A comparative analysis of the method of extratropical cyclone identification

Three methods for identification cyclones in extratropical latitudes of the Northern Hemisphere (NH) (20°–80° L) are compared based on reanalysis data (1948–2007) for the fields of the sea level pressure (SLP). Different characteristics of extratropical cyclones, namely, their number, intensity, size, and lifetime, are analyzed. The effect of orographic effects for the identification of cyclones and their trajectories is evaluated. The characteristics of extratropical cyclones are compared based on different reanalysis data (National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR), ERA-40, and ERA-INTERIM) with different spatial resolutions.     

Comparison of surface wind stress characteristics over the Tropical Atlantic (10°N–40°S) in fields derived from the UWM/COADS, NCEP/NCAR and QuikSCAT datasets

A comparison of monthly wind stress derived from winds of NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis and UWM/COADS (The University of Wisconsin-Milwaukee/Comprehensive Ocean-Atmosphere Data Set) dataset (1950–1993), and of NCEP/NCAR reanalysis and satellite-based QuikSCAT dataset (2000–2006), is made over the South Atlantic (10°N–40°S). On a mean seasonal scale, the comparison shows that these three wind stress datasets have qualitatively similar patterns. Quantitatively, in general, from about the equator to 20°S in the mid-Atlantic the wind stress values are stronger in NCEP/NCAR data than those in UWM/COADS data. On the other hand, in the Intertropical Convergence Zone (ITCZ) area the wind stress values in NCEP/NCAR data are slightly weaker than those in UWM/COADS data. In the South Atlantic, between 20° S–40°S, the QuikSCAT dataset presents complex circulation structures which are not present in NCEP/NCAR and UWM/COADS data. The wind stress is used in a numerical ocean model to simulate ocean currents, which are compared to a drifting-buoy observed climatology. The modeled South Equatorial Current agrees better with observations between March–May and June–August. Between December–February, the South Equatorial Current from UWM/COADS and QuikSCAT experiments is stronger and more developed than that from NCEP/NCAR experiment. The Brazil Current, in turn, is better represented in the QuikSCAT experiment. Comparison of the annual migration of ITCZ at 20° and 30°W in UWM/COADS and NCEP/NCAR data sources show that the southernmost position of ITCZ at 30°W in February, March and April coincides with the rainy season in NE Brazil, while the northernmost position of ITCZ at 20°W in August coincides with the maximum rainfall of Northwest Africa.     

Spectral characteristics of quasi-biennial oscillations of the equatorial stratospheric wind and the problem of synchronization

Spectral characteristics of the quasi-biennial oscillations (QBO) of the zonal velocity in the equatorial stratosphere are investigated in this work on the basis of data from the NCEP/NCAR and ERA40 reanalyses and numerical experiments with the atmospheric general circulation (GCM) model developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS). The problem of synchronizing QBO and semiannual oscillations (SAO) of the zonal velocity in the mesosphere is considered. It is shown that the process of synchronization to multiples of SAO periods is identifiable in the transition region between QBO and SAO. For all heights where QBO exist, their synchronization with SAO is expressed in the calculation of the period in terms of differences between the westerly maxima. The INM RAS GCM model is shown to satisfactorily reproduce the main spectral characteristics of QBO and SAO, as well as specific features of the variability of the QBO period obtained from reanalysis data. The possibility of synchronization with SAO or the annual cycle in the upper layers is shown on the basis of an investigation of QBO models with a small number of parameters, both for the absorption mechanism of planetary waves by the mean flow and for the breaking of short gravity waves. The QBO formation from different wave types, together with SAO and the annual cycle, can be considered a unified system of oscillations in the circulation of the equatorial upper atmosphere.     

