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1.
A 10,000-year long simulation has been made with the CSIRO Mark 2 coupled global atmospheric-oceanic model for present climatic conditions. The annual mean output from the model has been used to calculate global distributions of climatic trends. These trends were derived by linear regression using a least squares fit to a given climatic time series for a selected trend duration. Typically, this information cannot be obtained from the limited observational record, hence the simulation provides a documentation of many climatic trend characteristics not previously available. A brief examination of observed climatic trends is given to demonstrate the viability of the trend analysis. This is followed by a range of global trend distributions for various climatic variables and trend durations. At any one time only relatively small regions of the globe have trends significant at the 95% level. Markedly different trend patterns occur for a given trend duration computed for different times within the simulation. Decadal and multi-decadal trend patterns revealed consistent relationships for El Niño/Southern Oscillation (ENSO)-related climatic variables. It was found that within a given duration trend, noticeable shorter term counter-trends can exist, with the latter being much stronger. In general, a strong trend is indicative of a short duration, thus highlighting the danger of extrapolating such trends. Examination of time series of climatic trends emphasised the dominance of decadal variability and the essential residual nature of, especially longer term, trends. Rainfall trends over Australia are used to indicate the almost continent-wide changes that can occur in trend patterns within a few decades, in agreement with observation. The outcome emphasises that any changes in current, observed climatic trends should not automatically be attributed to greenhouse forcing. Importantly, it is noted that for conditions associated with naturally occurring climatic variability, the global mean of any climatic trend distribution should be zero or near zero. Departures from this situation imply the existence of an external forcing agency. Thousand year trends could be readily identified within the simulation, but the variations from millennium to millennium indicate the occurrence of secular variability. A probability density function distribution of 30-year duration trends within a selected millennium revealed a near-Gaussian outcome. This, together with other analyses, supports the conclusion that stochastic processes dominate the climatic variability within the simulation. 相似文献
2.
J. C. González Hidalgo M. De Luís J. Raventós J. R. Sánchez 《Theoretical and Applied Climatology》2003,75(1-2):117-130
Summary ?We have analyzed daily rainfall trends throughout the second half of the 20th century in the western Mediterranean basin (Valencia Region, E of Spain). The area is characterized by high torrentiality,
and during the second half of the 20th century some of the highest daily rainfall values in the Mediterranean basin have been recorded. In this area, mean annual
rainfall varies between 500 and 300 mm and is overwhelmingly dependent on just a few days of rain. Daily maximum rainfall
varies on average from 120 mm day−1 to 50 mm day−1, and represents a mean of 17% (coastland) to 9% (inland) of annual rainfall. The 10 days in each year with the heaviest rainfall
(called “higher events”) provide over 50% of the annual rainfall and can reach more than 400 mm on average. We compared the
annual rainfall trend and the trend of higher and minor events defined by percentiles, both in volume and variability. We,
therefore, tested whether annual rainfall changes depend on the trend of the higher (rainfall) events.
To overlap spatial distribution of trends (i.e.: positive, no significant and negative trends) we have used cross-tab analysis.
The results confirm the hypothesis that annual rainfall changes depend on changes found in just a few rainy events. Furthermore,
in spite of their negative trend, higher events have increased their contribution to annual rainfall.
As a consequence, although torrential events may have diminished in magnitude, future scenarios seem to be controlled by a
limited number of rainy events which will become more and more variable year on year. The high spatial density of data used
in this work, (97 observatories per 24.000 km2, overall mean 1 observatory per 200 km2), suggests to us that extreme caution should be applied when analyzing regional and sub-regional changes in rainfall using
GCM output, especially in areas of high torrentiality.
Received August 1, 2002; revised November 11, 2002; accepted December 1, 2002
Published online May 19, 2003 相似文献
3.
