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2013 Vol. 30, No. 1

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Model Evidence for Interdecadal Pathway Changes in the Subtropics and Tropics of the South Pacific Ocean
ZHANG Rong-Hua, WANG Zhanggui
2013, 30(1): 1-9. doi: 10.1007/s00376-012-2048-1
Numerical simulations using a version of the GFDL/NOAA Modular Ocean Model (MOM 3) are analyzed to demonstrate interdecadal pathway changes from the subtropics to the tropics in the South Pacific Ocean. After the 1976–77 climate shift, the subtropical gyre of the South Pacific underwent significant changes, characterized by a slowing down in its circulation and a southward displacement of its center by about 5o–10o latitude on the western side. The associated circulation altered its flow path in the northwestern part of the subtropical gyre, changing from a direct pathway connecting the subtropics to the tropics before the shift to a more zonal one after. This effectively prevented some subtropical waters from directly entering into the western equatorial Pacific. Since waters transported onto the equator around the subtropical gyre are saline and warm, such changes in the direct pathway and the associated reduction in equatorward exchange from the subtropics to the tropics affected water mass properties downstream in the western equatorial Pacific, causing persisted freshening and cooling of subsurface water as observed after the late 1970s. Previously, changes in gyre strength and advection of temperature anomalies have been invoked as mechanisms for linking the subtropics and tropics on interdecadal time scales. Here we present an additional hypothesis in which geographic shifts in the gyre structure and location (a pathway change) could play a similar role.
Comments on ``Direct Radiative Forcing of Anthropogenic Aerosols over Oceans from Satellite Observation"
Hye-Ryun OH, Chang-Hoi HO, Yong-Sang CHOI
2013, 30(1): 10-14. doi: 10.1007/s00376-012-1218-5
Previous observational studies have estimated anthropogenic aerosol direct radiative forcing over oceans without due consideration of cloudy-sky aerosols. However, when interaction between clouds and aerosols located below or above the cloud level is taken into account, the aerosol direct radiative forcing is larger by as much as 5 W m-2 in most mid-latitude regions in the Northern Hemisphere.
A Regional Ensemble Forecast System for Stratiform Precipitation Events in the Northern China Region. Part II: Seasonal Evaluation for Summer 2010
ZHU Jiangshan, KONG Fanyou, LEI Hengchi
2013, 30(1): 15-28. doi: 10.1007/s00376-012-1043-x
In this study, the Institute of Atmospheric Physics, Chinese Academy of Sciences - regional ensemble forecast system (IAP-REFS) described in Part I was further validated through a 65-day experiment using the summer season of 2010. The verification results show that IAP-REFS is skillful for quantitative precipitation forecasts (QPF) and probabilistic QPF, but it has a systematic bias in forecasting near-surface variables. Applying a 7-day running mean bias correction to the forecasts of near-surface variables remarkably improved the reliability of the forecasts. In this study, the perturbation extraction and inflation method (proposed with the single case study in Part I) was further applied to the full season with different inflation factors. This method increased the ensemble spread and improved the accuracy of forecasts of precipitation and near-surface variables. The seasonal mean profiles of the IAP-REFS ensemble indicate good spread among ensemble members and some model biases at certain vertical levels.
Intraseasonal Oscillation in Global Ocean Temperature Inferred from Argo
HU Ruijin, WEI Meng
2013, 30(1): 29-40. doi: 10.1007/s00376-012-2045-4
The intraseasonal oscillation (ISO; 14--97-day periods) of temperature in the upper 2000 m of the global ocean was studied based on Argo observations from 2003--2008. It is shown that near the surface the ISO existed mainly in a band east of 60oE, between 10oS and 10oN, and the region around the Antarctic Circumpolar Current (ACC). At other levels analyzed, the ISOs also existed in the regions of the Kuroshio, the Gulf Stream, the Indonesian throughflow, the Somalia current, and the subtropical countercurrent (STCC) of the North Pacific. The intraseasonal signals can be seen even at depths of about 2000 m in some regions of the global ocean. The largest amplitude of ISO appeared at the thermocline of the equatorial Pacific, Atlantic and Indian Ocean, with maximum standard deviation (STD) exceeding 1.2oC. The ACC, the Kuroshio, and the Gulf Stream regions all exhibited large STD for all levels analyzed. Especially at 1000 m, the largest STD appeared in the south and southeast of South Africa---a part of the ACC, with a maximum value that reached 0.5oC. The ratios of the intraseasonal temperature variance to the total variance at 1000 m and at the equator indicated that, in a considerable part of the global deep ocean, the ISO was dominant in the variations of temperature, since such a ratio exceeded even 50% there. A case study also confirmed the existence of the ISO in the deep ocean. These results provide useful information for the design of field observations in the global ocean. Analysis and discussion are also given for the mechanism of the ISO.
