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2014 Vol. 31, No. 6

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The Response of the East Asian Summer Monsoon to Strong Tropical Volcanic Eruptions
CUI Xuedong, GAO Yongqi, SUN Jianqi
2014, 31(6): 1245-1255. doi: 10.1007/s00376-014-3239-8
A 600-year integration performed with the Bergen Climate Model and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used to investigate the impact of strong tropical volcanic eruptions on the East Asian summer monsoon (EASM) and EASM rainfall. Both the simulation and NCEP/NCAR reanalysis data show a weakening of the EASM in strong eruption years. The model simulation suggests that North and South China experience droughts and the Yangtze-Huaihe River Valley experiences floods during eruption years. In response to strong tropical volcanic eruptions, the meridional air temperature gradient in the upper troposphere is enhanced, which leads to a southward shift and an increase of the East Asian subtropical westerly jet stream (EASWJ). At the same time, the land-sea thermal contrast between the Asian land mass and Northwest Pacific Ocean is weakened. The southward shift and increase of the EASWJ and reduction of the land-sea thermal contrast all contribute to a weakening of the EASM and EASM rainfall anomaly.
Effect of Baroclinicity on Vortex Axisymmetrization. Part I: Barotropic Basic Vortex
Melinda S. PENG, Jiayi PENG, Tim LI, Eric HENDRICKS
2014, 31(6): 1256-1266. doi: 10.1007/s00376-014-3237-x
The barotropic and baroclinic disturbances axisymmetrized by the barotropic basic vortex are examined in an idealized modeling framework consisting of two layers. Using a Wentzel-Kramers-Brillouin approach, the radial propagation of a baroclinic disturbance is shown to be slower than a barotropic disturbance, resulting in a slower linear axisymmetrization for baroclinic disturbances. The slower-propagating baroclinic waves also cause more baroclinic asymmetric kinetic energy to be transferred directly to the barotropic symmetric vortex than from barotropic disturbances, resulting in a faster axisymmetrization process in the nonlinear baroclinic wave case than in the nonlinear barotropic wave case.
Effect of Baroclinicity on Vortex Axisymmetrization. Part II: Baroclinic Basic Vortex
Jiayi PENG, Melinda S. PENG, Tim LI, Eric HENDRICKS
2014, 31(6): 1267-1278. doi: 10.1007/s00376-014-3238-9
The effect of baroclinicity on vortex axisymmetrization is examined within a two-layer dynamical model. Three basic state vortices are constructed with varying degrees of baroclinicity: (i) barotropic, (ii) weak baroclinic, and (iii) strong baroclinic. The linear and nonlinear evolution of wavenumber-2 baroclinic disturbances are examined in each of the three basic state vortices. The results show that the radial propagating speed of the vortex Rossby wave at the lower level is larger with the stronger baroclinicity, resulting in a faster linear axisymmetrization process in the stronger baroclinic vortex. It is found that the nonlinear axisymmetrization process takes the longest time in the strongest baroclinic vortex among the three different basic vortices due to the weaker kinetic energy transfer from asymmetric to symmetric circulations at the lower level. A major finding in this study is that the same initial asymmetric perturbation can have different effects on symmetric vortices depending on the initial vortex baroclinicity. In numerical weather prediction models, this implies that there exists a sensitivity of the subsequent structural and intensity change solely due to the specification of the initial vertical shear of the tropical cyclone vortex.
Predictability of the East Asian Winter Monsoon Indices by the Coupled Models of ENSEMBLES
Se-Hwan YANG, LU Riyu
2014, 31(6): 1279-1292. doi: 10.1007/s00376-014-4020-8
The seasonal predictability of various East Asian winter monsoon (EAWM) indices was investigated in this study based on the retrospective forecasts of the five state-of-the-art coupled models from ENSEMBLES for a 46-year period of 1961-2006. It was found that the ENSEMBLES models predict five out of the 21 EAWM indices well, with temporal correlation coefficients ranging from 0.54 to 0.61. These five indices are defined by the averaged lower-tropospheric winds over the low latitudes (south of 30N). Further analyses indicated that the predictability of these five indices originates from their intimate relationship with ENSO. A cross-validated prediction, which took the preceding (November) observed Niňo3.4 index as a predictor, gives a prediction skill almost identical to that shown by the model. On the other hand, the models present rather low predictability for the other indices and for surface air temperature in East Asia. In addition, the models fail to reproduce the relationship between the indices of different categories, implying that they cannot capture the tropical-extratropical interaction related to EAWM variability. Together, these results suggest that reliable prediction of the EAWM indices and East Asian air temperature remains a challenge.
