THE FLUCTUATIONS OF DRY AND WET CLIMATE BOUNDARY AND ITS CAUSAL ANALYSES IN CHINA*

Based on yearly precipitation and Φ20 evaporation pan data during 1951 to 1999 of 295 stations,the aridity index is calculated in this paper.According to the aridity index,the climatic regions in China are divided into three types:the arid zone,the semi-arid zone and the humid zone. Isoline 0.20 is the boundary between arid and semi-arid zones.Isoline 0.50 is the boundary between semi-arid and humid zones.The fluctuations of dry and wet climate boundaries are very substantial,have greatly regional difference,and have the features of the whole shifting along the same direction and of the opposite moving along the contrary direction over the past 50 years.The semi-arid zone is a transitional zone between humid and arid zones,a border belt of monsoon,and a susceptible zone of environmental evolution in China. In the period of the late 1960s to the early 1970s,remarkable change had occurred for dry and wet climate in China.It manifests significantly that climate is from wetter into drought in most regions of northern China.Moreover,drought has an increasing trend.The fluctuations of climatic boundaries and the dry and wet variations in climate have substantial inter-decadal features. The main factors affecting the dry and wet climate boundary fluctuations and the dry and wet variations of climate in China are East Asian summer monsoon,Indian Monsoon,plateau monsoon in the Tibetan Plateau,westerly circulation,and West Pacific subtropical high.The different types of circulations and the strong and weak combinations of these circulations result in the regional differences of dry and wet climate changes in China.Inter-decadal variations of the dry and wet climate boundary fluctuations and of the arid and humid climate result from the inter-decadal changes of East Asian summer monsoon,Indian Monsoon,plateau monsoon,westerly circulation, and West Pacific subtropical high.The anomalous general atmospheric circulation in the Northern Hemisphere during the late 1960s to the early 1970s is the causes of arid and humid climate remarkable change in China.     

Large Scale Aspects of India-China Summer Monsoon Rainfall

This study investigates the dominant modes of variability in monthly and seasonal rainfall over the India-China region mainly through Empirical Orthogonal Function (EOF) analysis. The EOFs have shown that whereas the rainfall over India varies as one coherent zone, that over China varies in east-west oriented bands. The influence of this banded structure extends well into India.Relationship of rainfall with large scale parameters such as the subtropical ridge over the Indian and the western Pacific regions, Southern Oscillation, the Northern Hemispheric surface air temperature and stratospheric winds have also been investigated. These results show that the rainfall over the area around 40°N, 110°E over China is highly related with rainfall over India. The subtropical ridge over the Indian region is an important predictor over India as well an over the northern China region. '     

Changes of Precipitation Intensity Spectra in Different Regions of Mainland China During 1961-2006

The spectral characteristics of precipitation intensity during warm and cold years are compared in six regions of China based on precipitation data at 404 meteorological stations during 1961-2006.In all of the studied regions except North China,with the increasing temperature,a decreasing trend is observed in light precipitation and the number of light precipitation days,while an increasing trend appears in heavy precipitation and the heavy precipitation days.Although changes in precipitation days in North China are similar to the changes in the other five regions,heavy precipitation decreases with the increasing temperature in this region.These results indicate that in most parts of China,the amount of precipitation and number of precipitation days have shifted towards heavy precipitation under the background of a warming climate;however,the responses of precipitation distributions to global warming differ from place to place.The number of light precipitation days decreases in the warm and humid regions of China(Jianghuai region,South China,and Southwest China),while the increasing amplitude of heavy precipitation and the number of heavy precipitation days are greater in the warm and humid regions of China than that in the northern regions(North China,Northwest China,and Northeast China).In addition,changes are much more obvious in winter than in summer,indicating that the changes in the precipitation frequency are more affected by the increasing temperature during winter than summer.The shape and scale parameters of the Γ distribution of daily precipitation at most stations of China have increased under the background of global warming.The scale parameter changes are smaller than the shape parameter changes in all regions except Northwest China.This suggests that daily precipitation shifts toward heavy precipitation in China under the warming climate.The number of extreme precipitation events increases slightly,indicating that changes in the Γ distribution fitting parameters reflect changes in the regional precipitation distribution structure.     

