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2012 Vol. 29, No. 1

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CCSC (climate change study in China)
An Approach to Quantify the Heat Wave Strength and Price a Heat Derivative for Risk Hedging
Samuel S. P. SHEN, Benedikt KRAMPS, Shirley X. SUN, Barbara BAILEY
2012, 29(1): 1-9. doi: 10.1007/s00376-011-1020-9
Mitigating the heat stress via a derivative policy is a vital financial option for agricultural producers and other business sectors to strategically adapt to the climate change scenario. This study has provided an approach to identifying heat stress events and pricing the heat stress weather derivative due to persistent days of high surface air temperature (SAT). Cooling degree days (CDD) are used as the weather index for trade. In this study, a call-option model was used as an example for calculating the price of the index. Two heat stress indices were developed to describe the severity and physical impact of heat waves. The daily Global Historical Climatology Network (GHCN-D) SAT data from 1901 to 2007 from the southern California, USA, were used. A major California heat wave that occurred 20--25 October 1965 was studied. The derivative price was calculated based on the call-option model for both long-term station data and the interpolated grid point data at a regular 0.1o×0.1o latitude--longitude grid. The resulting comparison indicates that (a) the interpolated data can be used as reliable proxy to price the CDD and (b) a normal distribution model cannot always be used to reliably calculate the CDD price. In conclusion, the data, models, and procedures described in this study have potential application in hedging agricultural and other risks.
Characteristics and Nonlinear Growth of the Singular Vector Related to a Heavy Rainfall Case over the Korean Peninsula
Yonghan CHOI, Joowan KIM, Dong-Kyou LEE
2012, 29(1): 10-28. doi: 10.1007/s00376-011-0194-5
In this study, singular vectors related to a heavy rainfall case over the Korean Peninsula were calculated using the fifth-generation Pennsylvania State University--National Center for Atmospheric Research Mesoscale Model (MM5) adjoint modeling system. Tangent linear and adjoint models include moist physical processes, and a moist basic state and a moist total energy norm were used for the singular-vector calculations. The characteristics and nonlinear growth of the first singular vector were analyzed, focusing on the relationship between the basic state and the singular vector. The horizontal distribution of the initial singular vector was closely related to the baroclinicity index and the moisture availability of the basic state. The temperature-component energy at a lower level was dominant at the initial time, and the kinetic energy at upper levels became dominant at the final time in the energy profile of the singular vector. The nonlinear growth of the singular vector appropriately reflects the temporal variations in the basic state. The moisture-component energy at lower levels was dominant at earlier times, indicating continuous moisture transport in the basic state. There were a large amount of precipitation and corresponding latent heat release after that period because the continuous moisture transport created favorable conditions for both convective and nonconvective precipitation. The vertical propagation of the singular-vector energy was caused by precipitation and the corresponding latent heating in the basic state.
Is the Isentropic Surface Always Impermeable to the Potential Vorticity Substance?
Chanh Q. KIEU, Da-Lin ZHANG
2012, 29(1): 29-35. doi: 10.1007/s00376-011-0227-0
The impermeability of isentropic surfaces by the potential vorticity substance (PVS) has often been used to help understand the generation of potential vorticity in the presence of diabatic heating and friction. In this study, we examined singularities of isentropic surfaces that may develop in the presence of diabatic heating and the fictitious movements of the isentropic surfaces that are involved in deriving the PVS impermeability theorem. Our results show that such singularities could occur in the upper troposphere as a result of intense convective-scale motion, at the cloud top due to radiative cooling, or within the well-mixed boundary layer. These locally ill-defined conditions allow PVS to penetrate across an isentropic surface. We conclude that the PVS impermeability theorem is generally valid for the stably stratified atmosphere in the absence of diabatic heating.
