基于大气不稳定参数的广东地区雷暴特征分析

利用广东省清远地区2011、2012和2014年6—8月地闪定位资料将每天发生的雷暴情况进行分级,并结合对应的探空资料,计算对流有效位能、沙氏指数、K指数等反映大气稳定性或能量关系的参数,分析其在发生时间和强度不同的雷暴发生前的分布情况。结果表明,沙氏指数、抬升指数、K指数、全总指数、强天气威胁指数和对流有效位能与雷暴强度有一定的相关性,而对流抑制能量、粗理查森数与雷暴强度间没有发现较好的相关性。广东地区雷暴发生前沙氏指数小于0℃,抬升指数小于-2℃,K指数大于30℃,对流有效位能大于500J/kg,更容易产生中强雷暴。广东地区的K指数高于青藏高原地区20℃左右,对流有效位能的平均值高于青藏高原及陕甘宁地区约300J/kg,其余参数分布特点与部分地区相似,进一步反映了广东地区雷暴特征的特殊性,加深了对广东地区雷暴特征的认识。     

1979—2012年中国探空相对湿度资料的非均一性检验与订正

利用加拿大环境部气候研究中心研发的PMTred非均一性检验方法,以ERA interim资料作为参考序列,应用中国区域各探空台站详细的元数据信息为主要断点判断依据,对1979—2012年我国125个探空台站各标准等压面月平均探空相对湿度资料进行了非均一性检验和订正。并结合详细的元数据信息分析了造成我国探空相对湿度序列非均一问题形成的主要原因及对资料的影响程度。结果表明：仪器换型、探测系统资料整理计算方式变化以及辐射订正方法改变和探测系统升级等是造成这一时段中国区域月平均探空相对湿度资料不均一的主要原因。其中,2002年以后的L波段雷达 电子探空仪换型造成了相对湿度资料非常明显的不连续问题,这主要是由于早期59 701型探空仪穿云挂水,造成探测到的相对湿度资料明显偏湿。两个观测时次相对湿度序列不均一的台站数和断点数随高度的增加而增加。各标准等压面上月平均相对湿度序列不均一的探空台站平均订正幅度也随着高度的升高而增大,并且订正量为负值的比例在整套订正资料中所占的比例较高,说明我国的探空月平均相对湿度原始观测资料有明显高估的问题。1979—2012年以来,从全国的情况来看,订正前全国850~300 hPa 5个标准等压面全部为相对湿度降低趋势。但是订正后,850~300 hPa这5个标准等压面在1979—2012年相对湿度的变化趋势均不显著。     

L波段探空仪器换型对高空湿度资料的影响

2002—2010年我国高空探测系统逐步完成了由原来的59-701型探空系统升级为L波段雷达-电子探空仪系统的工作,湿度传感器由原来的肠衣更换为碳湿敏电阻。该文对全国98个高空站相对湿度探测值在换型前后的差异进行了统计分析。结果表明:探空系统换型后,相对湿度探测值较换型前显著降低,表现为明显的干偏差,且随着高度的增加而增大,200,500 hPa和850 hPa相对湿度分别偏低14.6%,8.3%和5.3%。受太阳辐射的影响,这种干偏差在白天甚于夜间;换型前后相对湿度的概率分布也发生了明显变化,整个对流层相对湿度低于20%的低值出现频率明显高于换型前,200 hPa相对湿度小于20%的出现频率由换型前的10%增加到换型后的53%。最明显的变化是相对湿度为3%以下的出现频率,换型前各高度层出现频率均接近于0,但换型后200,500 hPa和850 hPa出现频率分别达到16.2%,9.9%和2.2%。     