The study evaluated CORDEX RCMs’ ability to project future rainfall and extreme events in the Mzingwane catchment using an ensemble average of three RCMs (RCA4, REMO2009 and CRCM5). Model validation employed the statistical mean and Pearson correlation, while trends in projected rainfall and number of rainy days were computed using the Mann-Kendall trend test and the magnitudes of trends were determined by Sen’s slope estimator. Temporal and spatial distribution of future extreme dryness and wetness was established by using the Standard Precipitation Index (SPI). The results show that RCMs adequately represented annual and inter-annual rainfall variability and the ensemble average outperformed individual models. Trend results for the projected rainfall suggest a significant decreasing trend in future rainfall (2016–2100) for all stations at p < 0.05. In addition, a general decreasing trend in the number of rainy days is projected for future climate, although the significance and magnitude varied with station location. Model results suggest an increased occurrence of future extreme events, particularly towards the end of the century. The findings are important for developing proactive sustainable strategies for future climate change adaption and mitigation. 相似文献
4.
B. G. Hunt 《Climate Dynamics》2011,36(3-4):509-521
Controversy continues to prevail concerning the reality of anthropogenically-induced climatic warming. One of the principal issues is the cause of the hiatus in the current global warming trend. There appears to be a widely held view that climatic change warming should exhibit an inexorable upwards trend, a view that implies there is no longer any input by climatic variability in the existing climatic system. The relative roles of climatic change and climatic variability are examined here using the same coupled global climatic model. For the former, the model is run using a specified CO2 growth scenario, while the latter consisted of a multi-millennial simulation where any climatic variability was attributable solely to internal processes within the climatic system. It is shown that internal climatic variability can produce global mean surface temperature anomalies of ±0.25?K and sustained positive and negative anomalies sufficient to account for the anomalous warming of the 1940s as well as the present hiatus in the observed global warming. The characteristics of the internally-induced negative temperature anomalies are such that if this internal natural variability is the cause of the observed hiatus, then a resumption of the observed global warming trend is to be expected within the next few years. 相似文献
5.
This study comprises (1) an analysis of recent climate trends at two sites in north-west India (Ludhiana in Punjab and Delhi) and (2) an impact and risk assessment for wheat yields associated with climatic variability. North-west Indian agriculture is dominated by rice-wheat rotation in which the wheat season (‘rabi’, November to March) is characterized by predominantly dry conditions—superimposed by very high inter-annual variability of rainfall (17 to 260 mm in Ludhiana and <1 to 155 mm in Delhi). While rainfall remained without discernable trend over the last three decades, minimum and average temperatures showed increasing trends of 0.06 and 0.03°C year???1, respectively, at Ludhiana. The site in (metropolitan) Delhi was apparently influenced by city-effects, which was noticeable from the decrease in solar radiation of 0.09 MJ m???2 day???1 year???1. The CERES-wheat model was used to calculate yields of rainfed wheat that were at both locations highly correlated with seasonal rainfall. An assessment framework was developed to quantify yield impacts due to rainfall variability in three steps: (1) data from different years were aggregated into four classes, i.e., years with scarce, low, moderate, and high rainfall, (2) yield records of each rainfall class were ranked according to yield to facilitate (3) a comparison of yields with identical rank, i.e. among the best yield of each class, the second-best, etc. The class with moderate rainfall was taken as baseline yield to compute yield impacts of other rainfall scenarios. Years with scarce rainfall resulted in only 34% (Ludhiana) and 35% (Delhi) of the baseline yield. The yields in years with low rainfall accounted for 61% (Delhi) and 49% (Ludhiana) of the baseline yields. In Ludhiana, high rainfall years resulted in 200% yield as compared to the baseline yield, whereas they reached only 105% in Delhi. Low-intensity (1× and 3×) irrigation decreased the relative yield losses, but entailed a higher vulnerability in terms of absolute yield losses. Only high-intensity (4×) irrigation buffered wheat yields against adverse rainfall years. Early sowing was beneficial for wheat yields under all rainfall scenarios. The framework could be a valuable decision-support tool at the farm level where seasonal rainfall variability is high. 相似文献
6.
Monthly sea surface temperature anomalies (SSTA) at near-global scale (60 °N–40 °S) and May to October rainfall amounts in
West Africa (16 °N–5 °N; 16 °W–16 °E) are first used to investigate the seasonal and interannual evolutions of their relationship.