A New Method for Quality Control of Chinese Rawinsonde Wind Observations
LIAO Jie, WANG Bin, LI Qingxiang
2014, 31(6): 1293-1304. doi: 10.1007/s00376-014-4030-6
In 2006, the National Meteorological Information Center (NMIC) of the China Meteorological Administration (CMA) developed its real-time quality control (QC) system of rawinsonde observations coming from the Global Telecommunications System (GTS) and established the Global Upper-air Report Dataset, which, with the NMIC B01 format, is generally referred to as the B01 dataset and updated on a daily basis. However, when the B01 dataset is applied in climate analysis, some wind errors as well as some accurate values with incorrect error marks are found. To improve the quality and usefulness of Chinese rawinsonde wind observations, a new QC method (NewQC) is proposed in this paper. Different from the QC approach used for B01 datasets, the NewQC includes two vertical-wind-shear checks to analyze the vertical consistency of winds, in which the constant height level winds are used as reference data for the QC of mandatory pressure level winds. Different threshold values are adopted in the wind shear checks for different stations and different vertical levels. Several typical examples of QC of different error types by the new algorithm are shown and its performance with respect to 1980-2008 observational data is statistically evaluated. Compared with the radiosonde QC algorithms used in both the Meteorological Assimilation Data Ingest System (MADIS, of the National Oceanic and Atmospheric Administration (NOAA) and the B01 dataset, the NewQC shows higher accuracy and better reliability, particularly when used to judge successive observation errors.
Numerical Experiments on the Impact of Spring North Pacific SSTA on NPO and Unusually Cool Summers in Northeast China
LIAN Yi, ZHAO Bin, SHEN Baizhu, LI Shangfeng, LIU Gang
2014, 31(6): 1305-1315. doi: 10.1007/s00376-014-3247-8
A set of numerical experiments designed to analyze the oceanic forcing in spring show that the combined forcing of cold (warm) El Nio (La Nia) phases in the Nio4 region and sea surface temperature anomalies (SSTA) in the westerly drifts region would result in abnormally enhanced NorthEast Cold Vortex (NECV) activities in early summer. In spring, the central equatorial Pacific El Niňo phase and westerly drift SSTA forcing would lead to the retreat of non-adiabatic waves, inducing elliptic low-frequency anomalies of tropical air flows. This would enhance the anomalous cyclone-anticyclone-cyclone-anticyclone low-frequency wave train that propagates from the tropics to the extratropics and further to the mid-high latitudes, constituting a major physical mechanism that contributes to the early summer circulation anomalies in the subtropics and in the North Pacific mid-high latitudes. The central equatorial Pacific La Niňa forcing in the spring would, on the one hand, induce teleconnection anomalies of high pressure from the Sea of Okhotsk to the Sea of Japan in early summer, and on the other hand indirectly trigger a positive low-frequency East Asia-Pacific teleconnection (EAP) wave train in the lower troposphere.
