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2014 Vol. 31, No. 1

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The 30-60-day Intraseasonal Oscillations over the Subtropical Western North Pacific during the Summer of 1998
LU Riyu*, DONG Huilin, SU Qin, and Hui DING
2014, 31(1): 1-7. doi: 10.1007/s00376-013-3019-x
The features of 30-60-day convection oscillations over the subtropical western North Pacific (WNP) were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP during summer 1998. It was found that 30-60-day oscillations were extremely strong in that summer over both the subtropical and tropicalWNP, providing a unique opportunity to study the behavior of subtropical oscillations and their relationship to tropical oscillations. Further analyses indicated that 30-60-day oscillations propagate westwards over the subtropical WNP and reach eastern China. In addition, 30-60-day oscillations in the subtropics are affected by those over the South China Sea (SCS) and tropical WNP through two mechanisms: (1) direct propagation from the tropics into the subtropics; and (2) a seesaw pattern between the tropics and subtropics, with the latter being predominant.
Greenland Ice Sheet Contribution to Future Global Sea Level Rise based on CMIP5 Models
YAN Qing*, WANG Huijun, Ola M. JOHANNESSEN, and ZHANG Zhongshi
2014, 31(1): 8-16. doi: 10.1007/s00376-013-3002-6
Sea level rise (SLR) is one of the major socioeconomic risks associated with global warming. Mass losses from the Greenland ice sheet (GrIS) will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice sheet behavior. We used the ice sheet model SICOPOLIS (SImulation COde for POLythermal Ice Sheets) driven by climate projections from 20 models in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to estimate the GrIS contribution to global SLR. Based on the outputs of the 20 models, it is estimated that the GrIS will contribute 016 (027) cm to global SLR by 2100 under the Representative Concentration Pathways (RCP) 4.5 (RCP 8.5) scenarios. The projected SLR increases further to 722 (733) cm with 2basal sliding included. In response to the results of the multimodel ensemble mean, the ice sheet model projects a global SLR of 3 cm and 7 cm (10 cm and 13 cm with 2basal sliding) under the RCP 4.5 and RCP 8.5 scenarios, respectively. In addition, our results suggest that the uncertainty in future sea level projection caused by the large spread in climate projections could be reduced with model-evaluation and the selective use of model outputs.
A Velocity Dealiasing Scheme for C-band Weather Radar Systems
LI Gang, HE Guangxin, Xiaolei ZOU*, and Peter Sawin RAY
2014, 31(1): 17-26. doi: 10.1007/s00376-013-2251-8
A dealiasing algorithm for radar radial velocity observed by C-band Doppler radars is presented as an extension of an existing S-band dealiasing algorithm. This has operational significance in that many portable and many commercial broadcast radars, as well as approximately one half of the Chinese weather radar network (CINRAD), are C-band radars. With a wavelength of about 5 cm, the Nyquist interval of C-band radars is just about one half that of S-band radars (wavelength of about 10 cm) and thus has more velocity folding. The proposed algorithm includes seven modules to remove noisy data, find the starting radials, dealias velocities, and apply least squares error checking in both the radial and azimuth directions. The proposed velocity dealiasing method was applied to one widespread rain case and three strong convective cases from radars operating in China. It was found that, on average, 92.95% of the aliased radial velocity data could be correctly de-aliased by the algorithm, resulting in 96.65% of the data being valid.