Transition of Zonal Asymmetry of the Arctic Oscillation and the Antarctic Oscillation at the End of 1970s
LIU Shan, WANG Huijun
2013, 30(1): 41-47. doi: 10.1007/s00376-012-2027-6
In this study, the interdecadal changes in the zonal symmetry of both Arctic Oscillation (AO) and Antarctic Oscillation (AAO) were analyzed. To describe the zonal asymmetry, a local index of AO and AAO was defined using the normalized sea level pressure (SLP) differences between 40o and 65o (latitudes) in both hemispheres. The zonal covariability of local AO and AAO can well represent the zonal symmetry of AO and AAO. Results show that the zonal asymmetry of both AO and AAO significantly changed in the late 1970s. AO was less asymmetric in the zonal direction in the boreal winter season during the latter period, while in the boreal summer it became more asymmetric after 1979. The zonal symmetry of AAO in both austral summer and winter has also significantly decreased since the late 1970s. These changes may imply interdecadal transition in the atmospheric circulation at middle and high latitudes, which is of vital importance to understanding climate variability and predictability across the globe, including the African--Asian--Australian monsoon regions.
Relationship between Bering Sea Ice Cover and East Asian Winter Monsoon Year-to-Year Variations
LI Fei, WANG Huijun
2013, 30(1): 48-56. doi: 10.1007/s00376-012-2071-2
In this study, the relationship between year-to-year variations in the Bering Sea ice cover (BSIC) and the East Asian winter monsoon (EAWM) for the period 1969--2001 was documented. The time series of total ice cover in the eastern Bering Sea correlated with the EAWM index at -0.49, indicating that they are two tightly related components. Our results show that the BSIC was closely associated with the simultaneous local and large-scale atmosphere over the Asian--northern Pacific region. Heavy BSIC corresponded to weaker EAWM circulations and light BSIC corresponded to stronger EAWM circulations. Thus, the BSIC should be considered as one of the possible factors affecting the EAWM variation.
Enhancements of Major Aerosol Components Due to Additional HONO Sources in the North China Plain and Implications for Visibility and Haze
AN Junling, LI Ying, CHEN Yong, LI Jian, QU Yu, TANG Yujia
2013, 30(1): 57-66. doi: 10.1007/s00376-012-2016-9
The Weather Research and Forecasting/Chemistry model (WRF-Chem) was updated by including photoexcited nitrogen dioxide (NO2) molecules, heterogeneous reactions on aerosol surfaces, and direct emissions of nitrous acid (HONO) in the Carbon-Bond Mechanism Z (CBM-Z). Five simulations were conducted to assess the effects of each new component and the three additional HONO sources on concentrations of major chemical components. We calculated percentage changes of major aerosol components and concentration ratios of gas NOy (NOyg) to NOy and particulate nitrates (NO3-) to NOy due to the three additional HONO sources in the North China Plain in August of 2007. Our results indicate that when the three additional HONO sources are included, WRF-Chem can reasonably reproduce the HONO observations. Heterogeneous reactions on aerosol surfaces are a key contributor to concentrations of HONO, nitrates (NO3-), ammonium (NH4+), and PM2.5 (concentration of particulate matter of ≤2.5 μm in the ambient air) across the North China Plain. The three additional HONO sources produced a ~5%–20% increase in monthly mean daytime concentration ratios of NO3-/NOy, a ~15%--52% increase in maximum hourly mean concentration ratios of NO3-/NOy, and a ~10%–50% increase in monthly mean concentrations of NO3- and NH4+ across large areas of the North China Plain. For the Bohai Bay, the largest hourly increases of NO3- exceeded 90%, of NH4+ exceeded 80%, and of PM2.5 exceeded 40%, due to the three additional HONO sources. This implies that the three additional HONO sources can aggravate regional air pollution, further impair visibility, and enhance the incidence of haze in some industrialized regions with high emissions of NOx and particulate matter under favorable meteorological conditions.
