災(zāi)害性天氣

災(zāi)害性天氣研究進(jìn)展

1. 災(zāi)害天氣國家重點(diǎn)實(shí)驗(yàn)室通過科技部組織的評(píng)估

2010年4月受科技部委托，國家自然科學(xué)基金委員會(huì)組織專家對(duì)災(zāi)害天氣國家重點(diǎn)實(shí)驗(yàn)室進(jìn)行了評(píng)估。災(zāi)害天氣國家重點(diǎn)實(shí)驗(yàn)室順利通過科技部評(píng)估，并獲得好評(píng)。評(píng)估專家對(duì)實(shí)驗(yàn)室的評(píng)估意見如下：災(zāi)害天氣國家重點(diǎn)實(shí)驗(yàn)室緊緊圍繞國家需求和學(xué)科前沿開展應(yīng)用基礎(chǔ)研究，抓住災(zāi)害天氣監(jiān)測(cè)與預(yù)測(cè)科學(xué)的前沿問題，開展災(zāi)害天氣動(dòng)力學(xué)理論的研究，災(zāi)害天氣監(jiān)測(cè)、預(yù)測(cè)新理論與新技術(shù)的研究，并致力于研究成果的業(yè)務(wù)應(yīng)用，研究方向和科學(xué)目標(biāo)定位明確。在本評(píng)估期內(nèi)，在災(zāi)害天氣中尺度結(jié)構(gòu)與機(jī)理研究，災(zāi)害天氣遙感監(jiān)測(cè)新理論與新技術(shù)研究，災(zāi)害天氣預(yù)測(cè)理論和方法的研究等方面取得了具有國際影響的研究成果，為我國災(zāi)害天氣科學(xué)、氣象部門業(yè)務(wù)建設(shè)和社會(huì)經(jīng)濟(jì)發(fā)展做出了重大貢獻(xiàn) 。

2. 主要成果及其業(yè)務(wù)應(yīng)用

（1）用CloudSat資料對(duì)比分析青藏高原-亞洲季風(fēng)區(qū)和北美副熱帶地區(qū)夏季深對(duì)流

利用2006—2009年6—8月CloudSat衛(wèi)星資料，對(duì)比分析了青藏高原、高原南坡、南亞季風(fēng)區(qū)的深對(duì)流，進(jìn)一步引入東亞、熱帶西北太平洋、北美西部和北美東部地區(qū)。研究發(fā)現(xiàn)，與發(fā)生在高原南坡和南亞季風(fēng)區(qū)的深對(duì)流相比，青藏高原上深對(duì)流發(fā)生更加不頻繁、深對(duì)流云頂和強(qiáng)回波頂更低，深對(duì)流系統(tǒng)的水平尺度也更小，這些說明高原上深對(duì)流活動(dòng)相對(duì)更弱，這與其環(huán)境大氣的對(duì)流零浮力層較低、水汽較少密切相關(guān)；7個(gè)地區(qū)相比，其中2個(gè)熱帶地區(qū)和4個(gè)副熱帶地區(qū)分別具有相似的深對(duì)流特征，但是熱帶和副熱帶相比有著顯著差別；高原南坡的深對(duì)流表現(xiàn)出一定的獨(dú)特性，這主要?dú)w因于其特殊的地形（陡坡）和低層潮濕的季風(fēng)氣流。

青藏高原（TP）、高原南坡（PSS）、南亞季風(fēng)區(qū)（SAMR）深對(duì)流內(nèi)部垂直結(jié)構(gòu)示意Schematics of deep convection over the TP, PSS, and in SAMR

（2）星載毫米波雷達(dá)探測(cè)能力分析和毫米波雷達(dá)反演云參數(shù)方法研究

2010年，中國氣象科學(xué)研究院災(zāi)害天氣國家重點(diǎn)實(shí)驗(yàn)室的毫米波雷達(dá)在天津用于檢驗(yàn)我國發(fā)展的星載毫米波雷達(dá)原理樣機(jī)，并在吉林省與云參數(shù)探測(cè)飛機(jī)進(jìn)行了聯(lián)合觀測(cè)。開展了地基雷達(dá)和機(jī)載雷達(dá)對(duì)比分析方法研究，發(fā)展了綜合利用毫米波雷達(dá)回波強(qiáng)度、徑向速度和速度譜寬反演層狀云降水參數(shù)的方法。