The Impact of Horizontal Resolution on the CNOP and on Its Identified Sensitive Areas for Tropical Cyclone Predictions
ZHOU Feifan, MU Mu
2012, 29(1): 36-46. doi: 10.1007/s00376-011-1003-x
In this study, the impacts of horizontal resolution on the conditional nonlinear optimal perturbation (CNOP) and on its identified sensitive areas were investigated for tropical cyclone predictions. Three resolutions, 30 km, 60 km, and 120 km, were studied for three tropical cyclones, TC Mindulle (2004), TC Meari (2004), and TC Matsa (2005). Results show that CNOP may present different structures with different resolutions, and the major parts of CNOP become increasingly localized with increased horizontal resolution. CNOP produces spiral and baroclinic structures, which partially account for its rapid amplification. The differences in CNOP structures result in different sensitive areas, but there are common areas for the CNOP-identified sensitive areas at various resolutions, and the size of the common areas is different from case to case. Generally, the forecasts benefit more from the reduction of the initial errors in the sensitive areas identified using higher resolutions than those using lower resolutions. However, the largest improvement of the forecast can be obtained at the resolution that is not the highest for some cases. In addition, the sensitive areas identified at lower resolutions are also helpful for improving the forecast with a finer resolution, but the sensitive areas identified at the same resolution as the forecast would be the most beneficial.
The Regional Surface Heating Field over the Heterogeneous Landscape of the Tibetan Plateau Using MODIS and In-Situ Data
MA Yaoming, WANG Binbin, ZHONG Lei, MA Weiqiang
2012, 29(1): 47-53. doi: 10.1007/s00376-011-1008-5
In this study, a parameterization scheme based on Moderate Resolution Imaging Spectroradiometer (MODIS) data and it in-situ data was tested for deriving the regional surface heating field over a heterogeneous landscape. As a case study, the methodology was applied to the whole Tibetan Plateau (TP) area. Four images of MODIS data (i.e., 30 January 2007, 15 April 2007, 1 August 2007, and 25 October 2007) were used in this study for comparison among winter, spring, summer, and autumn. The results were validated using the observations measured at the stations of the Tibetan Observation and Research Platform (TORP). The results show the following: (1) The derived surface heating field for the TP area was in good accord with the land-surface status, showing a wide range of values due to the strong contrast of surface features in the area. (2) The derived surface heating field for the TP was very close to the field measurements (observations). The APD (absolute percent difference) between the derived results and the field observations was <10%. (3) The mean surface heating field over the TP increased from January to April to August, and decreased in October. Therefore, the reasonable regional distribution of the surface heating field over a heterogeneous landscape can be obtained using this methodology. The limitations and further improvement of this method are also discussed.
Implication of the South China Sea Throughflow for the Interannual Variability of the Regional Upper-Ocean Heat Content
LIU Qinyan, Ruixin HUANG, WANG Dongxiao
2012, 29(1): 54-62. doi: 10.1007/s00376-011-0068-x
In this study the interannual variability of the upper-ocean heat content in the South China Sea (SCS) was revisited using simple ocean data assimilation (SODA) combined with objective analyzed data sets that included the horizontal and vertical structures. The results confirmed that the upper-ocean heat content in the SCS is lower than normal during the mature phase of El Nino events, and two super El Nino events, 1982/1983 and 1997/1998 were also included. The variability of the heat content was consistent with the variability of the dynamic height anomalies. The SCS throughflow (SCSTF) plays an important role in regulating the interannual variability of the heat content, especially during the mature phase of El Nino events.