It is shown that West African rainfall variability is associated with two types of oceanic changes: (1) a large-scale evolution
involving the two largest SSTA leading eigenmodes (16% of the total variance with stronger loadings in the equatorial and
southern oceans) related to the long-term (multiannual) component of rainfall variability mainly expressed in the Sudan–Sahel
region; and (2) a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical Atlantic due
to the linear combination of the two largest SSTA modes in the Atlantic (11% with strong inverse loadings over the northern
and southern tropics) which is associated with the interannual and quasi-decadal components of regional rainfall in West Africa.
Linear regression and discriminant analyses provide evidence that the main July–September rainfall anomalies in Sudan–Sahel
can be detected with rather good skills using the leading (April–June) or synchronous (July–September) values of the four
main oceanic modes. In particular, the driest conditions over Sahel, more marked since the beginning of the 1970s, are specifically
linked to the warm phases of the two global modes and to cold/warm anomalies in the northern/southern tropical Atlantic. Idealized
but realistic SSTA patterns, obtained from some basic linear combinations of the four main oceanic modes appear sufficient
to generate quickly (from mid-July to the end of August) significant West African rainfall anomalies in model experiments,
consistent with the statistical results. The recent negative impact on West African rainfall exerted by the global oceanic
forcing is primarily due to the generation of subsidence anomalies in the mid-troposphere over West Africa. When an idealized
north to south SSTA gradient is added in the tropical Atlantic, strong north to south height gradients in the middle levels
appear. These limit the northward excursion of the rainbelt in West Africa: the Sahelian area experiences drier conditions
due to the additive effect (subsidence anomalies+latitudinal blocking) while over the Guinea regions wet conditions do not
significantly increase, since the subsidence anomalies and the blocking effect act here in opposite ways.
Received: 26 June 1997 / Accepted: 3 October 1997 相似文献
7.
The aim of this paper is to identify and delineate large signals of climatic variation in the Asian monsoon region and try to understand the nature of transformation from one climate regime to another.It is found that the summer monsoon over the Indian and western Pacific oceans stows distinct climatic regimes with changes occurring in the years around 1875, 1900, 1940 and 1960. The change of about 1900 is the largest one, which occurs in step with the variation of global oceanic climate pointed out by Fletcher, et al. (1982).The main characteristics of the transformation from one regime to another is an alternation of meridio-nality of monsoon current. The transformation occurs most strongly in the western Pacific convergence zone, where monsoon has strong interaction with the trade wind systems.The variability of monsoon rainfall over India and East China also exhibits some large signals which are synchronous with those of wind field over the ocean: the monsoon rainfall increases (decreases) during the “meridional monsoon period” (zonal monsoon period) over the ocean.It should be noted that the apparent decreasing of plum rains in East China since 1958 which is well known in China would be linked mainly with the sudden increasing of U-component of SW monsoon over the South China Sea.Finally a kind of seesaw between Indian monsoon and East China monsoon with somewhat time-lag is discussed. 相似文献
8.
Recent trends in observed temperature and precipitation extremes in the Yangtze River basin,China 总被引：14，自引：1，他引：14
Summary The present study is an analysis of the observed extreme temperature and precipitation trends over Yangtze from 1960 to 2002
on the basis of the daily data from 108 meteorological stations. The intention is to identify whether or not the frequency
or intensity of extreme events has increased with climate warming over Yangtze River basin in the last 40 years. Both the
Mann-Kendall (MK) trend test and simple linear regression were utilized to detect monotonic trends in annual and seasonal
extremes.
Trend tests reveal that the annual and seasonal mean maximum and minimum temperature trend is characterized by a positive
trend and that the strongest trend is found in the winter mean minimum in the Yangtze. However, the observed significant trend
on the upper Yangtze reaches is less than that found on the middle and lower Yangtze reaches and for the mean maximum is much
less than that of the mean minimum. From the basin-wide point of view, significant increasing trends are observed in 1-day
extreme temperature in summer and winter minimum, but there is no significant trend for 1-day maximum temperature. Moreover,
the number of cold days ≤0 °C and ≤10 °C shows significant decrease, while the number of hot days (daily value ≥35 °C) shows
only a minor decrease. The upward trends found in the winter minimum temperature in both the mean and the extreme value provide
evidence of the warming-up of winter and of the weakening of temperature extremes in the Yangtze in last few decades.