A Relocation-based Initialization Scheme to Improve Track-forecasting of Tropical Cyclones
GAO Feng*, Peter P. CHILDS, Xiang-Yu HUANG, Neil A. JACOBS, and Jinzhong MIN
2014, 31(1): 27-36. doi: 10.1007/s00376-013-2254-5
A relocation procedure to initialize tropical cyclones was developed to improve the representation of the initial conditions and the track forecast for Panasonic Weather Solutions Tropical Operational Forecasts. This scheme separates the vortex perturbation and environment field from the first guess, then relocates the initial vortex perturbations to the observed position by merging them with the environment field. The relationships of wind vector components with stream function and velocity potential are used for separating the vortex disturbance from first guess. For the separation of scalars, a low-pass Barnes filter is employed. The irregular-shaped relocation area corresponding to the specific initial conditions is determined by mapping the edge of the vortex radius in 36 directions.Then, the non-vortex perturbations in the relocation area are removed by a two-pass Barnes filter to retain the vortex perturbations, while the variable fields outside the perimeter of the modified vortex are kept identical to the original first guess. The potential impacts of this scheme on track forecasts were examined for three hurricane cases in the 2011-12 hurricane season. The experimental results demonstrate that the initialization scheme is able to effectively separate the vortex field from the environment field and maintain a relatively balanced and accurate relocated first guess. As the initial track error is reduced, the following track forecasts are considerably improved. The 72-h average track forecast error was reduced by 32.6% for the cold-start cases, and by 38.4% when using the full-cycling data assimilation because of the accumulated improvements from the initialization scheme.
Retrieval of Vertical Distribution of Tropospheric Refractivity through Ground-Based GPS Observation
WU Xue*, WANG Xin, and LÜ Daren
2014, 31(1): 37-47. doi: 10.1007/s00376-013-2215-z
In the present reported study, the vertical distributions of local atmospheric refractivity were retrieved from groundbased GPS observations at low elevation angles. An improved optimization method was implemented at altitudes of 010 km to search for a best-fit refractivity profile that resulted in atmospheric delays most similar to the delays calculated from the observations. A ray-tracing model was used to simulate neutral atmospheric delays corresponding to a given refractivity profile. We initially performed a theoretical retrieval, in which no observation data were involved, to verify the optimization method. A statistical relative error of this theoretical retrieval (2% to 2%) indicated that such a retrieval is effective. In a practical retrieval, observations were obtained using a dual-frequency GPS receiver, and its initial value was provided by CIRA86aQ UoG data. The statistical relative errors of the practical retrieval range from3% to 5% were compared with co-located radiosonde measurements. Results clearly revealed diurnal variations in local refractivity profiles. The results also suggest that the general vertical distribution of refractivity can be derived with a high temporal resolution. However, further study is needed to describe the vertical refractivity gradient clearly.
Impact of Urbanization on Low-Temperature Precipitation in Beijing during 19602008
HAN Zuoqiang, YAN Zhongwei*, LI Zhen, LIU Weidong, and WANG Yingchun
2014, 31(1): 48-56. doi: 10.1007/s00376-013-2211-3
Daily precipitation and temperature records at 13 stations for the period 19602008 were analyzed to identify climatic change and possible effects of urbanization on low-temperature precipitation [LTP, precipitation of 0.1 mm d-1 occurring under a daily minimum temperature (Tmin) of 0C] in the greater Beijing region (BJR), where a rapid process of urbanization has taken place over the last few decades. The paper provides a climatological overview of LTP in BJR. LTP contributes 61.7% to the total amount of precipitation in BJR in the cold season (November-March). There is a slight increasing trend [1.22 mm (10 yr) -1] in the amount of total precipitation for the cold season during 1960-2008. In contrast, the amount of LTP decreases by 0.6 mm (10 yr) -1. The warming rate of Tmin in BJR is 0.66C (10 yr) -1. Correspondingly, the frequency of LTP decreases with increasing Tmin by -0.67 times per C. The seasonal frequency and amount of LTP in southeast BJR (mostly urban sites) are 17%20% less than those in the northwestern (rural and montane sites). The intensity of LTP for the urban sites and northeastern BJR exhibited significant enhancing trends [0.18 and 0.15 mm d-1 (10 yr) -1, respectively]. The frequency of slight LTP (0.2 mm d-1) significantly decreased throughout BJR [by about15.74% (10 yr) -1 in the urban area and northeast BJR], while the contribution of the two heaviest LTP events to total LTP amount significantly increased by 3.2% (10 yr) -1.