Estimates of the sensitivity of cyclonic activity in the troposphere of extratropical latitudes to changes in the temperature regime

Quantitative estimates of the sensitivity of the number and size of extratropical cyclones in the Northern Hemisphere to changes in the surface temperature are obtained with the use of NCEP/NCAR reanalysis data over a 60-year period and are compared with estimates on the basis of a relatively simple model of the cyclonic and anticyclonic activities in the atmosphere of extratropical latitudes associated with characteristics of atmospheric temperature stratification (MMPKh model). The model estimates are also obtained for a dry and moist atmosphere. With the use of the reanalysis data, extratropical latitudes are, on the whole, characterized by a general decrease in the number of cyclones and the density of their packing in extratropical latitudes as the surface temperature increases. However, in the MMPKh model for moist atmosphere, estimates of the parameter of sensitivity of the number of cyclones at midlatitudes and at extratropical latitudes in the Northern Hemisphere as a whole are close to those based on the reanalysis data. The influences of the meridional gradient of the surface temperature and the vertical temperature gradient in the troposphere on changes in the number and size of extratropical cyclones are estimated from the reanalysis data and model calculations. It is noted that the most significant changes in annual mean variations in the number and size of extratropical cyclones are associated with the vertical temperature gradient in the troposphere. In this case, an increase in the vertical temperature gradient in the troposphere decreases the size of cyclones. The relative influences of the vertical and meridional temperature gradients are different for different latitudinal zones.     

Coupled simulation of climate and vegetation dynamics

Experiments are performed with the climate model of the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), integrated jointly with the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). It is shown that the coupled model reproduces the distribution of basic plant functional types around the world quite well. In simulations of climate for the 21st century, this model predicts changes in dominant plant types and in the total area occupied by vegetation regionally. However, it does not reproduce the significant inverse influence that vegetation succession has on the simulated climate.     

On the relation of the number of extratropical cyclones to their sizes

Extratropical cyclones were identified on the basis of sea level pressure NCEP/NCAR reanalysis data for the Northern Hemisphere from 1948 to 2004. Cyclone positions were determined with a time interval of 6 h. Cyclone sizes were obtained with the use of a numerical scheme based on a rotation of the spherical coordinate system such that the pole of the new coordinate system coincided with the cyclone center. Cyclone sizes were determined at each step of the trajectory. The last closed isobar was assumed to be the outer boundary of the cyclone. The pressure deficit in the cyclone center was regarded as a characteristic of the intensity of a synoptic formation. The interrelation between the number of cyclones and their sizes was estimated for all extratropical cyclones of the Northern Hemisphere regardless of the stage of their development. The number of cases being analyzed is 1.5 × 10⁶. Cyclone areas vary from 0.13 × 10⁶ to 6.4 × 10⁶ km², and 80% of extratropical cyclones have an intensity of 1–15 hPa. The distribution of the number of cyclones depending on their intensities is shown to be of an exponential character. The distributions of the number of cyclones were approximated with a very high accuracy, so that the regularities obtained are very stable during the past several decades.     

Simulation of the quasi-biennial oscillations of the zonal wind in the equatorial stratosphere: Part II. Atmospheric general circulation models

The problem of simulating quasi-biennial oscillations (QBOs) of zonal velocity in the equatorial stratosphere in atmospheric general circulation models is considered. In accordance with the results from Part I of this study on the basis of the models developed at the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS), the possibility of implementing (in these models) mechanisms of QBO excitation through both the interaction of planetary waves with the mean flow and breaking of short gravity waves is investigated. A new high-resolution 2° × 2.5° × 80 version of the INM RAS model is designed, a climate simulation with the two 2° × 2.5° × 39 and 2° × 2.5° × 80 versions of the INM RAS model is briefly described, results of spectral analysis of equatorial wave activity are presented, and the QBO formation processes in these models are considered in detail. For the new 2° × 2.5° × 80 model, realistic QBOs of zonal wind are obtained as the result of the action of both mechanisms.     

