On the correlation of nonlinear variables containing secular trend variations： numerical experiments

Due to global warming, the general circulation, underlying surfaces characteristics, and geophysical and meteorological elements all show evident secular trends. This paper points out that when calculating the correlation of two variables containing their own obvious secular trends, the interannual correlation characteristics between the two variables may be distorted （overestimated or underestimated）. Numerical experiments in this paper show that if two variables have opposite secular trends, the correlation coefficient between the two variables is reduced （the positive correlation is underestimated, or the negative correlation is overestimated）; and if the two variables have the same sign of secular trends, the correlation coefficient between the two variables is increased （the positive correlation is overestimated, or the negative correlation is underestimated）. Numerical experiments also suggest that the effect of secular trends on the interannual correlation of the two variables is interchangeable, that is to say, as long as the values of the two trends are not changed, the two variables interchange their positions, and the effect of the secular trends on the interannual correlation coefficient of the two variables remains the same. If the two variables have the same-（opposite-） sign trends, the effect of secular trends on the interannal correlation coefficient is more （less） distinctive. A meteorological example is given.

Analysis on the Climate Characteristics of Thunderstorm in Fujian Province during 1960-2007

[Objective] The research aimed to study the activity characteristics and climate rule of thunderstorm in Fujian Province.[Method] Based on the daily thunderstorm data in 67 meteorological stations of Fujian Province during 1960-2007,the spatial and temporal distribution characteristics of thunderstorm in Fujian Province were analyzed by using the climate tendency rate,the trend coefficient and so on.[Result] The distribution of thunderstorm days showed the northeast-southwest direction and increased gradually from the coast to the inland in Fujian Province during 1960-2007.The high value zone was in Longyan,and the thunderstorm days in the coastal islands were the fewest.The thunderstorm days had the obvious decrease trend in Fujian Province in 48 years.The decrease speeds in the central coastal area and most of inland mountain area were 3.5 and 4.5 d/10 a.The decrease speed was 5.5 d/10 a in the north of Ningde,the east of Sanming and some areas in Nanping.The trend coefficient variation of thunderstorm days had the obvious regional characteristic.Especially the decrease trend in the inland mountain area was more obvious than that in the coast.The decrease of thunderstorm day trend coefficient in the north of Nanping was the most,and the trend coefficient was-0.65.But the decrease trend in the central coastal area wasn’t obvious,and the coefficient was only-0.15.The thunderstorm day had the obvious seasonal variation.The multi-occurrence period of thunderstorm was during March-september and reached the maximum value in August.Started from September,the thunderstorm quickly decreased.From October to February in next year,the thunderstorm happened seldom.The average first thunderstorm date in the northwest area was earlier than that in the southeast area.The difference of average final thunderstorm date in the north and south areas wasn’t big.For the first thunderstorm date in the north and west of Fujian was early,and the final thunderstorm date was later,the thunderstorm activity time in the whole year was longer than that in the coast.They differed by nearly one month.[Conclusion] The research provided the scientific basis for the climate feasibility demonstration of major project items,provided the theory basis about the weather climate aspect for the thunder prevention and disaster reduction,and also laid the foundation for further studying the formation mechanism of thunderstorm in Fujian.

Research for length change of four seasons over China in recent 47 years

Using daily temperature data from 599 Chinese weather stations during 1961-2007, the length change trends of four seasons dur- ing the past 47 years were analyzed. Results show that throughout the region, four seasons＇ lengths are： spring becomes shorter （-0.8 d/10yrs）, summer becomes longer （3.2 d/10yrs）, autumn （-0.5 d/10yrs） and winter （-1.6 d/10yrs） becomes shorter. This trend is different in spatial distribution, namely it is very obvious in northern than southern China, and also remarkable in eastern than western China. Summer change is most obvious, but autumn has little change comparatively. This trend is highly obvious in North, East, Central and South China. In the Southwest starting in the 21st century, summer becomes longer and winter shortens. The trend in the Plateau region since the 1980s is that spring becomes longer and winter shortens. The average annual temperature increased during the past 47 years, and the change of the average annual temperature precedes seasons＇ length. Thus, the average annual temperature has a certain influence on the length change of seasons.

Study on the Variation Characteristics of Precipitation Concentration Degree in Guangxi under the Background of Global Climate Becoming Warm

Based on the daily precipitation data of 87 meteorological observation stations in Guangxi during 1961-2008,the variation characteristics of precipitation concentration degree(PCD) in Guangxi were counted and analyzed by using Monte Carlo test method.The results showed that the climate warming in most areas of Guangxi was very obvious,and the annual precipitation concentration degree increased gradually from the northeast to the southwest in Guangxi.The precipitation concentration period was from the middle of April to the end of August and delayed from the northeast to the southwest in Guangxi.In the background which the global climate became warm,the annual precipitation in most areas of Guangxi had the trend which the precipitation concentrated strengthening.It was said that the probability of flood disaster had the increase trend.The precipitation concentration period had the earlier trend,which was more obvious in the north than in the south of Guangxi.The rainstorm concentration degree in the northwest of Guangxi and few parts had the decrease trend and had the increase trend in other areas.It was said that the probabilities of flood and mud-rock flow disasters increased.The rainstorm concentration periods in most areas had the later trend.