北极夏季大气垂直结构与空间分布特征

低层大气垂直物理剖面是研究大气边界层过程、模拟大气环流过程和进行天气预报的关键参数,海洋特别是北冰洋地区是气象实测资料的稀疏区甚至是空白区。因此,中国第6次北极科学考察期间(2014年7月21日至9月11日),我们使用GPS低空探空系统,对北极地区的大气垂直结构和边界层特征进行了观测实验。实地观测结果表明:(1)递减率对流层顶(LRT)和冷点对流层顶(CPT)均能准确的判断该地区对流层顶的高度和温度,NCEP再分析资料在较低纬度能够很好的反应对流层顶变化特征,但是在海冰密集的北极地区(海冰密集度达9成以上)则相对较差,所以很有必要在该区域开展探空观测研究。(2)在高空存在一个明显的低温区和高空急流,低温区和高空急流中心区的海拔高度与对流层顶高度一致;在晴天和少云天气,对流层顶高度变化不大;在多云和阴雨天气,随着纬度的升高对流层顶高度逐渐降低。在晴天和少云天气相比多云和阴雨天气,高空急流区的强度较弱,垂直和水平均范围较小。(3)CPT和高空急流的高度随着纬度有降低的趋势,75°N以北的区域降低显著;对流层垂直温度递减率随着纬度呈现出逐渐增大的趋势。(4)观测期间,在海拔3km以下均存在多个逆温层。其中风速切变在逆温层的消失或者减弱过程中起着重要作用,而在80°N以北区域,对流层顶逆温(TIL)明显小于其他区域。表明极点附近对流层与平流层之间的物质和能量交换相比其他区域更加强盛。     

区域GPS网对夏季降雨过程中大气可降水量的探测

利用GPS网的观测资料,通过GAMIT软件求得5个测站对流层天顶总延迟,进而求出各测站对流层湿延迟;利用湿延迟与大气可降水量之间的转换关系得到各测站的大气可降水量。将所得GPS-PWV值与同时段探空资料所得的大气可降水量以及地表实际降水量进行对比分析,结果表明:GPS-PWV值与探空资料所得的PWV值比较相符;在降水前后,GPS-PWV有比较明显的变化,降水一般出现在GPS-PWV值迅速增加的4-6h内;实际降水量峰值与GPS-PWV增量大小也有较强的相关性。     

Geoelectrical structure of the central zone of Piton de la Fournaise volcano (Réunion)

 A study of the geoelectrical structure of the central part of Piton de la Fournaise volcano (Réunion, Indian Ocean) was made using direct current electrical (DC) and transient electromagnetic soundings (TEM). Piton de la Fournaise is a highly active oceanic basaltic shield and has been active for more than half a million years. Joint interpretation of the DC and TEM data allows us to obtain reliable 1D models of the resistivity distribution. The depth of investigation is of the order of 1.5 km but varies with the resistivity pattern encountered at each sounding. Two-dimensional resistivity cross sections were constructed by interpolation between the soundings of the 1D interpreted models. Conductors with resistivities less than 100 ohm-m are present at depth beneath all of the soundings and are located high in the volcanic edifice at elevations between 2000 and 1200 m. The deepest conductor has a resistivity less than 20 ohm-m for soundings located inside the Enclos and less than 60–100 ohm-m for soundings outside the Enclos. From the resistivity distributions, two zones are distinguished: (a) the central zone of the Enclos; and (b) the outer zone beyond the Enclos. Beneath the highly active summit area, the conductor rises to within a few hundred meters of the surface. This bulge coincides with a 2000-mV self-potential anomaly. Low-resistivity zones are inferred to show the presence of a hydrothermal system where alteration by steam and hot water has lowered the resistivity of the rocks. Farther from the summit, but inside the Enclos, the depth to the conductive layers increases to approximately 1 km and is inferred to be a deepening of the hydrothermally altered zone. Outside of the Enclos, the nature of the deep, conductive layers is not established. The observed resistivities suggest the presence of hydrated minerals, which could be found in landslide breccias, in hydrothermally altered zones, or in thick pyroclastic layers. Such formations often create perched water tables. The known occurrence of large eastward-moving landslides in the evolution of Piton de la Fournaise strongly suggests that large volumes of breccias should exist in the interior of the volcano; however, extensive breccia deposits are not observed at the bottom of the deep valleys that incise the volcano to elevations lower than those determined for the top of the conductors. The presence of the center of Piton de la Fournaise beneath the Plaine des Sables area during earlier volcanic stages (ca. 0.5 to 0.150 Ma) may have resulted in broad hydrothermal alteration of this zone. However, this interpretation cannot account for the low resistivities in peripheral zones. It is not presently possible to discriminate between these general interpretations. In addition, the nature of the deep conductors may be different in each zone. Whatever the geologic nature of these conductive layers, their presence indicates a major change of lithology at depth, unexpected for a shield volcano such as Piton de la Fournaise. Received: 3 November 1999 / Accepted: 15 September 1999     