The monsoon climate implies that precipitation amount peaks in summer as does the occurrence of heavy rainfall events. While
the trend test has revealed a significant trend in summer rainfall, no statistically significant change was observed in heavy
rain intensity. The 1-day, 3-day and 7-day extremes show only a minor increase from a basin-wide point of view. However, a
significant positive trend was found for the number of rainstorm days (daily rainfall ≥50 mm). The increase of rainstorm frequency,
rather than intensity, on the middle and lower reaches contributes most to the positive trend in summer precipitation in the
Yangtze. 相似文献
9.
The study has analyzed the variability and trends in monthly, seasonal and annual rainfall and rainy days of four locations over different agro-ecological zones of Bihar, namely Samastipur (zone-I), Madhepura (zone-II), Sabour (zone-IIIA) and Patna (zone-IIIB). The Mann–Kendall nonparametric test was employed for detection of statistical significance and slopes of the trend lines were determined using the method of least square linear fitting. The variability and trends of onset of effective monsoon and length of monsoon period were also analyzed using the same method. The mean annual rainfall varies from 1137 mm at Patna to 1219 mm at Sabour. July is the rainiest month in all the zones followed by August. Maximum increase in annual rainfall was found at Sabour (40.1% of mean/30 years at 95% confidence level) and minimum for Patna (10.1% of mean/30 years). Significant increasing trend of rainfall during July, August and September at rates of 41.9, 83.2, and 112.7% of the mean/30 years, respectively has been noticed at Madhepura. Analysis of rainy days indicates that rainy days increased during winter and annually for all the sites. The mean effective onset of monsoon varies from 18th June at Sabour to 28th June at Patna. The trends in the date of effective onset of monsoon indicate that the date tends to be early in all the sites except Madhepura. But a significant delayed trend in the onset at a rate of 2.8% of the mean/30 years has been observed for Madhepura. The early trend of the effective onset of monsoon and increasing trends of length of monsoon season have been observed for Samastipur, Sabour and Patna. 相似文献
10.
Decreasing teleconnections with inter-site distance in monthly climatic data and tree-ring width networks in a mountainous Alpine area 总被引：3，自引：0，他引：3
C. Rolland 《Theoretical and Applied Climatology》2002,71(1-2):63-75
Summary The similarities in time series recorded at sites which are distant from each other are called teleconnections. In this paper,
the loss of such correlations with inter-site distance was investigated for both climatic and dendrochronological data sets,
with 70 tree-ring chronologies. A dense network of weather stations was studied in the southeastern French Alps, covering
complex climatic gradients over three departments. 78 sites with precipitation data (with a total of 48 756 monthly values),
and 48 stations that recorded temperature (with 20 722 monthly mean values) were analysed. In the same area, four coniferous
species (mountain pine and stone pine, European larch and Norway spruce) provided 37 ring-width chronologies for high elevation
sites near the timberline. Both silver fir and Norway spruce provided a second tree-ring chronology network for 33 different
sites at lower elevations.
The teleconnections between precipitation series were found to be higher than those observed for temperature over short distances,
but the maximum threshold distance was lower (193 km) compared to a positive correlation distance that exceeds 500 km for
temperature. The maximum temperatures had stronger teleconnections than minimum values (522 km versus 476 km), since the latter
are linked more with other site factors, such as slope, exposure and local topography.
