as Poyang Lake and wet land around it) could release heat f uxes to the boundary layer of typhoon, providing favorable condition for typhoon maintenance and rainfall. Sensitivity experiments on Poyang Lake demonstrate that a mesoscale vortex would be weakened in the absence of the lake to lead to the increase of sea level pressure in typhoon center. In addition, broader water bodies have less friction, which increases wind speed near the underground to enhance convergence over heavy rainfall area on the one hand. On the other hand, water bodies may release more surface heat f uxes to make air warmer and wetter in lower atmosphere, which is benef cial to typhoon heavy rainfall. (Li Ying)

2.9 The impact of cyclonic storms over the Bay of Bengal on the weather of China

A correlation analysis is used to investigate the relationship between rainfall of China and activities of cyclonic storms over the Bay of Bengal. Results show that the high correlation coeff cient areas are mainly found in the Southwest China, southeast of Tibet plateau, southeast of Northwest China, the lower reaches of Yangtze River and Taiwan Island. Storm activities can inf uence rainfall of the southwest area and the lower Yangtze region concurrently，and the impact is more signif cant in autumn than in summer. (Li Ying)

2.10 The impact of upper tropospheric cold low on abrupt turning of tropical cyclone movement

Statistical study indicates that when the relative distance between a tropical cyclone (TC) and an upper tropospheric cold low (UTCL) is less than 5 latitudes/longitudes, the average 12 h directional change of TC movement is obviously larger than the average western North Pacif c climatology. In addition, the TC average moving speed slows down under the impact of UTCL, especially that of the TCs with abrupt turning. Meranti (2010) is a typical typhoon which turned abruptly under the inf uence of an UTCL. A diagnostic study indicates that the UTCL changes the steering f ow when it is moving from the east of the central TC to the northwest, which is an important reason for abrupt turning of Meranti (Fig. 4). (Li Ying)

2.11 The role of super typhoon Danas in extreme precipitation associated with severe typhoon Fitow

Based on surface observational data, typhoon track data and ECMWF global reanalysis data, using the objective synoptic analysis technique (OSAT), tropical cyclone (TC) track similarity area index (TSAI), and the airf ow trajectory model (HYSPLIT4.9) and analyzing the characteristics and causes of the extreme precipitation over coastal Southeast China associated with the sever typhoon Fitow, this study reveals the intensification by a binary typhoon of an extreme precipitation. First, Fitow causes the maximum daily precipitation of 395.6 mm at both Yuyao and Fenghua, which rank the second most extreme daily TC precipitation in Zhejiang Province in record. The precipitation process has two distinct intense precipitation stages. Secondly, such a heavy and continuous rainfall during and after Fitow’s landfall is mainly due to the existence of super typhoon Danas. In the f rst stage, because of the binary tropical cyclone interactions, Fitow moves much faster than before. Moreover, Danas transports about 79% moisture to the raining region, which is an important contribution to the extreme precipitation over the southern coast of Hangzhou Bay. In the second stage, as the circulation of typhoon Fitow almost dissipates, the combined interaction of super typhoon Danas and cold air mainly causes the extreme precipitation. (Ren Fumin)

2.12 Differences of bimode patterns in TC activity and their possible causes in the Bay of Bengal and the Arabian Sea

To address the inadequate tropical cyclone datasets for comparison research purpose and to analyze the regional differences in TC bimodal patterns in the North Indian Ocean, a targeted study on these issues has been carried out using the Joint Typhoon Warning Center (JTWC) TC dataset and the India Meteorological Department (IMD) TC dataset. Results are as follows: time period (1990–2012) of IMD dataset is much shorter and data recording time is irregular, while time period (1977–2012) of JTWC dataset after the abrupt change in 1977 is much longer and data recording time is regular. Thus, JTWC dataset of 1977–2012 is adopted in TC climatic characteristics analysis. During 1977–2012, the Bay of Bengal (BoB) TC frequency decreases, while the Arabian Sea (AS) TC frequency increases signif cantly. Average TC frequencies are 3.6 and 1.5 in BoB and AS, respectively. Meanwhile, seasonal variations in TC frequency show a bimodal pattern with two peaks in both BoB and AS but with obvious differences in bimodal peak time, intensity and strength. It is revealed that vertical zonal wind shear and seasonal changes in relative vorticity might be the key factors affecting the bimodal patterns of TC activity in BoB and AS, respectively. Meanwhile, for the whole North Indian Ocean, before the onset and after the f nish of South Asian Summer Monsoon, below 10 m/s vertical zonal wind shear, positive relative vorticity, high sea surface temperature and high humidity are all favorable conditions for TC genesis. (Ren Fumin)

