Interdecadal Variability of the East Asian Summer Monsoon and Associated Atmospheric Circulations

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.

Dynamic and Thermodynamic Features of Low and Middle Clouds Derived from Atmospheric Radiation Measurement Program Mobile Facility Radiosonde Data at Shouxian, China

By using the radiosonde measurements collected at Shouxian,China,we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels.The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers.The maximum balloon ascent speed（5.3 m s^-1） was located in the vicinity of the layer with the maximum cloud occurrence frequency（24.4%）,indicating an upward motion（0.1-0.16 ms^-1）.The average thickness,magnitude and gradient of the temperature inversion layer above single-layer clouds were117±94 m,1.3±1.3℃ and 1.4±1.5℃（100 m）^-1,respectively.The average temperature inversion magnitude was the same（1.3℃） for single-low and single-middle clouds;however,a larger gradient[1.7±1.8℃（100 m）^-1]and smaller thickness（94±67 m） were detected above single-low clouds relative to those above single-middle clouds[0.9±0.7℃（100 m）^-1 and157±120 m].For the two-layer cloud,the temperature inversion parameters were 106±59 m,1.0±0.9℃ and 1.0±1.0℃（100 m）^-1 above the upper-layer cloud and 82 ± 60 m,0.6±0.9℃ and 0.7±0.6℃（100 m）^-1 above the low-layer cloud.Absolute differences between the cloud-base height（cloud-top height） and the lifting condensation level（equilibrium level）were less than 0.5 km for 66.4%（36.8%） of the cases analyzed in summer.

Atmospheric Circulation Cells Associated with Anomalous East Asian Winter Monsoon

Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon （EAWM） were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell （ZWC） in the tropic, the Hadley cell in the western Pacific （WPHC）, the midlatitude zonal cell （MZC） over the central North Pacific, and the Hadley cell in the eastern Pacific （EPHC）] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly （SSTA）.

Modeling Aerosol Climate Effects over Monsoon Asia:A Collaborative Research Program

This paper describes the latest progress of a collaborative research program entitled ＂Modeling Aerosol Climate Effects over Monsoon Asia＂, under the Climate Sciences agreement between the U.S. Department of Energy and the Chinese Academy of Sciences（in the early 1980 s, Professor Duzheng YE played a critical role in leading and formalizing the agreement）. Here, the rationale and approach for pursuing the program, the participants, and research activities of recent years are first described, and then the highlights of the program＇s key findings and relevant scientific issues, as well as follow-up studies, are presented and discussed.

中国东北地区17世纪后期的自然植被格局

通过整理、分析历史文献中的自然植被记录,复原了中国东北地区近代大规模农垦前(17世纪后期)的自然植被格局。结果表明,当时的主导植被类型是森林和草地,森林主要分布于山区,其中大兴安岭北端主要是寒温带落叶针叶林,长白山南端主要是温带落叶阔叶林,其余山区是针阔混交林,草地主要分布于东北平原和内蒙古高原,林-草的分界线与地表等高线有很好的对应关系;在三江平原分布有大面积的沼泽。潜在植被格局与历史自然植被格局基本一致,但是林-草分界线有明显差异,且潜在植被图中没有沼泽。

高效率颗粒物微物理模型简介与重污染过程应用分析

中国细颗粒物(PM2.5)导致的空气污染和雾霾天气问题越来越突出,在低层对流层中很多地方都有显著的二次颗粒物生成过程,因此对颗粒物物理化学转化过程的研究具有重要意义,其转化过程对空气质量模式模拟和预报的准确性有重要影响。高效率颗粒物微物理(APM)模型经过近20多年的研究和发展,在全球化学传输模型(GEOS-Chem)、区域性气象和化学预报模型(WRF-Chem)通用地球系统模型(CESM-CAM5)等气象及环境空气质量预报模型中取得了很好的应用验证,能够在全球/区域等不同尺度对粒子生成、长大、凝聚、消除等微物理过程以及气溶胶光学厚度(AOD)、直接/间接辐射强迫等进行模拟。应用GEOS-Chem-APM模式模拟了2014年2月京津冀区域的重污染过程。结果显示,湿度模拟的准确性对其他物理和污染物浓度等模拟结果有重要作用;2月20—26日的重污染过程模拟结果与实际观测较为吻合,主要污染特点是较高的湿度(90%以上),同时,二次颗粒物和包裹了二次物种的一次颗粒物(黑碳/有机碳)是低能见度的最大贡献者。