Simulation of Desert-Scrub Growth: A Forcing to Warmer and More Pluvial Climate

Desert-fringe vegetation growing over bright, sandy soils reduces the surface albedo from above 0.4 to well below 0.3. Called desert-scrub, these shrubs form a predominantly vertical clumps protruding from the soil-level, thereby significantly increasing the coefficient of turbulent heat transfer from the surface. The impact on global and desert-belt climate of changes in these two surface characteristics was simulated by a multi-layer energy balance tnodel. Evaluated only as a forcing to a further climatic change (that is, without accounting for any possible feedbacks) the results are: if vegetation (such as apparently existed under the warmer climate of 6,000 BP ) grows over large areas in the arid, currently bare-soil regions, the annual Northern Hemisphere surface temperature increases by 0.7t (by 0.6'C in July ), the surface temperature over land in the 20-30°N zone increases by 0.9℃ in both the annual and the July means, and the land-ocean annual temperature contrast in this zone increases by 0.     

Numerical Simulation of Regional Climate Change under IPCC A2 Scenario in China

Regional climate change in China under the IPCC A2 Scenario, was simulated for continuous 10-yr period by the MM5V3, using the output of an IPCC A2 run from CISRO Mark 3 climate system model as lateral and surface boundary conditions. The regional climate change of surface air temperature, precipitation, and circulation were analyzed. The results showed that （1） the distribution of mean circulation, surface air temperature, and precipitation was reproduced by the MM5V3. The regional climate model was capable to improve the regional climate simulation driven by GCM. （2） The climate change simulation under the IPCC A2 Scenario indicated that the surface air temperature in China would increase in the future, with a stronger trend in winter and the increasing magnitude from the south to the north. The precipitation distribution would appear a distinct change as well. Annual mean precipitation would remarkably increase in Northeast China, Yangtze and Huaihe River Valley, and the south area of the valley. Meanwhile, rainfall would show a decreasing trend in partial areas of North China, and many regions of Southwest and Northwest China.     

An aridity trend in china and its abrupt feature in association with the global warming

A distinct aridity tread in China in last 100 years is presented by applying a linear fitting to both the climate re-cords and the hydrological records, which is supported by evidence of environmental changes and seems to be associ-ated with a global warming trend during this period.The Mann Kendall Rank statistic test reveals a very interesting feature that the climate of China entered into a dry regime abruptly in about l920’s, which synchronized with the rapid warming of the global temperature at almost the same time.According to an analysis of the meridional profile of observed global zonal mean precipitation anomalies during the peak period of global warming (1930-1940), the drought occurred in whole middle latitude zone (25oN-55oN) of the Northern Hemisphere, where the most part of China is located in. Although this pattern is in good agreement with the latitude distribution of the difference of zonal mean rates of precipitation between 4 × CO2 and 1 × CO2 simu-lated by climate model (Manabe and Wetherald, 1983), more studies are required to understand the linkage between the aridity trend in China and the greenhouse effect.The EOF analysis of the Northern Hemisphere sea level pressure for the season of June to August shows an ab-rupt change of the time coefficient of its first eigenvector from positive to negative in mid-lP^s, indicating an enhancement of the subtropical high over Southeast Asia and the western Pacific after that time. This is an atmos-pheric circulation pattern that is favorable to the development of dry climate in China.     

2018: The Hottest Summer in China and Possible Causes

In 2018, China experienced the hottest summer since 1961. The maximum, mean, and minimum temperatures all reached the highest. Air temperatures in most regions were much higher than normal; in northern China especially,the temperature anomalies were above double of the standard deviations. Consistent variations of temperature anomalies appeared in the national mean and in northern China on different timescales from intraseasonal to annual, indicating that the above normal temperature in northern China contributed significantly to the record-breaking hot summer of entire China. Relationships among the high temperature in summer 2018, the tropospheric circulation, and the global sea surface temperatures(SSTs) are further analyzed. It is found that the intensified and more northward western Pacific subtropical high(WPSH), weakened Northeast China cold vortex(NECV), and positive geopotential height anomaly from northern China to the Sea of Japan resulted in the abnormally high temperature in summer 2018. From late July to mid August, the WPSH was stronger than normal, with its ridge line jumping to north of 40°N; meanwhile, the NECV was much weaker and more northward than normal; both of the two systems led to the persistent high temperature in northern China during this period. In addition, the SSTs in Kuroshio and its extension area(K–KE) in summer 2018 were also the highest since 1961 and the greatest positive SST anomaly in K–KE was favorable for the above normal geopotential height over North China–Northeast China–Japan at 500 hPa, giving rise to the exceptionally high temperature in northern China.     