Decadal Variations of Intense Tropical Cyclones over the Western North Pacific during 19482010
ZHAO Haikun, WU Liguang*, and WANG Ruifang
2014, 31(1): 57-65. doi: 10.1007/s00376-013-3011-5
Using Joint Warning Typhoon Center (JTWC) best track data during the period 19482010, decadal and interdecadal changes of annual category 4 and 5 tropical cyclone (TC) frequency in the western North Pacific basin were examined. By allowing all of the observed TCs in the JTWC dataset to move along the observed TC tracks in a TC intensity model, the annual category 4 and 5 TC frequency was simulated. The results agreed well with observations when the TC intensity prior to 1973 was adjusted based on time-dependent biases due to changes in measurement and reporting practices. The simulated and adjusted time series showed significant decadal (1218 years) variability, while the interdecadal (1832 years) variability was found to be statistically insignificant. Numerical simulations indicated that changes in TC tracks are the most important factor for the decadal variability in the category 4 and 5 TC frequency in the western North Pacific basin, while a combined effect of changes in SST and vertical wind shear also contributes to the decadal variability. Further analysis suggested that the active phase of category 4 and 5 TCs is closely associated with an eastward shift in the TC formation locations, which allows more TCs to follow a longer journey, favoring the development of category 4 and 5 TCs. The active phase corresponds with the SST warming over the tropical central and eastern Pacific and the eastward extension of the monsoon trough, thus leading to the eastward shift in TC formation locations.
The Interdecadal Changes of South Pacific Sea Surface Temperature in the Mid-1990s and Their Connections with ENSO
LI Gang*, LI Chongyin, TAN Yanke, and BAI Tao
2014, 31(1): 66-84. doi: 10.1007/s00376-013-2280-3
The characteristic changes of South Pacific sea surface temperature anomalies (SSTAs) for the period January 1979 to December 2011, during which the 1990s Pacific pan-decadal variability (PDV) interdecadal regime shifts occurred, were examined. Empirical Orthogonal Function (EOF) analysis was applied to the monthly mean SSTA for two sub-periods: January 1979 to December 1994 (P1) and January 1996 to December 2011 (P2). Both the spatial and temporal features of the leading EOF mode for P1 and P2 showed a remarkable difference. The spatial structure of the leading EOF changed from a tripolar pattern for P1 (EOF-P1) to a dipole-like pattern for P2 (EOF-P2). Besides, EOF-P1 (EOF-P2) had significant spectral peaks at 4.6 yr (2.7 yr). EOF-P2 not only had a closer association with El Niňo-Southern Oscillation (ENSO), but also showed a faster response to ENSO than EOF-P1 based on their lead-lag relationships with ENSO. During the development of ENSO, the South Pacific SSTA associated with ENSO for both P1 and P2 showed a significant eastward propagation. However, after the peak of ENSO, EOF-P1 showed a stronger persistence than EOF-P2, which still showed eastward propagation. The variability of the SSTA associated with the whole process of ENSO evolution during P1 and the SSTA associated with the development of ENSO during P2 support the existence of ocean-to-atmosphere forcing, but the SSTA associated with the decay of ENSO shows the phenomenon of atmosphere-to-ocean forcing.