The Roles of Spatial Locations and Patterns of Initial Errors in the Uncertainties of Tropical Cyclone Forecasts
CHEN Boyu, MU Mu
2012, 29(1): 63-78. doi: 10.1007/s00376-011-0201-x
In this study, a series of sensitivity experiments were performed for two tropical cyclones (TCs), TC Longwang (2005) and TC Sinlaku (2008), to explore the roles of locations and patterns of initial errors in uncertainties of TC forecasts. Specifically, three types of initial errors were generated and three types of sensitive areas were determined using conditional nonlinear optimal perturbation (CNOP), first singular vector (FSV), and composite singular vector (CSV) methods. Additionally, random initial errors in randomly selected areas were considered. Based on these four types of initial errors and areas, we designed and performed 16 experiments to investigate the impacts of locations and patterns of initial errors on the nonlinear developments of the errors, and to determine which type of initial errors and areas has the greatest impact on TC forecasts. Overall, results from the experiments indicate the following: (1) The impact of random errors introduced into the sensitive areas was greater than that of errors themselves fixed in the randomly selected areas. From the perspective of statistical analysis, and by comparison, the impact of random errors introduced into the CNOP target area was greatest. (2) The initial errors with CNOP, CSV, or FSV patterns were likely to grow faster than random errors. (3) The initial errors with CNOP patterns in the CNOP target areas had the greatest impacts on the final verification forecasts.
Inducing Unstable Grassland Equilibrium States Due to Nonlinear Optimal Patterns of Initial and Parameter Perturbations: Theoretical Models
SUN Guodong, MU Mu
2012, 29(1): 79-90. doi: 10.1007/s00376-011-0226-1
Due to uncertainties in initial conditions and parameters, the stability and uncertainty of grassland ecosystem simulations using ecosystem models are issues of concern. Our objective is to determine the types and patterns of initial and parameter perturbations that yield the greatest instability and uncertainty in simulated grassland ecosystems using theoretical models. We used a nonlinear optimization approach, i.e., a conditional nonlinear optimal perturbation related to initial and parameter perturbations (CNOP) approach, in our work. Numerical results indicated that the CNOP showed a special and nonlinear optimal pattern when the initial state variables and multiple parameters were considered simultaneously. A visibly different complex optimal pattern characterizing the CNOPs was obtained by choosing different combinations of initial state variables and multiple parameters in different physical processes. We propose that the grassland modeled ecosystem caused by the CNOP-type perturbation is unstable and exhibits two aspects: abrupt change and the time needed for the abrupt change from a grassland equilibrium state to a desert equilibrium state when the initial state variables and multiple parameters are considered simultaneously. We compared these findings with results affected by the CNOPs obtained by considering only uncertainties in initial state variables and in a single parameter. The numerical results imply that the nonlinear optimal pattern of initial perturbations and parameter perturbations, especially for more parameters or when special parameters are involved, plays a key role in determining stabilities and uncertainties associated with a simulated or predicted grassland ecosystem.
The Impact of Indian Ocean Variability on High Temperature Extremes across the Southern Yangtze River Valley in Late Summer
HU Kaiming, HUANG Gang, QU Xia, HUANG Ronghui
2012, 29(1): 91-100. doi: 10.1007/s00376-011-0209-2
In this study, the teleconnection between Indian Ocean sea surface temperature anomalies (SSTAs) and the frequency of high temperature extremes (HTEs) across the southern Yangtze River valley (YRV) was investigated. The results indicate that the frequency of HTEs across the southern YRV in August is remotely influenced by the Indian Ocean basin mode (IOBM) SSTAs. Corresponding to June--July--August (JJA) IOBM warming condition, the number of HTEs was above normal, and corresponding to IOBM cooling conditions, the number of HTEs was below normal across the southern YRV in August. The results of this study indicate that the tropical IOBM warming triggered low-level anomalous anticyclonic circulation in the subtropical northwestern Pacific Ocean and southern China by emanating a warm Kelvin wave in August. In the southern YRV, the reduced rainfall and downward vertical motion associated with the anomalous low-level anticyclonic circulation led to the increase of HTE frequency in August.