2010年9月17日14∶26 毫米波雷達(dá)觀測(cè)結(jié)果：（a）回波強(qiáng)度Z（dBZ）、垂直速度Vr（m/s）和速度譜寬Sw（m/s）;（b）反演的云參數(shù)：滴譜數(shù)密度N0（個(gè)/m3），液態(tài)水含量M（g/ m3）;（c）粒子中值半徑R0（μm）和用對(duì)數(shù)表示的譜寬σXObserved (a) reflectivity Z（dBZ）, velocity Vr（m/s）and spectrum Sw（m/s）width by cloud radar, (b) retrieved cloud drop concentration N0（個(gè)/m3），liguid water content M （g/ m3） and (c) median radius R0（μm）and logarithmic spread of the distribution σX at 14∶26, September 17, 2009

（3）C波段偏振雷達(dá)質(zhì)量控制技術(shù)及其在降水估測(cè)中的應(yīng)用

利用外場(chǎng)試驗(yàn)觀測(cè)到的數(shù)據(jù)，對(duì)實(shí)驗(yàn)室購置的車載雙偏振天氣雷達(dá)（PCDJ）的系統(tǒng)誤差及誤差來源進(jìn)行了深入分析。發(fā)展了一套差傳播相移(ΦDP)的質(zhì)量控制算法，能夠從中計(jì)算得到高分辨率的差傳播相移率(KDP)數(shù)據(jù)。利用KDP對(duì)反射率因子及差分反射率因子進(jìn)行衰減訂正后，雷達(dá)數(shù)據(jù)質(zhì)量有了明顯的改進(jìn)。根據(jù)質(zhì)量控制后的偏振雷達(dá)數(shù)據(jù)，綜合ZH 與KDP估測(cè)降水強(qiáng)度R(ZH,KDP)，并與地面雨量計(jì)實(shí)測(cè)降水強(qiáng)度R（gauge）進(jìn)行比較分析表明，與傳統(tǒng)的Z–R關(guān)系法估測(cè)的降水強(qiáng)度R(ZH )相比，當(dāng)降水強(qiáng)度大于5 mm/h時(shí)，偏振雷達(dá)的降水估測(cè)精度有明顯提高。

2008年8月22日14∶00至23日18∶00，珠海上川島站（區(qū)站號(hào)：59673）實(shí)際觀測(cè)降水量與ZH /KDP - R綜合法、Z–R關(guān)系法估測(cè)降水量對(duì)比曲線The rainfall circles of R(gauge), R(ZH) and R(ZH,KDP) in observatory (station code∶ 59673) from 14∶00 BST 22 to 18∶00 BST 23 Aug 2008

（4）自動(dòng)調(diào)整Z-R關(guān)系和反距離加權(quán)插值法改進(jìn)雷達(dá)估測(cè)降水的方法研究

雷達(dá)估測(cè)降水的誤差不僅是由于各種隨機(jī)噪聲而使估測(cè)存在系統(tǒng)性平均偏差，也存在雷達(dá)在各個(gè)估測(cè)點(diǎn)上誤差不一致的問題。本研究提出了雷達(dá)估測(cè)降水的兩步校準(zhǔn)法，即對(duì)雷達(dá)觀測(cè)的降水先采用擬合Z-I關(guān)系法在時(shí)間域上對(duì)雷達(dá)－雨量計(jì)的系統(tǒng)性平均偏差進(jìn)行校準(zhǔn)，然后再采用反距離加權(quán)插值校準(zhǔn)法在空間上做第2次校準(zhǔn)，實(shí)現(xiàn)對(duì)雷達(dá)－雨量計(jì)觀測(cè)誤差的兩步校準(zhǔn)，最大程度地減小雷達(dá)－雨量計(jì)之間的觀測(cè)誤差。利用2010年江淮流域暴雨過程的雷達(dá)和雨量計(jì)資料對(duì)上述方法進(jìn)行評(píng)估的結(jié)果表明，兩步校準(zhǔn)法不僅改善了雷達(dá)對(duì)強(qiáng)降水的低估，而且減小了與雨量計(jì)觀測(cè)的誤差。

