Significance of the normalized seasonality of wind field and its rationality for characterizing the monsoon

The significance of the normalized seasonality of wind field is theoretically studied and the intrinsic relationship between its critical value and the definition of the monsoon region is revealed. As a result, the rationality which the monsoon region is characterized by the significant normalized seasonality is proved. Based on this, by use of the NECP/NCAR reanalysis data during 1958–1997, the spatial structure of the significant normalized seasonality of wind field is investigated, and the significant baroclinity of the seasonal variation of the atmospheric general circulation in the vertical direction is verified. Moreover, in the tropics there exists an anti-symmetric distribution between the significant seasonality in the eastern hemisphere and that in the western hemisphere, and the monsoon is linked closely to some important systems such as the subtropical highs, the night jet and the west wind channels.     

岩溶山区不同利用方式下土地蓄水能力研究——以重庆市中梁山为例

分析研究了中梁山岩溶山区竹林、灌丛、草地、园地、坡耕地5种土地利用方式的凋落物和土壤的蓄水功能。结果表明,自然利用的竹林地、灌丛地、草地的凋落物蓄积量和最大持水量都远远大于其余两种农耕利用的土地。当自然利用土地改为园地、坡耕地以后,其表层土壤的最大蓄水能力下降31. 2%、非毛管蓄水能力下降65. 5%、坡耕地的毛管蓄水能力下降34. 3%。与此同时由于土地利用方式不同,还使园地整个土壤剖面( 60cm)蓄水潜力增大4. 4% ,坡耕地蓄水潜力减少6.1% ,园地、坡耕地剖面土壤非毛管蓄水能力较自然利用方式土地剖面非毛管蓄水能力下降55. 7%。毛管蓄水量和前期含水量具有极显著的正相关,整个剖面毛管蓄水量和前期含水量都以园地最高。从保水能力上考虑,园地是岩溶山区开垦土地较为理想的利用方式。建议加强园地凋落物的保护;在雨季尽量不让坡耕地空闲裸露,以防止水土流失。      

乌鲁木齐国际机场一次强雷暴天气分析

雷暴及伴随其出现的恶劣天气严重威胁飞行安全。利用常规气象资料、卫星云图、雷达回波结合湿位涡的诊断分析对2005年6月26日出现在乌鲁木齐国际机场的一次强雷暴天气进行了研究。结果表明：（1）雷暴出现时，机场的地面要素场和天气变化剧烈，气温剧降，湿度暴增，气压涌升，并伴有大风和强阵雨。（2）此次强雷暴天气是由飑线引起的。飑线的形成可能与冷性的中-α尺度的高压和生命史较短的中-β尺度热低压之间的相互作用有关。（3）逆温层的存在抑制了水汽和热量向上的输送和扩散，冷空气的冲击破坏了逆温层，使累积的不稳定能量得以释放，强对流天气爆发。（4）925hPa的湿对称不稳定区域对于预报雷暴天气的落区具有一定的指示意义，强雷暴出现在MPV〈0的大值区内。     

2004年云南秋季强降水位涡诊断分析

利用NCEP格点资料和常规观测资料对2004年云南秋季强降水进行位涡诊断分析，结果表明，干湿位涡均能较好地反映天气系统的演变特征，干位涡能很好地反映滇黔辐合强弱和地面冷空气的移动路径。湿位涡则能反映暖湿气流活动特征。强降水发生期间，中高层强干湿位涡向低层传送，低层负湿位涡向上伸展。对流层中高层的干湿位涡强中心向低层传送方向和强度变化与强降水雨带移动方向及雨强变化一致。此次强降水对流层中层的强干位涡源位于川东，表明该过程与9月2—6日川东大暴雨有关。     

湿位涡诊断分析在东南亚强降水中的应用

文章应用湿位涡理论 ,分析了发生在东南亚夏季的两个强降水个例 ,讨论了湿位涡与东南亚强降水形成的关系。东南亚夏季具有利于强降水发生的湿位涡场分布特征 ;强降水的发展与湿位涡的变化有很好的对应关系 :当对流层低层MPV1<0、同时MPV2 ≥ 0时 ,易产生强降水 ;当对流层高层MPV1正值区与低层MPV1负值区相互作用 ,即高层下滑的干冷空气与低层上升的高温高湿空气交汇 ,容易贮存和释放湿对流不稳定能量 ,有利于强降水产生。湿位涡理论在东南亚强降水诊断中有很好的应用前景。     