Interdecadal variability of temperature and precipitation in China since 1880

Reconstruction of a homogeneous temperature and precipitation series for China is crucial for a proper understanding of climate change over China. The annual mean temperature anomaly series of ten regions are found from 1880 to 2002. Positive anomalies over China during the 1920s and 1940s are noticeable.The linear trend for the period of 1880-2002 is 0.58℃ (100a)^-1, which is a little less than the global mean (0.60℃ (100a)^-l). 1998 was the warmest year in China since 1880, which is in agreement with theestimation of the global mean temperature. The mean precipitation on a national scale depends mainly on the precipitation over East China. Variations of precipitation in West China show some characteristics which are independent of those in the east. However, the 1920s was the driest decade not only for the east, but also for eastern West China during the last 120 years. The most severe drought on a national scale occurred in 1928. Severe droughts also occurred in 1920, 1922, 1926, and 1929 in North China.It is noticeable that precipitation over East China was generally above normal in the 1950s and 1990s;severe floods along the Yangtze River in 1954, 1991, and 1998 only occurred in these two wet decades.An increasing trend in precipitation variations is observed during the second half of the 20th century in West China, but a similar trend is not found in East China, where the 20- to 40-year periodicities are predominant in the precipitation variations.     

Trends of Temperature Extremes in Summer and Winter during 1971–2013 in China

The diurnal temperature range(DTR) has decreased dramatically in recent decades, but it is not yet obvious whether the extreme values of DTR have also reduced. Based on the daily maximum and minimum temperature data of 653 stations in China, a set of monthly indices of warm extremes, cold extremes, and DTR extremes in summer(June, July, August) and winter(December, January, February) were studied for spatial and temporal features during the period 1971–2013. Results show that the incidence of warm extremes has been increasing in most parts of China, while the opposite trend was found in the cold extremes for summer and winter months. Both increasing and decreasing trends of monthly DTR extremes were identified in China for both seasons. For high DTR extremes, decreasing trends were identified in northern China for both seasons, but increasing trends were found only in southern China in summer, while in winter, they were found in central China. Monthly low DTR extreme indices demonstrated consistent positive trends in summer and winter, while significant increases(P 0.05) were identified for only a few stations.     

Projected Changes in Kppen Climate Types in the 21st Century over China

Future changes in the climate regimes over China as measured by the Kppen climate classification are reported in this paper. The analysis is based on a high-resolution climate change simulation conducted by a regional climate model (the Abdus Salam International Center for Theoretical Physics (ICTP) RegCM3) driven by the global model of Center for Climate System Research (CCSR)/National Institute for Environment Studies (NIES)/Frontier Research Center for Global Change (FRCGC) MIROC3.2_hires (the Model for Interdisciplinary Research on Climate) under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. Validation of the model performances is presented first. The results show that RegCM3 reproduces the present-day distribution of the Kppen climate types well. Significant changes of the types are found in the future over China, following the simulated warming and precipitation changes. In southern China, the change is characterized by the replacement of subtropical humid (Cr) by subtropical winter-dry (Cw). A pronounced decrease of the cold climate types is found over China, e.g., tundra (Ft) over the Tibetan Plateau and sub-arctic continental (Ec) over northeast China. The changes are usually greater in the end compared with the middle of the 21st century.     