The Propagation of Wave Packets and Its Relationship with the Subtropical Jet over Southern China in January 2008
ZUO Qunjie, GAO Shouting, Lü Daren
2013, 30(1): 67-76. doi: 10.1007/s00376-012-1197-6
The propagation of wave packets and its relationship with the subtropical jet was investigated for the period 26–29 January 2008 over southern China using ECMWF Interim re-analysis data. Wave packets propagated from the north to the south side of an upper front with eastward development along the upper front during this period. Due to the eastward development of propagation, the acceleration of geostrophic westerly winds shifted eastward along the front. There were two primary sources of the propagation of wave packets at around 30oN. The first was the temperature inversion layer below 500 hPa, and the second was baroclinic zones located along the polarward flank of the subtropical jet in the middle and upper troposphere. Most wave packets propagated horizontally from the baroclinic zones and then converged on the zero meridional gradients of zonal winds.
TRMM-retrieved Cloud Structure and Evolution of MCSs over the Northern South China Sea and Impacts of CAPE and Vertical Wind Shear
LI Xiangshu, GUO Xueliang, FU Danhong
2013, 30(1): 77-88. doi: 10.1007/s00376-012-2055-2
Cloud structure and evolution of Mesoscale Convective Systems (MCSs) retrieved from the Tropical Rainfall Measuring Mission Microwave Imager (TRMM TMI) and Precipitation Radar (PR) were investigated and compared with some pioneer studies based on soundings and models over the northern South China Sea (SCS). The impacts of Convective Available Potential Energy (CAPE) and environmental vertical wind shear on MCSs were also explored. The main features of MCSs over the SCS were captured well by both TRMM PR and TMI. However, the PR-retrieved surface rainfall in May was less than that in June, and the reverse for TMI. TRMM-retrieved rainfall amounts were generally consistent with those estimated from sounding and models. However, rainfall amounts from sounding-based and PR-based estimates were relatively higher than those retrieved from TRMM-TMI data. The Weather Research and Forecasting (WRF) modeling simulation underestimated the maximum rain rate by 22% compared to that derived from TRMM-PR, and underestimated mean rainfall by 10.4% compared to the TRMM-TMI estimate, and by 12.5% compared to the sounding-based estimate. The warm microphysical processes modeled from both the WRF and the Goddard Cumulus Ensemble (GCE) models were quite close to those based on TMI, but the ice water contents in the models were relatively less compared to that derived from TMI. The CAPE and wind shear induced by the monsoon circulation were found to play critical roles in maintaining and developing the intense convective clouds over SCS. The latent heating rate increased more than twofold during the monsoon period and provided favorable conditions for the upward transportation of energy from the ocean, giving rise to the possibility of inducing large-scale interactions.
The Application of Flux-Form Semi-Lagrangian Transport Scheme in a Spectral Atmosphere Model
WANG Xiaocong, LIU Yimin, WU Guoxiong, Shian-Jiann LIN, BAO Qing
2013, 30(1): 89-100. doi: 10.1007/s00376-012-2039-2
A flux-form semi-Lagrangian transport scheme (FFSL) was implemented in a spectral atmospheric GCM developed and used at IAP/LASG. Idealized numerical experiments show that the scheme is good at shape preserving with less dissipation and dispersion, in comparison with other conventional schemes. Importantly, FFSL can automatically maintain the positive definition of the transported tracers, which was an underlying problem in the previous spectral composite method (SCM). To comprehensively investigate the impact of FFSL on GCM results, we conducted sensitive experiments. Three main improvements resulted: first, rainfall simulation in both distribution and intensity was notably improved, which led to an improvement in precipitation frequency. Second, the dry bias in the lower troposphere was significantly reduced compared with SCM simulations. Third, according to the Taylor diagram, the FFSL scheme yields simulations that are superior to those using the SCM: a higher correlation between model output and observation data was achieved with the FFSL scheme, especially for humidity in lower troposphere. However, the moist bias in the middle and upper troposphere was more pronounced with the FFSL scheme. This bias led to an over-simulation of precipitable water in comparison with reanalysis data. Possible explanations, as well as solutions, are discussed herein.