旱作物灌溉用水预测公式

从土壤湿润层水量平衡出发,推导出旱作物灌溉用水预测公式,利用历史实测灌溉用水及同期降雨资料率定有关参数,根据降雨预报资料预测灌溉用水量。方法简便,适用于种植结构不明的灌区,特别是数个灌区构成的灌溉区域。     

ISENTROPIC POTENTIAL VORTICITY ANALYSIS ON THE MESOSCALE CYCLONE DEVELOPMENT IN A TORRENTIAL RAIN PROCESS

The mesoscale model MM4 is used to simulate the torrential rain associated with Meiyu frontoccurring on 5—6 July.1991 in the Changjiang-Huaihe Basin.Based on the outputs of the model,the cause of the mesoscale cyclogenesis on the lower troposphere is investigated in terms of thepotential vorticity principle.The results show that because of the favorable pattern of moistisentropic surface,the absolute vorticity increases when cold air with high moist potential vorticityvalue rapidly slides down southwards along the moist isentropic surface,and then causes thecyclonic vortex development.     

Primary ionization coefficients for dry and moist air; secondary ionization coefficients for a water surface

Summary A comparison has been made between the Townsend primary ionization coefficient, , for dry air and for air with humidities typical of those in the atmosphere. is defined as the number of new electrons produced by an electron per centimeter of drift in a field. A range of field/pressure ratios,E/p ₀, of 40 to 100 V (cm torr)^–1 was employed. The variation of with humidity is very small.Over the range ofE/p ₀ from 50 to 100 V (cm torr)^–1, the secondary ionization coefficient, , of a water surface has been found from sparking potential data to be typically 2×10^–4. represents the fraction of primary ionizing collisions that ultimately result in the production of additional electrons at the surface.     

The derivation of moist baroclinic Ertel-Rossby invariant in fast manifold and its application to typhoons

Potential vorticity(PV)has been widely applied as a tracer because of its property of conservation in frictionless,dry adiabatic flow.However,PV itself is more effective in describing the slow-manifold flow at large scale.Therefore,we wish to find a materially conserved invariant other than PV to diagnose severe weather such as growing and mature tropical cyclones,whose velocity and dynamic pressure vary rapidly and locally.Starting from the absolute motion equation after elimination of the pressure gradient term by introducing moist entropy and moist enthalpy,the baroclinic Ertel-Rossby invariant(ERI)in moist flow is derived by the Weber transformation.Furthermore,the material conservation property of moist ERI is proven.Besides the traditional moist potential vorticity(MPV)term,the invariant includes the moisture factor that is excluded in dry ERI and the term related to gradients of pressure,kinetic energy and potential energy that reflects the"fast-manifold"property.Therefore,it is more complete to describe the fast motions off the slow manifold for severe weather than is the MPV term.The moist ERI is then applied to diagnose a triple-typhoon system,and is compared with MPV and dry ERI.Contrastive analysis shows that moist ERI is a better tool to diagnose the movements and intensity variations of several coexisting typhoons.The moist ERI can signify the movement and development of a multi-typhoon system.It has wide application prospects for a real moist atmosphere.     

Impacts of cloud-induced mass forcing on the development of moist potential vorticity anomaly during torrential rains

1. Introduction The Ertel (1942) potential vorticity (PV) has beenwidely used, especially in the studies of large-scale sys-tems (Hoskins et al., 1985; McIntyre and Norton, 2000;Wu et al., 1995; Wu and Liu, 1999). The vorticityequation in quasi-geostrophic ?ows only predicts thevariation of the vorticity and cannot provide a usefulconstraint to the vorticity. PV provides a constraintfor the variation of the vorticity in the baroclinic at-mosphere (Gao et al., 1990). The PV may not bec…