Investigation of Uncertainties of Establishment Schemes in Dynamic Global Vegetation Models
SONG Xiang and ZENG Xiaodong*
2014, 31(1): 85-94. doi: 10.1007/s00376-013-3031-1
In Dynamic Global Vegetation Models (DGVMs), the establishment of woody vegetation refers to flowering, fertilization, seed production, germination, and the growth of tree seedlings. It determines not only the population densities but also other important ecosystem structural variables. In current DGVMs, establishments of woody plant functional types (PFTs) are assumed to be either the same in the same grid cell, or largely stochastic. We investigated the uncertainties in the competition of establishment among coexisting woody PFTs from three aspects: the dependence of PFT establishments on vegetation states; background establishment; and relative establishment potentials of different PFTs. Sensitivity experiments showed that the dependence of establishment rate on the fractional coverage of a PFT favored the dominant PFT by increasing its share in establishment. While a small background establishment rate had little impact on equilibrium states of the ecosystem, it did change the timescale required for the establishment of alien species in pre-existing forest due to their disadvantage in seed competition during the early stage of invasion. Meanwhile, establishment purely from background (the scheme commonly used in current DGVMs) led to inconsistent behavior in response to the change in PFT specification (e.g., number of PFTs and their specification). Furthermore, the results also indicated that trade-off between individual growth and reproduction/colonization has significant influences on the competition of establishment. Hence, further development of establishment parameterization in DGVMs is essential in reducing the uncertainties in simulations of both ecosystem structures and successions.
Variability of Atlantic Meridional Overturning Circulation in FGOALS-g2
HUANG Wenyu, WANG Bin*, LI Lijuan, DONG Li, LIN Pengfei, YU Yongqiang, ZHOU Tianjun, LIU Li, XU Shiming, XIA Kun, PU Ye, WANG Lu, LIU Mimi, SHEN Si, HU Ning, WANG Yong, SUN Wenqi, and DONG Fang
2014, 31(1): 95-109. doi: 10.1007/s00376-013-2155-7
The variability of Atlantic Meridional Overturning Circulation (AMOC) in the pre-industrial control experiment of the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2) was investigated using the model outputs with the most stable state in a 512-yr time window from the total 1500-yr period of the experiment. The period of AMOC in FGOALS-g2 is double peaked at 20 and 32 years according to the power spectrum, and 22 years according to an auto-correlation analysis, which shows very obvious decadal variability. Like many other coupled climate models, the decadal variability of AMOC in FGOALS-g2 is closely related to the convection that occurs in the Labrador Sea region. Deep convection in the Labrador Sea in FGOALS-g2 leads the AMOC maximum by 34 years. The contributions of thermal and haline effects to the variability of the convection in three different regions [the Labrador, Irminger and Greenland-Iceland- Norwegian (GIN) Seas] were analyzed for FGOALS-g2. The variability of convection in the Labrador and Irminger Seas is thermally dominant, while that in the colder GIN Seas can be mainly attributed to salinity changes due to the lower thermal expansion. By comparing the simulation results from FGOALS-g2 and 11 other models, it was found that AMOC variability can be attributed to salinity changes for longer periods (longer than 35 years) and to temperature changes for shorter periods.
Variation Characteristics of Ultraviolet Radiation over the North China Plain
HU Bo* and WANG Yuesi
2014, 31(1): 110-117. doi: 10.1007/s00376-013-2319-5
In situ measured data of broadband solar radiation (Rs) and ultraviolet (Uv) radiation were used to investigate the spatiotemporal variation properties of Uv radiation and the ratio of Uv radiation to Rs over the North China Plain (NCP). Based on the analysis, an empirical model for estimating Uv radiation under all weather conditions in this region was developed. The results showed that the annual Uv radiation over the NCP ranges from 0.38-0.52 MJ m-2 d-1. The highest value during the study period was recorded at the Changwu site, which is located near the margin of the Loess Plateau, while the lowest value appeared at the station in Beijing. The seasonal variation pattern of the ratio of Uv radiation to Rs is similar to that of Uv radiation; namely, the highest value appears in August and then decreases gradually until the lowest value appears in November. A small increasing trend in the Uv radiation levels and the ratio of Uv radiation to Rs was observed over the NCP. The evaluation results showed that the empirical estimation model can be widely used to estimate Uv radiation under all atmospheric conditions. The relative error between the modeled and measured daily values were within 15%.