云三维结构对加热率廓线及通量影响的模拟

大气加热率强度与结构是驱动全球大气环流的关键因素,实际加热率分布与云三维结构密切相关。作者使用三维蒙特卡洛辐射传输模式,模拟计算了云分辨模式所得3个典型三维云场的加热率廓线及通量;定义了两个参数来同时描述加热率廓线的垂直分布和强度,通过与独立像素近似算法对比,定量统计分析了高分辨率下云三维结构对辐射的影响。结果表明,在高分辨率条件下云三维结构对加热率廓线和通量影响十分显著,且不同结构云场所体现的影响各具特点,提出需要考察现有大气模式中云三维结构对当前所用加热率计算方案的订正方向。

Agriculture Development-induced Surface Albedo Changes and Climatic Implications Across Northeastern China

To improve the understandings on regional climatic effects of past human-induced land cover changes,the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years,and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains.As a consequence,in the Northeast China Plain,the surface net radiation increased by 4-8 W/m 2,2-5 W/m 2,and 1-3 W/m 2,and the climate was therefore warmed by 0.1℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ in the spring,autumn and winter,respectively.In the surrounding mountain area,the net radiation decreased by less than 1.5 W/m 2,and the climate was therefore cooled too slight to be detected.In summer,effects of surface albedo changes on climate were closely associated with moisture dynamics,such as evapotranspiration and cloud,instead of being merely determined by surface radiation budget.The simulated summer climatic effects have large uncertainties.These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.

A Polarized Radiative Transfer Model Based on Successive Order of Scattering

Based on Successive Order of Scattering approach, a full Vector Radiative Transfer model （SOSVRT） for vertically inhomogeneous plane-parallel media has been developed. To overcome the computational burdens of convergence, a simple approximation technique by truncating scattering orders with a geometric series is used to reduce computational time. Analytical Fourier decomposition of phase matrix with three symmetry relationships and two mutual inverse operators have been implemented to further improve the computational efficiency. To improve the accuracy, a post-processing procedure is implemented to accurately interpolate the Stokes vector at arbitrary angles. Comparisons with the benchmarks for an atmosphere of randomly orientated oblate spheroids show excellent agreement for each Stokes parameter （within 0.1%）. SOSVRT has been tested for different atmospheric condition against RT3, which is based on doubling-adding method, and the results prove that SOSVRT is accurate and much more efficient in vector radiative transfer modeling, especially for optical thin atmosphere, which is the most common case in polarized radiative transfer simulations. SOSVRT is written in Fortran 90 and the code is freely accessible by contacting the author.

Temperature and Precipitation Changes in China During the Holocene

We review here proxy records of temperature and precipitation in China during the Holocene, especially the last two millennia. The quality of proxy data, methodology of reconstruction, and uncertainties in reconstruction were emphasized in comparing different temperature and precipitation reconstruction and clarifying temporal and spatial patterns of temperature and precipitation during the Holocene. The Holocene climate was generally warm and wet. The warmest period occurred in 9.6-6.2 cal ka BP, whereas a period of maximum monsoon precipitation started at about 11.0 cal ka BP and lasted until about 8.0-5.0 cal ka BP. There were a series of millennial-scale cold or dry events superimposed on the general trend of climate changes. During past two millennia, a warming trend in the 20th century was clearly detected, but the warming magnitude was smaller than the maximum level of the Medieval Warm Period and the Middle Holocene. Cold conditions occurred over the whole of China during the Little Ice Age （AD 1400-AD 1900）, but the warming of the Medieval Warm Period （AD 900-AD 1300） was not distinct in China, especially west China. The spatial pattern of precipitation showed significant regional differences in China, especially east China. The modern warm period has lasted 20 years from 1987 to 2006. Bi-decadal oscillation in precipitation variability was apparent over China during the 20th century. Solar activity and volcanic eruptions both were major forcings governing the climate variability during the last millennium.

