IAP-AGCM对QBO模拟的动量收支分析

平流程准两年振荡(QBO)是赤道平流层(～100-1 hPa)变率的主要模态,可对中高纬地区的环流产生重要影响,但目前利用通用大气环流模式(GCM)对其进行准确模拟仍然是一个挑战.本文利用IAP大气环流模式(IAP-AGCM)的中高层大气模式版本(IAP-AGCML69)对QBO进行模拟,并对其动量收支情况进行分析.研...     

Tropical drought patterns and their linkages to large-scale climate variability over Peninsular Malaysia

Ocean–atmosphere modes of climate variability in the Pacific and Indian oceans, as well as monsoons, regulate the regional wet and dry episodes in tropical regions. However, how those modes of climate variability, and their interactions, lead to spatial differences in drought patterns over tropical Asia at seasonal to interannual time scales remains unclear. This study aims to analyse the hydroclimate processes for both short- and long-term spatial drought patterns (3-, 6, 12- and 24-months) over Peninsular Malaysia using the Standardized Precipitation Index, Standardized Precipitation Evapotranspiration Index, and Palmer Drought Severity Index. Besides that, a generalized least squares regression is used to explore underlying circulation mechanisms of these spatio-temporal drought patterns. The tested drought indices indicate a tendency towards wetter conditions over Peninsular Malaysia. Based on principal component analysis, distinct spatio-temporal drought patterns are revealed, suggesting North–South and East–West gradients in drought distribution. The Pacific El Nino Southern Oscillation (ENSO), the South Western Indian Ocean (SWIO) variability, and the quasi-biennial oscillation (QBO) are significant contributors to the observed spatio-temporal variability in drought. Both the ENSO and the SWIO modulate the North–South gradient in drought conditions over Peninsular Malaysia, while the QBO contributes more to the East–West gradient. Through modulating regional moisture fluxes, the warm phases of the ENSO and the SWIO, and the western phases of the QBO weaken the southwest and northeast monsoon, leading to precipitation deficits and droughts over Peninsular Malaysia. The East–West or North–South gradients in droughts are related to the middle mountains blocking southwest and northeast moisture fluxes towards Peninsular Malaysia. In addition, the ENSO and QBO variations are significantly leading to short-term droughts (less than a year), while the SWIO is significantly associated with longer-duration droughts (2 years or more). Overall, this work demonstrates how spatio-temporal drought patterns in tropical regions are related to monsoons and moisture transports affected by the oscillations over the Pacific and Indian oceans, which is important for national water risk management.     

INTERANNUAL CHANGE OF EXTRA-TROPICAL METHANE INDUCED BY THE QUASI-BIENNIAL OSCILLATION OF TROPICAL WIND AND ITS FORMATION MECHANISM

Researchers have paid much attention to the influence of the tropical zonal wind quasi-biennial oscillation (QBO) on tropical methane, while generally ignoring the change in extra-tropical methane. The present study analyzed the interannual changes in the methane mixing ratio in extra-tropics of both the Southern Hemisphere (SH) and Northern Hemisphere (NH) using Halogen Occultation Experiment (HALOE) satellite data. The results show that interannual changes in extra-tropical methane exhibit QBO features in both hemispheres that are obviously different from those in the tropics. The extra-tropical methane QBO perturbations usually occur in two layers and are longitudinally asymmetrical about the equator. The amplitude of the methane QBO disturbance in the extra-tropics is smaller than that in the tropics from 10 to 1 hPa but much larger in the layer from 30 to 10 hPa. The interannual relative changes in the methane mixing ratio are similar in both the NH extra-tropics and the tropics in the middle and upper stratosphere. Using the National Center for Atmospheric Research two-dimensional, interactive chemical dynamical radiative model (SOCRATES), simulation was conducted to investigate the mechanism of the extra-tropical methane QBO. The results indicate that the tropical stratospheric zonal wind QBO results in the QBO of the induced residual circulation. It is the transport of methane by the induced residual circulation that causes the methane QBO in the extra-tropics. The induced residual circulations in the middle and upper stratosphere are not always longitudinally symmetrical about the equator, resulting in different distribution of the methane QBO in the SH and NH extra-tropics.     

QBO-like Oscillations Induced by Local Thermal Forcing

A zonal-vertical two-dimensional equatorial model is used to study the possibility that the long period oscillation of the zonal mean flow occurring in the lower equatorial stratosphere (QBO) is caused by local thermal ac-tivities at the tropical tropopause. The model successfully reproduces QBO-like oscillations of the zonal mean flow, suggesting that the local heating or cooling at the tropical tropopause is probably the main reason of QBO’s genera-tion. The analysis of the dependence of the oscillation on the wave fencing indicates that the oscillation is not sensible to the forcing scale. The model can reproduce QBO-like oscillations with any forcing scale if the fencing period and amplitude take appropriate values, proving that the internal gravity waves generated by local thermal source take much important roles in QBO.     