As expected, the tree-ring chronologies showed weaker teleconnections than the climatic series, with a threshold distance
of 374 km obtained for all high elevation forests. The coniferous species with high intra-specific teleconnections over large
distances were, in decreasing importance, Pinus uncinata (> 500 km), Picea abies (477 km), Pinus cembra (over 254 km) and Larix decidua (over 189 km only). The two former species showed the highest intra-specific correlations (with mean correlation R=0.625 and 0.666). The dendrochronological teleconnections were found to have a extent lesser for trees species that depend
on rainfall (such as larch, and stone pine). They are enhanced, however, for temperature sensitive species such as spruce
and mountain pine (a drought resistant tree). Therefore, these two latter conifers appear to be especially suitable for climatic
reconstruction over large distances in mountainous areas. However, teleconnections within silver fir (Abies alba) and spruce chronologies were sharply reduced (over 131 km and 135 km) in lower elevation forests, underlining the interest
of timberline forests for dendroclimatology.
A better knowledge of the spatial correlations in climatic series and ring-width data may enable the optimisation of weather
station networks. It may also permit a better choice of weather stations used for dendroclimatology, either for tree-ring
and climate relationship calibration or for climate reconstructions. In dendrochronology, wood dating also requires the knowledge
of to what extent remote ring-width chronologies can be used.
Received September 11, 2000 Revised March 26, 2001 相似文献
11.
Abstract An analysis of variance of the 1000–500 mb thickness field is performed to investigate the possibility of seasonal change in climatic variability during the period 1949 to 1975. The mean thickness and measures of transient eddy, standing eddy and north‐south variance, averaged over the region from 25°N to the Pole, are analysed for the annual average and for each of the four seasons. For the annually averaged data, the only statistically significant trend is a linear decrease in mean thickness. None of the variability measures display significant trends in annually averaged values. On a seasonal basis, a significant trend in mean thickness is found in three of the four seasons. Several seasonal measures of variability show statistically significant trends. The most notable result of the analysis is an apparent increasing trend in summer season values of both transient and standing eddy measures of variability. The results of this study reiterate those of a previous study that found no overall change in climatic variability during the period. In addition, however, the data suggest an increase in variability during the summer season although this increase is not sufficient to affect the overall annually averaged value. 相似文献
12.
Summary The aim of the paper lies in the identification of possible significant linear trends at monthly, seasonal and annual timescales
in the Mediterranean during the second half of the 20th century. Monthly and daily records of 63 stations have been used to
elaborate several precipitation indices: sum of daily precipitation (SDP) for rainfall >0.1 mm, >10 mm and >95th percentile, of number of rainy days (RD) >0.1 mm and >10 mm and of mean daily precipitation (MDP) >0.1 mm and >10 mm. For
each index the stations have been gathered together by Rotated Principal Component Analyses to determine 8 sub-areas which
can be considered as identical for all the timescales at the spatial scale of the research. Trends have been estimated from
the scores of each eigenvector retained in all RPCAs. They are mainly non existant or non significant decreasing, even if
a few monthly trends appear to be significantly diminishing, primarily during winter months, March in the Atlantic region,
October in the Mediterranean Spain, December in the Lions and Genoa Gulfs, January, winter and the year in Greece, winter
and the year in Italy and winter in the Near East and increasing in April in the two gulfs. Correlation coefficients between
SDP>0.1 mm and other indices have been computed: the significant trends seem mainly related to RD>10 mm, which represents
a high percentage of the total rainfall amount. Greece is remarkable: SDP>0.1 mm and >10 mm decrease significantly during
January, winter, the rainy season and the entire year whereas SDP>95th percentile increases significantly, in accordance with the climatic change scenarios for the end of this century as does
the decreasing of the total monthly and seasonal rainfall. 相似文献
13.
Patrick J. Michaels 《Climatic change》1982,4(3):255-271
The purpose of this research is to assess the climatic sensitivity of high yielding variety (‘HYV’) ‘green revolution’ wheat.
Improved multiple regression models were constructed for yields in India and Sonora, Mexico — the two most intensively planted
regions in the world. After isolating the most important climatic predictors (which, not surprisingly, are total rainfall
over the irrigation basins), the models were reduced to the pre-HYV period, and then re-run with successively more years of
HYV input. This test indicated that increased adoption of the HYV package is associated with a significant increase in yield
sensitivity to the most important climatic determinants of yield.