Modeling the water circulation in the North Atlantic in the scope of the CORE-II experiment

A numerical experiment on the reproduction of the variability in the state of North Atlantic water in 1948–2007 with a spatial resolution of 0.25° has been performed using the global ocean model developed at Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), and the Shirshov Institute of Oceanology (IO RAS) (the INM–IO model). The data on the state of the atmosphere, radiation fluxes, and bulk formulas of the CORE-II protocol are used as boundary conditions. Five successive 60-year calculation cycles have been performed in order to obtain the quasi-equilibrium state of a model ocean. For the last 20 years, the main elements of large-scale ocean circulation have been analyzed and compared with the WOA09 atlas data and the results of other models.     

黄海雾季开始日期的确定及其年际变化

根据山东省14个气象站1979—2007年4次/d的大气能见度观测资料、NCEP/NCAR再分析资料、JRA等资料,提出了黄海雾季开始时间的以候为时间尺度的标准,并对影响雾季开始的可能因素进行了分析。结果表明:黄海气候平均雾季开始在第20候,从此候开始,盛行风向、湿度平流、温度平流、大气层结等都有利于海雾的产生;不同年份雾季开始的时间有差别,导致不同年份雾季开始早晚的主要原因是海-气温差、湿度、盛行风;黄东海海温正(负)距平,且东海北部黄海南部海温正(负)距平比黄海北部海温正(负)距平强度更大时,黄海北部雾季开始时间较早(晚)。海-气温差<0℃是海雾季节开始的先决条件,但对海雾季节开始的早晚没有明显的影响。黄海反气旋对大气层结的稳定有一定的贡献,有利于雾的形成和维持。逆温对于雾季的形成和维持有重要作用,但逆温强度与雾季开始的早晚没有直接关系;逆温层的高度可能影响海雾季节的发生,雾季开始偏早年逆温层更接近地面。     

两个同源地不同路径热带气旋的大尺度场对比分析

本文利用NCEP/NCAR再分析格点资料,着重对8903号"BRENDA"和0601号"珍珠"两个同源地进入南海后不同路径的典型热带气旋的大尺度环境场进行对比分析。结果表明:西风槽的强弱和东移的快慢、西太平洋副高的形状变化和东退西进、冷空气的强弱和南下路径及热带气旋内部的不对称结构是造成二者移动路经差异的主要原因。另,印缅槽的变化也对其路径差异有一定的作用。     

Influence of direct sulfate-aerosol radiative forcing on the results of numerical experiments with a climate model of intermediate complexity

The climate model of intermediate complexity developed at the Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) is extended by a block for the direct anthropogenic sulfate-aerosol (SA) radiative forcing. Numerical experiments have been performed with prescribed scenarios of the greenhouse and anthropogenic sulfate radiative forcings from observational estimates for the 19th and 20th centuries and from SRES scenarios A1B, A2, and B1 for the 21st century. The globally averaged direct anthropogenic SA radiative forcing F _ASA by the end of the 20th century relative to the preindustrial state is ?0.34 W/m², lying within the uncertainty range of the corresponding present-day estimates. The absolute value of F _ASA is the largest in Europe, North America, and southeastern Asia. A general increase in direct radiative forcing in the numerical experiments that have been performed continues until the mid-21st century. With both the greenhouse and the sulfate loadings included, the global climate warming in the model is 1.5–2.8 K by the end of the 21st century relative to the late 20th century, depending on the scenario, and 2.1–3.4 K relative to the preindustrial period. The sulfate aerosol reduces global warming by 0.1–0.4 K in different periods depending on the scenario. The largest slowdown (>1.5 K) occurs over land at middle and high latitudes in the Northern Hemisphere in the mid-21st century for scenario A2. The IAP RAS CM response to the greenhouse and the aerosol forcing is not additive.     

