Decadal variation of different durations of continuous Meiyu precipitation and the possible cause

The features of the decadal evolution of different durations of continuous Meiyu precipitation and their possible cause from the viewpoint of the low-level intraseasonal oscillation(ISO) are examined in this study. It is found that the total frequency of Meiyu precipitation events of certain duration gradually decreases as the duration of the events increases,and the main center of the events moves from the northern Yangtze-Huaihe River Valley(YHRV) to the southern YHRV. The linear trends of different durations of continuous Meiyu precipitation indicate that longer-duration precipitation has become significantly less frequent since 2000,while 2-day and 3-4-day continuous precipitation processes have become more frequent. At the same time,a close relationship between the variation in the low-level ISO and the decadal evolution of frequency of longer-duration Meiyu precipitation is detected. Clearly,since 2000,the low-level ISO has significantly decreased,and a single peak of longer-duration events has been replaced by several peaks of shorter-duration events,which has resulted in a significant decrease in the frequency of longer-duration precipitation. Meanwhile,low-level baroclinicity increased(decreased) during each period,which is in accordance with the increasing(decreasing) frequency of longer-duration precipitation. It is confirmed that longer-duration precipitation has significantly decreased in recent years.     

“Climate effect” of the northeast cold vortex and its influences on Meiyu

The Northeast Cold Vortex (NECV) is an important weather system in the middle and high latitudes in East Asia. Its time scale is synoptic, yet the frequent activities of NECV have significant "climate effect" which influences not only the monthly temperature in the lower troposphere in Northeast China but also the Meiyu rainfall in East Asia. On the basis of ERA-40 reanalysis data provided by ECMWF, the "climate effect" of NECV and its relationship with Meiyu in East Asia are studied. It is shown that there is significant correlation between NECV during the Meiyu period and rainfall amount: strong NECV corresponds to more Meiyu rainfall and weak NECV corresponds to less rainfall. In strong NECV years, the dry and cold air from the north is led to the south by NECV, converges with the lower-level warm and wet southwesterly on the north verge of Meiyu region, thus forms an unstable stratification of "upper dryness and lower wetness" . Triggered by ascending motion, the Meiyu rainfall amount is more than usual. It is on the contrary in weak NECV years. The anomalous SST in north Pacific in the previ-ous year may be a factor that results in the anomalous NECV at Meiyu period. The land-sea thermal contrast in summer facilitates NECV, while that in winter inhibits NECV. All of the above provide a meaningful result for the short-term climate prediction of NECV and Meiyu.     

Regional relationship between the Jiang-Huai Meiyu and the equatorial surface-subsurface temperature anomalies

The Jiang-Huai Meiyu rainy season can be distinguished into the Jiangnan Meiyu spell and the Huaihe Meiyu spell. The Jiangnan Meiyu spell appears on the last ten days in June and the Huaihe Meiyu spell lasts from early July to middle July. An inter-decadal transition was observed in 1998 respectively from the anomalies of Jiangnan Meiyu rainfall, the sea surface temperature (SST), and the subsurface tem- perature in the equatorial Pacific. Since the beginning of the 21^_st century, opposite trends and biennial oscillations of the Meiyu rainfall are observed in the Jiangnan and Huaihe basins. Before the strong La Niña of 1999―2000, the positive SST anomalies usually occurred in the eastern equatorial Pacific. Since the beginning of the 21^_st century, a precursory warming signal of SST anomaly comes from the subsurface temperature which is centrally exposed near the dateline in the central equatorial Pacific. The above-normal Meiyu rainfall in 2003, 2005 and 2007 over the Huaihe basin followed the prior winter- spring positive SST anomaly near the dateline. A relationship shows that the more Jiangnan (Huaihe) Meiyu follows the winter-spring warm water in the eastern (central) equatorial Pacific.     

Interannual variability of the Meiyu onset over Yangtze-Huaihe River Valley and analyses of its previous strong influence signal

Meiyu onset (MO) over Yangtze-Huaihe River Valley (YHRV) possesses obvious characteristics of interannual variations. Based on NCEP/NCAR reanalysis data sets, NOAA OLR and ERSST data, the in-terannual variability of MO(IVMO) and its previous strong influence signal (PSIS) are investigated. The possible mechanisms that the PSIS affecting IVMO are also discussed. The results show that the pre-vious CP-ENSO (Central Pacific El Nio/Southern Oscillation) event is the PSIS affecting IVMO and it has a better accu...     