The Hiatus and Accelerated Warming Decades in CMIP5 Simulations
SONG Yi, YU Yongqiang, LIN Pengfei
2014, 31(6): 1316-1330. doi: 10.1007/s00376-014-3265-6
Observed hiatus or accelerated warming phenomena are compared with numerical simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) archives, and the associated physical mechanisms are explored based on the CMIP5 models. Decadal trends in total ocean heat content (OHC) are strongly constrained by net top-of-atmosphere (TOA) radiation. During hiatus decades, most CMIP5 models exhibit a significant decrease in the SST and upper OHC and a significant increase of heat penetrating into the subsurface or deep ocean, opposite to the accelerated warming decades. The shallow meridional overturning of the Pacific subtropical cell experiences a significant strengthening (slowdown) for the hiatus (accelerated warming) decades associated with the strengthened (weakened) trade winds over the tropical Pacific. Both surface heating and ocean dynamics contribute to the decadal changes in SST over the Indian Ocean, and the Indonesian Throughflow has a close relationship with the changes of subsurface temperature in the Indian Ocean. The Atlantic Meridional Overturing Circulation (Antarctic Bottom Water) tends to weaken (strengthen) during hiatus decades, opposite to the accelerated warming decades. In short, the results highlight the important roles of air-sea interactions and ocean circulations for modulation of surface and subsurface temperature.
Impacts of Uncertainty in AVOC Emissions on the Summer ROx Budget and Ozone Production Rate in the Three Most Rapidly-Developing Economic Growth Regions of China
WANG Feng, AN Junling, LI Ying, TANG Yujia, LIN Jian, QU Yu, CHEN Yong, ZHANG Bing, ZHAI Jing
2014, 31(6): 1331-1342. doi: 10.1007/s00376-014-3251-z
High levels of uncertainty in non-methane volatile organic compound (NMVOC) emissions in China could lead to significant variation in the budget of the sum of hydroxyl (OH) and peroxy (HO2, RO2) radicals (ROx= OH + HO2 + RO2) and the ozone production rate [P(O3)], but few studies have investigated this possibility, particularly with three-dimensional air quality models. We added diagnostic variables into the WRF-Chem model to assess the impact of the uncertainty in anthropogenic NMVOC (AVOC) emissions on the ROx budget and P(O3) in the Beijing-Tianjin-Hebei region, Yangtze River Delta, and Pearl River Delta of China. The WRF-Chem simulations were compared with satellite and ground observations, and previous observation-based model studies. Results indicated that 68% increases (decreases) in AVOC emissions produced 4%-280% increases (2%-80% decreases) in the concentrations of OH, HO2, and RO2 in the three regions, and resulted in 35%-48% enhancements (26%-39% reductions) in the primary ROx production and ~65% decreases (68%-73% increases) of the P(O3) in Beijing, Shanghai, and Guangzhou. For the three cities, the two largest contributors to the ROx production rate were the reaction of O1D + H2O and photolysis of HCHO, ALD2, and others; the reaction of OH + NO2 (71%-85%) was the major ROx sink; and the major contributor to P(O3) was the reaction of HO2 + NO (~65%). Our results showed that AVOC emissions in 2006 from \citeZhang2009 have been underestimated by ~ 68% in suburban areas and by 68% in urban areas, implying that daily and hourly concentrations of secondary organic aerosols and inorganic aerosols could be substantially underestimated, and cloud condensation nuclei could be underestimated, whereas local and regional radiation was overestimated.
Constraining Anthropogenic CH4 Emissions in Nanjing and the Yangtze River Delta, China, Using Atmospheric CO2 and CH4 Mixing Ratios
SHEN Shuanghe, YANG Dong, XIAO Wei, LIU Shoudong, Xuhui LEE
2014, 31(6): 1343-1352. doi: 10.1007/s00376-014-3231-3
Methane (CH4) emissions estimated with the Intergovernmental Panel on Climate Change (IPCC) inventory method at the city and regional scale are subject to large uncertainties. In this study, we determined the CH4:CO2 emissions ratio for both Nanjing and the Yangtze River Delta (YRD), using the atmospheric CH4 and CO2 concentrations measured at a suburban site in Nanjing in the winter. The atmospheric estimate of the CH4:CO2 emissions ratio was in reasonable agreement with that calculated using the IPCC method for the YRD (within 20%), but was 200% greater for the municipality of Nanjing. The most likely reason for the discrepancy is that emissions from unmanaged landfills are omitted from the official statistics on garbage production.