The Impact of Global Warming on the Pacific Decadal Oscillation and the Possible Mechanism
FANG Changfang*, WU Lixin, and ZHANG Xiang
2014, 31(1): 118-130. doi: 10.1007/s00376-013-2260-7
The response of the Pacific Decadal Oscillation (PDO) to global warming according to the Fast Ocean Atmosphere Model (FOAM) and global warming comparison experiments of 11 IPCC AR4 models is investigated. The results show that North Pacific ocean decadal variability, its dominant mode (i.e., PDO), and atmospheric decadal variability, have become weaker under global warming, but with PDO shifting to a higher frequency. The SST decadal variability reduction maximum is shown to be in the subpolar North Pacific Ocean and western North Pacific (PDO center). The atmospheric decadal variability reduction maximum is over the PDO center. It was also found that oceanic baroclinic Rossby waves play a key role in PDO dynamics, especially those in the subpolar ocean. As the frequency of ocean buoyancy increases under a warmer climate, oceanic baroclinic Rossby waves become faster, and the increase in their speed ratio in the high latitudes is much larger than in the low latitudes. The faster baroclinic Rossby waves can cause the PDO to shift to a higher frequency, and North Pacific decadal variability and PDO to become weaker.
Dynamic and Numerical Study of Waves in the Tibetan Plateau Vortex
CHEN Gong, and LI Guoping
2014, 31(1): 131-138. doi: 10.1007/s00376-013-1035-5
In terms of its dynamics, The Tibetan Plateau Vortex (TPV) is assumed to be a vortex in the boundary layer forced by diabatic heating and friction. In order to analyze the basic characteristics of waves in the vortex, the governing equations for the vortex were established in column coordinates with the balance of gradient wind. Based on this, the type of mixed waves and their dispersion characteristics were deduced by solving the linear model. Two numerical simulations with triple-nested domainsone idealized large-eddy simulation and one of a TPV that took place on 14 August 2006were also carried out. The aim of the simulations was to validate the mixed wave deduced from the governing equations. The high-resolution model output data were analyzed and the results showed that the tangential flow field of the TPV in the form of center heating was cyclonic and convergent in the lower levels and anticyclonic and divergent in the upper levels. The simulations also showed that the vorticity of the vortex is uneven and might have shear flow along the radial direction. The changing vorticity causes the formation and spreading of vortex Rossby (VR) waves, and divergence will cause changes to the motion of the excitation and evolution of inertial gravity (IG) waves. Therefore, the vortex may contain what we call mixed inertial gravity-vortex Rossby (IG-VR) waves. It is suggested that some strongly developed TPVs should be studied in the future, because of their effects on weather in downstream areas.
Impacts of Diurnal Variation of Mountain-plain Solenoid Circulations on Precipitation and Vortices East of the Tibetan Plateau during the Mei-yu Season
ZHANG Yuanchun, SUN Jianhua*, and FU Shenming
2014, 31(1): 139-153. doi: 10.1007/s00376-013-2052-0
Diurnal variations of two mountain-plain solenoid (MPS) circulations associated with first-step terrain [Tibetan Plateau (TP)] and second-step terrain (high mountains between the TP and east plains) in China and their influence on the southwest vortex (SWV) and the mei-yu front vortex (MYFV) were investigated via a semi-idealized mesoscale numerical model [Weather Research and Forecasting (WRF)] simulation integrated with ten-day average fields (mei-yu period of 110 July 2007). The simulations successfully reproduced two MPS circulations related to first- and second-step terrain, diurnal variations from the eastern edge of the TP to the Yangtze River-Huaihe River valleys (YHRV), and two precipitation maximum centers related to the SWV, MYFV. Analyses of the averaged final seven-day simulation showed the different diurnal peaks of precipitation at different regions: from the afternoon to early evening at the eastern edge of the TP; in the early evening to the next early morning in the Sichuan Basin (SCB); and in the late evening to the next early morning over the mei-yu front (MYF). Analyses of individual two-day cases confirmed that the upward branches of the nighttime MPS circulations enhanced the precipitation over the SWV and the MYFV and revealed that the eastward extension of the SWV and its convection were conducive to triggering the MYFVs. The eastward propagation of a rainfall streak from the eastern edge of the TP to the eastern coastal region was primarily due to a series of convective activities of several systems from west to east, including the MPS between the TP and SCB, the SWV, the MPS between second-step terrain and the east plains, and the MYFV.