2.13 Sensitivity of tropical cyclone rapid intensif cation to the initial vortex

The multiply nested, fully compressible, non-hydrostatic tropical cyclone model is used to examine and understand the sensitivity of the simulated tropical cyclone (TC) rapid intensif cation (RI) to its initial vortex structure, including the radial prof le of tangential wind and the size of the vortex. The results show that when the initial vortex is with a broader prof le outside but a narrower prof le inside the eyewall, the slower (faster) RI is in the simulated storms. The results also show that the larger and broader (smaller and narrower) the initial vortex is, the slower (faster) the RI is but the larger (smaller) inner-core size is in the simulated storms. (Xu Jing)

2.14 Technical study of how to forecast a land-sea-breeze and associated mesoscale convective weather in Hainan island

The annual, monthly and daily changes of land-sea-breezes in Hainan Island and their relations with the temperature and rainfall fields are investigated by using the observational data of year 2013. Results show that a land-sea-breeze obviously happens throughout the year with a sea breeze occurring between 11:00 and 20:00 LST (local standard time) and a land breeze occurring between 20:00 and 11:00 (the next day) LST. A close relation is shown between the rainfall and the convergence caused by the land-sea-breeze, in which the thermal heating difference determines the evolution of the land-sea-breeze. The convergence caused by the land-sea-breeze provides a good condition for the lifting of air, which can lead to significant rainfall when accompanied with suff cient water vapor. The relative humidity near the surface is a good indicator of water vapor conditions. (Liang Zhaoming，Wang Donghai)

2.15 The characteristic analysis of hourly precipitation over eastern China

Based on the hourly rain gauge data of 2420 stations across China from June 1st to August 31st during 1951 to 2013, the hourly precipitation sequence of 1489 stations for areas in China to the east of 105°E from June 1st to August 31st during 1980 to 2012 is established with the quality controlled and no-data records rejected. The annual average precipitation frequency, rainfall intensity, hourly extreme precipitation frequency, including the distribution of the summer rainfall intensity, are analyzed. The trend of summer precipitation frequency, that of the monthly summer rainfall intensity change, and the frequency of the extreme strong precipitation events is also investigated. The results indicate that the frequency of hourly precipitation in summer mainly declines while its intensity increases on the whole over east China. The frequency of hourly extreme precipitation decreases while its intensity increases as a whole (Fig. 5). (Zhao Linna)

3 Numerical weather prediction and key techniques in numerical modeling

3.1 Study of the high-resolution physical processes

The reasons of large raindrop and high radar ref ectivity simulated by CAMS cloud microphysics over the Tibetan Plateau are investigated at 1 km horizontal resolution. The relationship between cloud water content and cloud droplet concentration is analyzed using aircraft observations, and the cloud vertical structure over East Asia is explored with multi-satellite data. As a result, the performances of CAMS cloud microphysics are considerably improved over the plateau and South China. In addition, the surface exchange coeff cient in a semi-arid region is assessed and modif ed using the observations, while the calculations about surface exchange coeff cient, canopy damping parameter and surface heat f ux are also improved (Fig. 6). (Gao Wenhua, Yin Jinfang, Zhang Guo)

3.2 Quasi-uniform grid GRAPES model development

Using Schwarz method, the non-hydrostatic GRAPES model is successfully established on the Yin-Yang quasi-uniform grid with a first-type boundary condition and semi-implicit semi-Lagrangian solver. A longterm stable integration of the model dynamic core is conf rmed. The application of the ILU pre-conditioner accelerates the GCR solver for Helmholtz equations, and consequently the convergence rate is speeded up signif cantly in the temporal integration of the model on Yin-Yang grids. An overall second-order accuracy and excellent stability of the model frame are verif ed in the three-dimensional idealized test cases. The frame provides a possible solution for the next-generation high-resolution GRAPES model development (Fig. 7). (Peng Xindong)

3.3 Objective correction of short-term rainfall prediction

The Anomaly Numerical-correction with Observations (ANO) method and a high-resolution precipitation analysis data are used to test the model results of correction in a Sichuan rainstorm case in July 2013, which shows the amelioration of meso-scale circulation and high-resolution rainfall forecasting. Great improvement to the high-resolution circulation, especially near surface diurnal variations, is displayed. The geopotential height, temperature and relative humidity are prominently corrected at 550 hPa and 750 hPa. Notable improvement to the short-term rainfall forecasting with the WRF mesoscale model is demonstrated (Fig. 8). (Peng Xindong)