A Modeling Study of Seasonal Variation of Atmospheric Aerosols over East Asia
LI Jiawei, HAN Zhiwei
2012, 29(1): 101-117. doi: 10.1007/s00376-011-0234-1
In this study, a regional air quality model system (RAQMS) was applied to investigate the spatial distributions and seasonal variations of atmospheric aerosols in 2006 over East Asia. Model validations demonstrated that RAQMS was able to reproduce the evolution processes of aerosol components reasonably well. Ground-level PM10 (particles with aerodynamic diameter ≤10 μm) concentrations were highest in spring and lowest in summer and were characterized by three maximum centers: the Taklimakan Desert (~1000 μg m-3), the Gobi Desert (~400 μg m-3), and the Huabei Plain (~300 μm-3) of China. Vertically, high PM10 concentrations ranging from 100 μg m-3 to 250 μg m-3 occurred from the surface to an altitude of 6000 m at 30o--45oN in spring. In winter, the vertical gradient was so large that most aerosols were restricted in the boundary layer. Both sulfate and ammonium reached their highest concentrations in autumn, while nitrate reached its maximum level in winter. Black carbon and organic carbon aerosol concentrations reached maximums in winter. Soil dust were strongest in spring, whereas sea salt exerted the strongest influence on the coastal regions of eastern China in summer. The estimated burden of anthropogenic aerosols was largest in winter (1621 Gg) and smallest in summer (1040 Gg). The sulfate burden accounted for ~42% of the total anthropogenic aerosol burden. The dust burden was about twice the anthropogenic aerosol burden, implying the potentially important impacts of the natural aerosols on air quality and climate over East Asia.
Application of the Conditional Nonlinear Optimal Perturbation Method to the Predictability Study of the Kuroshio Large Meander
2012, 29(1): 118-134. doi: 10.1007/s00376-011-0199-0
A reduced-gravity barotropic shallow-water model was used to simulate the Kuroshio path variations. The results show that the model was able to capture the essential features of these path variations. We used one simulation of the model as the reference state and investigated the effects of errors in model parameters on the prediction of the transition to the Kuroshio large meander (KLM) state using the conditional nonlinear optimal parameter perturbation (CNOP-P) method. Because of their relatively large uncertainties, three model parameters were considered: the interfacial friction coefficient, the wind-stress amplitude, and the lateral friction coefficient. We determined the CNOP-Ps optimized for each of these three parameters independently, and we optimized all three parameters simultaneously using the Spectral Projected Gradient 2 (SPG2) algorithm. Similarly, the impacts caused by errors in initial conditions were examined using the conditional nonlinear optimal initial perturbation (CNOP-I) method. Both the CNOP-I and CNOP-Ps can result in significant prediction errors of the KLM over a lead time of 240 days. But the prediction error caused by CNOP-I is greater than that caused by CNOP-P. The results of this study indicate not only that initial condition errors have greater effects on the prediction of the KLM than errors in model parameters but also that the latter cannot be ignored. Hence, to enhance the forecast skill of the KLM in this model, the initial conditions should first be improved, the model parameters should use the best possible estimates.
Relationship between Net Radiation and Broadband Solar Radiation in the Tibetan Plateau
HU Bo, WANG Yuesi, LIU Guangren
2012, 29(1): 135-143. doi: 10.1007/s00376-011-0221-6
The characteristics of net radiation (Rn)(0.3--10 μm) in Lhasa and Haibei in the Tibetan Plateau were analyzed based on long-term in-situ measurements of surface radiation data. The monthly average of daily Rn reached a minimum during the winter period followed by an increase until May and then a decline until January. This variation is consistent with solar activity. The annual mean daily total Rn values were 0.92 MJ m-2 d-1 and 0.66 MJ m-2d-1 in Lhasa and Haibei, respectively. A relationship between Rn and broadband solar radiation (Rs) was demonstrated by a good linear correlation at the two sites. Rn can be an accurate estimate from Rs. The estimated Rn values were similar to the observed values, and the relative deviations between the estimates and measurements of Rn were 2.8% and 3.8% in Lhasa and Haibei, respectively. The application of the Rn estimating model to other locations showed that it could provide acceptable estimated Rn values from the Rs data. Furthermore, we analyzed the influence of clouds on Rn by different clear index (Ks), defined as the ratio of Rs to the extraterrestrial solar irradiance on a horizontal surface. The results indicate that more accurate results are associated with increased cloudy conditions. The influence of the albedo was also considered, but its inclusion in the model resulted in only a slight improvement. Because surface albedo is not usually measured, an expression based solely on global solar radiation could be of more extensive use.