A Study on Sulfate Optical Properties and Direct Radiative Forcing Using LASG-IAP General Circulation Model

The direct radiative forcing （DRF） of sulfate aerosols depends highly on the atmospheric sulfate loading and the meteorology, both of which undergo strong regional and seasonal variations. Because the optical properties of sulfate aerosols are also sensitive to atmospheric relative humidity, in this study we first examine the scheme for optical properties that considers hydroscopic growth. Next, we investigate the seasonal and regional distributions of sulfate DRF using the sulfate loading simulated from NCAR CAM-Chem together with the meteorology modeled from a spectral atmospheric general circulation model （AGCM） developed by LASG-IAP. The global annual-mean sulfate loading of 3.44 mg m-2 is calculated to yield the DRF of -1.03 and -0.57 W m-2 for clear-sky and all-sky conditions, respectively. However, much larger values occur on regional bases. For example, the maximum all-sky sulfate DRF over Europe, East Asia, and North America can be up to -4.0 W m-2. The strongest all-sky sulfate DRF occurs in the Northern Hemispheric July, with a hemispheric average of -1.26 W m-2. The study results also indicate that the regional DRF are strongly affected by cloud and relative humidity, which vary considerably among the regions during different seasons. This certainly raises the issue that the biases in model-sinmlated regional meteorology can introduce biases into the sulfate DRF. Hence, the model processes associated with atmospheric humidity and cloud physics should be modified in great depth to improve the simulations of the LASG-IAP AGCM and to reduce the uncertainty of sulfate direct effects on global and regional climate in these simulations.

EFFECTS OF CONDENSATION HEATING AND SURFACE FLUXES ON THE DEVELOPMENT OF A SOUTH CHINA MESOSCALE CONVECTIVE SYSTEM (MCS)

A sensitive numerical simulation study is carried out to investigate the effects of condensation heating and surface fluxes on the development of a South China MCS that occurred during 23 – 24 May 1998. The results reveal the following: (1) Condensation heating plays an important role in the development of MCS. In every different stage, without condensation heating, MCS precipitation is significantly reduced, and quickly dissipates. (2) Condensation heating demonstrates most importantly during the early development stages of MCS vortex; as the vortex develops stronger, the condensation heating effects reduces. (3) By affecting the MCS development processes, condensation heating also influences the formation of MCS mesoscale environment structure features such as low-level jet (mLLJ), upper-level divergence. (4) By changing the antecedent environmental circulation, the surface fluxes also play an important role in the development of MCS. Because of the surface heating, pressure declines over the heavy rainfall and MCS happening regions, which results in the intensification of southerly flows from the ocean along the South China coastline areas, and leads to the enhancement of horizontal convergence and increase of vapor amount in the lower layer. All of these make the atmosphere more unstable and more favorable for the convection.

SIMULATION STUDY ON CAUSES OF TROPICAL STORM FITOW (0114) HEAVY RAIN

With PSU/NCAR nonhydrostatic mesoscale model MM5, the rainfall process of tropical storm Fitow(0114) is simulated for 00:00 UTC 31 Aug. – 00:00 UTC 2 Sept. 2001. Mesoscale separation is performed on the results with the filtering scheme. Analyses show that the MM5 model well reproduced the position and intensity of heavy rain. Mesoscale characteristics of heavy rain were well represented in rainfall time scale, rainfall area, stream field and divergence at lower and upper levels. The interaction between inverted typhoon troughs and the mesoscale systems lead to heavy rain occurrence. The distribution of divergence fields at lower and upper levels can have a kind of indication for the rainfall. Heavy rains are closely associated with topography and land-sea distribution in South China. Weak instability is favorable to the generation of heavy rain.

