Methane,carbon monoxide and methylchloroform in the southern hemisphere

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.     

Mean annual poleward energy transports by the oceans in the southern hemisphere

A survey is made of the published estimates of the components of the poleward flux of energy by the atmosphere in the Southern Hemisphere in order to determine the total atmospheric transport. Together with recent measurements by satellite of the Earth's radiation budget this allows a new estimate of the required poleward energy transport by the oceans in the Southern Hemisphere for mean annual conditions. Results show that the ocean and atmosphere each contribute similar amounts for 0–30°S and that the ocean probably also transports about one third of the total at 60°S. The latter is in contrast to similar latitudes in the Northern Hemisphere where the ocean transport is negligible, but consistent with the different distribution of land and sea in the two hemispheres.     

High-frequency patterns of the atmospheric circulation over the southern hemisphere and South America

Summary Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed data obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to March) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990–1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in selected areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the western hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15° N and 70° S are discussed. The high-frequency winter and summer patterns for both variables feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the southeastern Pacific. Analysis of the western hemisphere data reveal that the wavetrain in the South American sector extends northeastward over the continent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequential instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.     

The effect of Antarctic sea ice on the Southern Hemisphere atmosphere during the southern summer

This study examines the influence of Antarctic sea ice distribution on the large scale circulation of the Southern Hemisphere using a fully coupled GCM where the sea ice submodel is replaced by a climatology of observed extremes in sea ice concentration. Three 150-year simulations were completed for maximum, minimum and average sea ice concentrations and the results for the austral summer (January?CMarch) were compared using the surface temperatures forced by the sea ice distributions as a filter for creating the composite differences. The results indicate that in the austral summer the polar cell expands (contracts) under minimum (maximum) sea ice conditions with corresponding shifts in the midlatitude Ferrell cell. We suggest that this response occurs because sea ice lies in the margin between the polar and midlatitude cells. The polarity of the Southern Hemisphere Annular (SAM) mode is also influenced such that when sea ice is at a minimum (maximum) the polarity of the SAM tends to be negative (positive).     

Signature of a southern hemisphere extratropical influence on the summer monsoon over India

The weakening relationship of El Nino with Indian summer monsoon reported in recent years is a major issue to be addressed. The altered relationships of Indian monsoon with various parameters excite to search for other dominant modes of variability that can influence the precipitation pattern. Since the Indian summer monsoon circulation originates in the oceanic region of the southern hemisphere, the present study investigates the association of southern extratropical influence on Indian summer monsoon using rainfall and reanalysis parameters. The effect of Southern Annular Mode (SAM) index during the month of June associated with the onset phase of Indian summer monsoon and that during July–August linked with the active phase of the monsoon were analysed separately for a period from 1951 to 2008. The extra-tropical influence over the monsoon is illustrated by using rainfall, specific humidity, vertical velocity, circulation and moisture transport. The June high SAM index enhances the lower level wind flow during the onset phase of monsoon over Indian sub-continent. The area of significant positive correlation between precipitation and SAM in June also shows enhancement in both ascending motion and specific humidity during the strong phase of June SAM. On the other hand, the June high SAM index adversely affects July–August monsoon over Indian subcontinent. The lower level wind flow weakens due to the high SAM. Enhancement of divergence and reduction in moisture transport results in the Indian monsoon region due to the activity of this high southern annular mode. The effect is more pronounced over the southwest region where the precipitation spell has high activity during the period. Significant correlation exists between SAM and ISMR, even after removing the effect of El Nino. It indicates that the signals of Indian summer monsoon characteristics can be envisaged to a certain extend using the June SAM index.     

A diagnostic study of the southern hemisphere summer circulation of the CCC general circulation model

Abstract

The medium‐scale wave regime, consisting largely of zonal wavenumbers 5–7, frequently dominates the summer Southern Hemisphere tropospheric circulation. We perform a diagnostic study of this circulation as simulated by the Canadian Climate Centre (CCC) general circulation model (GCM). The analysis of Hövmöller diagrams, space‐time and zonal wavenumber spectra shows that the CCC GCM is able to simulate the observed medium‐scale wave regime.

The zonally averaged meridional eddy heat and momentum transports and the associated baroclinic and barotropic energy conversions are also examined. The distributions of the transports on the vertical plane agree well with the observations. After comparison with the observed December‐January‐February 1979 distributions, some quantitative differences remain: the heat transport is too weak aloft and too large near the surface, whereas the momentum transport tends to be too weak. The baroclinic and barotropic conversions show a maximum in the medium‐scale waves. The time evolution of the Richardson number of the mean flow suggests that the medium‐scale wave is due to a baroclinic instability.     