To serve as a control, the U.S. Winter Wheat region was also modelled with a similar method. Overall, there is no significant
increase in yield sensitivity to climate during the same period that HYV's were adopted in Mexico and India.
Assuming that there is no change in overall climatic variability, this study indicates that production will nonetheless become
more variable, particularly as HYV culture is expanded. Ironically, countries with rapidly expanding populations, that rely
increasingly on HYV's, will experience the most significant fluctuations. 相似文献
14.
A coupled ocean-sea ice-atmosphere model is used to study interdecadal variability (∼40 years) of sea ice depth and concentration
in the Greenland-Iceland-Norwegian Sea. This oceanic region is represented by a meridionally aligned channel on a β-plane
with open zonal boundaries at 60 °N and 80 °N. The model consists of a one and a half layer reduced gravity ocean model, a
thermodynamic/dynamic sea ice model and an energy balance model of the atmosphere. The coupled model is driven by prescribed
surface wind stress, fluxes of heat, salt and ice at inflow points on the northern and southern open zonal boundaries and
annual distribution of solar radiation. It is shown that the coupled model supports unforced modes of interdecadal oscillation
resulting from a form of hydraulic control which regulates the total fluid volume in the oceanic active layer. The mechanism
for the oscillations relies on the presence of three key features: (1) a region of intense oceanic entrainment located in
the eastern part of the domain, (2) a vigorous southward flowing western boundary current, representing the East Greenland
Current (EGC), which supports most of the meridional transport across the domain, and (3) a marked buoyancy contrast between
the relatively salty domain interior and the much fresher western boundary region. During an oscillation excess water is pumped
into the domain via entrainment, thereby creating an active layer depth anomaly, which then propagates westward via long baroclinic
Rossby waves until it reaches the EGC where it is subsequently drained out of the domain across the southern open zonal boundary.
As the depth anomaly traverses the basin, an anomalous geostrophic circulation is established in which cold fresh Arctic water
enters the domain interior, and this eventually promotes enhanced thermodynamic sea ice growth. Consequently, the interdecadal
oscillations of the coupled model are characterised by pulse periods, typically spanning 20 years, during which there is an
abnormally large winter sea ice cover, separated by interpulse periods, lasting another 20 years, during which the winter
sea ice extent is nearly uniform and significantly smaller than in a pulse maximum. The duration of the interpulse periods
is dictated by the time it takes for the Rossby waves to traverse the basin. In addition to the interdecadal oscillation solution,
the coupled ocean-sea ice-atmosphere model is found to also have a stable cyclostationary state, with no interannual variability.
Stochastic forcing, in the form of randomly specified interannual anomalies of salinity (of maximum amplitude 0.1 ppt) or
ice inflow (of maximum amplitude 0.1 Sv) at the northern open zonal boundary, in both cases is capable of driving the model
from the cyclostationary state solution to the interdecadal variability one.
Received: 16 August 1996 / Accepted: 27 July 1998 相似文献
15.
Summary Reports of changes in the seasonal and annual rainfall in Nigeria suggests that a more detailed analyses of the geographic
extent of these changes and of their impact on agriculture could be of value. Variation in the growing season (April to September)
rainfall from stations across Nigeria was analysed over the 30-yr period, 1960–90. Regression analyses were used to examine
long-term trends. Principal component and cluster analyses were used to group stations with similar trends in standardised
seasonal rainfall. Mean accumulated standardised seasonal rainfall were used to examine short- and medium-term trends for
each of the groups identified. Significant (P ≤ 0.05) decreases in rainy season rainfall were found at 8 stations mostly in the Guinea and arid/semi-arid savannas of northern
Nigeria, whereas no station showed significant increases. Examination of the monthly (April through September) rainfall showed
that only three – Kano, Sokoto and Potiskum in the arid/semi-arid savanna – of the twenty-three stations used in the analysis
had declining rainfall trends for each of the months April to September and subsequently declining seasonal rainfall trends.
However, 12 to 15 stations had consistently declining rainfall trends in atleast some but not all the growing season months.
