利用ERBE和ISCCP资料反演青藏高原地表短波吸收辐射场

利用ＥＲＢＥ和ＩＳＣＣＰ卫星辐射及总云量资料,结合青藏高原地面日射资料,讨论了并提出了该地区地表短波吸收气候反演方法,该法的似合精度较高,平均误差为９．８Ｗ．ｍ＾－２据此计算出７５°Ｅ－９５°豚２５°Ｅ－４０°Ｎ间２．５°＊２．５°经纬网格点和高原６３个站点的各月平均地面吸收辐射通量密度,给制出其在高原的分布图,揭示其基本特征。     

Characteristics of the precipitation over the eastern edge of the Tibetan Plateau

Variations of precipitation over the eastern edge of the Tibetan Plateau are analyzed by using data over station Yaan including daytime, nighttime, and daily-mean precipitation and satellite-derived information. A comparison of some features over Yaan and other stations is also carried out. Over Yaan, light-moderate precipitation contributes significantly to both the number of rainy days (96.9%) and the amount (66.9%) of total precipitation. The light-moderate precipitation occurs more frequently at nighttime than at daytime (by 44.5 days, or 33.4%, and by 520.6 mm, or 134.4%, each year), and the nighttime precipitation is mainly in the form of light-moderate precipitation. The number of rainy days and the amount of total precipitation have decreased from the 1950s to the 1970s and during the recent 20 years, associated with negative trends of light-moderate precipitation. Similar features are also found in the Tropical Rainfall Measuring Mission satellite data. Local convective precipitation is the main form of the light-moderate precipitation over Yaan. The absorption of latent heat at the lower troposphere and the release of latent heat at the upper troposphere are larger at nighttime than at daytime by 1–2 times and 2–3 times, respectively. Both the peak value and the total release of latent heat over Yaan are significantly larger than those over the Tibetan Plateau, eastern China, and the western Pacific warm pool. These distinct local characteristics of the “rain city” Yaan are closely related to the interaction between the atmospheric circulation and the steep topography on the eastern edge of the Tibetan Plateau.     

QINGHAI-XIZANG SURFACE LONG-WAVE RADIATION PARAMETERIZATION WITH ITS CLIMATIC CALCULATION*

In the context of August 1982- July 1983 radiation balance data of the Qinghai-Xizang Plateau, detailed study is made of the relation between the active-surface temperature and surface temperature, proposing two parameterization schemes on surface long-wave radiation(SLWR)of the form U=kδσ(T₀+273)⁴ and U=δσ[(T₀+273)⁴+△T)]⁴, where k and △T are indicated by parameterization equations, separately, others being in conventional notation. Retrieved verification shows the two formulae to be of the same fitting accuracy with the mean relative error of 3.6% and suitable for computing instantaneous and mean flux density, alongside analyzed daily and annual variations of k and △T. Eventually. SLWR in the target area is investigated and its climatic characteristics examined.     

春季"冷区"冰雹天气分析及预报

冰雹是我省春季主要灾害性天气之一。当冷锋逼近我省或影响我省时造成的冰雹、雷雨大风等强对流天气,在实际预报中容易引起预报员重视,但当冷锋移过南岭后,我省处地面冷锋后部有时也会出现冰雹天气。这里我们称这种形势下出现的冰雹为“冷区”冰雹。“冷区”冰雹是预报中的一个难点。本文首先用常规的天气图方法,综合提炼出有利于我省“冷区”强对流天气发生的天气尺度背景条件,然后对冰雹天气的物理成因进行分析,得出一个较好的“冷区”冰雹预报模式。1“冷区”冰雹日选取及时空分布特征1．l“冷区”冰雹日的选取由于‘共区”冰雹一…     

黄河三门峡水库—小浪底水库间夏季降水量年际变化及水汽形势分析

利用1960~1999年全国600个站月平均降水资料,对黄河三门峡水库—小浪底水库间的夏季降水总量年际变化进行了统计分析,并应用功率谱诊断方法提取了夏季各月降水的振荡周期。在此基础上,选取了黄河三门峡水库—小浪底水库间降水量多与少的年份,利用NCEP再分析资料研究了其上空的水汽变化以及水汽输送量变化。结果表明,黄河三门峡水库—小浪底水库间降水量多的年份,其上空为较为明显的水汽辐合;降水量比较少的年份,其上空为明显的水汽辐散。选取多雨年(1982年)及少雨年(1997年),结合NCEP再分析资料以及TBB资料,进一步验证了上述结论。     