COSMIC掩星数据与L波段探空数据的对比分析

COSMIC(Constellation Observation System for Meteorology,Ionosphere and Climate)每天可以提供全球2000～3000条从40 km高空到近地面的大气温、压、湿的廓线资料,有效地弥补了常规探空资料在时间和空间上分辨率的不足。通过对2008年5月20日至2008年11月26日COSMIC资料与L波段探空秒数据进行比对,结果表明,在10 km高度以下,COSMIC反演的湿廓线资料与L波段探空数据偏差较小,温度偏差为-0.5℃,均方根误差为1.5℃;折射率偏差为1.4N,均方根误差为5.9N;气压偏差为2.0 hPa,均方根误差为4.7 hPa;水汽压偏差为0.1 hPa,均方根误差为1.1 hPa。COSMIC干廓线资料与L波段探空相比,在10～30 km高度内,温度偏差为-0.3℃,均方根误差为1.9℃;折射率偏差为0.4N,均方根误差为0.9N;气压偏差为1.4 hPa,均方根误差为2.6 hPa。表明COSMIC资料既具有较高的时空分辨率,又具有较好的精度,在数值模式中具有重要的潜在应用。     

风廓线雷达与L波段雷达探空测风对比分析

为了解风廓线雷达探测的准确性,对北京南郊大气探测试验基地2006-2008年3年的观测资料与常规高空探测资料即L波段雷达探空测风数据进行了对比,计算并分析了不同高度、不同时次、不同风速条件下的对比结果,进行了相关性分析,计算了平均差和标准差。结果表明,二者测风结果有较好的一致性,半小时平均水平风u、v分量的标准差在2.3m/s左右,为风廓线雷达和L波段雷达探空共同的测量误差及不同采样空间和时间的水平风的差异。     

微波辐射计与探空仪测值对比分析

利用武汉站高时空分辨力探空资料(3h,30m)与同址的MP-3000A型地基微波辐射计资料,分析了微波辐射计探测偏差的日变化及时间序列变化特征。结果表明,微波辐射计对大气要素的探测具有较高的探测准确度,但仍然存在一定的探测偏差。温度的探测偏差大值区出现在午后,相对湿度及水汽密度的探测偏差大值区则在凌晨;温度及相对湿度探测误差的时间序列表现为起伏较大,而水汽密度则相对平稳,降水,特别是强降水,会对微波辐射计的探测准确度产生较明显的影响。     

Variations in the lower level of the PBL associated with the Yellow Sea fog-new observations by L-band radar

The Chinese east coastal areas and marginal seas are foggy regions.The development of effective forecasting methodsrests upon a comprehensive knowledge of the fog phenomena.This study provides new observations associated with the sea fogsover the northwestern Yellow Sea by means of L-band radar soundings with a high vertical resolution of 30 m.The monthly tem-perature lapse rate,the Richardson Numbers,and the humidity show obvious seasonal variations in the lower level of the planetaryboundary layer (PBL) that are related to the onset,peak and end of the Yellow Sea fog season.The typical pattern of stratification forthe sea fog season in the northwestern Yellow Sea is that a stable layer of about 400 m thick caps a 150 m conditionally unstable layer.Besides,the differences between fogs and stratus clouds in terms of humidity,turbulence and temperature are analyzed,which is ofsignificance for sea fog forecast and detection by satellites.The thickness of the sea fogs varies in different stages of the fog season,and is associated with the temperature inversion.The numerical simulation proves that the seasonal variations obtained by the radarwell represent the situations over the Yellow Sea.