NUMERICAL STUDY ON INFLUENCE OF QINGHAI-XIZANG (TIBETAN) PLATEAU ON SEASONAL TRANSITION OF GLOBAL ATMOSPHERIC CIRCULATION

It is a worthwhile attempt to address the role of the Qinghai-Xizang Plateau in the seasonal transition of general circulation from a global prospective. In this paper, the CCM1 (R15L7)-LNWP spectral model is used to study the influences of the Qinghai-Xizang Plateau on the seasonal transfer of the general circulation, with the objective analysis form the State Meteorological Center for March 17, 1996 as the initial field. A mid-level heating source in regions on the same latitudes is shown to cause a warming center of 224 K to form on the level of 200 hPa that warms up the atmosphere by more than 7 K and a drop of temperature by about 6 K on most of the 200-hPa layer over the Antarctic continent, with the largest negative center being-8.28 K. It is favorable to the deepening and widening of the polar vortexes in the course of transition from summer to winter. The topographic effect of the plateau plays a vital role in forming and maintaining the mean troughs and ridges of the atmospheric circulation in Northern Hemisphere such that it strengthens (weakens) the south-north positive gradient of temperature on the northern (southern) side of the latitude zone in which the plateau sits and increases the north-south gradient of temperature near 30°N. The seasonal transition is thus favored so that the bulk travel of global westerly at the middle latitudes and the formation of Asian monsoon in early summer are made possible. In the equatorial and low-latitude areas where the geopotential is increased, the effect of the plateau terrain is also evident in that it is favorable for the northern withdrawal of the tropical high ridge in Southern Hemisphere and the northern shift of the subtropical high in Northern Hemisphere. In addition, the effect also helps increase the polar easterly over the Southern Hemisphere and weaken the low zone at 500 hPa. It acts as an increasing factor for the polar vortex around the Ross Sea and contributes to the genesis of the Somali Jet on the equator.     

THE CHARACTERISTICS OF TURBULENT TRANSPORT IN THE SURFACE LAYER OVER EASTERN TIBET DURING SUMMER 1986

The turbulent fluxes for sensible and latent heat and momentum are computed and analyses are carried outabout the factors in terms of the fluxes,with the profile methods,based on the data from the Tibetan(Xi-zang)Plateau Meteorological Experiment in 1986(TIPMEX-86).It is shown that the fluxes of various kindshave evident diurnal variation,and each decade mean diurnal variation is quite different from others.Thesensible heat flux is about 2/3 less in July than in June.The results indicate that the averaged drag coefficient,C_d,and the averaged bulk transfer coefficient of sensible heat,C_h,are 0.0052 and 0.0075 respectively,for theperiod 13 to 28 in June for Nagqu.But for Lhasa,the mean C_d is 0.0056,and the mean C_h is 0.0085,for the period of June 11 to July 20.It is found that C_d and C_h are not only the function of wind velocity,but also influenced by stability conditions and wind and temperature gradients.     

Sensitivity of Climate Changes to CO_2 Emissions in China

In this study, the authors demonstrate that the Coupled Model Intercomparison Project Phase 5 （CMIP5） models project a robust response in changes of mean and climate extremes to warming in China. Under a scenario of a 1% CO2 increase per year, surface temperature in China is projected to increase more rapidly than the global average, and the model ensemble projects more precipitation （2.2%/℃）. Responses in changes of climate extremes are generally much stronger than that of climate means. The majority of models project a consistent re- sponse, with more warm events but fewer cold events in China due to CO2 warming. For example, the ensemble mean indicates a high positive sensitivity for increasing summer days （12.4%/℃） and tropical nights （26.0%/℃）, but a negative sensitivity for decreasing frost days （-4.7%/℃） and ice days （-7.0%/℃）. Further analyses indicate that precipitation in China is likely to become more extreme, featuring a high positive sensitivity. The sensitivity is high （2.4%/℃） for heavy precipitation days （〉 10 mm d l） and increases dramatically （5.3%/℃） for very heavy precipitation days （〉 20 mm d-1）, as well as for precipitation amounts on very wet days （10.8%/℃） and extremely wet days （22.0%/℃）. Thus, it is concluded that the more extreme precipitation events generally show higher sensitivity to CO2 warming. Additionally, southern China is projected to experience an increased risk of drought and flood occurrence, while an increased risk of flood but a decreased risk of drought is likely in other regions of China.     