Impacts of Four Types of ENSO Events on Tropical Cyclones Making Landfall over Mainland China Based on Three Best-track Datasets
ZHANG Han, and GUAN Yuping*
2014, 31(1): 154-164. doi: 10.1007/s00376-013-2146-8
Impacts of El Nio Modoki (ENM), La Nia Modoki (LNM), canonical El Nio (CEN) and canonical La Nia (CLN) on tropical cyclones (TCs) that made landfall over mainland China during 19512011 are analysed using best-track data from China, the USA and Japan. Relative to cold phase years (LNM and CLN), landfalling TCs in warm years (ENM and CEN) have a farther east genesis location, as well as longer track lengths and durations, both in total and before landfall. ENM demonstrates the highest landfall frequency, most northerly mean landfall position, and shortest after-landfall sustainability (track length and duration), which indicate a more frequent and extensive coverage of mainland China by TCs, but with shorter after-landfall influence. CEN has low landfall frequency and the most southerly mean landfall location. LNM has the most westerly genesis location, being significantly farther west than the 19512011 average and leading to short mean track lengths and durations both in total or before landfall, all of which are significantly shorter than the 19512011 average. Variations in the low-level wind anomaly, vertical wind shear, mid-level relative humidity, steering flow, the monsoon trough and the western Pacific subtropical high (WPSH) can to some extent account for the features of frequency, location, track length and duration of landfalling TCs. Since ENSO Modoki is expected to become more frequent in the near future, the results for ENSO Modoki presented in this paper are of particular significance.
An Assessment of Improvements in Global Monsoon Precipitation Simulation in FGOALS-s2
ZHANG Lixia* and ZHOU Tianjun
2014, 31(1): 165-178. doi: 10.1007/s00376-013-2164-6
The performance of Version 2 of the Flexible Global Ocean-Atmosphere-Land System model (FGOALS-s2) in simulating global monsoon precipitation (GMP) was evaluated. Compared with FGOALS-s1, higher skill in simulating the annual modes of climatological tropical precipitation and interannual variations of GMP are seen in FGOALS-s2. The simulated domains of the northwestern Pacific monsoon (NWPM) and North American monsoon are smaller than in FGOALS-s1. The main deficiency of FGOALS-s2 is that the NWPM has a weaker monsoon mode and stronger negative pattern in spring-fall asymmetric mode. The smaller NWPM domain in FGOALS-s2 is due to its simulated colder SST over the western Pacific warm pool. The relationship between ENSO and GMP is simulated reasonably by FGOALS-s2. However, the simulated precipitation anomaly over the South African monsoon region-South Indian Ocean during La Nina years is opposite to the observation. This results mainly from weaker warm SST anomaly over the maritime continent during La Nia years, leading to stronger upper-troposphere (lower-troposphere) divergence (convergence) over the Indian Ocean, and artificial vertical ascent (descent) over the Southwest Indian Ocean (South African monsoon region), inducing local excessive (deficient) rainfall. Comparison between the historical and pre-industrial simulations indicated that global land monsoon precipitation changes from 1901 to the 1970s were caused by internal variation of climate system. External forcing may have contributed to the increasing trend of the Australian monsoon since the 1980s. Finally, it shows that global warming could enhance GMP, especially over the northern hemispheric ocean monsoon and southern hemispheric land monsoon.