A Differential Optical Absorption Spectroscopy Method for X_(CO_2) Retrieval from Ground-Based Fourier Transform Spectrometers Measurements of the Direct Solar Beam

A differential optical absorption spectroscopy （DOAS）-like algorithm is developed to retrieve the column-averaged dry- air mole fraction of carbon dioxide from ground-based hyper-spectral measurements of the direct solar beam. Different to the spectral fitting method, which minimizes the difference between the observed and simulated spectra, the ratios of multiple channel-pairs--one weak and one strong absorption channel--are used to retrieve Xc02 from measurements of the shortwave infrared （SWIR） band. Based on sensitivity tests, a super channel-pair is carefully selected to reduce the effects of solar lines, water vapor, air temperature, pressure, instrument noise, and frequency shift on retrieval errors. The new algorithm reduces computational cost and the retrievals are le^s sensitive to temperature and H20 uncertainty than the spectral fitting method. Multi-day Total Carbon Column Observing Network （TCCON） measurements under clear-sky conditions at two sites （Tsukuba and Bremen） are used to derive Xc02 for the algorithm evaluation and validation. The DOAS-like results agree very well with those of the TCCON algorithm after correction of an airmass-dependent bias.

LASG Global AGCM with a Two-moment Cloud Microphysics Scheme:Energy Balance and Cloud Radiative Forcing Characteristics

Cloud dominates influence factors of atmospheric radiation, while aerosol–cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment(mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model(FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing(CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere(TOA) and at the Earth’s surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2(1%) and 3 W m-2(3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region(AMR). The results indicate that FAMIL1.1 well reproduces the summer–winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.

花粉记录的青藏高原中部中全新世以来植被与环境

青藏高原中部的草甸/草原混合生态群落,对气候变化非常敏感.孢粉记录显示草原发育时期,莎草减少,区域气候是相对干旱的,在时间上对应季风相对弱的时期.依据唐古拉山垭口湖、阿洪错和错那3个淡水湖泊钻孔孢粉分析,定量重建的温度和降水指标,探讨该地区8200 cal a BP以来的植被与气候变化.8200～6500 cal a BP,尤其是8200～7200 cal a BP,植被以草甸/草原混合生态群落为主,显示强季风控制着青藏高原中部;6000～4900,4400～3900以及2800～2400 cal a BP时期区域植被以草原植被为主,应是3次百年尺度的干旱事件;4900～4400 cal a BP期间植被类型由草原向草甸转变;6500～5400和3000～1600 cal a BP出现两次大的变干事件;数值摸拟估计,高原中部接近于现今的环境,最早可能出现在6500cal a BP,自3000cal a BP以后高原中部季风性降水和湿度逐渐减少至现今水平,可能在700～300cal a BP出现一次小冰期变冷事件.

A modeling study of aerosol effects on cloud radiative property and precipitation

A two-moment (mass and number) warm cloud scheme together with ground and aircraft measurements over Beijing is used in a regional model to study the effects of aerosols on cloud radiative property and precipitation.Using a prescribed tri-modal lognormal aerosol size distribution,the aerosol numbers are calculated from prognostic aerosol masses,for which advection,diffusion,and cloud drop activation/deactivation are considered.Specifically,the accumulation mode of a tri-lognormal aerosol size distribution is fitted to the aircraft measured values for a cold front case passed through northern China during June 25-26,2005.In the simulations,the warm cloud scheme simulates explicitly the cloud drops and subsequently affects the radiative heating and cooling,and circulations.Simulations with different initial conditions for being fitted with aircraft measurements,continental and maritime aerosol numbers were conducted.It is found that more aerosols result in more but smaller cloud drops and more cloud water,leading to an increase in albedo.The effects on rains are complex:smaller cloud drops have less efficient coagulation for raindrop to form (autoconversion),leading to fewer raindrop numbers and less rainwater;while more cloud water enhances the accretion for raindrop growth.Nevertheless,for the whole cloud system,the impact of increasing aerosols inhibits precipitation.