A Quality Assurance Procedure and Evaluation of Rainfall Estimates for C-Band Polarimetric Radar
HU Zhiqun, LIU Liping, WANG Lirong
2012, 29(1): 144-156. doi: 10.1007/s00376-011-0172-y
A mobile C-band dual polarimetric weather radar J type (PCDJ), which adopts simultaneous transmission and simultaneous reception (STSR) of horizontally and vertically polarized signals, was first developed in China in 2008. It was deployed in the radar observation plan in the South China Heavy Rainfall Experiment (SCHeREX) in the summer of 2008 and 2009, as well as in Tropical Western Pacific Ocean Observation Experiments and Research on the Predictability of High Impact Weather Events from 2008 to 2010 in China (TWPOR). Using the observation data collected in these experiments, the radar systematic error and its sources were analyzed in depth. Meanwhile an algorithm that can smooth differential propagation phase (ФDP) for estimating the high-resolution specific differential phase (KDP) was developed. After attenuation correction of reflectivity in horizontal polarization (ZH) and differential reflectivity (ZDR) of PCDJ radar by means of KDP, the data quality was improved significantly. Using quality-controlled radar data, quantitative rainfall estimation was performed, and the resutls were compared with rain-gauge measurements. A synthetic ZH/KDP-based method was analyzed. The results suggest that the synthetic method has the advantage over the traditional ZH-based method when the rain rate is >5 mm h-1. The more intensive the rain rates, the higher accuracy of the estimation.
Interdecadal Modulation of the Influence of La Nina Events on Mei-yu Rainfall over the Yangtze River Valley
WANG Xin, WANG Dongxiao, ZHOU Wen, LI Chongyin
2012, 29(1): 157-168. doi: 10.1007/s00376-011-1021-8
The aim of this study was to investigate changes in the relationship between mei-yu rainfall over East China and La Nina events in the late 1970s, a period concurrent with the Pacific climate shift, using mei-yu rainfall data and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. This relationship was modulated by the climate shift: Before the 1977/1978 climate shift and after the 1992/1993 climate shift, mei-yu rainfall levels were above normal in most La Nina years, whereas during the period 1979--1991, mei-yu rainfall was usually below normal levels in La Nina years. Both composite analyses and results from an atmospheric general circulation model show remarkable detail in terms of La Nina's impacts on mei-yu rainfall in the late 1970s due to the change in the mean climatic state over the tropical Pacific. After the late 1970s, the tropical Pacific SSTs were warmer, and the mean state of low-level anticyclone circulation over the western North Pacific (WNP) weakened. Superimposed on La Nina--related cyclonic anomaly over the WNP, anticyclonic circulation weakened. Prior to the late 1970s, the mean state of low-level anticyclone circulation over the WNP was stronger and was less affected by La Nina--related anomalous cyclones. Anticyclone circulation may have brought moisture to the Yangtze River valley, leading to above-normal rainfall.
Possible Origins of the Western Pacific Warm Pool Decadal Variability
GAN Bolan, WU Lixin
2012, 29(1): 169-176. doi: 10.1007/s00376-011-0193-6
In this study, the impacts of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on the western Pacific warm pool (WPWP) were investigated. Our results show that the WPWP is linked with the PDO and the AMO at multiple time scales. On the seasonal time scales, the WPWP and the PDO/AMO reinforce each other, while at decadal time scales the forcing roles of the PDO and the AMO dominate. Notably, a positive PDO tends to enlarge the WPWP at both seasonal and decadal time scales, while a positive AMO tends to reduce the WPWP at decadal time scales. Furthermore, the decadal variability of the WPWP can be well predicted based on the PDO and AMO.