Recent temperature increase recorded in an ice core in the source region of Yangtze River

Interests on climate change in the source region of Yangtze River have been raised since it is a region with the greatest warming over the Tibetan Plateau (TP). A 70-year history of precipitation δ~(18)O has been recovered using an ice core record retrieved in a plat portion of the firn area in the Guoqu Glacier (33°34′37.8″N, 91°10′35.3″E, 5720 m a.s.l.), Mt. Geladaindong (the source region of Yangtze River), in November, 2005. By using a significant positive relationship between ice core δ~(18)O record and summer air temperature (July to September) from the nearby meteorological stations, a history of summer air temperature has been reconstructed for the last 70 years. Summer temperature was relatively low in 1940s and high in 1950s to the middle of 1960s. The lowest temperature occurred in the middle of 1970s. Temperature was low in 1980s and dramatically increased since 1990s, keeping the trend to the begin-ning of the 21st century. The warming rate recorded in the ice core with 0.5℃/10 a since 1970s is much higher that that in the central TP and the Northern Hemisphere (NH), and it becomes 1.1℃/10 a since 1990s which is also higher than these from the central TP and the NH, reflecting an accelerated warm-ing and a more sensitive response to global warming in the high elevation region.     

Decadal northward shift of the Meiyu belt and the possible cause

The feature of the decadal movement of the Meiyu belt and their association with East Asia atmospheric circulation for the period of 1979―2007 is examined in this study. It is shown that the Meiyu belt of China has a decadal shift in the late 1990s. There is a remarkable difference between the periods before and after 1999, with the Meiyu belt mainly located to the south of the Yangtze River valley before 1999, but afterward mainly located in the Huaihe River valley. At the same time, a distinctive tropospheric warming and stratospheric cooling trend is found in the mid-latitudes of East Asia, which causes the upper tropospheric pressure surfaces upward bulging and the tropoause elevated in the subtropics and associated widening of the subtropical area over East Asia. Accompanying the subtropics widening, the subtropical westerly jet over East Asia shifts northward and the East Asia tropical Hadley circulation expands poleward, which results in the northward shift of the Meiyu belt.     

Numerical simulation of Meiyu front and the diagnosis of moist vorticity vector

Moist vorticity vector is introduced to study the development and evolution of mesoscale convective vortex (MCV) in the Meiyu front precipitation with the Advanced Regional Predication System (ARPS). In this study, the heavy rainfall is simulated to investigate the genesis, development and dissipation of middle scale convective vortex, which occurred from 0000 UTC 3 July to 1200 UTC 5 July over the Jianghuai River valley. Moist vorticity vector (MVV) has zonal, radial and vertical components in its 3D spatial distribution. The simulation shows that the vertical component of moist vorticity vector well demonstrates the spatial distribution characteristics of middle scale convective vortex, especially in the process of Meiyu front precipitation. Diagnosis upon zonal, radial averaged and mass-integrated quantities of MVV shows that its vertical component and the surface precipitating ratio are in phase with a correlation coefficient of 0.68, indicating that the vertical component of MVV is closely associated with the Meiyu front precipitation. In addition, the tendency of the vertical component of MVV is mainly determined by the interaction between the vorticity and the zonal and radial gradient of condensational or depositional heating.     

Moisture transport source／sink structure of the Meiyu rain belt along the Yangtze River valley

Based on the analyses of the moisture transport structure in the whole layer of the troposphere along the Yangtze River valley during draught/flood years using the NCEP reanalysis data, this paper reveals that there exists a key region with a “Large Triangle” shape of transporting moisture for the Tibetan Plateau to Meiyu Belt and its“source/sink” structure; discloses that the interannual variation of the whole budget of inflow and outflow of moisture through the boundaries of a “Large Triangle” key region has the in-phase characteristic. Then a moisture transport structure over the skirt of the plateau and a conceptual model on the “transfer post” of moisture transport in the area of the South China Sea-Tibetan Plateau-Yangtze River valley in summer are put forward in this paper: the anti-phase feature of whole layer moisture transport flow patterns of Yangtze River valley during drought/flooding years is exhibited using the computational scheme of whole layer moisture transport correlation vector fields; a comprehensive dynamic model and its physical diagram of the teleconnection source/sink structure of the moisture transport of the Meiyu rain belt have been made. It shows that the moisture transfer effect over the skirt of the plateau from the ocean (Indian Ocean, South China Sea and west North Pacific) led to a moisture confluence belt in the Yangtze River valley and the teleconnection moisture transport source/sink structure over the “Large Triangle” shape area in flooding years.     