A Multi-Scale Urban Atmospheric Dispersion Model for Emergency Management
MIAO Yucong, LIU Shuhua, ZHENG Hui, ZHENG Yijia, CHEN Bicheng, WANG Shu
2014, 31(6): 1353-1365. doi: 10.1007/s00376-014-3254-9
To assist emergency management planning and prevention in case of hazardous chemical release into the atmosphere, especially in densely built-up regions with large populations, a multi-scale urban atmospheric dispersion model was established. Three numerical dispersion experiments, at horizontal resolutions of 10 m, 50 m and 3000 m, were performed to estimate the adverse effects of toxic chemical release in densely built-up areas. The multi-scale atmospheric dispersion model is composed of the Weather Forecasting and Research (WRF) model, the Open Source Field Operation and Manipulation software package, and a Lagrangian dispersion model. Quantification of the adverse health effects of these chemical release events are given by referring to the U.S. Environmental Protection Agency's Acute Exposure Guideline Levels. The wind fields of the urban-scale case, with 3 km horizontal resolution, were simulated by the Beijing Rapid Update Cycle system, which were utilized by the WRF model. The sub-domain-scale cases took advantage of the computational fluid dynamics method to explicitly consider the effects of buildings. It was found that the multi-scale atmospheric dispersion model is capable of simulating the flow pattern and concentration distribution on different scales, ranging from several meters to kilometers, and can therefore be used to improve the planning of prevention and response programs.
Intercomparison of the Impacts of Four Summer Teleconnections over Eurasia on East Asian Rainfall
LIN Zhongda
2014, 31(6): 1366-1376. doi: 10.1007/s00376-014-3171-y
East Asian summer climate is strongly affected by extratropical circulation disturbances. In this study, impacts of four atmospheric teleconnections over Eurasia on East Asian summer rainfall are investigated using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and Climatic Research Unit (CRU) land precipitation data during 1979-2009. The four teleconnections include the Scandinavian (SCA), the Polar/Eurasian (PEU), the East Atlantic/Western Russian (EAWR), and the circumglobal teleconnection (CGT). Moreover, the related changes of lower-tropospheric circulation are explored, specifically, the low pressure over northern East Asia (NEAL) and the subtropical high over the western North Pacific (WNPSH). The results presented are in the positive phase. The PEU and SCA induce significant negative anomalies in North China rainfall (NCR), while the CGT induces significant positive anomalies. In the past three decades, the PEU and SCA explain more than 20% of the variance in NCR, twice that explained by the CGT, suggesting a more important role of the former two teleconnections in NCR variation than the latter one. Meanwhile, the PEU and SCA reduce rainfall in Northeast China and South Korea, respectively, and the CGT enhances rainfall in Japan. The rainfall responses are attributed to the SCA-induced northward shift of the NEAL, and PEU-induced northward shift and weakening of the NEAL, respectively. For the CGT, the dipole pattern of rainfall anomalies between North China and Japan is affected by both westward extension of the NEAL and northwestward expansion of the WNPSH. In addition, the EAWR leads to an increase of sporadic rainfall in South China as a result of the eastward retreat of the WNPSH.
Impacts of the Diurnal Cycle of Radiation on Tropical Cyclone Intensification and Structure
GE Xuyang, MA Yue, ZHOU Shunwu, Tim LI
2014, 31(6): 1377-1385. doi: 10.1007/s00376-014-4060-0
To investigate the impacts of the diurnal cycle on tropical cyclones (TCs), a set of idealized simulations were conducted by specifying different radiation (i.e., nighttime-only, daytime-only, full diurnal cycle). It was found that, for an initially weak storm, it developed faster during nighttime than daytime. The impacts of radiation were not only on TC intensification, but also on TC structure and size. The nighttime storm tended to have a larger size than its daytime counterparts. During nighttime, the radiative cooling steepened the lapse rate and thus reduced the static stability in cloudy regions, enhancing convection. Diabatic heating associated with outer convection induced boundary layer inflows, which led to outward expansion of tangential winds and thus increased the storm size.