阿拉伯海热带气旋生成特征分析

利用印度气象局（India Meteorological Department,IMD）、国际气候管理最佳路径档案库（International Best Track Archive for Climate Stewardship,IBTrACS）提供的1982—2020年阿拉伯海热带气旋路径资料,美国国家环境预报中心（National Centers for Environmental Prediction,NCEP）再分析资料,对近39 a阿拉伯海热带气旋源地和路径特征、活跃区域、频数及气旋累积能量（accumulated cyclone energy,ACE）指数的季节特征和年际变化特征进行分析,并结合环境因素,说明其物理成因。结果表明：阿拉伯海热带气旋多发于10°~25°N,65°~75°E海域,5—6月、9—12月发生频数较高且强度较强,1—4月、7—8月发生频数较低且气旋近中心最大风速均小于35 kn;频数的季节变化主要受控于垂直风切变要素;阿拉伯海热带气旋发生频数和ACE近年有上升趋势,年际变化主要受控于海面温度（sea surface temperature,SST）和850 hPa相对湿度要素。     

Statistical characteristics of cyclones and anticyclones over the Black Sea in the second half of the 20th century

By using the NCEP reanalysis data for 1952–2000, we estimate the parameters of cyclones and anticyclones in the Black-Sea region and evaluate the statistical characteristics of their variability for each season. It is shown that the frequency of cyclones decreases in all seasons (except summer) as a result of the intensification of the North Atlantic Oscillation in the 1960–90s and the displacement of the predominant paths of synoptic disturbances to the north. For anticyclones, we reveal the opposite trend. The parameters of cyclones and anticyclones are characterized by quasiperiodic variations on the subdecadal scale also induced by the North Atlantic Oscillation. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 47–58, November–December, 2007.     

Methane cycle in the INM RAS climate model

The atmosphere-ocean general circulation model with the carbon cycle is coupled to a model of methane evolution, in which methane sources in the soil of wetlands and methane evolution in the atmosphere are calculated. A numerical experiment on the simulation of climate and methane-cycle changes in 1860–2100 has been conducted with the model forced by methane emissions prescribed from scenario A1B. The distribution of the sources of methane from soil agrees with the available estimates and amounts to about 240 Mt/year in the 20th century. The methane flux from soil increases to 340 Mt/year by the end of the 21st century. The model adequately reproduces an increase in the atmospheric methane concentration from 800 ppb in 1860 to about 1800 ppb in 2000, but does not produce the observed stabilization of methane concentration in the early 21st century. By 2060, the methane concentration in the model attains 2700 ppb. The increase in atmospheric methane concentration is due mainly to anthropogenic emissions. A similar numerical experiment with fixed sources of methane from soil at the 1860–1900 level suggests that the maximum methane concentration in the model in this case could amount to 2400 ppb. A temperature increase at the end of the 21st century relative to the 19th century is 3.5° for a simulated change in the methane flux from soil and 0.25° less for a fixed methane flux.     

Isopycnal displacements within the Cape Basin thermocline as revealed by the Hydrographic Data Archive

The transfer of upper kilometer water from the Indian Ocean into the South Atlantic, the Agulhas leakage, is believed to be accomplished primarily through meso-scale eddy processes. There have been various studies investigating eddies of the “Cape Basin Cauldron” from specific data sets. The hydrographic data archive acquired during the last century within the Cape Basin region of the South Atlantic provides additional insight into the distribution and water mass properties of the Cape Basin eddies. Eddies are identified by mid-thermocline isopycnal depth anomalies relative to the long-term mean. Positive depth anomalies (the reference isopycnal is deeper than the long-term mean isopycnal depth) mark the presence of anticyclonic eddies; negative anomalies mark cyclonic eddies. Numerous eddies are identified in the whole region; the larger isopycnal displacements are attributed to the energetic eddies characteristic of the Cape Basin and indicate that there is a 2:1 anticyclone/cyclone ratio. Smaller displacements of the less energetic features are almost equally split between anticyclones and cyclones (1.4:1 ratio). Potential temperature, salinity and oxygen relationships at thermocline and intermediate levels within each eddy reveal their likely origin. The eddy core water is not solely drawn from Indian Ocean: tropical and subtropical South Atlantic water are also present. Anticyclones and cyclones carrying Agulhas Water properties are identified throughout the Cape Basin. Anticyclones with Agulhas Water characteristics show a predominant northwest dispersal, whereas the cyclones are identified mainly along the western margin of the African continent, possibly related to their origin as shear eddies at the boundary between the Agulhas axis and Africa. Cyclones and anticyclones carrying pure South Atlantic origin water are identified south of 30°S and west of the Walvis Ridge. Tropical Atlantic water at depth is found for cyclones north of the Walvis Ridge, west of 10°E and for stations deeper than 4000 m, and a few anticyclones with the same characteristics are found south of the ridge.     