Meiyu in the middle and lower reaches of the Yangtze River since 1736

＂Yu Xue Fen Cun＂ records during the Qing Dynasty are used to identify the starting and ending dates of Meiyu at the period of 1736-1911. These results, along with the instrumental meteorological records, are used to reconstruct the series of length and precipitation of Meiyu during 1736-2000 over the middle and lower reaches of the Yangtze River. The characteristics of Meiyu are analyzed since 1736. Moreover, the strength of East Asian Summer Monsoon and locations of rainband are discussed, based on the relationship between the length of Meiyu and the Index of East Asian Summer Monsoon. It is found that the starting and ending dates and the length of Meiyu have significant interannual and interdecadal variations. Apart from 7-8 years, 20-30 years and 40 years cycles for the lengths of Meiyu, the centennial oscillation is also presented. The length of Meiyu, monsoon rainband movement over eastern China, and the strength of East Asian Summer Monsoon （EASM） have a very good correlation, which can be expressed in the following： during the periods of 1736-1770, 1821-1870 and 1921-1970, the EASM was stronger, and the monsoon rainband was located in North China and South China easily, corresponding to the decreased length of Meiyu. Whereas during the periods of 1771-1820, 1871-1920 and 1971-2000, the EASM was weaker and monsoon rainband usually stopped at the middle and lower reaches of the Yangtze River, corresponding to the increased length of Meiyu.     

Climate change in China in the 21st century as simulated by a high resolution regional climate model

Climate change in the 21st century over China is simulated using the Abdus Salam International Centre for Theoretical Physics (ICTP) Regional Climate Model version 3 (RegCM3). The model is one-way nested within the global model CCSR/NIES/FRCGC MIROC3.2_hires (Center for Climate System Research/National Institute for Environmental Studies/Frontier Research Center for Global Change/Model for Interdisciplinary Research on Climate). A 150-year (1951-2100) transient simulation is conducted at 25 km grid spacing, under the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC SRES) A1B scenario. Simulations of present climate conditions in China by RegCM3 are compared against observations to assess model performance. Results show that RegCM3 reproduces the observed spatial structure of surface air temperature and precipitation well. Changes in mean temperature and precipitation in December-January-February (DJF) and June-July-August (JJA) during the middle and end of the 21st century are analyzed. Significant future warming is simulated by RegCM3. This warming becomes greater with time, and increased warming is simulated at high latitude and high altitude (Tibetan Plateau) areas. In the middle of the 21st century in DJF, a general increase of precipitation is found in most areas, except over the Tibetan Plateau. Precipitation changes in JJA show an increase over northwest China and a decrease over the Tibetan Plateau. There is a mixture of positive and negative changes in eastern China. The change pattern at the end of the century is generally consistent with that in mid century, except in some small areas, and the magnitude of change is usually larger. In addition, the simulation is compared with a previous simulation of the RegCM3 driven by a different global model, to address uncertainties of the projected climate change in China.     

Microstructural evolution in the surface of Ti-10V-2Fe-3Al alloy by solution treatments

By solution treatments in vacuum and in air,the surface region of Ti-10V-2Fe-3Al exhibits different microstructures from the interior region of the alloy.When solution treated in vacuum,the microstructure of the specimen is composed of dominant β phase and a few of α " martensite in surface region,with a large amount of α" martensite and a little of β phase in interior.When solution treated in air,the specimen is characterized by dominant surficial a phase and interior β phase.In addition,the lattice parameter evolutions of a and β phases were observed in the surface region of the specimens by solution treatment in air.The mechanism for the surface effects is discussed in light of the structural stability and phase evolution in Ti-10V-2Fe-3Al alloy with solution treatments.     

Numerical study of flow pattern modulation in a vertical phase separation condenser tube

The passive phase separation concept was proposed to modulate flow patterns for heat transfer enhancement. By the flow pattern modulation, the gas tends to be near the wall and the liquid tends to be in the tube core. Experiment has been performed to verify the fresh idea and the flow pattern modulation mechanism was analyzed qualitatively. This paper focuses on the numerical simulation of the bubble dynamics for a single bubble in the vertical phase separation condenser tube to quantitatively explore the flow pattern mechanism, based on a multiscale grid system and the volume-of-fluid (VOF) method. It is found that: (1) the modulated liquid film thickness can be decreased by 70% compared to that in the bare tube region; (2) the modulated bubble traveling velocity can be doubled, causing the increased liquid velocity and velocity gradient in the annular region to weaken the fluid boundary layer; (3) the significantly increased bubble traveling velocity in the annular region promotes the mass and momentum exchange between the annular region and the core region, and yields the self-sustained pulsating flow in the core region. The above three factors are benefit for the performance improvement of the heat transfer facilities.     