Water Vapor Motion Signal Extraction from FY-2E Longwave Infrared Window Images for Cloud-free Regions: The Temporal Difference Technique
YANG Lu, WANG Zhenhui, CHU Yanli, ZHAO Hang, TANG Min
2014, 31(6): 1386-1394. doi: 10.1007/s00376-014-3165-9
The aim of this study is to calculate the low-level atmospheric motion vectors (AMVs) in clear areas with FY-2E IR2 window (11.59-12.79 m) channel imagery, where the traditional cloud motion wind technique fails. A new tracer selection procedure, which we call the temporal difference technique, is demonstrated in this paper. This technique makes it possible to infer low-level wind by tracking features in the moisture pattern that appear as brightness temperature (TB) differences between consecutive sequences of 30-min-interval FY-2E IR2 images over cloud-free regions. The TB difference corresponding to a 10% change in water vapor density is computed with the Moderate Resolution Atmospheric Transmission (MODTRAN4) radiative transfer model. The total contribution from each of the 10 layers is analyzed under four typical atmospheric conditions: tropical, midlatitude summer, U.S. standard, and midlatitude winter. The peak level of the water vapor weighting function for the four typical atmospheres is assigned as a specific height to the TB wind. This technique is valid over cloud-free ocean areas. The proposed algorithm exhibits encouraging statistical results in terms of vector difference (VD), speed bias (BIAS), mean vector difference (MVD), standard deviation (SD), and root-mean-square error (RMSE), when compared with the wind field of NCEP reanalysis data and rawinsonde observations.
A Study on the Physical Processes of the Formation of the ENSO Cycle
ZONG Haifeng
2014, 31(6): 1395-1406. doi: 10.1007/s00376-014-3224-2
The physical processes involved in the formation of the ENSO cycle, as well as the possible roles of the Hadley circulation (HC), Walker circulation (WC), and the propagating waves of the Southern Oscillation/Northern Oscillation (SO/NO) in its formation, were studied using composite and regression methods. The analysis showed that the convection and heat release triggered by ENSO in the central-eastern equatorial Pacific are the primary drivers for the 3-5 year cycle of the HC, WC and the meridional/zonal circulation. The HC plays a key role in the influence of ENSO on the circulation outside the tropics through angular momentum transportation. Meanwhile, the feedback effects of the anomalous circulation in the mid-high latitudes on ENSO are accomplished by the propagating waves of SO/NO associated with the evolutions of HC and WC. These propagating waves are the main agents of the connections among the meridional/zonal circulation outside the tropics, the Asian/Australian monsoon, the anomalous easterly/westerly winds over the tropical Pacific, and ENSO events. It was found that the 3-5 year cycle of the meridional/zonal circulation forced by ENSO is quite different from the several-week variation of the circulation index triggered by the inner dynamic processes of the atmosphere. The former occurs at the global scale with a definite flow pattern, while the latter occurs only in a wide area without a definite flow pattern. Finally, a physical model for the formation of the ENSO cycle composed of two fundamental processes at the basin and global scale, respectively, is proposed.
Impact of Vegetation Feedback on the Mid-Pliocene Warm Climate
2014, 31(6): 1407-1416. doi: 10.1007/s00376-014-4015-5
Studying the vegetation feedback during warm periods of the past can lead to better understanding of those in the future. In this study, we conducted several simulations to analyze vegetation feedback during the mid-Pliocene warm period. The results indicate that the main features of vegetation change in the mid-Pliocene were a northward shift of needleleaf tree, an expansion of broadleaf tree and shrub, and a northward expansion of grass, as compared to the pre-industrial period. The global annual mean warming ratio caused by vegetation feedback was 12.1%, and this warming ratio was much larger in northern middle and high latitudes. The warming caused by vegetation change was directly related to the surface albedo change and was further amplified by snow/sea ice-albedo feedback.