Estimation of the uncertainty of future changes in atmospheric carbon dioxide concentration and its radiative forcing

An ensemble experiment with the IAP RAS CM was performed to estimate future changes in the atmospheric concentration of carbon dioxide, its radiative forcing, and characteristics of the climate-carbon cycle feedback. Different ensemble members were obtained by varying the governing parameters of the terrestrial carbon cycle of the model. For 1860–2100, anthropogenic CO₂ emissions due to fossil-fuel burning and land use were prescribed from observational estimates for the 19th and 20th centuries. For the 21st century, emissions were taken from the SRES A2 scenario. The ensemble of numerical experiments was analyzed via Bayesian statistics, which made the uncertainty range of estimates much narrower. To distinguish between realistic and unrealistic ensemble members, the observational characteristics of the carbon cycle for the 20th century were used as a criterion. For the given emission scenario, the carbon dioxide concentration expected by the end of the 21st century falls into the range 818 ± 46 ppm (an average plus or minus standard deviation). The corresponding global instantaneous radiative forcing at the top of the atmosphere (relative to the preindustrial state) lies in the uncertainty range 6.8 ± 0.4 W m^?2. The uncertainty range of the strength of the climate-carbon cycle feedback by the end of the 21st century reaches 59 ± 98 ppm in terms of the atmospheric carbon dioxide concentration and 0.4 ± 0.7 W m^?2 in terms of the radiative forcing.     

Changes in climatic characteristics of Northern Hemisphere extratropical land in the 21st century: Assessments with the IAP RAS climate model

Assessments of future changes in the climate of Northern Hemisphere extratropical land regions have been made with the IAP RAS climate model (CM) of intermediate complexity (which includes a detailed scheme of thermo- and hydrophysical soil processes) under prescribed greenhouse and sulfate anthropogenic forcing from observational data for the 19th and 20th centuries and from the SRES B1, A1B, and A2 scenarios for the 21st century. The annual mean warming of the extratropical land surface has been found to reach 2–5 K (3–10 K) by the middle (end) of the 21st century relative to 1961–1990, depending on the anthropogenic forcing scenario, with larger values in North America than in Europe. Winter warming is greater than summer warming. This is expressed in a decrease of 1–4 K (or more) in the amplitude of the annual harmonic of soil-surface temperature in the middle and high latitudes of Eurasia and North America. The total area extent of perennially frozen ground S _p in the IAP RAS CM changes only slightly until the late 20th century, reaching about 21 million km², and then decreases to 11–12 million km² in 2036–2065 and 4–8 million km² in 2071–2100. In the late 21st century, near-surface permafrost is expected to remain only in Tibet and in central and eastern Siberia. In these regions, depths of seasonal thaw exceed 1 m (2 m) under the SRES B1 (A1B or A2) scenario. The total land area with seasonal thaw or cooling is expected to decrease from the current value of 54–55 million km² to 38–42 in the late 21st century. The area of Northern Hemisphere snow cover in February is also reduced from the current value of 45–49 million km² to 31–37 million km². For the basins of major rivers in the extratropical latitudes of the Northern Hemisphere, runoff is expected to increase in central and eastern Siberia. In European Russia and in southern Europe, runoff is projected to decrease. In western Siberia (the Ob watershed), runoff would increase under the SRES A1B and A2 scenarios until the 2050s–2070s, then it would decrease to values close to present-day ones; under the anthropogenic forcing scenario SRES B1, the increase in runoff will continue up to the late 21st century. Total runoff from Eurasian rivers into the Arctic Ocean in the IAP RAS CM in the 21st century will increase by 8–9% depending on the scenario. Runoff from the North American rivers into the Arctic Ocean has not changed much throughout numerical experiments with the IAP RAS CM.     