However, a similar pattern was not the case in terms of increasing rainfall trends, where only one to three stations had consistently
increasing rainfall trends in some but not all of the months from April to September. Stations that showed increasing rainfall
trends were in the southern parts of Nigeria.
Six groups with similar patterns in standardised seasonal rainfall were identified by Principal Component and Cluster analyses.
For most of the groups, the period from 1967 to 1973 was that of consistently below average seasonal rainfall. However, the
timing and extent of the decline varied with location. Common to stations in four of the six groups was a negative trend in
seasonal rainfall for the period considered. The geographic variation in seasonal rainfall trends has tremendous agricultural
significance since there are indications that the reliability of the season is decreasing from the humid forest zone with
positive seasonal trends to the arid/semi-arid savanna with significant negative seasonal trends.
Received June 24, 1998 Revised December 18, 1998 相似文献
16.
Olajire J. Olaniran 《Climatic change》1991,19(3):319-340
Annual series of light rainfall, moderate rainfall and heavy rainfall are computed for 4 zones arranged from south to north in Nigeria: Coastal, Guinea-Savanna, Midland and Sahelian zones. Daily rainfall data for the period 1919–85 are utilized. Each series is examined for evidence of change in structure in terms of pattern of decrease and increase in dry and wet years, the overall trend, and the occurrence of runs of dry and wet years. The northern Nigeria (Midland and Sahel) heavy rainfall series and the Sahel moderate rainfall series are found to depict evidence of climatic change as defined by Landsberg (1975) that climatic conditions must change to a new equilibrium position with the values of climatic elements changed significantly. On the other hand Landsberg's definition of climatic fluctuations as involving temporary deflection which can revert to earlier conditions is found to fit the 4 regional light rainfall series and the Midland area moderate rainfall series. The southern Nigeria moderate and heavy rainfall series are found to depict only evidence of high frequency oscillations about a stable long-term mean. The recent drought in Nigeria north of about 9° N is shown to be associated with a large decline in moderate and heavy rainfalls over this part of the country. 相似文献
17.
D. R. Kothawale A. A. Munot H. P. Borgaonkar 《Theoretical and Applied Climatology》2008,92(1-2):31-45
Summary The present study examines the long term trend in sea surface temperatures (SSTs) of the Arabian Sea, Bay of Bengal and Equatorial
South India Ocean in the context of global warming for the period 1901–2002 and for a subset period 1971–2002. An attempt
has also been made to identify the relationship between SST variations over three different ocean areas, and All-India and
homogeneous region summer monsoon rainfall variability, including the role of El-Ni?o/Southern Oscillation (ENSO). Annual
sea surface temperatures of the Arabian Sea, Bay of Bengal and Equatorial South India Ocean show a significant warming trend
of 0.7 °C, 0.6 °C and 0.5 °C per hundred years, respectively, and a relatively accelerated warming of 0.16 °C, 0.14 °C and
0.14 °C per decade during the 1971–2002 period.
There is a positive and statistically significant relationship between SSTs over the Arabian Sea from the preceding November
to the current February, and Indian monsoon rainfall during the period 1901–2002. The correlation coefficient increases from
October and peaks in December, decreasing from February to September. This significant relationship is also found in the recent
period 1971–2002, whereas, during 1901–70, the relationship is not significant. On the seasonal scale, Arabian Sea winter
SSTs are positively and significantly correlated with Indian monsoon rainfall, while spring SSTs have no significant positive
relationship. Nino3 spring SSTs have a negative significant relationship with Indian monsoon rainfall and it is postulated
that there is a combined effect of Nino3 and Arabian Sea SSTs on Indian monsoon. If the Nino3 SST effect is removed, the spring
SSTs over the Arabian Sea also have a significant relationship with monsoon rainfall. Similarly, the Bay of Bengal and Equatorial
South Indian Ocean spring SSTs are significantly and positively correlated with Indian monsoon rainfall after removing the
Nino3 effect, and correlation values are more pronounced than for the Arabian Sea.
