电离层电子总量水平梯度和相关系数

电离层电子总量水平梯度和相关系数是进行越境越障空间物理研究时的基本参量。本文分析了当同步信标卫星ATS-6停泊于东非地区上空时,在西欧观测到的太阳宁静年条件下电离层电子含量水平分布和空间相关性。指出纬向梯度、经向梯度、全梯度矢量的昼夜变化与季节特性。文中提出并论述中纬度TEC水平梯度矢量的指日效应:在北半球,冬季时梯度矢量指向的昼间进程是东南-南-西南,方位角变化小,幅值与幅值变化亦小;夏季时梯度矢量指向的昼间进程是东-南-西,方位角变化大,幅值与幅值变化亦大。梯度矢量箭头具有判然的指日性,即追随太阳方位角而变。梯度矢量幅值,在非低纬区条件下,随太阳仰角的增大而增大。文中还述及电子总量空间相关系数的表现规律并探讨了产生中纬度电离层这种时空行为的可能的动力学原因。     

Impact of the Subtropical High on the Extratropical Transition of Tropical Cyclones over the Western North Pacific

Recent publications have investigated the interactions between the extratropical transitions （ETs） of tropical cyclones （TCs） and midlatitude circulations; however, studies of ET events have rarely considered the relationship between the storm and the nearby subtropical high. The TC best-track data provided by the Regional Specialized Meteorological Center-Tokyo Typhoon Center of the Japan Meteorology Agency are used in conjunction with the NCEP/NCAR reanalysis data to discuss the potential effects of the subtropical high on ETs over the western North Pacific basin. When the western Pacific subtropical high （WPSH） is weakened and withdrawn toward the east, more TCs follow recurving paths and the midlatitude trough activity is intensified. These changes lead to enhanced ET activity. By contrast, when the WPSH strengthens and extends westward, the number of TCs that follow direct westward paths increases and the midlatitude trough is relatively inactive. These conditions lead to reduced occurrences of ET cases. Abnormal activity of the WPSH should be considered as an important factor in determining ET activity.     

北极增幅性变暖对欧亚大陆冬季极端天气和气候的影响:共识、问题和争议

北极增幅性变暖和北极海冰快速减少不仅使北极气候系统成为国际前沿性问题,且对其导致的中纬度极端天气气候的影响研究也备受关注,这一研究成为目前少数几个最活跃的气候研究领域之一。本文回顾了这一研究领域的早期探索,总结了最新的科学假设和科学问题、研究的进展、目前的共识以及亟待解决的问题和主要争论。最后提出了未来取得新进展的共性问题。     

北极放大的时空变化特征及其与北极涛动的联系

The Arctic near-surface air temperatures are increasing more than twice as fast as the global average–a feature known as Arctic amplification(AA).A modified AA index is constructed in this paper to emphasize the contrast of warming rate between polar and mid-latitude regions,as well as the spatial and temporal characteristics of AA and their influence on atmospheric circulation over the Northern Hemisphere.Results show that AA has a pronounced annual cycle.The positive or negative phase activities are the strongest in autumn and winter,the weakest in summer.After experiencing a remarkable decadal shift from negative to positive phase in the early global warming hiatus period,the AA has entered into a state of being enlarged continuously,and the decadal regime shift of AA in about 2002 is affected mainly by decadal shift in autumn.In terms of spatial distribution,AA has maximum warming near the surface in almost all seasons except in summer.Poleward of 20°N,AA in autumn has a significant influence on the atmospheric circulation in the following winter.The reason may be that the autumn AA increases the amplitude of planetary waves,slows the wave speeds and weakens upper-level zonal winds through the thermal wind relation,thus influencing surface air temperature in the following winter.The AA correlates to negative phase of the Arctic oscillation(AO) and leads AO by 0–3 months within the period 1979–2002.However,weaker relationship between them is indistinctive after the decadal shift of AA.     

Dynamic Seasonal Transition from Winter to Summer in the Northern Hemisphere Stratosphere

This study applied the modified spatial simi- larity coefficient method to define the seasonal transition （ST） from winter to summer in the extratropical strato- sphere of the Northern Hemisphere. The features of the ST were examined using European Centre for Medium- Range Weather Forecasts （ECMWF） Interim reanalysis data; and the results showed that the time and duration of the ST, which is affected by the activity of planetary waves （PW） in the stratosphere, largely depended on the geophysical locations. This study also investigated the interannual variability of the ST and its relationship with stratospheric sudden warming （SSW） and the qua- si-biennial oscillation （QBO）. It was shown that the late-onset SSW events （after 22 January） are close to the start of the ST. An easterly （westerly） QBO hastens （de- lays） the onset of the ST in high and low latitudes, whereas it delays （hastens） the ST in midlatitudes. The duration of the ST is significantly affected by the QBO. The influence of SSW and the QBO have different sig- nificance in different latitudes, so they are both important and irreplaceable factors.     