Development of the Convective Boundary Layer Capping with a Thick Neutral Layer in Badanjilin: Observations and Simulations
HAN Bo, LU Shihua, AO Yinhuan
2012, 29(1): 177-192. doi: 10.1007/s00376-011-0207-4
In this study, the development of a convective boundary layer (CBL) in the Badanjilin region was investigated by comparing the observation data of two cases. A deep neutral layer capped a CBL that occurred on 30 August 2009. This case was divided into five sublayers from the surface to higher atmospheric elevations: surface layer, mixed layer, inversion layer, neutral layer, and sub-inversion layer. The development process of the CBL was divided into three stages: S1, S2, and S3. This case was quite different from the development of the three-layer CBL observed on 31 August 2009 because the mixed layer of the five-layer CBL (CBL5) eroded the neutral layer during S2. The specific initial structure of the CBL5 was correlated to the synoptic background of atmosphere during nighttime. The three-stage development process of the CBL5 was confirmed by six simulations using National Center for Atmospheric Research (USA) large-eddy simulation (NCAR-LES), and some of its characteristics are presented in detail.
A Possible Cause for Different Diurnal Variations of Warm Season Rainfall as Shown in Station Observations and TRMM 3B42 Data over the Southeastern Tibetan Plateau
CHEN Haoming, YUAN Weihua, LI Jian, YU Rucong
2012, 29(1): 193-200. doi: 10.1007/s00376-011-0218-1
In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine observation stations in the Chinese National Meteorological Station Network to investigate the influences of station location on the different diurnal rainfall variations between station records and Tropical Rainfall Measuring Mission (TRMM) data products. The results indicate that the diurnal variation of warm season rainfall is closely related to location of stations. The prevailing nocturnal rainfall peak in observations at routine stations can be largely attributed to the relatively lower location of the stations, which are mostly situated in valleys. The records at Seqilashan stations on hillsides revealed an evident diurnal afternoon peak of warm season rainfall, similar to that indicated by TRMM data. The different diurnal phases between valley and hillside stations are closely related to the orographically induced regional circulations caused by the complex topography over the Tibetan Plateau. The results of this study indicate that the prevailing nocturnal rainfall associated with the relatively lower location of routine observation stations can partially explain the diurnal rainfall variations between observation station records and TRMM data.
A Regional Ensemble Forecast System for Stratiform Precipitation Events in Northern China. Part I: A Case Study
ZHU Jiangshan, Fanyou KONG, LEI Hengchi
2012, 29(1): 201-216. doi: 10.1007/s00376-011-0137-1
A single-model, short-range, ensemble forecasting system (Institute of Atmospheric Physics, Regional Ensemble Forecast System, IAP REFS) with 15-km grid spacing, configured with multiple initial conditions, multiple lateral boundary conditions, and multiple physics parameterizations with 11 ensemble members, was developed using the Weather and Research Forecasting Model Advanced Research modeling system for prediction of stratiform precipitation events in northern China. This is the first part of a broader research project to develop a novel cloud-seeding operational system in a probabilistic framework. The ensemble perturbations were extracted from selected members of the National Center for Environmental Prediction Global Ensemble Forecasting System (NCEP GEFS) forecasts, and an inflation factor of two was applied to compensate for the lack of spread in the GEFS forecasts over the research region. Experiments on an actual stratiform precipitation case that occurred on 5--7 June 2009 in northern China were conducted to validate the ensemble system. The IAP REFS system had reasonably good performance in predicting the observed stratiform precipitation system. The perturbation inflation enlarged the ensemble spread and alleviated the underdispersion caused by parent forecasts. Centering the extracted perturbations on higher-resolution NCEP Global Forecast System forecasts resulted in less ensemble mean root-mean-square error and better accuracy in probabilistic quantitative precipitation forecasts (PQPF). However, the perturbation inflation and recentering had less effect on near-surface-level variables compared to the mid-level variables, and its influence on PQPF resolution was limited as well.