（5）青藏高原天氣氣候影響機(jī)理研究

研究發(fā)現(xiàn)，從春季到夏季，青藏高原—黃土高原地氣溫差高值區(qū)西南—東北向的擴(kuò)展過程與梅雨帶東南—西北向的推進(jìn)具有一致性，提出中國大地形可能是梅雨降水的重要驅(qū)動(dòng)力。細(xì)致分析了2008年中國南方雨雪冰凍災(zāi)害的大氣動(dòng)力、熱力特征，并建立了物理圖像概念模型。結(jié)果表明，夏季亞洲季風(fēng)區(qū)內(nèi)穿越對(duì)流層頂高度的質(zhì)量輸送主要源于以青藏高原南側(cè)為代表的南亞季風(fēng)區(qū)，這進(jìn)一步強(qiáng)調(diào)了青藏高原及其周邊區(qū)域在全球?qū)α鲗酉蚱搅鲗淤|(zhì)量輸送（TST）過程中的重要地位。

中國區(qū)域3—7月梅雨帶（紅色曲線）和地氣溫差（藍(lán)色曲線）的逐月移動(dòng)示意，其中彩色陰影為地形高度，R3，R4，…，R7指示了梅雨帶邊界（用150 mm＜月降水量＜200 mm的站點(diǎn)分布來代表）3—7月的變化，△T3，△T4，…，△T7則指示了地氣溫差高值區(qū)從3—7月的推進(jìn)過程China’s topographic distribution (color-shaded), monthly movements of Meiyu rainbands (red curves), and monthly movements of land-atmosphere temperature difference (blue curves). R3, R4,…, R7denote boundaries of 150-200 mm total monthly rainfall amount, and△T3, △T4, …, △T7denote boundaries of land thermal forcing, respectively, from March, April, to July

（6）球面重力波的特征線快速求解

重力波快波的處理在很大程度上限制了數(shù)值模式的積分效率，通常在模式中采用隱式方法計(jì)算來放大時(shí)間步長(zhǎng)。利用流體中波動(dòng)和流動(dòng)的同一性本質(zhì)，通過黎曼變換將重力快波轉(zhuǎn)換為流動(dòng)的統(tǒng)一形式考慮，就可以和流動(dòng)一樣采用半拉格朗日方法計(jì)算重力快波的傳播，不受計(jì)算線性穩(wěn)定性的約束，從而提高高分辨模式的計(jì)算效率。圖中給出了淺水波模式計(jì)算地形重力波的大時(shí)間步長(zhǎng)（克朗數(shù)C=1.5）的第15天結(jié)果.

新開發(fā)球面重力快波特征線算法給出的地形重力波（Williamson試驗(yàn)5）Gravity wave solved with the characteristic method (CFL=1.5) in Williamson test 5

Severe Weather

Achievements in Disastrous Weather

1 The State Key Laboratory of Severe Weather has passed the evaluation check organized by the Chinese Ministry of Science and Technology

In April 2010, authorized by the Ministry of Science and Technology of China, National Natural Science Foundation of China convened some experts to give an evaluation check to the State Key Laboratory of Severe Weather (LaSW). The LaSW has passed the check and obtained a favorable evaluation.The evaluation panel has produced the following results and comments: the State Key Laboratory of Severe Weather (LaSW) works on applied basic research topics, in line with the national needs and cutting-edge developments in the area, including the major issues conf ning severe weather monitoring and prediction, theoretical study of severe weather dynamics, new theories and techniques for severe weather monitoring and forecast. In addition, LaSW has made efforts to turn research findings into something applicable to operational needs, under a clearly defined orientation and objective. During the period of evaluation, LaSW achieved a range of research results of international implications, including severe weather mesoscale structures and associated mechanisms, novel remote sensing theories and techniques for monitoring severe weather, and improved severe weather forecast theories and techniques. The efforts have rendered laudable contributions to the capacity building of China’s severe weather study and associated operations, and to the socio-economic development in the country as well.

2 Major accomplishments and applications

(1) Intercomparison of deep convection over the Tibetan Plateau-Asian monsoon region and subtropical North America in boreal summer using CloudSat data

Deep convection in the Tibetan Plateau-southern Asian monsoon region (TP-SAMR) was analyzed using CloudSat data for the boreal summer season from 2006 to 2009. Three subregions were defined - the TP, the southern slope of the plateau (PSS), and the SAMR - and deep convection properties were compared among these subregions. To cast them in a broader context, four additional regions are also discussed: East Asia, tropical northwestern Pacific, and western and eastern North America. The major findings are as follows: (1) Compared to the other two subregions of the TP-SAMR, deep convection over the TP is shallower, less frequent, and embedded in smaller-size convective systems, but the cloud tops are more densely packed. These characteristics of deep convection over the TP are closely related to the unique environment, namely, a signif cantly lower level of neutral buoyancy and much drier atmosphere. (2) In a broader context in which all seven regions are brought together, deep convection in the two tropical regions is similar in many regards. A similar conclusion can be drawn among the four subtropical continental regions. However, tropical oceanic and subtropical land regions present some significant contrasts.(3) Deep convection over the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon f ow.