河南省近10年汛期多雨时段大尺度环流特征

利用1995~2004年气象资料,分析了河南省降水最多年份汛期降水集中时段的大尺度环流特征,结果发现:降水集中时段100hPa南亚高压120°E脊线基本维持在25~32°N之间,降水集中时段开始前南亚高压有一个东移北跳过程,降水集中期间100hPa高度场上呈现东高西低形势,有利于副高西伸和北抬;西太平洋副热带高压相对稳定,在多雨时段副高进退次数较多,且较长时间稳定在25°N左右,有利于西南暖湿气流沿副高外围进入河南省境内,为暴雨提供了充足的水汽;在降水集中时段,中纬度西风急流轴位置被北抬到40°N以北, 40°N以南基本是东风,这种中纬度地转西风持续偏弱,有利于副热带高压北跳和北跳后稳定,使雨带稳定在河南省。     

正压准平衡海洋模型及其解（Ⅰ）：中纬度大尺度风场强迫情况

本文建立了风场强迫下考虑瑞利摩擦的水平二维正压准平衡海洋模型,并对中纬度大尺度风场强迫的情况做了解析求解。结果表明,在近地面西风急流的强迫下,在理想海洋的西海岸以东会出现由气旋涡与反气旋涡构成的涡旋偶;当西风强迫越大,粘性越小时其强度越大,而β越大,β通道的半宽越小,则其沿纬向的变化越剧烈;该涡旋偶的性质属准平衡的涡旋波。将该结果与北太平洋上层流场异常的复EOF分析的第一模态作比较后可见,两者有类似之处。最终,该海洋模型的解则趋于该风场强迫特解。     

高空急流与中纬度系统影响下台风暴雨的研究现状

我国暴雨天气中，台风是最强的Bao雨天气系统，当台风外围系统与西风槽相互作用时往往发生暴雨突然增幅现象，造成了严重灾害，以往大量的研究表明；台风和中纬度系统相互作用引起的远离台风的北段暴雨大多发生在西南风高空急流区的右后方，高空急流有明显的非纬向特征，而且暴雨增幅与高空急流的非纬向增强有关，对有关高空急流与中纬度系统影响下台风暴雨的研究进行了综述，并且对进一步深入研究提出了建议。     

陕、甘干旱地区不同时段地表径流递减率的分析

根据陕西,甘肃部分地区气象,水文实测资料的分析,证明本区径流系数在逐年下降。在径流减少原因中,当时间尺度分别在４０年,３０年,２０年,１０年时,自然因素导致的径流递减率分别为１７．５％,３４．２％,５１．７％,７０．３％,径流量分别减少０．１４％,０．３４％,０．５２％,１％。     

北太平洋冬季海-气耦合的主模态及其与瞬变扰动异常的联系

利用45年的ECMWF再分析资料,使用SVD方法研究了冬季北太平洋地区表层海温(SST)异常与大气环流异常间的主要耦合模态,探讨了大尺度海-气耦合型与天气尺度瞬变扰动的相互关系。分析结果表明,中纬度北太平洋地区冬季存在两种主要的海-气耦合型,第1种耦合型反映了与ENSO紧密相关的中纬度北太平洋冬季海温异常分布型以及大气的PNA型,第2种耦合型SST异常集中在东亚沿海以及中纬度北太平洋海流区,相应的大气场则为暖(冷)SSTA上空东西向带状区域内位势高度偏高(低),明显独立于ENSO型。进一步的合成分析表明,在第1种耦合型SST正(负)异常年里,冬季阿留申低压主体位置偏西南(东北),从东北亚到北美西海岸的西北—东南向带状区域内是低层大气温度正(负)异常区和高层西风负(正)异常区,西风负(正)异常中心位于西风急流出口处的北太平洋中东部,而西风急流主体区的风速变化很小。在第2种耦合型东亚沿海至中纬度北太平洋海流区SST偏暖(冷)时,阿留申低压整体偏弱(强),SST暖(冷)异常上空的大气温度偏暖(冷),高层西风急流区西风偏弱(强)。两种耦合型均显示出在北太平洋中纬度地区大气和海洋的异常相关中心有很好的空间对应性。在两种耦合型下,中纬度北太平洋冬季的大气斜压性也发生截然不同的改变,引起中纬度天气尺度瞬变扰动活动异常。瞬变扰动异常的动力强迫作用对北太平洋西风异常的形成存在正反馈作用,而其热力作用则试图破坏与两种海-气耦合模态相关的大气温度异常型。