Sensitivity of amplitude-phase characteristics of the surface air temperature annual cycle to variations in annual mean temperature

The ERA40 and NCEP/NCAR data over 1958–1998 were used to estimate the sensitivity of amplitude-phase characteristics (APCs) of the annual cycle (AC) of the surface air temperature (SAT) T _s. The results were compared with outputs of the ECHAM4/OPYC3, HadCM3, and INM RAS general circulation models and the IAP RAS climate model of intermediate complexity, which were run with variations in greenhouse gases and sulfate aerosol specified over 1860–2100. The analysis was performed in terms of the linear regression coefficients b of SAT AC APCs on the local annual mean temperature and in terms of the sensitivity characteristic D = br ², which takes into account not only the linear regression coefficient but also its statistical significance (via the correlation coefficient r). The reanalysis data were used to reveal the features of the tendencies of change in the SAT AC APCs in various regions, including areas near the snow-ice boundary, storm-track ocean regions, large desert areas, and the tropical Pacific. These results agree with earlier observations. The model computations are in fairly good agreement with the reanalysis data in regions of statistically significant variations in SAT AC APCs. The differences between individual models and the reanalysis data can be explained, in particular, in terms of the features of the sea-ice schemes used in the models. Over the land in the middle and high latitudes of the Northern Hemisphere, the absolute values of D for the fall phase time and the interval of exceeding exhibit a positive intermodel correlation with the absolute value of D for the annual-harmonic amplitude. Over the ocean, the models reproducing larger (in modulus) sensitivity parameters of the SAT annual-harmonic amplitude are generally characterized by larger (in modulus) negative sensitivity values of the semiannual-harmonic amplitude T _{s, 2}, especially at latitudes characteristic of the sea-ice boundary. In contrast to the averaged fields of AC APCs and their interannual standard deviations, the sensitivity parameters of the SAT AC APCs on a regional scale vary noticeably for various types of anthropogenic forcing.     

Simulation of characteristics of thermal and hydrologic soil regimes in equilibrium numerical experiments with a climate model of intermediate complexity

The IAP RAS CM (Institute of Atmospheric Physics, Russian Academy of Sciences, climate model) has been extended to include a comprehensive scheme of thermal and hydrologic soil processes. In equilibrium numerical experiments with specified preindustrial and current concentrations of atmospheric carbon dioxide, the coupled model successfully reproduces thermal characteristics of soil, including the temperature of its surface, and seasonal thawing and freezing characteristics. On the whole, the model also reproduces soil hydrology, including the winter snow water equivalent and river runoff from large watersheds. Evapotranspiration from the soil surface and soil moisture are simulated somewhat worse. The equilibrium response of the model to a doubling of atmospheric carbon dioxide shows a considerable warming of the soil surface, a reduction in the extent of permanently frozen soils, and the general growth of evaporation from continents. River runoff increases at high latitudes and decreases in the subtropics. The results are in qualitative agreement with observational data for the 20th century and with climate model simulations for the 21st century.     

海-气界面热通量算法的研究及在中国近海的应用

对计算海-气界面湍流热通量的Bulk算法的一些参数进行了改进。使用西沙实测资料、GSSTF2资料和NCEP/NCAR再分析资料以及改进后的算法,计算了中国近海地区的感热通量、潜热通量。计算结果与西沙实测资料、长年代的GSSTF2资料和NCEP/NCAR再分析资料进行比较验证,证明改进后的方法精度较高,基本可以保证湍流热通量的平均标准偏差在10W/m2左右,与多年的月平均做比较,相对偏差为25%左右;同时,不仅首次将计算热通量的空间尺度精确到0·1°×0·1°,而且基本模拟出了南海季风暴发期间热通量变化的主要特点以及中国近海热通量随季节、纬度和海岸地形的变化特征。