有机胺对我国典型城市大气中的大气新粒子形成的重要作用

大气新粒子形成事件对大气中颗粒物的数浓度有着显著贡献,对人体健康、云和降水特性、区域乃至全球气候变化有着重要影响.明确大气中新粒子形成机制有助于更为合理地量化评估大气粒子的环境和气候效应及污染物排放变化的影响.近年来,在实验室内开展的相对洁净大气状态下的新粒子形成机制有很大研究进展.

A DIAGNOSTIC STUDY OF FEEDBACK MECHANISM IN GREENHOUSE EFFECTS SIMULATED BY NCAR CCM1

This paper describes a diagnostic study of the feedback mechanism in greenhouse effects of increased CO_2 and oth- er trace gases(CH_4,N_2O and CFCs),simulated by general circulation model.The study is based on two sensitivity exper- iments for doubled CO_2 and the inclusion of other trace gases,respectively,using version one of the community climate model(CCM1)developed at the National Centre for Atmospheric Research.A one-dimensional(1-D)and a two-dimensional(2-D)radiative-convective models are used to diagnose the feedback effect.It shows that the feedback factors in global and annual mean conditions are in the sequence of surface albedo,water vapor amount,water vapor distribution,cloud height,critical lapse rate and cloud cover,while in zonal and annual mean conditions in the tropical region the above sequence does not change except the two water vapor terms being the largest feedback compo- nents.Among the feedback components,the total water vapor feedback is the largest(about 50%).The diagnosis also gives a very small feedback of either the cloud cover or the lapse rate,which is substantially different from the 1-D feedback analysis by Hansen et al.(1984).The small lapse rate feedback is considered to be partly caused by the convective adjustment scheme adopted by CCM1 model. The feedback effect for doubled CO_2 is very different from that of the addition of other trace gases because of their different vertical distributions of radiative forcing although the non-feedback responses of surface air temperature for both cases are almost the same.For instance,the larger forcing at surface by the addition of other trace gases can cause stronger surface albedo feedback than by doubled CO_2.Besides,because of the negative forcing of doubled CO_2 in the stratosphere,cloud height feedback is more intense.The larger surface forcing in the case of other trace gases can also in- fluence atmospheric water vapor amount as well as the water vapor distribution,which will in turn have stronger feedback effects.All these indicate that it is incorrect to use“effective CO_2”to replace other trace gases in the general circulation model.

Carbonaceous aerosol in ambient air: Parallel measurements between water cyclone and carbon analyzer

A water cyclone,developed to collect and preserve biological aerosols in a small liquid flow,was interfaced with a total organic carbon analyzer to measure the aerosol organic and inorganic carbon fractions.The total carbon was compared against parallel measurements of elemental carbon (EC) and organic carbon (OC) using a Sunset Real Time ECOC Analyzer between 12-29 January 2009.A National Institute for Occupational Safety and Health (NIOSH) like protocol for the measurements included four temperature steps ending at 840 ℃ for OC under a helium atmosphere followed by two temperature steps ramped to 850 ℃ for EC in a helium-oxygen atmosphere,Carbon data comparison between the water cyclone-TOC and the TOC measured by the analyzer indicated good agreement (r2 =0.82,linear regression slope =0.98,p < 0.001).Analyses of the relationship between total water organic carbon and OC,investigated using data sets from case studies spanning two different events,suggested it was possible to distinguish between the primary and secondary sources.