Simulation and Analysis of China Climate Using Two-Way Interactive Atmosphere-Vegetation Model （RIEMS-AVIM）

In this paper, an Atmosphere-Vegetation Interaction Model （AVIM） is coupled to the Regional Integrated Environment Model System （RIEMS）, and a 10-year integration for China is performed using the RIEMS-AVIM. The analysis of the results of the 10-year integration shows that the characters of the spatial distributions of temperature and precipitation over China are well simulated. The patterns of simulated surface sensible and latent heat fluxes match well with the spatial climatological atlas： the values of winter surface sensible and latent heat fluxes are both lower than climatological values over the whole country. Summer surface sensible heat flux is higher than climatological values in western China and lower in eastern China, while summer surface latent heat flux is higher than climatological values in the eastern and lower in the western. Seasonal variations of simulated temperature and precipitation of RIMES-AVIM agree with those of the observed. Simulated temperature is lower than the observed in the Tibetan Plateau and Northwest China for the whole year, slightly lower in the remaining regions in winter, but consistent with the observed in summer. The simulated temperature of RIEMS-AVIM is higher in winter and lower in summer than that of RIEMS, which shows that the simulated temperature of RIEMS-AVIM is closer to the observed value. Simulated precipitation is excessive in the first half of the year, but consistent with the observed in the second half of the year. The simulated summer precipitation of RIEMS-AVIM has significant improvement compared to that of RIEMS, which is less and closer to the observed value. The interannual variations of temperature and precipitation are also fairly well simulated, with temperature simulation being superior to precipitation simulation. The interannual variation of simulated temperature is significantly correlated with the observed in Northeast China, the Transition Region, South China, and the Tibetan Plateau, but the correlation between precipitation simu     

Simulation and Analysis about the Effects of Geopotential Height Anomaly in Tropical and Subtropical Region on Droughts or Floods in the Yangtze River Valley and North China

Previous study comes to the conclusion:based on the anomalies of the South Asian high (SAH),100-hPa geopotential height,and 100-hPa circulation over tropical and subtropical regions,we can predict precipita- tion anomaly in the Yangtze River Valley and North China.To test its validity,a series of experiments have been designed and operated,which include controlled experiment,sensitivity experiment (which has added anomalies into 100-hPa geopotential height and wind field),and four-composite experiments.Experiments based on the composed initial field such as EPR-CF,EPR-CD,EPR-HF,and EPR-HD,can reproduce the floods or droughts in the Yangtze River Valley and North China.It suggests that anomalies of the SAH,100- hPa geopotential height,and circulation over tropical and subtropical regions may probably imply summer precipitation anomalies in the two regions.Sensitivity experiment results show that anomalies of the SAH, 100-hPa geopotential height,and southwest flow in the previous period is a signal of droughts or floods for the following summer in the Yangtze River Valley and North China.And it is also one of the factors that have impact on summer precipitation anomaly in the two regions.Positive anomaly of 100-hPa geopotential height and the anomalous intensifying of the SAH and southwest flow will induce floods in the Yangtze River Valley and droughts in North China;while negative anomaly of 100-hPa geopotential height and anomalous weakening of the SAH and southwest flow will induce droughts in the Yangtze River Valley and floods in North China.     

A STATISTICAL PREDICTING SCHEME OF THE INTENSITY OF THE STH OVER THE WESTERN NORTH PACIFIC

By performing error analysis of the information from the 48-hr forecasting charts of the 500-hPa fields by the B model over eastern Asia in the period of July to September 1982 and expansions of the height fields of westerlies and the subtropical zone by use of the Chebyshev polynomial and EOF, respectively, a scheme is developed for predicting the synchronous STH coefficient (i. e. time coefficient) in terms of the Chebyshev one, thus making possible statistical forecasting of the 500-hPa subtropical field within 48 hr. Tests with independent samples indicate that, to a certain extent, this scheme can be used in operational prediction as a reference.     

Relationship Between Soil Temperature in May over Northwest China and the East Asian Summer Monsoon Precipitation

This study investigates the relationship between the soil temperature in May and the East Asian summer monsoon （EASM） precipitation in June and July using station observed soil temperature data over Northwest China from 1971 to 2000.It is found that the memory of the soil temperature at 80-cm depth can persist for at least 2 months,and the soil temperature in May is closely linked to the EASM precipitation in June and July.When the soil temperature is warmer in May over Northwest China,less rainfall occurs over the Yangtze and Huaihe River valley but more rainfall occurs over South China in June and July.It is proposed that positive anomalous soil temperature in May over Northwest China corresponds to higher geopotential heights over the most parts of the mainland of East Asia,which tend to weaken the ensuing EASM.Moreover,in June and July,a cyclonic circulation anomaly occurs over Southeast China and Northwest Pacific and an anticyclonic anomaly appears in the Yangtze and Huaihe River valley at 850 hPa.All the above tend to suppress the precipitation in the Yangtze and Huaihe River valley.The results also indicate that the soil temperature in May over Northwest China is closely related to the East Asia/Pacific （EAP） teleconnection pattern,and it may be employed as a useful predictor for the East Asian summer monsoon rainfall.     