Variation Characteristics of Sunshine Hours and Its Reason Analysis over Loess Plateau of Shaanxi

[Objective] The research aimed to study variation characteristics of sunshine hours over Loess Plateau of Shaanxi during 1961-2010.[Method] By using the climate tendency rate,climate trend coefficient and linear correlation,the temporal and spatial variation characteristics of sunshine hours in Loess Plateau of Shaanxi in recent 50 years were analyzed.Moreover,the main reason for inducing variation of sunshine hours in the zone was discussed.[Result] In recent 50 years,the variation of annual sunshine hours in Loess Plateau of Shaanxi mainly presented decrease trend.The decrease zones were mainly located in windy desert region along the Great Wall line,central loess hilly region,most areas of plateau remains region and most areas of arid plateau region in north Weihe River.The increase zones were mainly located in west and northeast plateau remains region,southwest plateau remains region,some areas of arid plateau region in north Weihe River.Seen from four-season variation trend,except in spring,the sunshine hours in other seasons presented varying decrease trends.The decrease amplitude in summer was 24.34 h/10 a,and was the most significant.The second one was-16.62 h/10 a in winter.The decrease amplitude in winter was 3.55 h/10 a,and was unobvious.Seen from spatial variation,the annual sunshine hours presented significant increase trend in Mizhi of loess hilly region and significant decrease trend in Dingbian,Shenmu of windy desert region along the Great Wall line,Qingjian,Yanchuan of plateau remains region,Longxian,Fengxiang,Chunhua and Hancheng of arid plateau region in north Weihe River.There was no obvious variation trend in other research zones.The annual and four-season sunshine hours all presented negative correlations with rainfall,relative humidity,total cloud amount,low cloud amount,water vapor pressure and fog days.The sunshine hours presented positive correlation with visibility.The correlation coefficients between sunshine hours and relative humidity,rainfall,total cloud amount,water vapor pressure,fog days and visibility were all bigger in each region.[Conclusion] The research provided basis for analyzing climate variation over Loess Plateau of Shaanxi.

Study on Trends of Change in Direct Input Coefficients of China

The objective of this paper is to study the trends of change in direct input coefficients of China. We reconstructed a time series of input\|output tables of China with 18 sectors for 1981, 1987, 1990, 1992 and 1995 at constant prices and current prices, and the tables for developed region, middle developed region and underdevelopd region. On the basis of these tables we found seven important trends on change in China′s direct input coefficients.

ANNUAL DISTRIBUTION FEATURES OF PRECIPITATION IN CHINA AND THEIR INTERANNUAL VARIATIONS

The hierarchy and definition of the precipitation-concentration degree and precipitation- concentration period of annual precipitation have been proposed by using the so-called vector method of annual distribution of precipitation,so that the two relevant parameters can represent the annual distribution of total precipitation correctly and indeed accurately.The relationship between the spatial and temporal distribution patterns and variations of the two parameters and the annual precipitation amount in China has been further investigated.Results demonstrate that the precipitation-concentration degree and the precipitation-concentration period increase from southeast to northwest gradually.Moreover there obviously exists a belt pattern:the largest variability of the precipitation-concentration degree and the precipitation-concentration period occurs in the Yellow River Valley and the middle and lower reaches of the Yangtze River, corresponding to the significant zones in which flood and drought take place frequently.It is found that there exist high correlations between the precipitation-concentration degree and precipitation- concentration period and the annual precipitation amount in Northeast China,North China,the middle and lower reaches of the Yangtze River. Furthermore,8-year and 22-year periodic oscillations in the precipitation-concentration degree and 6-year and 12-year cycles in the precipitation-concentration period are identified by use of their Morlet wavelet analysis.

TEMPERATURE,RAINFALL VARIATIONS AND THEIR ANOMALIES OVER CHINA UNDER THE COLD-WARM BACKGROUND IN THE 20TH CENTURY

In this study,the climate trend of the annual average air temperature and total annual rainfall in China in the present century has been examined.It is noted that in the Northwest,the Northeast and North China the climate has become notably warmer this century but the rainfall trend has not been evident,mainly negative.In the 1980s China's rainfall and temperature showed noticeable regional features: warm and dry in North China,cold and dry in the Southwest,warm and wet in the Northeast,cold and wet in the middle-lower reaches of the Changjiang River.Besides,the four interdecadal climate change features and ranges of this century have been studied.It is found that on the scale of several decades there was considerably less rainfall in the most part of China in the warm background than in the cold background.The increase of temperature which started from the 1970s mainly happened in the Northwest and Northeast,while to the south of the Huanghe River the temperature increase did not even as great as in 1940s.The corresponding rainfall feature is that most areas experienced much less rainfall except the area to the south of the Huanghe River and over the Changjiang and Huaihe River basin.