Effect of Boundary Layer Latent Heating on MJO Simulations
LING Jian, LI Chongyin, ZHOU Wen, JIA Xiaolong, Chidong ZHANG
2013, 30(1): 101-115. doi: 10.1007/s00376-012-2031-x
A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden--Julian Oscillation (MJO). The latent heating peak in the PBL was generated by very shallow convection, which prevented moisture from being transported to the free troposphere. Large amount of moisture was therefore confined to the PBL, leading to a dry bias in the free atmosphere. Suffering from this dry bias, deep convection became lethargic, and MJO signals failed to occur. When the latent heating peak in the PBL was removed in another simulation, reasonable MJO signals, including the eastward propagation and the structure of its large-scale circulation, appeared. We therefore propose that the excessive latent heating peak in the PBL due to hyperactive shallow convection may be a reason for a lack of MJO signals in some simulations by other GCMs as well.
Evaluating the Tree Population Density and Its Impacts in CLM-DGVM
SONG Xiang, ZENG Xiaodong, ZHU Jiawen
2013, 30(1): 116-124. doi: 10.1007/s00376-012-1271-0
Vegetation population dynamics play an essential role in shaping the structure and function of terrestrial ecosystems. However, large uncertainties remain in the parameterizations of population dynamics in current Dynamic Global Vegetation Models (DGVMs). In this study, the global distribution and probability density functions of tree population densities in the revised Community Land Model-Dynamic Global Vegetation Model (CLM-DGVM) were evaluated, and the impacts of population densities on ecosystem characteristics were investigated. The results showed that the model predicted unrealistically high population density with small individual size of tree PFTs (Plant Functional Types) in boreal forests, as well as peripheral areas of tropical and temperate forests. Such biases then led to the underestimation of forest carbon storage and incorrect carbon allocation among plant leaves, stems and root pools, and hence predicted shorter time scales for the building/recovering of mature forests. These results imply that further improvements in the parameterizations of population dynamics in the model are needed in order for the model to correctly represent the response of ecosystems to climate change.
Assessing Disagreement and Tolerance of Misclassification of Satellite-derived Land Cover Products Used in WRF Model Applications
GAO Hao, JIA Gensuo
2013, 30(1): 125-141. doi: 10.1007/s00376-012-2037-4
As more satellite-derived land cover products used in the study of global change, especially climate modeling, assessing their quality has become vitally important. In this study, we developed a distance metric based on the parameters used in weather research and forecasting (WRF) to characterize the degree of disagreement among land cover products and to identify the tolerance for misclassification within the International Geosphere Biosphere Programme (IGBP) classification scheme. We determined the spatial degree of disagreement and then created maps of misclassification of Moderate Resolution Imaging Spectoradiometer (MODIS) products, and we calculated overall and class-specific accuracy and fuzzy agreement in a WRF model. Our results show a high level of agreement and high tolerance of misclassification in the WRF model between large-scale homogeneous landscapes, while a low level of agreement and tolerance of misclassification appeared in heterogeneous landscapes. The degree of disagreement varied significantly among seven regions of China. The class-specific accuracy and fuzzy agreement in MODIS Collection 4 and 5 products varied significantly. High accuracy and fuzzy agreement occurred in the following classes: water, grassland, cropland, and barren or sparsely vegetated. Misclassification mainly occurred among specific classes with similar plant functional types and low discriminative spectro-temporal signals. Some classes need to be improved further; the quality of MODIS land cover products across China still does not meet the common requirements of climate modeling. Our findings may have important implications for improving land surface parameterization for simulating climate and for better understanding the influence of the land cover change on climate.
An Investigation into the Relationship between Surface Rain Rate and Rain Depth over Southeast Asia
HU Liang, LI Yaodong, DENG Difei
2013, 30(1): 142-152. doi: 10.1007/s00376-012-2097-5
The relationship between surface rain rate and depth of rain system (rain depth) over Southeast Asia is examined using 10-yr Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) measurements. Results show that, in general, a large surface rain rate is associated with a deep precipitating system, but a deep rain system may not always correspond with a large surface rain rate. This feature has a regional characteristic. Convective rain develops more frequently over land than over the ocean, while stratiform rain can extend to higher altitudes over the ocean than over land. A light surface rain rate has the largest probability to occur, regardless of rain depth. A convective rain system is more likely associated with a stronger surface rain rate than a stratiform rain system. Results show that precipitation systems involve complex microphysical processes. Rain depth is just one characteristic of precipitation. A linear relationship between surface rain rate and rain depth does not exist. Both deep convective and stratiform rain systems have reflectivity profiles that can be divided into three sections. The main difference in their profiles is at higher levels, from 4.5 km up to 19 km. For shallow stratiform rain systems, a two-section reflectivity profile mainly exists, while for convective systems a three-section profile is more common.