Effects of a Remotely Sensed Land Cover Dataset with High Spatial Resolution on the Simulation of Secondary Air Pollutants over China Using the Nested-grid GEOS-Chem Chemical Transport Model
LI Mingwei, WANG Yuxuan*, and JU Weimin
2014, 31(1): 179-187. doi: 10.1007/s00376-013-2290-1
A number of remotely sensed land cover datasets with spatial resolutions1 km have recently become available or are in the process of being mapped. The application of these higher resolution and more up-to-date land cover datasets in chemical transport models (CTMs) is expected to improve the simulation of dry deposition and biogenic emissions of non-methane volatile organic compounds (NMVOCs), which affect ozone and other secondary air pollutants. In the present study, we updated the land cover dataset in the nested-grid GEOS-Chem CTM with the 1 km resolution GLC2000 land cover map and examined the resulting changes in the simulation of surface ozone and sulfate over China in July 2007. Through affecting the dry deposition velocities of ozone and its precursors, using GLC2000 in the dry deposition module can decrease the simulated surface ozone by 3% (up to 6 ppb) over China. Simulated surface sulfate shows an increase of 3% in northwestern China and a decrease of 1% in northern China. Applying GLC2000 in the biogenic emissions of the NMVOC module can lead to a 0.54.5 ppb increase in simulated surface ozone over East China, mainly driven by the larger coverage of broadleaf trees in East China in the GLC2000 dataset. Our study quantifies the large sensitivity to land cover datasets with different spatial resolutions and time periods of simulated secondary air pollutants over China, supporting ongoing research efforts to produce high resolution and dynamically updated land cover datasets over China, as well as for the globe.
Ocean Model Open Boundary Conditions with Volume, Heat and Salinity Conservation Constraints
WANG Qiang, ZHOU Weidong*, WANG Dongxiao, and DONG Danpeng
2014, 31(1): 188-196. doi: 10.1007/s00376-013-2269-y
Open boundary conditions (OBCs) for a regional ocean model that can be integrated stably over a long timeframe, as well as satisfy the volume, heat and salinity conservation constraints, were developed. First, the idea that the inward and outward flux information can be treated separately in the OBCs was adopted. Second, in order to maintain the property that the volume, heat and salinity remains conserved in the simulation domain, conservation constraints were added to the OBCs, and an inverse method utilized to solve the constraint equations. Ideal experiments were designed to investigate the conservation property, and the OBCs were found to work efficiently to maintain the volume, heat and salinity conservation. It was found that simulations were comparable to observations when the OBCs were applied to a regional ocean model.
Mean FlowStorm Track Relationship and RossbyWave Breaking in Two Types of El-Nio
LIU Chengji, REN Xuejuan*, and YANG Xiuqun
2014, 31(1): 197-210. doi: 10.1007/s00376-013-2297-7
The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking (RWB) processes associated with Eastern Pacific (EP) and Central Pacific (CP) El-Nio. During EP El-Nio, the geopotential height anomaly at 500 hPa (Z500) exhibits a Pacific-North America (PNA) pattern. During CP El-Nio, the Z500 anomaly shows a north positive-south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP El-Niňo, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking (AWB) occurs less frequently in EP El-Nio years, while cyclonic wave breaking (CWB) occurs more frequently in CP El-Nio years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP El-Nio. When AWB events occur less frequently over the North Pacific during EP El-Nio, Z500 decreases locally and the zonal wind is strengthened (weakened) to the south (north). This is because AWB events reflect a monopole high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP El-Nio conditions, and over North America under EP El-Niňo condition, Z500 increases (decreases) to the northeast (southwest), since CWB events are related to a northeast-southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific-North America region linked with the two types of El-Nio.