Response of water budget to recent climatic changes in the source region of the Yellow River

Discharge in the source region of the Yellow River significantly declined after 1990.China Meteorological Administration(CMA) data show that precipitation in this region was low in the 1990s but returned to above normal after 2002;in recent decades there has been rapid warming of surface air,moistening and wind speed decrease.To investigate the influences of recent climatic changes on the water budget,this study simulates the surface water budget at CMA stations within and surrounding the source region during 1960-2006,using an improved land surface model.Results indicate that the spatial pattern of precipitation change is an important factor(except for precipitation amount and intensity) in determining the response of runoff to precipitation changes.Low runoff in the 1990s was consistent with precipitation amount and intensity.The recovery of precipitation after 2002 is mainly from increased precipitation in the dry area of the source region.Evaporation was mainly limited by water availability in this dry area,and thus most of the precipitation increase was evaporated.By contrast,energy availability was a more important influence on evaporation in the wet area.There was more evaporation in the wet area because of rapid warming,although precipitation amount partly decreased and partly increased,contributing to the reduction of runoff after 2002.This control on evaporation and its response,together with the modified spatial pattern of precipitation,produced a water budget unfavorable for runoff generation in the source region during recent years.     

Temporal and spatial variations of the active layer along the Qinghai-Tibet Highway in a permafrost region

Using monitored active layer thickness(ALT) and environmental variables of 10 observation fields along the Qinghai-Tibet Highway in permafrost region of the Qinghai-Tibetan Plateau(QTP),a model for ALT estimation was developed.The temporal and spatial characteristics of the ALT were also analyzed.The results showed that in the past 30 years ALT in the study region increased at a rate of 1.33 cm a-1.Temperatures at the upper limit of permafrost and at 50 cm depth,along with soil cumulative temperature at 5 cm depth also exhibited a rising trend.Soil heat flux increased at a rate of 0.1 Wm-2 a-1.All the above changes demonstrated that the degradation of permafrost happened in the study region on the QTP.The initial thawing date of active layer was advanced,while the initial freezing date was delayed.The number of thawing days increased to a rate of 1.18 da-1.The variations of active layer were closely related to the permafrost type,altitude,underlying surface type and soil composition.The variations were more evident in cold permafrost region than in warm permafrost region,in high-altitude region than in low-altitude region,in alpine meadow region than in alpine steppe region;and in fine-grained soil region than in coarse-grained soil region.     

Projected changes in climate extremes over China in the 21st century from a high resolution regional climate model (RegCM3)

Based on a consecutive simulation of the 21st century conducted by RegCM3, changes in climate extremes over China are investigated, following abasic validation of the model performances in simulating present climate. The model is one-way nested within the global model of CCSR/NIES/FRCGC MIROC3.2_hires. A total of 150-years (1951-2100) transient simulation is carried out at 25 km grid spacing under the IPCC SRES A1B scenario. The indices of the extremesincludes SU (summer days), FD (frost days), GSL (growing season length) for temperature, SDII (simple daily intensity index), R10 (no. of days with precipitation 10 mm/d), and CDD (consecutive dry days) for precipitation. Results show that the model can reproduce both the spatial distribution and the values of the present day annual mean temperature and precipitationwell, and it also shows good performances in simulating the extreme indices. Following the significant warming, the indices of SU and GSL for warm events will increase while the indices of FD for cold events will decrease over China. Heavy precipitation events as measured by SDII and R10 show an general increase over the region, except the decrease ofR10 in the Northeast and central Tibetan Plateau andless change or decrease of it along the middle and lower reaches of the Yangtze River. Decrease of drynessas measured by CDD over northern part of China while increase of it over the Tibetan Plateau, Sichuan Basin and other places in southern China are simulated by the model. This leads to the less change of the regional mean CDD in the time series in the 21st century unlike the other indices, which show clear trend of change following the time evolution.     

Interannual variation of annual precipitation and urban effect on precipitation in the Beijing region

The large scale character of the interannual variation of precipitation and the urban effect on local annual precipitation anomaly are investigated in this paper based on the 1960-2000 annual precipitation observations at 20 stations in the Beijing region.The results show that:the annual precipitation in the Beijing region possesses the large scale variation character with the linear trend of-1.197/10 yr,which corresponds to a total reduction of 27.82 mm in annual precipitation in the 41 years;the local annual precipitation anomalies(percent of the normal 1960-2000)show a positive center near the urban area,i.e.urban precipitation island(UPI),whose intensity increases with the linear trend of 0.6621%/10 yr,opposite to the interannual trend of large scale precipitation over the Beijing region;changes in the UPI are also associated with the intensity of synoptic processes of precipitation,and when the synoptic processes are strong(wet years),the intensity of UPI strengthens,while the synoptic processes are weak(dry years),and the UPI disappears in the Beijing region.     