Authors’ address: Dr. D. R. Kothawale, A. A. Munot, H. P. Borgaonkar, Climatology and Hydrometeorology divisions, Indian Institute
of Tropical Meteorology, Pune 411008, India. 相似文献
18.
B. G. Hunt 《Climate Dynamics》2006,27(7-8):677-694
The CSIRO Mark 2 coupled global climatic model has been used to generate a 10,000-year simulation for ‘present’ climatic conditions. The model output has been analysed to identify sustained climatic fluctuations, such as those attributed to the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Since no external forcing was permitted during the model run all such fluctuations are attributed to naturally occurring climatic variability associated with the nonlinear processes inherent in the climatic system. Comparison of simulated climatic time series for different geographical locations highlighted the lack of synchronicity between these series. The model was found to be able to simulate climatic extremes for selected observations for century timescales, as well as identifying the associated spatial characteristics. Other examples of time series simulated by the model for the USA and eastern Russia had similar characteristics to those attributed to the MWP and the LIA, but smaller amplitudes, and clearly defined spatial patterns. A search for the frequency of occurrence of specified surface temperature anomalies, defined via duration and mean value, revealed that these were primarily confined to polar regions and northern latitudes of Europe, Asia and North America. Over the majority of the oceans and southern hemisphere such climatic fluctuations could not be sustained, for reasons explained in the paper. Similarly, sustained sea–ice anomalies were mainly confined to the northern hemisphere. An examination of mechanisms associated with the sustained climatic fluctuations failed to identify a role for the North Atlantic Oscillation, the El Niño-Southern Oscillation or the Pacific Decadal Oscillation. It was therefore concluded that these fluctuations were generated by stochastic processes intrinsic to the nonlinear climatic system. While a number of characteristics of the MWP and the LIA could have been partially caused by natural processes within the climatic system, the inability of the model to reproduce the observed hemispheric mean temperature anomalies associated with these events indicates that external forcing must have been involved. Essentially the unforced climatic system is unable to sustain the generation of long-term climatic anomalies. 相似文献
19.
C. V. Singh 《Meteorology and Atmospheric Physics》2001,78(3-4):205-214
Summary
The paper deals with the variability of summer-monsoon rainfall during normal, flood and drought years over India. During
flood years the monsoon rainfall increases mostly all over parts of the country and large area less than 100 cm isohytel covers
Orissa and adjoining Madhya Pradesh. During drought years the rainfall amount decreases over the entire country and isohytel
of 100 cm shrinks to almost a point. The variability of monsoon rainfall from flood to normal to drought years depends upon
the number of depression/low-pressure area which form over the North Bay and move inland. To understand the intraseasonal
and interannual variability of the monsoon rainfall, daily and seasonal anomalies has been performed by using the Empirical
Orthogonal Function analysis. Further Empirical Orthogonal Function (EOF) analysis is carried out on these data to find out
the nature of rainfall distribution in different monsoon categories namely normal, flood and drought years. This technique
thus serves to identify spatial and temporal patterns characteristics of possible physical significance.
Received July 25, 2000/Revised September 26, 2000 相似文献
20.
The ecological consequences of climate change are determined by many climate parameters, not just by the commonly investigated
changes in mean temperature and rainfall. More comprehensive studies, including analyses of climate variability, extremes
and aggregate changes in the climate system, can improve the understanding of the nature, and therefore possible consequences,
of recent changes in climate. Here climate trends on the sub-Antarctic Marion Island are documented (between 1949 and 2003)
in more detail than previously. Significant trends in biologically-relevant, and previously unexplored, parameters were observed,
and the potential ecological consequences of these changes discussed. For example, the decline in precipitation experienced
on the island comprises a trend for longer dry spells punctuated by fewer and smaller precipitation events. This more detailed
understanding of the island’s drying trends enables more accurate predictions about its impacts, including, for example, particularly
severe effects on plant species growing in soils with poor water-holding capacity. Therefore, in addition to changes in average
conditions, more inclusive climate analyses should also examine trends in climatic variability and extremes, for individual
climate parameters as well as for the climate system as a whole. 相似文献