北半球夏季西北太平洋热带地区西南季风强弱变化与南半球环流型的关系

本文分析了1978年夏季西北太平洋西南季风的强弱变化与南半球500mb环流形势的关系,发现当南半球出现经向环流型时,西南季风相应增强,反之,出现纬向环流型时,西南季风则减弱。 在南半球稳定的经向环流形势控制下,冷空气可以影响到低纬地带,高空长波槽后冷高压北侧的东南大风在其相对固定的通道上形成一股强而持久的越赤道气流,在北半球环流条件有利的情况下,这股越赤道气流可以在西北太平洋上转向成西南气流,导致该地区西南季风增强。由于南半球的长波槽容易在澳洲大陆东西两岸同时停滞加深,因此越赤道气流的路径则相对集中在这两     

一九七九年七月南北半球低纬季风区大气环流特征

本文应用华盛顿气象中心所发布的1979年7月逐日每5度经纬度网格点上风的资料(范围:35°S—35°N,0—180°E),算出各层(1000、700、500、200和100毫巴共五层)7月的平均合成风及u、v分量,分别绘成月平均流线图和u、v等值线图,并用球极坐标上的连续方程算出各层月的散度和垂直速度。根据上述计算结果,分析了1979年7月低纬度平均水平环流、垂直经圈环流和纬圈环流的特征,及其对降水分布的影响,同时为了阐明1979年7月大气环流的特点,把它与常年情况做了比较,发现1979年7月亚洲夏季风比常年弱,表现为风速小,季风层浅薄,水平范围也小,而且亚洲大部分地区降水为负距平,相应的低纬对流层各高度上的环流系统及经圈和纬圈环流也弱,南半球的副热带高压也弱,最大西风轴偏南。我们认为引起这一系列差异的主要原因,可能是1979年7月对流层高层青藏高压弱、中心位置偏西以及与之伴随的热带东风急流弱等原因造成。最后对青藏高压偏西、偏弱的原因进行了探讨。     

Northward flux of zonal velocity due to quasi-stationary and nonstationary waves in the atmosphere during northern hemisphere winter

The zonal wind velocity flux induced by wave motions in the central month of winter (January) is studied from the NCEP/NCAR reanalysis data and the general circulation model (GCM) of the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS). It is shown that the model describes stationary wave processes with a sufficient accuracy and captures their synoptic period.     

Twentieth century simulation of the southern hemisphere climate in coupled models. Part 1: large scale circulation variability

The ability of five, global coupled climate models to simulate important atmospheric circulation characteristics in the Southern Hemisphere for the period 1960–1999 is assessed. The circulation features examined are the Southern Hemisphere annular mode (SAM), the semi-annual oscillation (SAO) and the quasi-stationary zonal wave 3 (ZW3). The models assessed are the National Center for Atmospheric Research Community Climate System Model Version 3 (CCSM3), the Commonwealth Scientific and Industrial Research Organisation Mark 3, the Geophysical Fluid Dynamics Laboratory Model, the Goddard Institute for Space Studies Model ER (GISS-ER) and the UK Meteorological Office Hadley Center Coupled Model Version 3. The simulations were compared to the NCAR–NCEP reanalyses. The models simulate a SAO which differs spatially from the observed over the Pacific and Indian oceans. The amplitudes are too high over the southern ocean and too low over the midlatitudes. These differences are attributed to a circumpolar trough which is too deep and extends too far north, and to the inability of the models to simulate the middle to high latitude temperature gradient. The SAM is well-represented spatially by most models but there are important differences which may influence the flow over the Pacific and in the region extending from the Ross to Weddell Seas. The observed trend towards positive polarity in the SAM is apparent in the ensemble averages of the GISS-ER and CCSM3 simulations, suggesting that the trend is due to external forcing by changes in the concentration of ozone and greenhouse gases. ZW3 is well-represented by the models but the observed trend towards positive phases of ZW3 is not apparent in the simulations suggesting that the observed trend may be due to natural variability, not external forcing.     