Retrieval of the Single Scattering Albedo of Asian Dust Mixed with Pollutants Using Lidar Observations
Sungkyun SHIN, Young Min NOH, Kwonho LEE, Hanlim LEE, Detlef M?LLER, Y. J. KIM, Kwanchul KIM, Dongho SHIN
2014, 31(6): 1417-1426. doi: 10.1007/s00376-014-3244-y
The vertical distribution of single scattering albedos (SSAs) of Asian dust mixed with pollutants was derived using the multi-wavelength Raman lidar observation system at Gwangju (35.10N, 126.53E). Vertical profiles of both backscatter and extinction coefficients for dust and non-dust aerosols were extracted from a mixed Asian dust plume using the depolarization ratio from lidar observations. Vertical profiles of backscatter and extinction coefficients of non-dust particles were input into an inversion algorithm to retrieve the SSAs of non-dust aerosols. Atmospheric aerosol layers at different heights had different light-absorbing characteristics. The SSAs of non-dust particles at each height varied with aerosol type, which was either urban/industrial pollutants from China transported over long distances at high altitude, or regional/local pollutants from the Korean peninsula. Taking advantage of independent profiles of SSAs of non-dust particles, vertical profiles of SSAs of Asian dust mixed with pollutants were estimated for the first time, with a new approach suggested in this study using an empirical determination of the SSA of pure dust. The SSAs of the Asian dust-pollutants mixture within the planetary boundary layer (PBL) were in the range 0.880.91, while the values above the PBL were in the range 0.760.87, with a very low mean value of 0.760.05. The total mixed dust plume SSAs in each aerosol layer were integrated over height for comparison with results from the Aerosol Robotics Network (AERONET) measurements. Values of SSA retrieved from lidar observations of 0.920.01 were in good agreement with the results from AERONET measurements.
Using Hourly Measurements to Explore the Role of Secondary Inorganic Aerosol in PM2.5 during Haze and Fog in Hangzhou, China
Roeland Cornelis JANSEN, SHI Yang, CHEN Jianmin, HU YunJie, XU Chang, HONG Shengmao, LI Jiao, ZHANG Min
2014, 31(6): 1427-1434. doi: 10.1007/s00376-014-4042-2
This paper explores the role of the secondary inorganic aerosol (SIA) species ammonium, NH4+, nitrate, NO3-, and sulfate, SO42-, during haze and fog events using hourly mass concentrations of PM2.5 measured at a suburban site in Hangzhou, China. A total of 546 samples were collected between 1 April and 8 May 2012. The samples were analyzed and classified as clear, haze or fog depending on visibility and relative humidity (RH). The contribution of SIA species to PM2.5 mass increased to ~50% during haze and fog. The mass contribution of nitrate to PM2.5 increased from 11% during clear to 20% during haze episodes. Nitrate mass exceeded sulfate mass during haze, while near equal concentrations were observed during fog episodes. The role of RH on the correlation between concentrations of SIA and visibility was examined, with optimal correlation at 60%70% RH. The total acidity during clear, haze and fog periods was 42.38, 48.38 and 45.51 nmol m-3, respectively, indicating that sulfate, nitrate and chloride were not neutralized by ammonium during any period. The nitrate to sulfate molar ratio, as a function of the ammonium to sulfate molar ratio, indicated that nitrate formation during fog started at a higher ammonium to sulfate molar ratio compared to clear and haze periods. During haze and fog, the nitrate oxidation ratio increased by a factor of 1.61.7, while the sulfur oxidation ratio increased by a factor of 1.21.5, indicating that both gaseous NO2 and SO2 were involved in the reduced visibility.