QUASI-BIENNIAL OSCILLATION IN RAINFALL OVER CHINA

Based on monthly rainfall data from 80 stations of China for the period of January 1951—February 1985analysed in terms of the maximum entropy spectrum and EEOF(extended empirical orthogonal function)techniques,the spatial and temporal features of quasi-biennial oscillation(QBO)in the rainfall are investigatedin a detailed manner,with some results of interest acquired.Highly evident is the QBO in rainfall over China,especially the mid and lower reaches of the ChangjiangRiver,the NE side of the Qinghai-Xizang Plateau,North China,the southern part of NE China,areas southof the Changjiang River and of the Nanling mountain region,and most of Xinjiang.The spatial wave described by the first and second eigenvectors of EEOF for eastern China is a type of wavetravelling from NE to SW,indicating the cycle of patterns(in the south to north direction):dryness(D)-wetness(W)-dryness(D)→southern W-northern slight D→W-D-W→southern D-northern slight W→D-W-D again,with the flooded region between the Changjiang and Huanghe Rivers for the D-W-D occurrenceand with the Changjiang River as the division for the southern W-northern slight D happening.The third andfourth eigenvectors show a standing wave-like feature for the same eastern part,indicating the cycle of D-W-D→transition→W-D-W→transition→D-W-D,again,where the transition means the generalweakening of drought and flooding and their subsequent reversal development.The amplitudes of the time coefficients of the first two eigenvectors are opposite in the trend of their changesto those of the next two and show a period of 10—14 years.     

黄河中下游地区夏季逐候降水量的低频振荡特征

本文使用主分量分析黄河中下游地区(河南省)68站1982—1987年夏季(6—8月)逐侯降水量的主要时空特征,并用非整波技术分析所提取的第一主要分量频谱分布的低频振荡特点.分析结果表明该地区降水主要低频振荡周期为6—12候(30—60天)月际振荡及季问振荡15—24候(75—120天).它们年际变化有准两年振荡,其中月际低频振荡与赤道地区的纬向风准两年周期振荡有同相关系.     

赤道平流层QBO与我国7月雨型的关联

根据1953～1991年赤道平流层纬向风资料分析,得出我国东部地区7月份主要雨带位置与赤道平流层30～50 hPa平均纬向风准两年振荡（以下简称赤道平流层QBO）有较好的关联。在西风位相条件下,我国7月主要雨带位置较偏北;在东风位相条件下,我国7月主要雨带位置易偏南。它们之间的关系主要是通过对对流层环流的影响相联系的。利用赤道平流层纬向风的变化规律并结合冬季北太平洋对流层环流特征,对我国7月主要雨带类型的预报,有一定实用意义。     

Combined effect of the QBO and ENSO on the MJO

本文研究了平流层准两年振荡与ENSO对MJO的协同作用。结果显示:在拉尼娜/准两年振荡东风位相,起源于印度洋到达西太平洋的MJO要比在厄尔尼诺年强。但是在拉尼娜/准两年振荡西风位相,这种关系不复存在。原因在于ENSO和准两年振荡对MJO事件的影响不同。厄尔尼诺年西太平洋地区正水汽平流有利于MJO加强,而准两年振荡西风位相下海洋性大陆地区较强的日循环会使得海洋性大陆屏障作用增强。在厄尔尼诺年,尽管MJO在准两年振荡西风位相下会受到抑制,但是在到达西太平洋是都能得到加强。在拉尼娜/准双周振荡的西风位相下,海洋性大陆较强日循环和西太平洋不利的背景条件都会抑制MJO。     

Low-Frequency CISK-Rossby Wave and Stratospheric QBO in the Tropical Atmosphere

1.IntroductionThelow~frequencyoscillation(LFO)isaveryimPOrtantweatherphenomenonintheatmosphere.The30--50--dayandquasichiweeklyoscillationsinthetropicalatmospherearemostintensivelystudied,andcomParativelyspeaking,anotherkindofLFOconcernillgtheQBOofthestratosphericzonalwindsismuchlessstudied,which,althoughoccurringinthestratosphere,bearsacloserelationtothetroposphericactivitiesandtheevolutionoflow--latitudecirculationssothatitisworthwhiletoexploreindepththephysicalmechanismfortheQBOoccurre…