On the Response of the Global Subduction Rate to Global Warming in Coupled Climate Models
LIU Chengyan* and WANG Zhaomin
2014, 31(1): 211-218. doi: 10.1007/s00376-013-2323-9
The response of the global subduction rate to global warming was assessed based on a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models. It was found that the subduction rate of the global ocean could be significantly reduced under a warming climate, as compared to a simulation of the present-day climate. The reduction in the subduction volume was quantitatively estimated at about 40 Sv and was found to be primarily induced by the decreasing of the lateral induction term due to a shallower winter mixed layer depth. The shrinking of the winter mixed layer would result from intensified stratification caused by increased heat input into the ocean under a warming climate. A reduction in subduction associated with the vertical pumping term was estimated at about 5 Sv. Further, in the Southern Ocean, a significant reduction in subduction was estimated at around 24 Sv, indicating a substantial contribution to the weakening of global subduction.
A Variant Constrained Genetic Algorithm for Solving Conditional Nonlinear Optimal Perturbations
ZHENG Qin*, SHA Jianxin, SHU Hang, and LU Xiaoqing
2014, 31(1): 219-229. doi: 10.1007/s00376-013-2253-6
A variant constrained genetic algorithm (VCGA) for effective tracking of conditional nonlinear optimal perturbations (CNOPs) is presented. Compared with traditional constraint handling methods, the treatment of the constraint condition in VCGA is relatively easy to implement. Moreover, it does not require adjustments to indefinite parameters. Using a hybrid crossover operator and the newly developed multi-ply mutation operator, VCGA improves the performance of GAs. To demonstrate the capability of VCGA to catch CNOPS in non-smooth cases, a partial differential equation, which has onoff switches in its forcing term, is employed as the nonlinear model. To search global CNOPs of the nonlinear model, numerical experiments using VCGA, the traditional gradient descent algorithm based on the adjoint method (ADJ), and a GA using tournament selection operation and the niching technique (GA-DEB) were performed. The results with various initial reference states showed that, in smooth cases, all three optimization methods are able to catch global CNOPs. Nevertheless, in non-smooth situations, a large proportion of CNOPs captured by the ADJ are local. Compared with ADJ, the performance of GA-DEB shows considerable improvement, but it is far below VCGA. Further, the impacts of population sizes on both VCGA and GA-DEB were investigated. The results were used to estimate the computation time of VCGA and GA-DEB in obtaining CNOPs. The computational costs for VCGA, GA-DEB and ADJ to catch CNOPs of the nonlinear model are also compared.
A Methodological Study on Using Weather Research and Forecasting (WRF) Model Outputs to Drive a One-Dimensional Cloud Model
JIN Ling, Fanyou KONG, LEI Hengchi*, and HU Zhaoxia
2014, 31(1): 230-240. doi: 10.1007/s00376-013-2257-2
A new method for driving a One-Dimensional Stratiform Cold (1DSC) cloud model with Weather Research and Forecasting (WRF) model outputs was developed by conducting numerical experiments for a typical large-scale stratiform rainfall event that took place on 45 July 2004 in Changchun, China. Sensitivity test results suggested that, with hydrometeor profiles extracted from the WRF outputs as the initial input, and with continuous updating of soundings and vertical velocities (including downdraft) derived from the WRF model, the new WRF-driven 1DSC modeling system (WRF-1DSC) was able to successfully reproduce both the generation and dissipation processes of the precipitation event. The simulated rainfall intensity showed a time-lag behind that observed, which could have been caused by simulation errors of soundings, vertical velocities and hydrometeor profiles in the WRF output. Taking into consideration the simulated and observed movement path of the precipitation system, a nearby grid point was found to possess more accurate environmental fields in terms of their similarity to those observed in Changchun Station. Using profiles from this nearby grid point, WRF-1DSC was able to reproduce a realistic precipitation pattern. This study demonstrates that 1D cloud-seeding models do indeed have the potential to predict realistic precipitation patterns when properly driven by accurate atmospheric profiles derived from a regional short range forecasting system. This opens a novel and important approach to developing an ensemble-based rain enhancement prediction and operation system under a probabilistic framework concept.