Surface Rainfall and Cloud Budgets Associated with Mei-yu Torrential Rainfall over Eastern China during June 2011
ZHAI Guoqing, LI Xiaofan, ZHU Peijun, SHEN Hangfeng, ZHANG Yuanzhi
2014, 31(6): 1435-1444. doi: 10.1007/s00376-014-3256-7
Surface rainfall and cloud budgets associated with three heavy rainfall events that occurred over eastern China during the mei-yu season in June 2011 were analyzed using 2D cumulus ensemble model simulation data. Model domain mean rainfall showed three peaks in response to three prescribed ascending motion maxima, primarily through the mean moisture convergence during the torrential rainfall period. Prescribed ascending motion throughout the troposphere produced strong convective rainfall during the first (9 June) and third (17-18 June) rainfall events, whereas strong prescribed ascending motion in the mid and upper troposphere and weak subsidence near the surface generated equally important stratiform and convective rainfall during the second rainfall event (14 June). The analysis of surface rainfall budgets reveals that convective rainfall was associated with atmospheric drying during the first event and moisture convergence during the third event. Both stratiform and convective rainfall responded primarily to moisture convergence during the second event. An analysis of grid data shows that the first and third mean rainfall maxima had smaller horizontal scales of the precipitation system than the second.
Variation of the North Equatorial Current, Mindanao Current, and Kuroshio Current in a High-Resolution Data Assimilation during 20082012
ZHAI Fangguo, WANG Qingye, WANG Fujun, Hu Dunxin
2014, 31(6): 1445-1459. doi: 10.1007/s00376-014-3241-1
Outputs from a high-resolution data assimilation system, the global Hybrid Coordinate Ocean Model and Navy Coupled Ocean Data Assimilation (HYCOM+NCODA) 1/12 analysis, were analyzed for the period September 2008 to February 2012. The objectives were to evaluate the performance of the system in simulating ocean circulation in the tropical northwestern Pacific and to examine the seasonal to interannual variations of the western boundary currents. The HYCOM assimilation compares well with altimetry observations and mooring current measurements. The mean structures and standard deviations of velocities of the North Equatorial Current (NEC), Mindanao Current (MC) and Kuroshio Current (KC) also compare well with previous observations. Seasonal to interannual variations of the NEC transport volume are closely correlated with the MC transport volume, instead of that of the KC. The NEC and MC transport volumes mainly show well-defined annual cycles, with their maxima in spring and minima in fall, and are closely related to the circulation changes in the Mindanao Dome (MD) region. In seasons of transport maxima, the MD region experiences negative SSH anomalies and a cyclonic gyre anomaly, and in seasons of transport minima the situation is reversed. The sea surface NEC bifurcation latitude (NBL) in the HYCOM assimilation also agrees well with altimetry observations. In 2009, the NBL shows an annual cycle similar to previous studies, reaching its southernmost position in summer and its northernmost position in winter. In 2010 and 2011, the NBL variations are dominantly influenced by La Niňa events. The dynamics responsible for the seasonal to interannual variations of the NEC-MC-KC current system are also discussed.
An Improved Method for Correction of Air Temperature Measured Using Different Radiation Shields
CHENG Xinghong, SU Debin, LI Deping, CHEN Lu, XU Wenjing, YANG Meilin, LI Yongcheng, YUE Zhizhong, WANG Zijing
2014, 31(6): 1460-1468. doi: 10.1007/s00376-014-3129-0
The variation of air temperature measurement errors using two different radiation shields (DTR502B Vaisala, Finland, and HYTFZ01, Huayun Tongda Satcom, China) was studied. Datasets were collected in the field at the Daxing weather station in Beijing from June 2011 to May 2012. Most air temperature values obtained with these two commonly used radiation shields were lower than the reference records obtained with the new Fiber Reinforced Polymers (FRP) Stevenson screen. In most cases, the air temperature errors when using the two devices were smaller on overcast and rainy days than on sunny days; and smaller when using the imported rather than the Chinese shield. The measured errors changed sharply at sunrise and sunset, and reached maxima at noon. Their diurnal variation characteristics were, naturally, related to changes in solar radiation. The relationships between the record errors, global radiation, and wind speed were nonlinear. An improved correction method was proposed based on the approach described by Nakamura and Mahrt (2005) (NM05), in which the impact of the solar zenith angle (SZA) on the temperature error is considered and extreme errors due to changes in SZA can be corrected effectively. Measurement errors were reduced significantly after correction by either method for both shields. The error reduction rate using the improved correction method for the Chinese and imported shields were 3.3% and 40.4% higher than those using the NM05 method, respectively.