Investigating the Dominant Source for the Generation of Gravity Waves during Indian Summer Monsoon Using Ground-based Measurements
Debashis NATH, CHEN Wen
2013, 30(1): 153-166. doi: 10.1007/s00376-012-1273-y
Over the tropics, convection, wind shear (i.e., vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams) and topography are the major sources for the generation of gravity waves. During the summer monsoon season (June--August) over the Indian subcontinent, convection and wind shear coexist. To determine the dominant source of gravity waves during monsoon season, an experiment was conducted using mesosphere-stratosphere-troposphere (MST) radar situated at Gadanki (13.5oN, 79.2oE), a tropical observatory in the southern part of the Indian subcontinent. MST radar was operated continuously for 72 h to capture high-frequency gravity waves. During this time, a radiosonde was released every 6 h in addition to the regular launch (once daily to study low-frequency gravity waves) throughout the season. These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves. Data available from collocated instruments along with satellite-based brightness temperature (TBB) data were utilized to characterize the convection in and around Gadanki. Despite the presence of two major sources of gravity wave generation (i.e., convection and wind shear) during the monsoon season, wind shear (both vertical shear and geostrophic adjustment) contributed the most to the generation of gravity waves on various scales.
Intensified Eastward and Northward Propagation of Tropical Intraseasonal Oscillation over the Equatorial Indian Ocean in a Global Warming Scenario
YANG Jing, BAO Qing, WANG Xiaocong
2013, 30(1): 167-174. doi: 10.1007/s00376-012-1260-3
Northward propagation in summer and eastward propagation in winter are two distinguished features of tropical intraseasonal oscillation (TISO) over the equatorial Indian Ocean. According to numerical modeling results, under a global warming scenario, both propagations were intensified. The enhanced northward propagation in summer can be attributed to the enhanced atmosphere--ocean interaction and the strengthened mean southerly wind; and the intensified eastward propagation in winter is associated with the enhanced convection-wind coupling process and the strengthened equatorial Kevin wave. Future changes of TISO propagations need to be explored in more climate models.
Long-term Stability and Oceanic Mean State Simulated by the Coupled Model FGOALS-s2
LIN Pengfei, YU Yongqiang, LIU Hailong
2013, 30(1): 175-192. doi: 10.1007/s00376-012-2042-7
We describe the long-term stability and mean climatology of oceanic circulations simulated by version 2 of the Flexible Global Ocean--Atmosphere--Land System model (FGOALS-s2). Driven by pre-industrial forcing, the integration of FGOALS-s2 was found to have remained stable, with no obvious climate drift over 600 model years. The linear trends of sea SST and sea surface salinity (SSS) were -0.04oC (100 yr)-1 and 0.01 psu (100 yr)-1, respectively. The simulations of oceanic temperatures, wind-driven circulation and thermohaline circulation in FGOALS-s2 were found to be comparable with observations, and have been substantially improved over previous FGOALS-s versions (1.0 and 1.1). However, significant SST biases (exceeding 3oC) were found around strong western boundary currents, in the East China Sea, the Sea of Japan and the Barents Sea. Along the eastern coasts in the Pacific and Atlantic Ocean, a warm bias (>3oC) was mainly due to overestimation of net surface shortwave radiation and weak oceanic upwelling. The difference of SST biases in the North Atlantic and Pacific was partly due to the errors of meridional heat transport. For SSS, biases exceeding 1.5 psu were located in the Arctic Ocean and around the Gulf Stream. In the tropics, freshwater biases dominated and were mainly caused by the excess of precipitation. Regarding the vertical dimension, the maximal biases of temperature and salinity were located north of 65oN at depths of greater than 600 m, and their values exceeded 4oC and 2 psu, respectively.
Impacts of Polar Vortex, NPO, and SST Configurations on Unusually Cool Summers in Northeast China. Part I: Analysis and Diagnosis
LIAN Yi, SHEN Baizhu, LI Shangfeng, ZHAO Bin, GAO Zongting, LIU Gang, LIU Ping, CAO Ling
2013, 30(1): 193-209. doi: 10.1007/s00376-012-1258-x
This study unveils the evolution of two major early signals in the North Pacific atmosphere--ocean system that heralded abnormal high-pressure blockings and cold-vortex activities across Northeast China, based on an analysis of the configurations of major modes including the polar vortex, the North Pacific Oscillation (NPO), and SST in the preceding winter and spring and atmospheric low-frequency disturbances in Northeast China. We analyzed these aspects to understand the atmosphere--ocean physical coupling processes characterized by the two early signals, and here we explain the possible mechanisms through which dipole circulation anomalies affect the summer low-temperature processes in Northeast China. We further analyzed the interdecadal variation background and associated physical processes of the two early signals.