Twentieth century simulation of the southern hemisphere climate in coupled models. Part II: sea ice conditions and variability

We examine the representation of the mean state and interannual variability of Antarctic sea ice in six simulations of the twentieth century from coupled models participating in the Intergovernmental Panel on Climate Change fourth assessment report. The simulations exhibit a largely seasonal southern hemisphere ice cover, as observed. There is a considerable scatter in the monthly simulated climatological ice extent among different models, but no consistent bias when compared to observations. The scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal winds suggesting that wind forced ice transport is responsible for much of this scatter. Observations show that the leading mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the Atlantic sector associated with anomalies of the opposite sign in the Pacific sector. The observed ice anomalies also exhibit eastward propagation with the Antarctic circumpolar current, as part of the documented Antarctic circumpolar wave phenomenon. Many of the models do simulate dipole-like behavior in sea ice anomalies as the leading mode of ice variability, but there is a large discrepancy in the eastward propagation of these anomalies among the different models. Consistent with observations, the simulated Antarctic dipole-like variations in the ice cover are led by sea-level pressure anomalies in the Amundsen/ Bellingshausen Sea. These are associated, to different degrees in different models, with both the southern annular mode and the El Nino-Southern Oscillation (ENSO). There are indications that the magnitude of the influence of ENSO on the southern hemisphere ice cover is related to the strength of ENSO events simulated by the different models.     

Consistent past half-century trends in the atmosphere, the sea ice and the ocean at high southern latitudes

Simulations performed with the climate model LOVECLIM, aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations, are able to reasonably reproduce the observed changes in the lower atmosphere, sea ice and ocean during the second half of the twentieth century. Although the simulated ice area slightly increases over the period 1980–2000, in agreement with observations, it decreases by 0.5 × 10⁶ km² between early 1960s and early 1980s. No direct and reliable sea ice observations are available to firmly confirm this simulated decrease, but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean. The simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation. However, the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results. Our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the Ross Sea and the salinity decrease on the Ross Sea continental shelf. Parts of those changes are likely related to the response of the system to the external forcing. Modifications in the wind pattern, influencing the ice production/melting rates, also play a role in the simulated surface salinity decrease.     

The energetics of error-growth and the predictability analysis in precipitation prediction

Sensitivity simulations are conducted in AREM (Advanced Regional Eta-Coordinate numerical heavy-rain prediction Model) for a torrential precipitation in June 2008 along South China to investigate the effect of initial uncertainty on precipitation predictability. It is found that the strong initial-condition sensitivity for precipitation prediction can be attributed to the upscale evolution of error growth. However, different modality of error growth can be observed in lower and upper layers. Compared with lower-level, significant error growth in the upper-layer appears over both convective area and high jet stream. It thus indicates that the error growth depends on both moist convection due to convective instability and the wind shear associated with dynamic instability. As heavy rainfall process can be described as a series of energy conversion, it reveals that the advection-term and latent heating serve as significant energy sources. Moreover, the dominant source terms of error-energy growth are nonlinearity advection (ADVT) and difference in latent heating (DLHT), with the latter being largely responsible for the rapid error growth in the initial stage. In this sense, the occurrence of precipitation and error-growth share the energy source, which implies the inherent predictability of heavy rainfall. In addition, a decomposition of ADVT further indicates that the flow-dependent error growth is closely related to the atmospheric instability. Thus the system growing from unstable flow regime has its intrinsic predictability.     

热带大气运动的特征

本文用小参数展开方法,探讨了热带大气中的特征运动及其基本属性.理论分析表明: 热带地区的超长波系统有中纬度长波的类似性质.其快过程是地转适应过程,有重力惯性波的活动;而慢过程在零级近似下是地转风,流场具有水平无辐散性质,在一级近似下是类似Rossby波的慢波,运动满足位涡度守恒的条件. 热带大气中的中间尺度运动,时间尺度远大于平流时间时为旋转风,是一种定常涡旋;时间尺度近于平流时间时,运动是水平无辐散的,且保持相对涡度守恒;若时间尺度远小于平流时间,则表现为重力波的活动. 热带大气中水平尺度近于10~6米     

大气中的耗散结构

大气中的台风、飑线、龙卷等可视为一种耗散结构,本文导出大气中出现耗散结构的判据     

Large-scale oscillations of the atmospheric circulation in the southern hemisphere and their influence on climate change in some regions of the globe in the 20th century

The Antarctic Oscillation and its connections with other modes of large-scale circulation and climate parameter variations are studied from the reanalysis data. The estimates of tendencies of the current Antarctic climate changes are presented. It is considered whether the reanalysis data are suitable in studying the Antarctic climate and its changes. The results of the intercomparison of the reanalysis data with station observation and with statistics calculated from these data are discussed.