MULTIMODEL CONSENSUS FORECASTING OF LOW TEMPERATURE AND ICY WEATHER OVER CENTRAL AND SOUTHERN CHINA IN EARLY 2008

Based on the daily mean temperature and 24-h accumulated total precipitation over central and southern China, the features and the possible causes of the extreme weather events with low temperature and icing conditions,which occurred in the southern part of China during early 2008, are investigated in this study. In addition, multimodel consensus forecasting experiments are conducted by using the ensemble forecasts of ECMWF, JMA, NCEP and CMA taken from the TIGGE archives. Results show that more than a third of the stations in the southern part of China were covered by the extremely abundant precipitation with a 50-a return period, and extremely low temperature with a 50-a return period occurred in the Guizhou and western Hunan province as well. For the 24- to 216-h surface temperature forecasts, the bias-removed multimodel ensemble mean with running training period(R-BREM) has the highest forecast skill of all individual models and multimodel consensus techniques. Taking the RMSEs of the ECMWF 96-h forecasts as the criterion, the forecast time of the surface temperature may be prolonged to 192 h over the southeastern coast of China by using the R-BREM technique. For the sprinkle forecasts over central and southern China, the R-BREM technique has the best performance in terms of threat scores(TS) for the 24- to 192-h forecasts except for the 72-h forecasts among all individual models and multimodel consensus techniques. For the moderate rain, the forecast skill of the R-BREM technique is superior to those of individual models and multimodel ensemble mean.     

Interdecadal Variability of the East Asian Summer Monsoon in an AGCM

It is well known that significant interdecadal variation of the East Asian summer monsoon （EASM） occurred around the end of the 1970s. Whether these variations can be attributed to the evolution of global sea surface temperature （SST） and sea ice concentration distribution is investigated with an atmospheric general circulation model （AGCM）. The model is forced with observed monthly global SST and sea ice evolution through 1958-1999. A total of four integrations starting from different initial conditions are carried out. It is found that only one of these reproduces the observed interdecadal changes of the EASM after the 1970s, including weakened low-level meridional wind, decreased surface air temperature and increased sea level pressure in central China, as well as the southwestward shift of the western Pacific subtropical high ridge and the strengthened 200-hPa westerlies. This discrepancy among these simulated results suggests that the interdecadal variation of the EASM cannot be accounted for by historical global SST and sea ice evolution. Thus, the possibility that the interdecadal timescale change of monsoon is a natural variability of the coupled climate system evolution cannot be excluded.     

Numerical Simulation of Long-Term Climate Change in East Asia

A 10-yr regional climate simulation was performed using the fifth-generation PSU/NCAR Mesoscale Model Version 3 (MM5V3) driven by large-scale NCEP/NCAR reanalyses. Simulations of winter and summer mean regional climate features were examined against observations. The results showed that the model could well simulate the 10-yr winter and summer mean circulation, temperature, and moisture transport at middle and low levels. The simulated winter and summer mean sea level pressure agreed with the NCAR/NCEP reanalysis data. The model could well simulate the distribution and intensity of winter mean precipitation rates as well as the distribution of summer mean precipitation rates, but it overestimated the summer mean precipitation over North China. The model's ability to simulate the regional climate change in winter was superior to that in summer. In addition, the model could simulate the inter-annual variation of seasonal precipitation and surface air temperature. Geopotential heights and temperature at middle and high levels between simulations and observations exhibited high anomaly correlation coefficients. The model also showed large variability to simulate the regional climate change associated with the El Nino events. The MM5V3 well simulated the anomalies of summer mean precipitation in 1992 and 1995, while it demonstrated much less ability to simulate that in 1998. Generally speaking, the MM5V3 is capable of simulating the regional climate change, and could be used for long-term regional climate simulation.