利用卫星资料试作青藏高原地表净辐射场的气候反演

利用 ERBE和 ISCCP卫星辐射及总云量资料 ,结合已提出的地表短波吸收辐射 ,大气逆辐射以及地表长波辐射的气候反演方法 ,计算出 2 5°～ 4 0°N,75°～ 95°E间 2 .5°× 2 .5°经纬度网络点及高原 63个站点的各月平均地表净辐射 ,绘制出其在高原的分布图 ,揭示其时空分布特征。     

Detection and Correction of AMSR-E Radio-Frequency Interference

Radio-frequency interference (RFI) affects greatly the quality of the data and retrieval products from space-borne microwave radiometry. Analysis of the Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E) Aqua satellite observations reveals very strong and widespread RFI contam- inations on the C- and X-band data. Fortunately, the strong and moderate RFI signals can be easily identified using an index on observed brightness temperature spectrum. It is the weak RFI that is diffi- cult to be separated from the nature surface emission. In this study, a new algorithm is proposed for RFI detection and correction. The simulated brightness temperature is used as a background signal (B) and a departure of the observation from the background (O-B) is utilized for detection of RFI. It is found that the O-B departure can result from either a natural event (e.g., precipitation or flooding) or an RFI signal. A separation between the nature event and RFI is further realized based on the scattering index (SI). A positive SI index and low brightness temperatures at high frequencies indicate precipitation. In the RFI correction, a relationship between AMSR-E measurements at 10.65 GHz and those at 18.7 or 6.925 GHz is first developed using the AMSR-E training data sets under RFI-free conditions. Contamination of AMSR-E measurements at 10.65 GHz is then predicted from the RFI-free measurements at 18.7 or 6.925 GHz using this relationship. It is shown that AMSR-E measurements with the RFI-correction algorithm have better agreement with simulations in a variety of surface conditions.     

江西夏季雷电天气热力条件及不稳定指数对比分析

选取2007年夏季两次强度不同的致灾雷电过程进行对比,并将其能量参数与典型历史个例进行比较。结果表明：（1）副高位置、500hPa低槽移速、中尺度辐合系统以及热力结构的差异是导致雷暴强度不同的原因之一;（2）中尺度辐合系统移向鄱阳湖时,对流天气更加剧烈,但对大尺度系统鄱阳湖的阻挡作用不显著;（3）对流层上干下湿的特征越明显,强雷电发生的概率越大;（4）CAPE〉632J/kg,K〉34℃,Si〈0℃,Li〈0℃,TT〉43℃,SSI〉43可以作为江西致灾雷电发生的阈值,超过阈值越多,强对流天气发生的概率越大;（5）能量参数的演变对致灾雷电的潜势预测、强度判别具有较好的指示,夏季对流参数的指示意义较春季更好。     

大理雨季开始期演变及异常环流特征分析

利用云南省大理州12个气象站1962～2008年共47a雨季开始期资料及NCEP／NCAR高度场及风场资料分析了大理雨季开始期的时空分布特征及异常年环流特征。EOF分析表明,大理雨季开始期存在多种空间分布类型,主要的分布型是一致偏早（晚）型及东南一西北型。Morlet小波分析表明,大理雨季开始期在20世纪60年代初到70年代中期偏早,70年代中期至90年代初偏晚,90年代初至今偏早;且存在约2a和10a的特征时间周期变化。异常偏早年5月高度距平场上北半球经向上呈“-＋-”的分布,异常偏晚年则相反,呈“＋-＋”的分布。异常年5月高、中低层的距平风场同样存在明显差异,异常偏早年高层存在增强伊朗高压的反气旋环流,低层存在偏强的南亚季风环流,异常偏晚年则是相反的环流特征。     

2005年3月一次寒潮天气过程的诊断分析

利用NECP1°×1°的6小时分析资料和常规观测等资料,对2005年3月10~13日一次全国性寒潮天气过程的环流背景、影响天气系统及成因进行了分析。结果表明:这次寒潮及寒潮天气主要成因是(1)西欧上空500hPa强暖平流致使在西伯利亚地区形成阻塞高压,建立横槽,横槽北侧的东北气流引导超极地冷空气和西路冷空气合并加强;形成了异常强的冷高压、锋区、冷温度中心和冷温度平流。(2)两个短波槽东移侵入阻塞高压,使得横槽两次建立和转为竖槽,导致强冷空气大举南侵。(3)寒潮带来大范围强降温、700hPa西南急流与冷空气交汇、1000hPa以上层气温在0℃以下的垂直分布,为南方大到暴雪提供了动力、水汽和凝结的温度条件。