(2) The observational capability examination and microphysical parameters retrieval by cloud radar

In 2010, ground-based Ka band cloud radars in State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences was used to examine the observational capability of the principle prototype spacebased cloud radar in Tianjin, and to observe cloud and precipitation systems with airplane in Jilin Province. The comparison algorithm between different wavelength radars, ground-based and airborne radars were developed. The ref ectivity, velocity and spectrum width observed by cloud radar in vertical observation model were used to retrieve the liquid water content and the size distribution in stratiform cloud.

(3) A quality assurance procedure and evaluation of rainfall estimates for C-band polarimetric radar

Using the observation data collected in field experiments, the mobile C-band dual polarimetric weather radar J type (PCDJ) systematic error and its sources were analyzed in depth. Meanwhile an algorithm that can smooth down differential propagation phase (ΦDP) for estimating the high-resolution specif c differential phase (KDP) was developed. After attenuation correction of reflectivity in horizontal polarization (ZH) and differential reflectivity (ZDR) of PCDJ radar by means of KDP, the data quality was improved signif cantly. Using quality-controlled radar data, quantitative rainfall estimation was compared with rain-gauge measurements. A synthetic ZH /KDP-based method was analyzed. The results suggest that the synthetic method has the advantage over the traditional ZH-based method when the rain rate is ＞5 mm/h. The more intensive the rain rates, the higher accuracy of the estimation.

(4) Improvement of radar quantitative precipitation estimation based on real-time adjustments to Z-R relationships and inverse distance weighting correction schemes

The errors of radar quantitative precipitation estimations consist not only of systematic bias caused by random noises, but also spatially non-uniform bias in radar rainfall at individual rain gauge stations.A two-step correction technique of radar quantitative precipitation estimations is proposed. To minimize the errors between radar quantitative precipitation estimations and rain gauge observations, a real-time adjustment to the Z-R relationship scheme is used to remove systematic bias on the time-domain. The gauge corrected by radar-based estimates scheme is then used to eliminate non-uniform errors in space. Based on radar data and rain gauge observations near the Huaihe River, the two-step correction technique was evaluated through heavy precipitation cases. The results show that the proposed scheme could be improved not only in the underestimation of rainfall, but also in reducing the root mean-square error and mean relative error of radar–gauge pairs.

(5) Study of the impact on weather and climate of the Tibetan Plateau

The research results show that the cascade of western China’s elevated lands toward the northeast seems to act as a ‘‘dynamic attractor’’ that causes the Meiyu rainband to move to the northwest. Analyses of precipitation, water vapor, difference of temperatures between Earth’s surface and near-surface air, and atmospheric circulation provide a clear picture of this land –ocean-atmosphere interaction.

In the winter of 2008, China experienced once-in-50 years (or once-in-100 years for some regions) snow and ice storms. These cases were revisited and comprehensive analyses of the storms’ dynamic and thermodynamic structure were conducted. Then the physical pictures of the large-scale dynamic and thermodynamic structures of the snowstorms were obtained.

We also found that in the Asian monsoon regions and summer, the mass transportation from the tropopause layer to the stratosphere was dominated by the South Asian monsoon region, represented by south of the Tibetan Plateau. This emphasized the importance of the Tibetan Plateau and its adjacent areas in the troposphere to stratosphere transport (TST) over the world.

(6) Characteristic solver for gravity wave on sphere

Model eff ciency and steps are rigidly restricted in the computation of rapid gravity wave. Implicit integration is usually used to expand model time steps. By means of the identical nature of flow and wave, gravity wave is transformed to f ow representation with a Riemann characteristic method. The wave transportation is then calculated the same as flow with the semi-Lagrangian algorithm, and therefore no limitation to the steps exists in terms of linear computational stability. High computational efficiency is then achieved for the rapid waves. An example for the topographical gravity wave is shown in the f gure, which is a 15-day integration of a shallow water model.