Effect of Ni addition on the glass-forming ability and soft-magnetic properties of FeNiBPNb metallic glasses

The effect of Ni addition on the glass-forming ability (GFA) and soft-magnetic properties of an (Fe1-xNix)75.5B14.5P7Nb3 (x=0-0.6) alloy system were investigated. We found that the addition of Ni was effective in allowing the alloy to approach a eutectic point as well as increasing the thermal stability of the supercooled liquid. By increasing the amount of Ni,the supercooled liquid region (ΔTx),the reduced glass transition temperature Trg (Tg/Tl) and the Y parameter [Tx/(Tg+Tl)] increased from 49 to 75 K,0...     

LA-ICP-MS dating of Zhangjiakou Formation volcanic rocks in the Zhangjiakou region and its geological signi?cance

The geological cross section of the Zhangjiakou Formation is originally established in the Zhangjiakou region. From the dating of four samples from typical cross sections of the Zhangjiakou Formation in the Zhangjiakou region, the age range is found to be mainly from 143.0 ± 3.7 Myr to 136.1 ± 1.4 Myr, which almost equals the sum of the age range of the Zhangjiakou Formation (136–135 Myr) and that of the Tuchengzi Formation (143–136 Myr) in the Luanping region, and the Zhangjiakou and Tuchengzi Formations in Zhangjiakou-Luanping of North Hebei are found to be conformable. The evidence above indicates that the Zhangjiakou and Tuchengzi Formations, which are distributed in Zhangjiakou-Luanping, were formed under the same geological setting. Volcanic activity was earlier and longer (143–136 Myr) in the western region (Zhangjiakou) than that in the eastern region (Luanping). The ‘‘Zhangjiakou Formation” in Chengde and Pingquan formed in the period in which the Yixian Formation in West Liaoning formed, so should be renamed the Yixian Formation.     

Oxygen isotope compositions of eclogites in Rongcheng,Eastern China

Collected from the Rongcheng region,Shandong Province,the three types of eclogites suffering the UHP (i.e.ultra-high pressure )metamorphism have obviously different oxygen isotope compositions.The eclogites occurring in regional orthogneisses and ultramafic rocks have the oxygen isotope compositions of normal eclogites in the world,but the eclogites existing in marbles are extremely enriched in ^18 O.By applying oxygen isotope geothermometry ,for the all types of exlogites,the temperature estimates of quartz-garnet pair,in principle,indicate the formation temperatures of eclogites,so that the peak-metamorphic temperatures are estimated to be averagely little higher than 800℃ ,which are consistent with the estimates by using other geothermometers according to cation partitioning between coesisting phases ,The δ^18O values of eclogitic inclusions hosted in marbles from Yangguantun,Rongcheng region ,are far higher than the values of eclogites (including eclogitic inclusions in marbles ) from the Dabieshan and other places of the Sulu,The oxygen isotope compositions of various minerals indicate that the formation temperatures of eclogites from the Rongcheng region ,in genceral ,are higher than that from the Dabieshan and the southwestern part of the Sulu ,but the dispersive temperatures estimated by different mineral pairs probably refect that the UHP eclogites from the Rongcheng region generally suffered overprinted metamorphisms during the exhumation.     

Mesoscale eddy effects on the wintertime vertical mixing in the formation region of the North Pacific Subtropical Mode Water

Mesoscale eddy effects on the wintertime vertical mixing in the formation region of the North Pacific Subtropical Mode Water （NPSTMW） are studied using hydrographic data from Argo profiling floats deployed in the Kuroshio recirculation region in February and March of 2001. Anticyclonic （warm） eddy enhances the wintertime vertical mixing and results in the deep mixed layer and the deep thermocline. Consequently, a large volumetric water mass with low potential vorticity corresponding to the prototype of NPSTMW tends to be formed. By contrast, cyclonic （cold） eddy is unfavorable for the vertical mixing process and halts the deepening of the mixed layer and thus the formation of mode water. Further analysis shows that cyclonic eddies prevail in the late 1990s in the formation region of NPSTMW, which lead to significant suppression of the wintertime vertical mixing （96-98） and thus are unfavorable for the formation of NPSTMW; while the situation is completely reversed in the early 1990s （93-95）.