Some Characteristics of the Surface Boundary Layer of a Strong Cold Air Process over Southern China
LIU Ximing, CHENG Xueling, WU Qiong, FU Minning, ZENG Qingcun
2013, 30(1): 210-218. doi: 10.1007/s00376-012-1223-8
In southern China, cold air is a common weather process during the winter season; it can cause strong wind, sharp temperature decreases, and even the snow or freezing rain events. However, the features of the atmospheric boundary layer during cold air passage are not clearly understood due to the lack of comprehensive observation data, especially regarding turbulence. In this study, four-layer gradient meteorological observation data and one-layer, 10-Hz ultrasonic anemometer-thermometer monitoring data from the northern side of Poyang Lake were employed to study the main features of the surface boundary layer during a strong cold-air passage over southern China. The results show that, with the passage of a cold air front, the wind speed exhibits low-frequency variations and that the wind systematically descends. During the strong wind period, the wind speed increases with height in the surface layer. Regular gust packets are superimposed on the basic strong wind flow. Before the passage of cold air, the wind gusts exhibit a coherent structure. The wind and turbulent momentum fluxes are small, although the gusty wind momentum flux is slightly larger than the turbulent momentum flux. However, during the invasion of cold air, both the gusty wind and turbulent momentum fluxes increase rapidly with wind speed, and the turbulent momentum flux is larger than the gusty wind momentum flux during the strong wind period. After the cold air invasion, this structure almost disappears.
Role of Western Pacific Oceanic Variability in the Onset of the Bay of Bengal Summer Monsoon
FENG Junqiao, HU Dunxin, YU Lejiang
2013, 30(1): 219-234. doi: 10.1007/s00376-012-2040-9
The influence of the tropical Indo-Pacific Ocean heat content on the onset of the Bay of Bengal summer monsoon (BOBSM) onset was investigated using atmospheric data from the NCEP and ocean subsurface temperature data from the Japan Metorology Agency (JMA). Results showed that the onset time of the BOBSM is highly related to the tropical Pacific upper ocean heat content (HC), especially in the key region of the western Pacific warm pool (WPWP), during the preceding winter and spring. When the HC anomalies in the WPWP are positive (negative), the onset of the BOBSM is usually early (late). Accompanied by the variation of the convection activity over the WPWP, mainly induced by the underlying ocean temperature anomalies, the Walker circulation becomes stronger or weaker. This enhances or weakens the westerly over the tropical Indian Ocean flowing into the BOB in the boreal spring, which is essential to BOBSM onset. The possible mechanism of influence of cyclonic/anti-cyclonic circulation over the northwestern tropical Pacific on BOBSM onset is also discussed.
Ground-Based In Situ Measurements of Near-Surface Aerosol Mass Concentration over Anantapur: Heterogeneity in Source Impacts
2013, 30(1): 235-246. doi: 10.1007/s00376-012-1234-5
Surface measurements of aerosol physical properties were made at Anantapur (14.62oN, 77.65oE, 331 m a.s.l), a semiarid rural site in India, during August 2008--July 2009. Measurements included the segregated sizes of aerosolsas as well as total mass concentration and size distributions of aerosols measured at low relative humidity (RH-3, with a mean value of 34.02±9.05 μm-3 for the entire study period. A clear diurnal pattern appeared in coarse, accumulation and nucleation-mode particle concentrations, with two local maxima occurring in early morning and late evening hours. The concentration of coarse-mode particles was high during the summer season, with a maximum concentration of 11.81±0.98 μm-3 in the month of April, whereas accumulation-mode concentration was observed to be high in the winter period contributed >68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, Af (= Ma/Mt) was highest during winter (mean value of Af ~0.80) and lowest (Af ~0.64) during the monsoon season. The regression analysis shows that both Reff and Rm are dependent on coarse-mode aerosols. The relationship between the simultaneous measurements of daily mean aerosol optical depth at 500 nm (AOD500) and PM2.5 mass concentration ([PM2.5]) shows that surface-level aerosol mass concentration increases with the increase in columnar aerosol optical depth over the observation period.